Dynamic drivers of heat and moisture transport into the Arctic

Abstract

The poleward flow of energy into the Arctic plays a fundamental role for thermodynamic processes and strongly influences synoptic weather features in the Arctic. In this study, we analyse atmospheric dynamical drivers of anomalous poleward latent heat transport in the Arctic. Besides, we study the influence of anomalous moisture transport on surface temperature, cloud cover and precipitation. The correlation between weekly zonal mean poleward heat transport and temperature anomalies at 70°N shows a strong seasonal variation with moderate correlation between November and March and only very little correlation during summer. Analysing the relation between anomalous latent heat transport and synoptic weather features, we observed that from November till March the 10% most positive daily zonal mean latent heat transport at 70°N are linked to strong positive cyclone anomalies over the Greenlandic east coast as well as positive blocking anomalies to the west of Scandinavia. These anomalous transports further lead to increased surface temperatures in the Barents and Kara Seas and strongly influence cloud cover, precipitation and atmospheric water vapor content in the Arctic (≥ 70°N). In a second part of the study we investigate the formation of anomalous moisture transport into the Arctic by analysing a large ensemble of 8-day backward trajectories which contributed to an anomalous positive moisture transport at 70°N. We found that the largest contribution to the poleward moisture flux at 70°N originates from the Atlantic sector. Furthermore, moisture is predominantly taken up north of 45°N – more than 83% of the moisture contributing to (moisture) transport at 70°N originates from the latitude segment between 45 - 70°N. Moreover, we analysed the thermodynamic evolution of air masses from the start of the moisture uptake until reaching 70°N by classifying the air masses according to their absolute change in temperature and potential temperature. Approximately one third of the air masses experience net diabatic cooling with no significant vertical motion. These air masses typically originate from a climatologically warmer region and are transported northward into a colder area (leading to an intense warm anomaly at roughly 800 hPa). Another 30% of the trajectories experience intense diabatic heating in combination with a strong ascending motion. These trajectories reach the Arctic at 70°N at a median height of 700 hPa with a potential temperature anomaly of almost 10 K. The remaining fraction of trajectories shows a net temperature increase caused by subsidence-induced adiabatic heating. This thesis confirms the importance of anomalous moisture transport into the Arctic with a systematic investigation of air mass transport and air mass transformation into the Arctic.