Arctic Temperature Trends
Research by the
International Arctic Buoy Programme (IABP)
and the
NASA EOS program Polar Exchange at the Sea Surface (POLES) Variations in Surface Air Temperature Observations in the Arctic, 1979 - 1997
1, Roger L. Colony2, and Seelye Martin3 1Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington 2International Arctic Research Center, University of Alaska, Fairbanks, Alaska 3School of Oceanography, University of Washington, Seattle, Washington
The statistics of surface air temperature observations obtained from buoys, manned drifting stations, and meteorological land stations in the Arctic during 1979–1997 are analyzed. Although the basic statistics agree with what has been published in various climatologies, the seasonal correlation length scales between the observations are shorter than the annual correlation length scales, especially during summer when the inhomogeneity between the ice-covered ocean and the land is most apparent. During autumn, winter, and spring, the monthly mean correlation length scales are approximately constant at about 1000 km; during summer, the length scales are much shorter, i.e. as low as 300 km. These revised scales are particularly important in the optimal interpolation of data on surface air temperature (SAT) and are used in the analysis of an improved SAT dataset called IABP/POLES. Compared to observations from land stations and the Russian North Pole drift stations, the IABP/POLES dataset has higher correlations and lower rms errors than previous SAT fields and provides better temperature estimates, especially during summer in the marginal ice zones. In addition, the revised correlation length scales allow data taken at interior land stations to be included in the optimal interpretation analysis without introducing land biases to grid points over the ocean. The new analysis provides12-hour fields of air temperatures on a 100-km rectangular grid for all land and ocean areas of the Arctic region for the years 1979–1997.
The IABP/POLES SAT data set is then used to study spatial and temporal variations in SAT. This data set shows that on average, melt begins in the marginal seas by the first week of June and advances rapidly over the Arctic Ocean, reaching the pole by 19 June, 2 weeks later. Freeze begins at the pole on 16 August, and the freeze isotherm advances more slowly than the melt isotherm. Freeze returns to the marginal seas a month later than at the pole, on 21 September. Near the North Pole, the melt season length is about 58 days, while near the margin, the melt season is about 100 days. A trend of +1°C/decade is found during winter in the eastern Arctic Ocean, but a trend of –1°C/decade is found in the western Arctic Ocean. During spring, almost the entire Arctic shows significant warming trends. In the eastern Arctic Ocean this warming is as much as 2°C/decade. The spring warming is associated with a trend toward a lengthening of the melt season in the eastern Arctic. The western Arctic, however, shows a slight shortening of the melt season. These changes in surface air temperature over the Arctic Ocean are related to the Arctic Oscillation, which accounts for more than half of the surface air temperature trends over Alaska, Eurasia, and the eastern Arctic Ocean but less than half in the western Arctic Ocean.
The format of these files is as follows:grid
point #, day * 10, AirT * 100, then 4 flags that we have been using to
check the dataset. The data has been interpolated to a 100.2701 km.
EASE grid
.
The coordinates corresponding to each grid point can be found in the file
latlon.
Please let
know if you encounter any anomalies.
SOME FIGURES DERIVED FROM THE DATA
The following figures show the mid-season, monthly mean fields and the seasonal trends of surface air temperature.
Observed Arctic Temperature Climatology
The mid-season, monthly mean fields show that over the entire Arctic region, January is the coldest month, while July is the warmest. Over the ocean, the coldest region is north of the Canadian Archipelago, and during summer the SAT over the ocean is help to an isothermal value of -0.2C.
Observed Arctic Temperature Trends
During fall, the trends show a significant warming of 2C/decade over the coasts of Greenland, near Iceland, and in Siberia but a cooling of 1C/decade over the Beaufort Sea and Alaska during fall.
During winter, the trends show a significant warming of up to 2C/decade in eastern Greenland and Europe and 2C/decade over Eurasia, extending north over the Laptev Sea; however, a cooling trend of 2C/decade is shown over the Beaufort Sea and eastern Siberia extending into Alaska. The cooling trend over eastern Siberia is significant.
During spring, a significant warming trend of 2C/decade can be seen over most of the Arctic.
Summer shows no significant trend.
ACKNOWLEDGEMENTS
This research was funded by the US Interagency
Arctic Buoy Programme (IABP)
and the NASA EOS program Polar Exchange at the Sea Surface (POLES).REFERENCES
