Abstract
From 1999 to 2014, four warm ENSO events occurred and shifted the convection process from the tropical western Pacific to the central and eastern Pacific causing decreased precipitation and severe droughts in northern Australia and the most part of the Indonesian Archipelago (95–150°E, 6°N-24°S). An anomalously cold sea surface temperature (SST) in the western Pacific marks the warm phase of ENSO events. Wood (2012) has shown that a cold SST is closely associated with the development of low-level clouds, whereas Schrage and Fink (2012) have shown that there is a connection between the formation of nocturnal low-level clouds (NLLCs) and nocturnal low-level jets (NLLJs) in West Africa. This study is to see if there exists the interannual variability of NLLC and NLLJ occurrence during the warm ENSO events in the domain within the 16-year period and how it is different from that during the cold ENSO events. This study is also to examine if the relationship found by Schrage and Fink (2012) is also true in this domain. The results of this study demonstrate that first, the domain is divided into two opposite SST anomaly regions during the warm and cold ENSO events, namely northern Australia and Papua (NAP) and western Indonesian Archipelago (WIA); second, the interannual variability of NLLC occurrence does exist: during the peak of warm (cold) ENSO events, the NLLC occurrence in NAP is anomalously positive (negative) whereas in WIA is anomalously negative (positive); third, the interannual variability of NLLJ occurrence exists only in NAP and not in WIA: during the peak of warm (cold) ENSO events, the NLLJ occurrence is anomalously positive (negative); fourth, the relationship between the formation of NLLC and NLLJ in the domain is hard to determine due to limited time resolution of the radiosonde data.