AGU 2000 spring Meeting,
Session SH31A-08, May 31, 2000, Wednesday, 8:30 a.m.,
Location: Hall D

Interstellar Hydrogen Atom Distribution Function in the Outer Heliosphere
Vlad Izmodenov (1,2) and Mike Gruntman (1)

(1) Department of Aerospace Engineering University of Southern California,  Los Angeles, CA 90089-1191, E-mails:,
(2) Moscow State University, Moscow, Russia


To explore the evolution (due to plasma-neutrals charge exchange coupling) of the interstellar atom velocity distribution in the heliospheric interface.


We use the Baranov-Malama model of the solar wind - LISM interaction to calculate the velocity distributions of the interstellar hydrogen atoms in the heliospheric interface.



We use the Monte-Carlo method with splitting trajectories (Malama, 1991) to calculate the velocity distribution function.


The calculated structure of the heliospheric interface is shown in Figure 1. Two shocks (BS and TS) and the heliopause (HP) divide the heliospheric interface in four (1,2,3,4) regions:

Figure 1

1 - the supersonic solar wind upstream the TS;
2 - the heliosheath - the region of the postshock (TS) solar wind plasma;
3 - disturbed LISM;
4 - undisturbed LISM.

Plasma has significantly different properties in these regions; Solar wind is disturbed upstream TS and interstellar plasma is disturbed upstream BS due to the charge exchange process.

We present below (fig. 3-8) the velocity distributions of H atoms in 12 points (1,2,...,12) shown in Figure 2.

Figure 2:


Figures 3-8 present velocity distributions of four (A,B,C,D) different atom populations.

In each figure below
A - original (primary) interstellar atoms;
B - secondary interstellar atoms created in region 3;
C - H atoms created in the heliosheath (region 2, Figure 1) by charge exchange with postshock solar wind protons;
D - H atoms created in the supersonic solar wind (region 1, Figure 1).

Figure 3:


Figure 4:

Figure 5:

Figure 6:

Figure 7:

Figure 8:


The velocity distribution of interstellar atoms is not Maxwe-llian anywhere in the heliosphere and the interface region. The charge exchange process has important kinetic consequences on the atom velocity distributions.


This work was partially supported by NASA Grant NAG5-6966,
Vlad Izmodenov has been supproted by NSF/NATO Fellowship GDE-9804533, INTAS-CNES cooperation Grant # 97512 and ISSI in Bern.