| 1. |
- Aldahan, Ala, et al.
(författare)
-
Atmospheric impact on beryllium isotopes as solar activity proxy
- 2008
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:L21812
-
Tidskriftsartikel (refereegranskat)abstract
- Reconstructing solar activity variability beyond the time scale of actual measurements provides invaluable data for modeling of past and future climate change. The 10 Be isotope has been a primary proxy archive of past solar activity and cosmic ray intensity, particularly for the last millennium. There is, however, a lack of direct high-resolution atmospheric time series on 10 Be that enable estimating atmospheric modulation on the production signal. Here we report quasi-weekly data on 10 Be and 7 Be isotopes covering the periods 1983-2000 and 1975-2006 respectively, that show, for the first time, coherent variations reflecting both atmospheric and production effects. Our data indicate intrusion of stratosphere/upper troposphere air masses that can modulate the isotopes production signal, and may induce relative peaks in the natural 10 Be archives (i.e., ice and sediment). The atmospheric impact on the Be-isotopes can disturb the production signals and consequently the estimate of past solar activity magnitude. Citation: Aldahan, A., J. Hedfors, G. Possnert, A. Kulan, A.-M. Berggren, and C. Soderstrom (2008), Atmospheric impact on beryllium isotopes as solar activity proxy, Geophys. Res. Lett., 35, L21812, doi: 10.1029/2008GL035189.
|
|
| 2. |
- Hedfors, Jim, et al.
(författare)
-
Clouds and Be-7: Perusing connections between cosmic rays and climate
- 2006
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:D2, s. D02208-
-
Tidskriftsartikel (refereegranskat)abstract
- [1] Time series data on Be-7, precipitation, temperature, and satellite imagery of cloud cover over Scandinavia, together with cosmic ray and sunspot activity, were used to elucidate the relationship between cosmic rays and clouds, and ultimately climate change. The results indicate a coherent negative correlation between total cloud cover and Be-7 on intraseasonal, seasonal, and decadal scales. Although the reasons behind this correlation are unclear, a full-scale implication of this feature is in the possible use of Be-7 and Be-10 records for proxy paleo-reconstruction of total cloud cover. This is a strongly needed, but generally difficult to quantify parameter in climate models.
|
|
| 3. |
- Kulan, Abdulhadi, 1962-
(författare)
-
Atmospheric Production and Transport of Cosmogenic 7Be and 10Be
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the atmospheric distribution of the cosmogenic isotopes 7Be (half-life 53 days) and 10Be (half-life 1.51 million years) as well as the anthropogenic isotope 137Cs (half-life 30 years) in aerosols and precipitation. Samples covering continuous or selected parts of the period 1972-2005 in Sweden and Europe are evaluated with respect to production, air mass transport and fallout processes. Such information is valuable in assessing the potential of these isotopes as indicators of air mass mixing and solar modulation factors that affect climate change. The results of 7Be and 10Be show seasonal variability and an 11-year cyclic pattern which is anti-correlated with the solar activity. Variations in seasonal trends of 7Be and 137Cs in aerosols during the post- and pre-Chernobyl period reflect tropospheric influence from 137Cs-heavily contaminated regions. A clear latitude dependence is observed in our beryllium isotope data where highest fallout is found in mid-latitudes compared to high and low latitude regions in the Northern hemisphere. This pattern reflects the general air mass circulation in the troposphere. However, stratospheric air mass influence was also identified in mainly single events and through tropopause folding during spring-summer seasons. The ratio of 10Be/7Be is used to estimate effects of air mass transport on production signal. The results show ratios between 1 and 3, much higher than the theoretically predicted value (0.6) in the atmosphere, which suggests contribution from 7Be-depleted (old) air masses. The relationship between monthly 7Be atmospheric activity and Total Fractional Cloud Cover (TFCC), collected from satellite imagery, over Sweden for the years (1991-2000) indicates a negative seasonal correlation. This observation can be related to depletion of aerosol from the atmosphere due to trapping in clouds.
|
|
| 4. |
- Kulan, Abdulhadi, et al.
(författare)
-
Distribution of 7Be in surface air of Europe
- 2006
-
Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 40:21, s. 3855-3868
-
Tidskriftsartikel (refereegranskat)abstract
- This study deals with long-term (span over three decades, 1972-2003) distribution of the cosmogenic isotope Be-7 in surface air at 5 stations in Europe, extending from latitude 47 degrees N to 68 degrees N. The results suggest annual variability in all the data sets as well as a decrease in average Be-7 activity with increasing latitude. Furthermore, a 9-10-year cyclical pattern is observed in the Be-7 distribution, which is anticorrelated with the solar activity cycle. Our data also indicate a dynamic range of Be-7 activity for each solar cycle and phase (maximum or minimum) which is higher at the middle compared to high-latitude regions. Additionally, about 10-20% relative deviation is observed in Be-7 activity during solar maxima and minima compared to the total average Be-7. This feature indicates that some deviation in the worldwide Be-7 activity data may relate to their acquisition, with respect to which part of a solar cycle they have been collected in (time span) and at which latitudinal spread. Estimate of Be-7 flux onto European surface boundary layer vary from 0.4 to 0.9 x 10(10) atoms m(-2) yr(-1) which is strongly latitude dependent and our average value is comparable to the similar to 0.7-0.8 x 10(10) atoms m(-2) yr(-1) across ocean and land.
|
|
| 5. |
- Kulan, Abdulhadi
(författare)
-
Seasonal Be-7 and Cs-137 activities in surface air before and after the Chernobyl event
- 2006
-
Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 0265-931X .- 1879-1700. ; 90:2, s. 140-150
-
Tidskriftsartikel (refereegranskat)abstract
- Seasonal fluctuations of cosmogenic Be-7 (T-1/2=53.4 days) and anthropogenic Cs-137 (T-1/2 = 30 years) activities in surface air (aerosols) have been extracted from a long data record (1972-2000) at high latitude (56 degrees N-68 degrees N, Sweden). Normalization to weekly average values was used to control long-term trends so that cyclical trends could be investigated. Enhanced Be-7 activity was observed in spring and summer seasons and likely relates to the seasonal thinning of the tropopause. Variations in the Cs-137 activity record seem to reflect how the isotope was injected in the atmosphere (stratospheric from bomb tests and tropospheric from the Chernobyl accident) and subsequent transport mechanisms. Accordingly, until 1986, the surface air Cs-137 activity was strongly related to nuclear weapons test fallout and exhibits temporal fluctuations resembling the Be-7. Conversely, since 1986 the Chernobyl-produced Cs-137 dominates the long-term record that shows annual cycles that are strongly controlled by atmospheric boundary layer conditions. Additionally, short-term data within the post-Chernobyl period suggest subtle intrusion of air masses rich in (CS)-C-137 that may occur throughout the year, and differences resulting from spatial occurrence at these latitudes. This is an important observation that may have to do with year-to-year variation and calls for caution when interpreting short-term data records.
|
|
