IRI electron density analytical model and its comparison with empirical data and high latitude models

Adv. Space Res.

0273-I

177(95)ooo97-6

Vol. 16, No. 1, pp. (lf47-(lf.%,

1995 Copyright 0 1995 COSPAR F%itttedin Great Britain. AN rights reserved. 0273-I 177195 $9.50 + 0.00

IRI ELECTRON DENSITY ANALYTICAL MODEL AND ITS COMPARISON WITH E~~R~CAL DATA AND HIGH LATIT~E MODELS N. Egorova, I. A. Nasyrov and T. N. Soboleva institt@e of Terrestrial Magnetism, tonqphere and Radio Wave Propagation, Russian Academy of Sciences, 142092 Troitsk, Moscow Region, Russia

ABSTRACT We have compared experimental electron concentration profiles in the high latitude range @=50 to 90” ,at heights from 80 to 1000 km and longitudes 180 and 300” E, in difI%rentsolar magnetic activity conditions to the profiles predicted by IRI, EMI- IZMIRAN and RMI-88 models. According to these models and to satellite dam, the ionospheric trough displacements were analyzed. Accuracy estimates of these models are p~~~.Hi~ latitude foE and fbF2 corrections the actual formulas are suggested by night at certain longitudes. INTRODUCTION Analytical ionospheric model of electron density and collision frequency are needed for propagation, forecasting purposes, and also with respect to geophysical problems. There exist a number of ionospheric models that describe the ~~~~ state of the ionosphere with su~ci~t accuracy. At high latitude, however, there remains the difficult problem of the influence magnetic activity. For these conditions, all models can only give a tentative answer. At present, for practical predictions one uses empirical analytical models based on a large set of experimental data. Models considered in the following are: International Retirenoes Ion~phere-I~, Global Analytical Equinoctial Model of Electron Con~t~tion of the Ionosphere-EMI- 1, IZMIM, Reference Model Ion~phe~-~1-88, Russia I1-71. ESTIMATION OF ACCURACY OF THE IRI MODEL AT HIGH LATITUDES The International Reference Ionosphere (IRI) /1,2/ gives a threedimensioual analytical description of the most important parameters of the ionospheric plasma such as electron density, ion composition, electron and ion temperatures. The widely used computer code (we use version IRI-89) is ~~uously improved. A firsts effort to create a realistic picture of the disturbed high latitude ionosphere was the model RMI-88 1.51based on a large set of empirical date / 6 / from which analytical predictions of foE and foF2 were drawn in order to improve IRI-82. The EMIis a global analytical model of electron density and collision frequency for the equinoctial conditions and distinct of solar activity levels. In the range 45 to 9OW( g~rn~~~) latitude, 180 to 300”E longitude ~u~~~ profiles have been calculated for suitably chosen conditions by IRI-89, EMIand RMI-88. These have been compared to empirical data as contained in the EM13 1 model/3,4/ to high latitude ionospheric souuding data and to satellites data of IK19 and Cosmos 900 for minimum and maximum solar activity R=lO; R=lOO /8,9/. Further, the latitudinal variations of electron density and altitudes at key points in the profiles were analyzed, in namely: D-, E-, and F2-peaks, bottom of EF-valley and n, at the altitude of 400 km /7,8/. The examples of this comparison are given in Figures l-3 and Tables 1,2( in the Appendix cl.

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DISGUSSION

For undistmkd day time, the IR.I, EMIand Rh@ models give similar v&es of ne and hmax ~~~~ in E, F region and in the valley at all the ~~i~r~ ~~~d~ and f-ar various s&r activities. The Gael ~ the ob and predkted proftres is rally masonably go& the di@Xence J.arfor moms and event hours. es exist, however, in does not exceed IO-20%. S The ~-~~r~~~ ~~~deh ma$Z given by the IRI mMfeJcan di&r fknn the ex~~e~~ values by ~~4-14~ f7!_ The ~~~ dif&emzes between the- IRI model data md the EMI- f model or the ~~~rneN~ values are observed by night and far ~~~~~1 v~~~~. For tke tight ~~~ti~~s~ the IRI model does not give realistic Iatitudinal and l~n~~~n~ variations of the electron density in D and Elayers (/7/, Figure 1, Table 1). In this case, differences betwm the IRI model and the experimental values can reach 20 to 700% and more. IRI admits longitudinal variations of less than 30% while the I I/. pasib& the mostly average ~bse~a~~~s skw changes up to a factor of IS for E and 3 facula and GCIR maps upon which the IRI is feuds typial h&h bide ef&cts# Qur .~~~S~~S show that the ~I~8 model to be better iB I-Ioweverz the mean model values given by the RMI in the E-layer and in the valley ~rn~es by up to 30 to 70%. The EMI- model r&e&s the helio~b~i~ and ~~~~~~ E-region ~~~ rather w& for spring season, Results for the F itre shown in Fimre I and 2 and Tables 1,2. In 181 I7 profiles, cakuh&d via the IRI and RMI models were -pared to vertical sounding and sateW.e data. Figure 2 shows ~~~~~e secure in the f~~~~~~ thee high latitude ionosphere range: (I) auroml region, (ii)main ionospheric ~~u~(iii~ subamoral region. As we see kkornFigure 2 and Tables 2 bath N-87 and WI-88 models give similar values in the lower part of F2 layer and get well coincidence with experiments, especially by day. The data of the WI-88 model agr@ better with satellite data,

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comparison of the &F2 cX&ukions by the RMI-88 and IRI - modeIs with satellite experkwal data on individual days o&n shows very great difkences, somekles up to 50%. Such ~~~ differences may be explained by a ~abih~ of trough kxation and c&&ration. Figure 3 presents the 1~~ ~~b~~on of the troughs at 23 LT at the altitude 400 km obtsined by Cosmos-900 sat&l&e on 25-27 of July 1979 compared by IRI and RMI. Conditioas were extreme& quiet Kp==@-1 for 25-26 Juty but on 2627 Juiy the Kp index increwed to 5-6. In the northeru fmemisphere,the trough kations given by t&e IRI model differ from the ~~~~~ data by A@’ -(Z-4) for Kp=O-I ; the RMI modei data show smaMe; diserences: A@-(O-3 ( invariant latitude). In the southern hemisphere, however, these values are (3-g) for the IRI and (2-8) for the RMI model. In this hemisphere the ~0~~~ variations given by the IRI model is nearer to experimental variations of Cosmos 900 and IK-19 /9,X2/ compared with the RMI model . During gmmagmG~y dish~btxl conditions, the iRi model does sot show the trough displacement to the equator. The accuracy in determiuing the trough Position is 2 to 7 in both hemispheres. The RMI reflects charwteristic trough displawmen ts to the equatorowitb increasing magnetic activity, but the difference between experiment and prediction can reach 6 . Thus, in the northern hemisphere, the RMI model reflects the trough variations correctly and better than the IRI model. For the southern hemisphere, both models require some improvement. If the Iatitude of the real trough position departs &om the model estimation by more tkn I0 , the error in the subauroral regkm may exceed 200%. This may be due to ~ffi~i~~y cousideration of f$2 latitudiuai and long&&al variations at high latitudes and with the l~~tio~s of the three - hour Kp index. It is lawm that the ionosphere may rapidly change at high latitudes. Better ~~~~0~ may be obtained with aa hourly index like AE.. Besides, it must be emphasized tha& when ~~~ high latitude. ionospberk models, it is very important to petiorm averaging without loosing the physical meaning of the process. Statistic.aI models may be preferable.

?lke comparison between the models aud the e-rime&al data has show that the IRI model requires some ~provem~t for high &it&es. It is important to correct the l~~~l~i~de aeons of f$E, GF2 and the trough Iocations, aspeciaIly for the southern hemisphere and with &nging magnetic activity. The problem of high latitude ionosphere modeI& is very important fbr prong the conditions of radiowave proton especially the in&ewe of emission power /f3,14/. (Tables in Appcendix C1 REFERENCES. 1. K&aver, Skmakrishnaq D.Bilitza, International Reference Ionosphere* WI, (1978). 2. K.Raver and D.Bilitza, IRI -plasma density: Status 1988, Adv. Space Res. 10, #8,5-l 14 (1990). 3. A.V.Gurevich, D.I.Fischuk, E.E.Tzedilina, Geomagnet.i ueron. 13, #l, 3140 (1973). 4. A.V.Gurevich, A.G.Israetel, T.N.Soboleva, I.A.Tushentsova, D.I.Fischuk, E,E.TzediI& RMI - 81, pnqwzt IZMIRAN 49a, Moscow (198 1). 5.Yu.K.Chasovitin,A.V.Shirochkov,A.Bespro zvaunaya, T.Scbuka, Adv. S&we Rm, 7, H&49-54 (1987). 6. A.S.Besprozvaunam A.V.Shimchkov, T.I.Schuka, Prediction of the io~as~~e~~ and radio wave p~~~ga~a~ c~~itia~s~ 4. E.M.~ul~ N.i.Se~o, Moscow, Nauka, 1985, p. 29. 7. T.L.G~y~v~ A.G.Israetel, T.Yu.~~~~ TNSoboleva, E.E.Tzedihua, HP and WF’ radio wave i~te~a~~a~ with the ~a~asp~er~,Moscow~ Nauka (1980}, p. 129-135. 8. E.M.Zhui~~ P.V.Kishcha, T.N.Soboleva, ASBespro warmaya, Yu.K.Chasovitin, ~o~~~~~~~ Resew&es, #49, ed. T.N.Soboleva, V.M,Sbashunk& MOSCOW,1993, p_ 13. 9. G.L.Gdakvich, L~N”No~o~ T.N..Sobokva, V.D.Ozerov, preprint EMIRAN, #48, Moscow (1990). IO. T.N.Soboleva. ~~~~f VINITI # 3504-71, Moscow (1971). If, A.V.Gurevich, A.L.Krylov~ E.E.Tsedilk, Space science Reviavs, 19, #I, 59-160 (1976). 12. V.V.~o~~ M.G.D~v, A+T.Karpa&w~ N~P.Ikikova, A.S.Besprozvatmayq L.V.Sh~o~ T.Scbmihwer and T.ISh&uka. George i QHWZ*32, # 2,75-78 ($992). 13. G.S.Bo&karev~ Pr~e~~~s of the llTfSuwfa UTRsfof the ~anas~e~ !JJJ~a~~~~~~ Radio waves (ISI M-31, Moacuw 1991, p.32. 14. G.S.Bwhkarev, L.V.Egorova, Yu.N.Komolov, I.A.Nasyrov, T.N.Soboleva, I.A.Shumilov, &fimnwa i ~iwnn in PLI”PC(E ( 1OQAi