The influence of fine particle tropospheric aerosol on local air and soil temperature in the central U.S.A.

The optical properties of two haze conditions prevalent during well-observed occasions in the central U.S.A. were estimated by Ball and Robinson (1982). A comprehensive, interactive, time-dependent model of the coupled atmospheric planetary boundary-upper soil (water) layers, specifically formulated to include such radiative parameters, is described in Brown et al. (1982) and earlier papers. A version of that model, including the Robinson and Ball radiative parameters, is applied with detailed micrometeorological measurements tabulated in Lettau and Davidson (1957), to obtain some quantitative estimates of the effects of haze on near-surface air and soil temperatures in agriculturally important regions of the central U.S.A.A calibration simulation of an observed two-day period in late summer over a dry-prairie surface shows the model's qualitative verisimilitude in the calculation of observed solar irradiance and near-surface air temperature. This is followed by a second model simulation experiment for late spring clear-sky conditions over a hypothetical moist bare-soil (sown cropland) surface, to estimate the effects of the two hazes on temperature and on the accompanying surface heat budgets. Significant alterations of near-surface temperatures, in the range 0.5 °C to 2.5 °C are found over a five-day simulation period. The alterations are such as to increase air-soil temperature difference, with relative warming of the air and relative cooling of the soil with both aerosol characterizations.