Characteristics of spectral energetics during contrasting rainfall years in Central India

Often, statistically significant spatial and temporal deviations from the seasonal mean rainfall result in either severe droughts (deficient rainfall) or floods (excess rainfall), impacting agriculture, quality of life, and the economy of India. Moreover, understanding and predicting these events are challenging because the problem is highly non-linear and often swamped by multi-scale interactions that result from this non-linearity. This study explored the precise nature of complex nonlinear energy interactions of Low Pressure Systems (LPSs), Intraseasonal Oscillations (ISO), and the seasonal mean flow over the Monsoon Core Zone (MCZ: 15°-28°N, 67°-88°E) of the Indian subcontinent using high-resolution ERA-5 reanalysis daily data. This study examined the climatology of the energy exchanges during the contrasting summer monsoon rainfall years using the framework of spectral energetics. We found that the baroclinic conversion of Available Potential Energy (APE) to Kinetic Energy (KE) is the primary source of KE for the seasonal mean flow and LPS. On the other hand, the primary source of KE on the ISO (10–90 day mode) scale is the KE transfer from the seasonal mean flow. These energy exchange anomalies show opposite characteristics during droughts and pluvial years. Moreover, these exchanges also possess distinct vertical profile characteristics with baroclinic conversion mostly positive and peaking up in the upper levels for LPS as well as ISO whereas barotropic KE conversions are mostly negative on the ISO scale (ISO modulating seasonal mean flow) in the upper atmosphere and positive in the middle levels. Barotropic conversions on the LPS scale are positive in the upper atmospheric levels and negative in the lower and middle levels, indicating that LPSs modulate seasonal mean flow in lower levels.