Upper Atmosphere Neutral Wind and Tide

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.