/tfFINAL REPORT

to

THE NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

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-CR- 177222) STUDIES OF DYN&M O FIELD

STEOCTURE AND BELATED .EFFECTS: DE SATELLITE

PEOJECT GUEST INVES1IGATOB FEOGEA M Final

Report (Texas Univ.) 28 p HC A03/MF A01

CSCL 04A G3/46

THE UNIVERSITY OF TEXAS AT DALLAS

P. 0. Box 830688

Richardson, Texas 75083-0688

(214) 690-2851

N86-27840

Unclas'

43315

NASA GRANT NO. NAG5-450

UTD NO. 23771-961

STUDIES OF DYNAMO FIELD STRUCTURE AND RELATED EFFECTS

DE SATELLITE PROJECT GUEST INVESTIGATOR PROGRAM

Principal Investigator

W. R. Coley
DE CJI FINAL UK I'OUT ORIGINAL PAGE' SS

r . A, M r, °*

 P°°R

Coley <v. McClure

This study has been dire.rted toward UK; establishment of l.lit: latitudinal and longitudij.

rial structure of the low latitude dynamo electric field using primarily data from the Unified

Abstract (UA) files of the Atmosphere Explorer 111 satellite. Our results are described in

detail in the atachcd paper which has been submitted for publication to the Journal of

Geophysical Research. The results are briefly summarized below in this section.

Figure la shows a "mass plot" of vertical drift data from AE-E obtained from the 15

second average values of the UA files. All vertical drift values in the file for DLAT < 20°

and in the August-September 1978 time period are plotted versus Solar Local Time (SLT).

During tins period the satellite was in a circular orbit of 360-390 krn altitude. Figure Ib

shows the same data set averaged into 30 minute bins. The dotted line represents the

24-hr average vertical drift. For comparison, Figure Ib also shows incoherent scatter radar

results from Jicarnarc.a for two different levels of solar activity (Fejer et al., 1979) as well as

the low latitude model generated by Richmond, 1980. In all cases we see the same general

features: downward flow at night reversing at 0600 SLT, a daytime peak followed by a

decline to a prereversal enhancement between 19 and 20 SLT, and a reversal to downward

flow at night.

AE-E was active and in circular orbit from the end of 1976 through mid 1981. We have

at UT-Dallas UA data only through the end of 1979: the 1980/1981 data is in principle

available via the Sigrna-9 computer, but not yd via the World Data Center. We have

informally requested this 1980/1981 data several times but not yet received it. presumably

because other Sigma-9 projects have had a higher priority. At present, we repeat our request,

1
based on the excellent quality of the AE UA data through late 1979 that we have been

working with on this project and on the scientific results that we are now finding it possible

to extract from this data set.

•a

We have searched our A I'! data base for variations of the various components of drift

velocity (e.g. vertical ion, horizontal ion, horizontal neutral,perpendicular ion, etc.)with

dip latitude, longitude, season, altitude, etc.. This examination has been accomplished by

"binning" the data appropiately. Over 500 different runs of our very flexible averaging algorithm have been made in the past year using "summary tapes" that hold highly condensed

versions of our original UA tapes. Twelve of the original tapes exist for each year, whereas

a single summary tape usually holds a year or more of data. As was discussed in the earlier

report, latitudinal structure is evident in the vertical drift during solstice periods (Coley

and McClure, 1984), one interpretation of this structure being that the dynamo induced

ion velocities are being modified by neutral wind flow,the meridional component of which

flows generally from the summer to winter hemisphere under solstice conditions.

Further latitudinal effects can be seen in Figure 2a which shows ion velocity vectors

in the meridian plane versus dip latitude. The UA data is put into one degree bins of

DLAT and only daytime data from 12-16 SLT is used. This 10 month average of 1979

data clearly shows the equatorial "fountain effect" which occurs during the day and which

is responsible for the Appleton anamoly in the ionosphere. Similarly Figure 2b shows the

downward motion of the F-region ionosphere occurring during the midnight to 0400 SLT

sector.

Further evidence of inlerhemispheric seasonally dependent ion flow also comes out of

this form of data presentation. Figures 3a and 3b show respectively the northern hemisphere

2

ORIGINAL

OF POOR QUALIT*
summer and northern hemisphere winter ion velocity vectors for the 18-22 SLT (sunset)

sector. At low values of 1)1,AT both plots show summer to winter hemisphere flow. At

higher latitudes there is seen a tcndancy for upward motion in the summer hemisphere

and downward motion in the winter. This is consistent with predictions-(jf the vertical ion

velocity in this time sector made by Dachev and Walker, 1982.

Resolving the measured ion and neutral (from NATE) motions into components parallel

and perpendicular to the geomagnetic field allows determination of the ion diffusion velocity

along B. The upper panel of Figure 4 shows a typical example of the correspondence

between the parallel ion and neutral velocities for a full orbit of AE-E. The two traces are

similar in both large- and medium-scale features with an average offset of approximately

80 m/s. At about, 78500 seconds U.T. there is a discontinuity in both the parallel ion and

neutral graces. This stepfunction is a result of the independent calculation by NASA of

the spacecraft attitude parameters (a and 8, the siderial coordinates of the momentum

wheel axis) for the first and last halves of this orbit and not the result of an instrumention

problem or a geophysical effect. In the center panel the perpendicular ion trace reverses

from upward to downward' flow near 19 hrs SLT after a slight pre-reversal enhancement of

the upward flow.

Investigation of longitude effects utilizing the UA data was delayed by the discovery

of errors in the geographic longitude of AE-E on the UA data tapes. We traced the errors

to faulty values of G.S.T. and informed the World Data Center-A of this : they have

taken extensive steps to fix this problem on their master tapes. Also, through the use

of Universal Time values and other orbital parameters correctly listed on the data tapes,

and an approximate expression for the equation of time, we generated our own longitude

3
values correct to within approximately d.0.2°, because we still have not received a full set

of corrected tapes from Goddard Space Flight Center.

In our longitude studies we obtained the average variation of the vertical ion drift

velocity component, nearly proportional to Keu>l Li, in the region near and immediately east

of Jicarnarca, where the geomagnetic field strength B has an absolute minimum (Figure 5a).

A similar average diurnal curve (Figure 5b) was obtained for an equatorial region centered

near Malasia, where B is on the average 33% larger than in the Peru-Brazil- South Atlantic

B-minimum region. The drift velocities arc not signifignantly different in the two regions.

Thus we conclude that the average east-west electric field is riot constant with longitude

as assumed in a model calculation by Dachev and Walker (1982). Instead, as one might

expect based on simple dynamo theory, if the induced dynamo field is proportional to U

X B where U is the neutral wind velocity responsible for the dynamo fields, and also is to

first order independent of longitude, the field is then approximately proportional to B and

the vertical drift Eew/B, riot the electric field Kew, is then approximately independent of

B.

REFERENCES

Coley, W. R. and J. P. McClure, Medium and large-scale variations of dynamo-induced

electric fields from AE ion drift measurements, Thermospheric Dynamics Conference, 1984.

Dachev, Ts. P. and J. C. G. Walker, Seasonal dependence of the distribution of largescale plasma depletions in the low-latitude F-region, J. Geophys. Res., 87, 7625, 1982

Fcjer, B.G. ,1). T. Farley, R. F. Woodman, and C. Calderon, Dependence of F region

vertical drifts on season and solar cycle, J. Geophys. Res., 84, 5792, 1979

Richmond, A. D., M. Blanc, B. A. Emery, R. M. Wand, B. G. Fejer, R. F. Woodman,

4

ORIGINAL PAGE- IS

OF POOR
S. Ganguly, P. Amayenc, R. A. Behnke, C. Caldcron, and .). V. Rvans, An empirical model

of quiet-day ionospheric electric fields at middle and low latitudes, .1. Geophys. Res., 85,

4685, 1980
.ORIGINAL PAGE* IS

POOR QfUALfTY

0 2 4 6 8 10 12 14 16 18 20 22 24

SOLAR LOCAL TIME

60

45

30

15

0

- 15

30

-45

•60

AE -E AUG OCT 1979

RlfcHMOHD 1980 MODEL

JICAMARC A EQUINOX 197S 1976

JICAMARCr. KQUIUOX 1968 197!

0 2 4 6 8 10 12 14 16 18 20 22 24

SOLAR LOCAL TIME

Figure 1
I I I M I I I I I M I I. I I I I I I I

-20 -16 -12 -8- 4 0

OTO ITACI tCIDCES

b)

JUL

-20 -16 -12 -8 -40 4

DIP LATITUDE

8 12 16 20

<m> ir»ci icincti

•Figure-2
-20 -16 -12 -8- 4 0 4 8 12 16 20

DIP LATITUDE

 OTO

 "ACt «

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-20 -16 -13 -8- 4 0 4 8 12 16 20

DIP LATITUDE

OTD fFACC «C I 0CKS

Figured
ORIGINAL

OF POOR

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to B

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AB-B ORBIT- 10B01 DATS- 70137

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Figure 4
VERTICAL

ION

VELOCITY

(M/S)

126

100

76

60

26

0

-26

-60

-76

-100

-126

8 10 12 14 16 18 20 22 24

SOLAR LOCAL TIME

<m> ITACI ICIDCEI

V.E. COLCT

VERTICAL

ION

VELOCITY

(M/S)

126

100

76

60

26

0

-26

-60

-76

-100 —

-126

I I I I I I I I I I I I I I I I I I I I I

8 10 12 14 16 18 20 22 24

SOLAR LOCAL TIME

DTD tFACf tCIBCIt

«.». COLIT

Figure 5
EQUATORIAL FOUNTAIN EFFECT AND DYNAMO DRIFT SIGNATURES

FROM AE-E OBSERVATIONS

W. R. Colcy and .1. P. McClure

Center for Space Sciences, University of Tex us at, Dallas, Richardson, Texas, 75080

Submitted to Journal of Geophysical Research .

"• j>

Abstract

Vertical and horizontal ion drift velocities for 1977-1979 from the Unified Abstract files

of the satellite Atmosphere Explorer E were used in preliminary studies of the behavior of

the low latitude (-20° to 20° dip latitude) F region. Sample diurnal variations obtained near

the September 1979 equinox are very similar to those measured by the incoherent scatter

radar at Jicamarca, Peru. Latitude profiles of the vector drift values clearly show the classic

"fountain effect" responsible for the Appleton anomaly during the day. By breaking the

data set into latitude bins systematic variations of the vertical drift with latitude become

evident. Investigation of longitude effects revealed that the average vertical drift velocity Vv

is independent of longitude, implying that the average east-west electric field is proportional

to B.

Introduction

In this paper we discuss spacecraft observations of ionospheric plasma motions in

the vertical and horizontal (approximately north-south) directions at low latitudes. Such

plasma drift results from the magnetic east-west dynamo electric field Eew, plasma diffusion,

gravity, and the magnetic meridional neutral wind, which act together to produce flow

patterns commonly refered to as the "fountain effect" \Martyn, 1955; Hanson and Moffett,

1966). We present average diurnal variations of the horizontal and/or vertical drift in

various latitude and/or longitude sectors. In addition to confirming that the fountain effect

actually exists in forms quite similar to those theoretically predicted decades ago, we also

present the first experimental verification of the approximate constancy with longitude of

the average vertical drift Vv — Eew/B at the dip equator. The geomagnetic field magnitude

B varies more than 60% with longitude, but elementary dynamo theory predicts that

ECW = U x B, where U is the average wind field component responsible for Eeui. Thus, on

the average, we find as expected that Eew is proportional to B and Vv is independent of B

(or longitude).

The ion drift meter (IDM) on the Atmosphere Explorer satellite AE-E was the source

of our data [Hanson et a/.,1973]. Similar data were (and are still being) used to study

magnetospheric convection at high latitudes [e.g. Heelis et a/., 1981; Heelis, 1982; Rich

et al., 1984) and to study the much weaker drift irregularities, sometimes as small as a

few m s"1 peak-to-peak, associated with equatorial "bottomside sinusoidal irregularities"

(BSS) [Va//adares et al., 1983; Cragin et al., 1985]. In contrast with these applications,

our use of data from the IDM presents a special problem. The absolute calibration of

the drift velocity data must be quite accurate if useful studies of dynamo electric fields

are to be made, whereas only relative drift values were required for the above studies of

BSS irregularities, and for high latitude convection studies absolute calibrations need be
arc.urate only t.o ;il>ont. 100 in s ' because convection <lnft,s arc tiinc.h larger l.lian dynamo

drifts. One of our iinporl.anl, conclusions is that by simple averaging of the IDM data

processed routinely many years ago we now ol>t,ain reasonable vertical plasma drift values

near the equator.

Most information on the vertical dynamo drift at the dip equator has been obtained at

the .licamarca Hadar Observatory in a series of measurements that began in 1968 | Wood-

. ;n;i/i,l970; McClun- ;ui<l /V/.erso/i. 1972; l-'i-ji-r <•!• ;il., 1979; l-cjcr <:t ;i/., 1081 j. Our average

diurnal drift variation results agree well with the Jicamarca curves. Iticliinond ci. fit. [l980|

generated an empirical model of low-solar activity ionospheric electric fields from four major incoherent scatter radars at middle and low latitudes. The model covers the latitude

range of the A10-10 satellite, which had an orbital inclination of 19.76°, allowing comparison

with AIO-IO data obtained in different latitude and longitude regions. The purpose of this

paper is to introduce a data set that will compliment and extend the current ground based

data, allowing the incorporation of more accurate latitudinal, longitudinal, and solar cyc.lc

variations into future models of low latitude dynamo fields.

Instrumentation

The IDM data presented here were obtained from the Unified Abstract (UA) files

of the satellite Atmosphere tOxplorer-E, which contains 15-second averages of the original

IDM measurements. The AE-E IDM measured the horizontal and vertical components

of ion drift perpendicular to the spacecraft velocity vector with a sensitivity of 0.016°

per bit, corresponding to a transverse velocity near 2.2 in s" 1; higher resolution drift

values, not used here, have,a bit size near 1.1 m s" 1. The satellite was in orbit from

the end of 1975 through June 1981, first in an elliptical and later, after November 1976,

in nearly circular orbits at altitudes between 230 and 480 km. The circular orbits were

well suited for the observation of low-latitude ion drifts caused by dynamo electric fields.

We used data between January 1977 and December 1979. This large data base can be

examined for variations of the ion drift with latitude, longitude, season, solar cycle, altitude,

and magnetic activity. This paper will deal primarily with latitudinal and longitudinal

variations of the drift features.

Figure 1 details UA AE-E data from a single orbit, 13406, a circular pass at w 315

km altitude. The lower panel presents the dip angle of the geomagnetic field and the

log of the ion density (A7,) versus UT and various other parameters. One of our primary

parameters for plotting and averaging the data is solar local time (SLT), also abbreviated

as LT. The post-sunset minima in Ar, at approximately 19 and 21 hrs LT are examples of

the plasma "bubbles" or depletions discussed by McClurc at, a/. [1977). The upper two

panels present the components of ion velocity that are parallel to the geomagnetic field

(13) and perpendicular to 13 in the magnetic meridian plane. As the component of ion

velocity in the direction of satellite motion (vx) was not generally available, the parallel

and perpendicular drifts were computed from the measured IDM values assuming that vx

was zero. For most data this is a reasonable assumption because x-Iii,,>risnntai 's generally

small. Just prior to sunset at about 18 hrs LT there exists a pre-reversal enhancement in

the perpendicular drift, with a reversal to downward flow at 19 hrs LT. This is consistent,

with the typical evening equatorial vertical drift signature seen by the incoherent scatter

radar at Jicamarca. Peru (Woodman, 1970; Fejor nl. a/., I979|. In examining other individual

orbits we often see examples of this signature, but on many other occasions the post sunset

ORIGINAL PAGE-IS

OF POOR QUALITY
drift enhancement, is absent. In order to begin l.o separate out the geophysical reasons for

the variations of this and other features it is necessary to deal with the data in sufficient

quantity such that meaningful average values can be determined.

Obsorv.-itions

We have made a preliminay search the At'i-E data base in the period of circular orbits

between the end of 1976 through the end of 197'.) for variations of the various components of

ion drift velocity (e.g. vertical, horizontal, perpendicular, etc.) with dip latitude, longitude,

season, etc. A flexibl e data averaging algorithm was used to generate' the samples shown in

Figures 2a and 2b. Figure 2a is a "mass plot," of vertical ion drift data. Almost all vertical

drifts in the UA file between -20° and 20° dip latitude (DLAT) for the August to October

1979 time period are plotted versus LT. A few points were arbitrarily excluded from the

average, including those having A7, < 104 cm" 3 (even though the drift measurements are

usually valid down to A7,- — 3 x 10'* cm"'* or lower) and points having a magnitude greater

than 125 m s~'. Data were used from times when the spacecraft was spinning ( about 4

rpm ) and when it was despun. In all there are some 11200 data points included. The

number of data points included in each plot of this type is often a strong function of local

time, depending on the spacecraft duty cycle. During this period the satellite was in a

circular orbit of 360 to 390 krn altitude. From examination of individua l orbits it can be

seen that the day to day variability of the data is as great or greater than the magnitude

of the average velocity. Figure 2b shows the same data averaged into 30-minute bins.

The horizontal dotted line represents the 24 hour average vertical drift. For comparison

Figure 2b also'shows some incoherent scatter radar results from Jicamarca for the equinox

months in 1968-1971 (sunspot maximum) and in 1975-1976 (sunspot minimum) [Fejer el

a7.,1979). In both the UA and Jicamarca data we see the same general features: downward

flow at night reversing to upwards near 06 hrs LT, a daytime peak followed by a decline

to a pre-reversal enhancement (PRE) around 19 hrs LT and a reversal to downward flow

at night. Richmond [1980], in modeling low latitude electric fields, used only data from

magnetically quiet solstice and equinox periods. The resulting model for the Jicamarca

region at equinox, also shown on Figure; 2b, is more sinusoidal in appearance than curves

produced from UA data and lack the prominent PRE that is usually apparent in averages

drawn from both magnetically quiet and active periods.

Latitudinal effects in the data base can be seen in Figure 3a, which shows ion velocity

vectors perpendicular to the satellite velocity vector versus dip latitude. The UA data has

been put into 1° bins of dip latitude and only daytime data from 12 to 16 hrs LT was used.

This 10 month average of 1979 data clearly shows the equatorial fountain effect which occurs

during the day and which is responsible for the Appleton anomaly in the F-region \Mnrtyn,

1955, Hanson and Moffctl, 1966]. Similarly, Figure 3b shows the downward motion of the

F-region occurring during the midnight to 04 hrs LT time period.

Evidence of seasonally dependent interhemispheric ion flow also comes out of this data

presentation format. Figures 4a and 4b show respectively the northern hemisphere summer

and northern hemisphere winter ion velocity vectors for the 18 to 22 hrs LT (sunset) sector.

At. low values of DLAT both plots show summer to winter hemisphere flow. At higher

latitudes there is a tendency for upward motion in the summer hemisphere and downward

motion in the winter. This is consistent with similar previous results of Wharton ct, al.

[1980) and Duchnv and Walkt-r (|982|.
Figures 5a and 5b show vertical ion drift data covering May to July 1979 from -20° to

20° DLAT. The spacecraft was in a circular orbit during this period at an altitude range of

450 to 475 km. There are sonic 17,000 points plotted on Figure 5a, most falling in a band

some 75 m s~' wide. The exception is the large spread in velocity in the post-sunset time

period. The averaged data shows a more or less classical .licarnarca drift pattern, with an

evening reversal at 20 hrs LT proceeded by a PRE. Morning reversal is at 06 hrs LT. This

compares with median values of 19 hrs LT and 06 hrs LT respectively found by Woodman

el a/. (1977) from .licamarca data. As expected, the average value for the driffVelocity falls

very near 0.

The same data set was then broken up up into four 10° wide bins of dip latitude : 10°

to 20°, 0° to 10°, -10°toO°,and -20° to-10°. The mass plots from the northernmost and

southernmost bins are shown in Figure 6. They indicate a generally much smaller spread of

from 30 to 50 m s"1 in the vertical ion velocity at any given local time, except immediately

after sunset. The averaged plots for the four bins (Figure 7) indicate a systematic variation

of the velocity with latitude. The largest average upward velocity is found in the most

northerly latitude bin (summer hemisphere). The most southerly bin (winter hemisphere)

has a net downward drift. Other features also show latitude dependence; the evening prereversal enhancement is strong in the summer hemisphere and weak or nonexistent in the

winter hemisphere. Other data covering the November 1977-January 1978 interval show a

similar pattern, with an upward bias of the drift during the summer and a downward bias

in the winter. Our interpretation of this pattern is that, as in the "fountain effect" figures

above (Figures 3 and 4), the dynamo-induced ion velocities are being modified by neutral

wind flow, the meridional component of which flows generally from the summer to winter

hemisphere under solstice conditions. Due to the inclination of the geomagnetic field lines

such a wind would cause an upward drift component in summer and a downward drift in

winter.

The magnitude of B varies greatly (from 25000 to nearly 41000 nT at the surface,

or more than 60%) with longitude at the dip equator. We investigated possible longitude

effects in the average magnitude of the vertical ion drift velocity Vv = Eew/B. We obtained

an average diurnal curve (Figure 8a) for a wide (-130° to 5°) longitude sector near and

immediately east of Jicamarca, where B has an absolute minimum, and a similar curve

(Figure 8b) for a zone centered near Malaysia (60° to 160° longitude). B is on the average

approximately one-third larger in the later region. Other arbitrary data selection criteria

were similar to those used for Figure 2: N< > 104 cm"3 and DLAT from -20° to 20°.

Data from March through December 1979 were used, which yielded nearly 20000 points for

Figure 8a and nearly 10000 points for Figure 8b.

If we compare the average magnitude of the vertical drift over 24 hours of local time

for the two regions, it is found that the values are close: 11.0 m s~' for the low B region

and 10.7 m s~' for the high B region. The algebraic drift averages were 2.6 and 2.5

m s~', respectively. From these similarities in the diurna l curves we conclude that the

average value of Vu is not proportional to B. Instead, as one might expect based on simple

dynamo theory, if the induced dynamo field is proportional to U x B where U is the neutral

wind velocity responsible for the dynamo fields and also U is to first order independent of

longitude, the electric field Eevi is then approximately proportional to B and the vertical

drift Vv — EK W/B is then approximately independent of B [Richmond, 1980). In a model

calculation by Dachev and Walker [1982] the assumption was made that Eew was constant.
llased on the above, ;i hotter assumption would he that l'j,.v,/H is constant.

Suimnary

W<: made mass plots of the vertical ion drift values from the UA files of satellite AE-E

for tlur years 1977, 1978, and 1979. The average diurna l variation of V,, withi n 20° of the

dip equator is remarkabl y simila r to that obtained at .licamarr.a in the same years by Kyer

f:l, til. 119811. The average meridional ion drift velocity vectors, obtained as a function of

latitude by combining the average vertical and horizontal (nearly north-south) ion drift

values from AE-E, showed the expected variations with local time and season based on the

well known equatorial fountain effect theory [Marty n, I9.r).r); Hanson and Moffett, 196(>|.

The average diurna l variation of the vertical drift was found for four different ranges of

dip latitude for a northern solstice season. The effect of transequatorial neutral winds was

as evident in this plotting format as in the meridional vector or "fountain effect" format just

mentioned, consistent with the results of previous studies using data from AE-E [Wharton

et a/., 1980; Dac/iev ami Walker, 1982. Finally, the average vertical drift velocity Vv, not

the east-west electric field Kf w , was found to be approximately independent of longitude,

as expected from dynamo theory [Richmond et al., 1980).

Acknowledgements. We thank W. B. Hanson and D. K. Harngboyc for useful comments

arid the World Data Center-A for providing AE-E Unified Abstract data tapes. This work

was supported by NASA grants NAG 5-450 and NCR \'1-004-120.

ORIGINAL PAGE IS

Of POOR QUALITY
REFERENCES

Cragin, 13. L., C. E. Valladares, W. B. Hanson, and .1. P. McClure, Bottomside sinusoidal

irregularities in tin: equatorial I1' region 2., cross-correlation and spectral analysis, .7.

Geophys. Res, <)(), 1721, 1985.

Dachev, Ts. P. and .1. C. (•'. Walker, Seasonal dependence of the distribution of large-scale

plasma depletions in the low-latitude F-region, .7. Geophys. Res., 87, 7625, 1982.r

Fejer, 13.C. ,1). T. Farley, R. F. Woodman, and C. Calderon, Dependence of equatorial

F-rcgion vertical drifts on season and solar cycle, .7. Geophys. Res., 84, 5792, 1979.

Fejer, 13. (I., I). T. Farley, and C. A. Gonzalcs, F-Region cast-west drifts at .licarnarca, .7.

Geophys. Res., 86, 215, 1981.

Hanson, W. B. and R. J. MofTctt, lonization transport effects in the equatorial F region,

J. Geophys. Res., 71, 5559, 1966.

Hanson, W. 13., D. R. Zuccarro, C. R. Lippincott, and S. Sanatani, The retarding potential

analyzer on Atmosphere Explorer, Radio Sci., 8, 333, 1973.

Hanson, W. B., and R. A. Heelis, Techniques for measuring bulk gas motions from satellites,

Space Sci. lnst,rum., 7, 493, 1975.

Heelis, R. A., W. B. Hanson, C. R. Lippincott, I). R. Zucc.aro, L. H. Harmon, B. J. Holt,

J. E. Doherty, and R. A. Power, The ion drift meter for Dynamics Explorer-B, Space

Sci. lustrum., 5, 511, 1981.

Heelis, R. A., The polar ionosphere, Rev. Geophys. Space Phys., 20, 567, 1982.

Martyn, D. F., Theory; of height and .jonization density changes at the maximum of .a

Chapman-like region, taking account of ion production, decay, diffusion, and total

drift, Proceedings Cambridge Conference, pp. 254-259, Physical Society, London,

1955.

McClure, J. P., and V. L. Peterson, Plasma transport in the equatorial F region, Radio

Sci., 7, 539, 1972.

McClure, J. P., W. B. Hanson, and J. H. Hoffman, Plasma bubbles and irregularities in

the equatorial ionosphere, ,7. Geophys. Res., 82, 2650, 1977.

Rich, F. J,, R. A. Heelis, W. B. Hanson, P. B. Anderson, B. J. Holt, L. L. Harmon, D. R.

Zuccaro, C. R. Lippincott, D. Girouard, and W. P. Sullivan, Cold plasma measurements on HILAT, APL Tech. Digest, 5, 114, 1984.

Richmond, A. D., M. Blanc, B. A. Emery, R. H. Wand, B. G. Fejer, R. F. Woodman,

S. Ganguly, P. Amayenc, R. A. Behnke, C. Calderon, and J. V. Evans, An empirical

model of quiet-day ionospheric electric fields at middle and low latitudes, J. Geophys.

Res., 85, 4685, 1980.

Spencer, N. W, L. H. Brace, and D. W. Grimes, The Atmosphere Explorer spacecraft

system, Radio Sci., 8, 267, 1973.

Valladares, C. E., W. B. Hanson, .1. P. McClure, and B. L. Cragiri, Bottomside sinusoidal

irregularities in the equatorial F region, J. Geophys. Res., 88,8025, 1983.

Wharton, L. E.. N. W. Spencer, and II. C. Brinton, Correlations between neutral meridiona l

winds and ion densities observed on AE-E, .7. Geophys. Res., 85, 4(>53, 1980.

Woodman, R. F., Vertical drift, velocities and east-west electric fields at. the magnetic

equator, .7. Geophys. Res., 75, 6249, 1970.

6

ORIGINAL

OF POOR QUALITY
Woodman, 11. I'., tt. C. llastogi, atul C. Caldc.rou, Solar cycle effects on the electric fields

in the equatorial ionosphere, J. Gvophys. Res., 82, 5257, 1977.
Figures

Figur e I. Ion drift, velocities parallel and perpendicular t,o the geomagnetic field for A 1C-10

orbit I.'{'JOG using data takon from the Unified Abstract (UA ) dies. The lower panel

shows the ion density N, and the dip angle of the geomagnetic field.

Figur e 2. a) Mass plot of vertical ion drift data taken between -20° and 20" dip latitude

during the August to September 1970 time period, b) The same data averaged into 30

minut e time bins (solid line). The symbols indicate .licamarca incoherent scatter radar

vertical drifts taken durin g equinox months for the 1968 1971 and the 1975-1976 time

periods |Fe/cr ct a/., 1979). The dashed line is the empirical model of liic.liniond (1980)

for the .licamarca region.

Figure 3. a) A10-E ion velocity vectors versus dip latitude durin g the 12-16 hrs LT interval

for the last 10 months of 1979. b) Same as a) for midnight to 04 hrs LT

Figure 4. a) Northern hemisphere summer ion velocity vectors for the 18-22 hrs LT sector

for the years 1977 and 1978. b) Same as a) for northern hemisphere winter.

Figure 5. a) Mass plot of vertical ion drift from May to July 1979 from -20° to 20° DLAT.

I)) Same data averaged into 30 minute bins

Figure 6. a) Mass plot using only data from Figure 5 in the 10° to 20° DLAT range, b)

Same as a) in the -20° to -10° DLAT range.

Figure 7. a)-d) Averaged drifts obtained by breaking the data set of Figure 5 into four 10°

wide bins of DLAT frorri north to. south respectively.

Figure 8. a) Average diurnal curve for low-B longitude region (-130 ° to 5° longitude), b)

average diurnal curve for high-B longitude region (60° to 160° longitude).
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Figure 7
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