Contribuição dos Distúrbios Ondulatórios de Leste para a chuva no Leste do Nordeste do Brasil: evolução sinótica média e simulações numéricas / Easterly Waves contribution for the eastern Northeast Brazil precipitation: mean synoptic evolution and numerical simulations

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

01/06/2011

RESUMO

This study purpose was to verify the contribution of Easterly Wave Disturbances (EWDs) in the observed precipitation over the eastern part of Northeast Brazil (ENEB) during rainy season (AMJJ) and evaluate seasonal rainfall forecasts from RegCM3 (Regional Climate Model version 3). For the EWDs subjective identification it was used infrared satellite images and ERA-Interim reanalysis streamlines and relative vorticity fields at 700 and 850 hPa, at the rainy periods from 2006 to 2010. About 90% of the observed troughs at 700 hPa were associated with 116 EWDs that reached the ENEB. This provides a 23 EWDs average per year with small interannual variability. Meteorological variables compositions were constructed from 2 days before (-2) until 2 days after (+2) EWDs reached the ENEB. The circulation showed cyclonic and confluent anomaly, cyclonic relative vorticity and convergence between days -2 and 0 in low levels, mainly in 1000 hPa. Negative anomalies were found for outgoing longwave radiation (OLR) and omega whereas relative humidity presented positive anomaly. The precipitation composition indicated that the EWDs account for: 70% or more of rainy seasons precipitation from northern coast of Alagoas (AL) to the eastern Rio Grande do Nortes (RN), 60% from ALs Zona da Mata to the RNs Agreste, and 50% between Sergipe and the other RN areas. On average, the EWDs presented a 5.3 days period, a wavelength of 4307 km and phase velocity of 9.5 m s-1. The RegCM3 simulated the observed westward troughs propagation at the 850-700 hPa levels, and their associated precipitation as well, for two EWDs occurred between 21 and 25 May 2006. For seasonal simulations, the RegCM3 with Grell parameterization predicted the spatial pattern similar to the observed rain, but overestimated it. Approximately 68% of the events subjectively obtained EWDs were also identified using Hovmöller diagrams. The tracking algorithm using OLR or vorticity was unsatisfactory in the detection of EWDs, identifying with OLR ~55% of the events subjectively obtained.

ASSUNTO(S)

numerical simulations contribuição.distúrbios ondulatórios de leste. chuva contribution easterly waves eastern northeast brazil evolução sinótica média leste do nordeste do brasil mean synoptic evolution precipitation simulações numéricas

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