The results obtained with the retarding potential analyzer on the OGO-6 satellite are discussed. The information obtained during the OGO-6 flight concerned the following subjects: (1) measurement of electron flux density in the plasmasphere, (2) latitudinal variations of ion temperature, (3) heating in the nighttime ionosphere by conjugate photoelectrons, (4) longitudinal variation in equatorial ion temperature at low altitude, and (5) identification of heavy ions in the upper F region

Hanson, W. B.

Sanatani, S.

English

NASA Technical Reports Server

fFinal Report
to
National Aeronautics and Space Administration
from
The University of Texas at Dallas
P. O. Box 30365
Dallas, Texas 75230
Dallas County
(NASA-CR-132943) OGO-6 EXPERIMENT F-03 N74-20542
Final Report (Texas Univ.) 11 p BC
$4.00 CSCL 22C nclasUnclas
G3/31 34327
Final Report for OGO-6
Experiment F-03
NASA Contract No. NAS 5-9311
W. B. Hanson
Principal Investigator
S. Sanatani
Co-Investigator
15 July 1973
https://ntrs.nasa.gov/search.jsp?R=19740012429 2020-03-23T11:31:37+00:00Z
Introduction
OGO-6 was retired in June, 1971, principally because of system
electronic problems that made data acquisition sporadic and unpredict-
able. The Retarding Potential Analyzer (RPA) of U.T. Dallas, designated
experiment F03, was still working perfectly at retirement, two years
after launch. A large body of data has been acquired and analyzed.
The retarding potential analyzer on OGO-6 turned out to be a
remarkably successful experiment. To date, 13 papers utilizing data
from this device have been published or accepted for publication
(excluding abstracts for papers presented at meetings). Many of these
papers relate to new phenomena that were discovered in the data from
this instrument.
These excellent and unique data deserve to be fully reduced and
analyzed. This process is about 75% complete and will be finished
by the end of 1973. Summaries of the data, plotted orbit by orbit
on microfilm, are now being made available to interested OGO-6
experimenters, and some other aeronomers, as they become available.
Several cooperative efforts involving data from several OGO-6
instruments are now being planned and will be implemented in the
reasonably near future.
It is expected that the entire set of RPA data in all forms
that it exists after processing will be placed in the World Data
Center within a year from this report date.
2RPA Science Contributions
A first look at OGO-6 RPA output shows that the quality of the
data is very good. The instrument appears capable of measuring ion
temperature to an accuracy of better than five percent in a quiet
ionosphere. Fluxes of electrons with energy greater than 10 ev of
6 -2 -1 -110 cm sec ster can be detected, and this capability permits
the observation of both photoelectrons and soft auroral electrons.
8 -2 -1During the daytime fluxes of the order of 10 cm sec are observed
that change rather smoothly within the plasmasphere but show rapid and
large variations at higher latitudes. The device also operates in a
mode that examines the horizontal changes in ion concentration (frac-
tional changes as small as 10- 3 can be observed) with a spatial
resolution from 350 meters to as small as 40 meters, depending on
the telemetry rate.
In the dawn-dusk plane the ion temperature is observed to vary from
10000 K to 40000 K; the higher temperatures being associated with higher
altitudes in the winter hemisphere. Molecular ion (n30 AMU) concentra-
tions from 25 cm-3 to 2500 cm3 are detected near perigee. These ions
constitute only a small fraction, from 2% to less than 0.1% of the oxygen
ion concentration. Fractional abundance of H and He+ as low as a few
percent of the 0+ concentration can be readily detected, but the
determination of the ratio of the concentrations of these ions (H /He + )
becomes reliable only when the light ion fraction exceeds approximately
25% (see Sanatani and Hanson, 1969; Hanson et al., 1970). At mid-latitudes
3+ H+
and higher altitudes-(>700 km) the lighter ions, H and He are both
present at approximately the 0+ concentration but their relative
importance decreases near and in the polar regions, presumably due
to polar winds. Both polar regions display large spatial fluctuations
in ion concentration and this behavior extends somewhat into the
plasmasphere.
Two papers and a report based on the OGO-6 RPA results were
presented at the 1971 spring meeting of AGU-URSI. The first of these
dealt with the latitudinal variations of ion temperature on nighttime
equatorial passes of OGO-6 during the month of November 1969 (see
Sanatani, Hanson, and McClure, 1971).
The second paper dealt with heating in the nighttime ionosphere
by conjugate photoelectrons. It utilized the data from both the RPA
and the Langmuir probe aboard the OGO-6 satellite (see Sanatani, Hanson,
and Nagy, 1971).
The report was presented at the special OGO Session in the 1971
Spring Meeting of the American Geophysical Union. It provided a more
general view of the observed thermal behavior of the ionosphere over a
wide latitude range, including seasonal and solar activity effects.
Special emphasis was given to the equatorial upper F region.
Another paper dealt with the longitudinal variation in equa-
torial ion temperature at low altitude (400 to 600 km). It is found
that the mean equatorial ion-temperature has a maximum over the
longitudinal range +100 to -700. It is found that the longitudinal
variation disappears on disturbed days (Sanatani and Hanson, 1971).
The solar array problems that arose two weeks after launch and
caused the vehicle to assume a high (> -20 volt) negative potential
when sunlit abated somewhat from late October, 1969, to the middle of
February, 1970. During this period the vehicle potential when sunlit
was only -13 to -14 volts, and we are able to analyze the data for ion
temperature. Perhaps surprisingly, this T. data joins smoothly onto the
1
satellite eclipsed T. data, in whose validity we have high confidence.
1
The T. data comparisons with the radar backscatter stations has1
been completed (McClure et al., 1973) and the results are extremely
encouraging. The temperature comparisons always agreed within the
error bars and usually within a few percent.
Heavy ions were discovered in the upper F region on the basis
of the RPA data; they were identified as Fe+ ions by Hanson and Sanatani
(1970). A much larger body of data has since been examined which con-
sistently supports the Fe hypothesis both experimentally and theoreti-
cally (Hanson et al., 1972).
The very striking relationship between ionospheric irregularities
and Fe+ ions near the equator discovered in this OGO-6 ion trap data
led to the suggestion that the two phenomena are causally related (Hanson
5and Sanatani, 1971). The nature of this causal relationship has since
been described by Hanson et al., 1973.
On some occasions, but always near the magnetic equator, the ion
temperature measured along the orbit shows deep depressions above 600 km.
The measured temperature goes well below the expected neutral gas temp-
erature. These temperature depressions have been explained in terms of
expansion cooling brought about by the flow of plasma from the summer
to the winter hemisphere (Hanson, Nagy, and Moffett, 1973; Bailey,
Moffett, Hanson, and Sanatani, 1973).
The OGO-6 RPA showed that on some occasions the bottomside of
the F layer was drastically depleted of ion content at the magnetic
equator, with Ni decreasing by 3 orders of magnitude in only a few
vertical kilometers. This behavior was attributed to transport result-
ing from turbulent electrostatic fields (Hanson and Sanatani, 1973).
The OGO-6 RPA, in conjunction with other OGO-6 instruments,
observed the behavior of the ionosphere while passing through several
midlatitude red arcs (SAR arcs). The data show unambiguously that the
arc energy is derived from thermal conduction from the magnetosphere,
not from any local excitation mechanism. This interpretation is
consistent with recent suggestions that the energy is ultimately
derived from energetic protons just inside the plasmasphere where ion
cyclotron wave interactions heat electrons at the expense of the
energetic protons. This work has been published (Nagy et al., 1972).
6Anticorrelations in molecular ion and oxygen ion concentrations
are frequently observed in the OGO-6 RPA data. Since the molecular
ions were thought to be formed by charge exchange with 0 , and removed
by recombination with electrons, one would expect no such anticorrela-
tions since the 0+ and electron concentrations are essentially equal
in the topside F layer. The explanation of this paradox seems to
require that the source of the molecular ions be independent of the 0+
concentration. In a recent publication (Rishbeth, Bauer and Hanson,
1972) we have suggested that N could provide this mysterious source
of molecular ions, even though a minor (n 10%) ion constituent, since
it reacts much more rapidly with 02 and N2 than does 0 .
The "duct detector" data from the RPA has revealed a spectacular
view of the small scale (as well as small amplitude) irregularities in
the F region. The general nature of these irregularities, and they
have many different characteristic forms, has been described by McClure
and Hanson (1973), together with their geographic occurrence. The most
common irregularities are stochastic, and the power distribution with
2frequency, f = (V /X), varies as (1/f) , quite independent of the
sat
amplitude of the irregularities in a given disturbed region. A detailed
examination of these stochastic properties is given by Dyson, et al.
(1973), as a guideline for theorists who are attempting to explain the
origin of the irregularities.
7Conclusions
This experiment has received very good financial and logistic
support from both the OGO-6 project personnel and from NASA headquarters.
While I believe the science output has justified this treatment I am
nevertheless grateful for it. I anticipate that several papers per
year will be generated from the RPA data bank for at least the next
five years.
Publications and Papers Presented on OGO-6 Retarding Potential Analyzer
Data
Bailey, G. J., R. J. Moffett, W. B. Hanson, and S. Sanatani, Effects
of interhemisphere transport on plasma temperatures at low
latitude, accepted for publication in J. Geophys. Res., 1973
Dyson, P. L., J. P. McClure and W. B. Hanson, In-situ measurements
of amplitude and scale size characteristics of ionospheric
irregularities, J. Geophys. Res., accepted for publication, 1973
Hanson, W. B., S. Sanatani, D. Zuccaro and T. W. Flowerday, Plasma
measurements with the retarding potential analyzer on OGO-6,
J. Geophys. Res., 75, 5483, 1970
Hanson, W. B., and S. Sanatani, Meteoric ions above the F2 peak,
J. Geophys. Res. 75, 5503, 1970
Hanson, W. B. and S. Sanatani, Relationship between Fe+ ions and
equatorial spread F, J. Geophys. Res., 76, 7761, 1971
Hanson, W. B., D. L. Sterling, and R. F. Woodman, Source and identifi-
cation of heavy ions in the equatorial F layer, J. Geophys. Res.,
77, 5530, 1972
Hanson, W. B., A. F. Nagy and R. J. Moffett, OGO-6 measurements of
supercooled plasma in the equatorial exosphere, J. Geophys. Res.,
78, 751, 1973
Hanson, W. B. and S. Sanatani, Large N. gradients below the equatorial
F peak, J. Geophys. Res., 78, 1167, 1973
Hanson, W. B., J. P. McClure and D. L. Sterling, On the cause of
equatorial spread F, J. Geophys. Res., 78, 2353, 1973
McClure, J. P., W. B. Hanson, A. F. Nagy, R. J. Cicerone, L. H. Brace,
M. Baron, P. Bauer, H. C. Carlson, J. V. Evans, G. N. Taylor,
and R. F. Woodman, Comparison of T and T. from OGO-6 ande 1
from various incoherent scatter radars, 78, 197, 1973
McClure, J. P. and W. B. Hanson, A catalog of ionospheric F-region
irregularity behavior based on OGO-6 retarding potential
analyzer data, accepted for publication, J. Geophys. Res., 1973
Nagy, A. F., W. B. Hanson, R. J. Hoch, and T. L. Aggsen, Satellite
and ground-based observations of a red arc, J. Geophys. Res.,
77, 3613, 1972
Rishbeth, H., P. Bauer, and W. B. Hanson, Molecular ions in the F2
layer, Planet. Space Sci., 20, 1287, 1972
Sanatani, S. and W. B. Hanson, Measurements of ion temperature and
composition with a planar ion trap in OGO-6, EOS, Trans. Am.
Geophys. U., 50, 652, 1969 (abstract)
Sanatani, S., W. B. Hanson, and J. P. McClure, Latitudinal variation
in ion temperature at low altitude, paper presented at URSI
Spring Meeting, Washington, D.C., April 1971
Sanatani, S., W. B. Hanson, and A. F. Nagy, Heating in the nighttime
ionosphere by conjugate photoelectrons, EOS, Trans. Am. Geophys.
U., 52, 305, 1971 (abstract)
Sanatani, S., and W. B. Hanson, Longitudinal variation of ion tempera-
ture from retarding potential analyzer on board OGO-6 satellite,
EOS, Trans. Am. Geophys. U., 52, 882, 1971 (abstract)
Wrenn, G. L., W. B. Hanson, and S. Sanatani, Light ion temperature,
EOS, Trans. Am. Geophys. U., 52, 886, 1971 (abstract)


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