Effects of soil moisture gradients on the path and the intensity of a West African squall line

D. Wolters, C.C. van Heerwaarden, J. Vilà-Guerau de Arellano, B. Cappelaere, D. Ramier

Research output: Contribution to journalArticleAcademicpeer-review

17 Citations (Scopus)

Abstract

During the West African monsoon season, precipitation is strongly coupled to soil moisture availability. This interaction is generally understood as a positive feedback mechanism, and has been considered on very different spatial and temporal scales. Past research has mainly focused on this feedback in terms of the effects on general precipitation patterns, not on a single convective system. In this research, a single squall line is reproduced using the Weather Research and Forecasting Advanced Research (WRF-ARW) mesoscale weather model. Model results are analyzed and compared with surface and upper-air observations. A sensitivity analysis on the influence of soil moisture on the squall line is performed through five numerical experiments. In four experiments, soil moisture is increased or decreased with respect to a control experiment. This is done in two manners: by affecting soil moisture most strongly in the wetter places in the modelled domain and by affecting soil moisture most strongly in the drier places. Minor deviations occur in the path of the squall line after modifying soil moisture most strongly in the wetter places. Systematic deviations occur in its path after increasing soil moisture most strongly in the drier places. A mechanism is proposed that connects the applied soil moisture modifications to larger-scale flow patterns that determine the path of the squall line. In all five experiments, the precipitation intensity of the squall line strongly declines when the systemmoves towards western areaswith lower soil moisture values. It is concluded that a positive effect of local soil moisture on precipitation intensity in passing squall lines is likely on the considered length-scale of 100 km. Until now, this mechanism has only been shown for much smaller spatial scales.
Original languageEnglish
Pages (from-to)2162-2175
JournalQuarterly Journal of the Royal Meteorological Society
Volume136
Issue number653
DOIs
Publication statusPublished - 2010

Keywords

  • mesoscale convective complexes
  • land-surface
  • monsoon
  • variability
  • sahel
  • model
  • precipitation
  • dynamics
  • system
  • field

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