Relationship between convection over Central America and the intensity of the jet stream bearing on the 1999 December European storms

During 26–28 December 1999, two very powerful and devastating extratropical cyclones hit Western Europe. These two storms were associated with an upper-level zonal jet, remarkable in its intensity and its large extension over the Atlantic Ocean. In this study, we focus on the relationship between the exceptional features of this jet stream and some heavy precipitation that occurred over Central America during mid-December. A Rossby-wave train excited by strong convective activity over this area is likely to play a key role in this teleconnection. To assess this tropical–extratropical interaction, several numerical experiments have been performed with the French global model ARPEGE. Firstly, the effects of convection have been neutralized within a domain localized over Central America. Then, to combine the model with observations, a new strategy has been devised. Within a selected window, the parametrized latent heat release has been deduced from Tropical Rainfall Measuring Mission (TRMM) precipitation data, translated in terms of a potential vorticity (hereafter PV) source and incorporated into the model using PV inversion. These simulations show, in particular, that the convective activity over Central America triggers a wave train that moves poleward and eastward with the group velocity, finally to strengthen the North Atlantic jet stream, leading to windstorms Lothar and Martin. Copyright © 2011 Royal Meteorological Society