The Complex Relationship Between the Spatial Variation of Wind and Surface Thermal Heterogeneity: Observations From a Highly Idealized Environment During IPAQS 2019

Abstract:

Wind in the atmospheric surface layer is a result of many different processes which can prove difficult to disentangle. By employing an array of sensors in an idealized environment which is nearly entirely homogenous aside from thermal variation, we are able to better identify the effect of temperature variation. During the Idealized Planar-Array for Quantifying Surface Heterogeneity (IPAQS) project in summer 2019 in the Great Salt Lake Desert, a 5 km distributed temperature sensing (DTS) cable measured surface temperature at a 12.5 cm and 1 s resolution and a 4x4 grid of sonic anemometers spaced 200 m apart measured wind speed at 20 hz. Both sets of measurements were temporally averaged to 1 minute, allowing spatial variation at 1 minute to be observed. From the 1 minute averages, spatial standard deviations (SSTD) and spatial means (SMEAN) of surface temperature and 2 m wind speed were calculated. The surface temperature SSTD increased in the morning and peaked in the early afternoon, while the SMEAN peaked in the late afternoon. The 2 m wind speed SSTD increased from the morning into the early afternoon, before decreasing in the late afternoon, while the SMEAN was inconsistent, but generally increased in the late afternoon. Calculated correlations between these four variables showed no correlation between 2 m wind speed SSTD and SMEAN, a strongly positive correlation between surface temperature SSTD and SMEAN, and positive correlations between 2 m wind speed SSTD and surface temperature SSTD and SMEAN. The nonexistent correlation between 2 m wind speed SSTD and SMEAN, indicates that these two measurements have different processes as their causes. Surface temperature SSTD is found to precede surface temperature increase, which could indicate that processes such as radiation, advection and diffusion become more effective at mediating surface temperature as temperature increases. The positive correlation between both surface temperature SSTD and SMEAN and 2 m wind SSTD are evidence of the role of convective processes in spatial wind variation in this idealized environment. Comparisons of spatial variations in surface layer wind and surface temperature allow for a more complete understanding of the relationship between surface temperature heterogeneity and wind.