LIMITING REGIMES OF THE SOLAR WIND/COMETARY

OUTFLOW INTERACTION AT LOW COMET GAS

PRODUCTIONSM.G. Lebedev

Moscow State University

The relevant parameters of the interaction are as follows:

Q, W, μ,

τ;

and the parameters characterizing other physical and chemical processes, such as charge exchange, ion-neutral friction, etc.

It is convenient to solve the interaction problem using dimensionless variables and dimensionless governing parameters, which can be introduced in different fashion

,,,, BnV

We will determine the scale length as follows:

Then the problem is governed by the following dimensionless parameters:

and, if the magnetic field is taken into account,

The parameter ζ is the rate of the solar wind mass loading by cometary ions via gas outflow from the comet surface (parameter Q) and their subsequent photoionization (parameter τ)

WVn

QL

4

V

W

WV

Q

W

L

,

4 22

,2V

B

The characteristic values of the relevant parameters for )400/1(km/s1 km/s,400 WV

Case Q, s-1 n, cm-3 τ, s L zeta

CG(a) 1 * 1024 0.9 1.1 * 107 0.34 3 * 10-8

CG(b) 8 * 1025 1.4 7.3 * 106 27 3.6 * 10-6

CG(c) 8 * 1026 2.5 4 * 106 270 7 * 10-5

CG(d) 5 * 1027 6.0 1.7 * 106 1660 10-3

GS 8 * 1027 6 106 3560 3.6 * 10-3

Halley 5 * 1029 6 106 0.4 * 106 0.4

HB 1 * 1031 6 106 7.3 * 106 7.3

Since the gas production of the CG comet is very low, it is believed that only in cases c and d the gasdynamic interaction model will be adequate, whereas at greater spacings between the CG comet and the Sun hybrid and kinetic models should be invoked to accurately describe the interaction process.

The purpose of this study is to establish certain limiting laws governing, as the main dimensionless parameter zeta vanishes and to determine a zeta interval on which these laws hold true

The results of numerical simulations show that in the dimensionless variables presented above the dependence of the cometocentric bow shock stand-off distance on the solar-wind mass-loading rate is as follows:

10

Thus, we obtain

The dependence derived by Biermann, Brosowski, and Schmidt in their pioneer study (1967) is similar in form:

The shape of the bow shock between the comet-Sun axis and the terminator is well approximated by the paraboloid

nWV

Qkk

L BSBS

4,8.2:0 0,

0,

]1)ˆˆ[(40,

cBS unWV

Q

8.2,07.0, 0

2

0

LL

y

L

x

Zeta-dependence of the cometocentric distances of the contact discontinuity and the inner shock at the comet-Sun axis for different cometary-outflow—to—solar-wind velocity

ratios

The solar wind mass densities of nucleons (a) and protons (c) and Mach number (b) (a) (b) (c)

Profiles of the proton, water-group-ion, and nucleon densities along the comet-Sun axis

IMF effect on the parameter distributions for the CG comet in positions c and d