Abstract
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.
Highlights
An important regional process in the context of global ENSO is its impact on monsoon onset over the Maritime Continent (see Chang et al (2004) and Robertson et al (2011) for comprehensive reviews of the Maritime Continent monsoon)
This paper addresses the onset of the monsoon during the seasonal transition from northern summer to southern summer, utilising the sea state scatterometer winds to develop a means of monitoring this transition
Sea-state-scatterometer surface wind was taken from the Cross-Calibrated Multi-Platform (CCMP) Ocean Surface Wind Vector Analyses (Atlas et al, 2011)
Summary
An important regional process in the context of global ENSO is its impact on monsoon onset over the Maritime Continent (see Chang et al (2004) and Robertson et al (2011) for comprehensive reviews of the Maritime Continent monsoon). In this paper a monsoon onset index, fracsign, is defined in terms of the transition of the surface winds to with 90◦ of the peak direction It will be shown the progression through the South China Sea (north of the equator) and into the Java Sea (south of the equator) has a different character in El Niño years to that in La Niña years. Seasonal precipitation follows in general, but the characteristics of the annual cycle at different locations in the Maritime Continent can be strongly affected by orography, so the wet season over certain regions can be during boreal spring, fall, summer, or even multiple seasons (Chang et al, 2005) This creates some difficulty in determining the status of the monsoon over the western Maritime Continent based on precipitation alone The study focuses on describing the monsoon progression over the sea regions of the western Maritime Continent and the South China Sea, to utilise the sea state scatterometer data set, and to complement the results of previous studies
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