Intraseasonal variation of monsoon activities associated with the rainfall over Bangladesh during the 1995 summer monsoon season

Ohsawa, Teruo; Hayashi, Taiichi; Mitsuta, Yasushi; Matsumoto, Jun

doi:10.1029/2000jd900499

Cited by 38 publications

(51 citation statements)

References 19 publications

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“…On the other hand, it was also shown that the lower tropospheric zonal wind was highly correlated with the NEIM rainfall in both July and August. This is consistent with the mechanism of the active and break cycle of the monsoon rainfall over Bangladesh analyzed by Ohsawa et al (2000), associated with the difference in the location of the monsoon trough. During the active periods, the monsoon trough was located along the foot of the Himalayas, though it shifted southward to the Bay of Bengal in the break periods.…”

Section: Impacts Of Wnpm Variability On Neim Rainfallsupporting

confidence: 71%

“…It causes a significant westerly anomaly only in August over the Bengal Plain (Fig. 12), which is a known favorable condition for the active phase of rainfall in Bangladesh and Meghalaya (Ohsawa et al 2000;Murata et al 2008;Fujinami et al 2011). The link between the first and second steps was highly affected by the variability at intraseasonal time scales (Fig.…”

Section: Discussionmentioning

confidence: 99%

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Impacts of Rapid Warm-To-Cold ENSO Transitions on Summer Monsoon Rainfall over the Northeastern Indian Subcontinent

Terao

Murata

Habib³

et al. 2013

Journal of the Meteorological Society of Japan

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In this study, the impacts of warm-to-cold El Niño-Southern Oscillation (ENSO) phase transitions on the summer rainfall over the northeastern Indian monsoon (NEIM) region were investigated. Extremely rapid warm-to-cold ENSO transitions were identified in 1983, 1988, and 1998. In these rapid ENSO transition years, during August, the NEIM rainfall tended to be higher than that in other years, leading to large river water discharge into Bangladesh in August and September through the Ganges and Brahmaputra. In summer (June, July, and August), the western North Pacific monsoon (WNPM) was significantly suppressed in association with the east-west sea surface temperature (SST) anomaly contrast between an above-normal SST over the Indian Ocean and a negative SST anomaly that developed over the central equatorial Pacific. The suppression of WNPM was highly likely to be a key factor linking rapid ENSO transition to the heavy NEIM rainfall in August. WNPM suppression caused a prominent lower tropospheric anticyclonic anomaly, which extended westward over the Indian Ocean and Indian subcontinent. Associated with this circulation anomaly, a lower tropospheric westerly anomaly developed over the Bengal Plain in August, which activated the NEIM rainfall. Thus, especially in August, WNPM suppression significantly correlated with heavy rainfall over a large area over the northeastern Indian subcontinent.In all three rapid warm-to-cold ENSO transition years, WNPM was extremely suppressed in summer. However, in the August of 1983, owing to atmospheric variations at intraseasonal time scales, WNPM suppression was damped, and both the lower tropospheric circulation anomaly and the NEIM rainfall activation were not clear. On the other hand, in 1988 and 1998, WNPM suppression enhanced the NEIM rainfall in August and increased flood risk in Bangladesh.

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Section: Impacts Of Wnpm Variability On Neim Rainfallsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Impacts of Rapid Warm-To-Cold ENSO Transitions on Summer Monsoon Rainfall over the Northeastern Indian Subcontinent

Terao

Murata

Habib³

et al. 2013

Journal of the Meteorological Society of Japan

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“…Northeastern Bangladesh, in particular, is known as an area of heavy rainfall. A characteristic of northeastern Bangladesh is the late night-early morning maximum of diurnal precipitation observed by rain gauges, the radar in Dhaka, and a geostationary meteorological satellite (Ohsawa et al 2000(Ohsawa et al , 2001Terao et al 2002;Islam et al 2005). These studies suggest that the late night-early morning maximum precipitation is associated with the Meghalaya Plateau.…”

Section: Introductionmentioning

confidence: 79%

Numerical Simulation on the Diurnal Variation of Precipitation over Northeastern Bangladesh: A Case Study of an Active Period 14-21 June 1995

Kataoka

Satomura

2005

SOLA

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The diurnal variation of precipitation over the Bengal region is numerically investigated using a nonhydrostatic mesoscale model. We focused on northeastern Bangladesh, where the maximum of late night-early morning precipitation is observed. Simulated characteristics of diurnal variation of precipitation agree, to a large extent, with observable evidence. The mechanism of the high late night-early morning precipitation in a case of June 14 to 21 is investigated using the model results.At night, strong southwesterly monsoon winds transport a large amount of moisture over Bangladesh. This high equivalent potential temperature ( e) air mass climbs the slope of the Meghalaya Plateau or climbs over a deep (several hundreds meters to 1 km) pool of cold air, and triggers precipitation over northeastern Bangladesh. The triggered systems develop into mesoscale squall lines and propagate southward or southsouthwestward at a speed of about 10 m s 1 . It is found that the katabatic mountain wind is not a major player in the diurnal variation of precipitation over the northeastern Bangladesh area.

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“…Previous studies have shown that the 10-20-day (quasibiweekly) rainfall oscillation, associated with the westwardmoving monsoon lows generated over the Bay of Bengal, is dominant over northeast India, including the Meghalaya Hills and Bangladesh (Ohsawa et al 2000;Murata et al 2007), while the 30-60-day periodicity (known as the MaddenJulian oscillation, MJO) is strongest for areas located in southern India (south of 23°N) (Hartmann and Michelsen 1989;Kripalani et al 2004;Kulkarni et al 2009). We defined excess and deficient monsoon years as one standard deviation departure from the long-term rainfall mean .…”

Section: Propagation Of the High Rainfallmentioning

confidence: 99%

Variation in the orographic extreme rain events over the Meghalaya Hills in northeast India in the two halves of the twentieth century

Prokop

Walanus

2014

Theor Appl Climatol

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The daily rainfall data for the twentieth century, from three stations across the region, constitute the basis for statistical analysis. However, the low signal-to-noise ratio makes it difficult to find any significant departure from the simplest null hypothesis of the stability of the rain record at individual stations in northeast India. Only the coarsest possible view, i.e. comparing the two halves of the century, provided strongly significant results in the numbers of days with extreme rain. Using a more general approach, the number of Fourier transform extreme amplitudes also differed significantly. Increasingly heavy events during the summer monsoon season, and partly in the pre-and post-monsoon seasons, are offset by a weakening in the winter monsoon season, so that the annual mean rainfall does not show a significant trend over the Meghalaya Hills. Apart from a greater number of years with noticeable extreme rainfall events in the second half of the twentieth century, we can also observe a more pronounced quasi-periodicity of 10-20 and 30-60 days during the same period. The detection of the latter periodicity indicates that the Madden-Julian oscillation plays an important role in the formation of extreme rainfall events over the Meghalaya Hills during extreme monsoon years.

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Intraseasonal variation of monsoon activities associated with the rainfall over Bangladesh during the 1995 summer monsoon season

Cited by 38 publications

References 19 publications

Impacts of Rapid Warm-To-Cold ENSO Transitions on Summer Monsoon Rainfall over the Northeastern Indian Subcontinent

Impacts of Rapid Warm-To-Cold ENSO Transitions on Summer Monsoon Rainfall over the Northeastern Indian Subcontinent

Numerical Simulation on the Diurnal Variation of Precipitation over Northeastern Bangladesh: A Case Study of an Active Period 14-21 June 1995

Variation in the orographic extreme rain events over the Meghalaya Hills in northeast India in the two halves of the twentieth century

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