Spatiotemporal Variability of AOD over the Dryland Ecosystem of the US Southwest using a Lens of Synoptic-scale Forcing

Synoptic disturbances can alter atmospheric aerosol concentrations, size, and chemical compositions, while aerosols, in turn, influence regional weather and climate dynamics by modifying frontal regimes, monsoon precipitation, and sea-surface temperatures. This intricate relationship, coupled with the inherent spatiotemporal variability of aerosols, and the rapidly evolving synoptic weather patterns driven by 21^st century climate change, underscores the necessity for a deeper, process-based understanding of how aerosol characteristics change under varying atmospheric conditions (e.g., changes in aerosol-radiation (ARI) and -cloud interactions (ACI) under synoptic-scale forcing). Moreover, aerosols are a major source of uncertainty in estimating anthropogenic radiative forcing in global climate models, largely due to a lack of conceptual understanding of both ARI and ACI, as emphasized in recent Intergovernmental Panel on Climate Change reports. Consequently, there is a strong need for exploring both regional- and global-scale variability in aerosol optical depth (AOD), a measure of the columnar attenuation of solar radiation. Recent studies have shown that both tropical and extra-tropical systems, including fronts, cold surges, monsoons, tropical cyclones, and long-range aerosol transport, are major drivers of AOD variability. However, past research on AOD variability across different temporal (e.g., seasonal, annual, interannual) and spatial (local, regional, continental) scales often averaged the observed variability across diverse weather conditions, including frequent synoptic disturbances. We hypothesize that such bulk averaging can lead to significant inaccuracies in the spatiotemporal patterns of AOD variability within a region. Furthermore, there is also a notable gap in observational studies addressing how specific synoptic weather patterns (e.g., dryline and frontal passages) alter AOD across geographical regions. This oversight can result in substantial errors in air quality assessments, particularly during periods of high emission scenarios (e.g., wildfires) coinciding with active synoptic events (e.g., frontal passages). This gap is especially critical in the drylands of the southwestern US, where the frequent intersection of dust-heavy environments and synoptic activity significantly impacts AOD.

In this study, we investigated the spatiotemporal variability of AOD pertaining to active synoptic disturbances in the drylands of the southwestern US from 2019 to 2024. We focus on the following research questions: (1) How does AOD fluctuate on a weather-scale (i.e., before, during, and after frontal, dryline, and monsoon passages) across diverse sites within the domain? (2) Are there discernible weather-scale climatological patterns in AOD regimes on various timescales (e.g., monthly, seasonal, and annual) across various sites located in a dryland ecosystem? The Southern High Plains provides an ideal setting for examining the influence of aerosol transport and associated physicochemical changes on AOD across different wavelengths, owing to frequent synoptic passages throughout the year. A new Aerosol Robotic Network (AERONET) site was established in Lubbock, Texas, in June 2023 as a part of NASA’s initiative to Increase Participation of Minority Serving Institutions (IPMSI) to obtain high-resolution AOD observations in west Texas. To identify weather-scale changes in AOD, particularly during active synoptic disturbances, we analyzed concurrent shifts in aerosol characteristics and meteorological parameters. This includes synergistic changes in AOD and near-surface thermodynamic features such as surface temperature, relative humidity, and direct shortwave radiation, using AERONET observations and high-resolution surface station measurements from the West Texas Mesonet. Furthermore, to track aerosol movement in the upper troposphere, we will identify key synoptic passages, especially those that exhibit significant AOD variability during the day, and assess the effects of diverse flow regimes, such as those resulting from long-range aerosol transport, on AOD variability using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) Model. By investigating AOD fluctuations in response to specific synoptic passages and identifying patterns of AOD variability across different spatial and temporal scales in a dryland ecosystem, this study will shed light on how localized atmospheric dynamics shape broader aerosol trends in arid regions. This understanding is essential for refining future climate projections, improving air quality assessments, and informing global environmental policies.