Abstract
AbstractFeedbacks between soil moisture and precipitation are important for understanding hydroclimatic variability in many regions. However, much uncertainty remains about how land surface fluxes influence the initiation of deep convection locally. While some studies consider only atmospheric and soil profiles, in a one‐dimensional sense, others have argued that horizontal variability in fluxes plays an important role in convective triggering, via mesoscale circulations. This paper presents the first comprehensive observational analysis over Europe linking convective initiation to soil moisture, based on satellite observations of cloud top and land surface temperature, and soil moisture. The results show that convective initiations are favored on the downwind side of dry surfaces, close to wetter areas. The signal is clearest following dry periods and under light winds, consistent with forcing by a mesoscale circulation. Overall, the detected signal in Europe is weaker than in previous Sahelian analysis, but key spatial characteristics are essentially the same.
Highlights
Soil moisture can influence rainfall by limiting evapotranspiration, which affects the development of the daytime planetary boundary layer (PBL) and thereby the initiation and intensity of convective precipitation [e.g., Eltahir, 1998]
This study focuses on snapshots of mesoscale LST anomalies (LSTAs) structures, where gradients in air temperature are expected to be small and are in part responding to soil moisture anomalies
The mean two-dimensional structure of LSTA is presented in Figure 2, based on the average of midmorning Terra data on the day of the event or, in cases of substantial cloud and/or no local overpass, the preceding
Summary
Soil moisture can influence rainfall by limiting evapotranspiration, which affects the development of the daytime planetary boundary layer (PBL) and thereby the initiation and intensity of convective precipitation [e.g., Eltahir, 1998]. A number of authors have analyzed this impact using simple one-dimensional models of the surface and PBL [Ek and Holtslag, 2004; Findell and Eltahir, 2003], and found that the sensitivity of moist convective initiation to soil moisture depends on the vertical profile of the atmosphere Another branch of the literature has focused on the role of mesoscale variations in soil moisture (and vegetation) in the development of daytime PBL circulations, which provide a favorable environment for the triggering of deep convection [Avissar and Liu, 1996; Pielke, 2001]. Robust relationships with preinitiation land surface temperature (LST) and soil moisture patterns are identified, which shed light on the relative importance of 1-D and 2-D mechanisms in Europe This complements the previous global study (T12) which focused on afternoon rain (not just initiation) and, because of the resolution of the data, could not distinguish between 1-D and 2-D processes. The paper proceeds with a description of the observational data sets and methods (section 2), and is followed in section 3 by the results and concludes with a discussion of the differences between processes dominating in Europe and the Sahel
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