Following moist intrusions into the Arctic using SHEBA observations in a Lagrangian perspective

S Mubashshir Ali,Felix Pithan

doi:10.1002/qj.3859

Abstract

AbstractWarm and moist air masses are transported into the Arctic from lower latitudes throughout the year. Especially in winter, such moist intrusions (MIs) can trigger cloud formation and surface warming. While a typical cloudy state of the Arctic winter boundary layer has been linked to the advection of moist air masses, direct observations of the transformation from moist midlatitude to dry Arctic air are lacking. Here, we have used observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) project to compile Eulerian observations along the trajectories of warm and cold air masses in a Lagrangian sense, showing the cooling and drying of air masses over sea ice and moistening over the open ocean. Air masses originating mostly over open water generate cloudy conditions over the observation site, whereas air masses originating over continents or sea ice generate radiatively clear conditions. We recommend using our case‐studies and the method of linking expeditions to station soundings via back‐trajectories for modelling work in future campaigns.

Highlights

The Arctic has a sparse observational coverage compared to lower latitudes
Sorting the 5-day back-trajectories based on the air mass state retrieved over the Surface Heat Budget of the Arctic (SHEBA) site shows a clear distinction in air mass origin between clear and cloudy cases
Air masses that occupy the cloudy state over SHEBA predominantly have an origin or at least travelled over open ocean outside the Arctic, whereas air masses in the clear state have typically travelled over sea ice and continents in the five days prior to their arrival at SHEBA (Figure 2)

Summary

Introduction

The Arctic has a sparse observational coverage compared to lower latitudes. Its hostile climate and the dynamical sea ice pose operational challenges for regular in-situ observations. The remarkable consistency of observations of the cloudy state at the SHEBA site suggests that most air-mass transformations affect the temperature and humidity profiles in a similar way.

Results

Conclusion