Articles | Volume 42
Adv. Geosci., 42, 51–60, 2016
https://doi.org/10.5194/adgeo-42-51-2016
Adv. Geosci., 42, 51–60, 2016
https://doi.org/10.5194/adgeo-42-51-2016

  24 Aug 2016

24 Aug 2016

The progression of the boreal winter monsoon through the western Maritime Continent as differentiated by ENSO phase

Shao-Yi Lee and John L. McBride Shao-Yi Lee and John L. McBride
  • Meteorological Service Singapore, Singapore

Abstract. The impact of global ENSO on the regional monsoon onset over the Maritime Continent is examined, using satellite-derived scatterometer surface winds over the sea channel from the South China Sea, through the Karimata Strait into the Java Sea. An index of monsoon onset, fracsign, is defined based on a positive dot-product between the monthly wind at each gridpoint and the "basis-wind" or climatological wind at the peak of the relevant monsoon season.

Rather than being delayed throughout the Maritime Continent during El Niño years, the monsoon is seen to arrive faster at and remain longer over the western Maritime Continent, and therefore delayed for the eastern Maritime Continent. The wind-based diagnostic can be further decomposed into two components that reflect the monsoon wind strength and the location of the wind convergence zone, respectively. During El Niño years, the monsoon strength post-onset is weaker than normal over the eastern maritime continent. However, there is no ENSO-related differentiation in monsoon strength post-onset over the western Maritime Continent.

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Short summary
Weather forecasters in Maritime Continent countries base their weekly outlooks on the seasonal progression of the monsoon wind systems. The onset of the monsoon was compared between El Niño and La Niña years using satellite sea surface winds. Rather than being delayed throughout the Maritime Continent during El Niño years, the monsoon was seen to arrive faster at and remain longer over the western Maritime Continent, and therefore delayed for the eastern Maritime Continent.