Diurnal Variation of Rainfall in the Presence of Large- and Small-Scale Precipitating Systems during Different Monsoon Seasons over a Complex Terrain (Gadanki) Region

Abstract

The diurnal cycle of rainfall by large-scale systems (LSS) and small-scale systems (SSS) has been studied over a complex terrain region (Gadanki) in southern peninsular India using eight years of data from a network of 36 rain gauges. The diurnal cycle of accumulated rainfall by LSS and SSS shows peaks at 22 LT and 19 LT, respectively, during the southwest monsoon (SWM) and 19 LT and ~17 LT during the northeast monsoon (NEM). Irrespective of the season and system size, the diurnal mode is the dominant mode of variation and explains ~60% (~43%) of variance during the SWM and ~54% (~36%) during the NEM in LSS (SSS) presence. The correlation structure of rainfall is anisotropic with an axis ratio of ~1.5 for LSS and ~1.4 for SSS. Propagating systems are prevalent (80 to 90% of times produce rain) in the presence of LSS during both seasons and play a dominant role in altering the diurnal cycle of rainfall over the Gadanki region. The conducive environment, like the presence of large RH, updrafts in lower- and mid-troposphere, and large lower- and small mid-tropospheric shears, favors convective initiation and propagation of precipitating systems during LSS in SWM and NEM. The atmosphere favors the convective initiation between 18 and 20 LT. The dry mid-troposphere and weak upward motion in the mid-troposphere inhibits mesoscale organization and forms SSS during the SWM. During the NEM, somewhat drier mid-troposphere than in LSS and small L-shear inhibits the convective organization and forms SSS between 15 and 18 LT.

Retrieval of Microphysical Parameters of Monsoonal rain Using X-band Dual-polarization Radar: Their Seasonal Dependence and Evaluation

“…The southwest monsoon (SWM-June through September) is the main monsoon season in which it receives ~53% of its annual rainfall. This region also receives considerable rainfall (35% of annual rainfall) during the northeast monsoon (NEM -October through December) and the remaining annual rainfall occurs during the premonsoon season (PRE -March through May) (Rao et al 2009;Radhakrishna and Rao, 2021). The rainfall is predominantly convective in nature (53.3% of total rainfall), while stratiform rain (30.2%) and shallow rain (16.6%) contributes considerably (Rao et al, 2008;Saikranthi et al, 2014).…”

Satellite-observed precipitation and total column water vapor

“…Liang et al (2020) find that precipitation increases with water vapor, and water vapor stimulates precipitation occurrences over the Tibetan Plateau. The role of water vapor at different levels of the atmosphere on precipitation intensity and areal extent is, also, well studied using observations in Chen et al (2017a); Chen et al (2017b) and Radhakrishna and Rao (2021). Furthermore, increases in water vapor are key to the development of severe weather and heavy precipitation events (Van Baelen et al, 2011;Chen et al, 2017a;Zhang et al, 2018;Liang et al, 2020).…”