Geophysical Research Letters
Supporting Information for
Extreme Detached Dust Layers near Martian Volcanoes: Evidence for Dust
Transport by Mesoscale Circulations Forced by High Topography
N.G. Heavens1,*, B.A. Cantor2, P.O Hayne3, D.M. Kass3, A. Kleinböhl3, D.J. McCleese3,
S. Piqueux3, J.T. Schofield3, and J.H. Shirley3
1
Department of Atmospheric and Planetary Sciences, Hampton University, 23 E. Tyler
St., Hampton, Virginia, 23669
2
Malin Space Science Systems, San Diego, CA, 92191
3
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA,
91109
*
Corresponding Author’s E-mail: Nicholas.Heavens@hamptonu.edu
Contents of this file
Text S1 to S7
Figures S1 and S2
Additional Supporting Information (Files uploaded separately)
Captions for Tables S1 and S2
Introduction
This file contains a description of the version of the Mars Climate Sounder retrievals
used in the paper, a short primer on converting density-scaled opacity to mass mixing
ratio, a justification for the definition of “extreme detached dust layers”, descriptions of
the automated retrieval survey and manual survey of the radiance observations, the
reasoning behind our estimate of the formation frequency of layers, references for the
supplemental text sections, two supplemental figures, and two supplementary tables
providing additional details about the surveys of Mars Climate Sounder data referred to
in the paper.
1
Text S1. Mars Climate Sounder Retrieval Database Version 4.3
Mars Climate Sounder retrievals at present consist of vertical profiles of dust opacity at
463 cm-1 (km-1), water ice opacity (km-1) at 842 cm-1, and temperature (K) on pressure
(Pa) coordinates retrieved from observations of radiance from the Mars Climate Sounder
(MCS) on board Mars Reconnaissance Orbiter (MRO) [McCleese et al., 2007, 2010;
Kleinböhl et al., 2009, 2011]. The retrievals also contain height information based on the
geometric pointing of the MCS instrument.
Version 4.3 of the retrieval dataset differs from previous versions in several
respects (A. Kleinböhl et al., No widespread dust in the middle atmosphere of Mars from
Mars Climate Sounder observations, submitted to Icarus): (1) where the limb is too
opaque to retrieve surface pressure, a climatological surface pressure is assumed; (2) a
hard altitude cut-off for aerosol retrieval was removed and replaced with a requirement
that the radiance at the maximum retrieved altitude exceed 1% of the maximum radiance
in the relevant channel and exceeds 5 times the noise level (this threshold is raised to up
to 3% over cold surfaces); and (3) when no on-planet measurements are available to
retrieve surface temperature, a climatological surface temperature is assumed but
corrected on the basis of the extrapolated column dust optical depth. These changes
increase the number of retrieved profiles during the times of year when column dust
opacity is high and allows measurement of significant aerosol opacity along a vertical
range comparable to the temperature retrievals.
Text S2. Density-Scaled Opacity
Using the ideal gas law, the ratio between opacity and atmospheric density can be
calculated from the retrieved profiles, forming the basis for an estimate of aerosol mass
2
mixing ratio from assumptions about the aerosol properties [Heavens et al., 2011, 2014].
The formula for conversion is:
q
4 A reff dz 
  

3 Qext 
(S1)
where density-scaled opacity is the term in brackets, A is the assumed density of the

aerosol (3000 kg m-3 for dust; 910 kg m-3 for water ice) and reff and Qext are the effective
radius and extinction coefficient for the particle size distribution assumed by the retrieval
algorithm. The conversion factors (the unbracketed term on the r.h.s. of Eq. S1) between
density-scaled opacity of dust and water ice in m2 kg-1 and mass mixing ratio in ppm are
12000 and 2200 respectively [Heavens et al., 2010, 2011]. The uncertainties in
converting density-scaled opacity to mass mixing ratio for water ice are discussed in
Heavens et al. [2010]. The uncertainties of the conversion process for dust are discussed
in Heavens et al. [2014].
Text S3. EDDL Definition
The definition for an “extreme detached dust layer” is based on comparing the vertical
dust distribution of Mars’s dayside tropical atmosphere inside and outside of global and
regional dust storm activity. The focus on the tropical dust distribution is due to the need
to utilize the dust storm catalog of Wang and Richardson [2015], which focuses on lowlatitude dust storm activity. Extreme detached dust layers may occur at higher latitudes.
The dust distribution is characterized by two parameters in all individual retrieved
profiles within 30º S–30º N from a particular period: (1) the largest dust mass mixing
ratio in the profile and (2) the altitude at which it occurs above the areoid. These
3
parameters differ from the magnitude and altitude of a detached dust layer, because there
is no guarantee that the largest mass mixing ratio corresponds to a resolved layer.
However, it is a good approximation.
The vertical dust distribution during four periods was then examined with
bivariate histograms of the two parameters (Figure S1). The first period (the 2007 Global
Dust Storm) was Ls=261.6º–305.5º of MY 28, during which a global dust storm formed
and began to decay [Wang and Richardson, 2015]. The second period was Ls=261.6º–
305.5º of MY 30, a period during which no low-latitude dust storm was observed in
visible imagery [Wang and Richardson, 2015]. The third period was Ls=231.4º–237.3º of
MY 29 (MY 29A Regional Storm), a period during which a regional dust storm in
Acidalia expanded to a maximum area of 1.61  107 km2 [Wang and Richardson, 2015].
Smaller regional dust storms do generate DDLs with properties similar to the highest
magnitude and altitude DDLs in global dust storms. Nevertheless, the Acidalia storm was
the only non-global storm in the Wang and Richardson [2015] catalog that was both
observed by MCS and met the size distribution-based size criterion for regional dust
storm proposed by Cantor et al. [2001]. The fourth period was Ls=231.4º–237.3º of MY
30, a period during which no low-latitude dust storm was observed in visible imagery
[Wang and Richardson, 2015]. Note that the third period is truncated at the beginning
from the period of activity listed in the dust storm catalog in order to avoid overlap with a
period in MY 30 with a low-latitude regional dust storm.
The vertical dust distributions in the non-dust storm periods are broadly similar.
There is a broad peak in the bivariate histograms at a dust mass mixing ratio value of ~10
ppm and altitudes from 15–30 km above the areoid, a broad peak at very low dust values
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at 40–55 km altitude, and a diffuse bell-shaped part of the distribution centered on ~40
km altitude and peaking at ~50 ppm (Figures S1c–d). The first feature is the High
Altitude Tropical Dust Maximum (HATDM) described by Heavens et al. [2011a, 2011b,
2014]. The second feature is due to the cutoff of retrievals at high altitudes due to the
limb becoming optically thick because of high dust or water ice opacity. The third feature
is not readily identifiable. It may be indicate a population of DDLs intermediate in
properties between the extreme population in global dust storms and the HATDM,
perhaps the result of local dust storms. However, its origin is irrelevant here. It is not due
to regional or global dust storm activity.
The bivariate histogram of the two dust profile parameters during the regional
dust storm period is similar to the non-dust storm periods (Figure S1b). However, the
diffuse bell-shaped part of the distribution is not bell-shaped but expands higher in mass
mixing ratio and altitude space. In the global dust storm case, the HATDM part of the
distribution is much smaller, either because it is hard to see or no longer exists. Just as in
the regional dust storm case, the diffuse bell-shaped part of the distribution is also not
bell-shaped and expands even higher in mass mixing ratio and altitude space (Figure
S1a).
Whatever the exact origin of these distributions, these bivariate histograms show
that global and regional dust periods are distinguished from non-dust storm periods in the
same seasons of the year by the presence of significant maxima in dust mass mixing ratio
at altitudes above 50 km. This criterion provides a threshold for EDDL altitude.
The threshold for EDDL magnitude is based on taking the peak column dust
opacity observed by the Mars Exploration Rovers during the 2007 global dust event
5
[Montabone et al., 2015], converting it to MCS dust opacity by dividing it by a factor of
7.0 [Montabone et al., 2015], and calculating the uniform mass mixing ratio that would
correspond to this column opacity in an isothermal atmosphere with surface pressure of
610 Pa and temperature of 220 K. It is therefore a first guess for the average dust mass
mixing ratio in the tropics during a global dust event.
Applying both of these thresholds results in 0% of the retrievals meeting the
EDDL definition during the non-dust storm periods, 0.5% of the retrievals meeting it
during the MY 29A Regional Dust Storm, and 13% of the retrievals meeting it during the
2007 Global Dust Storm (Figure S1), demonstrating that it is a good filter for DDLs
associated with regional and global dust storm activity.
Text S4. The Automated Survey of the Retrievals
The 23,578 retrievals that met the EDDL definition were filtered by automated methods
according to four criteria.
Criterion 1: to minimize any confusion of dust with carbon dioxide ice, the survey
excluded retrieved detached dust layers in air colder than the sum of the CO2 frost point
temperature, twice the statistical error in the temperature retrieval, and 20 K (to account
for gravity wave effects (see Spiga et al. [2012]). This criterion eliminated 210 retrievals.
Criterion 2: the survey excluded retrievals in which water ice opacity exceeds dust
opacity in the layer. When water ice opacity is high, the retrieval algorithm may
introduce dust to fit errors in water ice spectroscopy [Heavens et al., 2011a, 2014]. This
criterion eliminated 134 retrievals.
6
Criterion 3: the survey excluded nightside retrievals (solar zenith angles > 90º). A
high mass mixing ratio detached dust layer would be expected to rapidly heat the
atmosphere during the day and cool it rapidly at night [Heavens et al., 2011a,b].
Retrievals without a distinct warming feature coincident with the dust layer are reported,
as long as temperatures meet Criterion 2. But at night, it is possible that temperatures
near the CO2 frost point coincident with an high mass mixing ratio aerosol layer are due
to rapid infrared cooling of dust and do not necessarily demonstrate that carbon dioxide
ice is condensing. To avoid this ambiguity, nightside retrievals were excluded. This
criterion eliminated 766 retrievals.
Criterion 4: the survey excluded all retrievals from observations made during
regional and global dust storms catalogued by Wang and Richardson [2015] during Mars
Years 28–30. This catalog focuses on low latitude dust storm activity, and no comparable
peer-reviewed survey yet exists for the succeeding years. This criterion excluded 21,755
retrievals, 21,529 of which were observed during the global dust storm of 2007 as
catalogued by Wang and Richardson [2015].
Text S5. Manual Survey of the Radiance Observations
The radiance observations were surveyed in two ways. In the first survey, the radiance
data in each MCS channel was converted to brightness temperature (or counts for A6)
and manually inspected. Note that each MCS Level 1B file contains four hours of
calibrated radiance observations. The castellation features were identified and their time
of occurrence and location were noted. Table S2 also contains additional information
such as whether they are associated with EDDL-containing retrievals in the region of
7
interest and whether there was regional dust storm activity in the area at the same time, as
inferred from Wang and Richardson [2015] and the MARCI Weather Reports
(http://www.msss.com/msss_images/subject/weather_reports.html).
In the second survey, the radiance data associated with all of the EDDLcontaining retrievals not associated with regional or global dust storm activity was
manually inspected in the same way as the first survey. It was determined whether the
EDDL-containing retrievals overlapped with a castellation feature or a loop feature. In
the process, it was discovered that a small number of castellation features had been
missed, so the results of the first survey were updated. (The underlying issue in most
cases was castellation features spanning two files.)
In both surveys, castellation and loop features were required to be apparent in
MCS channels A1–A6 in order to identify features with stronger contributions from dust
than from condensate clouds. Dust would be expected to warm the atmosphere, resulting
in emission features in MCS channels A1–A3 as well as direct emission in A4 and A5
and reflection in A6, which is not necessarily true of water ice or CO2 ice.
The castellation feature survey (Table S2) contains three instances in which a
limb castellation is in the region of interest, is not contemporaneous with any known
regional or global dust storm activity, but is not associated with EDDL-containing
retrievals. These instances occur in three different bins of 10º of Ls and suggest that the
systematic bias against detecting EDDL-containing retrievals due to problems with
retrieving from castellation features is on the order of one orbit per bin.
Text S6. Estimating the Frequency of EDDL Formation
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We estimate their frequency of formation of EDDLs in a given region (e.g., 30 S–60 N,
100–180 W) by estimating the expected fraction of orbits MCS would observe such a
layer if one were always present, fE, and then comparing fE to the fraction of orbits MCS
actually observed such a layer, fO. If fO < fE, fO/ fE is the fraction of time that a layer is
present. If layers do not last multiple sols, fO/ fE is the frequency of layer formation in
units of sol-1.
In most cases, layers do not last multiple sols. (A possible exception is shown in
Figure 4b in the main text.) A dust layer of a few ppm mass-mixing ratio at 60 km above
the datum (~0.3 Pa) would be quickly removed by sedimentation. Following the
equations of Murphy et al. [1990], a dust particle of 1.06 m radius (the effective radius
of dust assumed by the retrieval algorithm) would fall initially at 3.5 ms-1 and be below
40 km in less than a sol. Mesoscale modeling by Spiga et al. [2013] suggests that
detached dust layers of 10s of ppm mass mixing ratio may rise during the day due to
buoyancy obtained by radiative self-heating, counteracting some of the effects of
sedimentation. In addition, smaller dust particles will sediment more slowly. However,
horizontal advection should gradually dilute layers. Yet even if layers do last multiple
sols, assuming they do not do so results in an upper bound for frequency.
We estimate fE under the assumption that the average longitudinal dimension of a
layer is on the order of 1000 km. In 17 cases (making up 120 of the 211 EDDLcontaining retrievals that are outside of dust storm activity and in the ROI), layers were
observed in successive orbits, arguing that their longitudinal dimension sometimes
exceeds 1500 km. However, there are 33 cases in which layers in the ROI were not
observed on successive orbits. Mesoscale modeling suggests a typical longitudinal
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dimension of 1000 km is plausible [Rafkin et al., 2002; Michaels et al., 2006]. Assuming
the layer is randomly distributed in longitude and using the fact that the average
longitudinal extent of the region is 4000 km, it is found that MCS has a 25% probability
of observing a layer during each MRO orbit. The parameter fO, is then the fraction of
orbits on which EDDL-containing retrievals were observed (Figure 2f), such that the
formation rate of EDDLs is simply 4 fO sol-1, where fO is expressed as a fraction rather
than as a percentage.
Text S7. References
Cantor, B.A. (2007), MOC observations of the 2001 Mars planet-encircling dust storm,
Icarus, 186, 60–96.
Heavens, N. G., J. L. Benson, D. M. Kass, A. Kleinböhl, W. A. Abdou, D. J. McCleese,
M. I. Richardson, J. T. Schofield, J. H. Shirley, and P. M. Wolkenberg (2010), Water ice
clouds over the Martian tropics during northern summer, Geophys. Res. Lett., 37,
L18202, doi:10.1029/2010GL044610.
Heavens, N. G., M. I. Richardson, A. Kleinböhl, D. M. Kass, D. J. McCleese, W. Abdou,
J. L. Benson, J. T. Schofield, J. H. Shirley, and P. M. Wolkenberg (2011a), The vertical
distribution of dust in the Martian atmosphere during northern spring and summer:
Observations by the Mars Climate Sounder and analysis of zonal average vertical dust
profiles, J. Geophys. Res., 116, E04003, doi:10.1029/2010JE003691.
Heavens, N. G., M. I. Richardson, A. Kleinböhl, D. M. Kass, D. J. McCleese, W. Abdou,
J. L. Benson, J. T. Schofield, J. H. Shirley, and P. M. Wolkenberg (2011b), Vertical
distribution of dust in the Martian atmosphere during northern spring and summer: Highaltitude tropical dust maximum at northern summer solstice, J. Geophys. Res., 116,
E01007, doi:10.1029/2010JE003692.
Heavens, N. G., M. S. Johnson, W. A. Abdou, D. M. Kass, A. Kleinböhl, D. J. McCleese,
J. H. Shirley, and R. J. Wilson (2014), Seasonal and diurnal variability of detached dust
layers in the tropical Martian atmosphere, J. Geophys. Res. Planets, 119, 1748–1774,
doi:10.1002/2014JE004619.
Kleinböhl , A., J. T. Schofield, D. M. Kass, W. A. Abdou, C. R. Backus, B. Sen, J. H.
Shirley, W. G. Lawson, M. I. Richardson, F. W. Taylor, N. A. Teanby, and D. J.
McCleese (2009), Mars Climate Sounder limb profile retrieval of atmospheric
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temperature, pressure, dust, and water ice opacity, J. Geophys. Res., 114, E10006, doi:
10.1029/2009JE003358.
Kleinböhl, A., J. T. Schofield, W. A. Abdou, P. G. J. Irwin, R. J. de Kok (2011), A
single-scattering approximation for infrared radiative transfer in limb geometry in the
Martian atmosphere, J. Quant. Spectrosc. Radiat. Transfer, 112, 1568–1580.
Kleinböhl, A., R.J. Wilson, D. Kass, J. T. Schofield, and D. J. McCleese (2013), The
semidiurnal tide in the middle atmosphere of Mars, Geophys. Res. Lett., 40, 1952–1959,
doi:10.1002/grl.50497.
McCleese, D. J., J. T. Schofield, F. W. Taylor, S. B. Calcutt, M. C. Foote, D. M. Kass, C.
B. Leovy, D. A. Paige, P. L. Read, and R. W. Zurek (2007), Mars Climate Sounder: An
investigation of thermal and water vapor structure, dust and condensate distributions in
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doi:10.1029/2006JE002790.
McCleese, D. J., N.G. Heavens, J.T. Schofield, W.A. Abdou, J.L. Bandfield, S.B. Calcutt,
P.G.J. Irwin, D.M. Kass, A. Kleinböhl, S.R. Lewis, D.A. Paige, P.L. Read, M.I.
Richardson, J.H. Shirley, F.W. Taylor, N. Teanby, R.W. Zurek (2010), Structure and
dynamics of the Martian lower and middle atmosphere as observed by the Mars Climate
Sounder: Seasonal variations in zonal mean temperature, dust, and water ice aerosols, J.
Geophys. Res. Planets, 115, E12016, doi:10.1029/2010JE003677.
Michaels, T. I., A. Colaprete, and S. C. R. Rafkin (2006), Significant vertical water
transport by mountain-induced circulations on Mars, Geophys. Res. Lett., 33, L16201,
doi:10.1029/2006GL026562.
Montabone, L., F. Forget, E. Millour, R.J. Wilson, S.R. Lewis, B. Cantor, D. Kass, A.
Kleinböhl, M.T. Lemmon, M.D. Smith, M.J. Wolff, (2015), Eight-year Climatology of
Dust Optical Depth on Mars, Icarus, in press, doi: 10.16/j.icarus.2014.12.034.
Rafkin, S. C. R., M. R. V. Sta. Maria, and T. I. Michaels (2002), Simulation of the
atmospheric thermal circulation of a martian volcano using a mesoscale numerical model.
Nature, 419, 697-699.
Spiga, A., F. González-Galindo, M.-Á. López-Valverde, and F. Forget (2012), Gravity
waves, cold pockets and CO2 clouds in the Martian mesosphere, Geophys. Res. Lett., 39,
L02201, doi:10.1029/2011GL050343.
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Wang, H. and M.I. Richardson (2015), The origin, evolution, and trajectory of large dust
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Figure S1. Bivariate histogram (% of total retrievals) of the highest value of mass mixing ratio in a retrieval and the altitude above the
areoid at which it occurs in all dayside retrievals from 30° S–30° N during: (a) Ls=261.6º–305.5º of MY 28; (b) Ls=231.4º–237.3º of
MY 29; (c) Ls=261.6º–305.5º of MY 30; (d) Ls=231.4º–237.3º of MY 30. Binning is in intervals of 1 ppm and 1 km. The red lines mark
the thresholds for the EDDL definition. The percentage of retrievals that meet the EDDL definition is given in the titles.
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Figure S2. A dust cloud over Arsia Mons observed by MRO-MARCI at Ls=177.05° of MY
29 (B04_011255_1771_MA_00N121W, observed around 12:00 UTC on 20 December
2008). The data has been calibrated and photometrically corrected as in Cantor [2007]
to emphasize the dust cloud and projected to 1 km resolution in simple cylindrical
coordinates.
Table S1. Results of the Manual Survey of Extreme Detached Dust Layers (attached as a
separate file). Table lists individual orbits with EDDL-containing retrievals. Latitudes
and longitudes are of the approximate center of the EDDL-containing retrievals. The
magnitude of the layer is defined as the highest magnitude EDDL-containing retrieval in
the orbit, while the altitude is defined as the altitude at which the maximum dust mass
mixing ratio (the magnitude) occurs in the highest magnitude retrieval in the orbit. Orbits
with retrievals identified as being associated with regional dust storms are marked in red.
Some of these instances span multiple orbits and so ranges of parameters are provided.
Orbits with EDDL-containing retrievals observed synchronously with dust storm activity
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over the volcanoes are marked in yellow. As in the main text, the Region of Interest is
defined as 30º S–60º N, 100º –180º W. When volcanoes are referred to, only Olympus,
Ascraeus, Pavonis, and Arsia Montes are meant.
Table S2. Results of the Castellation Feature Survey of MRO-MCS Calibrated Radiance
Observations (attached as separate file). As in the main text, the Region of Interest is
defined as 30º S–60º N, 100º –180º W. Latitudes and longitudes are of the approximate
centers of the features at the tangent point of the observation. Castellation features that
are in the Region of Interest, but are neither associated with regional or global dust storm
activity nor with EDDL-containing retrievals included in Table S1 are in bold. Further
details concerning the compilation of the table are in Text S6.
15