Comparaçao entre "Storm-tracks" no Atlántico norte encontradados nas reanálises do ECMWF e NCEP/NCAR

As trajectorias das depressoes (storm-tracks) na regiao do Atlântico Norte sao obtidas, aplicando um metodo de deteccao automatico ao campo do geopotencial aos 1000hPa (Z1000) das reanalises do ECMWF (ERA40) e do NCEP/NCAR, respectivamente. O metodo consiste na identificacao de isolinhas fechadas aos 000hPa, e no seguimento desses minimos de geopotencial procurando os centros mais proximos em cartas consecutivas. O estudo e realizado para o periodo compreendido entre Dezembro de 1958 e Marco de 2000, utilizando campos de Z1000 de 6 em 6 horas, sobre grelhas de 1.125ox1.125o (ECMWF) e 2.5ox2.5 (NCEP/NCAR), respectivamente. A analise dos sistemas depressionarios obtidos com as duas bases de dados mostra diferencas no padrao e frequencia de ciclogeneses, sobretudo em areas de grande actividade, e.g., junto a costa leste Americana, Gronelândia e no Mediterrâneo. As discrepâncias mais pronunciadas sao observadas na variabilidade interanual do numero de trajectorias em areas predefinidas; de um modo geral, observam-se tendencias mais pronunciadas (negativa no Mediterrâneo e positiva no Atlântico Nordeste) nos dados obtidos com as reanalises NCEP/NCAR. [EN]North Atlantic storm-tracks are obtained through an automatic storm detecting and tracking scheme applied to sea level pressure (SLP) fields from ECMWF (ERA40) and NCEP/NCAR reanalyses, respectively. The detecting and tracking scheme looks for closed isobars in SLP charts, and follows the detected centres by identifying the nearest neighbours in the next chart. This study is focused on the period between December 1958 and March 2000, using 6-hourly SLP fields, with 1.125ox1.125o (ECMWF) and 2.5ox2.5o (NCEP/NCAR) horizontal resolutions. The cyclone tracks obtained with the two datasets show differences in cyclogenesis patterns and frequencies, particularly within areas of high cyclogenetic activity (e.g., America’s eastern coast, Greenland, Mediterranean). The most marked discrepancies are obtained for the interannual variability of the number of storm-tracks in pre-defined areas; generally the number of cyclones exhibits more pronouced trends (positive over the Northeastern Atlantic, and negative in the Mediterranean) for the data obtained from the NCEP/NCAR reanalysis, than from ERA40.