On the Variability of Boundary Layer Moisture Regimes Under Synoptically Active and Benign Conditions over Drylands of Southwest US

Water vapor content in the atmosphere is one of the major decisive factors for initiation of convective processes, which in turn affect atmospheric stability. Since the spatiotemporal variability in water vapor concentrations is the prime ingredient of Earth’s hydrological cycle, it plays a significant role in modulating extreme weather events like droughts and floods. Drylands occupy about 41% of the land surface and are home to over a third of the global population. Being sensitive to climate change and anthropogenic emissions, investigation of meteorological processes over dryland is crucial for climate change study. Our work focuses on the investigation of moisture regimes particularly in the atmospheric boundary layer (ABL) over arid regions, spanning a period of several years. Erstwhile research has explored the hydrologic cycle, energy cycle, and entrainment processes in the ABL and land surface-ABL interactions. Yet there has not been sufficient investigation on the amount and spatiotemporal variation of water vapor in the ABL over arid regions, in particular, during rapid changes taking place under diverse local meteorological conditions (e.g., synoptically active and benign conditions). Research in this area could have applications in improving precipitation forecasts and its representation in General Circulation Models (GCM), enhancing data assimilation techniques, and design of remote sensing instruments. Here, we explored both vertical and spatial variability of radiosonde-derived water vapor mixing ratio (WVMR) profiles obtained at several arid and semi-arid sites located within the US NWS upper air network (e.g., Midland, Amarillo, Albuquerque) on various timescales (synoptic, monthly, seasonal, and interannual). Radiosonde observations at different sites in the South and Southwest US at 0000 UTC, which corresponds to late afternoon local time, were examined for multiple years. In particular, we focused on the years of anomalous precipitation regimes (e.g., extremely dry versus wet year compared to the climatological means of annual precipitation amounts). To this end, we analyzed daily vertical profiles of WVMR, potential temperature, horizontal wind, and associated stability regimes via estimating the Bulk Richardson number, RiB. We studied the contrasting behavior of WVMR and RiB in summer and winter, and explored possible connections among WVMR, winds, and the seasonal occurrence of anticyclones. Selected results will be presented at the AMS annual meeting. Additionally, for the first time, we applied hierarchical clustering analysis to ABL moisture regimes and categorized individual days into various clusters (e.g., warm-moist, cold-dry, each corresponding to different wind conditions). This classification will allow us to select appropriate parameterization schemes to be applied in Numerical Weather Prediction models.