Weather features, such as extratropical cyclones, atmospheric rivers (ARs), and fronts, contribute to substantial amounts of precipitation globally and are associated with different precipitation characteristics. However, future changes as well as the representation of the precipitation characteristics associated with these weather features in climate models remain uncertain. We attribute 6-hourly accumulated precipitation and cyclones, moisture transport axes (AR-like features), fronts, and cold air outbreaks, and the combinations thereof in 10 ensemble members of the CESM2-LE between 1950 and 2100 under the SSP3-7.0 scenario. We find that, despite some biases in both precipitation and weather features, CESM2-LE adeptly represents the precipitation characteristics associated with the different combinations of weather features. The combinations of weather features that contribute most to precipitation in the present climate also contribute the most to future changes, both due to changes in intensity as well as frequency. While the increase in precipitation intensity dominates the overall response for total precipitation in the storm track regions, the precipitation intensity for the individual weather features does not necessarily change significantly. Instead, approximately half of the increase in precipitation intensity in the storm track regions can be attributed to a higher occurrence of the more intensely precipitating combinations of weather features, such as the co-occurrence of extratropical cyclones, fronts, and moisture transport axes.

The water vapor transport in the extratropics is mainly organized in narrow elongated filaments. These filaments are referred to with a variety of names depending on the contexts. When making landfall on a coastline, they are generally referred to as atmospheric rivers; when occurring at high latitudes, many authors regard them as warm moist intrusions; when occurring along a cold front and near a cyclone core, the most commonly used term is warm conveyor belt. Here, we propose an algorithm that detects these various lines of moisture transport in instantaneous maps of the vertically integrated water vapor transport. The detection algorithm extracts well-defined maxima in the water vapor transport and connects them to lines that we refer to as moisture transport axes. By only requiring a well-defined maximum in the vapor transport, we avoid imposing a threshold in the absolute magnitude of this transport (or the total column water vapor). Consequently, the algorithm is able to pick up moisture transport axes at all latitudes without requiring region-specific tuning or normalization. We demonstrate that the algorithm can detect both atmospheric rivers and warm moist intrusions. Atmospheric rivers sometimes consist of several distinct moisture transport axes, indicating the merging of several moisture filaments into one atmospheric river. Finally, we showcase the synoptic situations and precipitation patterns associated with the occurrence of the identified moisture transport axes in example regions in the low, mid, and high latitudes.

The water vapor transport in the extratropics is mainly organized in narrow elongated filaments. These filaments are referred to with a variety of names depending on the contexts. When making landfall on a coastline, they are generally referred to as atmospheric rivers; when occurring at high latitudes, many authors regard them as warm moist intrusions; when occurring ahead of a cold front towards the core on an extratropical cyclone, the most commonly used term is warm conveyor belt. Here, we propose an algorithm that detects these various lines of moisture transport in instantaneous maps of the vertically integrated water vapor transport. The detection algorithm extracts well-defined maxima in the water vapor transport and connects them to lines that we refer to as moisture transport axes. By only requiring a well-defined maximum in the vapor transport, we avoid imposing a threshold in the absolute magnitude of this transport (or the total column water vapor). Consequently, the algorithm is able to pick up moisture transport axes at all latitudes without requiring region-specific tuning or normalization. We demonstrate that the algorithm can detect both atmospheric rivers and warm moist intrusions, but also prominent monsoon air streams. Atmospheric rivers sometimes consist of several distinct moisture transport axes, indicating the merging of several moisture filaments into one atmospheric river. We showcase the synoptic situations and precipitation patterns associated with the occurrence of the identified moisture transport axes in example regions in the low, mid, and high latitudes.

Poleward ocean heat transport is a key process in the earth system. We detail and review the northward Atlantic Water (AW) flow, Arctic Ocean heat transport and heat loss to the atmosphere since 1900, in relation to sea ice cover. Our synthesis is largely based on a sea ice-ocean model forced by a reanalysis atmosphere (1900-2018) corroborated by a comprehensive hydrographic database (1950-), AW inflow observations (1996-), and key long-term time series. The Arctic Seas, including the Nordic and Barents Seas, have warmed since the 1970s, especially on the shelves. This warming is congruent with increased ocean heat transport and sea ice loss, and has contributed to the retreat of marine terminating glaciers on Greenland. Heat loss to the atmosphere is largest in the Nordic Seas (60% of total): with large variability linked to the frequency of Cold Air Outbreaks and cyclones in the region, but the long-term positive trend is small. Heat loss from the Barents Sea (~30%) and Arctic Seas farther north (~10%) is overall smaller, but have large positive trends. The AW inflow, heat loss to the atmosphere, and dense outflow have thus all increased since 1900. These are consistently related through theoretical scaling, but the AW inflow increase is also wind-driven. The Nordic, Barents and other Arctic Seas CO2 uptake constitutes ~8% of the global uptake and seems largely driven by heat loss. This uptake has increased by ~30% over the last century - consistent with Arctic sea ice loss allowing more regional air-sea interaction.

Modeling air-sea interactions during cold air outbreaks poses a major challenge because of the vast range of scales and physical processes involved. Using the Polar WRF model, we investigate the sensitivity of downstream air mass properties to (a) model resolution, (b) the sharpness of the marginal-ice zone (MIZ), and (c) the geometry of the sea ice edge. The resolved sharpness of the MIZ strongly affects peak heat fluxes and the atmospheric water cycle. For sharper MIZs, roll convection sets in closer to the sea ice edge, increasing both evaporation and precipitation. This yields an increased heat transfer into the atmosphere while the net effect on the atmospheric moisture budget is small. Consequently, higher atmospheric resolution increases the probability that a cold-air outbreak triggers deep convection in the ocean. The geometry of the sea ice edge can induce convergence or divergence zones that affect the air-sea exchange.

Modeling air-sea interactions during cold air outbreaks poses a major challenge because of the vast range of scales and physical processes involved. Using the Polar WRF model, we investigate the sensitivity of downstream air mass properties to (a) model resolution, (b) the sharpness of the marginal-ice zone (MIZ), and (c) the geometry of the sea ice edge. The resolved sharpness of the MIZ strongly affects peak heat fluxes and the atmospheric water cycle. For sharper MIZs, roll convection is initiated closer to the sea ice edge, increasing both evaporation and precipitation. This yields an increased heat transfer into the atmosphere while the net effect on the atmospheric moisture budget is small. Overall, higher atmospheric resolution increases both the peak and net heat extracted from the ocean. The geometry of the sea ice edge can induce convergence or divergence zones that affect the air-sea exchange.