Convective processes in the polar atmospheric boundary layer: a study based on measurements and modelling

• Main Author: Tetzlaff, Amelie
• Format: Thesis
• Language: unknown
• Published: University Bremen 2016
• Subjects: Arctic Ocean; Climate change; Fram Strait; Sea ice
• Online Access: https://epic.awi.de/id/eprint/39607/; https://epic.awi.de/id/eprint/39607/1/ATetzlaff.pdf; http://nbn-resolving.de/urn:nbn:de:gbv:46-00105016-14; https://hdl.handle.net/10013/epic.46755; https://hdl.handle.net/10013/epic.46755.d001

Climate change is especially pronounced over the Arctic Ocean, where the atmosphere warmed twice as fast as in lower latitudes in the last few decades. This warming is associated with a rapid decline of the Arctic sea ice cover. For future predictions of changes in the Arctic climate system, profound knowledge of all processes influencing the surface energy budget in polar regions is essential. The focus of this thesis lies on improving our current understanding of convective processes and the related turbulent fluxes in the polar atmospheric boundary layer (ABL) over both the sea ice covered regions and over the open ocean at the sea ice edge. A major part of the analysis is based on aircraft measurements from the campaign STABLE, which was carried out over the pack ice in the northern Fram Strait in March 2013. These results are supplemented by modeling studies using a simple boxmodel and a one-dimensional mesoscale model. For the first time, comprehensive aircraft measurements over leads were conducted during the campaign STABLE. They are used to study the formation of convective plumes over leads and their impact on the polar ABL. It is found that the conditions over four wide leads are highly variable with respect to turbulent fluxes, as well as to the mean variables temperature, humidity, and wind. In one of the cases large entrainment fluxes exceeding 30 % of the surface fluxes are observed. The convective plumes over leads have a large influence on the vertical profiles of sensible heat and momentum fluxes, which are non-linear downstream of the leads with a distinct flux maximum in the core of the convective plumes. For the first time, it it shown based on measurements that the plume also affects the wind field by diminishing low level jets in the region influenced by the plume. In addition to the small scale impact of individual leads the regional impact of lead ensembles is studied using long transect flights. The analysis shows that near-surface atmospheric temperatures are clearly related to the ice ...