1. Middle and Lower Atmosphere Michael Kelley
Topics -
Vertical Coupling by Waves
Tidal Characterization and Variability
Instabilities
Global Coverage
Instrumental Requirements and Campaigns
Middle and Lower Atmosphere

2. Gravity Wave Coupling critical level Gravity Wave (GW) Sources:
GW excitation mechanisms.
Climatology of GW source distribution.
Spectral components of various wave sources.
==> Physics-consistent specifications of GW in GCM.
GW propogation and breaking
Quantify subgrid processes related to wave breaking.
Multiscale interactions:
Two way interactions with mean circulation, planetary waves, and tides.
Implications of GW geographical and temporal variability.
critical
level
Alexander and Holton (2000)
Middle and Lower Atmosphere

3. Middle and Lower Atmosphere
Tidal Variability
Gravity Wave Interactions :
Planetary Wave Interactions
Middle and Lower Atmosphere

4. Middle and Lower Atmosphere
Tides
Annual, daily, and subdaily atmospheric tides are seen in surface pressure, GPS-derived tropospheric delay, and mesospheric winds
Atmospheric tides dominate the dynamics of the mesosphere-lower thermosphere (MLT).
Middle and Lower Atmosphere

5. Middle and Lower Atmosphere
Wind Models
Climatology
The de facto neutral wind model in current use is HWM-93
In the MLT, data sources were MF radar, meteor radar, incoherent scatter radar, rocketsondes, rocket grenade sounding, and gradient winds
No direct Doppler wind measurements measured either by ground based or satellite based platforms were ever included in the Horizontal Wind Model for MLT winds
Presently, 15 years of HRDI, WINDII, and TIDI wind measurements plus a significant ground based database are ignored in HWM climatology
Space Weather
Significant differences exist in MLT winds as a function of longitude
Propose studies that advance:
Understanding long term MLT climatology
Better appreciation of longitudinal tidal differences
Middle and Lower Atmosphere

6. Middle and Lower Atmosphere
Why predict or assimilate the Mesosphere and Lower Thermosphere?
Couple the neutral atmosphere to high altitude “space weather” disturbances.
Couple MLT to troposphere: knowledge of gravity wave sources and intermittency factors are critical for GW parameterizations in MLT.
MLT low density and low thermal “inertia” make this region very sensitive to “change” (climate or otherwise), compared to troposphere.
Models estimates suggest a decline in MLT temperature associated with increases in CO2 and N2O concentrations. Models have addressed only the thermodynamic and radiative transfer aspects of the problem for a global mean. Long-term dynamic changes strongly affect the filtering of gravity waves, offering a continuing challenge for modelling efforts. Long-term observations are ambiguous regarding the direction of changes. Identification of the sources of variations on all time scales will help sort out the relative contribution of these sources to long-term change.
Middle and Lower Atmosphere

7. Middle and Lower Atmosphere

8. Middle and Lower Atmosphere

9. Middle and Lower Atmosphere
NLC over Finland
courtesy P. Parviainen
Ice Clouds in the Mesosphere and their Variability
Noctilucent clouds (NLC) were discovered over 100 years ago
They are the Earth’s highest clouds (~82 km) and comprise microscopic ice crystals (~50nm radius) that form and grow in the vicinity of the high-latitude cold summer mesopause (T < 130 K).
Satellite measurements have established the existence of extensive clouds in the Arctic and Antarctic summer polar mesosphere (called PMC)
Models of PMC formation show that super-saturated regions must be present for cloud nucleation. Yet, there are still no comprehensive knowledge of the chemical/thermal environment in which PMC form.
SNOE PMC data
Middle and Lower Atmosphere

10. Middle and Lower Atmosphere
Instabilities
Convective Instability (R.T.)
Thermal structure influenced by mean state (winter/summer), D&SD Tides, PW, and AGWs.
Shear Instability (K.H.)
Strong tides and tide/AGW coupling contribute
Effects
Overturning (heat and constituent transport), MILs, Ripples, Stress
Middle and Lower Atmosphere

11. Middle and Lower Atmosphere
Instruments with higher temporal and spatial resolutions
Lidars (T, winds) , imagers (airglow, ripples, temperture), radar (winds)
Simulations, models, waves,
NEW (Extend to lower altitudes and expanded information withing the MLT)
Tomography with multi-view, multispectral (airglow layer) image inversion
Lidar, Rayleigh with power (50-80 km)
Aircraft, rocket, and balloon correlative campaigns
Middle and Lower Atmosphere

12. Middle and Lower Atmosphere
Proposed AMISR/AkFPI ion-neutral coupling campaign
All-sky imagers would document particle preciptiation distribution
Green-shaded regions cover range of zenith angles from:
20° minimum to 45° maximum
Five common volume points would be observed in sequence so that 5 neutral wind vectors are fully determined.
These points, CV 1- CV 5, would be sequentially surveyed by the 3 FPI instruments in synchronized mode.
The AMISR would provide similar coverage re the 5 CV points.
Vorticity would be calculated for each of the four triangles shown. Variations would be particularly interesting during substorm activity. The CV points would be supplemented by additional points in the zenith, zonal and meridional directions for each FPI observatory. • 20 45
Middle and Lower Atmosphere

13. Middle and Lower Atmosphere
Prospects for the usefulness of tropospheric delay data (cont'd):
Sensitivity of GPS-derived ZTD appears to be sufficient to resolve subdaily oscillations including the lunar (gravitational) tidal oscillation at L2. Sidebands here reflect annual modulation of the S2 tide.
Enhanced power around S2 indicates modulation of the S2 tide by planetary waves.
A global network of dual-frequency GPS receivers allows one to analyze tropospheric tidal phenomena by wave decomposition. Network density will increase with the availability of low-cost dual-frequency receivers. Precise point positioning (PPP) allows ZTD to be calculated for any dual-frequency GPS receiver.
Future developments offer promise:
ZTD estimation strategy continues to be refined.
A second civilian GPS signal (~2010) will allow for accurate and inexpensive dual-frequency GPS receivers.
The advent of the European GPS system (Galileo) will increase accuracy and density of measurements.
Middle and Lower Atmosphere

14. Middle and Lower Atmosphere
Proposed Class I Instruments and Coordinated Campaigns
Beef up all 3 sodium lidars in the CRRL to 24-hour capability and large telescope
Mobile lidars in concert with AMISR
More stations (both radar and lidar) to cover minimal longitudes and latitudes as required by modelers
Community designed (led by modelers and wave specialists, reality-checked by instrument “owners”) coordinated campaigns..
Middle and Lower Atmosphere