Influence of the Pacific–Japan Pattern on Indian Summer Monsoon Rainfall

Abstract

This study discusses the impact of the Pacific–Japan (PJ) pattern on Indian summer monsoon (ISM) rainfall and its possible physical linkages through coupled and uncoupled pathways. Empirical orthogonal function analysis of 850-hPa relative vorticity over the western North Pacific (WNP) is used to extract the PJ pattern as the leading mode of circulation variability. The partial correlation analysis of the leading principal component reveals that the positive PJ pattern, which features anticyclonic and cyclonic low-level circulation anomalies over the tropical WNP and around Japan respectively, enhances the rainfall over the southern and northern parts of India. The northwestward propagating Rossby waves, in response to intensified convection over the Maritime Continent reinforced by low-level convergence in the southern flank of westward extended tropical WNP anticyclone, increase rainfall over southern peninsular India. Meanwhile, the anomalous moisture transport from the warm Bay of Bengal due to anomalous southerlies at the western edge of the low-level anticyclone extending from the tropical WNP helps to enhance the rainfall over northern India. The atmospheric general circulation model forced with climatological sea surface temperature confirms this atmospheric pathway through the westward propagating Rossby waves. Furthermore, the north Indian Ocean (NIO) warming induced by easterly wind anomalies along the southern periphery of the tropical WNP–NIO anticyclone enhances local convection, which in turn feeds back to the WNP convection anomalies. This coupled nature via interbasin feedback between the PJ pattern and NIO is confirmed using coupled model sensitivity experiments. These results are important in identifying new sources of ISM variability/predictability on the interannual time scale.

Three-ocean interactions and climate variability: a review and perspective

“…The tropical lobe of the PJ pattern is an anticyclone in the tropical WNP, often observed during the peak and decayed phases of El Niño. The mechanisms, based on local SSTrelated feedback and remoted SST forcing from the Indian Ocean to explain the anticyclone in the tropical WNP, may thus work for the PJ pattern (e.g., Srinivas et al 2018).…”

Why the Increasing Trend of Summer Rainfall over North China Has Halted since the Mid-1990s

“…To further demonstrate the robustness of the interdecadal variability of the summer rainfall over North China, the full data monthly product version 2018 of Global Precipitation Climatology Centre (GPCC) is also used. e GPCC with a spatial resolution of 1.0°× 1.0°is derived from quality-controlled station data from 1979 to 2016 and is widely used in the study of the interdecadal variation of local or regional rainfall [35][36][37].…”

Impact of El Niño Modoki on Indian summer monsoon rainfall: Role of western north Pacific circulation in observations and CMIP5 models

“…In general, low or high SLP anomalies over the WNP region are tightly coupled with low-level circulation (e.g., Wang et al, 2001;Feng and Wen, 2014;Xie et al, 2016;Chowdary et al, 2017). The influence of WNP circulation on ISM rainfall and its possible physical linkages through coupled and uncoupled pathways are discussed on interannual time scale (e.g., Kosaka et al, 2013;Srinivas et al, 2018;Chowdary et al, 2019). This motivated us to examine the relation between El Niño Modoki and WNP circulation and link them with the ISM rainfall.…”