Northeast Monsoon Rainfall Variability and its association with the Indo Pacific Ocean Modes in observations and numerical model simulations

Abstract

PREFACE newlineThe occurrence of half annual seasonal reversal of winds exclusively in the north Indian newlineOcean (NIO) other than anywhere else in the world ocean is due to the proximity of the newlineNIO to the land. Due to the proximity of land, the NIO receives an excess of thermal energy newlinein association with the seasonal movement of the sun. In boreal winter, the continental newlinetropical convergence zone (CTCZ) and the sub-tropical anticyclone move southward newlinerelative to the sun s position. With this southward movement of CTCZ, a trough gets newlineestablished over the south Bay of Bengal. Northeast monsoon (NEM) provides an ample newlineamount of rainfall mainly from the dry cold wind travelling towards Southern Peninsular newlineIndia (SPI) via Bay of Bengal and low-pressure systems that form over the Bay trough newline(e.g., Naidu et al., 2012). newline Various coupled oscillations like Siberian High Index (SHI), Southern Oscillation newlineIndex (SOI), El Niño Sothern Oscillation (ENSO), North Atlantic Oscillation (NAO), newlineEquatorial Indian Ocean Oscillation (EQUINOO), Madden Julian Oscillation (MJO) and newlineIndian Ocean Dipole (IOD) etc. are known to have significant impact on the NEM rainfall newlinevariability at various time scales (e.g., Dugam and Kakade, 1995; Bhanu Kumar et al., newline2004; Kripalani and Kumar, 2004; Kumar et al., 2007; Raj and Geetha, 2008; Sreekala et newlineal., 2012 and 2018). The Pacific Ocean mode, ENSO can effectively impact the NEM rainfall newlineover SPI by altering the sea surface temperature and atmospheric circulation over tropical newlineIndian Ocean and western Pacific (e.g., Huang and Sun, 1992; Chowdary et al., 2011). newlineDifferent modes of variability such as El Niño, La Niña and IOD are known to influence newlinethe global climate as well as Indian monsoon at different time scales. In general, during La newlineNiña years northwesterly/westerly wind anomalies suppress the climatological background newlinenortheasterlies and favor the moisture divergence over SPI and hence deficit NEM rainfall newline(e.g., Doraiswamy, 1946; Rao Krishna and Jagannathan, 1953; Rao, 1963; Rao and newlineRaghavend