[19] The decay phase of particle fluxes carries significant information on the interplanetary medium. The total amount of solar events detected by the instrument CPME on board IMP 8 during almost three solar cycles allows us to consider the dependence of the characteristic decay time on different factors. The performed analysis has shown the following:
[20] 1. In a significant amount of cases (up to 50%) when V remains constant during the whole decay, τ is described satisfactorily by the formula obtained under assumption, that convective transport and adiabatic cooling prevail over diffusion.
[21] 2. The distribution of the exponent n in the dependence τ(E) = CE-n makes it possible to split all solar events in energetic particles into three groups: (1) τ does not depend on the proton energy ( -0.1 < n < 0.1; 54 events); (2) τ diminishes with the proton energy ( n > 0.1; 72 events); and (3) relatively small group of events with τ increasing with the growth of proton energy ( n < -0.1; 21 events). In the first case the proton spectrum does not change in time during the event, in the second case the spectrum becomes softer, and in the third case it becomes harder. Thus, in the prevailing amount of cases, the decay rate τ either does not depend on particle energy or decreases with an energy growth. This result manifests the action of the diffusion mechanism of propagation along with convection and adiabatic cooling. The existence of events with spectrum becoming harder during the decay phase should become the object of further investigation.
[22] 3. The exponent n in the formula τ(E) = CE-n statistically does not depend on the heliolongitude of a flare, i.e., the source of particles on the Sun. Daibog et al. [2006] have obtained earlier the result confirming that the characteristic time of proton flux decay τ (for events associated with flares occurring eastward with respect to the foot point of the observer's magnetic field line) is statistically independent of the heliolongitude of the parent flare. This testifies that statistically the conditions of particle propagation up to 1 AU do not depend on heliolongitude of a flare with respect to the point of observation. Hence, there exist periods when the total amount of values of IS parameters in the inner heliosphere makes IS homogeneous and quasi-stationary over significant angular intervals.
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