Spatial and temporal variability of near-surface turbulent kinetic energy over the United States

A highly turbulent atmospheric boundary layer may contribute to extreme and erratic wildfire behavior. High resolution atmospheric mesoscale model simulations of fire-weather evolution during past wildland fire episodes suggest that periods of rapid fire growth are often accompanied by periods of significant near-surface turbulence, with values of turbulent kinetic energy (TKE) exceeding 3 m²s^-2. These findings have provided new insight into the variability of ambient atmospheric turbulence during large wildfire events over relatively short time periods and have led to the proposed use of near-surface TKE in combination with the well-known Haines Index as a possible new fire-weather index for quantifying the atmospheric potential for extreme and erratic fire behavior. However, the ultimate application of an atmospheric turbulence based index for fire-weather forecasting in the U.S. requires an understanding of the climatic patterns of near-surface TKE over the U.S. This study examines the spatial and temporal variability of near-surface TKE over the U.S. using the North American Regional Reanalysis (NARR) dataset. The NARR dataset includes 3-hourly atmospheric and land-surface hydrology data covering the 1979-present period, including computed TKE values from the NCEP Eta model using the Mellor-Yamada Level 2.5 closure scheme. Results from the study indicate there are preferred locations and periods for large near-surface TKE in the U.S., the temporal variability of near-surface TKE is regionally dependent, and there has been a general increase in near-surface TKE over much of the U.S. over the last 30 years.