Possible Cross Equatorial Influence of the Northeast Monsoon on the Equatorial Westerlies over Indonesia

摘要

Objectively analysed surface, 700 and 200 mb winds of nine winters are used to study the possible cross equatorial influence of the northern winter monsoon on the zonal wind along 10 deg S in the Indonesia-Arafura Sea region and to prepare a nine-year monthly mean climatology. Key circulation features are represented by area averaged and time composited parameters in an attempt to infer correlations between their perturbation. Specifically, the acceleration of the zonal wind along 10 deg S in the Indonesia-Arafura Sea region is used to define the onset of the southern summer monsoon and illustrate the timing between circulation features of interest in both hemispheres. While no conclusive results were achieved, some basic observations can be made. Midseason active phases in the southern monsoon appear to be influenced by surges in the northeast monsoon in the Northern Hemisphere while late season events appear to be primarily a result of Southern Hemispheric, mid-latitude, baroclinic effects. In both cases, the meridional extent of the southern summer monsoon is limited. Even in the mid-season event, variability in area-averaged cross equatorial flow may not be indicative of the nature of forcing of the Northern Hemisphere's monsoonal winds on the southern summer monsoonal winds along 10 deg S. Originator-supplied keywords include: Cross-equatorial flow, Southern summer monsoon, Interhemispheric influence, Monsoon onset, Australian monsoon, Tropical-midlatitude influence.