Coherent Life Cycle of Intraseasonal Tropical Convection and Extratropical Circulation during El Nino and La Nina years

Coherent life cycle of intraseasonal tropical convection and extratropical circulation has been studied with the NCEP/NCAR reanalysis and NOAA satellite data during boreal winters from 1979 to 2003. From the EOF analysis, eastward propagating life cycle of tropical and extratropical circulation anomalies are obtained using the composites of 1st and 2nd principal components using OLR. Extratropical circulation anomalies are found to be closely connected with tropical convection cells in 20-90 day life cycle. During El Nino, intraseasonal tropical convection intensifies over the eastern Pacific and during La Nina, it is strengthened to a little northward over the western Pacific. From these intraseasonal tropical forcings, mid- to high-latitude wave propagation activity seemed to show distinct contrast features during ENSO years. However, regions of north Atlantic and eastern part of North America showed no significant reactions from the tropical forcings. Wave-eddy feedbacks and the eddy energy over the extratropics are calculated to find the possible other reasons for this differences.