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 Velocity + Coriolis force Phase Meridional Zonal + In the Northern Hemisphere In the Southern Hemisphere + - Velocity Coriolis force
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
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 )
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
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
A view from Space Shuttle Airglow
Airglow Emission Rates 120 110 O2 O 2 (0,1) (0,0) lines 8650A O 557.7 5577A nm Altitude (km) 100 90 80 Na 589.3 5893 nm A 97 km 86 km 70 OH 8920 nma 60 0.1 1.0 10.0 100.0 1000.0 Volume emission rate (photons cm -3 s -1 ) solid=molecules, dashed=atoms
Thermosphere Airglow Emission Rates 300 280 Altitude (km) 260 240 O 630.0 6300 nm A 220 200 0.1 1.0 10.0 100.0 Volume emission rate (photons cm -3 s -1 )
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 + + ( 1 2 + e O O D ) Collisional deactivation of N2 3 1 N2( A Σ + u ) + O N2 + O( S) OH emission k 3 2 16 H+ O OH( 6 ν' 9) + O
Fabry-Perot Interferometer (FPI) Plate Post Coating
Etalon Incoming Light Optical Axis Fabry-Perot Interferometer 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 87 km West Zenith East 174 km FPI South 174 km (a) (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: 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
TIDI Measurement Viewing Directions 4 3 1 2 9 minutes 4 Satellite Travel direction 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.