The Earth's high-latitude regions are of critical importance in many climate-change scenarios, but a time continuous, spatially complete, and well-calibrated record of tropospheric temperatures is needed in order to assess past and future climate changes. Studies of recently compiled upper-air data sets show no evidence of CO2-induced warming, but the spatial pattern of tropospheric temperature variability in the Arctic has not been thoroughly examined. This study analyzes a 108-month segment of the data record from the TIROS Operational Vertical Sounder (TOVS) aboard NOAA polar-orbiting satellites to examine both the spatial and temporal variability of atmospheric temperature in the Arctic.

Temperature retrievals based on clear-column radiances archived at NOAA/NESDIS were done using algorithms tuned to Arctic conditions. The retrieved temperatures compared well with Arctic rawinsonde data, and include lowlevel inversions that are often problematic for satellite retrievals. The amplitude of the seasonal cycle in 500 mbar temperatures from the TOVS, NMC, and rawinsonde data generally agreed, whereas the phase comparisons produced mixed results. Principal component analyses of the TOVS and NMC temperatures revealed both monopole and dipole spatial patterns in the component loadings. Spatial patterns of the correlation between the upper-air data and the TOVS retrievals were similar to the principal component loading patterns. Whereas no significant trends were found in the station data for the same period as the TOVS record, a significant negative trend could be seen in the first principal component scores of the TOVS retrievals.

Four case studies are presented that focus on a joint analysis of AVHRR images with other independently obtained data sets to identify examples of both optically thick and thin polar stratospheric clouds (PSCs) over Antarctica. Optically thick PSCs are shown to be readily identifiable by the temperature signatures in AVHRR channel 5 images over the Antarctic Peninsula–Weddell Sea area. A time series of optically thick PSCs as seen in satellite images obtained at Palmer Station, Antarctica, is produced and discussed. Four events are identified and discussed where the areal coverage by cold temperatures indicative of PSCs expands to cover a significant portion of the area sampled. Plans for further research are outlined.

At the Bonanza Creek Experimental Forest (BCEF), past ecological research has been directed at forest successional processes on the floodplain of the Tanana River and adjacent uplands. Research at the Bonanza Creek site continues on the mosaic of forests, shrublands, and wetlands in a wide variety of successional stages on the Tanana floodplain. This paper reviews research since 1988 into the capabilities of Synthetic Aperture Radar (SAR) for monitoring, classification, and characterization of these forests using radar remote sensing and modelling techniques. Classifications of successional stages, obtained by use of different classifiers on multi-frequency and multi-polarimetric AIRSAR data, are contrasted; these classifications have been used to predict classification accuracies obtained with ERS-1 data, and to estimate the utility of an ERS-1 and RADARSAT combination for classification. Forest classifications, used in combination with ground-truth data for more than 50 forest stands, are used to summarize the distribution of biomass on the landscape. This will allow projections of future biomass. Monitoring of forest phenology, seasonality of flooding, and freeze–thaw transitions is ongoing. Also, direct monitoring of dominant tree species is demonstrating diurnal variation and interrelationships among environmental, physiological, and backscatter measurements.

The Finnish reindeer-herding area lies in the northern boreal forest zone. The herding area is divided into 57 reindeer management districts with a total area of 114,355 km2 (excluding water areas). The official number of reindeer in the year 1992 was 263,789, or 2.3 reindeer per square kilometre. In 1946 the density was only about one reindeer per square kilometre. The increased pressure on the mid-winter lichen pastures has reduced the volume of lichen. Also the decreased area of old coniferous forests with arboreal lichens has diminished the supply of food during the late-winter months. The lack of suitable winter pastures has led to the need for supplementary feeding with hay.

The intention of this study was to develop and test methods for cost-effective reindeer range land inventory and to assess the present state of pastures in seven districts. Use was made of Landsat 5 TM satellite imagery that was processed with remote sensing and GIS software. The analysis of well-known field sites proved the image classification to be between 80 and 90% accurate. By comparing field data and classification results, estimates can be made on the available fodder reserves in the different pasture types. The results show that mid-winter pastures are both scarce and degraded in six of the seven areas investigated. Only one area (Muotkatunturi) has mid-winter pastures in reasonably good condition. Late-winter pastures with arboreal lichens are more widespread than mid-winter pastures and determine the amount of additional winter feeding required. Summer pastures are abundant in all seven reindeer-herding districts and are therefore not a limiting factor. The method used is objective, inexpensive, and fast when compared to conventional methods. Information can be produced on the quantity and quality of reindeer pastures. This knowledge can be used to make better estimates of the natural grazing capacity of reindeer districts in Finland.

Carbon flux measurements made at an elevated point are associated with an effective upwind area or ‘footprint.’ Since Arctic tundra landscapes can exhibit substantial heterogeneity within the footprint of an eddy correlation tower, it may be necessary to determine the relative point source contributions to the observed flux if landscape properties are to be related to the flux. This study evaluates the potential importance of representing footprint source contributions in relationships that are developed between tower observations of net ecosystem exchange of carbon dioxide (NEE) and a remotely sensed spectral vegetation index. Satellite data collected over the foothills region of the North Slope of Alaska are used to determine spatial patterns of a spectral vegetation index in the calculated footprints of 30 randomly selected tower locations. A previously developed relationship between NEE and the vegetation index is used to calculate NEE at each tower location using two techniques, one that explicitly considers the footprint pattern of relative contributions to tower fluxes and another that ignores these patterns. The results indicate that if carbon fluxes measured at a tower are to be related to remotely sensed spectral vegetation indices, then it is necessary to consider the relative flux contributions from within the tower footprints for sites on the North Slope of Alaska.