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Articles 151 - 155 of 155

Full-Text Articles in Atmospheric Sciences

Beryllium 7 And Lead 210 In The Western Hemisphere Arctic Atmosphere: Observations From Three Recent Aircraft-Based Sampling Programs, Jack E. Dibb, R. Talbot, G L. Gregory Oct 1992

Beryllium 7 And Lead 210 In The Western Hemisphere Arctic Atmosphere: Observations From Three Recent Aircraft-Based Sampling Programs, Jack E. Dibb, R. Talbot, G L. Gregory

Earth Sciences

Concentrations of the natural radionuclides 7Be and 210Pb were determined in aerosol samples collected in the western hemisphere Arctic during the recent NOAA Arctic Gas and Aerosol Sampling Program (AGASP 3) and NASA Global Tropospheric Experiment/Arctic Boundary Layer Expeditions (GTE/ABLE 3A and ABLE 3B) missions. Beryllium 7 showed a free tropospheric concentration maximum between 4 and 5 km in the summer of 1990. Previous 7Be data obtained in the late 1950s and early 1960s also indicated a similar vertical distribution of 7Be near 70°N. Injection of stratospheric air through tropopause folds associated with the Arctic jet …


The Accumulation Of 210pb At Summit, Greenland Since 1855, Jack E. Dibb Feb 1992

The Accumulation Of 210pb At Summit, Greenland Since 1855, Jack E. Dibb

Earth Sciences

The decay corrected activity of 210Pb at the time of deposition shows considerable short term variability, but no clear seasonal or annual periodicity. 210Pb activity in surface snow at this site has averaged 0.7 pCi kg-1 since 1927, but the period 1915-1927 is characterized by a steady decline from higher levels. The average annual accumulation of 210Pb has markedly declined since at least 1870. Similar observation at Dye 3 suggest that 210Pb accumulation has decreased throughout this century over much of the Greenland Ice Sheet. If the records of 210Pb in the firn of the Greenland Ice Sheet are mainly …


Beryllium-7 And Lead-210 In The Atmosphere And Surface Snow Over The Greenland Ice Sheet In The Summer Of 1989, Jack E. Dibb Dec 1990

Beryllium-7 And Lead-210 In The Atmosphere And Surface Snow Over The Greenland Ice Sheet In The Summer Of 1989, Jack E. Dibb

Earth Sciences

The concentrations of 7Be and 210Pb were measured in surface air and fresh and aging snow samples from Summit (72°20′N, 38°45′W) and Dye 3 (65°10′N, 44°45′W) Greenland, during June and July 1989. The aerosol concentrations of these radionuclides showed rapid variations at both sites, but were nearly twice as high, on average, at Summit. Concentrations in the 16 fresh snowfall events that were sampled also showed wide variability, but the averages were the same at the two sites. The apparent difference in air-snow fractionation and the lack of coherence in the concentration in air time series between the …


Recent Deposition Of 210pb On The Greenland Ice Sheet: Variations In Space And Time, Jack E. Dibb Jan 1990

Recent Deposition Of 210pb On The Greenland Ice Sheet: Variations In Space And Time, Jack E. Dibb

Earth Sciences

Detailed 210Pb profiles were determined for four "Chernobyl dated' snowpits sampled during a wide-ranging survey of the Greenland ice sheet during the 1988 season. The profiles from widely separated pits show little or no coherence; even for two pits only 40 km apart the profiles differ in detail. There does not appear to have been any seasonality in the deposition of 210Pb onto the ice sheet in the two years since the Chernobyl accident. The total deposition of 210Pb during this period (10-20 bq m-2) was about 20 times less than has been observed at mid-latitude sites in the eastern …


The Chernobyl Reference Horizon (?) In The Greenland Ice Sheet, Jack E. Dibb Sep 1989

The Chernobyl Reference Horizon (?) In The Greenland Ice Sheet, Jack E. Dibb

Earth Sciences

Published reports of the presence of radioactive debris from the Chernobyl reactor accident in snow on the Greenland ice sheet raised the strong prospect that such debris might constitute a valuable time stratigraphic marker all over the ice sheet. Large volume snow samples to test this possibility were collected from 7 snowpits as part of a wide ranging regional snow chemistry survey conducted during 1987 and 1988. Snow “labeled” with Chernobyl derived radioactivity was detected in all of the pits. However, the total amount of radioactive debris found at the different locations varied over a 20 fold range. The variability …