The recent widespread, rapid, and intensifying climate change and associated global warming made the distinction between short-term weather phenomenon and long-term climatological patterns to merge into a continuum of atmospheric processes rather than two distinct phenomena. In arid and semi-arid regions (i.e., drylands), climate change is causing deeper droughts and longer fire seasons, yielding more catastrophic conditions, and putting humans in dire situations. Drylands are home to more than 2.5 billion people and occupy approximately 41% of terrestrial land surfaces globally. Additionally, the largest warming during the last 100 years was observed over drylands and accounted for more than half of the continental warming. More than 20% of Earth’s land surface is projected to cross an aridity threshold by 2100, which could lead to widespread desertification, including in the southwestern United States.

The atmospheric boundary layer (ABL), where humans live, is defined as the turbulent layer adjacent to the Earth’s surface. The ABL helps mediate the interactions between the surface and the free atmosphere (FA) by exchanging energy, mass, and momentum. An understanding of ABL features over drylands on different timescales (e.g., diurnal, semi-diurnal, annual, and inter-annual) and across diverse spatial scales (e.g., local, mesoscale, synoptic-scale) is key to this work. Additionally, a holistic approach to evaluate numerical weather prediction (NWP) models for drylands will be increased through incorporation of observations obtained with high temporal- and spatial-resolutions. Finally, untangling the multiscale effects of aridity and soil moisture regimes during early morning transition (EMT) and early evening transition (EET) and associated land-atmosphere interactions (LAI) is critical, especially across the interface between humid subtropical and cold semi-arid climates in the southwestern United States.

The overarching goals of this project, Exploring Land-Atmosphere Interaction over Dryland during Morning and Evening Transitions (XLAID-MET), are to utilize high resolution observations of near-surface meteorological conditions to explore the impact of soil moisture control and associated LAI on rapidly changing atmospheric conditions during both EMT and EET. To this end, the West Texas Mesonet (WTM) facilities, an integrated atmospheric observation network of 150 near-surface (10-meter) stations located in the southwestern United States will be leveraged and built upon. The WTM network adequately covers the mesoscale boundaries separating moist, maritime tropical air from dry, continental tropical air common in the southwestern Great Plains of the United States during the warm season. Finally, with close collaboration with NSF NCAR researchers, forecasts obtained via High Resolution Rapid Refresh (HRRR) model will be used to support the empirical findings and improve the model representations of turbulence exchange processes during EMT and EET periods and will conduct a novel weather-specific model validation effort.

Results from XLAID-MET will help obtain an improved understanding of the LAI controls on the near-surface meteorological and micrometeorological features during EMT and EET periods across myriad mesoscale and synoptic-scale weather events so that improved turbulence parameterization schemes could be developed for NWP models. Additionally, XLAID-MET findings will be directly used for development of new regime-specific model data mismatch (MDM) tools for model  verifications, rather than using the “bulk” statistics that are often performed yielding model performance averaged across all weather types, atmospheric conditions, and LAIs; thus, these analyses do not allow for the diagnosis of the “root” of the problems for model errors.