Neutral Winds in the Upper Atmosphere. Qian Wu National Center for Atmospheric Research

Transcription

1 Neutral Winds in the Upper Atmosphere Qian Wu National Center for Atmospheric Research

2 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.

3 Upper Atmosphere

4 Temperature Profile

5 Forbes, Comparative Aeronomy, 2002

6 Hagan et al. Global Scale Wave Model (GSWM, March)

7 Hagan et al. GSWM (March)

8 Semidiurnal Tide in Meridional Winds Hagan et al. GSWM (June)

9 Hagan et al. GSWM (June)

10 Phase Comparison

11 Coriolis Force Effect on Tidal Velocity + Coriolis force Phase Meridional Zonal + In the Northern Hemisphere In the Southern Hemisphere + - Velocity Coriolis force

12 Dynamics Equations, 0, ) ( cos ] ) cos ( [,, ) tan (, cos ) tan ( 0 0 / 1 Q Dt D w a v u e R H Y a u a u f Dt Dv X a v a u f Dt Du z H z z = = + + = Φ = Φ = Φ + + θ ρ ρ φ φ θ φ φ φ φ λ κ φ λ heating source forcing term, cos directions and vertical meridional, velocity in zonal, ),,, ( latitude) (longitude, ), ( sin 2 / 2 the density is temperature, the potential is 2/7) / ( ) / ( the geopotential, is the earth radius, is the scale height, is / 0 Q Y X z w a v a u t Dt D w v u f T c R p p T a g RT H day p s = = Ω = Ω = = = Φ = φ λ φ φ λ φ π ρ κ θ κ

13 Tidal Wave Function ~ { u ~, v~, Φ} e z / 2H e ik z z exp i( sλ Ωσt) s is the zonal wavenumber 2π is the wave period in days Ωσ k is the vertical wavenumber z t is the universal time λ TL = t + Ω ~ ~ { u ~, v, Φ} e If s = σ, then ~ ~ { ~,, z / u v Φ} e local time z / 2H 2H e e ik ik z z z z exp i( sλ Ωσ ( T exp i( ΩσT L L λ )) = e Ω z / 2H ) is migrating tide e ik z z expi(( s σ ) λ ΩσT L )

14 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 the migrating tide longitude modulation

15 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.

16 Neutral Wind Measurement

17 A view from Space Shuttle Airglow

18 Airglow Emission Rates O2 O 2 (0,1) (0,0) lines 8650A O A nm Altitude (km) Na nm A 97 km 86 km 70 OH 8920 nma Volume emission rate (photons cm -3 s -1 ) solid=molecules, dashed=atoms

19 Thermosphere Airglow Emission Rates Altitude (km) O nm A Volume emission rate (photons cm -3 s -1 )

20 Airglow Emission Sources at Night O 6300 Å red line O 5577 Å green line Electron impact Electron impact O + e O( 1 D) + e O + e O( 1 S) + e Dissociative recombination O + + ( e O O D ) Collisional deactivation of N2 3 1 N2( A Σ + u ) + O N2 + O( S) OH emission k H+ O OH( 6 ν' 9) + O

21 Fabry-Perot Interferometer (FPI) Plate Post Coating

22 Etalon Incoming Light Optical Axis Fabry-Perot Interferometer Imaging Lens Image Plane

23 Fabry-Perot Fringe Pattern

24 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

25 Instrument Operation North OH Airglow Layer 45 deg 87 km West Zenith East 174 km FPI South 174 km (a) (b)

26 FPI at Resolute

27 FPI at Resolute

28 Instrument Electronics

29 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

30 FPI Fringes Laser

31 Mesospheric Wind Semidiurnal Tide

32 Lower Thermospheric Wind Semidiurnal tide

33 TIMED Fact Sheet

34 Limb-Scan Measurements Airglow layer

35 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, km Primary emission observed: O 2 1 Σ (0-0) P9 Additional emissions observed: O 2 1 Σ (0-0) P15, O 2 1 Σ (0-1) P7, O( 1 S) green line Telescope Assembly Profiler

36 TIDI Measurement Viewing Directions minutes 4 Satellite Travel direction 1 3 2

37 TIDI Local Time Coverage Day Shifting 12 minutes per day in local time

38

39 TIDI Coldside Wind Vectors

40 TIDI Warmside Wind Vectors

41 TIDI Observations

42 Model Winds (GSWM) Oberheide and Hagan

43 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.

44 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.