DIAGNOSIS ON LOW FREQUENCY COMPONENT OF ENSO VARIABILITY-PART Ⅱ:ORIGIN OF THE COMPONENT

Diagnosis is undertaken on the origin for the low-frequency component(LFC) of ENSO variability in the context of 1979-1990 OLR and u-wind datasets.Evidence suggests that ① a power spectrum-yielded maximum,significant statistically,is derived from the OLR monthly anomalies in a 3-5-year period range over the tropical central/western Pacific;②compositean alysis of the signals of the monthly anomaly low frequency component(period3 years) confirms further the dynamic features of the component as documented in Part Ⅰ:③serving as forcing on ENSO,the related monsoon region represents the source area of the component;④the one-point correlation maps of unfiltered OLR monthly anomalies with zonal wind on a lagged,a simultaneous and a leading basis show clearly the close relation between the u wind-associated eastward travelling low-frequency wave and the low-frequency oscillation of low-latitude central/western Pacific large-scale convection and the east-moving mode is likely to be excited by the oscillation at a 3-5-year period range.It follows that the large-scale convection oscillation shows up as the origin of the eastward waves,i.e.,ENSO LFC.