SOLAR-CYCLE AND INTERPLANETARY HYDROGEN

The response of the interplanetary hydrogen gas to the solar cycle var iations in the solar radiation field and in the solar wind is studied. The solar cycle in the radiation field also affects the photoionizati on rate and modifies the radiation pressure force. The solar wind, whi ch is the main ionizing agent for hydrogen, has a strong solar cycle v ariation. We have calculated the density and velocity distributions of the interplanetary hydrogen gas including the time-dependent forces a nd ionizations. The calculation is carried out by the Monte Carlo simu lation. The time-dependent solution shows the alternation of the trave lling density waves and the depletion regions in the downwind side of the Sun. The time-dependent features are enhanced if the initial tempe rature of the incoming gas is low. In the case of the Sun the high tem perature of the interplanetary gas reduces the magnitudes of the time- dependent structures but the variations are still considerable. The ob served features in the time-dependent problem are related to the stati onary state solution which is possible to solve analytically.