Regional Heat Sources and the Active and Break Phases of Boreal Summer Intraseasonal (30–50 Day) Variability*

Abstract

The boreal summer intraseasonal variability (BSISV) associated with the 30–50-day mode is represented by the coexistence of three components: poleward propagation of convection over the Indian and tropical west Pacific longitudes and eastward propagation along the equator. The hypothesis that the three components influence each other has been investigated using observed outgoing longwave radiation (OLR), NCEP–NCAR reanalysis, and solutions from an idealized linear model. The null hypothesis is that the three components are mutually independent. Cyclostationary EOF (CsEOF) analysis is applied on filtered OLR to extract the life cycle of the BSISV. The dominant CsEOF mode is significantly tied to the observed spatial rainfall pattern associated with the active/break phases over the Indian subcontinent. The components of the heating patterns from CsEOF analysis serve as prescribed forcings for the dry version of the linear model. This allows one to investigate the possible roles that the regional he... Abstract The boreal summer intraseasonal variability (BSISV) associated with the 30–50-day mode is represented by the coexistence of three components: poleward propagation of convection over the Indian and tropical west Pacific longitudes and eastward propagation along the equator. The hypothesis that the three components influence each other has been investigated using observed outgoing longwave radiation (OLR), NCEP–NCAR reanalysis, and solutions from an idealized linear model. The null hypothesis is that the three components are mutually independent. Cyclostationary EOF (CsEOF) analysis is applied on filtered OLR to extract the life cycle of the BSISV. The dominant CsEOF mode is significantly tied to the observed spatial rainfall pattern associated with the active/break phases over the Indian subcontinent. The components of the heating patterns from CsEOF analysis serve as prescribed forcings for the dry version of the linear model. This allows one to investigate the possible roles that the regional he...