Electron density and temperature measurements obtained in the DEOS campaign

Ad\‘. Spcre Res. Vol. 29, No. 6, pp. 893-898, 2002 0 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Bntain 0273-I 177/02 $22.00 + 0.00

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ELECTRON DENSITY AND TEMPERATURE MEASUREMENTS OBTAINED IN THE DEOS CAMPAIGN C. T. Steigies, M. Hirt, and A. Pie1 Institute for Experimental and Applied Physics, CAU Kiel, Germany ABSTRACT In the DEOS

campaign

(Dynamics

atures have been measured

of the Equatorial

with impedance

an undisturbed

evening ionosphere

profile obtained

from ionosonde

was encountered

observat,ions

In the second flight, which was launched Both

instruments

inside the plasma bubbles a strong reduction A temperature

Over SHAR)

probes.

and the resuhing

during the flight

urlder ESF

spread-F

densities

(ESF).

In the first flight.

and agree well in the absolute temperature

large plasma bubbles

densities

measured.

profile taken under unperturbed

conditions

is presented

model.

werP detected

during

scale fluctuat,ions

The temperature

in the depleted region, as compared

with a

from t,he IRI-95

resolve the large scale feat,urtrs as well as the intcrmediatp

of the electron

and temper-

density profiles arc compared

with predictions

ant1

conditions.

electron

Three rocket, flights have been performed

ionosphere , shortly before and during equatorial

in the evening equatorial

the upleg.

ionosphere

and Langmuir

profiles show

with the ambient plasma.

and compared

with current

models.

by Elsevier Science Ltd. All rights reserved.

0 2002 COSPAR. Published

INTRODUCTION The post-sunset, scales,

equatorial

with uplifting

waves that results Several

in the formation

sounding

instruments

ionosphere

rocket

(Baker

shows a rich dynamical

of the ionosphere,

triggering

of plasma bubbles

campaigns

by ground

instability.

based

and in-situ

reports

details of electron

DEOS

FLIGHTS

In the DEOS = 12.7”).

(Thiemann

before the onset of ESF

were identically

equipped

The second rocket (F07),

problems

The DEOS densities. plasma.

developed

of

1981.

to the generalized

of this complex present

syst,cm

contribut,ion

resolution.

For this

here.

to study various plasma

on April 19th;

which was launched ESF

(Ossakow,

was invest,igated.

iustrumcnts

was launched

and will not be considered

2801, 1998 at 20:41 LT into already

studies

The

condit,ions

1974).

South India (80.2O E. 13.7” N. dip angle

with five scientific

over SHAR.

by tidal

with a variety

can be attributed

instruments.

under equinox

The first rocket. (F05)

Theoretical

with high spatial

were launched in 1998 from SHAR,

apogee of 420 - 430 km and a touchdown IMPEDANCE

measuremeuts

ionosphere

spread-F

to the understanding

with various plasma

and spat)ial

instabilit,y

et al., 1970, Haerendel,

equatorial

of plasma bubbles

et al., 1997).

at 20:21 LT, had technical on September

t,o study

contribut,es

and temperature

the equatorial

rockets

The payloads

campaign

measurernents

density

campaign

purpose three sounding parameters

The DEOS

on many temporal

Rayleigh-Taylor (Farlcy

et ul., 1986, Pfaff et 01.. 1974).

Huang et ul., 1996) have shown that the generation Rayleigh-Taylor

and spread-F

have been performed

et al., 1985, Kelley

evolution

of t.he generalized

The third rocket

conditions.

1998 at 19:21 LT,

on September

(F(X)

21st, 1998

was launched

Th(> rocket,s each reached an

range of 490 - 550 km.

PROBE impedance

Impedance A minimum

probe

(II’)

was selected

as the primary

probes make use of the frequency of admittance

occurs

instrument

dept~ndcnt, admittance

at the upper hybrid frequency.

893

to measure

absolut,c electron

of au antemla By applying

in a magnetized

a frequency

sweep

C. T. Steigies rr tif

DEOS F06:

28-Sep-1998

IP wake

DEOS F06: LPl

effect

28-Sep-1998

spin

correction

0.065 i '.'~$Eci~on ram

0.06.

direction

i I-

1

0 Fig.

wake

340 -

150

200

300

250

into

the

frequencies

346 seconds

resonance

ram sector dent

100

0 045

350

L

0

50

150

100

angle (deg)

IP is pointing reduced

I I

50

1. IP resonance

between

ram

flight

ram direction. frequency

resonance

recorded time.

during At

300”

In the wake

is visible,

frequency

200

angle

Fig.

2.

the

wake

corrected

region

whereas

is nearly

F06

a

in the

ulation

LPl

saturation values

of 6O/b The

F06 between

340 -

currents with

data

250

300

35

(deg)

(black

an assumed

shown

345 seconds

squares) density

were. recorded flight

and mod-

during

time.

indepen-

of the orientation.

of typically 1 - 20MHz to the antenna and detecting the resonance frequency, the plasma frcqueucy and t,hus the electron density can be determined, when the intensity of the ambient magnetic field and t,hus the gyrofrequency is known. In the DEOS IP the frequency sweep is generated by a digit,al direct synthesis (DDS) chip and the signal is digitized by a 12-bit A/D converter. This design allows for a fast measuring cycle of z 40 ms with high accuracy. More technical details of the IP arc described in (Steigies et ul., 2000). With the low spin rate of the DEOS payloads (1.5 - 2.7rps). the IP was able to perform at, least, 9 measurements per spin, which allows to identify and account for wake effects by the payload body. In Figure 1 resonance frequencies are shown versus the spin angle. For the following density evaluations, only resonance frequency recorded in the central part of t,he ram sector are used. LANGMUIR PROBE The DEOS Langmuir probe instrument consists of two identical spherical sensors. Part of the lower third of the 25 mm diameter spheres is used as a guard ring and electrically isolated from the rest of the sensor. The sensors were made of solid brass, which was gold plated for the flights F06 and F07 t,o avoid deterioration of the sensor surface. One sensor (LPl) is used in sweep mode (+4V+ -2V+ +4V) for 40 1x1s:followed by 120ms at a fixed bias of +4V. The second sensor (LP2) is operated in fluctuation mode wit,11 a bias of +4V. The signal from LPl in fixed bias mode shows a sine modulation with t,he spin angle of the payload. In Figure 2 the saturation current, from LPl versus spin angle is shown (black squares) where? bccausc of the relative angular position of the sensors. the LPl sensor is oriented in the ram direction for an angle of 75”. This modulation was corrected by the model function ne((psp~rL) =

9ze0 [1 +

a (COS(Pspin

-

111

:

where r~,o is considered as the true density. The corrected currents are shown as grey dots in Figure modulation a takes typical values between 3% on the upleg and 9% on the downleg. In the following all currents rneasured by LPl were corrected by this model function. The plasma parameters electron temperature T,. density 12,) and the plasma potential @,J can be by evaluating the probe characteristics. Usually @‘p is fourid by locating the zero-crossing of the derivative of the clect,ron current 1?(U). yielding also the densit,y rbe(Ie((ap)), using the formula

(1) 2. The figures, derived sr~:ond

(2)

895

DEOS F05:

L5. 3---

2

DEOS F05: 19-Apr-1998

19-Apr-1998

2

___-

10"

5

10’2

5

2

2 IP n, (10”

63)

ne (mm3)

Fig.

3.

from

F05.

with

a scaled

upleg

Upleg

profile

ionogram

The electron

electron

the

IP and

and

IRI

a smooth

at 420 km.

are found

regime.

downleg from

shows

F-maximum pletions

and

Profiles

density

1999) a different,

T, is computed

problems

approach

functiou

with

gradient

bottomside

a steep

of the

density

whereas

F-

gradient

is

at the bottom

is observed.

values

probe

from

function

in the elert,ron

the full probe

charactjcristics:

0.65 - 0.75. the shape

in a magnetoplasma

@II. Tc, rt,<,and

wit,11 the free paramet,ers

an exponential

a lack of data

by evaluating

y taking

of a spherical

Malql~ardt,-L(~vc~~lbc~rg

at the

Here,

de-

by fitting

associated

is taken

I he free parameter

With

to the full model

bubbles

F05.

at the top of the bubble,

a gentle

to the

plasma

Plasma

during

found

The

increase

downleg

4.

layer

edge of the F layer.

lower

temperature

Due 6o several

Fig.

profiles

95 predictions.

On the

at the

density

LP are compared

(Sonmor

7 is fit,tcd

to 1, in the electron repellent

of this and

function

regime

is an approximat,ion

Laframboise.

t,o the measured

repellent (Hirt, et uI.,

1991).

electron

The

model

currc>nt, I,(U)

by a

t,ypt: algorithm.

RESULTS Electron DEOS

density flight

SHAR show with

the: spread-F

the IP instrument

was scaled The

profiles

FO5 was laurlched

with

squares

ionosontlc:

only

from

addit,ional

in Figure

(Titheridge.

of IRI-95. input,

a quiet

postsunset

20:20 LT onwards.

F05 are shown

package

the prediction

as opt.ional

rise in density

using

1985).

for t,hc IRI-95

270 - 280 km altitude. The F-maximum 10” n-’ I. Ionosonde and IRI-95 agree in shape

the in-situ

measurement,s.

However,

thr absolute

which

was recorded

at 19:15 LT,

is shown and

as circles

density, The

3.

by the

show

a density

and location

are by a factor

in Figure

as observed profiles

at 320 km with

of the profile

densities

at

performed

calculation.

is fourld

recorded

measurements

ionogram height

Ionograms

density

3. An ionogram,

the F-maximum

parameters

ionosphere.

Electron

The scaled

near

in-situ . I of 8.8 with

during

the POLAN

mark

at, 19:21 LT into

signals

a sharp measured

of the F-maximunl

of 2-3 higher

than

the in-sit,u

nieasurcmcnt,s. During

the downleg

the ambient

density

this

of F05, at the lower edge of thr is detected

part. of the profile.

at) the top and a weaker section

of a plasma

The

concurrently shape

gradient,

bubble,

with

of the dcnsit,y towards

as originally

depression

tile bottom. prcdict,ed

E-layer,

a sudden

the IP and LPl This

&nsity

instruments.

reduction Figure

is markedly

asymmetric

characteristic

asymmetry

by the mod(,l

from

Ossakow

and

of about

4 shows with

a steep

is typical Chartuvedi

50% of

a blowup

of

gradient

of the: head (1978)

C.

X96

T.Steigies

et nl

28-Sep-1998

DEOS F06:

28-Sep-1998

DEOS F06:

IPn. (10"

6')

440 420 ,400 yE 380 Y360 ;

340

g

320

O 300 280 260 li

/

a

2

10"

5

Fig.

5. F06

scaled tions

5

1o12

2

Upleg

and

downleg by the

ionogram.

encountered

On the below

electron

density

profiles

IP are compared upleg,

large

360 km.

with

density

A smooth

Fig. a

depleprofile

to the

is

it was rapidly descending

In Figure 5 electron recorded

density

right.

dependent

the

A close

during

agreement

instruments,

even

the

upleg

current between

of

is shifted the two

in the fine details

in-

of the

is observed.

At 20:20 LT the F-layer to 240 km altitude

depletions LP saturation

at 20:41 LT, after the onset of spread-F.

signals from 20:05 LT onwards.

315 km, afterwards

Large

For clarity,

irregularities

flight F06 was launched

show spread-F

6.

F06.

on the downleg.

ionogram,

40

Cm31

measured

are observed

DEOS

20

0

LP current (,,A)

ne

from

2

Ionograms

had reached

recorded

at SHAR.

its highest, altitude

of

at 22:00 LT.

density profiles from the IP during up- and downleg are shown as well as the scaled

at 19:55LT,

which was the last ionogram

was again found near 270 km altitude,

before

onset

of spread-F.

density

altitude.

Above this altitude and during the complete downleg, a smoot,h densit,y profile is fourld. Comparing

upleg and downleg profiles, ambient

plasma

understood

as exiting

large depletions Electron alt,itudes

sudden

the perturbed

are identically

obvious, transition,

that

the large irregularities

at 360 km alt,itude!

In the DEOS

of electron

temperatures

inside plasma

with a temperature

campaign

it becomes

The electron

IP and LPl

possible

temperature

bubbles

probe aboard

a reduction

density

(Figure

of t,hc

profile can b(> insitlc these

6).

scatter

between

280 - 320 km.

2000 K. Here corresponding

have only been made at, higher

the Hinotori

to study T, inside plasma

profiles obtained

bubbles

(Oyama

et al.,

in an earlier state

regime from 270 - 380 km is seen. wit,h

Near the apogee the electron temperatures

satcllitc

on the upleg and downleg of flight, FOG are

in Figure 7. On the upleg a strong rise of T, in the altitude

at, approximately

represent

t,o a smooth

up to 360 km

plasma channel at the east wall. The fine scale st,ructures

resolved by both in-sit,u instruments,

above the F-maximum

a pronounced

are present

profiles

measurements

of development. presented

it, becomes

The

temperature

Previous 1988).

density.

but large irregularities

A sharp rise in

electron

temperature

attains

are also found on t,he downleg.

a plateau

In the altitude

regime of 270 - 390 km, however, 280 km a strong scatter urlperturbed

by ESF,

it becomes

density profiles is significantly

apparent

that the electron

temperature

inside the depressions

found in the

reduced by up to 800 K.

In Figure, 8 the temperatures model by Watanabe

only a gradual decrease of T, from 1900 - 1600 K is observed. Below If the downleg profile of F06 is taken as a reference profile of an ionosphere

is found.

of the downleg of F06 are compared

et al. (1995).

The IRI-95

profile shows electron

with profiles computed temperatures

by IRI-95

of approximately

and a 920 K

wit,11only a slight decrease t,o 900 K at altitudes below 230 km. The rnodel of Watanube et (~1. (1995) shows higher temperat,ures, with a plateau ranging frorn 1300 - 1500K throughout the whole altitude regime of 200 - 450 km.

Our observations

for the unperturbed

plasma

conditions

on

the downleg.

however:

show

Electron

Density

and Temperature

in the DEOS Cnmpnign

28-Sep-1998

DEOS F06:

28-Sep-1998

DEOS F06: 450

400 t g350, i $ 2 5 300

I

i 2601

, 500

0

-_ 1000

1500

2000

2

I 501

2oo~ 0

;

1000 TeK

500

Te 6)

Fig.

7.

Electron

of flight ture

temperature

On the

on upleg

downleg

of 1800 K is observed.

below the

F06.

360 km the

upleg

downleg

Fig.

tempera-

perturbed

temperature

to be reduced

higher temperatures distortion

In the

electron

is found

and

an electron

region

measured

on

8. Comparison

95 and

a model

temperatures higher

by

than

10

of electron

electron erably

I Watanabe et al.

j

temperatures

Watanabe

et al.

measured

with

(1995).

IRIThe

by the LP are consid-

the predictions

of the IRI-95

model.

by up to 800 K.

of 1800 K with a mean scatter

of the probe characteristics

of f130

K. These

high values could be attributed

due to the presence of a surface contamination

layer

to a

the LP sensor.

on

DISCUSSION The critical agreement

comparison

between

of the electron

the two methods.

the large scale structures measurements

from ionosondes

shows a good agreeme&

yield reduced

electron

attributed

to the density

reduction

The electron

temperatures

densities

the temperature

measured

observation

supports

bottomside

of the F-layer.

compared

as measured

by LPl

in the shape of the profiles,

at t,he bott,omside

show a significantly

good indication

depletion

of the F-layer

and the small vertical

that the observed

that has not yet reached

density depletions

techniques.

inside

with ground-based however both in-situ

This

reduced electron

conditions

tendency

temperat,ure

during the downleg.

can be

contain

cold, low-density

separation

the asymmetric

of the structures

are part of a single plasma bubble

This

plasma from the

in-situ below 360 km altitude,

size and horizontal

in the

In part,icular.

agrees well with that, inside the bubbles.

that the plasma bubbles

The fact, that the plasma bubbles in F06 have been detected shape of the density

shows a good

of the payload body.

with the unperturbed

the interpretation

IP and LPl

finer scale structures

the in-sit,u measurements

to ground-based

due to the presence

plasma region when compared

of the instruments

are capable of detecting

and they agree very well. Comparing

techniques

perturbed

density measurements

Both instruments

arc a

or plasma channel,

the F-maximum.

CONCLUSIONS In the DEOS perturbed

campaign

and unperturbed

factor of 2-3 compared plasma bubbles measured

electron

densitiy

by equatorial

with predictions

have been observed

inside these bubbles

and temperature

profiles have been measured

spread F. The elect,ron densities by the IRI-95

measured

under conditions

l.n Situ arc reduced by a

model and ground based mcasurcmcnts.

in two different early phases of development,.

is found to be subst,antially

The electron

lower than in the unperturbed

Furthermore, temperature

ionosphere.

898

C.T.Steigies

etcrl

ACKNOWLEDGEMENTS DEOS is part of the DLR-ISRO cooperation between Germany and India. Both: the impedance and the Langmuir probe are supported by DLR under contract 50oe9503. We are deeply indebted to Heinz Thiemann, the principal investigator of the DEOS campaign, who suddenly died on 6 August 2000. We thank J. Grygorczuk (Polish Academy of Sciences, Space Research Centre) for the construction of the impedance probe sensor mechanics and W. Noack (Arbeitsgruppe Weltraumphysik und -technologie, Frciburg) for manufacturing the IP flight units and his assistance during the integration and launch campaigns. REFERENCES Baker, K. D., LaBelle, J., Pfaff, R. F., Howlett, L. C., Rao, N. B., Ulwick, J. C. and Kclley, M. C., Absolute electron density measurements in the equatorial ionosphere, J. Atmos. Terr. Phys., 47, pp. 781 789, 1985. Farley, D. T., Balsley, B. B., Woodman, R. F., and McClure, J. P., Equatorial spread-F: Implications of J. Geophys. Res., 75(34), pp. 7199-7216, 1970. VHF radar observations, Haerendel, G., Technical report, Max-Planck Inst. fiir Phys. und Astrophys., Max-Planck Inst. fiir Phys. und Astrophys., Garching, 1974. Hirt, M., Steigies, C. T., and Piel, A., DEOS: D_ynamics of the Equatorial Ionosphere over SHAR.: IIIstrument: Langmuir Probe, In 14th ESA Symposium on European. Rocket and Balloon Progru.mmes anal Related Research, number SP-437, pp. 417-422, 1999. Huang, C. S., and Kelley, M. C., Nonlinear evolution of equatorial spread F, 2, Gravity wave seeding of J. Geophys. Res., 101, pp. 293-302, 1996. Rayleigh Taylor instability, Kelley, M. C., LaBelle, J., Kudeki, E., Fejer, B. G., Basu, Sa., Basu, Su., Baker, K. D., Hanuise, C., Argo, P., Woodman, R. F., Swartz, W. E., Farley, D. T. and Meriwether, J. W., The Condor Equatorial Spread F Campaign: Overview and Results of the Large-Scale Measurements, J. Geophys. Res., 91, pp. 5487-5503, 1986. Ossakow, S. L., Spread-F theories - a review, J. Atmos. Terr. Phys., 43(5/6); pp. 437-452, 1981. Ossakow, S. L. and Chaturvedi, P., Morphological Studies of Rising Equatorial Spread F bubbles. J. Geophys. Res., 83(A8), pp. 2085-2090, 1978 Oyama, K.-I.: Schlegel, and Watanabe, S., Temperature structure of the plasma bubbles in the low latit,ude ionosphere around 600 km altitude, Planet. Space Sci., 36(6), pp. 553-567, 1988. Pfaff, R. F., Sobral, J. H. A., Abdu, M. A., Swartz, W. E., LaBelle, J. W., Larsen, M. F., Goldberg, R. A., and Schmidlin, F. J., The Guard campaign: A series of rocket-radar investigations of the Eart,h’s upper atmosphere at the magnetic equator, Geophys. Res. Lett., 24(13), pp. 1663-1966, 1997. Somnor, L. J. and Laframboise, J. G. (1991), Exact current to a spherical electrode in a collisionless, large-debye-length magnetoplasma, Phys. Rev., 3(9), pp. 2472-2490, 1991. Steigies, C. T., Block! D.? Hirt, M., Hipp, B., Piel, A.! and Grygorczuk, J., Development of a fast impedance probe for absolute electron density measurements in the ionosphere, J. Phys. D, 33(4), pp. 405 413, 2000. Thiemann, H., Mayer, G., Piel, A., Steigies, C. T., Primdahl, F., Sridharan, R.! Gupta, S. P., Rangarajan, G. K.! Rao, D. R. K., and Rao, P., DEOS: Dynamics of the Equatorial Ionosphere Qver SHAR.: Indo-German low-latitude rocket project, In 13th ESA Symposium on European Rocket and Balloon Programmes and Related Research, number SP-397, pp. 349-354, 1997. Titheridge, J. E., Ionogram analysis with the generalised program POLAN, Technical report. World Data Center A, 1985. Watanabe, S.. Oyama, K.-I., and Abdu, M. A., Computer simulation of electron and ion densities and temperatures in the equatorial F region and comparison with Hinotori results; J. Geophys. Res.. lOO(A8). pp. 14581.-14590, 1995.