Wednesday, 1 August 2001
Mesoscale processes and impact of FASTEX cyclones through momentum, heat, and water budgets (IOPs 11, 12, 16, 17)
The field phase of FASTEX (Fronts and Atlantic Storm-Track EXperiment) took place from January to February 1997. This unique dataset allows the mesoscale processes involved in secondary cyclogenesis to be investigated in depth. It also allows an original study of the impact of secondary cyclogenesis on the large-scale environment. In the present study, the 3D fields of reflectivity, wind and thermodynamic perturbations are first retrieved from airborne Doppler radar data and UKMO dropsondes within four case studies that are very different in terms of development stage. The 3D structure of these four cyclones and the associated mesoscale processes are analyzed in detail. From the previous 3D documentation, the vertical transport of horizontal momentum and heat budget are derived and interpreted for the IOP16 cyclone. It is found that this cyclone results in a significant warming and drying throughout the troposphere, with some indication of cooling and moistening due to evaporation in the low levels (below 1 km). These quantities are computed both at the scale of the cyclone and within the smaller-scale embedded precipitation entities. It is shown that transports are mostly occuring on the mesoscale, except within the narrow cold frontal rainband where convective-scale transports are significant. The quantification of the water budgets relies on the retrieval of the precipitation and cloud mixing ratios. This retrieval is performed using a new method combining microphysical in-situ measurements, dropsondes, radar reflectivity, and the continuity equation for the total water substance. The retrieval method and the interpretation of the derived water budget will be discussed during the presentation.