Galactic cosmic ray intensity variations at a high latitude sea level site 1937–1994

Abstract

Abstract. We have created an extended cosmic ray data string (1937 -1994) by combining data obtained with ion chambers at Cheltenham/Fredericksburg (1937 -1972) and Yakutsk (1953Yakutsk ( -1994. Both represent high-latitude, sea level sites, with an atmospheric cutoff of about 4 GV. Their common median rigidity of response to galactic cosmic ray spectrum is 67 GV. This data string represents the longest continuous cosmic ray intensity variations record yet. Therefore it is useful for the cosmic ray modulation studies over a longer time period. We show that there is no striking quantitative correspondence between the amplitudes of solar activity cycles and cosmic ray modulation over six cycles. However, an inverse correlation is apparent between the two. Moreover, the results on the durations of the two are ambiguous. Flat-topped recovery pattern predicted for even cycles (A > 0), at lower rigidities, is not observed in the ion chamber data. We speculate that three solar activity cycle quasi-periodicity may be present in the extended data string. Its origin is not identified yet. The quasiperiodicity is shown to exist also in the planetary index Ap data. As such, it may represent a characteristic feature of the solar wind source region on the Sun as yet unexplored. The odd cycles, with a negative polarity in the solar northern hemisphere, yield a better linear correlation between galactic cosmic ray intensity decrease and Ap than even cycles and A > 0 epochs.

Long‐term variations in the magnetic fields of the Sun and the heliosphere: Their origin, effects, and implications

“…The level of activity was quantified by Mayaud [ 1972], who developed the aa index, using the range of the fluctuations of the horizontal component of the field observed in 3-hour intervals at these stations. The aa index was designed to be very well correlated with other planetary indices of geomagnetic activity; for example, the variations in annual means of aa and the Ap index are almost identical since the start of the Ap data series in 1932 [Mayaud, 1972;Ahluwalia, 1997]. This is true for both the solar cycle and the longer-term variations.…”

Cosmic ray detector response to transient solar modulation: Forbush decreases

“…The reader may note that underground MTs are much more sensitive to rigidity-dependent changes in modulation than are NMs [Ahluwalia and Ericksen, 1971]. As such, MT data are very useful for transient solar modulation studies, such as the Forbush decreases; in this case, one does not have to worry about the instrumental drifts [Ahluwalia, 1997]. In Table 3, we quote some R m values given by Fujimoto et al for the underground MT data used in this paper.…”

“…[2] Over the past seven decades, a phenomenological understanding of galactic cosmic ray (GCR) intensity modulation, over a range of time and spatial scales and rigidities (R), has been arrived at based on the analyses of data from the global network of ion chambers [Ahluwalia, 1993[Ahluwalia, , 1994[Ahluwalia, , 1996[Ahluwalia, , 1997[Ahluwalia, , 2005, underground muon telescopes (MTs) [Regener et al, 1970], neutron monitors (NMs), and detectors on spacecrafts. These data contain information pertaining to GCR transport parameters in the tangled interplanetary magnetic field (IMF) that permeates the heliosphere.…”

Galactic cosmic ray diurnal modulation, interplanetary magnetic field intensity and the planetary index Ap

“…In general there is a correlation between the long term variations of Ap and the observed GCR modulation [Ahluwalia, 1997[Ahluwalia, , 1998, and references therein]. In an earlier analysis [Ahluwalia, 1992] …”