Hernandez-Carrascal, A. (Instituto Nacional de Meteorologia)
It is well known that the southwest of Europe and surrounding seas is a region of high frequency of cut-off low (COL) systems. The purpose of this work is to study the geographical distribution of COL frequencies in this area, and the month-to-month and interannual variability.
The data source for the study is the ECMWF (European Centre for Medium-Range Weather Forecasts) operational initialised analyses (00 and 12 UTC). The method followed is partly objective and partly subjective: an objective criterion to detect COLs is defined, but the decision concerning the link between consecutive events is subjective. Only the systems appearing in three or more consecutive charts were considered.
Results show that COL systems have a tendency to gather in time and a considerable month-to-month and interannual variability. The area between Gibraltar Strait, Canary Islands, Madeira and Lisbon is a region of high frequency of COLs in all the seasons except winter. Other regions of high frequency of COLs are the Tyrrhenian Sea in spring and summer, the southeast of Iberia during most of the year and North Africa during autumn and winter.