PROJECT TITLE
“Mapping The E-region vertical and zonal (horizontal) winds near a stable auroral arc using a nearhorizontal chemical release trail”
PROJECT SUMMARY
With this proposal, we address two critical aspects of thermospheric dynamics – small-scale motions and
vertical mixing. The gradients of most atmospheric quantities are strongest in the vertical direction. Thus,
vertical winds disrupt the atmosphere more than horizontal winds, because they carry air parcels directly across
parameter isosurfaces.
The consequences of vertical winds are poorly understood, although some key points are:
 Strong thermospheric vertical winds occur mostly at auroral latitudes, where they are highly localized
geographically.
 In-situ spacecraft observations show significantly modified thermospheric composition within these
regions of strong vertical wind.
 Ground-based observations suggest, but cannot prove, that the large vertical wind events driving the
composition changes actually originate in the E-region, just poleward of discrete auroral arcs.
 Ultraviolet images from space show that horizontal advection eventually causes these composition
changes to affect large geographic areas.
Here, we propose to “zoom in” on this apparent source region for large amplitude vertical wind events.
To do so, we propose a novel rocket experiment, in which a chemical trail will be deployed nearly horizontally
across an auroral arc, at around 160-km altitude. Photographing this trail’s drift will allow measurement of
vertical and horizontal zonal winds, each resolved over geomagnetic latitude. An on-board spin-scan
photometer and electron density probe will establish, in detail, the spatial relationship between the observed
vertical wind field and associated auroral structures. A smaller, second rocket will be launched immediately
following the first, on a conventional steep trajectory. This rocket will deploy a near-vertical trail that will map
the surrounding altitudinal structure of the wind field, both above and below the previously established
horizontal trail.
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1. OBJECTIVES AND EXPECTED SIGNIFICANCE OF THE PROPOSED RESEARCH
Overview
We believe that the two most critical pathways that couple thermospheric dynamics to other processes in
the thermosphere and ionosphere are small-scale motions and vertical mixing. We suggest that these pathways
have not been examined adequately to date, an omission that now limits further understanding of the coupled
thermosphere-ionosphere system as a whole.
Rocket deployed chemical release trails have been used since the 1960s to provide high-resolution in-situ
measurements of upper atmospheric winds. In the standard technique, a rocket deploys the trail nearly
vertically, yielding measurements of both horizontal wind components with very good altitude resolution
(typically 2 km). These experiments have shown that otherwise unexpectedly strong vertical gradients are in
reality an almost ubiquitous feature of the horizontal wind between 90 and around 140 km altitude [Larsen,
2000, and references therein]. The origin of these gradients is a vigorous topic of current research. Here,
however, our emphasis is on the consequences of dynamical processes, rather than on their origins per se. For
this objective, our focus is on the horizontal structure of the vertical wind, rather than the vertical structure of
the horizontal wind.
Winds modify the atmosphere by advection. Because the gradients of most atmospheric quantities are
strongest in the vertical direction, vertical advection influences the atmosphere the most, by carrying air parcels
directly across parameter isosurfaces. By contrast, horizontal winds blow parallel to these isosurfaces and are
less disruptive. Even if the horizontal wind is strongly structured in the vertical, the various layered flows do
not exchange material – unless vertical advection is also involved.
While many individual observations do exist, the detailed consequences of vertical advection remain
almost entirely speculative. Current thinking in this regard can be summarized as:
 Strong thermospheric vertical winds occur mostly at auroral latitudes, where they are highly localized
geographically.
 In-situ spacecraft observations show significantly modified thermospheric composition within these
regions of strong vertical wind.
 Ground-based observations suggest, but cannot prove, that the large vertical wind events driving the
composition changes actually originate in the E-region, just poleward of discrete auroral arcs.
 Ultraviolet images from space show that horizontal advection eventually causes these composition
changes to affect large geographic areas.
Here, we propose to “zoom in” on this apparent source region for large amplitude vertical wind events, to
map its meridional structure with high spatial resolution. To do so, we propose a novel rocket experiment, in
which a chemical trail will be deployed nearly horizontally across an auroral arc, at around 160-km altitude.
This altitude is inaccessible to passive optical remote sensing, as it falls between the source heights for the
bright airglow and auroral emissions.
Photographing the chemical trail’s drift will allow measurement of vertical and horizontal zonal winds,
each resolved over geomagnetic latitude down to a few km of horizontal spatial resolution. An on-board spinscanned photometer and electron density probe will allow us to establish, in detail, the spatial relationship
between the observed vertical wind field and associated auroral structures that the rocket flies through. A
smaller, second rocket will be launched immediately following the first, on a conventional steep trajectory.
This rocket will deploy a near-vertical trail that will map the surrounding altitudinal structure of the wind field,
both above and below the previously established horizontal trail.
The global-scale geographic distribution of vertical wind disturbances
The diurnal cycle of solar heating causes constant pressure surfaces in the thermosphere to oscillate
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vertically with periods of 24-hours and at higher harmonics of this. This is a global phenomenon, the amplitude
of which seldom exceeds ~5 m s-1. It occurs slowly compared with the time needed to re-assert hydrostatic
equilibrium following a perturbation and does not transport air parcels across isobaric surfaces. Superimposed
on this placid “breathing” is a broad spectrum of disturbances due to waves and tides, and in some cases,
driven by impulsive or even explosive in-situ forcing. In the high-latitude F region, the velocity distribution of
disturbances above a fixed site has a 1/e half-width of several tens of m s-1, but the distribution’s tails extend
out to hundreds of m s-1 [Conde and Dyson, 1995].
By far the vertical wind data set with best global coverage is that obtained by the Dynamics Explorer-2
(DE2) spacecraft’s Wind and Temperature Spectrometer (WATS) instrument between August 1981 and
February 1983. Very little has been published from these data, although Spencer et al. [1982] and Johnson et
al. [1995] each presented vertical wind data from several orbits. We have examined the complete DE2-WATS
data set, which is now freely available from NASA, as well as ground-based observations from a wide range of
geographic latitudes. The data invariably show greatest vertical wind activity at high latitudes, contrasting with
relative quiescence elsewhere (figure 1).
The lower panel of figure 1 shows ion temperature measurements for the same orbit. Examination of
many orbits suggests that large peaks in the ion temperature measurements are a signature of auroral oval
crossings. Thus, figure 1 also indicates an association between the aurora and large vertical winds. Clearly,
studies of thermospheric vertical mixing must emphasize auroral latitudes. Note that the spacecraft auroral oval
crossings occurred at around 400-km altitude, at which height the full width at half maximum of the observed
vertical wind features spanned ~5 of geographic latitude, or ~500 km in meridional distance.
Figure 1: Vertical wind and ion
temperature measurements recorded in-situ
by the DE2 satellite on November 29,
1982, during orbit number 7295. The
spacecraft
altitude
varied
between
approximately 300 and 500 km during the
observations shown here.
The height distribution of vertical wind events
Price et al. [1995] measured vertical winds using a ground-based Fabry-Perot spectrometer (FPS)
observing simultaneously at both 557.7-nm and 630.0-nm, corresponding to emission altitudes of 130 and
240 km respectively (figure 2). Two examples that showed upwelling events occurring simultaneously at both
heights were presented, with peak velocities reaching ~40 m s-1 at 130 km and ~140 m s-1 at 240 km. These
observations indicate that upwelling can occur as a single coherent event throughout the entire thermosphere
above 130 km, thus connecting the E and F regions of the ionosphere. This result is also predicted by
thermospheric numerical models, which show that upwelling driven by E-region heating can extend as high as
the upper thermosphere and topside ionosphere [e.g. Fuller-Rowell, 1985; Chang and St.-Maurice, 1991;
Millward et al., 1993; Fujiwara et al., 1996].
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The vertical velocity derived from the 630-nm observations was ~3.5 times that obtained from 558-nm
data. Smith and Hernandez [1995] reported a similar factor for the relative speeds between 630-nm and
558-nm vertical wind estimates, i.e. 4.3, based on the slope of a linear regression fit of data points gathered
over one day. During auroral oval crossings above 400-km, DE2 recorded vertical wind events with typical
speeds of 150 m s-1 or more, again suggesting that
vertical wind speeds increase with height. However,
they do so more slowly than may be expected from
a simple inverse proportion to the atmospheric
density (which, to conserve mass flux, would yield a
factor of 50 or so increase in speed between 130and 240-km altitude at solar maximum). This latter
behavior suggests, not surprisingly, that upwelling
is also accompanied by horizontal expansion.
Figure 2: Vertical-wind measurements derived
from 630-nm (top) and 557.7-nm (bottom),
observations recorded at Poker Flat on March 21,
1991. Note the upward event in both traces just
before 13 UT. Horizontal wind speeds in the
eastward and northward directions are also shown.
[Adapted from Price et al., 1995]
The effect of vertical winds on neutral and ion composition
Through this experiment, we hope to improve understanding of vertical mixing associated with spatially
localized vertical wind events. It is known that one consequence of vertical mixing is to modify the
thermosphere’s neutral and ion compositional structure [e.g. Fuller-Rowell, 1984; Rishbeth et al., 1985, 1987;
Burns et al., 1989a, b; Fuller-Rowell et al., 1991; Millward et al., 1993; Grossman et al., 2000]. Figure 3
shows actual observations of these compositional effects, again based on data from the Dynamics Explorer-2
satellite.
In figure 3, the top panel shows a time
series of vertical wind measurements, the center
panel shows molecular-nitrogen densities, and
the bottom panel shows ion temperatures. Note
that the spacecraft altitude changed during the
period shown, from around 250 km near the
center of the time series, to 550 km near either
end. To simplify interpretation of the N2
densities, they have been crudely “projected” to
equivalent values at 300 km for this figure,
using a scale height calculated from the neutral
temperature measured in-situ.
Figure 3: DE2 measurements of vertical
wind (top), N2 density (middle) and ion
temperature (bottom). The measurements were
taken during orbit number 7232, on November
25, 1982.
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An upward wind of ~120 m s-1 was observed at ~15.4 UT, coincident with a spike in the ion temperature
and a 50% increase in the N2 densities. A more modest vertical wind was also seen 14.65 UT, again
accompanied by fluctuations in the N2 density and ion temperature. Both events corresponded to auroral oval
crossings. Although we have only shown data from a single orbit, such effects appear very frequently in the
DE2 data.
Figure 4: The effect of the vertical
winds on the O+(4S) profile for summer
(noon) conditions. Negative velocities are
directed downward, while the upward
direction is positive. Typical vertical winds,
in the range +/- 50 m s-1 cause shifts of ~100
km in the main ionospheric peak height.
(Figure by Sergei Maurits, personal
communication, 1999).
Vertical winds also modify the ionosphere, by driving vertical ion and neutral advection. The effect of
this is shown in figure 4, which is based on a simple one-dimensional ionospheric model. Self-consistent threedimensional numerical models also predict complex neutral and ion composition changes, including changes to
the mean molecular mass and the mixing ratios of O, N2, and O2 within an upwelling region. These
composition changes can have significant ionospheric effects following an upwelling event – decreases in
NmF2 of 50% or more, along with increases of hmF2 of as much as 100-km. The NmF2 decreases are driven by
increased ion recombination rates, due to transport of molecular species to higher altitudes than normally
occurs under conditions of diffusive equilibrium.
Small-scale wind motions
There are experimental reasons to believe that the thermospheric wind field contains power at higher
spatial frequencies than have so far been resolved either by experiments or models. For example, Mikkelsen
and Larsen [1993] compared ion and neutral velocities observed in four chemical release experiments with
general circulation model simulations of the atmosphere during these events. The observed ion velocities were
over twice as high as needed in the model to drive the observed neutral winds. To account for the missing
neutral momentum they concluded “strong turbulent dissipation of energy and momentum must be present at
smaller scales in the real atmosphere.” In another experiment, Larsen and Mikkelsen [1990] estimated
thermospheric vertical winds using horizontal divergences calculated from 3 chemical release trails deployed
at the vertices of a triangle with sides 150-200 km long. The resulting vertical speeds, less than 2 m s-1 at all
heights between 90 and 160 km, were in some cases 2 orders of magnitude smaller than those derived from
Fabry-Perot spectrometers or from the fall speeds of barium clouds deployed during the very same rocket
experiment. They concluded that the discrepancy was due to large-scale spatial averaging of the divergence
over their triangular measurement area. By contrast, Fabry-Perot and barium cloud experiments effectively
take point measurements. They noted that simple scaling arguments applied to the continuity equation suggest
that the much larger vertical winds seen in the point measurements “must be localized in the horizontal
domain.”
A curious data set, but one which is impossible to dismiss, is that presented by Rieger [1974], based on
the fall speeds of 48 barium clouds released above a range of geographic locations at altitudes between 140
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and 260 km. In two-thirds of the experiments, no significant vertical motion was observed at all, whereas
speeds up to 42 m s-1 were observed in the remainder. Such a velocity distribution is hard to understand, unless
strong vertical winds only occur in geographically isolated patches, embedded in an otherwise calm
background. The vertical drift speed of some clouds was even observed to change significantly between
successive 100-second intervals. Reiger [1974] concluded, “Vertical winds, therefore, seem to be a locally and
temporally restricted phenomenon.”
There is a compelling reason to verify unequivocally whether such small-scale wind systems really do
occur. Even if the large-scale spatial average of these motions may be zero, their cumulative effect is not.
Strong small-scale motions greatly enhance large-scale mixing. This is especially important in the vertical
direction, where the positive temperature gradient would otherwise yield a stratified and unmixed
thermosphere. A recent example of the potential large-scale consequence of such vertical mixing is shown in
figure 5. Geographically large “oxygen depleted patches” were observed in DE1 ultraviolet images by
Strickland et al., [1999] following a
thermospheric storm. They concluded that
the high-latitude oxygen depletions of up to
50% “seen in all images are signatures of
heating and subsequent upwelling in the
vicinity of these structures.” Numerous
examples of similar events are presented in
the earlier work by Craven et al. [1994],
Nicholas et al. [1997], and Immel et al.
[1997].
Figure 5: Oxygen depleted patches,
colored blue and green, inferred from
Dynamics Explorer 130.4-nm FUV
dayglow images by Strickland et al.,
[1999].
Limitations of existing techniques for mapping vertical winds
Unfortunately, the lowest height at which the DE2 spacecraft measured vertical winds near the auroral
oval was ~300 km, and often it was at 400 km or more. At these altitudes, horizontal advection associated with
the horizontal expansion of upwelling regions will “smear out” any fine spatial structure present in the vertical
wind field lower down. It is also impractical to resolve instantaneous fine spatial structure in the vertical wind
field using ground-based remote sensing. This is because the ground-based geometry only allows an
observatory to measure the vertical wind in one location, i.e. directly overhead. Detailed mapping of the
vertical wind field would require a prohibitively large array of ground stations (figure 6). Even with such an
array, the vertical wind is not expected to be amenable to
interpolation (either spatially or temporally) between the stillsparse ground-based measurements.
Figure 6: This figure shows the useable fields-of-view
of nine ground-based Doppler vertical wind instruments.
Spatial mapping of the thermospheric vertical wind would
require a prohibitively large and geographically dispersed
array of many stations to cover a region the size of Alaska.
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Vertical circulation near individual arcs
Although the DE2 data indicate a general association between the aurora and the largest and most
important vertical wind events, they cannot resolve the details of this association (for reasons outlined above).
Ground-based, single-point wind measurements (representative of lower altitudes) can provide some additional
information about this small-scale geometry. As arcs move with respect to the observatory over time, the
instrument samples the wind field at different locations relative to the arcs. Any persistent spatial relationship
between the vertical wind and the aurora will appear as a trend in wind data sorted by arc location. Using this
approach, Price et al. [1995] derived the configuration shown in figure 7.
Figure 7: The distribution of
thermospheric upwelling associated with
pre-midnight auroral arcs, proposed by Price
et al. [1995], who suggested that upwelling
events occur persistently in a region
immediately poleward of the discrete aurora.
Both the upwelling speeds and the latitudinal
extent of this region increase with altitude.
Note, however, that individual events may
well be smaller in extent than that of the
region shown.
Other studies have also presented data
that are consistent with figure 7 [Rees et al.,
1984; Wardill and Jacka, 1986; Crickmore
et al., 1991; Price et al., 1991; Innis et al.,
1996, 1997]. Figure 8 shows another example, recorded by a Geophysical Institute Fabry-Perot spectrometer
located at Inuvik, Canada. Auroral ultraviolet images recorded simultaneously by the POLAR spacecraft’s
UVI imager show that strong upwelling seen just before 6 UT coincided with a time when Inuvik lay poleward
of the aurora.
Thus, the deduced wind structure summarized in figure 7 is now a widely used paradigm for the behavior
of vertical winds near the aurora. However, it must be emphasized that the total number of observations
supporting this picture remains small. More seriously, the flow geometry relative to the aurora is not the only
factor that determines how ground-based wind data appear when ordered by arc location. This is because arc
locations themselves are determined by other factors, such as magnetic local time, and the instantaneous size
of the polar cap. It may be that upward winds are observed from the ground more often on the poleward side of
the aurora simply because upward winds only occur when the aurora is active and the oval is expanded. The
single-station, ground-based data cannot distinguish this from a pre-existing and persistent region of upwelling
moving over the instrument along with the auroral expansion. It is just not known whether figure 7 describes a
persistent feature of the real circulation near a typical arc. There has never been an experiment that mapped the
actual E-region vertical wind field near an individual auroral arc.
Thus, here we pose a specific hypothesis that can be tested by conducting our proposed experiment, i.e.,
that “the thermospheric vertical wind field near a typical stable pre-midnight auroral arc is similar to that
depicted in figure 7.” In section 2, we will describe details of this experiment. These details have been guided
by our hypothesis; the experiment is specifically designed to test it.
Although we only propose one rocket campaign, we will target a stable auroral arc that has been located
~350 km north of Poker Flat for at least one hour. This condition occurs very commonly in Alaska during the
early evening. If there is any persistent geometry associated with the wind field near an auroral arc (including a
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geometry similar figure 7), then we should observe it.
Figure 8: F-region vertical winds recorded at
Inuvik, in northwest Canada. Also shown are 3
ultraviolet auroral images from the POLAR UVI
instrument, with the location of Inuvik marked as a
black square. The large upward wind event just prior
to 6 UT occurred when Inuvik lay poleward of the
aurora, which is consistent with the geometry shown
in figure 7.
Horizontal zonal winds
Figure 7 does not depict the horizontal wind that will inevitably be superimposed on the vertical
circulation. For a typical pre-midnight scenario, the horizontal flow would be aligned zonally and generally
directed into the page, seen from the perspective of figure 7. By releasing a continuous north-south horizontal
chemical trail, we will also obtain a latitude-resolved profile of this zonal flow. In reality, we propose to deploy
the trail as a series of discrete “dashes” that will allow measurement of the horizontal meridional wind as well,
albeit with less latitudinal resolution.
As before, a major strength of the zonal wind measurement will be its ability to resolve small-scale
horizontal spatial structure. In this case we will be particularly interested in latitudinal shear of the zonal wind,
and its spatial location with respect to the observed auroral structures. At F-region heights, this shear appears
to be a permanent feature of the wind field near pre-midnight auroral arcs (figure 9). Here, we will be
particularly interested in how effectively this known shear penetrates from the F-region down to the E-region
altitude of our chemical trail. Further, the kinematic viscosity is lower at 150 km than it is at 250 km, which
makes it possible for the E-region to sustain sharper wind gradients. Although this is possible, it is unknown
whether wind shears actually are sharper in the E-region. If so, this high-spatial-resolution experiment will
provide the first chance to observe them.
Gravity waves
Periodic fluctuations in the thermospheric vertical wind have been observed in several studies and
interpreted as signatures of gravity waves [e.g. Hernandez, 1982; Wardill & Jacka, 1986; Johnson et al.,
1995]. The periods of these waves ranges between 30 min and 2 hours, and their horizontal wavelength is 500
km or longer. Waves with shorter periods and wavelengths should dissipate rapidly in the thermosphere due to
viscosity and thermal conduction. We thus consider it unlikely that this experiment will resolve wavelike
vertical wind signatures over the relatively short 210-km horizontal trail length, unless we fortuitously
encounter a packet of short-period waves close to its source.
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Figure 9: An example of Fregion (geomagnetic) zonal winds
sheared
with
respect
to
(geomagnetic) latitude. The white
arrows
show
the
F-region
thermospheric horizontal wind
field, derived from a ground-based
Fabry-Perot spectrometer. These
are superimposed on ground-based
and POLAR-VIS space-based
images of the aurora. Also shown
(in pink and blue hues) is the
latitudinal profile of the auroral
electrojet. Note the line of wind
shear that is spatially coincident
with the poleward edge of the
discrete aurora. Figure from Conde
et al. [2000].
2. TECHNICAL APPROACH AND METHODOLOGY TO BE EMPLOYED
To test our above hypothesis, we propose to fly a rocket payload north from Poker Flat along an
innovative trajectory that would, if superimposed on figure 7, pass directly across the center of this figure,
traveling horizontally from left to right. This payload will carry 3 experiments: a pair of canisters that will
release a 210-km long chemical trail using 8 kg of liquid trimethyl aluminum (TMA), a spin-scan narrow-band
photometer, and a relative electron density probe. We will launch a second small rocket soon after the first, in
this case following a conventional steep trajectory. Drifts of TMA “puffs” released by the second rocket will
show how the 3-component wind field varies with altitude above and below our horizontal trail. The various
aspects of this proposed experiment will now be described in more detail.
The horizontal trajectory
In consultation with NASA Wallops personnel, we have identified a preliminary configuration capable of
achieving a near-horizontal trajectory suitable for our experiment. Although we will refer extensively to this
scenario in the following discussion, it should be emphasized that many of the details may change following
the Mission Initiation Conference, particularly once the payload weight is accurately defined. (For now, we
have assumed 140 kg.) The main point is that there is plenty of flexibility in all key design parameters, so that
our desired trajectory appears highly feasible using existing systems.
Our planning scenario uses a two-stage Black-Brant V/Nihka vehicle, launched at a quadrant elevation
(QE) of 80. Following first-stage separation, the combined Nihka and payload assembly will coast until
T=+100 seconds, reaching a height of 100 km. Then, an attitude control system (ACS) will be used to reorient
the combined Nihka and payload assembly to an elevation of 12. We have allowed 30 seconds for this
maneuver, which is generous given that roll, pitch, and yaw rates of up to 10 per second are possible. (If
needed, it would be possible to initiate this ACS maneuver as much as 20 seconds earlier, at an altitude of
around 80 km.) At T=+130 seconds, the Nihka will ignite, and burn for 16.3 seconds. Second-stage burnout
will be at about 140 km altitude, when the payload will be traveling at just under 3 km s-1 at an elevation angle
of 12.3. The subsequent trajectory will be a long and flat parabola, with apogee at T=+210 seconds, 160-km
altitude, and 289-km downrange.
Assuming the ACS system is functioning properly, we can expect pointing errors 3. The angular width
of the flight zone that we will use (Poker Flat Zone 4, Arctic Extension) is approximately 13, easily wide
enough to accommodate the anticipated range of trajectory azimuths following the second-stage burnout. We
have also examined the effect of ACS errors on the altitude, range, and time of apogee. If the Nihka ignites
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when directed at 9 elevation, apogee would be occur at T=+223 seconds, 170-km altitude, and 327-km
downrange. Conversely, Nihka ignition at 15 elevation would shift the apogee to T=+198 seconds, 153-km
altitude, and 252-km downrange. All of these trajectories would be acceptable for our experiment, for which
the desired range of apogees is approximately 140-180 km.
Another source of variability is that nominally identical rocket motors do not produce identical total
impulse. In our case, varying the first-stage impulse mostly modifies the apogee height, whereas the second
stage mostly determines the apogee range. However, acceptable trajectories still occur even if either or both
stage’s impulses vary by 10%. Figure 10 shows an example trajectory, in this case producing an apogee at
172 km.
Safety
An ACS failure could orient the vehicle incorrectly at second-stage ignition. Thus, a flight termination
capability will be required, to prevent the possibility of sending rocket components outside the permitted flight
zones. The flight termination decision must be derived from two independent sources of vehicle positionversus-time information. One such source will be from ground-based radar; the other must come from an onboard GPS receiver. This implies that the payload will also need a telemetry encoder capable of both downlink
(for GPS data) and uplink (for the destruct command). All modules required for the flight termination
capability are available in standard hardware.
Figure 10: An example of a suitable trajectory for the proposed experiment. In this case, the Nihka is
oriented -8 from horizontal at the time of ignition, and apogee is at 172 km. The heavy section of the
trajectory curve indicates the approximate extent of the chemical release trail. [Figure adapted from
documents provided by NASA Wallops Flight Facility].
Vertical trail
Vertical mixing can arise through Kelvin-Helmholz billows that are associated with unstable vertical
shear layers in the horizontal wind [Larsen, 2000]. To quantify this source, we propose to measure the vertical
shear in the horizontal wind by launching a second, smaller sounding rocket, as soon as logistically possible
after the first. This will be a Taurus-Orion (or similar) vehicle, following a conventional steep trajectory. It will
release a conventional “vertical” TMA trail between 100- and 200-km altitude on the down leg of its flight,
which should occur within the latitude range spanned by the horizontal trail released by the first rocket. The
same downrange camera sites will be used to photograph both the horizontal and vertical trails. Potentially,
this rocket could also release a trail on the up leg of its trajectory. While this option is not ruled out, the extra
payload weight would reduce the distance north that we can obtain for the down-leg release. It is essential that
this latter release overlap the horizontal trail. However, the second rocket’s steep trajectory already limits the
range achievable by it. An up-leg release would not be justified if it prevented the down leg from reaching the
horizontal trail.
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The TMA chemical releases
The bottom payload module of the main rocket will contain two 4 kg canisters of liquid trimethyl
aluminum (TMA). These will be deployed in rapid succession, to yield a continuous “double-length” trail.
(The reason for using two small 4 kg canisters is that a single large one is likely to be too unwieldy.) The
second rocket will contain a single 4 kg canister, to be deployed during the down-leg of its trajectory. Our
Clemson University co-Investigator, Dr. Miguel Larsen, who has considerable prior experience with chemical
releases, will provide the TMA canisters.
We have chosen TMA over other possible tracers, such as sodium or lithium, because it reacts
chemiluminescently with oxygen, yielding a trail that is visible even under non-sunlit conditions. This is
important for our experiment, because there is only a very brief period each evening when the atmosphere is
simultaneously sunlit at the relatively low release altitude of 160 km, yet dark enough to permit low-light
photography from the ground. Further, we do not wish to expose our payload photometer to the possibility of
viewing direct sunlight. TMA is also known to work well as tracer over broad range of heights surrounding
our horizontal trail’s 160-km apogee, i.e. from 90 km up to as high as 235 km [Larsen et al., 1989].
Because the main rocket’s trajectory is not perfectly flat, an along-trail horizontal wind would yield an
apparent vertical displacement of the trail that would be indistinguishable from the effect of a real vertical
wind. The effect is small, but unfortunately not negligible, as near the trail ends a 100 m s-1 along-trail wind
would appear like a 12 m s-1 vertical wind. As the trail will be deployed approximately due north-south, the
ambiguity will arise if there is a significant meridional wind. For our proposed launch conditions, the expected
meridional wind is small, because ion drag will be driving the horizontal wind westward. Nevertheless, we still
need to account for it, so the horizontal TMA trail will be deployed as a series of 4 to 5 long “dashes,” with
short gaps between. This modulation will be achieved by closing the liquid TMA release valve briefly. By
tracking the drift of the trail’s gaps, we will be able to measure the background meridional wind at several
points along the trail. An alternate source of meridional wind estimates will also be available from the second
rocket’s vertical trail. (The vertical trail will also be modulated, in this case by a “1-second on, 2-second off”
release cycle. The resulting trail will appear as a series of “puffs.”)
After the first rocket’s Nihka motor burns out, we plan a second ACS maneuver to orient the auroral
photometer correctly for its spin-scanning observations. However, the TMA canisters and Nihka motor will
separate from the upper payload prior to this second ACS maneuver. Without this separation TMA would
likely contaminate the other measurements, both optically and chemically, because the TMA molecules’ meanfree-path will be large compared to the payload length. The TMA canisters do not need telemetry, and will
operate autonomously by providing their own power and event-timing signals.
The horizontal chemical release itself will last 70 seconds, yielding a trail approximately 210 km long. It
will be controlled by a timer, programmed to activate the first of the two canisters 45 seconds before the
expected time of apogee. This canister should last until apogee, when the second canister will begin deploying.
The result will be a single trail centered about the nominal apogee point. The trail height will only vary by ~5
km over its entire 210-km length. Its steepest slope will be 6.6, which will occur at both trail ends. Previous
experience indicates that the trail will be visible for at least 10 minutes.
We do not have an experimental determination of the TMA molecule’s cross-section for momentum
transfer collisions with the major thermospheric species, O and N2. However, it is certain to be greater than
that of atomic oxygen, whose cross-section of 510-15 cm2 can be used to estimate upper limits for the trail’s
diffusive properties. By applying this cross section and a solar-maximum MSIS model atmosphere to the
method of Rieger [1974], we calculate that at 160-km altitude the trail’s sedimentation rate (fall speed) will be
less than 1 m s-1. The TMA mean free path and collision frequency are expected to be less than 60 m and
greater than 15 Hz, respectively. We have used these values in a simple Monte Carlo simulation of the
diffusive expansion of the trail. The simulated trail diameter was ~10 km after 5 minutes of elapsed time.
Experience has shown that the trail’s centroid location can be estimated from photographs to a precision better
than ~10% of the trail diameter. This corresponds to a position uncertainty of 1000 m after 300 seconds,
suggesting that an upper limit to the wind uncertainty due to diffusion effects will be ~3 m s-1. This is perfectly
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adequate, compared to the expected maximum vertical velocities of several tens of m s-1, or more.
Ground-based camera stations
The wind measurements will be obtained by video- and still-camera imaging of the chemical trail(s) from
several ground stations. Triangulation will be used to estimate the 3-component velocity vector of trail sections
over their expected 10-minute period of visibility. We propose to operate cameras from 3 downrange sites,
plus one at Poker Flat itself. The choice of downrange sites is determined by a combination of the need for
good triangulation geometry, and logistical considerations.
For good triangulation geometry, we want the lines-of-sight from the cameras to the trails to intersect as
close to perpendicular as possible. For two sites, this can be achieved by placing one beneath the horizontal
trail and the second displaced to one side by a distance several times the apogee height. Alternately, the two
sites can be displaced roughly one apogee-height to either side of the horizontal trail. For the planned three
sites, we will place one station roughly beneath the trail, with the two others displaced either side by 1-to-2
apogee-heights. With this deployment, triangulation is possible using any two of the three sites. Given this
geometry, logistic considerations suggest
that the 3 best sites are Toolik Lake,
Arctic Village, and Old Crow (in
Canada’s Yukon Territory). We have
contacted the Canadian agency that is
responsible for issuing research permits
for Old Crow. This is the Heritage
Branch of the Yukon Department of
Tourism. They did not identify any
special
concerns
associated
with
operating a camera site there, and
confirmed that their standard permitting
process would be appropriate. Figure 11
shows a map of these sites. To visualize
how the horizontal TMA trail will appear
from each site, figure 12 shows it mapped
onto sky views from each one.
Figure 11: A map of northeast
Alaska, showing the approximate ground
track of the proposed rocket trajectory
(red) and the horizontal TMA trail
(black). The vertical trail would be
released somewhere conveniently within
the heavy black region that indicates the
horizontal trail. Also shown are the
locations of Poker Flat and the three
proposed downrange camera sites.
We wish to measure winds to a precision of 5 m s-1. We expect the trails to be visible for at least 10
minutes. However, for planning, we will only rely on 5 minutes of visibility, which means we will want to
resolve trail displacements of around 1.5 km. As these displacements will not always be perpendicular to the
camera’s line-of-sight, we will assume that we really need to resolve 1-km displacements. A 1-km
displacement occurring at the most distant part of the horizontal trail would subtend angles of 0.23, 0.30, and
0.17 when viewed from Toolik Lake, Arctic Village, and Old Crow, respectively. The prime imaging systems
for recording the trail will be intensified white-light CCD video cameras. One or more additional cameras will
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12
also be deployed at each site, for high-resolution imaging. These will be either 35-mm or medium-format film
cameras or, potentially, professional quality digital cameras. (Anticipated technical advances over the next ~18
months will make high-end digital imaging very attractive for this experiment. A particular advantage is the
ability to display images as they are acquired, which will allow exposure times etc. to be optimized during the
brief period of trail visibility.)
We will digitize the video frames at a resolution of 512480 pixels. This dictates that for two pixels per
resolution element, the maximum useable field-of-view per camera is 5559, 7277, and 4043 for
Toolik Lake, Arctic Village and Old Crow, respectively. The horizontal trail will actually span 65, 90, and
40 respectively, at the 3 sites. Thus, each site will need a minimum of two video cameras. In each case two
cameras operating at minimum angular resolution would actually cover a very generous field compared to that
actually needed; we will probably trade some of this for higher-than-minimum angular resolution by using
slightly smaller fields-of-view than the allowed maximum (while still keeping some margin for pointing
errors). A single narrow-field intensified CCD video camera will also operate from Poker Flat. This site will be
of limited value for triangulating the horizontal trail, but will be critical for the vertical trail. During analysis,
the viewing angles mapped to each image pixel will be derived from a 2-dimensional numerical fit of
background stars to a digital sky atlas.
Because all downrange sites need a minimum of 3 cameras, we will require two operators at each site.
Nominally, each site will have one co-Investigator and one graduate student. As a minimum, all downrange
sites will have telephone communications, used to receive the verbal countdown as well as to exchange
weather and general launch status information. At least one, Toolik Lake, will also offer T1 Internet access.
Telephone use will be limited to periodic updates until T-5 minutes, after which open phone lines will be
maintained until several minutes after the trail brightness falls below detection level.
Figure 12: Calculated appearance of the horizontal trail in the sky, for the 3 proposed down-range
camera sites, as well for the launch site at Poker Flat.
Spin-scan auroral photometer – description and performance analysis
To test our hypothesis adequately, we will require detailed knowledge of the auroral arc structure(s) that
the rocket flies through. The targeted auroral arc will lie ~350 km north of Poker Flat. In this location, the
three ground-based camera sites operated by Poker Flat will be viewing the arc significantly off-zenith. This
means that small-scale latitudinal structure of the arc itself will not be resolved from the ground. For example,
the ground cameras would be unable to resolve multiple parallel curtains.
Because rocket’s the second-stage trajectory maneuver already requires ACS and telemetry functions, we
can use these to support two on-board auroral monitoring instruments that will together define the auroral arc
structure with the latitude and altitude resolution that we require. The first of these will be a narrow-field spinscanned auroral photometer observing at either 557.7 nm or 391.4 nm.
Following second-stage burnout, we will use a second ACS maneuver to reorient the spin axis so that it
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lies both horizontal and perpendicular to the payload velocity vector. As the photometer will view
perpendicular to the spin axis, it will sample auroral luminosities in the plane of the payload trajectory over
360 of look angle. With each successive rotation, the moving payload will view the aurora from a slightly
different perspective. McDade et al. [1991] demonstrated that the time sequence of these spin scans may then
be used to reconstruct, tomographically, a latitude-versus-height cross section of the auroral luminosity. We
will use this same technique, although we expect to achieve better-conditioned tomographic inversions from
our flat trajectory. Because we will target a stable arc, we expect only minimal time variations in the auroral
brightness distribution during the 3-minute period of photometer observations. Nevertheless, ground-basedcamera and MSP data will characterize such variation, to improve the tomographic inversion accuracy. The
absolute brightness of the 557.7-nm (or 391.4-nm) emission, along with its altitude distribution, will be used
to derive quantitative estimates of the auroral electrons’ energy flux and characteristic energy.
Angular dimensions of the instantaneous photometer field-of-view will be  = 0.5° vertical and 2.5°
horizontal, with continuous sampling in consecutive time intervals of duration t. Equivalent linear
dimensions will be 0.35 and 1.75 km, respectively at 40-km distance, applicable for nadir viewing within an
arc from 160-km altitude to a maximum volume emission rate occurring at 120-km altitude. A payload rotation
rate of 3.0 revolutions per second (t=0.463 ms for 0.5° rotation and 2160 samples per second) will yield
single “pixel” angular dimensions of 1.0° and 2.5°, with a two-pixel spatial resolution of 1.40 km, in plane.
Primary mechanical elements of the photometer will be the cylindrical instrument section (inserted as a
payload section), whose diameter will equal that of the rocket body (~44 cm), and the photometer mechanical
housing, which will include all mechanical supports for optical, sensor, and electronics components. Optical
elements will include optical baffles, aperture lens, entrance pupil, field stop, collimating lens, and narrow
passband optical filter. Electronics and electrical components will include the sensor, power supply, signal
conditioning, interface to the TM package, and electrical harnessing. Figure 13 is a schematic view of the
proposed photometer and its orientation within its payload section.
Flexible,
light-tight
seal
Rotation axis and
thrust axis
Digital & analog electronics, blocking HV
power supply, TM interface (estimated)
Ejectable
cover
PMT assembly
(estimated)
Optical axis
Objective lens:
40 mm aperture,
150 mm focal length
Field
stop
Filter
Collimating lens
(simplified)
Mounting
base-plate
Payload section 440mm diameter
Note: No details provided on internal
baffles, thermal insulation (etc)
Figure 13: A schematic view of the proposed spin-scan photometer.
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For a lens aperture of area A and focal length f, focal-plane field stop of width w and length nw (area
nw2, n=5), lens transmissions ta and tc, and filter transmission tf, the number of photons at the sensor will be
N = A n 2 t ta tc tf 109 / 4 = 3.41 A photons / kR-sample,
where  = 8.73 mrad, ta = tc = 0.9, and tf = 0.3. A focal length of 15 cm and nominal entrance pupil diameter of
4 cm (A = 12.6 cm2, f/3.75) will be used, providing N = 38.6 photons / kR-sample. The choice of focal length
and angular field-of-view result in a field-stop width w = 1.31 mm (and length nw=6.54 mm).
Final selection of the entrance pupil diameter and transverse field-stop dimension will be determined by
balancing conflicting objectives of sensitivity for the weaker auroral forms when viewed from larger zenith
angles versus unsaturated measurements in the magnetic nadir direction along an arc. The baseline design for
monochromatic observations allows the use of a simple lens (coated for maximum throughput at the selected
wavelength) rather than a more elaborate compound lens system. The maximum marginal ray-path angle
before the field stop will be 8.8°.
A small, fast, compound lens (~ f/0.7) placed after the field stop will reduce the maximum marginal raypath angles to  ~ 2.5° for transmission through the narrow passband interference filter. It will also reduce the
beam diameter to that of the sensor active area. Minimizing image aberrations is not important for a lens in this
application. Sufficient space must be provided between the collimating lens and sensor active area for the
interference filter and extension of magnetic shielding by ~2 cm in front of the sensor photocathode (see
below). Wavelength shift through the filter will be
 = - 0.5 o ( / )2 = 0.24 nm,
where  ~ 1.5 is the effective refractive index of the filter and o the wavelength (557.7 or 391.4 nm) at peak
transmission for normal incidence at the planned operating temperature. A FWHM passband of 1.0 nm is more
than adequate, with out-of-band rejection <10-4. Temperature control deep within the photometer for the short
flight time is not considered difficult.
The baseline selection for sensor is a miniature ruggedized PM tube (e.g., Hamamatsu R1463P ) with
multialkali photocathode of quantum efficiency Q = 0.15, yielding a sensor digital response R = 5.78
counts/kR-sample, or 12.5 k-counts/kR-s. The tube must be magnetically shielded for quantitative
measurements in a rotating magnetic field environment. Sensitivity will be reduced sharply at rates in excess of
~1 Mcount/s (~80 kR) due to bright aurora or other intense light sources using the same flight-proven backbiasing technique developed by co-Investigator J. D. Craven and applied successfully with the three DE-1 SAI
photometers in nearly 10 years of flight operation [Frank et al., 1981]. Modest cooling at the photocathode
will reduce thermoionic emission, which is not a significant source of noise in individual samples for the
planned rapid sample rate.
Alternate sensor configurations are being evaluated, including intensified avalanche photodiode
configurations and silicon photodiode arrays. However, fast phosphor response becomes a significant issue.
No benefit is found in the use of an intensified CCD array for which numerous pixel contents would be
summed for the present mission configuration.
The maximum number of counts in t for an 80-kR aurora is 462 counts, or 9 bits, and one extra bit is
used to indicate gain status. For a frame rate of 2160 samples/sec, the minimum TM requirement for one
photometer data channel is 2.2 Mbits/s. Simple compression techniques can be considered for the higher
sensor rates. Several analog channels will be required for monitoring instrument performance. TM must
provide information on rotation axis orientation and the spin phase must be known relative to an inertial frame
to better than 0.25°.
Relative electron density probe
The second instrument will be a simple current probe designed to monitor the relative density of the
ambient plasma before, during, and after the TMA releases. This probe can also detect plasma variations that
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might result from upwelling plasma associated with vertical winds near auroral arcs.
The current probe will consist of a conductive band approximately 15 cm in width that is wrapped around
the circumference of the rocket payload. This azimuthally symmetric geometry was selected to minimize ramwake effects that would otherwise result from the payload spin. A programmable bias voltage between ±10 V
will be applied between the current collecting surface and the payload, and the resulting current to the probe
will be measured. The primary current collection surface will be bordered above and below by guard rings that
are biased at the same potential as the current probe surface. Measuring only the current flowing to the primary
surface will minimize electric field fringing effects at the edges and corners.
The typical ion thermal velocity is less than 1 km/s at the expected horizontal TMA release altitude of
140–180 km. The proposed payload velocity of 3 km/s is significantly greater than the ion thermal velocity, so
the ion current to the probe will be dominated by the ions that are scooped up by the probe as it moves through
the ionosphere. Applying a negative potential to the current probe relative to the payload body will result in
repelling most of the electrons without significantly changing the ion current. By making a number of
simplifying assumptions (e.g., payload body at plasma potential, thin sheath approximation in which the
DeBye length is small compared to the probe size, ion temperature Ti = 0, etc.), the ion probe current can be
approximated as
ii = ni e v A,
where ni is the ion density, v is the payload velocity, and A is the effective probe area presented to the velocity
vector. For the proposed mission, in which the longitudinal axis of the payload will be perpendicular to the
velocity vector, the effective area of the probe will be approximately 550 cm2. Typical probe ion currents
would range from 0.0025-25 µA as the ambient plasma density increases from 102 to 106 cm-3.
The current probe will provide three analog output channels corresponding to (1) probe current–high
gain, (2) probe current–low gain, and (3) probe offset voltage, respectively. The high gain channel will provide
good resolution of plasma densities ranging from 102 to 104 cm-3, while the low gain channel is scaled for
plasma densities ranging from 104 to 106 cm-3. All channels will be scaled for output voltages from 0 – 5 volts,
and should be sampled at 1 kHz with 8-bit A-D converters. This will provide plasma density measurements
every 3 meters when the payload is traveling at the maximum velocity of 3 km/s. The probe electronics will
include internal power converters to derive all internal voltages from a standardized power bus, and a micro
controller to step the probe offset voltage through pre-programmed sequences.
This current probe will be designed and constructed by students at the University of Alaska Fairbanks.
Students enrolled in a Space Systems Engineering course at UAF will complete the initial conceptual design
during the Fall 2000 semester. Enhancements and alternatives to the probe design proposed here will be
examined at this time, including the addition of an internal microprocessor-controlled swept-voltage mode that
would allow the current probe to function similar to a Langmuir probe. Prototyping and fabrication will take
place during 2001. The Alaska Space Grant Program will contribute matching funds totaling $10,000 per year
for three years in the form of Space Grant Fellowships to the students working on this project.
Supporting measurements
Ground-based support will be required from a number of standard Poker Flat instruments. Most critically,
we will need the all-sky cameras and meridian-scanning photometers (MSP) at both Poker Flat and Kaktovik,
plus the all-sky camera at Fort Yukon. These data will assist with the launch decision and will also be valuable
to characterize temporal variations of the aurora, for improved tomographic inversion of payload photometer
data. The Fort Yukon camera will also yield valuable back-up images of the TMA trail itself. We will need
magnetometer data from the Alaska meridian chain, along with the real-time calculation of the electrojet
current density profile that is derived from these magnetometers. Internet access from Poker Flat to SEC and
other real-time space-weather sites will be essential for verification that our launch conditions are likely to
remain stable during the flight.
Several additional instruments will be used to support data interpretation after the flight. These include, in
approximate order of priority, the Poker Flat all-sky imaging Fabry-Perot spectrometer, the Kodiak and Prince
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George superDARN radars, the Inuvik, Eagle, and Poker Flat zenith-pointed Fabry-Perot spectrometers, the
Alaska meridian chain of ionospheric tomography receivers (to become operational in the fall of 2000), the
Anchorage VHF auroral radar, and the College digital ionosonde. All of these instruments operate routinely
and are funded separately from this proposal. We are not dependent on any of them; nevertheless, we will
certainly benefit from the anticipated availability of these data sets.
Launch conditions
We propose to deploy the chemical trail across an auroral arc. Of course, the aurora is an enormously
complex and dynamic phenomenon that can never be characterized by a single instance of an experiment such
as this. To provide results that are understandable, and relevant for inferring processes occurring at other times,
we propose to deploy the trail under the simplest geophysical conditions that we can reasonably expect to
encounter. That is, we will deploy the trail across a quiet arc in the pre-midnight local time sector (from dusk
until around 1030 UT), which has been lying relatively stationary at about 350 km north of Poker Flat for at
least one hour. The targeted arc should exhibit a surface brightness of at least 2 kilo-Rayleighs at a wavelength
of 557.7 nm when viewed from Poker Flat. Because this experiment will depend heavily on highly sensitive
ground-based cameras, we will also require clear skies over at least 2 of the 3 downrange sites, the moon to be
set, and the sun to be 12 below the horizon. A desirable (but not essential) extra condition for launch will be
that the Poker Flat all-sky Fabry-Perot spectrometer is indicating that the F-region horizontal wind field is
sheared toward the west in the instrument’s northern viewing zones (i.e. viewing zones that map into the TMA
release region). This condition would suggest that significant Joule heating was occurring in the thermosphere,
which would likely drive a strong upwelling event. It would also be favorable for our secondary scientific
objective of examining the penetration of F-region wind shears into the E-region.
Our preferred launch season is post-midwinter in the year 2003. Ephemeris calculations indicate that the
useable windows in 2003 are January 6-23 and February 4-20. Either window is acceptable; each has
advantages. The January window provides longer periods of pre-midnight darkness, whereas ion-neutral
coupling in the thermosphere should be getting stronger by February. To verify our expectation that the desired
launch conditions are not infrequent, we examined Poker Flat meridian scanning photometer data, recorded in
the months of January to early March in the years 1997, 1998, and 1999. For each observing night, we made a
visual assessment of auroral and cloud conditions to decide whether our experiment could have launched.
Suitable conditions occurred on 77 of the 174 nights that we examined, i.e. 44% of the time. The longest
continuous period without viable launch conditions was 7 nights. Of course, we could only include the cloud
conditions over Poker Flat in this assessment, whereas in reality we would also need clear skies at two of our
three down range camera sites. We were also unable to allow for other factors, such as the occurrence
frequency of unacceptably strong or variable surface winds for rocket operations. Although these other factors
would decrease the percentage of useable nights, the likelihood of a launch within one 16- or 17-day window
remains high.
Recovery
Payload recovery is not required. It may nevertheless be desirable, given that the upper payload will
contain our two flight instruments, plus ACS, GPS, and telemetry modules. Unfortunately, recovery may be
expensive, as the payload will impact onto pack ice drifting several hundred km north of the Alaska coast.
Should recovery prove cost effective, we would use it as an opportunity to post-calibrate the flight instruments.
In no case will the TMA canisters be recovered; they will separate from the upper payload and free fall along
their own trajectories.
3.
EXPECTED IMPACT ON THE STATE OF KNOWLEDGE IN THE FIELD
To emphasize the anticipated power of this experiment, figure 14 is a hypothetical depiction of how our
assimilated set of results would appear if presented using the same layout as figure 7. Notice that the
measurements will yield much higher spatial resolution than is shown in figure 7, or has been achieved in the
past.
Our experiment will “zoom in” on the apparent source region for large amplitude vertical wind events,
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mapping it over latitude down to ~2-km resolution. The literature, as well as our own ground-based
observations, suggest that upwelling is a persistent feature of the wind field poleward of the discrete aurora,
even for quiet and stable arcs. If the vertical wind field observed near the targeted auroral arc is not consistent
with this, then our hypothesis would be violated. If the targeted arc is indeed representative of typical stable
aurora, then a new paradigm for vertical winds will be needed – and presumably, provided, by our results.
Even if the vertical wind that we observe is close to zero all along the trail, this finding will be very valuable
scientifically. It would disprove the current belief that upwelling is a persistent feature, and motivate further
experiments to quantify the conditions that are required to initiate the upwelling events that are observed from
the ground.
Conversely, if the hypothesis proves correct, we will have established confidence in the Price et al.
[1995] model. This model could then be used as an empirical parameterization of auroral vertical winds within
thermospheric general circulation models (which lack the spatial resolution to generate such winds selfconsistently). It would also provide a baseline result against which to test the behavior of high-resolution
nested-grid models. If a nested-grid model failed to generate vertical winds similar to our results and to figure
7, then the modeler would know that it missed or misrepresented some processes.
In either case, our experiment will map the vertical wind field, and the associated aurora’s optical and
plasma structure, simultaneously. The significance of these combined measurements is that, for the first time,
we will be able literally to see inside the postulated region of upwelling and observe how it happens. Whatever
the observed wind field, we will be able to examine the detailed microphysics that produced it.
Figure 14: A schematic sketch
of how some of our combined
measurements may appear. This
figure illustrates how the TMA
trails, tomographically inverted
photometer scans, and ambient
plasma probe data would appear if
presented in the same layout as
figure 7. Together, our data will
yield a detailed view of the physical
processes occurring within our
targeted auroral arc. Not shown here
are the zonal wind measurements
that will also be obtained from each
TMA trail, or the supporting
observations from ground-based
instruments.
4. RELEVANCE TO PAST, PRESENT, AND FUTURE NASA OSS PROGRAMS
Sun-Earth connection
This proposal is targeted directly at the “Ionospheric, Thermospheric, and Mesospheric (ITM) Physics”
science discipline component of the Office of Space Science’s Geospace Sciences Cluster. This cluster
addresses the “Sun-Earth Connection,” which is one of four themes chosen by NASA for space science
research. The proposed vertical wind experiment will examine a critical two-way coupling mechanism
operating between the ionospheric and thermospheric fluids, as well as between different pressure layers
within these fluids. The operation and consequences of this coupling are, today, virtually unknown.
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Supporting research and technology (SR&T)
Although we have submitted this proposal to a “low cost access to space (LCAS)” program, we believe it
also offers a strong SR&T component. Specifically, many new experiments will become possible once we
demonstrate the ability to fly payloads across auroral arcs at nearly constant altitude. If this experiment
succeeds, we will certainly propose follow-on missions involving multiple horizontal TMA trails and more
flight instruments. For example, several horizontal TMA trails could be deployed between 110 and 200 km
altitude, to map the vertical extent of the vertical mixing. It would also be desirable to measure directly the
compositional changes driven by the observed vertical mixing. Another critical quantum leap in measurement
capability that will be enabled by the horizontal trajectory is mapping the wind field’s horizontal divergence at
a few tens of km of spatial resolution. For this, a pair of TMA canisters would separate after the second-stage
burn to deploy two parallel puffed trails, at the same height, but separated by 20-50 km of longitude.
These experiments, plus numerous others, are dependent upon the innovation to map thermospheric field
variables at near-constant altitude, with high spatial resolution, as a function of latitudinal distance from the
aurora.
Relevance to TIMED
This experiment will complement the scientific return of the NASA TIMED mission. TIMED is
specifically intended to study atmospheric energetics and dynamics from 60 to 180 km altitude. Of this range,
the region above ~120 km is by far the least well studied, as few remote sensing techniques work at those
heights. The proposed apogee height of 150-160 km (for the horizontal trail) will return data from the heart of
this atmospheric “terra incognita.”
Although the TIDI instrument on TIMED will measure winds, its oblique limb-viewing geometry means
that it cannot address either of our two priority topics, viz. vertical winds and small-scale structure. Thus, our
measurements will directly complement those of TIDI. Also, the GUVI instrument is designed to measure
thermospheric composition, which, as we have shown, is strongly influenced by the vertical wind field that we
propose to map.
Of course, it is unlikely that our launch will occur during one of the brief periods when TIMED is
observing above Alaska. (Because our launch criteria specify periods when the aurora is not changing rapidly,
we actually would be willing to delay the launch briefly if an overpass were imminent). However, because we
propose to launch through the most stable and reproducible auroral condition that exists, we are hopeful that
our results will provide a generic model for the vertical circulation near the auroral oval, applicable during
many of the TIMED overpasses.
Education and public outreach (E/PO)
Co-investigator Dr. Joseph Hawkins has submitted an education and public outreach proposal linked to
this experiment. Dr Hawkins is the Director of the Alaska Space Grant Program, which conducts a broad range
of programs to enhance teaching, research, and educational outreach within aerospace-related disciplines
throughout Alaska. Although not formally included in the E/PO proposal, we also note that the payload’s
electron density probe will be developed by undergraduate and graduate students working within the Alaska
Student Rocket Program, again under the direction of Dr. Hawkins.
5.
MANAGEMENT STRUCTURE
Overall management of the “customer” elements of this project will be the responsibility of the P.I., M.
Conde, who will work in conjunction with the NASA Sounding Rocket Program Office’s appointed Mission
Manager. Where differing strategies are available to complete the mission, P.I. Conde will be responsible for
decisions regarding the relative scientific merits of these strategies. The specific responsibilities of each
investigator are as follows:
 P.I. Conde: Overall management of the “customer” portion of the mission; final authority regarding
scientific aspects of the mission; leadership of the launch-team at Poker Flat; leadership of the data
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analysis, interpretation and publication phase.
 Co-I Larsen: Design, construction, and integration of the TMA canisters for flight; data analysis,
interpretation, and publication.
 Co-I’s Wescott & Nielsen: Design, assembly, deployment, and operation of the down range imaging
systems; leadership of the image analysis effort (i.e. triangulation that will yield the wind results); data
analysis, interpretation, and publication.
 Co-I Craven: Design, construction, calibration, and integration of the spin-scan auroral photometer; data
analysis, interpretation, and publication – with particular emphasis on photometer data.
 Co-I Hawkins: Leadership of the students from the Alaska Student Rocket Program, who will design,
assemble, and integrate the electron density probe, as well as analyze data from it; leadership of
education and public outreach efforts.
 Co-I Lummerzheim: Deriving latitude-resolved estimates of the energy flux and characteristic energy of
precipitating auroral electrons, based on the spin-scan photometer data; data analysis, interpretation, and
publication.
 Co-I Smith: Will participate at no cost, and will assist with both the launch decision and with subsequent
data analysis, interpretation, and publication.
6. WORK PLAN AND KEY MILESTONES
Assuming funding became available in the spring of 2001, the normal initial phases of a sounding rocket
project would commence. These tasks include the Mission Initiation Conference, team assignment,
Requirements Definition Meeting, design, and Design Review. We would hope to commence payload
fabrication in the fall of 2001, continuing until summer of 2002. Fall of 2002 would be available for
environmental testing, Pre-integration Review, integration and testing, and the Mission Readiness Review.
Shipping to Poker Flat would be planned for December 2002, with the launch window scheduled for January
or February 2003. Preliminary mission results and the Post-Flight report would be submitted within a few days
of launch. The spring and summer of 2003 would be used for detailed analysis, with the first comprehensive
results being presented at the 2003 Fall AGU meeting. This timeline is outlined in the table below.
YEAR
SEASON
ACTIVITY
2001
Spring
Mission Initiation Conference, team assignment, Requirements
Definition Meeting.
2001
Summer
Design Phase, breadboard payload electronics, Design Review
2001-2002
Fall 2001-Summer 2002
Payload Fabrication
2002
Fall
Pre-Integration Review, Environmental testing, integration,
Mission Readiness review
2003
January – February
Launch, preliminary post-flight report.
2003
Fall
Initial presentation of comprehensive results at Fall AGU
2003-
Ongoing
Subsequent analysis and presentation of results
GI 00-130
20