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Low-Level Cloud Development and Diurnal Cycle in southern West Africa during the DACCIWA Field Campaign: Case Study of Kumasi Supersite, Ghana
  • Jeffrey Nii Armah Aryee,
  • Leonard K Amekudzi,
  • Edmund Ilimoan Yamba
Jeffrey Nii Armah Aryee
Kwame Nkrumah University of Science and Technology

Corresponding Author:jeff.jay8845@gmail.com

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Leonard K Amekudzi
Department of Physics, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi-Ghana
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Edmund Ilimoan Yamba
Kwame Nkrumah University of Science and Technology (KNUST)
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The presence, spatial extent and persistence of low-level clouds (LLCs) largely impact on the diurnal surface radiation and energy balance, as well as, the regional climate. Notwithstanding, there is limited understanding on their evolution and processes, particularly in southern West Africa. This paper assesses the development of LLCs and their dominant formative factors, as well as, their relationship with radiation and energy balance. Firstly, ceilometer and radiosondes deployed during the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) field campaign were used in identifying the LLC. Afterwards, the cloud fraction was employed to characterize different LLC phases. Averagely, break-up, dissipation and build-up of LLC were marked at 0900 GMT, 1200 GMT and 2200 GMT respectively. Moreover, composites of LLC diurnal evolution and their relationship with net radiation, energy storage and surface stability showed that LLCs significantly impact on net radiation flux, by reducing downwelling shortwave radiation. Additionally, LLC onsets were characterized by a near-steady state in net radiation flux, whereas the rate of energy storage within the lower layers marginally oscillated about equilibrium. Finally, with observations from selected intensive observation periods (IOPs), the dominant factors influencing LLC development were evaluated. Horizontal cold air advection, with enhancement by nocturnal low-level jets, was observed to primarily influence the development of LLCs for the study period. Findings of this paper are necessary for improving the understanding of LLC characteristics, formation and interactions with surface properties, particularly over southern West Africa.
16 Jun 2021Published in Journal of Geophysical Research: Atmospheres volume 126 issue 11. 10.1029/2020JD034028