S. A. Zaitseva, S. N. Akhremtchik, M. I. Pudovkin, and Ya. V. Galtsova
Physics Research Institute, St.Petersburg State University, St. Petersburg, Russia
B. P. Besser
Space Research Institute, Austrian Academy of Sciences, Austria
R. P. Rijnbeek
Space Science Center, University of Sussex, Brighton, UK
The idea on the existence of a close relationship of solar activity with the state of the lower atmosphere, though being under discussion, is accepted by many geophysicists. During the last 30 years, numerous evidences were obtained in favor of that hypothesis [Bauer, 1982; Brown and John, 1979; Bucha and Bucha, 1998; Donarummo et al., 2002; Hoyt and Schatten, 1997; Hurrell, 1996; Kelley, 1977; Kondratyev and Nikolsky, 1983; Ram and Stolz, 1999; Schuurmans and Oort 1969; Svensmark and Friis-Christensen, 1997; Tinsley and Deen, 1991; Tinsley and Heelis, 1993; Tinsley et al., 1989; Veretenenko and Pudovkin, 1995, 1997, 1999].
Physical mechanism of this relationship was proposed by Tinsley et al. . According to their hypothesis, the connection between the solar activity and the state of the lower atmosphere is realized by means of cosmic rays, the flux of which is modulated by the varying magnetic field of the solar wind. In turn, variations of the cosmic ray intensity cause changes in the state of cloudiness and trigger some internal atmospheric processes associated with the release of the energy accumulated in some form, e.g., as the latent heat of water vapours.
On the other hand, the mechanism proposed by M. I. Pudovkin and colleagues supposes that variations of the cosmic ray flux and, possibly, of the solar Roentgen and UV radiation cause changes of the atmospheric transmittance and the state of cloudiness. As a result, the direct solar radiation input into the lower atmosphere also exhibits significant variations. During Forbush-decreases of Galactic Cosmic Rays (GCR) the solar energy input increases, and the lower atmosphere at high latitudes is heated, and during Solar Proton Events (SPE) the atmospheric transmittance decreases, and the lower atmosphere temperature decreases also [Pudovkin et al., 1995a, 1995b].
However, distinct variations of the cosmic ray flux intensity are observed not only during short-term solar wind disturbances but also in the course of solar cycles. Thus, one may expect existence of corresponding long-term variations of cloudiness, atmosphere transmittance, air temperature, and, as a result, of the dynamics of the lower atmosphere [Pudovkin and Babushkina, 1992b; Pudovkin and Morozova, 1997].
In this paper, we consider long-term variations of the lower atmosphere parameters and their possible connection to the solar activity. Special attention is paid to the search of physical agents responsible for that connection.
For the analysis, data are used on the air temperature in St. Petersburg ( j=60 o N, l=30 o E), Stockholm ( j=59 o N, l=18 o E), English Midlands ( j=50 o N, l=2 o W) (ftp://ftp.cru.uea.ac.uk/people/mikehulme/outgoing/misce\-llaneous/cet.dat), and Salzburg ( j=48 o N, l=13 o E) (Jahrbücher der ZAMG, 1867-2000) for the last two centuries, solar activity indices (Wolf numbers), and North Atlantic Oscillation indices (http://www.cgd.ucar.edu/cas/climind/nao\_monthly.html).
The connection between NAO indices and the ground level air temperature in Salzburg (Austria) is less clear ( r=0.44), though it still exists.
Thus, the air temperature, at least in northwestern Europe, really is closely associated with variations of NAO indices. However, what is the cause of the NAO indice variations?
Figure 5b (bottom) shows variation of NAO indices for winter months of 1955-1957 years when the correlation between long-term variations of NAO and W is positive (see Figure 4). As is seen in Figure 5b, short-term increases of the solar activity on the years under consideration are associated, as in the case of long-term variations, with the increase of NAO indices.
Thus, the correlation between the long-term variations of NAO and W indices has the same sign as that for short-term variations of them on the same years. Correspondingly, the change of that sign cannot be explained by the phase shift of long-term variation and rather has some physical reasons, such as the state of the background lower atmosphere, or the characteristics of the solar radiation. In this connection, it is worth remembering that the value of NAO is defined as the difference of normalized sea level pressure between Azores ( j=40 o N) and Iceland ( j=65o ) and hence is determined by the state of the lower atmosphere in two significantly spaced Earth regions which may be influenced by different components of the solar radiation.
obtained from the multiple regression of data presented in Figures 3 and 6a. The curves given in Figure 6b illustrate a rather close agreement between the observed and calculated values of NAO: the coefficient of calculation between them equals 0.57 at the significance level 0.95. Thus, the variations of the NAO indices really are influenced by the variation of the solar energy input to the lower atmosphere at the boundaries of the latitudinal belt under study.
Naturally, there arises a question on the cause of the observed variations of the atmosphere's transmittance. To answer this question, in Table 1 we represent a fragment of a related table from Pudovkin and Veretenenko .
Table 1 presents the coefficients of partial correlation of values of dQ65 and dQ50 with the variation of the cosmic ray flux (Climax neutron monitor data), of the geomagnetic AE index and of the Kleczek flare index I fl ( Solar Geophysical Data, 1997); the values in parentheses show the significance level of the obtained coefficients of correlation.
Data presented in Table 1 show that variations of the solar energy input into the lower atmosphere at the both latitudinal belts are determined mainly by variations of two cosmophysical factors: of the cosmic ray intensity and of the solar flare index. However, influence of those factors is different at different latitudes: at high latitudes, the atmosphere transmittance is determined mainly by the cosmic ray flux intensity variations, while at lower latitudes, by solar flares. The latters may characterize intensity of the solar Roentgen and UV radiation responsible for the ozone content variation and hence for the atmosphere transparency at low latitudes [Haigh, 1996]. Thus, the observed apparently irregular variations of NAO indices really may be explained by non synchronous variations of the cosmic ray flux intensity, solar wave and corpuscular radiation.
Data presented above and their analysis allow us to arrive at the following conclusions.
This allows us to suppose that the observed relationship of the air temperature and NAO indices with the solar activity is not occasional and has some physical grounds.
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