Neutral Winds in the Upper
Atmosphere
Qian Wu
National Center for Atmospheric
Research
Outline
• Overview of the upper atmosphere.
• Ozone heating.
• Neutral wind tides (the strongest dynamic
feature).
• Why do we need to understand upper
atmospheric winds?
• How do we measure upper atmospheric winds?
• Observational results.
• Satellite and Balloon borne instruments.
Upper Atmosphere
Temperature Profile
Forbes, Comparative Aeronomy, 2002
Hagan et al. Global Scale Wave Model (GSWM, March)
Hagan et al. GSWM (March)
Semidiurnal Tide in Meridional
Winds
Hagan et al. GSWM (June)
Hagan et al. GSWM (June)
Phase Comparison
Coriolis Force Effect on Tidal
Phase
Velocity
+
Coriolis force
+
In the Northern Hemisphere
In the Southern Hemisphere
+
Coriolis force
Velocity
Meridional
Zonal
Dynamics Equations

Du
u t an
(f 
)v 
 X,
Dt
a
a cos

Dv
u t an
(f 
)u 
 Y , H  RT / g is thescale height,
a is theearth radius,
Dt
a
a
 is thegeopotenti
al,
 z  H 1 Re z / H ,
[u  ( v cos ) ]
a cos
D
 Q,
Dt

(  0 w) z
0
  T ( p s /p ) (  R / c p  2/7) is thepotentialtemperature,
 0,
 0 is thedensity
  2 / Tday
f  2 sin 
( ,  )  (longitude, latitude)
(u, v, w), velocityin zonal,meridional, and verticaldirections
D

u
 v 

 

w
Dt t a cos  a 
z
X , Y forcingterm
Q heatingsource
Tidal Wave Function
~
{u~, v~, }  e z / 2 H e ikz z exp i ( s  t )
s is thezonal wavenumber
2
is the wave periodin days

k z is the verticalwavenumber
t is theuniversal time
TL  t 


local time

~
{u~, v~, }  e z / 2 H e ikz z exp i ( s   (TL  ))  e z / 2 H e ikz z exp i ((s   )  TL )

If s   , then
~
{u~, v~, }  e z / 2 H e ikz z exp i ( T ) is migratingtide
L
Migrating tides
Nonmigrating tides
Sun-synchronous
westward
non Sun-synchronous
westward, eastward, standing
zonal wavenumber: 1/period(days)
(diurnal tide : 1 semidiurnal: 2)
zonal wavenumber: any
radiative forcing, …
latent heat
PW/tidal interaction, …
comparable to / exceed
migrating tide
longitude modulation
the
Why do we need to know upper
atmosphere neutral wind tide?
• Tides are generated in the stratosphere and
strongly affected by changes in that region such
as:
– Gravity wave activities,
– Quasi-biennial oscillation (QBO) in the equatorial
region
– Sudden stratosphere warming in the high latitudes
• Long term trends in tides may be linked with
changes in the stratosphere.
• Tides also have a great impact on the
equatorial ionosphere through dynamo effect.
Neutral Wind Measurement
Airglow
A view from Space Shuttle
Airglow Emission Rates
120
Altitude (km)
110
O 2 (0,1)
(0,0)
O2
lines
8650A
557.7
nm
O
5577A
100
97 km
90
86 km
80
Na
5893
589.3
nm A
70
OH8920
892 nmA
OH
60
0.1
1.0
10.0
Volume emission rate (photons cm
solid=molecules, dashed=atoms
100.0
-3
s - 1)
1000.0
Thermosphere Airglow Emission
Rates
300
Altitude (km)
280
260
630.0
nm A
O
6300
240
220
200
0.1
1.0
Volume emission rate (photons cm
10.0
-3
100.0
-1
s )
Airglow Emission Sources at Night
O 6300 Å red line
O 5577 Å green line
Electron impact
Electron impact
O  e  O(1S )  e
O  e  O(1D)  e
Collisional deactivation of N2
Dissociative recombination
O2  e  O  O(1D)
N2 ( A3u )  O  N2  O(1S )
OH emission
16
H  O3 
 OH(6   '  9)  O2
k
Fabry-Perot Interferometer (FPI)
Plate
Post
Coating
Etalon
Incoming
Light
Optical
Axis
Fabry -Perot
Interf erometer
Imaging
Lens
Image
Plane
Fabry-Perot Fringe Pattern
FPI Configuration
Major Components
•
•
•
•
•
•
•
Sky scanner
Filters & filter wheel
Etalon & chamber
Thermal & pressure control
Focusing lens
Detector
Computer system
•
•
•
•
•
Highlights
Computerized micrometer
Daily laser calibration
High degree automation
Michigan heritage
NCAR enhancement
Instrument Operation
North
OH Airglow Layer
45 deg
FPI
West
Zenith
87 km
174 km
South
174 km
(a)
East
(b)
FPI at Resolute
FPI at Resolute
Instrument Electronics
FPI Operational Mode
Emission
Integration
time
Wind Errors Altitude
OH 8920 A
3 minutes
6 m/s
87 km
O 5577 A
3 minutes
1 m/s
97 km
O 6300 A
5 minutes
2-6 m/s
250 km
FPI Fringes
Laser
8920
5577
6300
Mesospheric Wind Semidiurnal Tide
Lower Thermospheric Wind Semidiurnal tide
TIMED Fact Sheet
Limb-Scan Measurements
Airglow layer
The TIDI Instrument
The TIMED Doppler Interferometer (TIDI) is
a Fabry-Perot interferometer for measuring
winds in the mesosphere and lower
thermosphere.
Primary measurement: Global neutral wind
field, 60–120 km
Primary emission observed: O2 1 (0-0) P9
Additional emissions observed: O2 1 (0-0)
P15, O2 1 (0-1) P7, O(1S) “green line”
Telescope Assembly
Profiler
TIDI Measurement Viewing Directions
4
1
3
2
9 minutes
Satellite
Travel direction
4
1
3
2
TIDI Local Time Coverage Day
80 2002
Shifting 12 minutes per day in local time
TIDI Coldside Wind Vectors
TIDI Warmside Wind Vectors
TIDI Observations
Model Winds (GSWM)
Oberheide and Hagan
Stratosphere Balloon Borne Fabry-Perot
Interferometer
• Allow daytime observation of
thermospheric winds due to low
solar scatter background at high
altitudes.
• Inexpensive compared to satellite
instrument.
Summary
 Upper atmospheric winds contain strong global
scale waves (e.g. tides).
 Tides are related to changes in the stratosphere
and can affect the ionosphere.
 Upper atmospheric winds are the key to a better
understanding of the ionosphere.
 There is a lack of observation upper
atmospheric winds on a global scale.
 I see a great opportunity for future balloon and
satellite missions.