Earth and Atmospheric Sciences, Department of


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Published in Meteorology and Atmospheric Physics (2023) 135:46.



Used by permission.


Atmospheric moisture transportation associated with the occurrence of relatively wet and dry southwest monsoon (SWM) years over Sri Lanka is still not fully understood. This study focused on investigating the role of moisture transport in contrast SWM years. We selected seven wet (SWMWet) and nine dry (SWMDry) years for 1985-2015 and found that the whole country experiences above-average (below average) rainfall in SWMWet (SWMDry) years. In SWMWet years, strengthening moisture-laden low-level jets (LLJ) from the Arabian Sea bring a large amount of moisture towards Sri Lanka. In contrast, the weakening of the LLJ from the Arabian Sea direction is observed in SWMDry years. As a consequence, the climatological mean of net moisture flux (4.35 ×105 kg s-1) over the study domain is increased (5.33×105 kg s-1) and decreased (3.98 ×105 kg s-1) in SWMWet and SWMDry years, respectively. With respect to long-term Vertically Integrate Moisture Flux Divergence (VIMFD, –3.28×10-5 kg m-2 s-1), negative anomalous VIMFD (–1.78×10-5 kg m-2 s-1 ) in SWMWet years and positive anomalous VIMFD (1.44×10-5 kg m-2 s-1 ) in SWMDry years are recorded, which ascribed above-average and below-average rainfall over the country. Furthermore, strong moisture convergence (divergence) center in the western/ southwestern part of Sri Lanka during the SWMWet (SWMDry) years explain why strong positive and negative SWM rainfall anomalies are concentrated in these two regions. Furthermore, results highlighted a strong relationship between net moisture flux availability and SWM rainfall (r= 0.63) that may explain the observed SWM rainfall variability over the country.