VTEC BEHAVIOR IN THE AMERICAN SECTOR DURING HIGH SOLAR ACTIVITY

Transcription

1 XA3338 VTEC BEHAVIOR IN THE AMERICAN SECTOR DURING HIGH SOLAR ACTIVITY R.G. Ezquer - 23, C. Brunini, A. Meza, F. Azpilicuea, M. Moser 5 and S. M. Radicella" ] FRT, Universidad Tecnologica Naional, Argenina, 2 Laboraorio de lonosfera, Universidad Naional de Tucuman, Argenina, 2 CONICET, Argenina, 3 FCAG, Universidad Naional de La Plaa, Argenina, CASLEO, Argenina, 5 The Abdus Salam Inernaional Cenre for Theoreical Physics, Ialy Absrac: The behavior of he verical oal elecron conen (VTEC) obained from GPS signals received during he high solar aciviy year 999 a saions placed in he American secor, is repored. The considered laiude range exends from 8. o -6.7 and he longiude ranges from 28.3 o Median, lower and upper quariles are used o specify variabiliy, because hey have he advanage of being less affeced by large deviaions ha can occur during magneic sorms. The resuls show ha he VTEC values corresponding o equinox are greaer han hose of solsice and ha, he highes VTEC values are observed a low laiude saions. In general, he variabiliy during dayligh hours is abou 3% of median or less, and ha observed for nighime hours is greaer han he menioned percenage, paricularly a las hours of he nigh near he norhern peak of he equaorial anomaly. Inroducion The ionosphere produces several effecs on ransionospheric radio waves. These effecs are proporional o he number of free elecrons encounered by he wave on is passage hrough he ionosphere (oal elecron conen, TEC). The highes TEC values in he world occur a he equaorial anomaly peaks locaed a approximaely 5 eiher side from he magneic equaor. Using geosynchronous saellies signals received near he Souhern peak of he equaorial anomaly TEC sudies have been done in Argenina (Ezquer e al., 989, Ezquer e al., 995, Ezquer e al., 998). For saellie orbi deerminaion, he saellie posiion and velociy are deermined wih he help of radio signals ransmied beween he saellie and he ground saion. The ionospheric correcions ha have o be applied o deermine he saellie posiion accuraely are proporional

2 52 o he TEC along he radar-saellie pah (Harmann and Leiinger, 98). So, for ionospheric correcions, TEC predicions from ionospheric models can be a useful ool. Several models have been developed o predic he behaviour of he ionosphere (Chiu, 975; Ben e al., 976; Anderson e al., 987; Biliza, 99; among oher). One of he mos widely used empirical model is he Inernaional Reference Ionosphere (Biliza, 99; 2), which gives he value of TEC. Neverheless, in general, he models give he average behaviour of he ionosphere. The developmen of a model for ionospheric variabiliy is useful for he user of ionospheric models. A saellie designer or operaor needs o know no only he monhly average condiions bu also he expeced deviaions from hese mean values. The purpose of he presen paper is o conribue o he sudy of verical oal elecron conen (VTEC) variabiliy and o compare he VTEC values observed a differen American laiudes and seasons. Wih his in mind, he behaviour of he verical oal elecron conen, obained from GPS signals received during equinox and solsice of he high solar aciviy year 999 a en saions of he American secor, is repored. Daa and discussion The considered saions are STATIONS PURS MARA RIO BAMBA AREQUIPA BAHIA BLANCA Laiude Longiude Geomag. La Geomag. Lon Median, lower (Q IO ) and upper (Q up ) quariles are used o specify variabiliy, because hey have he advanage of being less affeced by large deviaions ha can occur during magneic sorms. The following coefficien was calculaed V = [(Q up - Qio ) / median] χ ()

3 Figures land 2 show he VTEC behaviour for June solsice (Rzl2: 93.). I can be seen ha he VTEC values observed a low laiudes are greaer han hose corresponding o oher saions. In he Norhern Hemisphere he highes VTEC values were observed a Bogoa, while hey were observed a Arequipa in he Souhern Hemisphere. For he Norhern saions, hi general, he variabiliy is lower han 3% of median. For he oher saions cases wih variabiliy greaer han 3 % are observed a nigh. The resuls for Sepember equinox (Rzl2: 2.) are shown in figures 3 and. They show ha he VTEC values corresponding o equinox are greaer han hose of solsice. Excep for PUR 3, he variabiliy a las hours of he nigh is greaer han 3 %. V values greaer han 6 % are observed during ha period a Bogoa, saion placed near he norhern peak of he equaorial anomaly. A high laiude, in general he variabiliy is greaer han 3% a all hours of he day. The comparison of he values of coefficien V show ha, in general, he variabiliy during equinox is greaer han ha observed during solsice, paricularly a nigh. Taking ino accoun ha hese resuls correspond o a high solar aciviy period, addiional sudies considering oher condiions are needed in order o provide useful informaion for he developmen of a model for ionospheric variabiliy. Conclusions The behaviour of he VTEC over en saions of he American secor during a high solar aciviy period was repored. The resuls show ha he VTEC values corresponding o equinox are greaer han hose of solsice and ha, he highes VTEC values are observed a low laiude saions, hi general, he variabiliy during dayligh hours is abou 3% of median or less, and ha observed for nighime hours is greaer han he menioned percenage, paricularly a las hours of he nigh. Moreover, for mos of he considered saions he variabiliy observed during equinox is greaer han ha observed during solsice. Addiional sudies considering oher condiions are needed in order o provide useful informaion for he developmen of a model for ionospheric variabiliy References Anderson, D. N., M. Mendillo and B. Hernier, A semiempirical low laiude ionospheric model, Radio Sci., 22,292,987. Ben, R.B.; S.K. Llewelyn, G. Neserczuk and P.E. Schmid, he developmen of highly - successful world - wide oal elecron conen invesigaions, hi Effec of he Ionosphere on Space Sysems and communicaions, ed. By J. goodman, pp. 3-28, Springfield, va

4 5 Biliza, D., Inernaional reference Ionosphere 99, Naional Space Cener / World Daa Cener Ζ for Rockes and Saellies 9-22, Maryland USA, 99. Biliza, D., Inernaional reference Ionosphere 2, Radio Sci., 36,26,2. Chiu, Υ. Τ., an improved phenomenological model of he ionospheric densiy, J. Amos. Terr. Phys., 37,563,975. Ezquer R.G. and N.O. de Adler, Elecron conen over Tucuman, Journal of Goephys res., 9, N A7, ,989. Ezquer R.G., N.O. de Adler, S.M. Radicella, M. Moser and J.R. Manzano, IRI and BPM oal elecron conen predicions for Tucuman, Adv. Space Res. 5 N 2,2-2,995. Ezquer R.G., C.A. Jadur and M. Moser, ERI-95 TEC predicions for he souh american peak of he equaorial anomaly, Adv. Space Res. 22 N 6, 8-8,998. Harmann G. K. and R. Leiinger, Range error due o ionospheric and ropospheric effecs for signals frequencies above MHz, Bull. Geod. 58,9-36,98.

5 VTEC Variabiliy of VTEC [%] PUR3 A» ί{ ι : b 5~! - I 3s»»k & 2 Cj 2, L - - A --Qup =N =s? 5~ IfV! PURS SO 3 kj 2 ϊ"ί " "»" MARA inn..._ - - I A/ r T ' ± _ E - - A - -Qup !- - c- 6 i V < - s»-< ~»N +- -#-< g - 3 i - H-,Η P-<, / f -&,j Jr Κ $T! 3 i 8, f v~\ v' me<lia - - -A - -Qup - "Φ- Is r+ /V' ο RiOBAMBA RIOBAMBA 7 - y - Η is" 2 lk" - ' / /J f fl A Λ ι rj "-, A" med an - A - -Qup " _ ίφη '] AREQUIPA /' k χ ϋϋίΐ A.» I-! - media _. A - -Qup -- fe 8? 6 mn 6 V 2 ' rv \ V V V V v / s S ' AREQUHA V -A- \Λ Α ~~(V V- Φ-" Fig. VTEC (median, upper quaril QUP, lower quaril Qu), and Variabiliy of VTEC [%], June solsice 999 (Rz2:93.), on PURS (Gg.la.8., Gg.long.292.9, Gm.la.2.8, Gm.long.3.); MARA (Gg.la.7, Gg.long.288.3, Gm.laL 22., Gm.long ), Bogoa (Gg.la..6, Gg.long.285.9, Gm.la6.5, Gm.long.355.5), Riobamba (Gg.la.-.6, Gg.long.28.3, Gm.la.9.7, Gm.long.35.) and Arequipa (Gg.la.-6., Gg.long.288.5, Gm.la.-5., Gm.long.358.).

6 56 VTEC Variabiliy of VTEC [%] uu -,,,,,,,,,,,,, 3 -! = Hfe -Έ=$rir / " xi'j.a"' Xf! γ."a V: < L Τ ""< «media A - -Qup W-, - - -i , () Ιΰ a $ Ρ NN-H-fe yi f A/. ji \ Ί - A» edian - - A - -Cup Clo Λ \ Jy : A D ir < - rf I BAHIABLANCA '<' ' ". : K A- -- s» mklra- A - A - -Q P ' 8 8 g "S /»-< s v» 'V,A <!-. A V- V< S s V V ' Ά ' S v BAHIABLANCA J Ν V Λ- -Ν y Λ~ / \ V - = ' i i-ar- sea '(. C A/ media π A - -Qup Fί inn g 6-? 5, 3-2', (, / V ' -< + s, ( LJ /A 9 8 Λ f Ϊ r 6, \ 5 \-. _ me 3 j f % Ί φ<»- s A A / K- A f \ - E3 -A L ι A /-,_j " h Γ ' 2 2 Μ Z \ v v / Ρ Fig. 2 VTEC (median, upper quaril Q,»,, lower quaril QL O ), and Variabiliy of VTEC [%], June solsice 999 (Rz2:93.), on Tucumon (Gg.la.-26.8, Gg.long.29.7, Gm.la.-5.5, Gm.long..), Saniago (Gg.la.-33., Gg.long.289.3, Gm.la.-2.7, Gm.long.359.2), Bahia Blanca (Gg.la.-38.7, Gg.long.297.7, Gm.la-27.,Gn.long.6.6), Rio Grande (Gg.la.-53.8, Gg.long , Gm.la.-2., Gm.long..6) and Palm (Gg.la.-6.7, Gg.long.295.9, Gm.la-53.3, Gn.long..).

7 ' 57 6 f 2 -, J~j - VTEC PUR3 ( r-., A jv -«U? ' media A - -Qup "fe=» » Variabiliy of VTEC [%] PUR3 2 Μ ~ f ' V ' ' ~+ A A "v -n - MARA fj Φ-Ι r Vl JL, Λ s -Ί?H, ;$s - A - -Qu s L A l_~) - 8 g 6 π / _ V MARA / s «- / '»' V S '--! f a - 2 so , '5 F- f Γ i. ~ - - A - madi Qup ' ' <» -A """ 2 o V" / \«A ' ΧX IN - l -» ' 2 8 (H A - Qup s - Q V ' <. 2 ihr- RIOBAMBA r, J i r- ; / AREQUIPA ;,Λ / - S, IS" ; A.»s,. 'is median» -A - -Qu - -Ql) A] -r ' g 6 2,Γ J L / w RIOBAMBA ~wt < ν V \ \\\v vy S x j AREQUIPA / =% \ \ ( \ A Γ "Κ -Φ- ls»-<s / l Fig. 3 VTEC (median, upper quaril Qgp, lower quaril Q LO ), and Variabiliy of VTEC [%], Sepember equinox 999 {Rz2: 2.), on Pur3 (Gg.la.8., Gg.long.292.9, Gm.la.2.8, Gm.long. 3.), Mara (Gg.la..7, Gg.long , Gm.la. 22., Gm.ong.358.9), Bogoo (Gg.la..6, Gg.long.285.9, Gm.la6.5, Gm.long.355.5), Riobamba (Gg.la-.6, Gg.long.28.3, Gm.la9.7, Gm.long.35.) and Arequipa (Gg.Gg.long.38.5, Gm.la.-5.,Gm.long.358.)

8 58 VTEC Variabiliy of VTEC [%] 3QI ς-α- 2 - h [- ' i- 3 7~, X' /' s r' / A r medi an A - -Qup -. v N 2 β β 2 β V s» 8 i? 6 ' 2 Λ N Λ Λ J ' A f, V \l\uj\ \l UT sa N β r j if Ϋ, /- ί' -median - A - Qup Qlo ( ί s k \.N k so 3Γ 6 - s,; SL ) - / ι ι W V -» V ι-φ-ι s I V \) V 's 2 6 a 2 E I L ?= BAHIA BLANCA?/ ' ' ' -A 2 6 β , ' l '- CA- n ' A =ο I,Α Sφ Γ -K Λ Μ BAHIA BLANCA < ik, Λ f\ ' A-, --, k-a k»-, -l-' 2 Λ ' ' j. A "S, #, A ; f r - median A - -Qup «- -Qlo - I =f- A s/\/ rs-» V\ ί' «-. -S -» < fl - ~ J Jk A i j- -,» ~-i - φ _ - A - -Quf - -Qlo A r i- r-a- ' A-J χ A S '» ' A 8 g 6 2 s \ / \. χ ' V «N Ά -«- Fig. VTEC (median, upper quaril Q, lower quaril Q LO ), and Variabiliy of VTEC [%], Sepember equinox 999 (Rz2: 2.), on Tucuman (Gg.la.-26.8, Gg.long.29.7, Gm.laL-5.5, Gm.long..), Saniago (Gg.la-33., Gg.long.289.3, Gm.la -2.7), Bahia Blanca (Gg.la.-38.7, Gg.long.297.7, Gm.la-27., Gm.long.6.6), Rio Grande (Gg.laL-53.8, Gg.long.292.2, Gm. la.-2., Gm.long..6) and Palm (Gg.la.-6.7, Gg.long.295.9, Gm.la Gm.long..).