Influence of atmospheric rivers and associated weather systems on precipitation in the Arctic

Abstract

Abstract. In this study, we analyse the contribution of Atmospheric Rivers (ARs), cyclones, and fronts to the total precipitation in the Arctic. We focus on two distinct periods of different weather conditions from two airborne campaigns: ACLOUD (May/June 2017) and AFLUX (March/April 2019). Both campaigns covered the northern North Atlantic sector, the area in the Arctic that is affected by the highest precipitation rates. Using ERA5 reanalysis, we identify pronounced regional anomalies with enhanced precipitation rates compared to the climatology during ACLOUD due to these weather systems, whereas during AFLUX enhanced precipitation rates occur over most of the area. We have established a new methodology, that allows us to analyse the contribution of ARs, cyclones, and fronts to precipitation rates based on ERA5 reanalysis and different detection algorithms. Here, we distinguish whether these systems occur co-located or separately. The contributions differ seasonally. During ACLOUD (early summer), the precipitation rates are mainly associated with AR- (40 %) and front-related (55 %) components, especially if they are connected, while cyclone-related components (22 %) play a minor role. However, during AFLUX (early spring) the precipitation is mainly associated with cyclone-related components (62 %). For both seasons, snow is the dominant form of precipitation, and the small rain occurrence is almost all associated with ARs. About one-third of the precipitation can not be attributed to one of the weather systems, the so-called residual. While the residual can be found more frequently as convective than as large-scale precipitation, the rare occasion of convective precipitation (roughly 20 %) can not completely explain the residual. The fraction of precipitation classified as residual is reduced significantly when a precipitation threshold is applied that is often used to eliminate "artificial" precipitation. However, a threshold of 0.1 mm h−1 reduces the total accumulated precipitation by a factor of two (ACLOUD) and three (AFLUX) especially affecting light precipitation over the Arctic Ocean. We also show the dependence of the results on the choice of the detection algorithm serving as a first estimate of the uncertainty. In the future, we aim to apply the methodology to the full ERA5 record to investigate whether the differences found between the campaign periods are typical for the different seasons in which they were performed and whether any trends in precipitation associated with these weather systems can be identified.

Surface impacts and associated mechanisms of a moisture intrusion into the Arctic observed in mid-April 2020 during MOSAiC

“…We find that the atmospheric river components of the WAI contribute about 30% to the total precipitation (27% snowfall, 3% rainfall) at the grid cell nearest to RV Polarstern. A similar magnitude of contribution was calculated during two other campaigns in the Arctic (Lauer et al, 2023). Even larger fractions are discovered further east and south, at the marginal sea ice zone.…”

Using variable-resolution grids to model precipitation from atmospheric rivers around the Greenland ice sheet

“…We hypothesize that the VR grids will simulate ARs more accurately than the coarser resolution grids through better resolution of finer-scale physical processes and topography, as has been seen in other studies investigating moisture intrusions in the Arctic (Bresson et al, 2022). Accurately modeling precipitation from ARs is important because it has been suggested that during early summer nearly 40% of precipitation in Greenland is due to ARs (Lauer et al, 2023). The model output is compared to ARs detected by ERA5 and MERRA2, two observation-based meteorological reanalysis datasets, as in other studies involving simulated ARs (Bresson et al, 2022;Viceto et al, 2022;Zhou et al, 2022;Mattingly et al, 2023).…”

The nexus between detection uncertainty and quantifying meteorological extremes of the Euro-Atlantic atmospheric rivers

“…Strong winds can mix air masses vertically and horizontally, potentially bringing warmer air to the surface from aloft or redistributing air masses in a way that leads to surface warming. Additionally, systematic studies highlight the significant role of ARs in the meridional transport of atmospheric latent heat, affecting climatic parameters in sub-polar regions, with a notable impact in the northern hemisphere due to the absence of constant blocking effects [83], [32]. At the same time, the decrease in mean TN over the Iberian peninsular could be due to the dominating effect of reduced direct irradiance owing to increased cloud cover rather than anomalous downwelling longwave radiation.…”