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Abstract Extreme rainfall events in the West African Sahel can be impactful, yet we do not completely understand why such storms develop. Here, we utilize NASA long‐term Integrated Multi‐satellitE Retrievals for Global precipitation measurement (IMERG) rainfall estimates, various atmospheric reanalyses, and Weather Research and Forecasting (WRF) convection‐permitting simulations to further examine the regional/local conditions that led to the development of two extreme events over the Damergou Gap of Niger/Nigeria identified in a prior study. The August 20, 2019 central Niger event is associated with the passage of a westward‐moving convective line. A strong thermal low over eastern Niger preconditions the environment by increasing the atmospheric moisture and vertical wind shear. Cold‐pool outflow boundaries generated from afternoon convection over the higher terrain ahead of the approaching line enhances convergence along the line while slowing down the system's movement, resulting in higher‐intensity rainfall for a longer time over the region. The July 19, 2001 northern Nigerian event has rainfall developing over the Jos Plateau in the afternoon. Guinean Highland ridging combined with low pressure over Niger/Chad produces a strong low‐level height gradient associated with the development of a strong southwesterly flow surge that transports tropical moisture into the region. This surge interacts with the equatorward migration of the Sahel–tropical Africa dryline, enhancing the convergence and convection north of the Jos Plateau. Our results indicate that while extreme rainfall in the Damergou Gap is likely to occur in anomalously moist environments, it is not necessarily associated with highly unstable environments (e.g., convective available potential energy [CAPE] >2,500 J·kg−1). Furthermore, interactions with cold‐pool outflow boundaries generated from other convective areas is important, and local terrain features are influential in the development of such convective areas.
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The Oceanic Barrier Layer in the Eastern Indian Ocean as a Predictor for Rainfall Over Indonesia and Australia
Abstract Barrier layers in the tropics trap heat in a shallow and stable near‐surface layer and limit entrainment of cooler water from below. Both processes act to increase sea surface temperature and enhance atmospheric convection. The high resolution fully coupled pre‐industrial Energy Exascale Earth System Model version 0 (E3SMv0) is used to investigate the relationship between barrier layers in the eastern Indian Ocean during the wet season with local atmospheric convection and remote rainfall. A partial least squares regression reveals a significant relationship between Australasian rainfall and the barrier layer thickness (BLT) west of Sumatra, occurring one month earlier. The largest positive regression coefficients are over northern Australia. The region west of Sumatra is strategically located where the East‐Asian monsoon moisture flows toward northern Australia. Thickening of the west Sumatra BLT intensifies evaporation and local convection and amplifies the moisture transported to Australia acting to increase the terrestrial rainfall.
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- Award ID(s):
- 1851316
- PAR ID:
- 10375683
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 22
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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