Land-Surface Contrasts and Thermally Driven Flows at Dugway Proving Ground, Utah

Dramatic land-surface contrasts and complex terrain combine at the US Army's Dugway Proving Ground (DPG), located in the northwest corner of Utah, to produce unique thermal characteristics in the planetary boundary layer. Wind circulations arising from these thermal contrasts offer a forecast challenge to daily operations at DPG and offer an opportunity to better understand wind patterns in complex terrain.

A large area of seasonally flooded basin floors or playas occupies the western edge of DPG, with much of the remainder consisting of low salt-tolerant shrubs and grasses. Several mountain ranges typical of Basin and Range topography rise near the edge of the playa. These ranges tend to be rocky with sparse grass and juniper ground cover. A dense network of permanent and mobile meteorological surface stations are deployed at DPG in support of operations there. The 26 permanent stations and 7 temporary stations used in this study represent all the different landforms – playa, shrub, slope and mountain-tops.

The diurnal range of temperature over the playa is suppressed relative to the areas with shrubs. Nighttime temperatures above the playa are higher and daytime temperatures lower than those over vegetated surfaces. In general, higher soil moisture conditions exist on the playa, leading to decreased sensible heating during the day and a greater ground heat flux at night. Further, net radiation on the playa is reduced due to a higher albedo. These playa-shrubland temperature contrasts lead to playa breezes.

Analysis of data from 1994-2008 shows that temperature contrasts between the playa and shrub areas are maximized during the early morning hours, when the playa is often 3-6°C warmer than the shrub area. Large temperature contrasts also occur preferentially in the fall. Variables such as precipitation, solar radiation and wind speed cannot fully explain these temperature contrasts and the circulations they produce. Detailed information about the surface energy balance and soil properties of the playa and shrub areas is necessary to gain a fuller understanding of the circulations.

As a result of the thermal contrast, an on-playa breeze is expected to form during the night, with an off-playa breeze during the day. However, upslope/downslope and up-valley/down-valley flows off the surrounding terrain make it difficult to attribute flows to these individual diurnal wind systems. Climatological techniques and case studies will be used to evaluate the relative roles of the three diurnal wind systems on the mean flow over DPG.