[1] The differential energy spectrum of galactic cosmic rays in the vicinity of the Earth can be parameterized by the so-called force field model which has only one parameter, the modulation potential f, for a given local interstellar spectrum. Here we present the series of monthly values of the modulation potential f since February 1951, reconstructed using the data from the worldwide neutron monitor network and calibrated with precise balloon and space-borne direct measurements of cosmic ray energy spectrum. This work provides a long series of a parameter allowing for a quantitative estimate of the average monthly differential energy spectrum of cosmic rays near the Earth. A comparison with other occasional direct measurements of cosmic ray spectra confirms the reliability of the present reconstruction. The results can be applied in studies of long-term solarterrestrial relations and the global evolution of the heliosphere.

[1] We present a quasi-steady two-dimensional (axisymmetric) model of the heliospheric transport of galactic cosmic rays. The model is based on stochastic simulation techniques and includes all the modulation mechanisms that cosmic rays experience in the heliosphere: convection, adiabatic cooling, diffusion, and drifts. A special emphasis is given to the cosmic ray transport in the vicinity of the heliospheric current sheet (HCS), and a new method to calculate the wavy current sheet drift is presented. We study cosmic ray modulation in different solar modulation conditions and levels of waviness of the current sheet. We discuss changes in the cosmic ray spectrum and the dominant streaming patterns of cosmic rays in the heliosphere for different solar polarities and HCS tilt angles.Citation: Alanko-Huotari, K., I. G. Usoskin, K. Mursula, and G. A. Kovaltsov (2007), Stochastic simulation of cosmic ray modulation including a wavy heliospheric current sheet,

No abstract

We study empirical relations between the modulation of galactic cosmic rays quantified in terms of the modulation potential and the following global heliospheric parameters: the open solar magnetic flux, the tilt angle of the heliospheric current sheet, and the polarity of the heliospheric magnetic field. We show that a combination of these parameters explains the majority of the modulation potential variations during the neutron monitor era 1951 -2005. Two empirical models are discussed: a quasi-linear model and a model assuming a power-law relation between the modulation potential and the magnetic flux. Both models describe the data fairly well. These empirical models provide a simple tool for evaluating various cosmic-ray related effects on different time scales. The models can be extended backwards in time or used for predictions, if the corresponding global heliospheric variables can be independently estimated.

Some airborne hyperspectral sensors (e.g. AISA) can measure spectral downwelling irradiance using an additional cosine sensor mounted on a roof of an aircraft. The downwelling irradiance data, however, are rarely used for any atmospheric correction or compensation of different sun-sensor geometry, partly because they are sensitive towards continuous motion of the airborne platform. The airborne hyperspectral system AISA Eagle (Specim, Ltd., Finland), combined with the Fiber Optic Downwelling Irradiance Sensor (FODIS), were used for ground-based outdoor static measurements. The FODIS sensor was tilted into various zenith and azimuth angles. The data analysis revealed high sensitivity of the raw recorded FODIS signal towards different angular position. Simple cosine corrections reduced variation in the recorded FODIS signal. The variability (standard deviation of all measurements) decreased by 88% after the cosine correction was applied.

No abstract