The multipurpose ARM trajectory (ARMTRAJ) VAP ameliorates knowledge gaps stemming from the Eulerian nature of ARM observations by providing airmass back and forward trajectory calculations. The VAP includes four trajectory data sets initialized at ARM deployment coordinates and configured using ARM data sets. The four trajectory data sets support aerosol, cloud, planetary boundary layer, and related research (aerosol-cloud interactions, etc.).
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Trajectory calculations use the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model informed by the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) reanalysis data set at its highest spatial resolution (~31 kilometers). ARMTRAJ data include ensemble run statistics that enhance trajectory consistency, while ensemble variability data serve as uncertainty metrics for airmass coordinates and state variables.
ARMTRAJ trajectory data can inform on plausible airmasses’ hysteresis before their ARM site overpasses, such as origin and surface interaction. Moreover, back and forward trajectories can suggest other observational site overpasses upwind and downwind, respectively. ARMTRAJ data also enable better synthesis of ARM observations with satellite observations and can provide boundary conditions for modeling studies constrained by ARM data.
Note that ERA5 reanalysis is based on the ECMWF Integrated Forecasting System (IFS) model, which does not resolve turbulent flow. Therefore, airmass deviations are more likely in turbulent events and at near-surface levels. Using ARMTRAJ’s ensemble data mitigates some of these limitations.