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Tecnicas de analise multivariada sao aplicadas aos dados de ar superior coletados em Petrolina com o objetivo de identificar fatores fisicos na atmosfera para janeiro de 2004, mes chuvoso no semiarido brasileiro. As chuvas sao frequentes na area de Petrolina a partir do dia 10, associadas a ventos em superficie fracos e com direcao variavel. Na media troposfera o teor de umidade e muito baixo nos dias sem precipitacao, em contraste com o teor de umidade elevado nos dias chuvosos. A aplicacao da analise fatorial de componentes principais aos dados de ar superior resulta em um modelo com tres componentes, retendo 96% e 93% da variância total dos dados no nivel de 850 hPa e 500 hPa, respectivamente. O primeiro fator retido para cada nivel isobarico e associado a adveccao horizontal. No nivel de 850 hPa, com 45% da variância total explicada, o fator e relacionado a adveccao de temperatura pela componente meridional do vento; no nivel de 500 hPa, com 46% da variância total explicada, ele esta ligado a adveccao de umidade pela componente zonal do vento. A aplicacao da analise de agrupamentos aos fatores retidos possibilita identificar quatro grupos no nivel de 850 hPa: os Grupos 1 e 2, formados por dias sem registro de chuva, e os Grupos 3 e 4, formados por dias com precipitacao. No nivel de 500 hPa sao identificados tres grupos, com caracteristicas similares as dos grupos do nivel de 850 hPa. Normal 0 21 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; color:black; mso-themecolor:text1; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} ABSTRACT Multivariate analysis techniques are applied to upper air data collected in Petrolina aiming to identify physical factors in the atmosphere on January 2004, a rainy month in the Brazilian semiarid. Starting on the 10 th , rainfall is frequent in the Petrolina area associated with weak and variable surface winds. In the middle troposphere the moisture content is very low in rainless days, in contrast with high moisture content in rainy days. Factorial analysis by principal components applied to upper air data results in a three component model, retaining 96% and 93% of the total variance in the data, at the 850 hPa and 500 hPa levels, respectively. Both isobaric levels have the first retained factor associated with horizontal advection. At 850 hPa, with 45% of the total variance explained, the factor is related to temperature advection by the meridional wind component, while at 500 hPa, with 46% of the total variance explained, the factor is related to moisture advection by the zonal wind component. Cluster analysis applied to the retained factors allows identification of four groups at the 850 hPa level: Groups 1 and 2 are formed by rainless days, while Groups 3 and 4 are comprised by rainy days. Three groups were identified at the 500 hPa level, whose characteristics are similar to those of the 850 hPa groups. Keywords : extreme event, precipitation, principal component analysis, cluster analysis, Northeast Brazil

FATORES FÍSICOS NA ATMOSFERA DO SEMIÁRIDO BRASILEIRO EM JANEIRO DE 2004 (ATMOSPHERIC PHYSICAL FACTORS IN THE BRAZILIAN SEMIARID IN JANUARY 2004)