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Large Scale Features Associated with Strong Frontogenesis in Equivalent Potential Temperature in the South American Subtropics East of the Andes : Volume 22, Issue 22 (13/10/2009)

By Arraut, J. M.

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Book Id: WPLBN0003998895
Format Type: PDF Article :
File Size: Pages 6
Reproduction Date: 2015

Title: Large Scale Features Associated with Strong Frontogenesis in Equivalent Potential Temperature in the South American Subtropics East of the Andes : Volume 22, Issue 22 (13/10/2009)  
Author: Arraut, J. M.
Volume: Vol. 22, Issue 22
Language: English
Subject: Science, Advances, Geosciences
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2009
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

Citation

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J. Barbos, H. M., & Arraut, J. M. (2009). Large Scale Features Associated with Strong Frontogenesis in Equivalent Potential Temperature in the South American Subtropics East of the Andes : Volume 22, Issue 22 (13/10/2009). Retrieved from http://www.ebooklibrary.org/


Description
Description: Centro de Ciências do Sistema Terrestre, Instituto Nacional de Pesquisa Espaciais, Av. dos Astronautas, 1758, São José dos Campos SP 12227-010, Brazil. South American subtropics east of the Andes exhibit a region of intense climatological frontogenesis in equivalent potential temperature (EPT) in the December to March season, mostly produced by deformation of the wind field. The goal of this paper is to investigate the large scale features associated with intense and weak frontogenesis by deformation (FGD) in EPT in the region where it attains its climatological maximum. This can be approximately delimited by 32–42° S and 66–69° W, which is small enough as to contain only one synoptic perturbation at a time. The spatial average of the positive values of frontogenesis at 850 hPa over the whole region (DFG+) is used to represent the strength of the perturbation. ECMWF ERA-40 reanalysis data set is used to calculate DFG+ at six hour intervals for 21 seasons (1981–2002). Compositing analysis is carried out for strong (above the 0.75 quantile) and weak (below the 0.25 quantile) events. For strong events the geopotential field at 850 hPa exhibits the North Argentinean Low (NAL), a transient trough and the Low Pressure Tongue East of the Andes (LPT). Upon comparison with the composite field of FGD it can be observed that FGD exhibits a strong maximum over the Argentinean Col (AC) which separates the NAL and the trough. These features are absent in the weak frontogenesis composite, which exhibits a stronger South Pacific Subtropical High close to the continent. At 250 hPa the strong FGD composite exhibits a trough over the Andes with a wind speed maximum to its east. Both of these features are associated with the deepening of the NAL in the literature. These are not present in the weak FGD composites. Strong events show an intense quasi meridional corridor of water vapor transport from the Amazon to the subtropics that encounters westerly flow in the neighborhood of the AC. This is absent in weak events. A preliminary analysis of precipitation is carried out using the GPCP daily data set. An intense precipitation nucleus appears slightly northeast of the AC, with maximum intensity in the day that follows the strong events. Weak events exhibit a drying of the subtropics instead, between one and three days after the events. Higher precipitation over the oceanic South Atlantic Convergence Zone can be also observed. Analogous composites were constructed for the presence and absence of both the AC and the LPT, showing similar characteristics to the strong and weak FGD event composites respectively, but with lower intensities. This shows that by selecting strong FGD events, intense NAL and LPT events are also singled out.

Summary
Large scale features associated with strong frontogenesis in equivalent potential temperature in the South American subtropics east of the Andes

Excerpt
Arraut, J M.: Fronts and frontogenesis during summer: geometrical and dynamical aspects and the influence over rainfall on the South American subtropics, Ph.D. thesis, Centro de Previsão de Tempo e Estudos Climáticos – INPE, Rodovia Presidente Dutra Km 40 Cachoeira Paulista, São Paulo, Brasil, online available at: prefixhttp://urlib.net/sid.inpe.br/mtc-m17@80/2007/12.19.10.53, 2007 (In Portuguese).; Arraut, J M. and Barbosa, H. M J.: Large Scale Features Associated with Strong Frontogenesis in Equivalent Potential Temperature in the South American Subtropics East of the Andes, Adv. Geosci., this special volume, 2009.; Barbosa, H. M J. and Arraut, J M.: A quantitative evaluation of the role of the Argentinean Col and the Low Pressure Tongue East of the Andes for frontogenesis in the South American subtropics, Adv. Geosci., this special volume, 2009.; Bolton, D.: The Computation of Equivalent Potential Temperature, Mon. Weather Rev., 108, 1046–1053, 1980.; Ferreira, L.: Causes and Variability of the Northwestern Argentinean Low and Impacts Over Local Circulation Patterns (in Spanish), Ph.D. thesis, Universidade de Buenos Aires, 2008.; Garreaud, R D.: Cold Air Incursions Over Subtropical South America: Mean Structure and Dynamics, Mon. Weather Rev., 128, 2544–2559, 2000.; Garreaud, R D. and Wallace, J M.: Summertime Incursions of Midlatitude Air into Subtropical and Tropical South America, Mon. Weather Rev., 126, 2713–2733, 1998.; Huffman, G J., Adler, R., Morrissey, M., Curtis, S., Joyce, R., McGavock, B., and Susskind, J.: Global precipitation at one-degree daily resolution from multi-satellite observations, J. Hydrometeorol., 2, 36–50, 2001.; Kleeman, R.: A Modeling Study of the Effect of the Andes on the Summertime Circulation of Tropical South America, J. Atmos. Sci., 44, 3344–3362, 1989.; Kodama, Y.-M.: Large-Scale Common Features of Subtropical Precipitation Zones (the Baiu Frontal Zone, the SPCZ and the SACZ) Part I: Characteristics of Subtropical Frontal Zones, J. Meteorol. Soc. Jpn, 70, 813–835, 1992.; Kousky, V E.: Frontal influences on northeast Brazil, Mon. Weather Rev., 107, 1142–1153, 1979.; Lichtenstein, E R.: La depresion del noroeste argentino (The northwestern Argentinian low), Ph.D. thesis, Departamento de Ciencias de la Atmosfera, Ciudad Universitaria (1428) Buenos Aires, Argentina, 1980.; Marengo, J., Douglas, M., and Silva Dias, P L.: The South American Low Level Jet East Of the Andes During the 1999 LBA-TRMM and LBA-WET AMC Campaing, J. Geophys. Res., 107, 47-1–47-11, 2002.; Marengo, J., Soares, W., Saulo, C., and Nicolini, M.: Climatology of the Low Level Jet East of the Andes as derived from the NCEP-NCAR reanalysis: characteristics and temporal variability, J. Climate, 17, 2261–2280, 2004.; Marengo, J., Cornejo, A., and Satyamurty, P. et~al.: Cold Surges in Tropical and Extratropical South America: the Strong Event in June 1994, Mon. Weather Rev., 125, 2759–2786, 1997.; Ninomiya, K.: Characteristics of Baiu Front as a predominant subtropical front in the summer northern hemisphere, J. Meteorol. Soc. Jpn, 62, 880–894, 1984.; Parmenter, F C.: A southern hemisphere cold front passage at the equator, B. Am. Meteorol. Soc., 57, 1435–1440, 1976.; Petterssen, S.: Weather analysis and forecasting, McGraw-Hill, New York, 2nd edn., 1956.; Seluchi, M E., Saulo, C., Nicolini, M., and Satyamurty, P.: The Northwestern Argentinean Low: A study of two typical events, Mon. Weather Rev., 132, 2361–2378, 2003.; Virji, H.: A preliminary study of summertime tropospheric circulation patterns over South America estimated from cloud winds, Mon. Weather Rev., 109, 599–610, 1981.

 

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