A study on cutoff low vertical structure and prec

Authors: F Porcù A Carrassi C M Medaglia F Prodi A Mugnai

Publish Date: 2006/12/20

Volume: 96, Issue: 1-2, Pages: 121-140

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Abstract

Cutoff lows are common features of Mediterranean meteorology in warm months and are often related to severe weather The present work introduces a classification of cutoff episodes based on the vertical extension of the depression and the presence of a linked surface vortex also analyzing precipitation patterns Ten years of waRMSEason ERA40 reanalysis available every six hours on a 25° × 25° grid are processed to extract a database of cutoff lows and surface cyclones along with the related total and convective precipitation at the ground The high temporal resolution of the dataset permits a detailed characterization of short lasting events so far poorly analyzedThe results show the relative abundance 41 of the total of cutoff events lasting less than 24 hrs sharing most of the characteristics of longer living cutoff in terms of structures and precipitation pattern A large part of the 273 events identified in our database about 54 appear as high level signatures of depressions extending through a large portion of the troposphere and in 38 of cases a well defined cyclonic structure is found at the ground Most of these events carry precipitation with relatively high rainrates over wide areas with well developed frontal rain bands Among the cutoff events without a deep vertical structure 46 about half do not produce precipitation while the others produce relatively high rainrates although confined to small areas indicating the presence of convective systems developing beneath the cutofflow system Such precipitation patterns are also confirmed at smaller scales by cloud resolving model runs Finally cutoff lows characterized by relatively high potential vorticity values in the midupper troposphere seem to have the potential for precipitation

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