Simultaneous Episodes of Heavy Rainfall in Morocco and Southern Alps: 2. Time Scales and Mapping of Remote and Local Evaporative Sources

摘要

A mesoscale modeling system, previously used to evaluate the evaporation sources during the August 2002 Central-European Floods (ACEF), is now adapted to analyze the 14-16 November 2002 simultaneous torrential rains in the Alps and Morocco. The meteorology of the selected episode and the climatology and time of recurrence of similar episodes were discussed in the companion article. Contrary to the ACEF estimations, the vapor sources keep almost constant for the 3-day rainfalls, in accordance with a quasi-stationary large-scale forcing. They show a dominance of marine sources (60% and 93% of the total attributed precipitations in the Alps and Morocco, respectively) with a main role of the Western Central Mediterranean for the Alpine targets and the Atlantic Ocean for Morocco. A share of 12%, comparable with the August episode, comes from direct rain-column evaporation in the Alps. Vapor loading rates of the target vapor show an exponential increase during the last 3-4 days before the initiation of the episode, while for the ACEF episode we estimate a longer period of 6-7 days. Three areas of intense marine evaporation are observed, two in the North Atlantic Ocean and one in the Mediterranean Sea, related with the rainfall targets and corresponding with regions of enhanced sea surface temperature decrease. Vapor from the main terrestrial source in North Africa, including the tropical region, is transported inside the prefrontal secondary circulation into the Alpine region. A similar circulation and evaporative source distribution are documented during other simultaneous episodes.