The boundary between the northern and southern Sq current loops over the African continent

The boundary between the northern and southern Sqcurrent loops over the African continent

The regular produced

quiet day geomagnetic

by electric current

togcthcr

with

their

induced

SKISSER

currents fioxing

hemisphere

e.xternal d:ril)

The

Sy current

studied

ha\c

been

northern

since the early found

to

summer

developed

than

and

A complicating low latitudes

from

the

west to east known

of CH~IM~X

occur. the

For

example,

northern

the southern

and tends

south ofthepeo@raphicalequator

durmg

loop

is more

to penetrate

IP~~c~zand WILKISS.

IY)hj) The

f~~rm of the daily

decltn:ltron

(1)~ .lt

m;l~nstlcallv

a

relatl\e

SIOLI.

lY631 Thus

\tatll)n

the \ou~h\rard

the mornlnp$ declln.ttlon.

~~11

loops

at a moderate

latitude

component

produce

III

theafternoon

follo\red cxpcctcd

to hho\r

daily

and no regular pattern. the morning

compared

seasonal solar controlled the current station

Ilo\\

by a minimum

in the

hemisphere stations

loops

in theshape

be underdilTerent

to the afternoon.

loops the daily

be of

loopsin

Because ofthe

boundary

declination

near the geographical

near

would

of small amplitude

Due todistortion

shift ofthe

flou 01

in east declination

the current variations

III

In the eastward

peak. Magnetic

between

thc:\ol-tlcc:\?~t~chstationscan

sinplc

a peak

mlnimum

hx an afternoon

the boundary

northern

of current

In the southern

there I\ ould he a morning

:i of

(PKICF and

due to thenortherly

currents.

o\d~c~~d

on

of the position

to the current

This \rill be follo\ved

decltnatlon

of the mapnctlc obseriatorj

qutet da> IS Indicative

the station

the

variation

magnetic

bet\teen

variations

equator

houndciry

at a

can show

all threet~p~\ofbehaviouratdifferenttimesofthe)’ear.

297

currents.

1.7 S) b>

Nairobi

under

the southern

in Aupust..lanuar~

feature \\ hen stud>lng

is the intense band ofcurrent as the equatorial

in erect. a local intensllicatlirn

and

latitude

and

respecti\,el!

the

changes in these parameter>

(J)

nearthe

of

at the world

(geographic

Curves -4. R And Cshoiv

of the northern

April:October

and these have been

work

(1973).

currentsand

in

in F-I~. I \\ hlch shows such carlatmns

at Nairobi

the influence

in the southern intensity

observed

observatories

B~H~I I \ (IY-IO). Seasonal

side of

clockwise

can be deduced

variations

nrtti w-l\ ofmagnetIc much

shape

systems

the outer

take the form of two counter

and clockwise

size.

geomagnetic

within

On the daylight

the Earth the ionospheric

hemisphere

This is illustrated

currents

large I~~ps with currents the northern

(SC/) arc

observed

laycrb of the Earth.

conducting

variations

systems in the ionosphere

Sqcurrenth Ilouinp

electrqlet.

of the Sr/ current

at

from This is. uh~ch

S

298

occurs

v.irhin

magnetic

a rcti degrees

dip equator.

enhanced

electrical

conductivity

B4KER

obsrr\ed

in the geomagnetic

enhancement the dall)

of. and centred

A theoretical

given by

daily

variations

is a local

2 in the amplitude

of the horironral

component

of

(H) of

field.

R (-under S loop) variations

at

I I .Afrlcan observa~ories(lisred

in Table I)on aseries of

fi\e

In each of the months

magnetically

to-da) to

April,

quiet

days

July and October

and morning-to-afternoon

olthe

boundary

occur.

In

equators equator

Africa

the

America

(studied

bq Ht,rros.

magnetic

equator

is at about

studies

special interest brtuecn

ij

and

Figure \;tmtion~

northern

2 \ho\\

5 sketcho

111saqt

declination

current

loop.

and ICI the h[,und;lr! near equ:llorlitl

constant hh,iped parameter

latitude d.111\

R. \ho\\n

idealixd

rlw

tn

daily

under (a) the current

to he under

and ‘tfternoon

‘T‘h~s pi\es

between

loop

the laoph. Frequently.

I\ not al\\.i!\

\arl;tllon\

the

(b) the southern

lo~>p\ In the mrlrning

iT any.

SC/ system.

rot- xtationb

het\\een

I).

I

S loop

I

latitude.

arc thus of

the relationship.

or

Dm

in

of South

1967a and b) where the

5tatlOn appears

the hi)und;!l-!

side

I? S geographic

external

I

am N IOOD

geographic

aXis and the houndar!

d llie

loops

I

and the magnetic

on the western

in determining

I

R zero o+jboundary

, c

loops were found

In these two regions

the electrojer

lhe current

that

shifts in the position

liesclose to IO h geographiclatltude.Thisis to the situation

currenl

E u

magnetic

contrast

5

‘0

1969. Seasonal, day-

between the current

have a large separation.

Comparatl\e

R (+ under N loop)

this region w’as

This paper studies rhe daily declination

January.

I

[or

(1953). The main efl’ect

h) a factor ofabout

the eeomagetic

SH.XH

;tnd L

on. the

explanation

wlthin

and MARTYS

lariation

J SLI\XIK

parallel

a

different indicating

IU ;i hne of

to td! “91” or (el “W”

The

diurnal

range

in t.ig. 1. \$a\ ~~22 lo locale

Ihe

boundar! taking

in a quantitatll

positive

values south.

with

(Fig.

3) enable

determined

with

show “M” separate Figure

baundar!,

pm.

latitude

011

boundar!

3a-d

conclusions

were plotted

particular

da!>. ma!

be

for the five international Table

between the northern

and southern

the boundar!

geographic

latitude,

Hecauseofthe

solar contrill

ol”lono~phrric

electron that

current month>.

was stable at about degree\

south

&the

dcnslly

III

rhe

orthe boundar\

except for the morning

it ~+as several

he expected

April. Jul! and

2 summarises

\vith regard to the positron

each day. F-or the two cqumoctial

u,hen

bc

but with lo\\ time re\olution.

1969 respecti\el!.

October.

queer to

When station>

position,

quiet days for the four months Januar!,. October

itsell

for gi\cn

accurac\.

type variation\

a.m. and

determined.

the

Iarnude

reasonable

or “W”

nrgati\e

zero range at the boundar!

Plots ofR against geopraphlcal da)5

It ma! be regarded ‘1,

e \\ a).

values north of the boundar!.

systems on April

and

II N i 2 of 23 April

of the equator

latitudsdlstrlburl,,n the E replon it mlghr

nenr rhe equlno\c<

the hounder!

shouldlieclose~~~the~eo~raphicalequatorandthat

the

0

. A

D ;

3rd

-

IO th

6th

*

19th

IO th l3Th 29th

‘3

r

23rd

l

26

a

; + A

0

th

omtopn

am top1 ll

. 0 +

0

Jan 1969

Apr

1969

~240

__-_ 3c

2.

, !i

4th

3

1:

19th

/v

20th

!. Lm

.’

*.

eo-

v

29th topm

__ ,-,

7 :.-7-

/ d

I20 -

5 th

I?

‘c

8Ih

,*

14th

‘C ‘0

15 th 26th

I.

30th

40-

B ;‘

1 5 C \ z

I d .

+

O--

-4c-

Qz

.

8”

E’ .

-8O-

-120-

1

-160-

-2oo-

I

30 ‘k

20

IO

0 Lotltude

IO

I 20

I 30

act

1969

-j 4c :S

Y

iotlfude

Ik~g -7 (.II_(~I Show plot> elf R against lalltude for the I I observarorles llstsd in Table I. for qulrr &I!, 11, 4prll. July and October 1969 respecrively. The boundary positIon< for each da! h;t\c h?
300

J. SKIS\EK and E SHAH

N

Table 2 The latitude of the boundary betueen the current loops on the selected qmel days In 1969

Date

Boundary posltlon a m. pm

I969

Summary

for the monlh

Januar!

X 5 50.5 N 6 +2s 2 &I s

6

IO Ii 29 April IO 19 21 23 26 July 4 5 19 20 29 Ocrober 8 I4 15 26 30

norrhern

and

similar Africa

current

latitude

of the magetic

equator

ris r3 s +‘S 22s +2S

I2 II IO II II

i_ I.5 X kl5K A2 N .1.5X xI.iN

was south of the equator

dependence ion

responsible

electron

would

for

the

the

Sy currents

that Huctuations

from

of geopraphic

of the resulting

Sq currents.

as expected.

boundary

was clearly

equatorial position.

produce

latitude

5;

analysis

for

workers,

of the Sq field from

Polar

between was iii The

example

is the

Year geomagnetic

WILKISSI

1963lTheyplot

eqlrlpotentialsR(ratherthancurrents)forJmonths(l.e. summer).

and along the Greenwich

the R = 0 equipotential Sat

12OOLT.

In January, would

the converse

be expected

strengthening northern

with

and

hemisphere. position

to the sttuation

the southern

pushing

the

for quiet

occurred

There boundary latitude equator.

boundary is thus

shift of about during

of the magnetic

3 towards

equator

the dip

a much

larger

of the five days the

was at about clear

from

between 2-S and

the day with

a fairly

the

days in 1969 when the

was found to be quite variable

between thecurrent especially

loop

into

this does not accord

shaft on one day (6th). On three afternoon

for July

current

boundary

However

with results obtained boundary

meridian

shows a shift from 44 Sat 0800

equator

on

south shown

and BARTELS( 1930)

A good

system

of the geographical

11 N in the afternoon

by GAPMAX

later

day to day with limits in the mornings

the

system on

so that it dips further

arm and this trend is also clearly

on charts of Sq drawn and by many

the magnetic

current

control

and in the mornings

the day so that the boundary

range

on INSwestern

8.5 N. A northvvard

fourofthefivedaystherewasanorthvvardshift the

the

There 15

current

was thus towards

such days must bedistorted

to II In

field dependence

and geomapnctic

of movement

The shape of the northern

northern IS

vAB forces. It is likei!

well south

on

ll’k2’N

data for 1932-J by PRIcEand

field

on four days being close to 17 S. lHowe\er.

8 and 22 during

II

(throuph

the

which

the northern

and strengthened

the

which

of the Sr/ current\.

thus a mixture In July,

when

in the latter are largely responsible

the day to day variabilit!

equator.

of

will ,rls~~ha\e a magnetic

since they. arise hasic‘ili!

the

of the electrojrt.

the boundary

Eh4F.s

equator.

the magnetic

formation

dynamo

direction

over

with

conductivitics

boundaryat

be of

show that rhc

gyrofrequencies)

may also inllucnce

addition.

expanded

that

of the ionospheric and

electrojet

therefore

h!

as a m. same as a.m Zdme iis a.m as a.m.

in the morning

11 N after the development

to

seems possible

day

boundary al I I .5 N f I except a.m on 23rd when at 6.S

>ams as a.m.

the results

group

boundary shms N during - 3 (but by 17 on 6th)

boundary al 12-S+ I’ m the mornings on 4 days northward shift of between 8-X 4 days during the day

13 13 I2 II 5

in this

posibon variable day b!

II *l-N same as am.

and the axis of the

boundary shifted

the one day

boundary day

same as a.m same as a.m. same as a.m

1I N, coincident

was at about On

the

N 5 S h

+I +I +2 21

loops

electrojet.

It

I\:

I2 12 6 II5

for quiet days in April and October

boundary

N

115 xl

and sizes. However.

+05-N II N I &2X I +2h’ II iI N

s

7 51

8 ‘I_

southern

shapes

I05

1I

N.

general

trend.

The

loops is much nearer the than the geographical

at the equinoxes.

.4t other

times.

when the boundary IS south of the magnetic equator in

latitude between the tuo contments is more than 20

the mornings.

This

it tends t0 stabilize

along the magnetic

suggests that the dipequator posttinn. whtch also

equator later in the day. No cases of movement of the

differs in the same sense by about the same amount

boundary

between the tu’o continents. IS important in intiuencmg

away from

the magnetic equator

were

the boundary

observed. HL.TTOL

t 1967a and b) analysed declination data for

the IGY from a number ofclosely observatories

with latitudes

31.7 S in South

spaced geomagnetic

in the range 5S”N

America. As mentioned earlier.

gives the opp~~rtunity to compare the African reported

here with

those from

current,

this

contrjbutions

the complementary

situation m South America where the magneticequator

as it

period. This boundary during

mdivtdual days in the threecon\~entional seasons from inspection

of stacked 5 variations

for the range of

stations. There was considerableday-to-day

variability

during the post midd;i!

from the magnettc

during

of the northern

Europe/Africa.

the 1.G.Y.. noted

and southern

10. further

equator to about 1-Z Sin the morning but the boundary

daily revoiutton.

shifted

side of the

December solstice about S,N

the southern

In the

loops penetrated to

in the morning, shifting to about 5% in the

afternoon. and in the northern summer the boundary well south

of the magnetic equator in the morning

moving

to about

equator.

in the afternoon.

tit The boundary further

is

south

in

I:! S. the latitude

between South

of the magnetic

It is clear that the current Amertca

: in

Africa,

cspcc‘iall! in the .I and E seasons when its difference

in

the Sy current

Earth

shoax

of the magnetic

the two

mam current

displacement

equator. loops

hers.

system on the da&tit latitudes.

system as a whole appears to “run” “rail”

than in

one complete

a complicated

at IOR and moderate

and espectall!

loops is much

than

ffexures

SC/foci were on

Their results. and those reported

suggest that as the Earth rotates through

d:l\

that the

south in the Americas

average, the northern vortex penetrated south ofthedip to about 7 S in the afternoon.

equator

hours.

vartations

position

north

southern

the houndar!

PRICE and STC)TE( 1964). in their analysts ofquiet magnetic latitudes

on

and

tends to stabilize

is far removed

morning

averageabout

a gtv’en day. At the equinoxes,

This

the da?. to dra\t

northern

happens frequently, even on days when the

in the position of the boundary in all seasons and in the within

during

both

close to theastsoftheelectrojet

Hutton

on a number of

intensifies from

current systems.

at that time was at about 13-S geographic latitude. noted the boundary position

and southern

(ii) The trend tn both continents is for the electrojet

and

results

between the northern

current systems.

pattern Although

in some M a! on the

the boundur! may she\\

from the dip equator in the local morning

nt the

bet\ve,-11

consrderahk

;tt ccrtatn pertod.

W~MW