The main aim of this paper is to simulate monsoon heavy rainfall episodes that caused floods across some parts of Andhra Pradesh (AP) state, India during 29th September through 2nd October, 2009. A heavy rainfall quan...The main aim of this paper is to simulate monsoon heavy rainfall episodes that caused floods across some parts of Andhra Pradesh (AP) state, India during 29th September through 2nd October, 2009. A heavy rainfall quantity of 21 cm was observed near Amaravathi station (16.15°N;80.5°E) in Guntur district due to a meso-α low pressure system extended from the Bay of Bengal and widespread rainfall episodes were also appeared to many adjoining places in other three districts namely Mahaboob Nagar, Kurnool and Krishna in AP state simultaneously on 29th September. The rainy situation continued till 2nd October and caused floods over above districts of AP state which lead to a death toll of 33 people and heavy crop loss. To quantify the above catastrophic monsoon heavy precipitation events a high resolution (9 km) Weather Research and Forecast (WRF-ARW) model is centered at Amaravathi station to simulate rainfall episodes over the study region. In the present case study the simulated sensitive experiment highlights the dynamical characteristics of the meso-α system interms of circulation changes at different levels. Secondly, the thermodynamical characteristics for the generation of convective activity of this meso-α event in terms of Convective Available Potential Energy (CAPE) and Convective Inhibition Energy (CINE) are also simulated. Dynamical and thermodynamical simulated results support heavy rainfall episodes due to a low pressure system around Amaravathi station. Thus circulation changes, high CAPE and low CINE magnitudes have well defined not only the strength of meso-α system, but also quantum of rain-fall to a tune of 19 cm near Amaravathi station on 29th September. The observed rainfall was 21 cm on 29th September and thus this model underestimates rainfall about 9.5% not only at Amaravathi station, but also at other stations as well. Similar results are noticed over the study region on other three days. In this numerical study heavy rainfall events are better represented by Kain-Fritsch (KF) scheme than Betts-Miller-Janjic (BMJ) and Grell-Deveneyi (GD) schemes. Finally simulated circulation features and rainfall quantities are validated with observed rainfall of the India Meteorological Department (IMD) and satellite derived datasets of KALPANA-1, while CAPE and CINE quantities are checked against available Wyoming University observations. The results are promising.展开更多
Summer monsoon and its synoptic, meso-scale systems provide 80% of total annual rainfall over India. Monsoon depressions are weak, low-pressure circulation within the monsoon trough that forms in the head Bay of Benga...Summer monsoon and its synoptic, meso-scale systems provide 80% of total annual rainfall over India. Monsoon depressions are weak, low-pressure circulation within the monsoon trough that forms in the head Bay of Bengal and moves northwestward and westward across the Indian sub-continent during summer monsoon season. Another convective system from this planetary scale circulation is the Intraseasonal Oscillation (ISO) also occurs in the daily mode. It is very important to study the impact of monsoon depressions in synoptic scale on ISOs through its strength, frequency and duration. In the recent decades, frequency of monsoon depressions and sea surface temperature over head Bay is decreasing while the intensity is increasing over Bay of Bengal. The study brings out the relationship between the ISOs and monsoon depressions over Bay of Bengal through their structure and movement for the period 1990-2014. Composites of monsoon and no monsoon depression days are calculated and found that rainfall is mainly occupied over Kerala and Interior Peninsula within the range of 10 - 50 cm during monsoon depression days. Relative vorticity brings out that the shallower layer of convergence mainly from 1000 - 850 hPa level and a deeper layer of weak divergence above it is mainly associated with the depression. Next, thermodynamic structure of monsoon depression and its intensity is directly proportional to the increasing of CAPE. Wavelet spectrum also indicates the intraseasonal oscillations are very active during monsoon depression days. Finally this study helps to bring out plausible reasons through circulations, dynamic and thermodynamic characteristics involved in monsoon depression days in association with the ISOs.展开更多
文摘The main aim of this paper is to simulate monsoon heavy rainfall episodes that caused floods across some parts of Andhra Pradesh (AP) state, India during 29th September through 2nd October, 2009. A heavy rainfall quantity of 21 cm was observed near Amaravathi station (16.15°N;80.5°E) in Guntur district due to a meso-α low pressure system extended from the Bay of Bengal and widespread rainfall episodes were also appeared to many adjoining places in other three districts namely Mahaboob Nagar, Kurnool and Krishna in AP state simultaneously on 29th September. The rainy situation continued till 2nd October and caused floods over above districts of AP state which lead to a death toll of 33 people and heavy crop loss. To quantify the above catastrophic monsoon heavy precipitation events a high resolution (9 km) Weather Research and Forecast (WRF-ARW) model is centered at Amaravathi station to simulate rainfall episodes over the study region. In the present case study the simulated sensitive experiment highlights the dynamical characteristics of the meso-α system interms of circulation changes at different levels. Secondly, the thermodynamical characteristics for the generation of convective activity of this meso-α event in terms of Convective Available Potential Energy (CAPE) and Convective Inhibition Energy (CINE) are also simulated. Dynamical and thermodynamical simulated results support heavy rainfall episodes due to a low pressure system around Amaravathi station. Thus circulation changes, high CAPE and low CINE magnitudes have well defined not only the strength of meso-α system, but also quantum of rain-fall to a tune of 19 cm near Amaravathi station on 29th September. The observed rainfall was 21 cm on 29th September and thus this model underestimates rainfall about 9.5% not only at Amaravathi station, but also at other stations as well. Similar results are noticed over the study region on other three days. In this numerical study heavy rainfall events are better represented by Kain-Fritsch (KF) scheme than Betts-Miller-Janjic (BMJ) and Grell-Deveneyi (GD) schemes. Finally simulated circulation features and rainfall quantities are validated with observed rainfall of the India Meteorological Department (IMD) and satellite derived datasets of KALPANA-1, while CAPE and CINE quantities are checked against available Wyoming University observations. The results are promising.
文摘Summer monsoon and its synoptic, meso-scale systems provide 80% of total annual rainfall over India. Monsoon depressions are weak, low-pressure circulation within the monsoon trough that forms in the head Bay of Bengal and moves northwestward and westward across the Indian sub-continent during summer monsoon season. Another convective system from this planetary scale circulation is the Intraseasonal Oscillation (ISO) also occurs in the daily mode. It is very important to study the impact of monsoon depressions in synoptic scale on ISOs through its strength, frequency and duration. In the recent decades, frequency of monsoon depressions and sea surface temperature over head Bay is decreasing while the intensity is increasing over Bay of Bengal. The study brings out the relationship between the ISOs and monsoon depressions over Bay of Bengal through their structure and movement for the period 1990-2014. Composites of monsoon and no monsoon depression days are calculated and found that rainfall is mainly occupied over Kerala and Interior Peninsula within the range of 10 - 50 cm during monsoon depression days. Relative vorticity brings out that the shallower layer of convergence mainly from 1000 - 850 hPa level and a deeper layer of weak divergence above it is mainly associated with the depression. Next, thermodynamic structure of monsoon depression and its intensity is directly proportional to the increasing of CAPE. Wavelet spectrum also indicates the intraseasonal oscillations are very active during monsoon depression days. Finally this study helps to bring out plausible reasons through circulations, dynamic and thermodynamic characteristics involved in monsoon depression days in association with the ISOs.
