The role of the inversion population in barium cloud ionization in the upper atmosphere

Atmospheric und Terrestrial

Journal of Printed in Great

Physics, Vol.

55, No.

1, pp. 123-124,

1993

0021-9169/93 55.00+ .Bll Pergamon Press Ltd

Bntain.

BRIEF REPORT The role of the inversion population in barium cloud ionization in the upper atmosphere E. I. GOLBRAIKH* and S. SH. NIKOLAISHVILI Institute of Applied Geophysics, Moscow. 129128, Russia (Received injnalform

1 June 1992)

28 August 1991; accepted

Abstract-The influence of the population of barium atoms on barium cloud ionization in the upper atmosphere is investigated. It is shown that the experimental values of the effective time for barium cloud ionization

is determined

by the metastable

3D states’ inversion

population.

One of the problems of modelling the barium cloud (BC) luminosity, dynamics and kinetics in the upper atmosphere (UA) is a discrepancy between the experimental (Q) and theoretical (7,) values of the ionization time constant. Experimental values of z0 are z 15-35 s (HALLINAN, 1988; RIEGER et al., 1970), and the theoretical Z, is z 50-70 s (DRAPATZ, 1972 ; GOLBRAIKH et al., 1990). The aim of our work is to investigate the influence of the initial BaI population (going out of the injector) on BC ionization in the UA. Optically thin BC spectroscopy in the UA is considered by GOLBRAIKH et al. (1990). A Boltzmann distribution was taken in this work for the BaI initial population, and it was found that, for an optically thin BC that was sunlit, the value t, z 66 s. However, usually artificial barium clouds are generated by chemical reactions of considerable energy. Because of this, the metal barium part turns into a vapour (ROSENBERGand BEST, 1971) and its initial population can differ from the Boltzmann distribution. The main method of barium ionization by sunlight is ionization from the metastable states, ‘D and 3D, the energies of which are 1.4 and 1.1 eV, respectively. It follows from this that metastable levels can be populated in the metal barium evaporation process. Calculation of the BC shows that the anomalous initial ‘D level population does not lead to much of a change of T, value. This result is due to the metastable ‘D resonant ‘pumping over’ to the ground state (‘S) through higher levels. As the 3D state does not have channel for this ‘pumping over’, the transition time to the ground state is therefore much more than the

ionization time from this state. In this way, the initial 3D metastable level population is the main influence on the speed of BC ionization. The dependence of z, on the initial population, y = N(3D)/N, (where NOD) is the concentration of barium atoms in the 3D state; N, is the total concentration in BC) is computed and is shown in Fig. 1. A value of T,, = 15-35 s found in experiments conforms to an initial population width y x 0.65-0.8 ; therefore, barium atoms can have an inversion population (to state ‘D) when leaving the injector.

* Permanent address : Physics Department, Ben-Gurion University of the Negev, Beer-Sheva 84100, Israel.

Fig. 1. The effective time constant for ionization of a barium cloud. The experimental values conform to y N 0.65-0.8.

70 60 3 .g

: ._ ti Q 5

50 40 30

0

0.2

0.4

0.6

0.6

1.0

Y

E. I. GOLBRAIKH and S. SH. NIKOLAISHVLI

124 Indirectly, firmed

our calculations

by the results

BEST (1971).

of the y value are con-

of the work of ROSENBERG and

It was shown

here that the anomalous

intensity

in the

observed

in the first 5 s after the injection.

osity conforms

wavelength

to the resonant

region

z 611 nm

transition

was

3D and the 3P state. If the population occurs in accordance luminosity experimental

between

method

the

in the region

In this way, perhaps,

This lumin-

data

of barium atoms

with the Boltzmann

distribution,

x 611 nm has small intensity. the Q values

are

closely

determined

connected

with

from the

of BC formation.

REFERENCES DRAPATZ S. W.

1972

GOLBRAIKHE. I., KOSAREVN. I., NICOLAISHVILYSH. S. and SHKEDOV I. M

1990

HALLINANT. G.

1988

RIEGERE., NEUSSH., LUTSR., MEYERB., HASERL., LODE H., STOCKER J. and HAERENDEL G. ROSENBERG N. W. and BE_ST G. T.

1970

1971

The radiative transfer problem

in freely expanding gaseous clouds and its application to barium cloud experiments. Planel. Space Sci. 20,663. Ionization of optically thin barium cloud. Geomagn. Aeron. 30, 350. Observed rate of ionization in space-charge release of barium in the ionosphere. J. geophys. Res. 93,8705. High altitude releases of barium vapour using a rocket. Ann. Geophys. 26,845. Chemistry of barium released at high altitudes. J. them. Phys. 75, 1417.