Abstract

An automatic meteorological station lias been operating at the Arctic Station (69'15'N, 53"31'W) in West Greenland since 1990. This paper summarizes meteorological parameters during 1997, including snow and sea ice cover, ground temperatures and active layer development, opment,and presents comments on the local permafrost thickness.

Keywords

Climate, arctic, permafrost, active layer, snow cover, sea ice cover,
Greenland, Disko.

N. Nielsen, O. Humlum & B.U. Hansen: Institute of Geography, University
of Copenhagen, Øster Voldgade W, DK 1350 Copenhagen K,
Denmark.

Outline of the Meteorological Year 1997

The mean annual air temperature (MAAT) at the Arctic Station 1997 was -3.3°C (Table 1), which is somewhat higher than the average since the station was established in late 1990 (Nielsen et al., 1995). The MAAT at the station is -4.9°C for the whole period 1991-1997. According to official meteorological data 1961-1990 the MAAT at Qeqertarsuaq is -3.9°C. The higher MAAT 1997 is primarily the result of higher winter temperatures, while summer temperatures were close to normal. The lowest 1997 air temperature (-29.4°C) occurred on 8 March, while the highest air temperature (14.8°C) was registered on 21 June. The warmest period, however, was in early and mid- June, while the remaining part of the summer was cooler (Fig.l). A maximum solar radiation of 902 W/m² was registered in early June, within the above warm period.

The mean annual wind speed was 3.9 m/s, with a maximum
of 17.6 m/s (daily mean), which occurred in mid-
March in connection with a foehn situation with easterly

winds. During December the 12^th a peak of 26.6 m/sec occurred fron the east. In general, however, the wind speed was comparatively low during the winter and somewhat higher during the summer and autumn (Fig.l). Easterly winds due to air masses flowing off the Greenland Ice Sheet to the east prevailed during periods of the winter and autumn, while southwesterly winds were more frequent during the summer.

The annual total liquid precipitation was 374 mm, which is high compared to the mean annual total precipitation (including snow) of 477 mm w.e. (ASIQ 1997). This high annual total is mainly derived from a wet August, culminating with no less than 118 mm rain on 11 August and 47 mm on 12 August in the morning - 165 mm in \Vz day. This corresponds to about 5 mm per hour with a maximum peak of 7 mm in 30 minutes. This represents a quite unusual event in this part of Greenland. The amount of precipitation in the form of snow during the winter is not

measured. The winter 1996-97 the snow cover had a typical thickness of about 20 cm and lasted until mid May. The subsequent winter 1997-98 the snow cover was established in early October, and had a typical thickness of 15-20 cm throughout November and December.

The winter 1997 was exceptional concerning the sea ice occurrence. M/S Porsild, the research vessel of the Arctic Station, was ice bounded in the Qeqertarsuaq harbour only about 3 months in contrast to normally 5-6 months, Fig. 2.

The mean annual ground temperature at 5 cm depth was -O.B°C, which is 2.5°C above the MAAT. At 60 cm and 175 cm depth, the mean annual ground temperature was - O.5°C and -O.5°C, respectively. The maximum temperature registered at 175 cm depth was O.5°C, and the active layer in 1997 at the station presumably was about 185 cm thick, which is close to normal for the measurement period 1991-97.

The date for initiation of thawing of the active layer, defined as the time in spring when the near-surface ground temperature (5 cm depth) became stable above O°C, was on 19 May. The date where the maximum thawing depth was reached was on 29 August, inferred from the temperature at 175 cm depth. Initiation of autumn freezing, defined as the time from where the near-surface temperature (5 cm depth) was consistently below O°C was on 29 September. Finally, the time for complete freezing of the active layer, defined as the time from which ground temperatures at all levels in the active layer again were below -I°C, was not reached before the end of 1997. All levels in the active layer demonstrate a zero curtain effect during autumn freeze-back, especially at 60 cm and 175 cm depth (Fig.l).

At Godhavn, the complete 1991-97 data series indicate that the initiation of the spring ground thaw usually is in early June, although in some years it may occur in May or even as early as in late April. In this respect 1997 represents resentsa somewhat early initiation of ground thaw. The maximum thaw depth occurs more constantly in mid- or late-September, so again 1997 represents an early date for this parameter. Autumn freezing typically begins in late September or early October, which was also the case in 1997. The complete freezing of the active layer occurs, more variably, from late December to late January, and in this respect 1997 was normal.

No systematic mapping of permafrost or permafrost related terrain features have been carried out in this part of West Greenland. Weidick (1968) and Brown et al. (1997), however, both place Disko Island within the zone of continuous permafrost. Adopting a standard continental geothermal gradient of about 0.033 °Cm~¹ (Kappelmeyer and Haenel, 1974), and knowing that the mean ground temperature typically are a few degrees above the average air temperature as demonstrated above, the Qeqertarsuaq MAAT of-3.9°C (1961-1990) indicates a typical permafrost thickness of 40-80 m in southern Disko Island. These estimates are presumably somewhat conservative, as the Little Ice Age MAAT most likely was at least 2°C below modern values (Humlum, 1996), which would provide conditions for a somewhat thicker permafrost layer than is suggested by modern meteorological values.

References

Klima-Info, ASIAQ, 1997

Brown, J., Ferrians, O.J. (Jr.), Heginbottom, J.A. and Melnikov, E.S., (Editors) 1997. Cirkum-Arctic Map of Permafrost and Ground Ice Conditions (scale 1:10000000). International Permafrost Association. United States Geological Survey (production).

Humlum, 0., 1996. Origin of Rock Glaciers: Observations from
Mellemfjord, Disko Island, central West Greenland. Permafrost
and Periglacial Processes, 7: 361-380.

Kappelmeyer, O. and Haenel, R., 1974. Geothermics with Special
Reference to Application.Geopublication Associates, Geoexploration
Monographs, Series 1, No. 4, 238 pp.

Nielsen, N., Hansen, 8.U., Humlum, O. & Rasch, M. (1995): Meteorological Observations at Arctic Station, Qeqertarsuaq (Godhavn), Central West Greenland. Danish Journal of Geography, 95:97-104.

Weidick, A. , 1968. Observations on some Holocene glacier
fluctuations in West Greenland. Meddelelser om Grønland,
164(6): 202 pp.