The precipitation of high energetic electrons during and after strong geomagnetic storms into heights below 100 km in middle and subauroral latitudes is markedly modulated by the structure of the interplanetary magnetic field (IMF). Under relative quiet conditions the D-region ionization caused by high energetic particle precipitation (energies greater than 20 to 50 keV) depends on changes of the interplanetary magnetic field and also on the velocity of the solar wind. To test this assumption, the influence of the IMF-sector boundary crossings on ionospheric absorption data of high and middle latitudes by the superposed-epoch method was investigated

Bremer, J.

Lauter, E. A.

English

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DEPE_|DI_CE OF TIlE IIIGH LATITUDE MIDDLE ATt_OSPIIEREIONIZATION
ON STRUCTURES I}! INTERPLAN,";TARYSPACE
Q
J, Brewer and E. A. Lauter
Academy of Sciences of the GDR, :
Central Institute of Solar-Terrestrial Physics, z!
Observatory cf Ionosphere Research, DDR-2565 Kuhlun_sborn, GDR
/
As known frou LAUTER etal. (1978) the precipitation of high-energetic
electrons during and after strong _eoma_netic stor_s into heights below I00 kln
in middle and $ubauroral latitudes is markedly _odulated by the structure of
the interplanetary magnetic field (I_). In the present paper we want to show
that also tmder relative quiet conditions the D-region ionization caused by high
enerBetic particle precipitation (energies greater 20 - 50 keV) depends on
changes of the interplanetary _.ognetic field and also on the velocity of the
solar wind.
Fo_lowln$ investigations by D_{GEY (1961) and by RUSSEL and HcPHERRC_
(1973) the negative B component of the interplanetary _agnetic field in theZ
solar magnetospheric coordinate syst_ should play an importan_ role for the
f_\ interaction of the solar wind with the raagnetosphere and the aces=partying
acceleration processes. Such negative B co_ponente are induced in the solar
• . z .
magnetospherxc coordxnate syste_ by the normal IHF sector structures only ,n de-
pendence on regular daily and seasonal ch_ges of the po_:._n of the dipole
, ' axis of the Earth's magnetic field in respect to the solar axis. If ve assu_e a
_ean IhT f£eldstren_th of 5 nT we obtain a _easonal _ar£ation of the vertical
I _gneti¢ fieldstrength in the solar t_agnetospheric coordinate system as shown in
, Fig. I. IIerewe have calculated only daily _ean values, neglecting the daily
variation of Bz. _ereas T-sectors induce in spring _aximum negative an_ in
autumn maxi_u_ positive values, A-sectors cause opposite results. As we believe
that negative B -values should favor particle precipitation into the lower
ionosphere but [_aitive B -values should reduce precipitation we define A- """
sectors in autumn and T-sectors in spring as so called 'pro-sectors', and T- . • "
sectors in autumn and A-sector_ in spring as 'anti-sectors'.
To test this ass,_ption, we have investigated the influence of I_[F-sector
boundary crossings on ionospheric absorption data of high and middle latitudes
by the superposed-epoch ncthod, with the first day of a nc_ sector as "zero"
key day. The dates of the sector crossings were taken from the catalog of
SVALGAARD(1975), or from Solar Geophysical Data. In Fig. 2, the result of
this analysis can be seen for noontime absorption measurements at vertical in-
cidence on 1.75 t_Izand 3.0 _{z as well as O_A observations on 22.4 l_[z,ob-
tained by the GDR participation groups during the 21at - 23rd Soviet Antarctic
; Expeditions at _ovolazarevskaya (II.83"E, 70.77"S). A total of 67 sector cross-
ings between June 1976 and _ovc_ber 1978 have been used. In the upper part of
Fig. 2 the influence of all sector boundary crossings on the absorption data is
presented (dashed-dotted lines) whereas in the lower part these data are sub-
divided into transitions fro_ pro- to anti-sector (dotted lines) and from anti-
to pro-_ector conditions (full lines). In cunts t to the small variations of
absorption if all sector crossings arc superimposed, a very pronounced influence
of the IHF sector structure can be observed during the transition from anti- to
i pro- or pro- to anti-sector conditions. Absorption differences of about 8 -
https://ntrs.nasa.gov/search.jsp?R=19850012177 2020-03-22T18:19:33+00:00Z
• i f
" t ,
i
|
: 201
J r M A M J J A $ O N O
~ _ z , , , ......A T
?
' "' _ PRO/ ",PRO,,, "/
T A
-2
Figure 1. Heart seasonal variation of the _ -component in
anlar-_agnetospheric coordinate system fo_ an undisturbed
interplanetary r_agneticfield (_gnitude B = 5 aT) with
A- end T-polarization.
| _o_vs_ 1
.. :6:4 :z o t == -6 -4 -,, o z _ :6 -_ :t o=_ = 6
41 12
r-. : _ " "-_'l. _" . '
, , I
:
: Figure 2. Variation of ionospheric absorption at high latitudes
,'. Oiovolazarevskaya:70.8°S; ll.8°E) during IHF-sector boundary cross-
: in&s
-.-.-.-: all sector crossings
• • • , - . , __.___.: only crossings from anti- to pro-zector
. . . . .: only crossings from pro- to anti-sector
: 10 dE at 1.75 or 3 _tz, and about 0.4 dB at 22.4 }_z, d_onstrate the haportance
of negative B -values of the IHF for the precipitation of high-energetic par-
, ticles in hig_ latitudes.
For the sane sector boundary passages ve have also investigated the be-
havior o£ f • -data from ionosonde measur_ents in different latitudes. Fig.
_In , . .
3 shows the results. Vhereas zn ||xgh _,atttudes a strong dependence of the
fmin-data on pro- and anti-sector condition could be detected, thi= influence
is smaller in middle latiLudes. A somewhat larger effect can be seen again at
Port Stanley where particle precipitation is more effective because of the
South Atlantic anomaly of the Earth's magnetic field. In lower latitudes there"
seems to be also a retardation of about 3 or 6 days of the ionospheric effect
in respect to tl_ sector crossing, =oat clearly seen for the anti- to pro-sector
: transition at Juliusruh and Port Stanley. Th_s effect may be caused by the
L
• . / .'
.' I
rb¢," .... t_'-\'. - . .
L , '>.'_ "
l
2O2
• , 20.
2O _.11 _ .J
r. j
[_J _l _J Figure 3. Variation of fL:.-data during IMP-sector
boundary crossings in d_ndence on laCltude (geogr.
fql_ fat. in brackets)
t8 _ , . . .: crossings from anti- to pro-sector
.... : crossings from pro- to anti-sectorf4
I0
: //
diffusion o_ hlgh-energetic electron_ from high to _iddle latitudes, an effect /
; which we know also from investigations of post star= events (LAUTER et al.,
I 1979), /
i
l Besides the IMF sector structure, the velocity of the solar wind could be
im_rtant for particle precipitation, especially in high latitudes. Therefore,
we have also tested the influence of solar "high speed plasma streams" after a
catalogue o_ LIND_LAD and LUNDSTEDT (1981). llighspeed plasma stre_s were
mainly defined as solar p!as=a screws which increase their velocities by more _'I
than 100 _Is within 24 hours with simult_eous enh_cements of their ion den- -:
sity and/or chenges of the interplanetary ¢mgnetic field. From the period be-
twe_ 1964 and 75 we used 171 such streams with a duration of more than 4 days
and investigated their influence on f . -data of Halley Bay, and on the geo-
magnetic AE index, m,n
Tn Fig. 4 the results of a corre;ponding auperposed-epoch analysis _ith
the f . -data are represented. The "zero" key day is the beginning of the
hzgh speed plasma strew. The data znalysia was made for two _ata sets: high
speed plasma streams with smalllVelocity changes A_ _230 k_s- (a) and large
velocity changes _v _ 300 kms- (b). With the beginning of the plasma stre_
also the ionospheric absorption increases, rather slightly at low velocity
stre_as (a) but very pronouncedly with high velocity streams (b). In the lower
part o_ Fi_. 4 the two _llcctlves of data were again divided into stre_s with
l_F of pro- and anti-sector conditions. For low velocity stre_s (c) the influ-
ence of the sector structure dominates m.rkedly, e.g* plasma stre_s during
anti-sector conditions cause far less particle precipitation than before the
occurr_ce of the stre_s. At high velocity streams (d) the precipitation _ "
" " during the strem is always higher than before_ but again markedly modulated by _ :
the I1_ sector str,cture. _ .
• ' i ,
• I i
t _6 _ i J_
, , j_) ,
t _€i i F
I } j
5
-n--1jr
i
....2" ts p'-i, i.r_.
• : _ -_-rL .-l ;
.!
Figure 4. Variation of fmin-data (lialley Bay) during high speed plasma
/ • • streams(lISPS)with2,v_30 km/s(aandc) era u >300k_/s(bandd).
In (c) and (d) the data of (a) and (b) are subdivided corresponding to
their IHF polarity during pro- and anti-sector conditions.
: For investigatinga co=parabledependenceof the lowerenergeticparticle
,. precipitation we have chosen as indicators the ge_agnetic A index and the
' auroral electrojet index, AE, which are minly produced by i_nospherlc currents
'" in polarlatitudesbetween about I00 and 120 km correspondingto I - 10keY
electronprecipitation,in contrast to the absorption measurements whichmay be
influenced below 1OO k_ corresponding to energies of =ore than 20 keV. Fig. 5
shows the result of a. superposed-epoch analysis of AE-values for the Fame high _-
speed plasma streams as in Fig. 4. The lower-energetic particle precipitation " "
":_' is positively correlated with the velocity changes o£ the plasma stremns, too_
but in contrast to the f . -values the influence of sector structure changes
is obviously not so domuxant. For instance, with low velocity plasma stre_s
the AE Index is enhanced also with IHP anti-sectvr conditions, contrarily to the
f . -_ariations in Fig. 4. These differences in particle precipitation at
dxl_erent energies indicate that the higher-energetic electron precipitation is ..
stronger controlled by sector structure changes than the lover one. This can he
a hint that the IHF structures do differ_.tiate the magnetospheric acceleration
prate, sen of energetic particles. Finally the following conclusions should be
mentioned: _he presented results on the dependence of particle precipitation
on the negative B -component of the interplanetary rmgnetic field and on the
velocity of the s_lar wind support the concept of AV_SOFU'a energy transfer
function (PERREAULT and A_.SOF0, 1978) as a first approximation for the de-
scription of the energy transfer fro_ the solar wind into the at=osphere. The
observed differences in the precipitation of particles in dependence on their
energy, however, cannot be explained by this energy transfer function.
_" For investigations of the influence of ItlFsector boundary crossings upon
the plasma of the middle atmosphere the diff£rent physical behavlour of the
204
-6-,_ -2 0 2 /, 6 -6-4-2 l 4 6
400 ..
a) ; _ -LI
I
1 i
I 1
!
300. II _
At" ,
o 1
I
J
!
Figure 5. S,_e as in Fig. 4 but for AE-data.
l_-sectors during the spring and autumn halfyear should be taken into consider-
ation. Our classification of IHF-sectors after their B -components in the so-
lag magnetospheric coordlr_te syste= (pro-_ anti-sectors_ see_s to be more ap-
propriate than the usual classification after the direction of the IHF in re-
lation to the arm (A- and T-sectors).
As the excessive D-region ionization due to precipitation of high energetic
particles markedly influences the radio wave propagation especially in high ~..
latitudes, the derived d_pendence of particle precipitation on structures of the -'.
.... • .interpl_netary _gnetlc field can i_prove the prediction of radio propagation
conditions in polar region,.
REFERI_CES
Dungey, J. N. (1961), Phyn, Rev_ Letttp 6j 47.
Lautsr, E. A., J. Lastovicka and T. ZS. Rnpoport (1978), PhyA, Soleriterr.,
Potsdans No. 7, 73.
Lauter, E. A., A. Grafe, B. Nikutc_ski. J. Taubenheim and C. U. Wagner (1979)s
Cerlands Beirr_ Ceophys. , Leipzig, 888,73.
Lindblad, B. A. and R. Lundstedt (1981), Solar Physics s __6,197.
Pcrreault, P. and S. I. Akasofu (1978), _o_hys , J, R. Astr, Soc., _4, 547.
Russels C. T. and R. L. _cPhcrron (1973), J..Geophvs. Res., 78 s 92.
_olar Geophysical Darn. _OAA, Hational Geophysical Data _entcr, _oulder_ Colo-
rado.
..... Svalgaa.,d,L. (1975), SUIPR Report No. 629.
UAC-Reports t;o.22, 29, 31, 33, 37, 39, 45, 47, 59, 73, 76, l_VCA for Solar-
Terr. Phys. NOAA Boulder, Colorado. .


Dependence of the High Latitude Middle Atmosphere Ionization on Structures in Interplanetary Space

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