The Great Plains Low-Level Jet (LLJ) During the Atmospheric Radiation Measurement (ARM) Intensive Observation Period (IOP)-4 and Simulations of Land Use Pattern Effect on the LLJ

The Great Plains low-level jet (LLJ) is an important element of the low-level atmospheric circulation. It transports water vapor from the Gulf of Mexico, which in turn affects the development of weather over the Great Plains of the central United States. The LLJ is generally recognized as a complex response of the atmospheric boundary layer to the diurnal cycle of thermal forcing. Early studies have attributed the Great Plains LLJ to the diurnal oscillations of frictional effect (Blackadar 1957), buoyancy over sloping terrain (Holton 1966), and the blocking effects of the Rocky Mountains (Wexler 1961). During ARM IOP-4 (June 15-25, 1993), LLJs were well Recent investigations show that the speed of the LLJ is observed on June 16, 17, 21, 22, 23, and 24 (Figure 1). also affected by the soil type and soil moisture (Fast and During the period, powerful storms swept through the McCorcle 1989). Some studies also suggest that synoptic nation's midsection, accompanied by tornadoes, high wind, patterns may play an important role in the development of large hail, and heavy rain. According to the National the LLJ (Uccellini 1980; Chen and Kpaeyeh 1992). Oceanic and Atmospheric Administration (NOAA) weekly