Numerical simulations of three different MAP IOPs and the associated microphysical processes

Franck Lascaux,Jean-Pierre Pinty,Evelyne Richard

doi:10.1256/qj.05.197

Abstract

The data collected during three contrasting Intensive Observing Periods (IOPs) of the Mesoscale Alpine Programme (MAP) were used to assess the performance of the Meso-NH model with particular emphasis on precipitation and microphysical processes. The model was able to reproduce the intense and moderate convective rain of IOPs 2A and 3, respectively, and also the stratiform precipitation associated with IOP 8. Microphysical budget computations were used to derive the mean vertical distribution of the hydrometeors and to quantify the relationships among the different water species. The results of IOP 8 exhibit a shallow stratiform system in which the dominant ice hydrometeor is snow, growing efficiently by vapour deposition. In contrast, the results of IOP 2A show a much deeper system in which graupel and its associated growth modes play an important role. These results are consistent with the two conceptual models of orographic rain that were derived from the MAP radar observations. Copyright © 2006 Royal Meteorological Society

Highlights

Like most of the major mountain ranges, the European Alps exert a strong influence on the space and time distribution of precipitation
HYDROMETEOR DISTRIBUTIONS AND DOMINANT MICROPHYSICAL PROCESSES In a study based upon the Monte Lema radar observations from autumn 1998 and 1999, Houze et al (2001) found that the nature of the precipitation over the Lago Maggiore region is strongly dependent on the Froude number of the flow, Fr, which determines whether the flow is blocked or rises over the terrain
A variety of three Mesoscale Alpine Programme (MAP) contrasting cases have been simulated with the French non-hydrostatic model Meso-NH in order to investigate the capability of the model to reproduce intense orographic precipitation and associated microphysical processes

Summary

INTRODUCTION

Like most of the major mountain ranges, the European Alps exert a strong influence on the space and time distribution of precipitation. Both fields exhibit an elongated precipitation pattern, oriented south-west/north-east, and located over the Ticino-Toce watershed. The 500 hPa geopotential chart from the ECMWF re-analysis of 12 UTC on 20 October (Fig. 3(e)) shows a deep cut-off low located north of Spain and the corresponding surface chart (Fig. 3(f)) indicates a strong southerly flow impinging on the southern tip of the Alps and the Apennines. These contrasting performances between the three IOPs could indicate that the orographic forcing (much stronger in IOPs 2A and 3 than in IOP 8) may help to overcome the assumed lower predictability of convective situations relative to stratiform ones

HYDROMETEOR DISTRIBUTIONS AND DOMINANT MICROPHYSICAL PROCESSES

CONCLUSION