ANT-XXIV/4, Weekly Report No. 1
Temperature and humidity profile from the HATPRO microwave radiometer and from the DWD radiosonde. Grafic by Bernhard Pospichal.
Calibration of the HATROP microwave radiometer with liquid nitrogen. Photo by Martin Hieronymi.
On board: Paralomis granulosa. Photo by Astrid Wittmann
Day 1. Scientists and DWD of ANT-XXIV/4, nearly complete. Photo: John Kalisc
18 to 24 April 2008: Stormy Beginning
On April 16 POLARSTERN arrived in Punta Arenas on schedule, the scientific crew disembarked the following day. The first day of the new science team started on April 18 with boarding and assembling of instruments and laboratory equipment. At 19:00 POLARSTERN left Punta Arenas exactly on time heading to Bremerhaven with one stop in Las Palmas to pick up AWI staff who will check ship instrumentations.
Depending on the weather situation, daily stations of up to 50 minutes duration each are utilized for measurements of phytoplankton and subsurface solar radiation down to 200 m depth.
A full CTD down to the ocean floor is planned at the Vema Channel. This CTD will contribute to long-term monitoring of decadal variability of the Antarctic deep water formation.
In addition to the 42 crew members, 19 scientists and two DWD employees are on board the ship.
A major part of the work consists of the continuous monitoring of the atmosphere, the biochemical properties of the upper ocean, and the energy and material exchange between ocean and atmosphere. Furthermore, phytoplankton concentrations, the marine light availability, spatiotemporal light fluctuations as well as aerosol and trace gases in the near-surface atmosphere air are being measured. Finally, the Chilean crab species Paralomis granulosa and Lithodes santolla are transported to the AWI for further investigations.
The first day still in the harbour with excellent weather conditions was used to assemble instruments. As soon as we left the Strait of Magellan we passed through a storm track with 9 Beaufort wind. However, all installations in the exterior and in the ship's laboratories could be successfully finished.
Very quickly a diurnal work schedule was established: Weather briefing with the ship's meteorologists at 9:00, CTD and marine light measurements from 13:00 – 13:50 h, seminar at 19:30 followed by table tennis. As soon as we will have reached the Subtropics with few clouds and calm sea conditions, sea surface tilt and fluctuation of marine light down to 30 m will be measured from a zodiac to avoid wind and light shadows from the ship. The Bio-Optics group is working hard from 6:00 to 2:00 filtering the CTD-borne phytoplankton samples. On the other side, the atmospheric group only works from dawn till dusk on observing surface-near trace gases, atmospheric aerosol, humidity and temperature profiles, cloudiness, solar and thermal irradiance as well as turbulent fluxes of heat, humidity and CO2. All measurements run automatically and require only occasional re-calibrations.
Especially our „Humidity And Temperature PROfiler“ HATPRO is critically observed and is recalibrated if the observed microwave brightness temperatures start to show a drift. The calibration includes the use of liquid nitrogen and provides a little happening on the observation deck.
The radiosonde ascents that are performed by the DWD on a daily basis at 12:00 UTC provide an excellent opportunity to test the performance of the HATPRO, although the in-situ observation along a strongly horizontally drifting balloon with indirect microwave remote sensing directly above the ship is not perfectly well comparable. Figure 3 shows an example comparison where HATPRO quite nicely detects the temperature profile but shows large deviations for the humidity. During this cruise we will investigate to which extent it may be possible to improve the HATPRO retrieval. In our clouds-and-radiation group we are more interested in the total amount of water vapour and liquid water, which is quite well detected by the radiometer, every second!
Weatherwise, after the storm track we are influenced by a high pressure system with shallow convective cloudiness and lots of sun shine. Ideal conditions for the aerosol and cloud observations. Also the Bio-Optics group ran five CTD and light profiles successfully and quickly, thus saving some station time, which will give us more flexibility for the second part of the cruise.
All measurements are carried out continuously during the entire expedition. Therefore, each weekly report will try to highlight a certain topic. This time remote sensing of the atmosphere, in the following more on Bio-Optics, Marine Biology, Marine Chemistry, Synoptics, ...
Best regards on behalf of all,
Andreas Macke