Heterogeneity in soil and vegetation parameters complicates efforts in measurement and modeling of the land-surface. In fact, the fundamental problem in quantifying the impact of the land surface upon the atmosphere lies in the determination of the radius of influence as determined by a single point value. The radius of influence (RI) of a variable has important implications for both sampling strategies and for modeling efforts. If the RI of surface fluxes of heat and moisture, as measured by a single site, are limited to the microscale, then model validation of the land surface using in-situ data becomes impossible. Likewise, the RI represented at a single grid point determines the degree to which subgrid-scale parameterizations of fluxes are required. Unfortunately, the RI of surface parameters varies in time and space, as a function of soil moisture and type, vegetation type and coverage, and climate.

The spatial and temporal impact of land-surface and atmospheric variables can be determined from long-term, in-situ measurements given a dense enough observational network. The Oklahoma Mesonet and Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) networks measure a suite of meteorological and surface components across all of Oklahoma with an average spacing of 30 km between sites. Data are collected in real-time every 30-minutes at 89 sites across the state. This study examines the spatial and temporal relationships among all near-surface and soil data collected during the year 2000.

The results of this study quantified the arial influence of in-situ measurements of air temperature, relative humidity, wind speed, skin temperature, solar radiation, net radiation, sensible heat flux, ground heat flux, and soil moisture at 5 cm, 25 cm, 60 cm, and 75 cm depths. In general, the radius of influence (RI; defined as R > 0.6) of atmospheric parameters extended to > 100 km, while the RI of flux and soil parameters was restricted to < 50 km. Autocorrelations of surface fluxes and some atmospheric parameters were limited to several days while some soil and atmospheric parameters retained a much longer autocorrelation.