Climatological patterns of subseasonal eddy flux transfer based on the co‐spectral analysis over the Indian region and the derivation of an index of eddy transfer for operational tracking

Abstract

AbstractThe heat and momentum flux transfer by transient eddies from the extratropical to the tropical (E2T) region causes a significant variation of weather and climate in the tropical region. Such transports also cause a regional departure from zonally symmetric large scale circulation patterns caused by the Hadley type transports. During boreal summer monsoon season, the zonally symmetric Hadley type circulation is typically considered in theoretical as well as modelling studies. The current study introduces a method based on the calculation of the E‐vector components and co‐spectra analysis to diagnose the zonally asymmetric climatological patterns of E2T transport and its subseasonal variability. The spectral analysis identifies the climatological as well as low and high frequency patterns of the transient eddy heat and momentum flux transfer over the Indian region and compares the result with traditional Eliassen‐Palm (EP) Flux based stationary eddy patterns. The study identifies the zonal, seasonal, and vertical asymmetries in the transport of transient eddy heat and momentum flux. The study also clearly categorizes the seasonality and frequency dependence of northeast to the southwest tilt of transient eddies transporting momentum and heat flux. Based on the climatological patterns, the wavelet transform approach is used to study the subseasonal variability of the eddy transport indices. We define a set of indices, which identify the subseasonal temporal variation of the E2T transfer mechanism. These indices could be used to operationally track the E2T eddy flux transfer both in observation and in forecast models.