Role of the Pacific-Japan Pattern in Shaping Sri Lanka Rainfall

Abstract

Recent studies have shown that the Pacific-Japan (PJ) pattern is the dominant climate mode and has a relationship with rainfall anomalies in East Asia. However, the influence of the PJ pattern on the rainfall of Sri Lanka remains largely unclear. Therefore, the present study examines the impact of the PJ pattern on the rainfall of Sri Lanka during the boreal summer utilizing observational and reanalysis datasets from 1981 to 2020. It is noted that the PJ pattern has a significant positive relationship with rainfall in Sri Lanka during the boreal summer. Furthermore, based on the composite analysis, we found that Sri Lanka experiences wet conditions during the positive phase of the PJ pattern in the summer, while the negative phase of the PJ pattern contributes to dry conditions. During the positive phase of the PJ pattern, moisture convergence over Sri Lanka is associated with the easterlies extending from the southern flank of Western North Pacific anomalous anticyclonic circulation, which results in enhanced convection and wet conditions over Sri Lanka. On the other hand, moisture divergence over Sri Lanka is linked with the westerlies extending from the southern flank of the Western North Pacific anomalous cyclonic circulation, decreasing the convection and dry conditions over Sri Lanka. This study suggests that the PJ pattern is a significant climate mode for understanding the rainfall pattern in Sri Lanka.