Adv. SpaceRes. Vol. 8, No. 4, pp. (4)49—(4)50, 1988 0273—1177/88 $0.00 + .50Printedin Great Britain. All rights reserved. Copyright© COSPAR

EXPERIMENTAL TECHNIQUE OF LOWERIONOSPHERE ELECTRON DENSITYMEASUREMENTS BY MEANS OF PARTIALREFLECTIONS

W. Singer,J. PrieseandP. HoffmannAcademyof Sciencesof the G.D.R., Heinrich-Hertz-Instituteof AtmosphericResearchand Geomagnetism,RudowerChaussee5, Berlin 1199, G. D.R.

1. INTRODUCTION

The partial-refleetion(FR) equipmentoperating since 1982 at Juliusruh(54.60 N,13.4° 5)uses the FN - CW radar techniqueat a frequencyof 3.18 MHz with atransmitting power of1 kW, and a sweeptime of 0.6 seconda. The amplitude-height information of the PR-signalsare estimatedfrom the audio frequencycomponentsof the mixer spectrumusing a hardwarerealized Fourier-analyzer /1/. The amplitude profile is analyzedfor 30 height channelsfrom 47.5 km to 91 km in steps of 1.5 km correspondingto the height resolution.Representa-tive A IA -profiles canbe derived for sampling times of absut5 to 10 minutes (200 to 400amplitudeprofiles for eachnode). The electrondensity profile hasbeenestimatedfollowingthe basic theory for the differential absorptionexperiment/2/ but using the improved QL-approximationof the exact Sen-Wyller refractive index after Flood /3,4/.

2. RESULTS

The complexmonitoring of the lower ionospherewith PR-observationsandother ground-basedradio wave propagationmeasurementswill be demonstratedfor the winter period 1982/83(Fig-ure 1). Winter dayswith enhancedradio wave absorption(‘winter anomaly”) andwith ‘nor-mal’ absorptionvalueswere identified from the curves L(Al)and L(A3) of Figure 1. Corre-sponding noon-time electrondensity profiles of “anomalous”and “normal” days (27.12.1982,23.1.1983)are presentedin Figure 2, the numbersdenotethe numberof day. They show thaton winter anomalydays electrondensities in the height range76 - 82 km are generallygreater than on normal days by a factor between2 and 6, associatedwith a downward shiftof the steepestportion of the profile by several kilometers, An excessiveenhancement ofelectron density is exhibited by the prof11 measuredon January11, 1983, after a geomagne-tic disturbancewhich is clearly recognizedIn the Ap curve of Figure 1.

7982 sec JAN ,,,~ ~ 10’ 70”

0I—CoOm

~— ~ ~0

&‘! ~ ~ w30 33 ~ o ®

‘70 030283 06.02.83 010283 0&02.43 085243 70T UT 09.50 0550 0955 71.25 11.55

L~A3) V1f~ 40 % 750 729’ 723’ 71.1’ 658’

~ ~ :~: ~700 7~ ©

- 70 ~ ~ a~ Isosas 1202.13 700 “ ° or ass, 09.50 70.30 09.50 0950.,+ 4.~,‘ 5 70.1’ 77.7’ 654 777’ 708’~“

1~820CC JAM ‘ FEB’~ &ECTRO”l o..owsirrFig, 1.Lower ionospherecharacteristics Fig’ 3.Electron density profiles during

in the period winter 1982/53. the PSE-eventin February,1983.

(4)49

(4)50 W. Singer er al.

I / 1/ /Jet

Yin ,/ /,~c/ ~I J

75 /70 /2a

L~cgnbe’~2 ,/wwy 7983x~ir

—E~fr —

839 5* 59 0’ se’ V~

Fig. 2. Electron densities on days with low and high radio wave absorption,

90 Gorky x~’r ~

km — * — Juliusruh / / /1 1’ ~‘~.7McI28dB

J.4~’~/42de~P (f,~,/Al.absorpf~rm

JuI,vstah)0 ~,—“ a C

23Mc/ / I.P I23Mc!68d8 p

1/ /~s~(I,,,,Moscow) /Z~iwc

70 11.1.1983 12 1.1.985 201.1985—EI~ctrrsn~4’ —

10’ 10’ ~o, 70, rn’3

Fig, 4 Electron density profiles by P5-measurmentsat Gorky andJuliusruh.

In the winter period 1982/83 an event of excessiveimnization enhancement In the mid-latitude D region occured after the stronggeomagneticstorm of February5, 1983 CAp143) .The lower ionosphere PSE, developing from February6 or 7 onward during quiescentgeomagnetic activity, is evident in the Al and A3 radio wave absorption (Figure 1), whichreturn to approximately normal level not earlier than on February 13. For this eventelectrondensity profiles have beenderived from February 3 trough February14.A sampleofthese data is presentedin Figure 4,with the same numbersas used in Figure 1 .The largestexcess of electron densities by a factor up to 10 occurred at heights between 84 and 86km. From the observedelectron density profiles fluxes of precipitating high energeticparticles as well as the excessive nitric oxide (NO) enhancement are derived by a simplemodel interpretation /5/. After that maximum NO Increaseby a factor of 5 was detected near86 km.

A comparison of the electron density profiles at Juliusruh with other electron densitymeasurementsIn Middle Europe(Figure4) could be done only for electron density profilesobtainedat Gorky, USSR (56.1N,44.3E) using the PR-imp.ils technique/6 /.If the ionosphericconditiones arecomparable,theobservedprofiles agree very well (11.1.1983, 17.l.1985).Inthe samemanner the profiles measuredon January, 20, 1985, with low absorption at Julius-ruh and high absorption at Gorky after the fmin-values of Moscow show the expected in-creaseof the electron density values obtained at Gorky.

REFERENCES

1. J. PrieseandW. Singer, Handbook for M~10, 39 (1984)2. I.S. Belroseand M.J. 3.irke, iL. Geo~hvs~~es’ 69, 2799 (1964)3. W.A, Flood, Sadio ~ci. 15, 797 (1980)4. J. BremerandW. Singer, Adv,SpaceSen., this issue.5. W. Singer, J. Bremer, P. Hoffmann and J, Taubenheim,~riznda

~ Geo~hvs.ik96,352 (1987)6. N.P. Gontsharovand V.D. Vyakirev, private communication.