1. African easterly wave dynamics in a full-physics numerical model. Gareth Berry and Chris Thorncroft. University at Albany/SUNY, Albany, NY,USA.

2. Approach. - Using a full-physics mesoscale model to simulate AEW cases. - Analysis of model output will be subjected to synoptic analysis with an emphasis put upon the evolution of the potential vorticity (PV) field to identify the dominant physical processes. Problem. - We don’t know enough about the physical processes that occur within an AEW, especially how those on different scales interact. - Recent research (e.g. Berry and Thorncroft, 2005) has suggested that the synoptic scale AEW and mesoscale convection can feedback on one another and promote mutual growth.

3. Model details. - Using the Weather Research and Forecasting (WRF) model with full physics suite to simulate the continental life cycles of AEWs. - The case shown in this presentation is from 2004 and was chosen for being an ‘average’ AEW based on the analysis of Berry, Thorncroft and Hewson (2006). - Using a 50km horizontal resolution with 30 levels between surface and 10hPa on a large domain (14000x5000km): - Model run with a 120s timestep out 144hr. - Domain initial conditions and 6-hourly lateral boundary conditions come from NCEP FNL analysis. - Using following parameterizations: WSM-3 Microphysics, Grell-Devenyi Cumulus, YSU PBL, RRTM/Dudhia Radiation schemes and RUC Land Surface model.

4. 4/9/04 12UTC 5/9/04 12UTC 6/9/04 12UTC 7/9/04 12UTC 8/9/04 12UTC 9/9/04 12UTC t+24 hours t+48 hours t+72 hours t+96 hours t+120 hours t+144 hours Red line = location of objective AEW trough. METEOSAT Infrared, 700hPa trough line (GFS analysis) Simulated cloud top temperature, 700hPa trough line (WRF Model)

5. PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+0hrs

6. PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+6hrs

7. PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+12hrs

8. PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+18hrs

9. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+24hrs PV averaged 1-10km in red box

10. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+30hrs PV averaged 1-10km in red box

11. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+36hrs PV averaged 1-10km in red box

12. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+42hrs PV averaged 1-10km in red box

13. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+48hrs PV averaged 1-10km in red box

14. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+54hrs PV averaged 1-10km in red box

15. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+60hrs PV averaged 1-10km in red box

16. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+66hrs PV averaged 1-10km in red box

17. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+72hrs PV averaged 1-10km in red box

18. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+78hrs PV averaged 1-10km in red box

19. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+84hrs PV averaged 1-10km in red box

20. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+90hrs PV averaged 1-10km in red box

21. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+96hrs PV averaged 1-10km in red box

22. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+102hrs PV averaged 1-10km in red box

23. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+108hrs PV averaged 1-10km in red box

24. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+114hrs PV averaged 1-10km in red box

25. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+120hrs PV averaged 1-10km in red box

26. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+126hrs PV averaged 1-10km in red box

27. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+132hrs PV averaged 1-10km in red box

28. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+138hrs PV averaged 1-10km in red box

29. X PV at 3.5km (coloured),  and winds at 1km (thin black) Objective troughs (thick black) and jets (dashed purple) at 3.5km t+144hrs PV averaged 1-10km in red box

30. AEW Energetics: - Following Moore and Montgomery 2005 (“Reexamining the Dynamics of Short-Scale, Diabatic Rossby Waves and Their Role in Midlatitude Moist Cyclogenesis”). - Ratio of diabatic conversion of eddy APE (GE) and conversion of basic state APE to eddy APE (CA) gives relative order of magnitude importance of diabatic and baroclinic processes. - Computations are performed within the red box shown on the previous sequence. S = diabatic heating

31. Using a 10x10 degree box, centred on 3.5km trough/jet intersection (red box in PV plots). Until crossing coast, ratio of GE/CA is 1.22; both baroclinic and diabatic processes are equally important in the growth of the synoptic AEW.

32. The maintenance of deep convection. - Both reality and the WRF model show that deep convection tends to be focused close to the AEW trough. - Previous work has suggested that the synoptic AEW promotes convection via: (i) Adiabatically forced ascent (e.g. Thorncroft and Hoskins, 1994). (ii) Advection of low-level basic state  e distribution by the AEW, altering CAPE/CIN (e.g. Berry and Thorncroft, 2005). (iii) Balanced temperature response to the presence of the AEW PV anomaly altering the convective stability.

33. The maintenance of deep convection. - Both reality and the WRF model show that deep convection tends to be focused close to the AEW trough. - Previous work has suggested that the synoptic AEW promotes convection via: Isentropic motion computed from the WRF run suggests vertical motion is weak (~few cm/s) and not rooted in the boundary layer. (i) Adiabatically forced ascent (e.g. Thorncroft and Hoskins, 1994). (ii) Advection of low-level basic state  e distribution by the AEW, altering CAPE/CIN (e.g. Berry and Thorncroft, 2005). (iii) Balanced temperature response to the presence of the AEW PV anomaly altering the convective stability.

34. The maintenance of deep convection. - Both reality and the WRF model show that deep convection tends to be focused close to the AEW trough. - Previous work has suggested that the synoptic AEW promotes convection via: Isentropic motion computed from the WRF run suggests vertical motion is weak (~few cm/s) and not rooted in the boundary layer. In this case the  e flux divergence is slightly lower (i.e. increased convergence) ahead of the AEW trough, but this signal is weak and incoherent. (i) Adiabatically forced ascent (e.g. Thorncroft and Hoskins, 1994). (ii) Advection of low-level basic state  e distribution by the AEW, altering CAPE/CIN (e.g. Berry and Thorncroft, 2005). (iii) Balanced temperature response to the presence of the AEW PV anomaly altering the convective stability.

35. Temperature excess of a parcel lifted adiabatically from the lowest model level: Cross-section of lifted parcel  T (coloured) and PV (contours) along 10N at t+94hrs. 800hPa lifted parcel  T and 3.5km PV at t+94hrs - Pattern showing column of positive buoyancy in PBL, centred on AEW PV anomaly. Clearest before local noon due to strong diurnal cycle in the WAM region. A A B B

36. AEW26 Parcel buoyancy (coloured), PV and circulation (vectors), averaged 7-17N at t+46

37. AEW26 Parcel buoyancy (coloured), PV and circulation (vectors), averaged 7-17N at t+70

38. AEW27 AEW26 Parcel buoyancy (coloured), PV and circulation (vectors), averaged 7-17N at t+94

39. AEW26 AEW27 Parcel buoyancy (coloured), PV and circulation (vectors), averaged 7-17N at F+120

40. Conclusions. -The WRF model can produce physically plausible AEWs. - Energetic calculations indicate that adiabatic and diabatic processes are almost equally important in the AEW dynamics. -It is suggested that convection is favoured close to the AEW trough due to the lower to mid level thermodynamic structure imposed as a balanced response to the PV maxima associated with the AEW trough. - PV analysis (not shown here for brevity) shows that most of these diabatic processes are associated with the model representation of MCSs. When run without convective systems (by removing cumulus and microphysical parameterizations) the AEW weakens considerably. - Further work modeling an individual MCS within this AEW case, using a 2km nest has demonstrated that the heating profiles and PV tendencies are very close to those seen in the 50km run.