Micro-meteorology
Micrometeorology and Climate Change
The Greenland Ice Margin Experiment (GIMEX)
Søndre Strømfjord, Jun 25 - July 25, 1991
Background
The GIMEX campaigns formed a part of a long-term research program on land ice and sea level change, carried out at the Insitute for Marine and Atmospheric Research (Utrecht University, the Netherlands), in collaboration with the micrometeorology group of the Faculty of Earth Sciences (Vrije Universiteit Amsterdam, the Netherlands) and the Institute of Physical Geography and Soil Science (University of Amsterdam, the Netherlands).
Melting zones have been avoided by meteorologists, because transportation over the surface is very difficult (crevasses, meltwater lakes, streams). Even the use of helicopters requires great care, as landing can be difficult in areas where slush dominates on the surface. Installing automatic stations poses another problem: the melting rates are so high (up to 5 meters of ice in an ablation season) that sensors mounted on masts drilled into the ice do not maintain a constant distance to the ice surface. Especially when fluxes have to be calculated from profiles, this is unacceptable. The Dutch component in the program was centered around Søndre Strømfjord (see Google map above). It had the advantage of being close to an airport with relatively easy access to the ice sheet. The figure on the right shows the setup of the experiment in the Summer of 1991. I was part of the team that ran site number 9 in this profile, the boundary-layer station. More background information can be found in this article in the Bulletin of the American Meteorological Society, vol. 74 (see below).
Science on the ice sheet
At site number 9, the camp of the Vrije Universiteit Amsterdam, a detailed study of the atmospheric boundary layer<SUP>2</SUP> was made. This camp, at an elevation of about 1,500 meters, accomodated me and three other people. Wind speed, temperature and humidity were measured at 8 levels along a 31-meter high tower, wind direction at heights of 2 and 31 meters. Turbulence data were obtained in two ways: first, at four levels along the tower, dry- and wet-bulb fluctuations (see "scientific background" section for more details and the article attached to this page for some results) were measured with a sample rate of 5 Hz. Second, eddy flux measurements with sonic anemometers, thermocouples and Lyman-Alpha's were carried out at the top of two shorter masts (13 meters and 4 meters), with a 20-Hz sampling rate. For remote probing of the atmospheric boundary layer an acoustic sounder (SODAR) and a RASS system were used, so that wind speed (three components) and temperature profiles up to about 400 meters at 20 levels could be obtained with an averaging period of 1 minute. Radiation (global radiation, albedo and net radiation) and snow temperatures were also determined. Thus, all components of the energy budget were determined.
A photographic impression of the site is given in the "Photo archive" section.
The more specific scientific goals of the meteorological experiments near and on the ice margin in West Greenland, GIMEX-90 and GIMEX-91, were to obtain better understanding of how glacier mass balance is related to meteorological conditions
to investigate how the large thermal contrast between the ice-free tundra and the ablation zone1 of the ice sheet affects local circulations and associated heat transport
to make a detailed study of the atmospheric boundary layer over a melting ice/snow surface.
rapidly, especially at the hight of the melting season. Since that was the subject of our research, that was the time we had to be there. The realization that we were living on top of about 1 kilometer of ice was quite staggering. We arrived on a hard frozen snow/ice surface, which soon turned into, sometimes knee-deep, sludge.Scientific background
1ablation zone: the area in which annual loss of snow through melting, evaporati on, iceberg calving and sublimation exceeds annual gain of snow and ice on the s urface
2The planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL) or peplosphere, is the lowest part of the atmosphere and its behavior is directly influenced by its contact with a planetary surface. It responds to surface forcings in a timescale of an hour or less. In this layer physical quantities such as flow velocity, temperature, moisture etc., display rapid fluctuations (turbulence) and vertical mixing is strong.
Life on the ice sheet Nothing is simple about staying on a ice sheet for a considerable amount of time, except one thing: you'll have no shortage of drinking water. The logistics of getting a measuring station as well-equipped as ours to a location high up on the ice sheet is logistically far from trivial. A helicopter is the only practical means of transporation. Will the helicopter be able to land? Will it be able to come back afterwards? What to do if a snow storm occurs? Is there any danger from melt water lakes? Sometimes fountains of melt water erupt when sub-surface water gets pushed upwards because of ice motion. In short, the region of the ice sheet close to the ablation zone is pretty dynamic, somtimes in dramatic ways. Another practical challenge is: how to erect a 31-meter mast and keep it stable? The helicopter dropped us off and picked us up again 1 month later... it's a pretty long walk to the closest supermarket! So, having the right kind and quantity of food is an important thing to think about. The location was carefully picked, but conditions near the equilibrium line can change
