Performance of RegCM4 for Dynamically Downscaling of El Nino/La Nina Events During Southwest Monsoon Over India and Its Regions

Abstract

The southwest monsoon (SWM) is the world's most important monsoon system that affects nearly one third of the world population. The SWM maintains a periodicity annually in which more than 80% of the annual precipitation occurs during June-September and represents significant spatial and temporal variation which is dependent upon climatic and topographical features of the Indian subcontinent. The spatial and temporal interannual variability of Indian summer monsoon rainfall (ISMR) leads to large-scale drought and flood, resulting in a major effect on agriculture and the economy of the country (Guhathakurta & Rajeevan, 2006; Naidu et al., 2015; Parthasarathy et al., 1994; Turner & Annamalai, 2012). The strong influence of the Tropical Ocean on the variability of ISMR has been studied and epitomized by the El Nino Southern Oscillation (ENSO) phenomena (Shukla, 1987; Sikka, 1980; Webster & Yang, 1992). ENSO is a phenomenon of coupled ocean-atmosphere used to explain unusual climatic and weather patterns and also disrupt the ecosystem, agriculture, tropical cyclone, drought and flood, and other extreme weather events across the globe. The large-scale ocean-atmosphere climate interaction is linked to the periodic warming in the sea surface temperature (SST) across central and east equatorial Pacific Ocean termed as El Nino. On the other hand, La Nina (a cold event) represents

El Niño‐Southern Oscillation Modulation of Springtime Diurnal Rainfall Over a Tropical Indian Ocean Island

“…The El Niño/Southern Oscillation (ENSO) is one of the climate modes that can modulate the interannual variations of rainfall over the Indo‐Pacific regions through the east‐west oscillation of the tropical Walker circulation (Huang et al., 2019; Krishnamurthy & Goswami, 2000; Kumar et al., 1999). During El Niño (La Niña) events, a divergence (convergence) zone at low‐levels frequently appears over the western Pacific towards South Asia, resulting in drier (wetter) conditions over South Asia (Rasmusson et al., 1999; Verma & Bhatla, 2021). The El Niño (La Niña) events can also modulate the southward (northward) movement of the local Hadley circulation over the Indian Ocean, which can subsequently delay (advance) the monsoon onset process (Choudhury et al., 2021).…”

Sensitivity of Australian rainfall to driving SST datasets in a variable-resolution global atmospheric model

“…Dynamical downscaling has emerged as a widely employed approach for investigating the teleconnections between ENSO/IOD and localized rainfall patterns (e.g., Boulard et al 2013, Ratna et al 2017, Whan and Zwiers 2017, Worku et al 2018, Verma and Bhatla 2021, Safari et al 2023. Regional Climate Models (RCMs) with typical resolutions higher than 30km are employed to simulate the atmosphere driven by reanalysis or general circulation model (GCM) outputs with coarser resolutions exceeding 100km.…”

“…However, it is also challenging to reduce computational costs effectively when including both the Pacific Ocean and Indian Ocean basins in RCMs. Furthermore, it is worth mentioning that outcomes from dynamical downscaling concerning regional ENSO/IOD influences are occasionally unsatisfactory and can even yield counterintuitive responses of rainfall to ENSO/IOD events (e.g., Boulard et al 2013, Verma andBhatla 2021).…”

Holocene Monsoonal Variations Over Southern India: Looking Into Its Antecedents

“…From 1813-1820 to 1911-1920, there were 25 deficit years against 11 surplus years, but upto 2006 (86 years), there were 16 surplus years against seven deficit years, suggesting a trend of increasing rainfall than deficit. According to Verma and Bhatla (2021), the interannual variation in SWMR precipitation has been linked to El Nino in recent years, and this had a significant impact on the Eastern Ghats in the southern peninsular region. During the La Nina years, however, SWMR rainfall variation from the mean was large in the southern peninsular region.…”