Climatological features of cutoff low systems in the Southern Hemisphere

• Published in: Journal of Geophysical Research: Atmospheres 2010-09, Vol.115 (D17), p.n/a
• Main Authors: Reboita, Michelle Simões, Nieto, Raquel, Gimeno, Luis, da Rocha, Rosmeri Porfírio, Ambrizzi, Tércio, Garreaud, Rene, Krüger, Luiz Fernando
• Format: Article
• Language: English
• Subjects: Atmospheric research; Atmospheric sciences; Autumn; Climate science; climatological features; Climatology; cutoff low systems; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geophysics; Mathematical models; Meteorology; Seasonal variations; Southern Hemisphere; Summer; Weather; Weather forecasting; Winter
• ISSN: 0148-0227; 2169-897X; 2156-2202; 2169-8996
• DOI: 10.1029/2009JD013251

Cutoff lows (COLs) pressure systems climatology for the Southern Hemisphere (SH), between 10°S and 50°S, using the National Center for Environmental Prediction–National Center for Atmospheric Research (NCEP‐NCAR) and the ERA‐40 European Centre for Medium Range Weather Forecast (ECMWF) reanalyses are analyzed for the period 1979–1999. COLs were identified at three pressure levels (200, 300, and 500 hPa) using an objective method that considers the main physical characteristics of the conceptual model of COLs. Independently of the pressure level analyzed, the climatology from the ERA‐40 reanalysis has more COLs systems than the NCEP‐NCAR. However, both reanalyses present a large frequency of COLs at 300 hPa, followed by 500 and 200 hPa. The seasonality of COLs differs at each pressure level, but it is similar between the reanalyses. COLs are more frequent during summer, autumn, and winter at 200, 300, and 500 hPa, respectively. At these levels, they tend to occur around the continents, preferentially from southeastern Australia to New Zealand, the south of South America, and the south of Africa. To study the COLs at 200 and 300 hPa from a regional perspective, the SH was divided in three regions: Australia–New Zealand (60°E–130°W), South America (130°W–20°W), and southern Africa (20°W–60°E). The common COLs features in these sectors for both reanalyses are a short lifetime (∼80.0% and ∼70.0% of COLs at 200 and 300 hPa, respectively, persisting for up to 3 days), mobility (∼70.0% and ∼50% of COLs at 200 and 300 hPa, respectively, traveling distances of up to 1200 km), and an eastward propagation.