Change in the rigidity dependence of the galactic cosmic ray modulation in 2008–2009

Observations of charged particle fluxes in the stratosphere of the polar regions represent the cosmic rays variations with energy above 100 MeV. At the end of 2009 these fluxes reached the highest level for the time of observations from mid 1957 and were by 17% higher than the previous extremum value of May 1965. In the mean time the ground-based neutron monitors showed the remarkably less count rate enhancement. These results argue for the significant change in the energy spectrum of incoming particles in 2008–2009 in the energy range of ∼100–1500 MeV/n.     

Long-term (50 years) measurements of cosmic ray fluxes in the atmosphere

Since the middle of 1957 till present time the group of researchers of P.N. Lebedev Physical Institute of the Russian Academy of Sciences has carried out the regular balloon borne measurements of charged particle fluxes in the atmosphere. The measurements are performed at polar (northern and southern) and middle latitudes and cover the interval of heights from the ground level up to 30–35 km. Standard detectors of particles (gas-discharged counters) have been used. More than 80,000 measurements of cosmic ray fluxes in the atmosphere have been performed to the present time. In the data analysis the geomagnetic field and the Earth’s atmosphere are used as cosmic ray spectrometers.     

Cosmic Ray Induced Ion Production in the Atmosphere

An overview is presented of basic results and recent developments in the field of cosmic ray induced ionisation in the atmosphere, including a general introduction to the mechanism of cosmic ray induced ion production. We summarize the results of direct and indirect measurements of the atmospheric ionisation with special emphasis to long-term variations. Models describing the ion production in the atmosphere are also overviewed together with detailed results of the full Monte-Carlo simulation of a cosmic ray induced atmospheric cascade. Finally, conclusions are drawn on the present state and further perspectives of measuring and modeling cosmic ray induced ionisation in the terrestrial atmosphere.     

On The Stratospheric Measurements of Cosmic Rays

The results of measurements of cosmic-ray intensity in the Earth's atmosphere from 1957 up to now are presented. Balloon launchings performed several times a week at northern and southern polar latitudes as well as at midlatitudes yield a homogeneous data series for the study of the spatial distribution and temporal changes in the cosmic-ray intensity. The 11- and 22-year solar modulation, north-south asymmetry, energy hysteresis and a long-term trend in the cosmic-ray intensity are discussed. The fluxes and energy spectra of protons with energy > 100 MeV for about 100 solar energetic particle events in 1958-1992 are given. The role of cosmic rays in terrestrial atmospheric processes is briefly discussed.     

The heliospheric magnetic field and its relation to the temperature,density, and velocity of solar plasma: Experimental evidence

Using daily and hourly data on solar plasma parameters at the Ulysses spacecraft orbit and at 1 AU it is demonstrated that there is a simple relationship between plasma temperature and density with the heliospheric magnetic field (HMF). A mathematical expression connecting HMF with plasma temperature and density is suggested. Correlation coefficients and regression equations for measured and calculated magnetic fields are presented for the 1990–2009 period according to Ulysses spacecraft data and for 2003–2010 at 1 AU (OMNI database). The roles played by density, temperature, and high-speed solar wind streams in forming the magnetic-field peaks are demonstrated using hourly data of OMNI2 and Ulysses.     

Galactic cosmic rays and parameters of the interplanetary medium near solar activity minima

The time behavior of intensity of cosmic rays with relatively low (~1–6 GeV) and high (>10 GeV) energies are considered together with characteristics influencing the modulation of cosmic rays in the heliosphere. The periods under study are close to solar activity minima in cycles 21/22, 22/23, and 23/24. Diffusion and convection in small-scale magnetic fields of the heliosphere are demonstrated to play some role only at sufficiently weak disturbances of the field (B/δB > 1.3). In this case, a negative correlation is observed between B/δB and a tilt of the surface of the heliospheric current sheet. The analysis of characteristics of the interplanetary medium in periods of solar activity minima shows that the energy anomaly of cosmic rays in the minimum of cycles 23/24 is caused by deficit of high energy particles rather than by an excess of particles of relatively small energies.     

On the relationship between quasi-biennial variations of solar activity,the heliospheric magnetic field and cosmic rays

Quasi-biennial oscillations (QBO) of solar activity (T ≈ 1–4 years) are considered to be a variation of basic solar activity, associated with the solar dynamo process. They are transferred into interplanetary space by the open magnetic flux of the Sun, generating QBO in the intensity of cosmic rays (CR). This paper discusses the observational characteristics of QBO in CR and their relationship with QBO on the Sun and in the interplanetary medium. The delay time of QBO in CR relative to the solar and heliospheric magnetic field suggests that the formation of QBO in the open magnetic flux of the Sun occurs within 3–5 months. The paper considers the question of the prominent periodicity of CR (T = 1.6 years) that has prevailed in CR and in the heliospheric magnetic field for more than 10 years but was not stable over 60 years of observations. Distinctions in the characteristics of QBO and long-term variations of CR suggest features of the mechanism of their formation.