Mechanism of high rainfall over the Indian west coast region during the monsoon season

Maheskumar, R. S.; Narkhedkar, S. G.; Morwal, Savita B.; Padmakumari, B.; Kothawale, D. R.; Joshi, Ranjan; Deshpande, C. G.; Bhalwankar, Rohini; Kulkarni, J. R.

doi:10.1007/s00382-013-1972-9

Cited by 49 publications

(23 citation statements)

References 39 publications

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“…In the past, studies on orographic precipitation (e.g., Biasutti et al, 2012;Kumar & Bhat, 2017;Kumar et al, 2014;Maheskumar et al, 2014;Nesbitt & Anders, 2009;Romatschke & Houze, 2011;Sahany et al, 2010;Shige & Kummerow, 2016;Shrestha et al, 2015;Tawde & Singh, 2015;Xie et al, 2006), and its intraseasonal variability (e.g., Romatschke & Houze, 2011;Shige et al, 2017) over the WG, were mainly based on satellite and reanalysis data sets. There are few studies on the role of WG on simulating the summer precipitation characteristics using regional model (e.g., Flynn et al, 2017;Sijikumar et al, 2013;Wu et al, 1999;Zhang & Smith, 2018).…”

Section: Introductionmentioning

confidence: 99%

Observed Vertical Structure of Convection During Dry and Wet Summer Monsoon Epochs Over the Western Ghats

et al. 2019

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Summer precipitation over the Western Ghats is an important facet of Indian monsoon. The vertical structure of mesoscale convection during dry and wet epochs of regional precipitation is studied using X‐band Doppler radar, for the first time. The observed characteristics are distinctly different in terms of small‐scale convective and large‐scale atmospheric features for the dry versus wet regimes. The depth and intensity of convection is analyzed using various echo‐top heights (ETHs). The frequency distribution of 0‐ and 15‐dBZ ETH exhibits bimodality during the dry period, which changes to unimodal in wet period. Top heights of precipitating convection (characterized by 30‐dBZ echoes) decreased with low‐level static stability, suggesting preponderance of shallow convection with little stratiform clouds. Suppressed heating in the dry period is a signature of reduced 0‐dBZ ETH occurrence. However, its enhanced occurrence during the wet period resulted in cooling below 2 km and increased heating aloft with maxima at 6 km. Near high precipitation events, midtropospheric humidity rapidly builds up over 2–3 days prior to increase in cloud‐top heights and areal coverage. Observations indicate large amplitude of ETH diurnal cycle during the dry period (especially over leeside) accompanied by weak upstream winds. However, during the wet period, smaller amplitude of ETH is evident (throughout the radar domain) under strong upstream wind conditions. Convective activity during the late afternoon hours produces higher lighting flashes in the dry period compared to the wet. The lightning occurrences are related with penetrations of 30‐dBZ ETH above the freezing level and convective area fractions.

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Section: Introductionmentioning

confidence: 99%

Observed Vertical Structure of Convection During Dry and Wet Summer Monsoon Epochs Over the Western Ghats

et al. 2019

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“…Tawde and Singh (2015) investigated orographic features that influence spatial rainfall distribution over the region using TRMM data. Maheskumar et al (2014) proposed a mechanism for high monsoon rainfall over IWC using reanalysis data. Deshpande et al (2015) discussed the radar-derived divergence profiles of shallow, deep, and stratiform cloud systems, in the Western Ghats.…”

Section: Introductionmentioning

confidence: 99%

Statistical Characteristics of Convective Clouds over the Western Ghats Derived from Weather Radar Observations

et al. 2017

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X‐band radar observations at Mandhardev (18.04°N, 73.85°E) are used to investigate statistics of convective clouds over the Western Ghats during monsoon season (June–September 2014). Convective storms (cells) are identified using an objective‐tracking method to examine their spatiotemporal variability, thus quantifying the time‐continuous aspects of convective cloud population over the region for the first time. An increased frequency of storm location and initiation along the windward mountains compared to coastal and lee side highlights orographic response to southwesterly flow, with superimposed diurnal cycle. An eastward progression of convective activity from upstream the barrier through windward slopes of mountains over to the lee side is observed. Storm area, height, and duration follow lognormal distributions; wherein, small‐sized storms contribute more to total population and unimodal distribution of 35 dBZ top heights (peaking at 5.5 km) depicts the dominance of shallow convection. Storms exhibit a pronounced diurnal cycle with a peak in afternoon hours, while the convective area maximum is delayed by several hours to that of precipitation flux. Cell lifetime and propagation show that cells move with slow speeds and have mean duration of 46 min. They align east‐west nearly parallel to mountain ridges, and their direction of movement is steered mostly by large‐scale winds at lower levels. Based on top heights, convective cells are further classified into cumulus, congestus, and deep clouds. In general, congestus (deep) cells are most abundant in the windward (leeward) side. A lead‐lag relationship between congestus and deep cells indicates midtroposphere moistening by congestus cells prior to deep convection.

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“…Orographic precipitation over and near the mountains is caused when storms (or mesoscale systems) form or move over a complex terrain [Houze, 2012]. Several studies suggested that the vertical wind speed arises from the upslope mountain hills or the channeling effect causes forced condensation process leading to early onset of precipitation [Sarkar, 1966;Smith and Lin, 1983;Whiteman, 2000;White et al, 2003;Houze, 2012;Maheskumar et al, 2013]. Sarkar [1966] indicated that due to the upper level (above 6 km) easterly winds, clouds do not grow deeper over the WG.…”

Section: Introductionmentioning

confidence: 99%

Microphysics of clouds and rain over the Western Ghat

et al. 2014

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In an attempt to unravel the interactions between cloud microphysics and dynamics that make shallow clouds precipitate heavily in this region, some unique observations of rain and cloud microphysical parameters are presented here from two stations, Pune and Mahabaleshwar, one each on the lee and windward sides, respectively, of the Western Ghat (WG) mountains in peninsular India. To elucidate rain microphysics, we used the raindrop size distribution (DSD) by fitting three parameter Gamma functions to the observed raindrop spectra. Over Pune, during stratiform rain with bright band (BB) at 0°C isotherm; concave upward DSD shapes are observed below the BB which becomes concave downward at lower altitudes. It is due to breakup process of large raindrops which increases drop concentration at midsizes suggesting coalescence, collision, and breakup processes. Both slope and intercept parameters of Gamma DSD decrease during no BB condition as altitudes decrease, signifying collision and coalescence processes. Over Mahabaleshwar, bimodal and monomodal DSD are observed during light and heavy rainfall, respectively. With shallow storm heights, small raindrops mainly contribute to both types of rainfall. The DSDs are parameterized, and their radar reflectivity factor-rainfall intensity relationships are evaluated suggesting the dominance of collision-coalescence processes. Aircraft measurements of orographic clouds over the WG suggest interaction of cloud mass with the ambient updraft speed. The orographically forced updrafts foster rapid condensational growth of cloud droplets triggering coalescence process within few hundred meters of cloud depth. Hence, these clouds are dynamically forced to produce precipitation over the WG.

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Mechanism of high rainfall over the Indian west coast region during the monsoon season

Cited by 49 publications

References 39 publications

Observed Vertical Structure of Convection During Dry and Wet Summer Monsoon Epochs Over the Western Ghats

Observed Vertical Structure of Convection During Dry and Wet Summer Monsoon Epochs Over the Western Ghats

Statistical Characteristics of Convective Clouds over the Western Ghats Derived from Weather Radar Observations

Microphysics of clouds and rain over the Western Ghat

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