1. A CASE STUDY OF GRAVITY WAVE GENERATION BY HECTOR CONVECTION
Georgiy Stenchikov (Rutgers University, New Brunswick, NJ)
Kevin Hamilton (IPRC, University of Hawaii, Manoa, HI)
Objectives:
Gravity wave generation by strong tropical convection
Conduct simulations using realistic meteorological conditions, terrain, and SSTs
Comparisons with Radar and Airglow observations
Interaction of waves with the mean flow
Stratosphere-troposphere interactions
Mixing at the tropical tropopause level

2. Simulations from 1-st principles and parameterizations
Parameterization of a non-local wave effects depends on the resolution of the driving GCM
Local/non-local conditions for convective parameterizations
Non-local parameterizations are required for the models with finer spatial resolution
Intermediate resolutions when nothing is working, e.g., 10-km resolution for convective parameterization

3. Dawex airglow observation sites

4. Model
Regional Atmospheric Modeling System (RAMS)
Nonhydrostatic
Semi-implicit time-split finite-difference numerical scheme
1-km resolution terrain
1-km resolution vegetation cover data set
Land surface model – LEAF2
Vertical mixing – Mellor-Yamada turbulent closure
Horizontal mixing – Smagorinsky-Lilly
Nesting
Bulk microphysics, Delta-Eddingthon Radiative transfer scheme
Open lateral boundary conditions; Sponge layers

5. Simulation Setup
Time period: November 16, DAWEX IOP2
Domain: 400 x 200 x 110 km
Resolution: Longitude: 2 km, Latitude: 2 km,
Altitude grid spacing: from 30 to 1000 m
Time step: 3 sec; 200x100X130 grid points
Initialization from soundings on 11/16/01 at 0211 UTC
From 0 to 30 km (Toshitaka Tsuda)
UKMO 2001 U and T below 56km; URAP winds and CIRA-86 Temperature above 56 km (Robert Vincent)
Simulation started at 0000 UTC

7. Simulated storm starts in the western part of the Tiwi’s at about 0400 UTC and reaches maximum intensity at about 0700 UTC or a little earlier. The location and timing of the storm is in a good agreement with observations.
Streamlines are shown at 100 m altitude

8. Vertical wind (m/s) in altitude-longitude cross section at 11.5S.
The field above 80 km near right boundary is contaminated by reflection from the boundary.
Vertical wind (m/s) at 90 km. The top of the domain is at 110 km. In this calculations we used 130 vertical grid points.

9. Vertical wind (m/s) in the altitude-longitude cross section at 11.5S.
Latent heat release (K/day) in the same cross section.
Negative heating rates correspond to melting of falling ice particles

10. Experiments with Increased Domain Oriented in South-North Direction
Domain: 200 x 500 x 110 km
Time step: 3 sec; 100x250X130 grid points
Nudging of mean potential temperature above 50 km
Exponential sponge layer near lateral boundaries
Experiment 7
All winds weakly nudged south of 12.5S
Experiment 9
Damping of W south of 12.5S
Experiment 10
Damping of W and Water Vapor south of 12.5S

11. Experiment 7

12. Experiment 9

13. Experiment 10

14. Provided by Jim Hecht

15. Experiment 7

16. Experiment 9

17. Experiment 10

18. Experiment 7

19. Experiment 9

20. Experiment 10

21. Experiment 7

22. Experiment 9

23. Experiment 10

24. Experiment 7

25. Experiment 9

26. Experiment 10

27. Experiment 7

28. Experiment 9

29. Experiment 10

30. Experiment 9

31. Expeiment 9

32. A keogram constructed from airglow images taken at Katherine on November 16, 2001 (provided by Alan Liu)
Waves were propagating Southward and Eastward

33. Conclusions
500 km domain in South-North direction allows to simulate the wave signal in the vicinity of Katherine and Wyndham sites but larger domain is desirable
Simulated storm has good timing and location
Lateral boundary conditions work fairly reasonable
Latent heat release is consistent with W and rate of precipitation at ground
Convection over continent affects timing and distribution of wave activity, directionality
Simulated GW have reasonable parameters: λ~40km, T~15min
Zonal flow effectively filters upward propagating GW
Simulated wave propagation is consistent with the airglow observations