Moisture Budget Estimates Derived from Airborne Observations in an Arctic Atmospheric River During its Dissipation

Abstract. This study quantifies the evolution of the moisture budget components of an Arctic atmospheric river (AR) derived from airborne observations from two research flights on consecutive days. We investigate how poleward transport of warm and moist air masses by AR generates precipitation near the sea ice edge, and how advection and evaporation additionally affect the local moisture amount during the dissipation phase of the AR.

Using the High Altitude and LOng Range Research Aircraft (HALO), we derive the atmospheric moisture budget components (local tendency of moisture, evaporation, moisture transport divergence and precipitation) within an intense Arctic AR event during the HALO-(𝒜𝒞)³ aircraft campaign. The components are quantified in sectors ahead of the AR-embedded cold front by airborne observations from dropsondes, radiometers and a radar. They are compared with model-based values from reanalyses and numerical weather prediction simulations.

The observational moisture budget components in the pre-cold frontal sectors contribute up to ± 1 mm h^-1 to local moisture amount. The moisture transport divergence primarily controls the local moisture amount within the AR, while surface interactions are of minor importance. Precipitation is heterogenous but overall weak (<0.1 mm h^-1) and evaporation is small. Although the AR decreases in strength, the budget components change from drying to significant moistening, mainly due to moisture advection. For this AR, we demonstrate the feasibility of the budget closure using single aircraft measurements, although we find significant residuals. Model-based comparisons suggest that these residuals stem from grid sub-scale variability within the AR corridor.