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A Lagrangian analysis of the sources of rainfall over the horn of Africa drylands

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Abstract
The Horn of Africa drylands (HAD) are among the most vulnerable regions to hydroclimatic extremes. The two rainfall seasons-long and short rains-exhibit high intraseasonal and interannual variability. Accurately simulating the long and short rains has proven to be a significant challenge for the current generation of weather and climate models, revealing key gaps in our understanding of the drivers of rainfall in the region. In contrast to existing climate modeling and observation-based studies, here we analyze the HAD rainfall from an observationally-constrained Lagrangian perspective. We quantify and map the region's major oceanic and terrestrial sources of moisture. Specifically, our results show that the Arabian Sea (through its influence on the northeast monsoon circulation) and the southern Indian Ocean (via the Somali low-level jet) contribute & SIM;80% of the HAD rainfall. We see that moisture contributions from land sources are very low at the beginning of each season, but supply up to & SIM;20% from the second month onwards, that is, when the oceanic-origin rainfall has already increased water availability over land. Further, our findings suggest that the interannual variability in the long and short rains is driven by changes in circulation patterns and regional thermodynamic processes rather than changes in ocean evaporation. Our results can be used to better evaluate, and potentially improve, numerical weather prediction and climate models, and have important implications for (sub-)seasonal forecasts and long-term projections of the HAD rainfall.
Keywords
Horn of Africa, rainfall, moisture transport, FLEXPART, ATMOSPHERIC MOISTURE, LONG RAINS, PRECIPITATION, EVAPORATION, VARIABILITY, LAND, NETWORK, DIPOLE

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MLA
Koppa, Akash, et al. “A Lagrangian Analysis of the Sources of Rainfall over the Horn of Africa Drylands.” JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, vol. 128, no. 12, 2023, doi:10.1029/2022JD038408.
APA
Koppa, A., Keune, J., MacLeod, D. A., Singer, M., Nieto, R., Gimeno, L., … Miralles, D. (2023). A Lagrangian analysis of the sources of rainfall over the horn of Africa drylands. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 128(12). https://doi.org/10.1029/2022JD038408
Chicago author-date
Koppa, Akash, Jessica Keune, Dave A. MacLeod, Michael Singer, Raquel Nieto, Luis Gimeno, Katerina Michaelides, et al. 2023. “A Lagrangian Analysis of the Sources of Rainfall over the Horn of Africa Drylands.” JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 128 (12). https://doi.org/10.1029/2022JD038408.
Chicago author-date (all authors)
Koppa, Akash, Jessica Keune, Dave A. MacLeod, Michael Singer, Raquel Nieto, Luis Gimeno, Katerina Michaelides, Rafael Rosolem, George Otieno, Abebe Tadege, and Diego Miralles. 2023. “A Lagrangian Analysis of the Sources of Rainfall over the Horn of Africa Drylands.” JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 128 (12). doi:10.1029/2022JD038408.
Vancouver
1.
Koppa A, Keune J, MacLeod DA, Singer M, Nieto R, Gimeno L, et al. A Lagrangian analysis of the sources of rainfall over the horn of Africa drylands. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. 2023;128(12).
IEEE
[1]
A. Koppa et al., “A Lagrangian analysis of the sources of rainfall over the horn of Africa drylands,” JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, vol. 128, no. 12, 2023.
@article{01HF6HR1AYP1YWFJ8H505CB84J,
  abstract     = {{The Horn of Africa drylands (HAD) are among the most vulnerable regions to hydroclimatic extremes. The two rainfall seasons-long and short rains-exhibit high intraseasonal and interannual variability. Accurately simulating the long and short rains has proven to be a significant challenge for the current generation of weather and climate models, revealing key gaps in our understanding of the drivers of rainfall in the region. In contrast to existing climate modeling and observation-based studies, here we analyze the HAD rainfall from an observationally-constrained Lagrangian perspective. We quantify and map the region's major oceanic and terrestrial sources of moisture. Specifically, our results show that the Arabian Sea (through its influence on the northeast monsoon circulation) and the southern Indian Ocean (via the Somali low-level jet) contribute & SIM;80% of the HAD rainfall. We see that moisture contributions from land sources are very low at the beginning of each season, but supply up to & SIM;20% from the second month onwards, that is, when the oceanic-origin rainfall has already increased water availability over land. Further, our findings suggest that the interannual variability in the long and short rains is driven by changes in circulation patterns and regional thermodynamic processes rather than changes in ocean evaporation. Our results can be used to better evaluate, and potentially improve, numerical weather prediction and climate models, and have important implications for (sub-)seasonal forecasts and long-term projections of the HAD rainfall.}},
  articleno    = {{e2022JD038408}},
  author       = {{Koppa, Akash and Keune, Jessica and  MacLeod, Dave A. and  Singer, Michael and  Nieto, Raquel and  Gimeno, Luis and  Michaelides, Katerina and  Rosolem, Rafael and  Otieno, George and  Tadege, Abebe and Miralles, Diego}},
  issn         = {{2169-897X}},
  journal      = {{JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}},
  keywords     = {{Horn of Africa,rainfall,moisture transport,FLEXPART,ATMOSPHERIC MOISTURE,LONG RAINS,PRECIPITATION,EVAPORATION,VARIABILITY,LAND,NETWORK,DIPOLE}},
  language     = {{eng}},
  number       = {{12}},
  pages        = {{16}},
  title        = {{A Lagrangian analysis of the sources of rainfall over the horn of Africa drylands}},
  url          = {{http://doi.org/10.1029/2022JD038408}},
  volume       = {{128}},
  year         = {{2023}},
}

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