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The impact of soil moisture modifications on CBL characteristics in West Africa: A case‐study from the AMMA campaign
Author(s) -
Kohler M.,
Kalthoff N.,
Kottmeier C.
Publication year - 2010
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.430
Subject(s) - latent heat , environmental science , water content , albedo (alchemy) , precipitation , sensible heat , atmospheric sciences , moisture , bowen ratio , convection , troposphere , climatology , advection , convective available potential energy , meteorology , geology , geography , art , physics , geotechnical engineering , performance art , thermodynamics , art history
Within the framework of the AMMA campaign in 2006, the response of surface properties to precipitation and their effect on the state of the convective boundary layer (CBL) and on convective instability were analysed. The observation periods covered the pre‐monsoon onset (SOP 1) and the mature monsoon phase (SOP 2) and were performed in southwest Burkina Faso. Precipitation caused a distinctive increase in the volumetric soil moisture content in the upper 20 cm of the soil. Coupled with the increase in soil moisture, a continuous decrease of surface and soil temperature with time was observed. Changes in surface temperature, albedo, and a higher availability of water affected the partitioning of the energy balance. Highest values of the Bowen ratio were found during SOP 1 when the surface was dry and vegetation sparse. In SOP 2, a higher vegetation cover made the albedo and Bowen ratio less sensitive to changes in soil moisture. Modifications of surface fluxes influenced the CBL conditions. The CBL height in SOP 1 was 1658 m and in SOP 2 877 m. The heat budget of the CBL was dominated by sensible heat flux convergence, whereas the moisture budget was controlled by both advection and latent heat flux convergence. It was confirmed by the measurements that the diurnal development of convective instability was dominated by the CBL evolution and controlled by changes in the mid‐ or upper troposphere to a minor degree only. Linear correlations were found between the near‐surface equivalent potential temperature and both convective available potential energy and convection index. Copyright © 2009 Royal Meteorological Society