Linear relationships between root-zone soil moisture and atmospheric processes in the planetary boundary layer

Soil moisture modulates the exchange of mass and energy between the atmosphere and the land surface. This study focuses on the relationship between soil moisture and atmospheric processes at and near the Norman Mesonet site using both automated and field samples of hydrologic and atmospheric parameters. During 1999, measurements were made during an intensive observing period (IOP) that spanned the dates of 1 June to 12 August. Analysis of the observations revealed 13 days were characterized by strong radiative forcing and weak shear in the lower troposphere (defined as ideal or golden days). Though the total number of ideal study days was somewhat limited, observations were collected over a wide range of atmospheric and soil moisture conditions. The results of this study demonstrate that soil water content in the root‐zone at the Norman Mesonet site during the summer of 1999 was linearly correlated with daily‐maximum values of sensible heat flux and latent heat flux on ideal days. Furthermore, the relationship between the mean evaporative fraction calculated during daylight hours and soil water in the root‐zone was strong and linear. However, the relationship between soil water in the surface layer and the mean evaporative fraction was weak and nonlinear. Significant linear relationships were also found to exist between soil water in the root‐zone and atmospheric parameters in the planetary boundary layer including the daily maximum air temperature at 1.5 m, mean potential temperature in the 925‐850 mbar layer, mixing ratio at 1.5 m, and mean mixing ratio in the 925‐850 mbar layer.