Mesoscale analysis and impact on simulation of IOP14 of the MAP experiment

Abstract

AbstractThis paper examines the benefit on quantitative precipitation forecasts of assimilating a mesoscale network of surface observations. The analysis is performed with an optimal interpolation system tuned for meso‐β scale (10 km resolution). The case‐study is chosen in the framework of the Mesoscale Alpine Program (MAP). It corresponds to a frontal system crossing France on 2 November 1999 followed by moderate to strong convective activity which developed over the Alps and Italy on 3 November (MAP Intensive Observation Period (IOP) 14).Model sensitivity to the various initial conditions (European Centre for Medium‐Range Weather Forecasts analysis, mesoscale analyses with dense surface observations) and to the resolution (meso‐β versus meso‐γ (2.5 km scale)) is investigated. A comprehensive network of rain‐gauges is used for validation. Conventional objective scores (correlation and equitable threat) are produced for precipitation accumulated over short durations (6 and 1 h) for consistency with the target horizontal scales (meso‐β, meso‐γ). The positive contribution of the surface network to precipitation forecasts is confirmed by a novel and powerful validation method based on the comparison of METEOSAT synthetic radiances (infrared and water vapour channels) computed from the simulations to the corresponding satellite observations. Copyright © 2005 Royal Meteorological Society