A climatological study of the duration of Northern Hemisphere Cut-off low systems

Cut-off low-pressure systems-COLS- are usually closed circulations at middle and upper troposphere developed from a deep trough in the westerlies. The importance of their study is due to both the convective severe events that can occur if they are over warm ocean and because they are important mechanisms of Stratosphere-troposphere exchange- STE-. A COL system would last about a couple of days before being destroyed by diabatic heating if there were not injection of new air into the COL with high potential vorticity. In the practice their duration range from 1 day to 17 days. There are previous climatological studies about the duration of COLs, but limited to five years. In this work we extended the study to a period of 41-year period (1958 to 1998). The identification of COLs were done using an approach based in imposing the three main physical characteristics of the conceptual model of COL (a. closed circulation and minimum of geopotential, minimum of equivalent thickness, and two baroclinic zones, one in front of the low and the other behind the low). Data from NCAR-NCEP reanalysis were used. Results confirmed previous studies that most of COL systems have a short time of life. The majority of COLs lasted 2-3 days and very few lasted more than 10 days.