The Effects of Northern Hemisphere Dynamical Flow Patterns on the Active-Break Cycle of the Indian Summer Monsoon

Abstract

The Indian Summer Monsoon (ISM) brings episodes of intense rain across the country from June to September each year. The heavy rains allow the agricultural industry to prosper, but intervening periods of drought decrease crop yield. The movement of the ISM and the knowledge of which regions of India will experience rainfall versus drought are largely unpredictable beyond a few days. Intra-seasonal circulation regimes reflecting the active-break cycle (wet and dry spells, respectively) have been identified using five characteristic patterns to describe the evolution of pentads (five-day means) of the ISM (Straus 2021). Previous research proposes that wave trains from the mid-latitudes can influence the break phases and thus the behavior of the ISM. The goal of this project has been to map and analyze Z200 geopotential height data to further explore the effects of the Northern Hemisphere upper-level mid-latitude circulation on the ISM. Using the previously collected geopotential height data at the 200 hPa height field, we created a parabolic time series to find the climatological seasonal cycle and, from that, deduce the anomalies. The anomalous Z200 associated with each regime (both simultaneous and time-lagged) is explored to better understand the dynamics of the preferred intra-seasonal circulation of the ISM. Future research will focus on using variables other than Z200 to determine to what extent the ISM is responding to mid-latitudes, and to what extent it can drive the mid-latitude circulation.