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

AbstractThe 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.