Gerd Wendler

The Significance of the 1976 Pacific Climate Shift in the Climatology of Alaska

Abstract The 1976 Pacific climate shift is examined, and its manifestations and significance in Alaskan climatology during the last half-century are demonstrated. The Pacific Decadal Oscillation index shifted in 1976 from dominantly negative values for the 25-yr time period 1951–75 to dominantly positive values for the period 1977–2001. Mean annual and seasonal temperatures for the positive phase were up to 3.1°C higher than for the negative phase. Likewise, mean cloudiness, wind speeds, and precipitation amounts increased, while mean sea level pressure and geopotential heights decreased. The pressure decrease resulted in a deepening of the Aleutian low in winter and spring. The intensification of the Aleutian low increased the advection of relatively warm and moist air to Alaska and storminess over the state during winter and spring. The regime shift is also examined for its effect on the long-term temperature trends throughout the state. The trends that have shown climatic warming are strongly biased by...

Atmospheric net transport of water vapor and latent heat across 70°S

The annual net atmospheric transports of water vapor and latent heat poleward across 70oS are estimated using the latest compilation of surface mass balance for the Antarctic ice sheet and new estimates of precipitation and evaporation in sectors of the southern oceans and of seaward drifting snow transport in particular sectors of the ice sheet. The mass and energy exchange rates at the ice sheet-atmosphere and ocean-atmosphere interfaces are integrated strictly for areas within that latitude. The estimates of net southward water vapor transport (6.6 + 1.3 kg m -1 s -1) and latent heat transport (18.9 + 3.6 MJ m -1 s -1) are larger than reported in all preceding studies, based on atmospheric advection and moisture data collected at stations located between 66oS and 80oS, and are generally in agreement with those based on surface mass balance data and seaward drifting snow transport across the ice terminus which extends between 65oS and 79oS.

Precipitation decrease in the western Arctic, with special emphasis on Barrow and Barter Island, Alaska

Over the Arctic during the last few decades a decrease in annual precipitation and snow depths have been observed; this decrease is especially pronounced during the winter months. This decrease was not only found over northern Alaska but also over the high latitude Canadian stations and Russian drift stations. Further, satellite monitoring of North America snow cover has revealed a significant decreasing trend in mid-spring cover since 1972. The temperature increased during the last few decades in the Arctic, hence the simplest explanation—normally increased temperature leads to high precipitation—is not valid. A causal explanation for these trends had been related to the shift of the Aleutian low and Arctic high. This study, with special emphasis on the surface observation data from Barrow and Barter Island, indicates: (i) not only the frequency, but the mean intensity of precipitation has decreased; (ii) the amount of total cloud cover, and in particular, low cloudiness, has decreased with time; (iii) sea-level pressure did not show any significant trends. Variability in atmospheric pressure, however, decreased with time, suggesting that either the intensity and:or frequency of cyclones has decreased; (iv) a shift in seasonal resultant winds at Barrow has been observed.

The Heat Balance of the Icy Slope of Adelie Land, Eastern Antarctica

Abstract A complete but budget investigation was carried out in summer at a site in Adelie Land, some 100 km from the edge of the Antarctic ice sheet. For an average day, the all wave radiation budget based on the fluxes toward the surface being positive was positive for about 11 h, which is a short time considering that the sun was above the horizon between 22 and 24 h a day during the observational period. It is a result of the high albedo, which, on average, was found to be about 83%. Furthermore, with increasing cloudiness, a more positive radiation budget was found, which is in contrast to most studies at lower latitudes. The heat flux in and out of the snow cover was small, and showed a typical sinusoidal diurnal variation. The mean daily values of snow heat flux were negative, as the snow cover was warmed during the observational period. The latent heat flux was negative, on the average, as sublimation took place for most of the time. Deposition was observed only on a few nights. The sensible heat ...

Climatology of the East Antarctic ice sheet (100°E to 140°E) derived from automatic weather stations

A decade ago, automatic weather stations (AWS) were placed in remote areas of Antarctica where little or no information on the meteorological conditions was available. These stations report to the ARGOS data collection system onboard polar orbiting satellites of the NOAA series. The Australian National Antarctic Research Expeditions (ANARE) and the United States Antarctic Research Program (USARP) of the National Science Foundation (with logistic support from the French Expeditions Polaires Francaises (EPF)) have built up two AWS data nets in East Antarctica. There are a total of 16 stations in the area 55°–145°E and 65°–75°S, stretching from sea level to above 3000 m altitude. The records of 10 of these stations are sufficiently long to be adequate for a climatological study of the basic parameters of surface temperature, pressure, and wind and have been used in this study. The station data were reduced to a common format and interpreted jointly to describe the broad-scale climatic features of the ice sheet. Climatological results include (1) an absolute lowest minimum temperature of −84.6°C at Dome C; (2) no minimum below −40°C at D10 near the coast; (3) a “coreless” winter temperature regime, without seasonal temperature trends for 6 months, at all stations; (4) mean surface wind speeds increasing to maxima near, rather than at, the coast; (5) high directional constancy in all seasons, with directions closer to the fall line in winter and during night hours than in summer and during day hours; (7) a distinct semiannual pressure variation with a main minimum in spring (September) and a secondary minimum in autumn (March); and (8) interrelationships among surface temperature, pressure, and wind related to the ice sheet topography.

The Diurnal Variation of the Boundary Layer in Summer in Adelie Land, Eastern Antarctica

Abstract The data from the boundary-layer experiment carried out in November and December 1985 in Adelie Land, Antarctica, are analyzed. This area is famous for strong surface winds, with highly constant wind direction, which have been explained by the baroclinicity associated with surface radiational cooling over sloping terrain. However, during daytime in summer at D47, the net radiation was found to be positive, and the Richardson number as negative, indicating that the surface boundary layer was unstable. Unexpectedly, the wind directional constancy remained high. It was caused by the highly constant wind direction in the free atmosphere, which could be due to the large horizontal temperature gradient existing between the Antarctic ice sheet and the ice-free ocean along the coast of Adelie Land. A low level wind maximum was found, which was strong at night and weak during daytime. During nighttime, it was due to the slope induced baroclinicity, and during daytime, to the meso-scale baroclinicity cause...

A comparison of ultraviolet radiation measured at an arctic and an alpine site

Abstract Ultraviolet radiation contributes relatively little energy to the solar spectrum; however, it is very important because it is biologicaly very active. Measurements were carried out at a high altitude station in Switzerland (Jungfraujoch 3576 m), and at a high altitude station in Alaska (Fairbanks 64.82°N) with identical instrumentation. For all season the UV flux for Jungfraujoch was larger than for Fairbanks. In summer the differences between the stations were less pronounced because the lower solar elevation is compensated by a longer day length. In winter the differences are more severe. For both stations we find an increased relative intensity of the UV (UV/Global) with increasing cloudiness, while the absolute values decreased with increasing cloudiness. This shows that the clouds absorb more in the near IR than in the UV region of the solar spectrum. For Fairbanks, the UV values in spring were substantially higher (mean value 18%) than for identical solar elevations after summer solstice. Cloudiness could not account for this, because we also observed differences for clear sky conditions. A simple model was developed, which took multiple reflections of the highly reflecting snow cover in spring into account, which correctly explained 83% of the observed differences.

Strong Temperature Increase and Shrinking Sea Ice in Arctic Alaska

Barrow, the most northerly community in Alaska, observed a warming of 1.51°C for the time period of 1921- 2012. This represents about twice the global value, and is in agreement with the well-known polar amplification. For the time period of 1979-2012, high quality sea ice data are available, showing a strong decrease in sea ice concentrations of 14% and 16% for the Beaufort and Chukchi Seas, respectively, the two marginal seas bordering Northern Alaska. For the same time period a mean annual temperature increase of 2.7°C is found, an accelerated increase of warming over the prior decades. Looking at the annual course of change in sea ice concentrations, there is little change observed in winter and spring, but in summer and especially autumn large changes were observed. October displayed the greatest change; the amount of open water increased by 44% and 46% for the Beaufort and Chukchi Seas, respectively. The large amount of open water off the northern coast of Alaska in autumn was accompanied by an increase of the October temperature at Barrow by a very substantial 7.2°C over the 34 year time period. Over the same time period, Barrows precipitation increased, the frequency of the surface inversion decreased, the wind speed increased slightly and the atmospheric pressure decreased somewhat.

On Mertz and Ninnis Glaciers, East Antarctica

Two large glacier tongues, which extend substantially across the coastline of King George V Land in East Antarctica, have been studied by remote sensing (synthetic aperture radar, JERS-1). The tongue of Mertz Glacier is in a state of advance, while the Ninnis Glacier tongue is retreating. Some more specific points are: The distinctive surface structure and the form of the glacier tongues indicates that they are floating. While the tongue of Ninnis Glacier has lost about two-thirds of its area since 1913, the Mertz Glacier tongue has advanced substantially and has about doubled its areal extent over the same time period. The annual movement of the tongue of Mertz Glacier was determined as about 1.2 km. This is close to the value of the advance of the tip of the tongue since 1963, which was determined as 0.9 km year -1 .

THE EFFECT OF BLOWING SNOW ON KATABATIC WINDS IN ANTARCTICA

An acceleration of the katabatic winds during periods of blowing snow was observed in Adelie Land, Antarctica. Data collected by Automatic Weather Stations (A WS) showed a change in the relationship between the katabatic term of the surface geostrophic wind (katabatic force) and the wind speed for periods of blowing snow. When measurements of the katabatic force were plotted against cube of the wind speed, the slope was steeper for wind speeds at less than a threshold speed for blowing snow. The difference between these two slopes was partly explained by the effect of blowing snow entrained into the atmospheric boundary layer.