10: ESCAPE AND IONIZATION OF ATMOSPHERIC GASES

William H. Smyth

Atmospheric and Environmental Research, Inc.

840 Memorial Drive

Cambridge, Massachusetts 02139

December 1983

Interim Report for Period

April 15, 1983 - October 15, 1983

Prepared for

NASA Headquarters
TECHNICAL REPORT STANDARD TITLE PACE

1. Report No. 2. Government Accesvion No

4 Title ond Subtitle

Io: Escape and lonization

of Atmospheric Gases

7 Author(s)

William H. Smyth

9. Performing Organisation Nome and Address

Atmospheric and Environmental Research, Inc.

840 Memorial Drive

Cambrdige, Massachusetts 02139

12. Sponsoring Agency Nome ond Address

NASA Headquarters

Headquarters Contract Division

Washington, D.C. 20546

15. Supplementary Notes

3. Recipient's Cotolog No.

5. Report bate

December 1983

6. Performing Orgonitotion Code

8 Performing Orgoniiation Report No

10. Work Unit No.

11. Contract or Grant No.

NASU-ISm

13. Type of Report and Period Covered

Interim Report

April 15-October 15

1983

14. Sponsoring Agency Code

HWC-2

16. Abstract

Progress in obtaining a description for the partitioning of the

major ion densities throughout the torus is reported. This

description is required as input information for the Io oxygen and

sulfur cloud models. In the radial interval from 4.9 to 5.4 R^ ion

partitioning information obtained from Bagenal (1983) is used to

initially explore the impact of charge exchange reactions between

the neutral gas clouds and the plasma torus ions. Because of the

spatial distribution of torus ions, these reactions may be able to

introduce a magnetic longitudinal effect in the plasma torus properties. Modeling efforts for the Io oxygen and sulfur clouds and

for the sodium cloud data scheduled during the second half of this

project year are also discussed.

17. Key Words (Selected by Author(s)) 18. Distribution Statement

satellite atmospheres

planetary magnetospheres

19. Security Clossif. (of this report) 20. Security Clossif. (of this poge)

unclassified unclassified

21. No. of Pages 22. Price*

10

•For sale by che Clearinghouse for Federal Scientific and Technical Information, Springfield. Virginia 22151.
I. SUMMARY OF RESEARCH PROGRESS FIRST AND SECOND QUARTER

Introduction

Emphasis during the first two quarters has been carefully limited and, in

particular, restricted to seeking the spatial distribution of ion densities in

the lo plasma torus and to determining the impact of these ions on the 01 and

SI cloud models. The specification of these ion densities throughout the

plasma torus is required as input information for the oxygen and sulfur cloud

models, without which calculations including the effects of charge exchange

reactions cannot be performed. Because this information has been only

partially available (with more information expected in the near future),

modeling efforts have, where possible, been conserved until the second half of

the project year. Progress made in the first two quarters is summarized

below.

Ion Partitioning Data

During the first two quarters, a two-dimensional (radial and vertical)

description for the densities of the major ions in the plasma torus within the

radial interval from 4.9 to 5.4 R. was obtained from Bagenal (1983). These

ion densities were determined from a recent re-analysis of the Voyager PLS

data that properly accounted for the different vertical distributions of

various ions and of the electrons along the magnetic field lines. The ion

densities throughout the remaining plasma torus are to be approximately

defined in the near future by combining an extended analysis of the Voyager

PLS data by Bagenal (1983) with a new analysis of the Voyager UVS data

undertaken by Shemansky (1983).

Impact of Charge Exchange Reactions

Using the limited ion partitioning data, the impact of charge exchange

reactions between the neutral clouds and the plasma torus ions has been

initially explored. The lifetime of atomic oxygen and sulfur in the plasma

torus is determined by the charge exchange reactions and the electron impact

ionization reactions summarized in Table 1. The charge exchange cross

sections are velocity dependent and are determined in accordance with Johnson

and Strobel (1982) and Johnson (1983). Using the ion data of Bagenal in the

radial interval of 4.9 to 5.4 R together with these cross sections to deduce
TABLE 1

Charge-Exchange and Electron Impact Reactions for

Neutral Oxygen and Sulfur

Reaction

1. O4 4- 0 -> 0 + 0+

2. 0+ 4-.S -»- 0(3P) H

-». O^D) H

3. S+ + S ->• S 4- S4

4. S+ + 0 ->- S 4- O4

5. S** + S -»- S 4- S4"*

•*• sVs)

6. S44 + 0 * S+(

2

P)

* S+(

2

D)

4-,2 ,

* S ( D)

* S4(

4

S)

7. O44 4- 0 -*- 0 4- d"1"*

•*• o

+(4s)

•*• 0+(

2

D)

8. O"*^ 4- S + 0+(

4

S)

-»• 0+(

2

D)

* 0+(

2

P)

• s

+(2p)

' S+(

2

D)

+ 4 4

4- S (3s, 3p*; *P)

4- 04(

2

D)

4- 0+(

2

D)

4- 2 4- 0 (^P)

+ 0+(

2

P)

4- 0+(2s, 2p4;

 4P)

4- 0+(2s, 2p4;

 4P)

+ (s4)*

4- (s4)*

+ (s4)*

-»• 0(2D° 3d,

 3P°) 4- S44" -»• 0+ 4- S'

9. S4** + 0 -»• S^Od,

-c S4+(4s,

- S+(

2

fc* V ^P /)

-»• S+(

2

D)

1 /

•»• s^C^s)

10. S444 + S ->• S4+(4p,

4+

* S^(3d,

44- *

-»• (s )

4- *

* (S+) 4

11. e 4- 0 -*• O4 4- 2e

12. e 4- S -». S+ + 2e

13. O4 + e -»• 0 4- hv

4-

14. S 4- e -j. S 4 hv

3P) 4- 0+

(

4

S)

3

P) + 0+(

4

S)

1 1 0

4•- v 0 \ ( * P /)

+ 044-(1D)

t t 1

4- O44^)

3

D) + S+(

4

S)

J"? 4-2

P) 4- S (ZP)

4- 2

+ S CD)

4-1.

S^

4- e
charge exchanger rates and using the electron impact ionization rate of Smyth

and Sheraansky (1983), the lifetimes of 01 and SI in the centrifugal plasma

plane have been calculated and are compared for these two processes in Figure

1. As can be seen, the minimum charge exchange lifetimes at 5.2 R.= for 01 and

SI, occurring in the cool inner torus where the electrons have no ionizing

capability, are comparable to the minimum electron impact lifetimes at 7.2 R.

occurring in the warm outer portion of the plasma torus.

The charge exchange lifetimes in Figure 1 are, however, effective only

near the centrifugal plane as illustrated in the two-dimensional lifetime

plots for 01 ad SI shown respectively in Figure 2 and Figure 3. This occurs

because ions are cool and thereby energetically confined close to the

centrifugal plane. The temperature of the ions, however, increases rapidly as

one moves from 5.2 R. to lo's orbital position at 5.9 R. . The charge exchange

lifetimes will therefore be vertically more extended for radial displacements

from Jupiter equal to or greater than the orbital position of lo. As the

plasma torus oscillates about the satellite plane, charge exchange reactions

.may therefore introduce magnetic longitudinal effects in the plasma torus

preferentially inside of lo's orbit. This longitudinal dependence could,

however, be modified and even eliminated if a corotational lag of order 1% or

more were present in the plasma torus. Corotational lags of order 6i4% have

been attributed to the plasma torus at 5.9 R. by Brown (1983), but may equally

well be explained as strict corotational flow that is not azimuthally

symmetric as noted by Barbosa and Kivelson (1983). Magnetic longitudinal

variations in the ion emission brightnesses have however been measured by

Morgan (1983) and may possibly be related to this longitudinal dependence of

the ion source.
at

w

3

O

0)

100

10

1

0 1•

: « "MV

II

: i! i!

\ \

\ \\ \

- \ 1

Oxygen-, ! 1

Z~ lit

E \L K 1 '

~* i

W l

1

i

hf k

r U

I Sulfur J

—

I I

O

f

f 1 1 1 1 M 1 1 1 1 1 1 1 1 I 1

4 5

1 1 1 1 '-

S <.

r' I /

1

'

i

i /•—— '— —

/ f _

Oxygen — ^ / - I

(I3.62ev) \/ /

7 / s / . \ / / \ / / \-.^' i/

\ Sulfur ->. / —

\ -"

—

0

jit

6 7 8 9 10 11

Radial Displacement from Jupiter in the Centrifugal Plane (Rj)

Figure 1. The lifetimes of 01 and SI for electron impact ionization

and charge exchange reactions of Table 1 are calculated

in the centrifugal plane of the plasma torus as described

in the text and shown separately. The solid contours

between 4.9 and 5.4 Rj are for the charge exchange reactions.
— 4

Q?

 r

\_

2

"o

^J i

uJ

"a

cr>

8 10 11.

CD

O

<D

£ 0

o

a>

o

_g

*••v•

) * -p»

O

a

o

-3

1 11 11111 1 11111111 1 111 1 11 111 1 i M 111 111 1 11 111 1 n iiT i * * i m i i 11 r i rrn i •-

i

1

- 500

1100

I 30

ICOO hrs

500s

Vertical Oscillation of lo

•iJ I M I I I f I i i if I I I II I I I I l» » f M I I 1 H I H It I H I I II M I I I I I II I Hf I I I I I I I I I 

0

-1

8 10 11

Radial Displacement from Jupiter (Rj)

Figure 2. The lifetimes of 01 for electron impact ionization and charge

exchange reactions of Table 1 are calculated in the plasma

torus as described in the text and shown separately. The

Heavier contours between 4.9 and 5.3 Rj are for the charge

exchange reactions.
8 10 11.

a

§• 2 LJ

o»

I ' "c

a>

£ 0

o

I "

<D

Q

*0

500

I 10

I I II I I I I I I i t I i I I I 1 I I I I I I I I I I I I I I I I I I I I I I I I 1 I I 1 I I T 1 I I I I I I 1 I I I I I l l-

"I"

500 hrs

Vertical Oscillation of lo

MI i i 111 ! i 11 i 11 i 11 I 111 f i i 11i I MM i 11 11 11 111 111 t i 11 11 11 j it i I i i i

-l

-2

8 10 11

-3

Radial Displacement from Jupiter

Figure 3. The lifetimes of SI for electron impact ionization and

charge exchange reactions of Table 1 are calculated in

the plasma torus as described in the text and shown

separately. The heavier contours between 4.9 and 5.3 R,

are for the charge exchange reactions.
II. PROGRAM FOR THE NEXT TWO QUARTERS

Io Oxygen and Sulfur Cloud

Efforts in the last half of this project year will be directed toward (1)

obtaining a distribution for the densities of the major ions in the plasma

torus, (2) incorporating these ion densities in the model to calculate the

lifetime of 01 and SI and other relevant physical quantities describing ion

input rates, and (3) performing model calculations to describe the spatial

morphology of the neutral clouds and their impact on the plasma torus. As

noted earlier, the ion densities will be sought from analyses of Bagenal

(1983) and Shemansky (1983). Actions to improve the execution efficiency of

our numerical models for 01 and SI will also be undertaken.

Io Sodium Cloud

Model analysis for selected sodium D-line profile data will be performed

in the last two quarters and consistency with atom ejection conditions

appropriate to the directional features analyzed and explained by Pilcher et.

al. (1983) will be investigated. A number of exploratory line profiles have

been evaluated using the new sodium cloud model at AER that incorporates the

oscillating plasma torus sink. These line profiles and others yet to be

calculated will be used to select appropriate modeling basis functions for

interpretation of the data. Limited model analysis will also be considered

for selected slit intensity data as a second method of providing constraints

for the modeling basis functions.
REFERENCES

Bagenal, F. (1983) Private communication.

Barbosa, D.D., and Kivelson, M.G. (1983) Dawn-dusk electric field asymmetry of

the lo plasma torus. Geophys. Res. Lett., 10, 210.

Brown, R.A. (1983) Observed departure of the lo plasma torus from rigid

corotation with Jupiter. Ap. J_. Lett., 268. L47.

Johnson, R.E. and Strobel, D.F. (1982) Charge exchange in the lo torus and

exosphere. J. Geophys. Res., 87, 10,385.

Johnson, R.E. (1983) Private communication.

Morgan, J. S. (1983) Low resolution spectroscopy of the lo torus. Ph.D.

Thesis, Astronomy Dept., University of Hawaii.

Pilcher, C.B., Smyth, W.H., Combi, M.R., and Fertel, J.H. (1983) lo's sodium

directional features: Direct evidence for a magnetospheric-driven gas

escape mechanism. BAAS., 15, 810.

Shemansky, D.E. (1983) Private communication.

Smyth, W.H., and Shemansky, D.E. (1983) Escape and ionization of atomic oxygen

from lo. Ap. J_., 27JL, 865.

10