Abstract
The concentration of 7 Be at near surface air has been determined over 2009, a year of a deep solar minimum, in the region of Thessaloniki, Greece at 40 ◦ 62 � N, 22 ◦ 95 � E. In geomagnetic latitudes over 40 ◦ N, the elevation of the tropopause during the warm summer months and the vertical exchange of air masses within the troposphere cause greater mixture of the air masses resulting in higher concentration levels for 7 Be in surface air. The positive correlation between the monthly activity concentration of 7 Be and the tropopause height (0.94, p< 0.0001), and also between 7 Be concentration and the temperature T ( ◦ C) (R =0 .97, p< 0.001), confirm that the increased rate of vertical transport within the troposphere, especially during warmer summer months, has as a result the descent to surface of air masses enriched in 7 Be. However, the 7 Be concentration levels in near surface air are not expected to respond immediately to the change of elevation of the tropopause. It was found that there’s a time lag of ∼ 3 days between the change in the daily surface concentrations of 7 Be the change in the elevation of the tropopause. ∗ E-mail: anta@physics.auth.gr
Highlights
IntroductionIts flux on the Earth’s surface varies with the 11-year solar cycle and has a latitudinal dependence with higher values around the magnetic poles and lower values in the equatorial region
Beryllium-7 (t1/2 = 53.3 d) is a cosmic ray produced radionuclide, which is formed in the upper troposphere and lower stratosphere by spallation reactions of light atmospheric nuclei
In geomagnetic latitudes over 40◦N, the elevation of the tropopause during the warm summer months and the vertical exchange of air masses within the troposphere cause greater mixture of the air masses resulting in higher concentration levels for 7Be in surface air
Summary
Its flux on the Earth’s surface varies with the 11-year solar cycle and has a latitudinal dependence with higher values around the magnetic poles and lower values in the equatorial region. The cosmic ray flux and, the production rate of cosmogenic nuclides depends on the altitude. The combined effects of high 7Be production rates in the stratosphere (about 70%; [2]) and the relatively rapid removal of aerosol-associated species from the troposphere, produce stratospheric 7Be concentrations about an order of magnitude higher than those just below the tropopause [3]. The concentration of 7Be in the troposphere and near the ground level show variations, which are connected with exchange of air between the stratosphere and the troposphere in situation of tropopause folding events
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