TRITA-EPP-84-05 ROCKET AND SATELLITE OBSERVATIONS OF
Transcript of TRITA-EPP-84-05 ROCKET AND SATELLITE OBSERVATIONS OF
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TRITA-EPP-84-05
ROCKET AND SATELLITE OBSERVATIONS OF
ELECTRIC FIELDS AND ION CONVECTION
IN THE DAYSIDE AURORAL IONOSPHERE
G. Marklund and R.A. Heelis*
June 1984
Department of Plasma Physics
Royal Institute of Technology
S-100 4 4 Stockholm, Sweden
*Centre for Space Sciences, The University of Texas at Dallas,P.O. Box 688, Richardson, TX 75080, USA
ROCKET AND SATELLITE OBSERVATIONS OF ELECTRIC FIELDS
CONVECTION IN THE DAYSIDE AURORAL IONOSPHERE
G. Marklund(1) and R.A. Heelis(2)
Abstract
AND ION
Electric field observations fro» two high-altitude rocket,
flights in the polar cusp have been combined with satellite
observations of ion drifts to infer details of the electric.
field and convection pattern of the dayaide auroral
ionosphere. A region of shear flow reversal can be inferred
from the electric field observations on one flight near 15,30
MLT 20 minutes after the Dynamics Explorer 2 satellite crossed
trough the same region. The drift patterns observed by the
eo spacecrafts wsre very similar although shifted by 0.5
Agrees, a shift which i 3 expected from the observed ch&nge in
m e interplanetary magnetic field (IMF) B component during
.his time. A regica of rotational flow reversal was covered by
the other flight shortly after Ut&qaetic noon, at the same time
the DE-2 satellite travelled along roughly the dawn-dusk
meridian. Ey joining points of equal potential, integrated
from the two datasets and assuming the reversal boundary to be
an equipotential, the instantaneous convection pattern could
be drawn showing cre3cent~shaped convection contours in the
dusk cell and more circular shaped contours in the dawn cell.
In order to reproduce this pattern using the convection model
recently proposed by Heelis e,fc _ a,j. (1982) it was found
necessary to introduce a local-time dependence of the decay of
the electric field with distance from the reversal boundary.
Moreover this pattern is 3hown to be qualitatively in
agreement with the predictions of a geometrical model by
Crooker (1979) when the IMF is oriented towards dawn. The same
characteristic patterns but with the du»? and dawn cells
reversed, as presented in a recent radar-satellite study for
the IMF oriented towards dusk may serve as additional evidence
in favour of this model.
(1 ) Dept of Plasma P h y s i c s . . The Jfoynj. TnsV.it.U.K of T<;chro l o g y , S-'.OO <-,4S t o c k h o l m j J,W(jiieri
( 2 ) C c n t r ' . : f o r : S p a c e - a c j ^ n c - , . , 'jh.t.- 'iv '<•« , - ; - ; ' . t .y >f ' " . • ; •«? . a'. Di-.j J .- ir- , I ' . ' . ' , '^y
Page 2
1.
The daysxde auroral ionosphere and the polar cusp have
attracted specific interest due to the fact that fundamental
processes taking place in the; outer magnetoaphere, its
boundary regions and the magnef-.osheath are reflected here and
focused to a relatively small area easily accessible for
observations by spacecraft and trow tb» ground.
Electric fields have been measured in this region either
directly by double probes on satellites (Cauffaann and
Gurnett, 1972), rockets (Maynard £$L~H- . 1974; Ungafcrup eJL_&l,
1975; Primdahl £i__al. 1979, 1984; Joxgenaen ä£_ftl, 1980;
Kintner et aj. • , 1978; Daly and a.uå Vhalen, 1978) and balloons
(Mozer et; al • 1974} or indirectly fro» the motxon of Barium
clouds (Weacott ££_Ä1- *'V/6) or the acfcient ion drift as
observed toy back? c-s.t ter radars (Foster iLfc_/li.> 1981). Many of
these studies *uVfei from en inisufficient data coverage to
enable an instancaneou.-- pic-cur*; of the large jjcale electric
field oj. convection ^Ht'-.erii to b« constructed. In the vicinity
of auroral arcs, axc-ÄBsocxa';ed electric f.i.elda associated
with Bi eke land currents -^m" poi.sri.3ati on eiectexe fields may
drastically change anc- complicate 'r.he pic cure (Marklund
1383, 1984). Direct iaeapureBient,3 of the plasma motion as
observed by earth orbxeing sa.teili.tew (Han»on and Keelia,
1975) formed the starting point for more systematic studies of
the large scale convection pattern. Not until recently was an
attempt made to reconstruct the instantaneous convection
pattern using simultaneous satellite (DE-2 5 and radar
observations (Chatanika, Millstone Hill) for a number of
events with the interplanetary magnetic field pointing toward»
duak (Heelis et al, 1983). By joining point» of equal
potential integrated from the various datasets, instantaneous
equipotential contours could be constructed showing -i
crescent-shaped and narrow dawn cell and a wider and
circular-shaped duak ceil The only local ti ne sector for
which the data coverage was poor or missing was between 11.00
MLT and 16.00 MLT i.e. un important part of the dayside
auroral cval.
Page 3
In this study we have concentrated upor» this region to enable
a detailed picture of the Wayside convection pattern clone to
the convection reversal boundary. Thus, a region of rotational
flow reversal is covered by cr,e. rocket flight shortly afc&x
magnetic noon while tihe L'E-2 satellite travelled in
essentially the dawn iusk serijional plane. For this event
detailed equipotentiel contours could be dtawrt base! on the
two datasets described in Section 4
The other rocket parsed through a xsqior» of shiar flow
reversal a3 inferred frow electric field observations close to
15.30 MLT. 3ince tiie ssue xayi.oti w.x passed within >'C sinutas
by the DE-2 satellite; the two datasets together provide verv
detailed information on the convection reversal itself but
cannot be used tc draw the .inst&nt&ij«i.>u,* convection pattern at;
in the other case.
Addition-ni plasxadxiit. observations are provided by th^ Sachs
Harbour radar trom a regiotx close to the r*:v«u"3al boun«Iaiy
nore towards noon than the rockets.
An important point is chat he two events uifscusaed here
geomagnetically quiet, with a relatively stable orientation of
the IMF, as will be described in more detail in Section 3.
This implies chat eny large temporal variations are not likely
to have occureU during the short tiae intervals between the
different datasets.
2.
As part of the Project CENTAUR twe Black Srant 10 rockets were
launched fro» Cape Parry (invariant: latitude 75°), Canada in
December 1981, to study tht; electrodynamics of the polar cusp.
The payloads carried detectors to measure the energetic
particle composition, DC and AC electric and magnetic fjelda,
plasma density and temperatu/e and finally the ion drift. We
shall here concentrate on the observations made by The Royal.
Institute of Technology iRIT) double probe electric field
experiments on the two rockets observations of tht other
Page 4
parameters mentioned abov* will be described in companion
papers. The RIT experiment C&A be operated in two mode». the
high impedance mode providing vector electric field
measurements with a tame resolution of 3 »» and the Langmuir
node providing information on plasma density and temperature
every 5 a. A detailed description cl the operational »odes for
a similar experiment, is qiwtn in Marklund #.£_AA (1531). A£t.er
subtraction of the v*rB contribution the electric £2 eld has
oeert transformed to ?. local geomagnetic coords »»ate system with
the north axis oriented &pt>r<. ximataly 3fc clockviae froie
geographic north.
At the time of the two CENTAOB flights the DE--2 satellite
crossed the high -latitude northern Aeaisphsre along
approximately the dawn-dusk meridian. During these passes,
taking about 20 minutes between the 50 invariant latitude on
the dawn and dusk side, the ion drift velocity is measured
every second alrmg the satellite track. Oiily the component
perpendicular to the trajectory is dvailaole for these two
events. Detail3 of this experiment and the DE 2 satellite have
been given by Hoffmann (1981).
A number of ground-based experiments delivered important
information on the geophysial condition» during the two
events. These will be discussed in Section 3. The Sachs
Harbour radar provided plasma irregularity drift observations
as deduced from the received scattered. 3igua,l3 originating
from a satellite transmitter. Due to the gftonetry of the
irregularities and the viewing direction of the radar only the
drift component in roughly the geomagnetic north-south
direction is available.
Page 5
3. Gc.ophyg;ictt,L
fr 1; December 1 • 13,8 \
The CENTAUR 35.001 rocket was launched fAonj Cape Parry at
01.38 vjy ( 15.00 MLT) during « geomagnetical] y v«ry quiet
period ao demonstrated by viq. 1a, showir-ij the magnetometer
H - component, fro» the. Alaska meridian chain for a 24 hour
period including the flight. The 3-hour K - index waa 0+. In
Fig. 2a the interplanetary magnetic field data are plotted as
vectors in the x--y and y-z planes respectively. The vectors
have been averaged over the time intervals indicated by the
attached numbers, during which the IMF-orientation was
relatively stable ft. toward 3ector of the IMF with a strong
sunward component (B >O), a somewhat weaker component towards
dawn (B <C) and an even smaller z~component that changed from
negative to positive about one and a half hour before launch,
characterised this e
2J
The CENTAUR 35.002 rocicet WÖS launched at 27.54 Wl* { 12.30
MLT) on December 13, a day characterized by moderate
geoaagnetic activity as can be seen in Fxg. 1b.
Several hours before launch, however, the activity dropped
away aLaost completely. The 3 hour K -index during this flight
was 1. The IMF data are plotted in Fig. 2b as vectors averaged
over 15 minute» intervals starting at the indicated time»
before launch.
The two rockets were launched Iron: Cape Parry (invariant
latitude 75. ) in a direction roughly towards local
geomagnetic north. They reached an apogee ot about: 670 k» 7.5
»inute» after launch and traversed 7° ot invariant latitude.
The spin axe:? of the rccketa were kept closely paiilL^l to the
direction» of the local magnetic field wi.th «n Almost
negligible coning angle.
Page 6
k inoxe coapreher.sive xepoil on -Je project CENTAUR and the
geophysical conditions and initiaj result0 will be given ia a
companion paper.
4.1 Rocket and radar observations
The result of the eiecLric .field ct ta anal"s.is for the two
CENTAUR flrght3 on December 1 (afternoon> <*ni ^eceabur 3
(noon) are plotted in Figs. 3a and 3b respectively. A similar
trend can be recognised tor the two events nameiv a reversal
of the geoisagnetxc earthward component wiiiie the eastward
component, i? positivt* throughout vixe flight a:?.ci shovs Ies'3
variation. Detaaeps are se^n it- Fi^ 3s corresponding *.o
peri.ods for whicn rr.f- •ei-ictric Ei.eJc proi-e« w-tre -53iv-'.;r'ii.tccf and
intense ion ibefisas ve.-e c-p wxv.i.i , rhi.r< wi.i I nor. DH ti^Äted hex-e
bur in a sepa.rat« paf'-u: In FJ..TS. 4;i a rue, 4b '0 t a^exsg^a o£
the 'lata shown at-'>v« a.'t plotted •:;« fle^Uio f.:»5ia vectors
every hall; minuet -i;.ong the 100 icrc ?«9;K^ it f ;oc.i;.-o.irii: of the
rocket trajectory By coiapaxing the revs*ssis tor the two
events one notes thf; tox:.o*t±nq >
1) The reversal for the afternoon event (Event 1) occured
almost two degrees more pol^Kard than for the noon event
(Event 2)
2) The eastward component of the electric ilield tends to zero
at the reversal boundary for the afternoon event thus
indiceting an equjpotential boundary. Thi« i» not the case
for the noon event.
3) Poleward of the reversal boundary an abrupt variation is
seen in Fi-j. 3a in the northward "jl«ctric f', eld component.
An almost 1 : 1 correspondence is found between thi.8 and the
magnetic di3turb^rco in the perpendicular direction as
observed by the onboard magru-./torsev.*iö (data not shown
here), r e f k e t m j <? paa.-i.igc '-hrcugn u-ivrjenr fi«ld aliened
Page 7
current sheets.
(Pri^ndahl
This, is *.n separate paper
4) The electric field was very intense during vise noon event
especially poleward ct tie reversal where it exceeds '»OO
»V/w, while it was weaker for the afternoon event.
2In Fiy. 5 the ExB/B ' drif ts &a inferred frön the <?l«o*vl <:•
field <?c;t.i for ché (,vo »-vent are preseittca in .1»
invariant-lati tude vi a&tjr-.&tic local i viw MI&Siari, 'A
rotational ravexsal with relatively strong north*-n.rd år i i t f
can be recognised for tihe r'oorj evert and a •ilv.:.*?. flow zi*vr ci,a'i
for the ^fLGinoor;
obaerva-Jori 2 above.
fc &u t-?.! t-nt aescrxpr ion of
hvj rö cowpcnerit o£ the
f»> tl».e Sa -ha Harbour radar,
iti,. re^pectj vcly, xn the
.-VÄCS^I i'r'und.':;:v. For the
tlv.i.fL W.AS v«.ry siaiili as
ia and 6b dhew tht ii
i rregulari ty dr i f t s , --.?. Okwyrv
duriiig the aitc-rro.>n ai-d n m e
vicini ty of the ÄT/£ -CJOI-:
afternoon evet:.t, "ch?. r-.octriw .c
expecteU for a &htis.t £1-.;* reversal, »vhiJc fox the noon evert
tha drs.ft v?as coiisid i'ctfci.Y larger- cDrifsÄoterm with »•
rotational flow revtrKi.. A zcl<» civey good ^.gxeeiaent can be
seen betveen the rorkst anc re<if.i observation» i.Vi tii« region
of cLofest approach å»etwf-e» fcht; two th^t i s .: n<ii.f;-ut«Q by the
shaded area.
In Fiq. 7 are shown the »lectton <3exigi';y a:v<J temperature as
deduced from tha f»angauir aweeo^ of the HIT experiment on the
noon flight. The electro^ density variation reflects an11 - 3altitude variation with an F-regxon peak of about 10
seen close to 400 k?n altitude during the upleg. An increase in
T e fro» about 2000°K tc 3000°K can be seen in the latex part
of the flight, within the polar cap. Corresponding data for
flight 1 have not yet b«en evaluated.
Page 8
DE-2 observations
In Fig. 8a the DE-2 perpendi.cu.lar ion drifts are shown trom a
northern hemisphere crossing between 1.15 UT and 1.35 UT on
December 1 shortly before the launch of the CENTAUR 35.001
rocket at 01.38 UT. A pronounced region of sunward convection
on the duskside accompanied by somewhat more structured
antisunward flow in the polar cap is seen. The division
between plasma circulating around the dawnside and around the
duskside narked by the location of a "zero potential* line
occurs close to the noon midnight meridian and the maximum and
minimum potentials of +3 kV and -15 kV observed by DE-2 occur
at 82° and 79° invariant latitude, respectively. By comparing2
with the ExB/B drift vectors calculated for this flight, as
shown in Fig. 5, one notes that the rocket and satellite
trajectories almost overlap close to the the dusk reversal
boundary, and that its location Agrees well between the two
datasets. This is more clearly seen in Fig. 9, showing the
DE-data together with the sunward component of the CENTAUR
driftvectors, which have been projected to DE trajectory along
circles of constant invariant latitude. Note that the observed
drift patterns are very similar although a poleward shift of
0.5 to 1 degree can be recognized during the twenty minute
interval between the DE and the CENTAUR observations. Such a
shift is consistent with a shrinking polar cap that might be
expected for the observed change in the IMF B -component from
south to north, taking place roughly one hour before the
rocket launch. Relatively small drift velocities prevailed
along the entire dawn-dusk meridian during this flight.
In Fig. 8b the perpendicular ion drifts are shown for a DE-2
crossing between 22.25UT and 22.45 UT on December 13, shortly
before launch of the CENTAUR 35.002 rocket at 22.54 UT. A
two-cell convection pattern of a more common form can be
recognized for this event with antisunward flow in almost the
entire polar cap region between invariant latitude 75° and 76°
on the dawn and dusk side respectively. The flow velocities
were obviously larger for this event, increasing from the dawn
to the dusk side.
Page 9
Due to the good data coverage b>- the rocket close to magnetic
noon and by the HE 2 sf-tel lite in roughly the dawn-dusk
meridional plane, separated in tin'.e by leas than 30 minutes, a
detailed picture of the dayaide convection pattern can be
inferred. In Fig. 10a the high-latitude region above invariant
latitude 70 from Fig. 8b ha& been enlarged and supplemented
in the following way: Points of equal potential integrated
from the rocket and satellite data along their respective
trajectories have been joined under the assumption that the
convection reversal boundary is almost &n equipotential; and
with the requirement that the drift vectors are tangential to
the equipotential surfaces. The latter requirement can be used
only on the rocket data since the longitudinal component of
the DE-2 drifts is missing. Thus., there is still some
uncertainty about the exact orientation of the equipotential
surfaces along the satellite path although they are accurately
located. It can be a«en that the dayside pattern is
characterized by crescent-shape-d convection contour?; in the
dusk cell compressed towards noon with a reversal boundary
potential of about -37 kV and a potential distribution in the
dawncell indicative of an anticlockwise circuiarshaped flow
pattern with a reversal boundary potential of about 13 kV.
Assuming the convection reversal boundary forms a circle
passing through the dawn and dusk reversals at invariant
latitude 76. 5 and 75° respectively given by the DE-2 data and
the rotational reversal at 77.°2 close to noon given by the
rocket data, the polar cap radius become3 about 14.6° with a
centre shift of 2° towards magnetic midnight. A »ore detailed
picture of the dusk cell is shown in Fig. 10b.
5. Discussion
The high-latitude convection pattern is known to respond
sensitively to variations in the interplanetary magnetic
field. Any fruitful attempt to picture the instantaneous large
scale convection pattern requires geophysically stable
conditions over a period which exceeds both the typical
response times for changes ia the IMF and the data-taking
periods. Since these times aie typically 30 min, her» and
Page 10
since it was geomaynet.} cally q>jiiet for 3everai hours prior to
launch (ef. Figs. 1a and 1b> ana the IMF was stable for more
than one hour (cf. Figs. 2a and 2b) for both events the above
requirement was reasonably well fulfilled.
For both events the IMc b -component was negative (c£. Figs,
2a and 2b). When the 1KF B -component is negative the above
condition is known t.o prodnce ar asyaaetiy in. r.he convection
pattern such that electric field naxiifla c-cuT. on the 3us.k ai'.'e
of the northern polar <;.sp and the da^n si.<ä« ot thy souths»*
polar cap, as shown by e o Beppi,eT ;i^7^v- .fid Mo-.-.t-i ( '-374).
This asymmetry is clearly fwi.rtert j.'» *ig. flh oi. Fi<3. 'Oa
showing an increase .».n cue drift vvlocitifis f.r >r: the da^n to
the dusk aide. The M&r; cuii pt.-tentr a i on fchw '.1,'.k &.id-.» »as -1b
kV for the Deceaiber "> evtnt and -:n ?cV foi trs r>ecerofc»-..'i- 13
event -and the correspondin«j viiiuea ;a th?; ''-n.'1 s.d« w»-.-«•:•(* +3 kV
and +13 kv\ inferred frca the inte^rai ion of *-t-e niv- 2 data.
The enhanced electron tenpc;rai..urs of 3000v'K observed bv the
rocket within the polar cap <cf. Fig. 7) Stay be ..re'ared to the
intense electric fields reaching 100 v>V;?u a net oorresponcliris/
intense drifts within this egion.
For the December 1 event, goo>1 agreement between the rocket
and satellite measurement? of £ x fi rtr.ift is obtained in the
duskside auroral zone-., The cJiaxacte-Tiifttioo of: a global
convection pattern la made difficult by the northward IHF
conditions prevailing foe this event and by the *act that the
rocket and satellite data were taken in about, the same
location. Several features are worthy of «ote. The. corvectxon
signatures rtxe generally coiisistetit with two convection ceils
with sunward convection in the auroral aones both or, tne
dawnside and the duakside, In the polar cap, identified by the
absence of plastmasheet electrons observed oa DE-2, the
convection is extremely structured bat has a small antisunward
component.
Page 11
For the December 13 event, a much clearer and more easily
characterized signature of the. convection pattern is seen.
This is possibly due to the fact that the IMF was here almost
entirely directed toward dawn. In this pass the two convection
cells appear to occupy about the aame area on the dayside but:
crescent-shaped flow contours nxiat only for the higher
negative potentials on the dusksiOe. We loote that, at /.east
some of the rotational reversal, region seen by the. rocket
exists on the duskside of Local noo;i.
The general flow patterns may be understood in ter«a of a.
geometrical model by Crooker (1975) Fig. 11 is a -.reproduction
of Fig. 5 in this paper showing predicted poj.av ca.p convection
patterns for various orientations of I'M!' in the y--s plane,
attributabis to merging of ant i para i Z .el field linet.
The predicted pattern for the- December 1 'jvent involves only
one cell circulating ;.'oTr<;c) ev.»»ly within the polar cap. We
cannot of. coura« rule cuh. su:;h ,-». pt r-svoiU.ty 3ir.ee the
convection velocities xnvo.lveä s:*/ bo .•;««!. 1 and extremeJ. y
structured. NevertheJ.ess?, the most ^torain^nt feati/res include
two convection celJ.s that include sunward convection i.r\ the
dawn and dusk auroral ?.cnca. Xne eJ.o«:."i.ro3tat.ic potentials
associated with these cells are quite small and could be
attributable to additional viscous interaction processes
operating at the nagnetopause (Ctooker, 1977),
For the event of December 13 the preoicted and observed
convection patterns axe root.'» consistent. The crescent-shaped.
convection contours on the dusksioe arc consi^teit- with both
dayaide merging and vit-cous interactiori, and we have not
distinguished the relative importance of these mechanisms. On
the dawns ide the transit..) or* fro» sunward to ant i sunward flow
is very structured and some »mail regions of sunward flow may
exist within the polar cap as required by the model. It
appears, however, that most of the fJ.ow is attributable to
day3ide merging even in this rather extreme orientation of the
IMF.
Page 12
In a similar study Keelia fi±._ai (t(itf3) pxese/it, on basis of
radar and satellite observations, instantaneous pictures of
the convection patterns for &ix events when the IMF
B -component instead ws,a positive. As expected the
characteristic shapes of the dawn and dusk cells were reversed
fitting qualitatively with the predicted patterns shown in
Fig. 11 for various positive IMF 8 -orientations. The multiple
observations covered essentially the entire ni gfctsidi? fro»
local morning to local evening but not the afternoon sector on
which we have concentrated in th« present study.
To summarize, there is strong evidence in favour of the
geometrical model by Crooker (1975), both from the da^side
convection patterns observed in this study for IMF » < 0 and
from the satellite-radar study by Heeiis e_-fc_al. M983} for IMF
B 0.
An attempt was also made to reproduce t,h<* instantaneous
dayside pattern drawn in Fig. 10 by firting ihe model
parameters in th«: convection model by Heel is &t_.ai.- (1982). I*-
was then found necessary to introduce some modifications in
the model. For example, the clusk cell is, according to Fig.
10, more compressed close to magnetic noon than it i.3 at dusk,
especially poleward of the reversal boundary. By introducing a
local time dependence for the electric field decay index
describing how rapidly the fi^ld decays away from the reversal
boundary this could be accounted for. An exponential increase
in the decay index r- from about 2 at dusk to 5 at noon was
found to reasonably well reproduce the observed pattern.
7. Concluaiona
In this study a combination of electric field observations on
two CENTAUR rocket flights in the polar cusp, ion drift
observations on the DE~2 satellite along the dawn-dusk
meridional plane and irregularity drift observations from the
Sachs Harbour radar have been used to infer details of the
electric field and the convection pattern of the dayside
auroral ionosphere, during two geoa&gnetioiiXy quiet event»
Page 13
when the IMF
3unnarized as follows
B -component was negative The resulta tan be*
On December 1, the same region, with a shear flow reversal,
was traversed fir3t by the DE-2 satellite and twenty
minutes latex by the 35 001 rocket. The drift patterns
observed by the two spacecrafts were ver1/ similar altheuqh
shifted by 0.5 degrees, a shift which is expected fro» the
previously observed change in tbe IMF B -coBponent.
Additional evidence that the reversal is of the shear type
and not the rotational type is given froa fiaultaneous
radar observations of almost negligible uoxthward drifts at
the reversal boundary.
2. On December 13, a xegioa with a rotational flow reverse!
centered around 77.°5 was traversed by the 35.002 rocket
close to magnetic noon, 0:1 the DE-2 Satellite passed ever
the dawn and dusk reversal boundaries at 05.30 KLT an«5
16.30 MLT respectively. Intense northward drifts as
observed by the Sachs Harbour radar at the reversal
boundary aerve as additi nal evidence that the reversal is
of the rotational type. A detailed picture of the
instantaneous dayside convection pattern could be drawn by
joining points of equal potential integrated from the
rocket and satellite data. The result shows a
crescent-shaped dusk cell convection contours compressed
towards noon and a more circular shaped dawn cell.
This detailed dayside pattern for the December 13 event and
that inferred qualitatively for the December " event are
shown to be generally consistent with those predicted from
a geometrical model by Croaker (1979) for the given-
IMF-orientations with B negative. The addition of
convective flow from a viscous interaction type »echanism
is required when the IMF has a northward component. The
sane characteristic shape» but wjth the 3usk and dawn cells
reversed, as presented in a recant zaiiar- satellite study
for 8 > 0, may pervf as aååii.tonal evidence in favour of
Page 14
this »oöei
In order to reproduce the layside convection pattern
presented above usircg the convection model by Heelia et a.1.
(1983) it was found necessary to introduce a iocal-tiae
dependent electric field decay index increasing
exponentially towards noon.
Acknowledgements
The authors thank ft. Mehra for part of the 3ata analysis of
the rocket data, L Blockr C.-C-, Falthammar &nå D.W.
Winninghan for helpful cosnBent3, S.-I, äkasofu for providing
ground magnetometer data and J,h. McDougalj for the Sachs
Harbour radar observations, K Foraberg for snaking the
excellent drawings and. E. Flcrman for typing the a-.anuscrj.pt.
This research was supported by the Swedish Board of Space
Activities and by NASA grant HAG 5-?>O6 and Ait Force
Geophysics Laboratory grant F^€28-S3~K-OO2£ to UTC.
Paae 15
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Cauffsan, D.P. anä Gurxiett • I! £ . , Satellxtft ^asureise^ts of
High-Lat-itude ConvaetiGu Elecv.ris: Fields, S-a.c<: Sci. Rev..
Q , 369, 1972.
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Geometrically Explicit Model, J. Geophys. Res , £.£ 362"i>,
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Res., M r 951, 1S79.
Geophys
Daly , P.W. and Wn&ler-, h h . . R o c k e t - B o r n e K'saaure^-^vc
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cf
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Gas Motions fro» Satellites; Space Set jLii
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Heppner J.F.f Polar-Cap Electric Field Distributions xels.ted
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H«elis, R.A., Lowell, J.K. and Sp.iro, H.W., A Kedc-l of
High-Latitude Ionospheric Convection. J ^eoph^sr - RH> . . $ J.,
6339: 1982
Heelis, R.A , Foster, J.C , df: la Baau jaidiére. O and Holt,
J., Mult '.atdtion HCniauxfibifttTts of !-!iqh ••i- tit'-d*.» Ivi
Convection, J. Ceot;hyr. !^;r; . M ; »O'-'ii, '.?£>.*,
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Hoffaaann, R A , uynaaii :u HJ
1981 .
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Correlated Electric Field and Low-Eneigy STffctxoa
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Measure»ents of Electric Fields, Electron Density and
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Gxound-Based St.ady of an Auroral Breakup Event, l;lanet.
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Marklund, G. , Auroral Arc: ux^sai f ication Scneajp Brssed on the
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1974.
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Bes., 8A, 6458, 1979.
Primdahl, F.r Bahnsen, A... £jiri, M., H^eg, P., Marklund.; C,
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L.J., Rocket-Borne atsc CAOund-BasevJ Ohsei vat.iojis *-.f
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Spangsiev, F. , Heikkila, W.J.r Kluzpar, D.H., Wiraingh3i3,
J.D. , Fahles!onä U.# Falthainsiax, C-G. ar.d Peder en, Ä..
Rocket-Borne Particle» Field and Plassa Observations in the
Cleft Regions Geophys. Res. Lett., 2, 345, 1975.
Wescott, E.M., Stenbaek-Nielsen, H.C.. Davis, T.N., Jeffries,
R.A. and Roach, W.H., Th« Tordo i Polar Cusp Barium Plasisa
Injection Experiiaer.t, J. Geophys. Ras., ä2, 1565, 1978,
Page f t
Figure captions
Fig.1 H-co»ponent of the ground magnetic disturbar»ce a?
measured by the Alaska laexiiian cliain of
during a) the Dec. 1 event and b) the Oecr 13
The shaded area? rei-xeasnt the flight period:?.
Fig. 2 Projections to the y-~ &n-3 x~i- plx-r*
interplanetary »<t iit;t.ic field A- J ! ^ i ^
during a) the Dec, 1 event t>r;d fc> ths Dec.
? ot the
;3 evert.
Fig. 3 Horizontal electric fielö componentp '/s fJi.ght.
(s), altitude (X.*) and universal tj.s*e in a coordinat.e
system with local geccsagnetic north 36 clockwise of
geographic north. Derived from the RIT experiaent, on a)
CENTAUR 35.CO1 on Dec. 1 and b) CENTAUR i5.002 on Dae.
13.
Fig. 4 Vector representation of the results presented in Fig.
3 along ths i00 Ka «agr»etic footpoxn'c of the rocket a)
15.001 on Dec. 1 and b) 35.002 on Dae:. 13.
2Fig.5 E x B/B drifts corresponding to the electric
observations presented in Figs. 3 and 4 plotted in an
invariant latitude vs magnetic local tiiee diagram.
Fig.6 Geomagnetic northward component of the irregularity
drift as seasuxed by the Sachs Harbour radar during a)
the Dec. 1 event and b) the Dec. 13 event. For
comparison the corresponding drift component calculated
fzon the rocket electric field data has been included,
Fig.7 Electron temperature and electron density vs flight
time, altitude and universal time ns deduced from the
RIT Lanyemir sweeps on ilight 35.002, Dec. 13.
Page 19
Fig.8 The perpendicular ion drift velocity measured by the
DE-2 satellite ai between 01.15 and 01-35 UT on Dec. 1
and b) between 22.25 and 22 45 ÖT on Dec. 13. Also
indicated are the potential distributions along the
respective trajectories, as integrated from the DE-2
data
Fig.9 Comparison of the 3unv»ard drift component observed on
DE-2 and CENTAUR 35.001 in the dusk hemisphere around
01.40 UT on Dec. 1, 1981. For explanation, see text.
Fig.10a An instantaneous picture of the dayside convection
pattern as inferred froa the integrated CENTAUR
electric field and DE-2 ion drift observations around
23.00 UT on Dec. 13, 1984. The estimated polar cap
location is also indicated in the figure.
Fig.10b A detailed picture of the convection contours in the
dusk ceil, presented in Fig. 10a.
Fig.11 Reproduction of Fig 5 in a paper by Cxooker (1979)
showing predicted polar cap convection patterns in the
dayside northern hemisphere, viewed from above, for
various orientations of the interplanetary magnetic
field (IMF) in the y-z plane, attributable to merging
of antiparallfel field lines. The shaded regions are
convection gaps. The IMF-orientation during the two
events discussed here are also inserted in the figure
ALASKA CHAIN OF MAGNETOMETERS, H TRACETOTAL SCALE IS £000 GAMMA
MOB ,522 -
CPY5
t !!
qht\35.Q01
06
DEC ?, 598?
j 1,
UT 12
335
TOTAL SCALfc IS 5(;00 GAMMA
MOB20
SAH
CPV5
INK6
FYU10
COL11
TLKV2
•- <•
.»i- - ^
."»V. /
- ^ • '
V2
Fig, ID
m"3':
75
50
J 25
0
-25
SO
25
Z 0z
Ui
-25
-50
-75
RIT DC-Electric Field CENTAUR 35.001launched 01.3a01 UT dec 1, 1961
— ^
-
-
200
4001
i
\ *
I
5001 •
i
•v 'I— -yr~
$. ,
i
550—i
i
j
6C01—
l
—;*?*_
*****
i
+•
t 1 !
Eastward
_ ... _
Northward
-.i ; i
650~ UO
1
electric
electric
6ÖG
. +
6CC
f —
i i
field
field
r
i i
550 500
Right tirr,e(5)
Af 11 k> de (km)
Fjg. 3a
100
RIT DC-e?ectnc Fieid CENTAU"? 35.002iaunched 22.5^.25 UT, dec. 13,
UI
I OUJ
-100
i i f T T !
200
t »•
-.-""'v ' ' • • ' / ' * ' ' • • " • ' • / ' • : •
Eastward electric field
Northward electric fieid
600 600
-+400 500 550 600 640 560 640 600 5*0 500, , , | A • _ , • . i • i i l i M I j „ - , _ _ ! ! , [ iii i i i I i « u t i ! • • i - ( , . i , , , m,_ ,ml „ , J . I ir i¥ T . j
2258 2100 ' 2302 2104 23JO6 Univ. Time
Flighi
Aliitude (km)
Fig. 3b
1800
E x B / B 2 drifts calculated from the RIT DC electric field observations
on CENTAUR flights 35.001 (01.38 UT, dec.1) and 35.002 (22.54 UT, dec. 13),
1500
1200
INVARIANT LATITUDE VS MAGNETIC LOCAL TIME
Fig. 5
2000 m/fc
0600
Drift velocity
(nys)
600
600
400
200
ROCKET-RADAR COMPARISON OF NORTHWARD DRIFTCOMPONENT
35.001d«c.1, 1981
CENTAUR 35.00» Riaht
01.01 UT .15
-200
-400
Drift velocity
(m/s)'
1200
1000
800
600
400
200
launch
Fig. 6aimpact
-200
35.OO2d«c. 13, 1961
55 23.00 .05
CENTAUR 35.002 Flight
launch
.10 .15
impact
.20
Time
(UT>
<—»— N-ward irregular drift a» observed by Sachs Harbour radar.
» « N-ward E I S / B 2 drift as calculated from CCNTAUR electric field.
&M Periods of closest approach and same invariant latitude between the twodatasets.
Fig. 6b
RIT Plasma parameters. CENTAUR 35.002launched 22.54.25 UT. dec., 1981
4000
3000
2000
1000
5x10 11
Ec
101!
100
22.56
electron temperature
electron density
•+-200 300
300 400-t-
400I
500 600-H » » 1 h-500 550 600 640 660
4- H h640 600 550 500
22.58 23.00 23.02•+-
23.04
Right time(s)
Altitude
2 3.06 Univ. Time
Fig. 7
DE-B ION DRIFT VELOCITIESMLT V ILAT NORTHERN HEMISPHEREDAY 81335 UT 1=23 ORBIT 1770
1 ? •••
I KM/SEC
DE-B ION DRIFT VELOCITIESMLT V ILAT NORTHERN HEMISPHEREDAY 81347 UT 22 = 31 ORBIT 1962
o
So'
!KM/SEC
Fig. 8a Fig. 8b
1200 MLT
1000 mA
nllllmllllllllll
1800
EXPLORER8
OE p«rp«ndicularion drift
CENTAUR correspondingCENTAUR driftcomponent
INV. LAT
1200 MLT
AWNPOTEMTIALMAXIMUM
POLAR CAP CENTRENiGHTSfOE SHIFT -= 2°
-1/9
/DUSK POTENTIAL MAXIMUM« -36^8 kV
Fig. 10a
TRITA-EPP-84-05 ISSN 03S8-7539
The Royal Institute of Technology, Department of Plasma Physics,
S-100 44 Stockholm. Sweden
ROCKET AND SATELLITE OBSERVATIONS OF ELECTRIC FIELDS AND ION
CONVECTION IN THE DAYSIDE AURORAL IONOSPHERE
G. Marklund and R.A. Heelis
June 1984, 31 pp. incl. illustr., in English
Electric field observations fro» two high-altitude rocket
flights in the polar cusp have been combined with satellite
observations of ion drifts to infer details of the electric
field and convection pattern of the dayside auroral
ionosphere. A region of shear flow reversal can be inferred
fro» the electric field observations on one flight near 15.30
MLT 20 minutes after the Dynamics Explorer 2 satellite crossed
through the same region. The drift patterns observed by the
two spacecrafts were very similar although shifted by 0.5
degrees, a shift which is expected fxcm the observed change in
the interplanetary magnetic fia!<3 (IMF) B component during
this time. A region of rotational flow reversal was covered by
the oth«sr flight shortly af':er maan^tic noon, at the same time
the DE-2 satellite travelled along roughly the dawn-dusk
meridian. By joining points of equal potential, integrated
from the two datasets and assuming the reversal boundary to be
an equipotential, the instantaneous convection pattern could
be drawn showing crescent-shaped convection contours in the
dusk cell and more circular shaped contours in the dawn cell.
In order to reproduce this pattern using the convection raodel
recently proposed by Heelis efr a,j. {1982} it was found
necessary to introduce a local-time dependence of the decay of
the electric field with distance from the reversal boundary.
Moreover this pattern is shown to be qualitatively in
agreement with the predictions of a geometrical model by
Crooker (1979) when the IMF is oriented towards dawn. The same
characteristic patterns but with the dusk and dawn cells
reversed, as presented in a recent radar-satellite study for
the IMF oriented towards dusk
Keywords; Convection pattern, Electric'fields, Polar
Rotational reversal, Shear reversal.