Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 431499
Title Some observational and model evidence for dry soils supporting cumulus onset
Author(s) Westra, D.; Steeneveld, G.J.; Holtslag, A.A.M.
Source In: 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA). - Boston : American Meteorological Society - p. 12A.3 - 12A.3.
Event Boston : American Meteorological Society 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, Boston, 2012-07-09/2012-07-13
Department(s) Meteorology and Air Quality
Publication type Contribution in proceedings
Publication year 2012
Abstract The tendency of relative humidity at the top of a clear convective boundary layer (RHtop) is studied as indicator of cumulus cloud formation over a semi-arid region. As such observations and the conceptual framework introduced by Ek and Holtslag (2004, J. Hydrometeorology, 5, p. 86-99) is utilised. The latter framework is based on a mixed layer model, coupled to the land surface via the surface energy budget. Typically in a regime of relatively high soil moisture, the tendency of RHtop increases if the evaporative fraction at the land surface increases (confirming intuition). The latter supports boundary-layer moistening but only when boundary-layer growth is limited by atmospheric factors, such as dry air entrainment and limited boundary-layer growth. This regime was confirmed earlier by Cabauw observations over relatively moist surface conditions. Here we provide the first observational evidence that the tendency of RHtop can also increase (favouring cloud formation) when the surface becomes more dry. The latter is consistent with a second regime of the conceptual framework. The observations are taken from the AMMA intensive observational campaign near Niamey, Niger, June 20-25, 2006. We also evaluate whether various versions of the WRF single-column model confirm the different regimes of the conceptual framework for typical days in the AMMA campaign. It appears that the model also confirms that dryer soils can support cloud formation.
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