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

摘要

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; ② composite analysis of the signals of the monthly anomaly low frequency component (period > 3 years) confirms further the dynamic features of the component as documented in Part Ⅰ: ③ serving as forcing on ENSO. the related monsoon region represents the source area of the component: ④ the 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.