Abstract
Abstract. The impacts of inhomogeneity of the oasis interior on the oasis self-maintenance mechanism are investigated by using the mesoscale model MM5 (the fifth-generation Pennsylvania State University National Center for Atmospheric Research (NCAR) mesoscale model) with satellite observations of land use types, vegetation fraction and surface-layer soil moisture from MODIS (Moderate Resolution Imaging Spectroradiometer) data. Four simulations were performed, among which the CTL (control simulation) and MOD (moderated simulation with parameters replaced by MODIS data) were used to validate the model results; EXP1 (experiment 1) and EXP2 (experiment 2) were designed to study the inhomogeneity of oasis interior. Results show that the changes of oasis heterogeneity influence the surface heat-flux partitioning, which leads to a larger "cold-wet" effect over the oasis. Vertical sections of humidity illustrate the existence of a moisture-inversion level, and the deeper moisture inversion of EXP1 and EXP2 further indicates that the relative homogeneity in the oasis interior helps produce stronger humidity inversion over the oasis, thus limiting evaporation. This is further verified by the analysis of the secondary circulation, which shows that the more homogeneous land surface conditions lead to stronger secondary circulation and less turbulent drafts over the oasis interior, playing a positive role in the oasis self-maintenance and development.
Highlights
The interaction between the atmosphere and the underlying surface is primarily manifested in the heat, moisture, and momentum exchanges between air masses and soil or water (Kukharets and Nalbandyan, 2006)
The MOD experiment produces similar simulations for air temperature and specific humidity at 2 m above ground and better results for sensible and latent heat fluxes than the CTL, errors can be seen in both simulations
The influence of inhomogeneity of the oasis interior on the oasis self-maintenance mechanism was investigated by using the mesoscale model MM5 with satellite-derived land use type, vegetation fraction and surface-layer soil moisture from Moderate Resolution Imaging Spectroradiometer (MODIS) data
Summary
The interaction between the atmosphere and the underlying surface is primarily manifested in the heat, moisture, and momentum exchanges between air masses and soil or water (Kukharets and Nalbandyan, 2006). Surface heterogeneity complicates interactions between the atmosphere and the underlying surface, affects moist convection, and systematically produces responses in both local circulation and regional climate (Courault et al, 2007; Reen et al, 2006; Yuan et al, 2008; Yates et al, 2003; Zhang et al, 2010) In many situations, these locally induced circulations are important in determining mesoscale weather conditions (Wu and Raman, 1997). Surface heterogeneities induce spatial variability in surface heat fluxes that can create “inland breezes”, “oasis effects” and “glacier winds”, similar to sea–land breeze systems (Mahfouf et al, 1987; Gao et al, 2004; Lu et al, 2004a; Sun et al, 2007) Such phenomena are known to contribute significantly to energy, water and mass transfer (Bastin and Drobinski, 2006; Meng et al, 2009)
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