A study on cut-off low vertical structure and precipitation in the Mediterranean region

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• 作者：F. Porcù ; A. Carrassi ; C. M. Medaglia ; F. Prodi and A. Mugnai
• 刊名：Meteorology and Atmospheric Physics
• 出版年：2007
• 出版时间：April, 2007
• 年：2007
• 卷：96
• 期：1-2
• 页码：121-140
• 全文大小：820 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Meteorology and Climatology
  Atmospheric Protection, Air Quality Control and Air Pollution
  Climate Change
  Mathematical Applications in Environmental Science
  Terrestrial Pollution
  Waste Water Technology, Water Pollution Control, Water Management and Aquatic Pollution
  
• 出版者：Springer Wien
• ISSN：1436-5065

文摘

Cut-off lows are common features of Mediterranean meteorology in warm months and are often related to severe weather. The present work introduces a classification of cut-off episodes, based on the vertical extension of the depression and the presence of a linked surface vortex, also analyzing precipitation patterns. Ten years of warm-season ERA-40 reanalysis, available every six hours on a 2.5° × 2.5° grid, are processed to extract a database of cut-off 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 analyzed. The results show the relative abundance (41% of the total) of cut-off events lasting less than 24?hrs, sharing most of the characteristics of longer living cut-off 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 rain-rates over wide areas, with well developed frontal rain bands. Among the cut-off events without a deep vertical structure (46%), about half do not produce precipitation, while the others produce relatively high rain-rates, although confined to small areas, indicating the presence of convective systems developing beneath the cut-offlow system. Such precipitation patterns are also confirmed at smaller scales by cloud resolving model runs. Finally, cut-off lows characterized by relatively high potential vorticity values in the mid-upper troposphere seem to have the potential for precipitation.