On the method of the GCR partial intensities related to the main physical processes of solar modulation

Abstract

Abstract. We discuss in more details the earlier suggested method to decompose the calculated GCR intensity into the partial intensities connected with the main physical processes (the diffusion, convection, adiabatic cooling and magnetic drift) of the solar modulation. The expressions for the partial intensities connected with the convection and adiabatic cooling are improved and some results are illustrated. IntroductionThis work deals with some additional calculations that can be made in the course of the usual numerical solution of the boundary problem for the GCR intensity. The aim of these calculations is to improve our understanding of behavior of this intensity in the heliosphere.But first, why are we not fully satisfied with the conventional approach and look for some additional means? Of course, all physics of modeling the GCR modulation lies in the Transport Partial differential Equation (TPE) with the boundary and "initial" conditions for the intensity and in the models of the TPE coefficients used. So one solves the boundary problem, compares the results with the observations and makes the conclusions about the degree of understanding of the modulation process. However, observations of the GCR intensity and heliospheric characteristics are very incomplete; besides, even in the simplest case the calculated GCR differential intensity J(⃗ r 0 , T 0 , t 0 ) for the position ⃗ r 0 , energy T 0 and time t 0 is the result of complex interplay between several main physical processes (the diffusion, convection, drift, adiabatic cooling) for all higher energies (T > T 0 ) and in previous moments (t < t 0 ) in the whole heliosphere. And the details of this interplay are still unrevealed in the calculations, only its result. But to understand this interplay, in particular, the contribution of different processes to the calculated intensity, is very interesting and important.In [1, 2] we suggested the method to decompose the calculated GCR intensity into the partial intensities connected with the main physical processes. In [3] the method was applied to understand the mechanisms forming the time profiles of the GCR intensity near the Earth during the last three periods of low solar activity. In this paper, first, we shall briefly discuss the usual process of modeling the GCR intensity and specify which additional calculations could be made and how they can be used for our purpose. Second, the expressions used earlier for the partial intensities connected with the convection and adiabatic cooling will be improved. Then some results will be illustrated and discussed.

On the causes and mechanisms of the long-term variations in the GCR characteristics

“…On the causes and mechanisms of the variations in the GCR characteristics M. Krainev full calculated intensity [17,20].…”

“…In more details the method is described in [20], where it is also demonstrated how it can be used for studying the mechanisms of the GCR intensity modulation and the heliospheric structure during the solar minima with opposite HMF polarities (A > 0, A < 0) and without drift effects (A = 0).…”

“…This difference in the intensity gradients can be very significant and so the diffusion, drift and convection of the particles, that is all the processes depending on the gradients, carry out differently in each of the runs. On the other hand, the decomposition of the calculated GCR intensity into the partial intensities connected with the main physical processes in [17,18,20] is carried out in the run with all the modulating factors changing in time simultaneously, not disturbing the overall distribution of the gradients and hence the modulating processes. Probably, it is one of the causes of different results on the relative contribution of the drift and diffusion to the GCR intensity near the Earth during the unusual solar minimum 23/24 which were obtained in [30] and [18].…”

“…According to [30] the relative contribution of the drift and diffusion is approximately the same, while in [18] the drift partial intensity is always much smaller than the diffusion partial intensity the latter being almost compensated by the large negative partial intensity connected with the adiabatic energy losses. It should be said that the results of [18] strongly depend on the models used (too simple and outdated in [12,18,17,20]) and there are unresolved questions in the method of partial intensities [17,20]. However, what we are looking for is the numerical instrument, which can be applied to any model.…”

“…The drifts reduce modulation for both A > 0 and A < 0 periods, since drifts assist GCR particles to penetrate into the inner heliosphere faster in both polarity cases (either along the pole or at the HCS) [14,33,32]. Another picture arising from the consideration of the energy dependence of the gradients and the partial GCR intensities in the whole heliosphere [20], is that the changes in the intensity distribution start at the highest energy in the outer heliosphere and accumulate with decreasing energy and radial distance. The main result is the change of the intensity gradients which influences the diffusion and other fluxes in such a way that the GCR intensity increases for both HMF polarities.…”