Scientific background

Everybody knows that the Antarctic meteorological conditions on the ground are rather unique, with low temperature, strong winds and very low precipitation. In addition the troposphere (up to 10 km) and the stratosphere (up to 60 km) are very different from the Arctic troposphere and stratosphere. The very low temperature in the stratosphere during the Antarctic winter has lead to the development of the ozone hole since human activities have substantially changed the atmosphere’s chemical composition. The chlorine loading in the stratosphere is four times the natural abundance (WMO, 2002) causing, since the beginning of the 1980s, severe ozone depletion between 13 and 23 km in the late winter period, commonly called the ozone hole.

Ground-based instruments all over the world are now monitoring the atmosphere for variation and trends in ozone and other atmospheric constituents. Satellites are also used for this task, but despite the valuable global coverage under their lifetime they still need groundtruth data for validation purposes.

Ground-based monitoring at the Swedish Antarctic station Wasa would provide one more data point in the sparse distribution of measurements on the Antarctic continent. Observations at additional Antarctic stations are also of great value in order to investigate the chemical evolution as well as transport processes of stratospheric and tropospheric trace gases. In particular simultaneous measurements with the nearby German Georg von Neumayer-Station offers a great potential for related studies. The fate of air masses passing both stations can be studied in detail. Such studies are of great importance and have never before been performed in Antarctica.

The aim of this part of the project was to investigate the environmental and logistical prerequisites for continuous observation of stratospheric and tropospheric trace gases with a MAX DOAS instrument (Multi-Axis Differential Optical Absorption Spectrograph), which would allow us to address the above mentioned scientific questions (Hönninger 2004 and Friess 2004).

The second part of this project was to identify a suitable location for the ‘Moveable Atmospheric Radar for Antarctica’ (MARA) with respect to prevailing wind conditions at Wasa. MARA will be installed at Wasa station during the Antarctic summer 2006/07 for the observation of atmospheric waves. The MARA experiment will be operated during the summer months and we will investigate the suggested connection between planetary wave activity and the observed decadal variability of noctilucent clouds (NLC or PMC) and polar mesospheric summer echoes (PMSE), which could not yet be explained sufficiently.

The polar upper mesosphere (between 50 and 90 km altitude) in summer is the site of the lowest temperatures in Earth’s atmosphere, as low as -150°C. These cold conditions lead to the formation of ice clouds called NLC (noctilucent clouds, or polar mesospheric clouds, PMC) at around 85 km and of charged aerosol-particle layers (PMSE).

PMC and PMSE are expected to be affected by solar radiation and meteor input from above, by temperature oscillations and winds due to atmospheric waves propagating up from below and by changes in greenhouse gases in the atmosphere.

The location of MARA with its long dipole antennas needs to be chosen carefully in order to protect the antenna field from gusts and extraordinarily high wind speeds. Measurements of wind speed and direction have been obtained at a place on the glacier on the wind protected region behind the nunatak with Wasa and Aboa stations on its top. Photo 3 shows the meteorological station on the glacier.

The third part of this project was to revive the Air–Earth-current instrument installed at Wasa station in 2003 which was supposed to study the ‘fair weather current’ between the ground and the ionosphere above around 90 km altitude. This instrument stopped operating during 2004 and unfortunately could not be revived during the SWEDARP 2004/05 expedition.

The measurements and results

The MAX-DOAS feasibility study

MAX-DOAS measurements were performed continuously after the instrument was installed at a mast close to the generator container. The instrument collected sunlight that was scattered into the direction of observation of the DOAS. By variation of the elevation angle it is possible to distinguish between gases scattering in the troposphere (up to 10 km) and stratosphere (between 10 and 60 km).

The measurements turned out to be very stable as long as the direct sunlight did not reach the instrument. The heating due to direct sunlight could not be counteracted by the internal cooling system and the measurements could not be analysed. Proper shading of the MAX-DOAS instrument is obviously an important issue for a future long-term operation at Wasa station.

Extensive cooling might lead to increased power consumption, which might be a problem when the instrument is operated on Wasa station batteries after the dark winter season during which it has been idle. Meteorological conditions such as wind and low temperature (up to 25 m/s and down to -15°C, respectively) did not affect the MAX-DOAS instrument, except for strong snowdrift, which led to moderate snow accumulation in the open part of the instrument. A suitable construction to keep the snowdrifts away has to be developed for a DOAS instrument permanently installed at Wasa station.

However the main issue for a long-term operation of a future MAX-DOAS at Wasa station is still the telecommunication, that is the data transfer and the remote control of the instrument. These questions have to be solved by the Swedish Polar Research Secretariat in order to ensure a continuous operation at Wasa.

Meteorological measurements

A meteorological station was installed at the glacier adjacent to the foot of the nunatak Basen (picture 3). An area with a small rocky ridge sticking out of the glacier was chosen as the location for the measurements. Once the meteorological station was put up it measured continuously until the last day of the expedition. The results are presented in the figure. The conclusions drawn from the measurements are: The average wind speed down at the glacier was lower than on top of the nunatak close to Wasa station. However the gusts were stronger than on top of the nunatak. Since the extreme wind speed is a problem for the MARA rather than continuous strong winds the site close to Wasa station will be the favorable site for the future MARA experiment. This will also easily solve the problem with the power supply for the experiment.