Apr. 18, 2008 For the first time, a German has taken part in a Russian drift expedition and has explored the atmosphere above the central Arctic during the polar night. Jürgen Graeser, a member of the Potsdam Research Unit of the Alfred-Wegener-Institute for Polar and Marine Research in the Helmholtz Association, has just returned home to Germany. As a member of the Russian expedition NP 35 (35. North Pole Drift Expedition), which consisted of 21 persons, he has spent seven months on a drifting ice floe in the Arctic.
The 49-year-old scientific technician has gained observational data from a region, which is normally inaccessible during the Arctic winter and therefore widely unexplored. Ascends with a tethered balloon up to an altitude of 400 metres as well as balloon borne sensor ascends up to an altitude of 30 kilometres provided data which will contribute to ameliorate existing climate models for the Arctic.
In spite of its importance for the global climate system, the Arctic is still a blank on the data map. Up to now, continuous measuring in the atmosphere above the Arctic Ocean is missing. „We are not able to develop any reliable climate scenarios without disposing of data series with high temporal and local resolutions about the Arctic winter. The data which Jürgen Graeser has obtained in the course of the NP 35 expedition are unique, and they are apt to considerably diminish the still existing uncertainties in our climate models“ said Prof. Dr. Klaus Dethloff, project leader at the Alfred Wegener Institute for Polar and Marine Research.
Since 1937/38, the Russian Institute for Arctic and Antarctic Research (AARI) has already operated 34 Russian North Pole drift stations. In the course of the International Polar Year 2007/2008, for the first time a foreigner was allowed to take part in a drift expedition (NP 35). Due to their close co-operation with the AARI, the scientists of the Potsdam Research Unit of the Alfred Wegener Institute now could realize a project to research the polar atmosphere in the hardly accessible region of the Arctic Ocean.
The expedition NP 35
From September 2007 to April 2008, the scientific technician Jürgen Graeser from the Potsdam Research Unit was a member of the NP 35 team. For seven months, the 49-year-old has lived and worked together with twenty Russian colleagues on an ice flow the size of three times five kilometres. While Graeser concentrated on measuring the Arctic atmosphere, the Russian scientists performed investigations of the ocean top layer, the characteristics of the sea ice, the snow coverage and the energy balance above the ice surface. Moreover, they recorded atmospherical data concerning temperature, moisture, wind and air pressure by means of earth stations as well as with ascends of radio sensors. In the course of the winter the ice floe drifted 850 kilometres in northwestern direction over the Arctic Ocean.
In April Jürgen Graser was picked up from the ice floe by Polar 5, the research aircraft of the Alfred-Wegener-Institute. A specialised pilot, Brian Burchartz from Enterprise Airlines Oshawa, Canada, accomplished the difficult landing and take-off operation on the ice. “I experienced my stay on the ice floe as an incredible enrichment, under personal as well as professional aspects,” Jürgen Graeser said. The Russian colleagues will continue their measurements until the planned evacuation of the station in September 2008.
The exploration of the atmospheric boundary layer
During the drift Jürgen Graeser has explored the atmosphere above the Arctic Ocean. In order to measure the meteorological structure of the Arctic boundary layer and its temporal changes, he regularly sent out a tethered balloon filled with helium. The six sensors fixed on the tether registered data for temperature, air pressure, moisture and wind and sent them to Greaser’s computer. The exchange processes of heat, impulses and moisture between the earth surface and the atmosphere, which are important for the climate, take place in the layer between the ground and an altitude of about 400 metres.
For the first time now the local and temporal structure of ground-level temperature inversions was measured during the complete polar night. To evaluate and interpret the data, the scientists in Potsdam performed simulations with a regional climate model of the Arctic. Preliminary comparisons of temperature profiles measured on the ice floe with those from the regional climate model underline the importance of the measurements performed by Jürgen Graeser. Considerable deviations are shown between the observed data and model data in the region between the ground and an altitude of about 400 metres. Subsequent research activities in Potsdam focus on the connection of the Arctic boundary layer with the development and the tracks of low-pressure areas.
The investigation of the atmosphere – ozone
Vertical high-resolution ozone data from the central Arctic are rare. To close this data gap, Jürgen Graeser regularly launched a research balloon equipped with a radiosonde and an ozone sensor. These balloons carry the sensors up to an altitude of about 30 kilometres. In the past winter, the region of the ozone layer in an altitude of about 20 kilometres was exceptionally cold, thus continuing the trend to colder conditions in this altitude that was observed in the past. The cold conditions have fostered considerable destruction of the Arctic ozone layer in the past winter. The unique measurements of NP 35 will significantly contribute to determine precisely how much of the ozone destruction is caused by human activities.
„The high amount of work caused by the extensive measuring program let the time on the ice flow go by extremely fast“, Jürgen Graeser said on his return. Daily life was structured by the measurements on the one hand and by the meals with the colleagues on the other. A cook was responsible for the meals of the whole team, but each overwinterer helped him with the kitchen work for one day every three weeks. This kitchen service coincided with the station service controlling the condition of the ice floe and the presence of polar bears near the station. These tasks turned out to be very important, for in the course of the winter the ice floe produced crevices several times, but those crevices closed again. Moreover, frequent visits of polar bears regularly caused for alarm among the participants. Jürgen Graeser had the possibility to communicate with the Potsdam colleagues via satellite telephone and to relay the actual measuring data promptly.
The long-term aim is to significantly reduce the great imprecision of present climate models in polar regions. To create models, mathematical descriptions for physical processes taking place under natural conditions are used. These so-called „parameterizations“ are based on measured data, and only an excellent data base can enable them to produce realistic climate simulations. In November 2008, the scientists taking part in the NP-35 project will discuss the results of their expedition in the course of an international workshop in Potsdam. Altogether, the NP-35 project is one more significant milestone for the Potsdam atmospheric researchers. The results deliver an important base for the international focal projects CliC (Climate and Cryosphere) and SPARC (Stratospheric Processes and their Role in Climate Change) by the World Climate Research Programme (WCRP, wcrp.wmo.int/)
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