Effects of solar activity and galactic cosmic ray cycles on the modulation of the annual average temperature at two sites in southern Brazil

Abstract

Quasi-periodic variations in solar activity and galactic cosmic rays (GCRs) on decadal and bidecadal timescales have been suggested as a climate forcing mechanism for many regions on Earth. One of these regions is southern Brazil, where the lowest values during the last century were observed for the total geomagnetic field intensity at the Earth's surface. These low values are due to the passage of the center of the South Atlantic Magnetic Anomaly (SAMA), which crosses the Brazilian territory from east to west following a latitude of ∼ 26 • . In areas with low geomagnetic intensity, such as the SAMA, the incidence of GCRs is increased. Consequently, possible climatic effects related to the GCRs tend to be maximized in this region. In this work, we investigate the relationship between the ∼ 11year and ∼ 22-year cycles that are related to solar activity and GCRs and the annual average temperature recorded between 1936 and 2014 at two weather stations, both located near a latitude of 26 • S but at different longitudes. The first of these stations (Torres -TOR) is located in the coastal region, and the other (Iraí -IRA) is located in the interior, around 450 km from the Atlantic Ocean. Sunspot data and the solar modulation potential for cosmic rays were used as proxies for the solar activity and the GCRs, respectively. Our investigation of the influence of decadal and bidecadal cycles in temperature data was carried out using the wavelet transform coherence (WTC) spectrum. The results indicate that periodicities of 11 years may have continuously modulated the climate at TOR via a nonlinear mechanism, while at IRA, the effects of this 11-year modulation period were intermittent. Four temperature maxima, separated by around 20 years, were detected in the same years at both weather stations. These temperature maxima are almost coincident with the maxima of the odd solar cycles. Furthermore, these maxima occur after transitions from even to odd solar cycles, that is, after some years of intense GCR flux. The obtained results offer indirect mathematical evidence that solar activity and GCR variations contributed to climatic changes in southern Brazil during the last century. A comparison of the results obtained for the two weather stations indicates that the SAMA also contributes indirectly to these temperature variations. The contribution of other mechanisms also related to solar activity cannot be excluded.

Multi-point galactic cosmic ray measurements between 1 and 4.5 AU over a full solar cycle

“…After that period (green points and black fit), the count rate variation and the ratio are in very good agreement with the expectation of a positive radial gradient of about 2.9 % AU −1 (e.g. Vos and Potgieter, 2016;Gieseler and Heber, 2016).…”

“…Negative latitudinal gradients have been reported (e.g. Potgieter et al, 2001) but only for a fraction of 1 % •−1 (Gieseler and Heber, 2016). During the comet phase, Rosetta moved from around −7.5 to +7.5 • heliolatitude, which could not account for the decrease in GCR fluxes.…”

“…The GCR intensity therefore varies with the solar wind velocity, the magnitude of the interplanetary magnetic field, solar activity, the heliospheric current sheet tilt angle and the solar polarity change. The study of the effects of GCRs on the Earth's atmosphere and climate is also a fascinating field of research (e.g Carslaw et al, 2002;Pierce, 2017;Frigo et al, 2018).…”

New perspectives in the study of the Earth’s magnetic field and climate connection: The use of transfer entropy

“…Recent works (e.g. [ 31 , 60 , 61 , 62 , 63 ]) have found interesting correlations between solar and galactic cosmic rays periodic variations and climatic (such as temperature and rainfall) variations in the region where the SAA is located. The entrance of galactic cosmic rays at the atmosphere depends both solar and Earth’s magnetic fields, hence these correlations could also be influenced by a factor depending on the low geomagnetic intensity due to the SAA presence in the region and its continuous increasing for the last centuries.…”

On the slow-time geomagnetic field modulation of cosmic rays

“…The negative health implication of some cosmic ray phenomena (e.g ground level enhancement) for airplane crew members is well expected and has been reported by some authors (Matthia et al, 2009;Mishev et al, 2015), and most recently a simulation by Kataoka et al (2015) has suggested that solar energetic particle events without ground level enhancements could even pose significant treats to humans travelling by air. Most recently, Frigo et al (2018) investigated the effect of cosmic rays on climate. They observed that temperature maxima were almost coincident with the maxima of the solar cycle years.…”