Spring Time Atmospheric Boundary Layer Experiment (STABLE)

STABLE was as a joint project of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, of the  University of Hamburg (ZMAW), of University Hannover (IMUK), and  of  the Finnish Meteorological Institute (FMI).

The general goal of STABLE was to obtain in-situ data of processes in the polar atmospheric boundary layer over sea ice during cold conditions as being typical during early spring. The campaign had several priorities.

1. Measurement and analysis of turbulent processes over leads (key aspect of the campaign)

Different flight patterns were flown which concentrated on the larger scale impact of the integrated lead impact on the atmospheric boundary layer. Other ones were arranged to study the small scale impact on the atmospheric flow over individual leads.

Most important results related to the lead impact were published by Tetzlaff et al. (2015) and Tetzlaff (2016). They document the strong impact of leads on ABL turbulence and the large variability of processes depending on the forcing conditions such as wind speed, surface temperature, sea ice cover on the leads, atmospheric stability and height of the mixed layer. For the first time it was found that leads have a large impact not only on the heat fluxes but also on momentum transport since the convective plumes over leads interact with the wind field. Another new result was that the effect of sensible heat fluxes and vertical entrainment of warm air caused by the plume’s penetration into the capping inversion have similar importance for the ABL heating over leads.

References:

Tetzlaff, A. (2016) Convective processes in the polar atmospheric boundary layer: a study based on measurements and modelling, PhD thesis, University Bremen.

Tetzlaff A., Lüpkes C., Hartmann, J. (2015) Aircraft-based observations of atmospheric boundary-layer modification over Arctic leads, Q. J. R. Meteorol. Soc. 141: 2839–2856, DOI:10.1002/qj.2568

2. Study of coldair outbreaks over Fram Strait.

Section Polar Meteorology has carried out already a large number of flights in coldair outbreaks during earlier campaigns (starting with REFLEX). During STABLE our investigations were based on drop sondes which have been released over Fram Strait during several flights. We found that conditions were extraordinary during STABLE which was a consequence of the unusual orientation of the sea ice edge close to Svalbard (from Southwest to Northeast) going along with an unusually large Whalers Bay polynya north of Svalbard during Spring 2013. As a result the ABL height was extreme with 2.5 km at 79 N during one of the flights. Such large values have never been reported earlier. These results are published in Tetzlaff et al. (2014) and by Tezlaff (2016). Further research on this topic is still ongoing.

  1. Investigation of the flow over fjords of Svalbard (still ongoing research)

  2. Measurement of methane concentration over sea ice and especially its relation to lead cover (still ongoing research)

References:

Tetzlaff, A. (2016) Convective processes in the polar atmospheric boundary layer: a study based on measurements and modelling, PhD thesis, University Bremen.

Tetzlaff A., Lüpkes C., Birnbaum, G., Hartmann, J., Nygard, T., Vihma T. (2014) Brief Communication: Trends in sea ice extent north of Svalbard and its impact on cold air outbreaks as observed in spring 2013 The Cryosphere, 8, 1757–1763, doi:10.5194/tc-8-1757-2014