ARK-XXIV/3, Weekly Report No. 4
Pyranometer measures the reflected solar radiation from the sea surface. Photo: Niko Renkosik
Net radiation budget in the North Atlantic
RV 'POLARSTERN' ARK-XXIV/3
Reykjavik – Bremerhaven
Weekly Report No. 4, 24 August to 30 August 2009
At the beginning of the week, we finally reached easier ice conditions. Now, the experiments could proceed as planned. On Monday evening, the ship sailed southward to prepare another deep seismic sounding program in the Boreas Basin. The geophysicists were busy deploying 28 ocean bottom seismometers along a long profile. Along a mid-ocean ridge, the Knipovich Ridge, some instruments have been specially deployed to record small earthquakes, which are generated during the continental drift at this junction. This experiment was finished on Sunday. Parallel to the geophysical experiment, other programs were conducted, e.g. to determine the net radiation budget. About 30% of the solar energy reaching the earth is reflected back into space by clouds, air or the earth’s surface. The remaining solar energy is absorbed by the atmosphere (20%), the surface of the continents, or oceans. The net radiation budget at the surface is the driving force for many physical processes in the climate system.
On the left hand side the pyranometer (solar radiation) and the pyrgeometer (longwave radiation), on the right hand side the full sky imager with a fish-eye objective. Photo: Niko Renkosik
Our project aims at observing both, the radiation budget and the state of the cloudy atmosphere as accurately as possible, in order to provide realistic atmosphere-radiation relationships for the use in climate models and remote sensing. A special focus is placed on the effects of clouds and sea-ice on the radiation at the surface. A pyranometer, a pyrgeometer, a sky-imager and a sea-ice imager, producing data with high temporal resolution, have been installed on Polarstern. Additionally, aerosol optical thickness is measured with a hand-held sun photometer and manual albedo measurements take place every few hours if sea-ice is present. Radiative transfer modeling of spatially inhomogeneous cloud and sea-ice distributions will follow our observations. A coupled ocean/atmosphere/sea-ice model is used for energy budget studies in order to quantify the role of clouds in this system.
Cleaning the instruments on the container. Photo: Alrun Tessendorf
After some minor initial problems with installing our measurement equipment, everything has been working well. It was interesting for example, to climb under very windy conditions onto the container of the wheelhouse deck to install some of our instruments. It wasn't dangerous, though, as we were secured by ropes. Since then, we haven’t had much wind again which made cleaning the glass domes of our instruments on the container much more agreeable. Up to now, we could take only very few measurements of the aerosol concentration because of the mostly cloudy or foggy weather. A few days ago, we had sunshine but a cable of the photometer broke. Fortunately, it could be easily repaired the next morning. Also, the weather has become more variable during the last few days, making our cloud and radiation observations more interesting.
On Sunday the ship headed again towards Northeast Greenland to pick up the geologists, who have sampled the fresh water lakes for almost two weeks. Though the ice situation has slightly improved during the last weeks, there is still some tension as to how fast we will be able to finish this operation next week.
Best wishes to the readers at home Wilfried Jokat
August, 30th, 2009 East Greenland shelf 78°18’N 005°27’W -1.7°C/fog