This study is a continuation of an earlier work [Findell and Elahir, 1997] on the soil moisture-rainfall feedback using a data set of biweekly neutron probe measurements of soil moisture at up to 19 stations throughout Illinois. This earlier work showed that soil moisture can play a significant role in maintaining drought or flood conditions during the summer. Results of a linear correlation analysis between initial soil saturation and rainfall in the subsequent three weeks showed that a positive correlation between these two variables was present from early June to mid-August. This correlation was more significant than the serial correlation within precipitation, suggesting the likelihood of a physical mechanism linking soil moisture to subsequent rainfall. Further investigations probed the nature of such a physical pathway linking soil moisture to subsequent rainfall: these analyses are presented in this paper. Near-surface hourly observations of pressure, temperature, wet-bulb temperature, and relative humidity from 13 stations in and close to Illinois were used as indicators of near-surface air conditions. Time series of the spatial average of each of these and other quantities were then calculated by averaging data from the 13 stations at each hour. An analysis of the connections between an average daily soil saturation time series for the whole state of Illinois with these state wide average air conditions did not yield the anticipated positive correlation between soil moisture and moist static energy (MSE). It is not clear if this is due to limitations of the data or of the theory. Other factors, such as clouds, could potentially be masking the impacts of soil moisture on the energy of the near-surface air. There was evidence , however, that moisture availability (or lack thereof) at the surface has a very strong impact on the wet-bulb depression of near-surface air, particularly from mid-May to the end of August, showing good correspondence to the period of significant soil moisture-rainfall association. The final set of analyses performed included an investigation of hourly boundary layer and rainfall data. Data from 82 hourly rainfall stations were averaged to compare state wide hourly rainfall to state wide hourly boundary layer conditions. A link between high MSE and high rainfall was noted during some summer months, and a link between low wet-bulb depression and high rainfall was evident for all of the months analyzed (April through September). These analyses then suggest that the significant but weak correlation between soil moisture and rainfall in Illinois summers is at least partially due to soil moisture controls on the wet-bulb depression of near-surface air.
