Flash drought is characterized by a period of rapid drought intensification with impacts on agriculture, water resources, ecosystems, and the human environment. Addressing these challenges requires a fundamental understanding of flash drought occurrence. This study identifies global hotspots for flash drought from 1980–2015 via anomalies in evaporative stress and the standardized evaporative stress ratio. Flash drought hotspots exist over Brazil, the Sahel, the Great Rift Valley, and India, with notable local hotspots over the central United States, southwestern Russia, and northeastern China. Six of the fifteen study regions experienced a statistically significant increase in flash drought during 1980–2015. In contrast, three study regions witnessed a significant decline in flash drought frequency. Finally, the results illustrate that multiple pathways of research are needed to further our understanding of the regional drivers of flash drought and the complex interactions between flash drought and socioeconomic impacts.

[1] Limited time period running trends are created from various microwave sounding unit (MSU) difference time series between the University of Alabama in Huntsville and Remote Sensing System (RSS) group's lower troposphere (LT) and mid troposphere to lower stratosphere channels. This is accomplished in an effort to determine the causes of the greatest discrepancies between the two data sets. Results indicate the greatest discrepancies were over time periods where NOAA 11 through NOAA 15 adjustments were applied to the raw LT data over land. Discrepancies in the LT channel are shown to be dominated by differences in diurnal correction methods due to orbital drift; however, discrepancies from target parameter differences are also present. Comparison of MSU data with the reduced Radiosonde Atmospheric Temperature Products for Assessing Climate radiosonde data set indicates that RSS's method (use of climate model) of determining diurnal effects is likely overestimating the correction in the LT channel. Diurnal correction signatures still exist in the RSS LT time series and are likely affecting the long-term trend with a warm bias. Our findings enhance the importance of understanding temporal changes in the atmospheric temperature trend profile and their implications on current climate studies.

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This paper demonstrates the capability of AFIT/CDE's Laser Environmental Effects Definition and Reference (LEEDR) model to accurately characterize the meteorological parameters and radiative transfer effects of the atmospheric boundary layer with only surface observations of temperature, pressure, and humidity. The LEEDR model is a fastcalculating, first principles, worldwide surface to 100 km, atmospheric propagation and characterization package. This package enables the creation of profiles of temperature, pressure, water vapor content, optical turbulence, atmospheric particulates and hydrometeors as they relate to line-by-line layer transmission, path and background radiance at wavelengths from the ultraviolet to radio frequencies. Physics-based cloud and precipitation characterizations are coupled with a probability of cloud free line of sight (CFLOS) algorithm for air-to-air, air-to-surface, and surface-to-air (or space) look angles. In general, LEEDR defines the well-mixed atmospheric boundary layer with a worldwide, probabilistic surface climatology based on season and time of day, and then computes the radiative transfer and propagation effects from the vertical profile of meteorological variables. However, the LEEDR user can also directly input surface observations. This research compares the LEEDR vertical profiles created from input surface observations to actual observations from balloon launches. Results are then compared to the LEEDR ExPERT climatological sounding for the same time of day and season. RMSE are calculated and it was found that closer for those profiles made from surface observations than those made from climatological data for the same season and time. Impacts of those differences are shown with a relevant tactical scenario in AFIT/CDE HELEEOS program.

This paper demonstrates the capability of the Laser Environmental Effects Definition and Reference (LEEDR) model to accurately characterize the meteorological parameters and radiative transfer effects of the atmospheric boundary layer with surface observations or climatological values of temperature, pressure, and humidity (''climatology''). The LEEDR model is a fast-calculating, first-principles, worldwide surface-to-100-km, ultraviolet-to-radio-frequency (UV to RF) wavelength, atmospheric characterization package. In general, LEEDR defines the well-mixed atmospheric boundary layer with a worldwide, probabilistic surface climatology that is based on season and time of day and, then, computes the radiative transfer and propagation effects from the vertical profile of meteorological variables. The LEEDR user can also directly input surface observations. This research compares the LEEDR vertical profiles created from input surface observations or numerical weather prediction (NWP) data with the LEEDR climatological profile for the same time of day and season. The different profiles are compared with truth radiosonde data, and the differences from truth are found to be smaller for profiles created from surface observations and NWP than for those made from climatological data for the same season and time. In addition, this research validates LEEDR's elevated aerosol extinction profile vertical structure against observed lidar measurements and details the advantages of using NWP data for atmospheric profile development. The impacts of these differences are demonstrated with a potential tactical high-energy-laser engagement simulation.