Seminars
Lecturer: Joël Arnault
Date: 2011-06-16 10:30
Place: Aniara
Eventual Evolution into Tropical Cyclones of Convective Disturbances in West Africa and Eastern Tropical AtlanticThe formation of Cape Verde Cyclones is the result of an interaction between several processes: troughs and ridges of the mid-level African easterly wave, the low-level monsoon flow and trade winds off the West African coast, convective developments, the mid-level Saharan anticyclone, the low level Saharan heat low, and mid-and upper level troughs of mid-latitude origin.
These processes are investigated in a climatological study of five seasons of European Center for Medium-range Weather Forcast analyses and Meteosat images.
This is complemented with two case studies modeled with Méso-NH (the non-hydrostatic mesoscale atmospheric model of the French research community): (1) the perturbation which spawn Hurricane Helene (2006), (2) the so-called ?Perturbation D?, a non-developing case observed during AMMA / SOP-3 (African Monsoon Multidisciplinary Analysis - Special Observing Period 3) in Dakar in September 2006. The simulated evolutions are quantified with energy and vorticity budgets.
The main result of this thesis is that geostrophic adjustment of wind field to a pressure perturbation of convective origin in the Cape Verde Islands area occurs only if there is a production of eddy kinetic energy through barotropic conversion and a horizontal advection of cyclonic vorticity. This confirms the well-known hypothesis that tropical cyclogenesis is the result of an interaction between convective systems and a favorable environment.
Created 2011-05-19 11:11:51 by Uwe RaffalskiLast changed 2011-05-19 12:10:11 by Uwe Raffalski
