The interannual variability of summer monsoon precipitation over the Indochina Peninsula (ICP) is characterized using the first empirical orthogonal function of 5-month total precipitation (May to September). The leading mode, with a monopole pattern, accounts for 30.6 % of the total variance. Dynamic composites and linear regression analysis indicate that the rainy season precipitation over the ICP is linked to El Niño-Southern Oscillation (ENSO) on interannual scales. The preceding winter [D(−1)JF(0)] negative sea surface temperature (SST) over the Niño-3.4 region is predominantly correlated with the rainy season precipitation over the ICP. Notably, the simultaneous correlation between remote SST anomalies in the Niño-3.4 region and the rainy season precipitation over the ICP is weak. The interannual variation of tropical cyclones modulated by ENSO is a significant contributing factor to the rainy season precipitation over the ICP. However, this relationship is not homogeneous over the ICP if ENSO is considered. Before removing the ENSO signal, enhanced precipitation is present over the northeastern part of the ICP and reduced precipitation appears in the western ICP, especially in coastal areas. In contrast, after removing ENSO, only a minor significant positive precipitation anomaly occurs over the northeastern part of the ICP and the negative anomaly appears particularly in the western and eastern coastal regions. The results obtained through the present study are useful for our understanding of circulation mechanisms and provide information for assessing the ability of regional and global climate models in simulating the climate of Southeast Asia.
El monzón del sudeste asiático se presenta todos los años de junio a septiembre en la mayor parte del subcontinente indio, lo cual incluye a Paquistán, la India y Bangladesh. Estos vientos ricos en humedad son forzados a elevarse por la cordillera del Himalaya, lo que ocasiona precipitación extrema en varias partes del subcontinente, especialmente en Paquistán. El objetivo de este estudio es analizar las características y distribución de la conversión de energía atmosférica durante la intensa precipitación registrada en Sindh, Paquistán, durante el periodo agosto-septiembre de 2011. Los resultados muestran que la atmósfera cambia culaciones atmosféricas y las condiciones del terreno, la energía cinética es bloqueada por las montañas y convertida de manera continua en energía potencial dentro del sistema de precipitación. Cuando la fase de energía máxima persiste por un tiempo considerable, puede ocasionar precipitaciones intensas cuya humedad procede principalmente del Mar Arábico y la bahía de Bengala.
The topography influences monsoon precipitation and gives rise to significant rainfall events in South Asia. The physical mechanism involved in such events includes mechanical uplifting, thermodynamics, small scale cloud processes, and large scale atmospheric circulations. The investigation into orographic precipitation is pursued by synoptic and model analysis. Deep convection occurs as warm moist airflow is channeling over steep mountains. WRF model coupled with Morrison double moment scheme is used to assess the relative impact of topography on extreme rainfall event of 26–30 July 2010 in Pakistan. Two sensitivity tests with full topography (CTL) and reduced topography by 50% (LOW) are carried out. Two distinct precipitation zones over Hindukush and Himalaya mountains are identified. The topographic changes significantly affect moisture divergence and spatial and temporal distribution of precipitation. A low level jet is created on windward side of big mountains, yielding enhanced moisture flux and instability. Eddy kinetic energy significantly changes with orographic height. Energy flux created further unstabilized atmosphere and deep convection, producing wide spread heavy rainfall in the area in Himalaya foothills. Under the set synoptic conditions, orographic orientation enhanced the moisture accumulation and deep convection, resulting in occurrence of this extreme event.
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