Initial observations of cold surge frequency over Southeast Asia in relation to ENSO-induced anomalies

Abstract

Over the Southeast Asian region, strong surges of cold northeasterly winds are common during winter of the southern hemisphere. For these cold surges, the occurrence frequency is known to vary in conjunction with the El Nino-Southern Oscillation (ENSO) phenomenon. This preliminary study looks at the correlation between cold surge frequency (CSF) and two indicators of ENSO-induced anomalies — the Southern Oscillation Index (SOI) and the Oceanic Nino Index (ONI). ENSO events are detected when each of these indices exceed certain anomaly threshold values for a specified prolonged period. These anomaly threshold values (AT SOI and AT ONI ) are used as conditions for logical filtering. Four unrelated rounds of logical filtering are applied to 20 seasons of data. Correlation values are then calculated. The results show that the CSF has a more significant one-to-one correlation with the anomaly of atmospheric pressure (which is indicated by the SOI) than the anomaly of sea surface temperature (indicated by the ONI). However, the findings suggest that the approach of logical filtering using both anomaly indices (together) is more effective, when observing CSF in relation to ENSO. Also, it is suggested that CSF per normal seasons is in the range of 16 to 17 events during DJF. (These results apply to an area between 110° and 117.5°E along 15°N.)