Spatial Coherence and Seasonal Predictability of Monsoon Onset over Indonesia

Abstract

The seasonal potential predictability of monsoon onset during the August–December season over Indonesia is studied through analysis of the spatial coherence of daily station rainfall and gridded pentad precipitation data from 1979 to 2005. The onset date, defined using a local agronomic definition, exhibits a seasonal northwest-to-southeast progression from northern and central Sumatra (late August) to Timor (mid-December). South of the equator, interannual variability of the onset date is shown to consist of a spatially coherent large-scale component, together with local-scale noise. The high spatial coherence of onset is similar to that of the September–December seasonal total, while postonset amounts averaged over 15–90 days and September–December amount residuals from large-scale onset show much less spatial coherence, especially across the main islands of monsoonal Indonesia. The cumulative rainfall anomalies exhibit also their largest amplitudes before or near the onset date. This implies that seasonal potential predictability over monsoonal Indonesia during the first part of the austral summer monsoon season is largely associated with monsoon onset, and that there is much less predictability within the rainy season itself. A cross-validated canonical correlation analysis using July sea surface temperatures over the tropical Pacific and Indian Oceans (20°S–20°N, 80°–280°E) as predictors of local-scale onset dates exhibits promising hindcast skill (anomaly correlation of ∼0.80 for the spatial average of standardized rain gauges and ∼0.70 for standardized gridded pentad precipitation data).

Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon concept

“…The long-term patterns are similar for the two proxies, with drier (wetter) summer conditions and longer (shorter) dry season during interglacials (glacials). The fact that a longer dry season corresponds to a wetter summer monsoon agrees with present inter-annual monsoon dynamics; El Niño years are characterized by a shorter and wetter summer monsoon season, and the dry season lasts longer (Moron et al, 2009(Moron et al, , 2010Taschetto et al, 2009). The long-term pattern follows the glacial/interglacial cycles with a ∼100 yr periodicity (Fig.…”

Observations of the temporal variability in aerosol properties and their relationships to meteorology in the summer monsoonal South China Sea/East Sea: the scale-dependent role of monsoonal flows, the Madden–Julian Oscillation, tropical cyclones, squall lines and cold pools

“…This period is typically towards the end of the boreal summer southwest monsoon (henceforth SWM) system, approximately 2-3 weeks before the transition period to the boreal winter/spring northeast monsoon (NEM). A general overview of the summer monsoonal system can be found in Chang et al (2005), Moron et al (2009) and the book by Chang et al (2011). An overview of how monsoonal weather features relate to smoke emissions and transport from progressively larger to finer scales can be found in Reid et al (2012), Xian et al (2013), Mahmud (2009a, b) and Wang et al (2013), respectively.…”

Observing and understanding the Southeast Asian aerosol system by remote sensing: An initial review and analysis for the Seven Southeast Asian Studies (7SEAS) program

“…Peak fire activity then progresses eastward across the MC in time, with a maximum in Papua in November. The end date of burning in the MC also progresses eastward in time, as related to the eastward progression of winter monsoon onset in the MC (e.g., ending in Sumatra in late September, Borneo in October, Papua in mid-November, Moron et al, 2009;Reid et al, 2012). After another brief period of relative quiescence, the cycle then repeats itself beginning in late December and early January.…”

“…However, the very recent publication of Chang et al (2011) provides many useful chapters on SEA's summer and winter monsoonal period. For monsoonal flows, we also recommend Chang et al, 2005a;Moron et al, 2009;Wang et al, 2009 as important reading. In addition to the references above, we would like to draw attention to specific broad-scoped papers on meteorology-aerosol relationships such as the review paper on South Asia by Lawrence and Lelieveld (2010) and meteorological context of biomass burning in the MC by Reid et al (2012).…”

“…If one wishes to move from the qualitative to even the semi-quantitative, one must consider SEA's many highly interrelated climate and meteorological features. Nominally there are five atmospheric scales of concern over greater SEA, from largest to smallest: 1) Interannual features such as El Niño Southern Oscillation (ENSO Rasmusson and Wallace, 1983;Mcbride et al, 2003), ENSO Modoki (Ashok et al, 2007) and the Indian Ocean Dipole (IOD, Saji et al, 1999;Saji and Yamagata, 2003;Schott et al, 2009); 2) Seasonal migration of the Intertropical Convergence Zone (ITCZ) and its associated summer and winter monsoonal period and transitions (Chang et al, 2005a;Moron et al, 2009;Wang et al, 2009); 3) Intraseasonal synoptic phenomenon such as the 30-90day oscillation or the Madden Julian Oscillation (MJO) (Madden and Julian, 1971;Zhang, 2005;Wu and Hsu, 2009;Wu et al, 2009), the quasi-monthly oscillation , Borneo Vortex (Chang et al, 2005b), the west Sumatran low (Wu et al, 2009a), or at the most northern extent of our domain, the Meiyu front (Ding, 2002;Ding and Chan, 2005); 4) Wave and mesoscale features such as fronts and tropical cyclones (Goh and Chan, 2010) in northern SEA, and equatorial waves, such as the Kelvin, Rossby, and Easterly waves in the MC (Wheeler and Kiladis, 1999;Kiladis et al, 2009), tropical cyclones, or mid-level dry tongue (Ridout, 2002;Yasunaga et al, 2003;Zhang et al, 2003); and 5) Regional convection from localized weather phenomena, such as fair weather cumulus, orographically modified flows, thunderstorms, isolated small or trade convection, convective cold pools, sea breeze circulation, etc. (Schafer et al, 2001;Yang and Smith, 2006;Mahmud, 2009a,b;Mahmud, in press;Li et al, 2010;Sow et al, 2011;…”