摘要:

After indicating the basis of the technique, its use with a cryogenic SQUID magnetometer is outlined, particular emphasis being given to the need for stringent reliability criteria. Comparison of results for some samples is made with results obtained using the Shaw alternating‐field technique, and the agreement is satisfactory. Determinations made on 14 samples fired during the last 150 years give results which on average are in close agreement (within 2%) with observatory‐based values, the standard deviation of a sample from the predicted value being

ISSN:8755-1209    

DOI:10.1029/RG026i001p00001

年代:1988

数据来源: WILEY

摘要:

After indicating the basis of the technique, its use with a cryogenic SQUID magnetometer is outlined, particular emphasis being given to the need for stringent reliability criteria. Comparison of results for some samples is made with results obtained using the Shaw alternating‐field technique, and the agreement is satisfactory. Determinations made on 14 samples fired during the last 150 years give results which on average are in close agreement (within 2%) with observatory‐based values, the standard deviation of a sample from the predicted value being

ISSN:8755-1209    

DOI:10.1029/RG026i001p00003

年代:1988

数据来源: WILEY

摘要:

After indicating the basis of the technique, its use with a cryogenic SQUID magnetometer is outlined, particular emphasis being given to the need for stringent reliability criteria. Comparison of results for some samples is made with results obtained using the Shaw alternating‐field technique, and the agreement is satisfactory. Determinations made on 14 samples fired during the last 150 years give results which on average are in close agreement (within 2%) with observatory‐based values, the standard deviation of a sample from the predicted value being

ISSN:8755-1209    

DOI:10.1029/RG026i001p00013

年代:1988

数据来源: WILEY

摘要:

Present techniques for obtaining palaeomagnetic intensities can fail to detect mineral alteration occurring during heating in the laboratory. It is very likely that this alteration is responsible for much of the poor reproducibility of ancient intensities of the geomagnetic field. A technique is described which can detect it, with a significant improvement in both the reproducibility and accuracy of the results.

ISSN:8755-1209    

DOI:10.1029/RG026i001p00015

年代:1988

数据来源: WILEY

摘要:

After indicating the basis of the technique, its use with a cryogenic SQUID magnetometer is outlined, particular emphasis being given to the need for stringent reliability criteria. Comparison of results for some samples is made with results obtained using the Shaw alternating‐field technique, and the agreement is satisfactory. Determinations made on 14 samples fired during the last 150 years give results which on average are in close agreement (within 2%) with observatory‐based values, the standard deviation of a sample from the predicted value being

ISSN:8755-1209    

DOI:10.1029/RG026i001p00023

年代:1988

数据来源: WILEY

摘要:

Results from general circulation models (GCMs) have indicated that a predicted climate warming resulting from an increase in atmospheric carbon dioxide (CO2) will be amplified in the polar regions and that temperature increases in the polar regions will be several times greater than the global average. Some GCMs predict a 4°–5°C average air temperature increase in the Arctic by the middle of the next century. Evidence from the polar regions indicates that a warming in the cryosphere may already be in progress. A 2°–4°C rise in permafrost temperature, measured in northern Alaska, is believed to have occurred during the last 100 years. In addition, many small valley glaciers and ice caps have experienced retreat and appear to have contributed up to 50% to the observed rise (10–15 cm) in sea level during the last century. Other work shows that increased snowfall which can be associated with warmer temperatures has caused thickening of some Alaskan glaciers. Though a decrease in snow and sea ice cover would be a likely consequence of global warming, a sustained decrease in global snow and sea ice extent has not been found from analysis of more than 20 years of image data (1.1‐km pixel resolution) from National Oceanic and Atmospheric Administration meteorological satellites and more than 7 years of scanning multichannel microwave radiometer snow data (30‐km pixel resolution) on the Nimbus 7 satellite. Snow and sea ice are sensitive to atmospheric temperature changes because of their large surface to volume ratio. While measurements of snow and sea ice extent, snow depth, and sea ice concentration are possible using visible, near‐infrared, or microwave sensors on satellites, it is not feasible to measure the mass balance of the ice sheets with these sensors directly. Estimates by glaciologists show that the Greenland Ice Sheet is in approximate equilibrium and that the Antarctic Ice Sheet has a positive mass balance. Satellite radar altimetry (and in the future, laser altimetry) is a promising technique for measuring the surface elevation of ice sheets. Satellite‐borne laser altimetry in conjunction with imagery on ice sheet extent will permit direct measurements of changes in mass balance of the ice sheets through time. The terminus positions and ablation area boundaries of valley glaciers are indicative of glacier mass balance; these can be studied using visible and near‐infrared data from the Landsat satellite series and data from the French Systeme Probatoire d'Observation de la Terre (SPOT) satellite and synthetic aperture radar data. Lake ice freeze‐up and breakup dates are sensitive to regional air temperature and may also be good indicators of climate trends. Monitoring the onset of lake freeze‐up and breakup dates is feasible with radar and visible image data. The very important role of snow and ice in global processes is being highlighted as large‐scale, satellite‐derived geophysical data sets have become available and are beginning to be used

ISSN:8755-1209    

DOI:10.1029/RG026i001p00026

年代:1988

数据来源: WILEY

摘要:

The Antarctic is an interesting land that has become the focus of much attention in the last decade. Its undisturbed geological record dating back to the last interglacial period, a locale with seas and lakes populated with interesting organisms, a land with beautiful twilights and lovely cirrus and stratospheric cloud formations, a whole continent dedicated by international treaty to scientific research–these factors provide good reasons for the renewed interest. A recent review byWeller et al.[1987] explores in more detail the many scientific ideas that make Antarctica an attractive laboratory. Studies relating to sundry aspects of the Earth's geosphere‐biosphere system draw scientists from the whole spectrum of scientific discipli

ISSN:8755-1209    

DOI:10.1029/RG026i001p00041

年代:1988

数据来源: WILEY

摘要:

Automatic weather station (AWS) units have been deployed in Antarctica since 1980 by the U.S. Antarctic Research Program. As of June 1987, 25 AWS units are operating in Antarctica in support of meteorological research. The AWS units measure air temperature, wind speed, and wind direction at a nominal height of 3 m above the surface and air pressure at the height of the electronics enclosure. Some AWS units measure relative humidity at 3 m and air temperature difference between 3 m and 0.5 m above the surface. Three to five values for each sensor are updated at 10‐min intervals and transmitted at 200‐s intervals to data collection systems on the NOAA series of polar‐orbiting satellites. The AWS units in Antarctica are sited to support research on katabatic winds, barrier winds, surface heat fluxes, and climate. Results from the katabatic wind experiment along a line upslope from the Adelie Coast show that the katabatic wind is stronger in winter than in summer and is strongest inland from the coast. The potential temperature difference from the south pole to the Adelie Coast has the largest negative value in winter, supporting the stronger katabatic winds. The katabatic flow down the glaciers of the Transantarctic Mountains to the Ross Ice Shelf requires synoptic support because the potential temperatures on the Ross Ice Shelf are lower than at higher elevations such as the south pole. Data from AWS sites on the Ross Ice Shelf along the Transantarctic Mountains generally have southerly monthly resultant wind directions along the mountains. Ross Island with its 3000‐m‐high volcanoes deflects the southerly wind flow, resulting in an easterly wind direction at McMurdo Station. AWS units equipped to measure vertical air temperature difference and relative humidity provide estimates of the latent and sensible heat flux on the Ross Ice Shelf. Generally, the sensible heat flux is negative, and the latent heat flux is small. The collection of the AWS data by a local user terminal at McMurdo Station makes possible the use of the AWS data to support air o

ISSN:8755-1209    

DOI:10.1029/RG026i001p00045

年代:1988

数据来源: WILEY

摘要:

The National Oceanic and Atmospheric Administration program of Geophysical Monitoring for Climatic Change (GMCC) has operated a background atmospheric monitoring observatory in Antarctica at the United States Amundsen‐Scott South Pole Station since 1972. The program objectives at South Pole, as at the other three GMCC observatories, include the determination of concentrations, variations with time, and other properties of atmospheric trace gases and aerosol particles which can potentially impact climate. In addition, GMCC monitors solar radiation and meteorological factors to determine long‐term means and any trends that could be associated with climatic changes as well as to examine correlations between meteorological and air chemistry parameters. This discussion emphasizes the long‐term GMCC South Pole air chemistry record for carbon dioxide, total ozone, surface ozone, methane, halocarbons, nitrous oxide, and aerosol concentrations. Comparisons of South Pole findings with other global GMCC data are also given. The total ozone discussion includes the results of recent GMCC ozonesonde operations and an assessment of Dobson ozone spectrophotometer data taken at South Pole by NOAA since 1964. These data sets are directly applicable to Antarctic “ozone hole” investigations, and current findings related to this phenomenon are

ISSN:8755-1209    

DOI:10.1029/RG026i001p00063

年代:1988

数据来源: WILEY

摘要:

Atmospheric emission measurements were made in 1978 from an LC 130 aircraft from Point Mugu, California to McMurdo Station, Antarctica, and from McMurdo over the Antarctic continent on several different flights. These included a number of flights over the south pole. In December 1980, infrared solar spectra were obtained from the ground at South Pole Station. Infrared solar spectra were also obtained from South Pole during late November and early December 1986. These latter measurements were extended to cover additional spectral regions to obtain column densities of a number of additional constituents. The results obtained from these measurement series are reviewed and where measurements were made during both periods, compared. Spectral absorption or emission features due to HNO3, NO, NO2, HCl, H216O, H218O, HDO, CH4, and N2O were used to obtain data on the total column abundances for these compounds.

ISSN:8755-1209    

DOI:10.1029/RG026i001p00081

年代:1988

数据来源: WILEY