Moisture transport associated with southwest monsoon rainfall over Sri Lanka in relatively wet and dry rainfall years

Atmospheric moisture transport is the most important part of the atmospheric branch of the water cycle, and its anomalies strongly influence rainfall variability. Atmospheric moisture transportation associated with southwest monsoon (SWM) years over Sri Lanka is still not fully understood. Using ERA...

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Bibliographic Details
Published in:Meteorology and atmospheric physics 2023-10, Vol.135 (5), p.46, Article 46
Main Authors: Shelton, Sherly, Dixon, Ross D.
Format: Article
Language:English
Subjects:
Anomalies
Aquatic Pollution
Atmospheric moisture
Atmospheric Sciences
Climatological means
Convergence
Deforestation
Earth and Environmental Science
Earth Sciences
Fluctuations
Hydrologic cycle
Hydrological cycle
Low-level jets
Math. Appl. in Environmental Science
Meteorology
Moisture
Moisture effects
Moisture flux
Monsoon rainfall
Monsoons
Original Paper
Precipitation
Rainfall
Rainfall variability
Southwest monsoon
Terrestrial Pollution
Variability
Waste Water Technology
Water Management
Water Pollution Control
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Summary:Atmospheric moisture transport is the most important part of the atmospheric branch of the water cycle, and its anomalies strongly influence rainfall variability. Atmospheric moisture transportation associated with southwest monsoon (SWM) years over Sri Lanka is still not fully understood. Using ERA5 daily data, we investigated the role of moisture transport in relatively wet (SWM Wet ) and dry (SWM Dry ) SWM years. Based on composite analysis, seven wet (SWM Wet ) and nine dry (SWM Dry ) years were selected from 1985 to 2015. We observe positive (negative) anomalous rainfall in SWM Wet (SWM Dry ) years, while the strong anomalous rainfall is concentrated on the western and southwest parts of Sri Lanka. In SWM Wet years, strengthened moisture-laden low-level jets from the Arabian Sea bring excess moisture toward Sri Lanka, while a contrasting pattern is observed in SWM Dry years. As a consequence, the climatological mean of net moisture flux (9.46 × 10 5  kg s −1 ) over the study domain is increased by 12.37 × 10 5  kg s −1 , resulting in above-average rainfall in SWM Wet Years. The results show a decrease in the net moisture flux (5.37 × 10 5  kg s −1 ), prescribed below-average rainfall in SWM Dry years. The strong relationship ( r  = 0.63) between net moisture flux and SWM rainfall may explain the observed SWM rainfall variability over the country. Compared to the climatological Vertically Integrated Moisture Flux Convergence (VIMFC, 8.56 × 10 −4  kg m −2  s −1 ), positive anomalous VIMFC (2.63 × 10 −4  kg m −2  s −1 ) in SWM Wet years and negative anomalous VIMFC (− 3.70 × 10 −5  kg m −2  s −1 ) in SWM Dry years are recorded. These results indicate that the free-tropospheric moisture and moisture flux convergence contributes to strong SWM rainfall by creating environments favorable for producing and maintaining moist absolutely unstable layers. This study helps us understand that the dynamic processes of the atmosphere are more important in regulating the variability of SWM rainfall over the country.
ISSN:0177-7971
1436-5065
DOI:10.1007/s00703-023-00986-x