Atmospheric rivers (ARs) are essential for the Arctic water cycle, but observations quantifying the moisture processes of individual Arctic ARs are sparse. This study quantified the evolution of the moisture budget components of an Arctic AR derived from airborne observations from two research flights on consecutive days. We investigated how poleward transport of warm and moist air masses by ARs generates precipitation near the sea ice edge and how advection and evaporation affect the local moisture amount during the dissipation of the AR. Using observations from the High-Altitude and LOng-Range Research Aircraft (HALO), we derived the atmospheric moisture budget components (local tendency of moisture, evaporation, moisture transport divergence, and precipitation) within an Arctic AR during the HALO-(𝒜𝒞)³ aircraft campaign. The budget components were quantified in sectors ahead of the AR-embedded cold front using airborne observations from dropsondes, radiometers, and a radar device and compared with values derived from reanalyses and numerical weather prediction simulations.

We found that the observed moisture budget components in the pre-cold frontal sectors contribute up to $\pm \mathrm{1}\mathrm{mm}{\mathrm{h}}^{-\mathrm{1}}$ to the 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 heterogeneous but overall weak ($<\mathrm{0.1}\mathrm{mm}{\mathrm{h}}^{-\mathrm{1}}$), and evaporation is small. As the AR dissipated, the budget components changed from drying to moistening, mainly due to moisture advection. We demonstrated the feasibility of closing the moisture budget using single aircraft measurements, even though we found significant residuals that model-based comparisons attribute to subscale variability.