Two-meter Air Temperature

The University of Washington's International Arctic Buoy Program/Polar Exchange at the Sea Surface (IABP/POLES) temperature analysis fields are the basis for the Atlas gridded temperature fields. The IABP/POLES data set was chosen because we believe it is the best representation of the true two-meter air temperature field for the following reason: IABP/POLES unites the two most extensive sources of Arctic Ocean air temperature data. These are the International Arctic Buoy Program (IABP) data and the Russian North Pole (NP) drifting station data. The IABP data in IABP/POLES Temperature Data Set were carefully quality-controlled, and a warm bias was removed using the NP data as a standard.

Reanalysis products, such as those from NCEP/NCAR (see "Description of the NCEP/NCAR Global Reanalysis pressure data" section) or from the European Centre for Medium-range Weather Forecasting (ECMWF) are other sources for temperature fields. But IABP/POLES temperature fields show better correlation with NP drifting station data than do NCEP or ECMWF gridded products, particularly in the summer.

Data source for temperature fields

IABP/POLES 2-Meter Air Temperature Data Set fields can be obtained from the University of Washington (http://iabp.apl.washington.edu/AirT/index.html). At this site, these data are available for every 12 hours, for 1979 through 1998 (with periodic updates). I. Rigor and M. Ortmeyer, with the Polar Science Center at the Applied Physics Laboratory, University of Washington, provided IABP/POLES air temperature fields to NSIDC in EASE-Grid with a 100 km cell size.

Method of constructing the temperature field products

Data (12 hour fields, 1981 through 1998) obtained from the University of Washington IABP/POLES project were re-gridded from 100 km EASE-Grid to the Meteorological Atlas EASE-Grid format (250 km cell size) using cubic convolution. Decadal averages were computed prior to re-gridding.

Gridded temperature field products

Gridded temperature products are:

The browse versions of these files are shown as .gif format images with a color bar and contours every two degrees Celsius. These browse files are for the purpose of quickly visualizing the content of the corresponding ASCII data files. The IDL routine used to color-map the images gives a smooth and visually pleasing result, but keep in mind that the gridded ASCII files have one value only for every grid cell. The grid cell centers are shown as red dots. For information on the structure of the gridded files, see the section on "EASE-Grid".

Description of IABP/POLES 2-meter temperature fields

The IABP/POLES Temperature Data Set is a gridded 12 hour, two-meter air temperature data set for the Arctic, developed at University of Washington using optimal interpolation of temperature data. [Rigor et al., 2000] (http://iabp.apl.washington.edu/AirT/index.html). The IABP/POLES analysis evolved from a POLES analysis that used Russian NP drifting station, IABP, and coastal station data to produce temperature fields over the Arctic Ocean only. The development of this data product is described in Martin and Munoz [1997]. The IABP/POLES fields build on the earlier work by applying seasonally and spatially varying correlation length scales in the optimal interpolation. This method takes account of the fact that the correlation between observations taken at coastal stations and at ocean stations, or between coastal and interior stations, varies by season. For instance, the correlation length scale between stations of the same type is about 1000 km throughout the year, but the correlation between ocean and coastal stations drops to about 300 km in the summer. The use of these correlations allows for the inclusion of inland station data in the analysis. The data set is extended over land using data from the National Center for Atmospheric Research (NCAR) data set ds464.0, NCEP ADP Global Sfc Obs, daily Jul 1976-on.

The IABP/POLES data set begins in 1979, when the first IABP buoys were deployed [Untersteiner and Thorndike, 1982]. Over the years, the IABP buoy types, types of thermistors, and the height at which they were mounted changed, making it difficult to assess accuracy. (The Russian North Pole drifting station air temperature data were acquired at a consistent height of 2 m). Martin and Munoz [1997] estimate that overall, the temperature recorded by a thermistor on an IABP buoy should equal two-meter air temperature to within about one degree Celsius.

NCAR data set ds464.0, NCEP ADP Global Sfc Obs, daily Jul 1976-on, contains worldwide synoptic observations collected from the Global Telecommunications System by the National Center for Environmental Prediction (NCEP). Some quality control is applied at NCEP. Note that some but not all of the data from the 65 Russian stations included in the Coastal Stations section of this Atlas are included in this data source. The percentage of Russian coastal stations appearing in ds464.0 varies with time, but is on the order of 30 percent.