Evolution and solar modulation of 7 Be during the solar cycle 23
- PDF / 665,127 Bytes
- 12 Pages / 595.276 x 790.866 pts Page_size
- 83 Downloads / 202 Views
Evolution and solar modulation of 7Be during the solar cycle 23 F. Pin˜ero-Garcı´a • M. A. Ferro-Garcı´a
Received: 18 July 2012 / Published online: 19 December 2012 Akade´miai Kiado´, Budapest, Hungary 2012
Abstract The modulation of 7Be-aerosols concentration due to solar activity during the cycle 23 is studied in the present research. For that purpose, was analyzed the differences in the long-term variation of geomagnetic and solar activity to assess the physical effects over the evolution of 7Be during the period 1996–2010. Furthermore, exploratory data analysis was applied to understand better the behavior of 7Be-aerosols in the surface atmosphere. This study shows that there is an inverse relationship among 7Be measured in the near ground air and solar activity. The modulation of 7Be-aerosols during the cycle 23 was divided in two steps. In the first stage, ascending phase, 1996–2002, the solar activity played an important role in the production rate of 7Be, r = -0.75. However, during the descending phase, 2002–2009, the role of the solar activity was secondary, r = -0.30, allowing that 7 Be-aerosols reached the maximum concentration, 9.33 mBq m-3 in August-09 when the solar activity was zero. Moreover, the remaining solar activity after the end of the ascending phase and the last important solar storm (December-06) caused the slowdown of 7Be production rate from 2001 to 2004 and the rupture of the seasonal behavior of 7Be in 2007, respectively. Finally, this research highlight the necessity to take into account the solar cycle phase, ascending or descending, to model studies of atmospheric process with 7Be as tracer since the contribution of the variables studied are so different in these stages.
F. Pin˜ero-Garcı´a M. A. Ferro-Garcı´a (&) Radiochemistry and Environmental Radiology Laboratory, Inorganic Chemistry Department, Faculty of Sciences, University of Granada, Av. Fuentenueva, 18071 Granada, Spain e-mail: [email protected]
Keywords 7Be Solar activity Solar cycle 23 Sunspot number Cosmic rays Geomagnetic index Atmospheric aerosols
Introduction 7
Be is a natural cosmogenic radionuclide, which is produced continuously in the atmosphere by spallation processes of the primary and secondary components of cosmic ray (protons and neutrons) with nuclei of light elements such as N, C and O atoms, according to the following reactions. 14 7 N
þ11 p !74 Be þ 242 He
14 7 N
þ10 n !74 Be þ83 Li
16 8 O
þ11 p !74 Be þ10 5 Be
16 8 O
þ11 p !74 Be þ73 Li þ32 He
16 8 O
þ10 n !74 Be þ10 4 Be
16 8 O
þ10 n !74 Be þ62 He þ42 He
12 6 C
þ11 p !74 Be þ63 Li
12 6 C
þ10 n !74 Be þ62 He
Its production rate varies considerably with altitude, with approximately 70 % of 7Be produced in the stratosphere, where cosmic-ray intensity is highest, and the remaining, 30 %, produced in the upper part of the troposphere. Soon after its production, 7Be become attached primarily to submicron sized aerosols and are transported to ground level and deposited with them. These submicron particles are composed mostly of su
Data Loading...
