MO HINH DONG DIEN XICH DAO Ttr SO LIEU VE TINH CHAMP

32(1), 48-57 Tap chi CAC KHOA HOC VE TRAI DAT 3-2010

MO HINH DONG DIEN XICH DAO Ttr SO LIEU VE TINH CHAMP

LE TRLTONG THANH, DOUMOUYA VAFI, LE HUY MINH, H A DUYEN C H A U I. Md DAU

Hien tugng tang bdt thudng bien dO ngay dem thanh phdn nam ngang cua trudng dja tu trong mgt dai hep ±3° khoang dgc theo xich dao td gay bdi mOt he ddng dien hudng v6 phia dOng chay trong Idp E eua tdng dien ly, dugc Chapman [5] ggi la ddng dien xich dao (Equatorial Electrojet - EEJ).

Tren the'gidi da cd rdt nhidu nghien cdu vd EEJ hay mO hinh ly thuye't v6 EEJ dugc cOng bd [ 1, 6, 7, 14, 18] nha't la tu khi thie't lap dugc tram ghi sd lieu gdn xich dao tu tai Huaneayo (Peru) va nhieu dai quan sat dia tu vd ca hai phia cua xich dao tu.

Ngay nay, viec nghien cdu EEJ cung da dua tren nhi^u loai sd lieu khac nhau nhu sd lieu tu cae tram radar, ten lira [4, 18|, tu nhieu ve tinh khac nhau (POGO, Orsted, Magsat, CHAMP...[1, 12|).

Mgt sd mO hinh ly thuye't vd EEJ cua A.D. Rich- mond [14], T.J. Sabaka [15], R.J. Stening [16| xay dung da gdp phdn gidp chdng ta hie'u ro han vd co che hinh thanh, thdi gian xudt hien, cudng dg cung nhu cae kich thudc hinh hgc (dO cao, b^ rgng...) eua EEJ. Sau nay, nhd cd chudi sd lieu vdi thdi gian dai hon cua eac tram gdn xich dao tu, cho phep xay dung nhung mO hinh phuc tap hon (Agu [ 11).

Viec nghien cihi v6 EEJ cung dugc nhidu nha nghien ciiu dja tu Viet Nam quan tam [9,10,11,17[, trong hdu he't cae cOng trinh nay eac tac gia da sii dung sd lieu tu cac tram dja tu tren mat ddt eua Viet Nam (Bac Lieu) va cua mgt sd nude khac tren the' gidi (An DO, Peru...). Tuy nhien, viec sii dung sd lieu trudng dja tu cua cac tram tren mat ddt ed han che do viec phan bd cac tram khOng ddng ddu, va nhdt la viec khOng cd .sd lieu d cac dai duong, nen xay dung mO hinh EEJ theo .so lieu mat ddt thudng khOng chinh xac. Tai Viet Nam chua ed mgt nghien cim nao vd EEJ dua tren sd lieu thu dugc tu cae ve tinh, trong bai bao nay chdng tOi ,su dung sd lieu

trudng tu ghi tren ve tinh CHAMP de nghien ciiu ve EEJ tren toan cdu nhd dp dung phuang phap mdi de' tach phdn anh hudng cua EEJ tu sd lieu trudng tu thu dugc. Dua vao bien dO EEJ tinh dugc, chdng tOi da xay dung mO hinh phan bd cua EEJ tren toan cdu cung nhu tinh toan cae thanh phdn trudng td do EEJ gay ra, tao co sd ban ddu cho nghien cdu ve EEJ mgt each he thdng se tie'n hanh sau nay nhu tim hie'u vd EEJ d vung Viet Nam, so sanh EEJ thu dugc tren ve tinh va sd lieu mat ddt hay nghien ciiu bie'n thien theo thdi gian cua EEJ.

II. TIN HIEU EEJ Tir SO LIEU VE TINH CHAMP /. Gidi thieu ve ve tinh CHAMP

Ve tinh CHAMP dugc thie't ke' va che' tao bdi Trung tam Khoa hgc Qudc gia Ddc vdi trgng lugng 750 kg, dugc phdng tu be phdng COSMOS eua Nga, bat ddu cho sd lieu lien tue tu ngay 15-7-2000 de'n nay. Tren boong ve tinh cd nhidu thie't bj cho phep thu dugc nhidu loai sd lieu khac nhau nhu trudng trgng luc, ndng dO khi oxy, khi nito, thdi gian ehud'n (dung ddng hd thach anh), djnh vj GPS, trudng td (trudng tdng F, va ba thanh phdn X, Y, Z, vdi dO phan giai 0,01 nT). Vdi thie't ke'dac thu de nghien cdu vung xich dao tu, nen ve tinh CHAMP cd dg cao bay kha thdp d khoang 390 - 450 km so vdi be mat Trai Dd't, quy dao gdn nhu vuOng gdc vdi xich dao dja ly (nghieng 87.3°). Trung binh, mOt ngay ve tinh CHAMP bay qua xich dao tu khoang 30 Idn (bay 90 phdt cho mgt vdng quanh Trai Dd't), nhung cd nhiing thdi gian khOng bay qua xich dao vao giua trua (gid dja phuang) va quy dao cQng nhu dO cao dugc didu khid'n tuy theo muc dich nghien cdu nen cdn phai chu y trong qua trinh xii ly sd lieu.

2. Xuly sd'lieu

Trong bai bao nay chdng tOi su dung mOt tdp hgp sd lieu trudng tdng (F) ca nam 2003 thu dugc

tu ve tinh CHAMP (sd lieu do Vien Vat ly Dja cdu Paris cung edp), bao gdm 158 ngdy trudng td yen tinh (chgn nhdng ngay cd chi sd am < 20 nT [13]).

Vdi ban 2 trieu die'm do cho 1.345 lat cdt .sd lieu ve tinh ngang qua xich dao vao giiia trua dja phuang (td 10 de'n 14 gid dja phuang), quy ude mgt lat cat sd lieu la tap hgp sd lieu khi quy dao cua ve tinh bay qua xich dao tu theo mOt kinh tuye'n bdt ky.

COng viec ddu tien cua qua trinh xii ly sd lieu la loai bd nhieu trong qua trinh do dac, do tdc dg Idy mdu tren ve tinh la 1 Hz nen trong chudi .sd lieu ghi dugc thudng xudt hien nhieu do dac, viec Ige nhieu dugc thuc hien nhd cac bO Ige khac nhau, trong bdi bao nay chdng tOi su dung bO Ige la cae da thde bac rdt cao (bac trong khoang 60-90) trong qua trinh tinh toan de' loai bd nhirng gia trj ndm ngoai quy luat. Tie'p theo, chdng ta phai tach dugc phdn anh hudng cua EEJ td sd lieu do dac.

Nhu chdng ta da bie't, trudng tdng (F) do dac tai mOt die'm bdt ky tren mat ddt cung nhu tren ve tinh dugc ddng gdp bdi 3 phdn chinh : trudng tu chinh cd ngudn gdc ben trong nhan Trai Ddt (Fp), trudng cua vd Trai Ddt (Fc), trudng tu ed ngudn gdc ben ngoai (Fe) vd :

Fp + Fc + Fe (1)

- Fp : ed the' tinh dugc nhd mO hinh trudng tu ehud'n qudc te' (IGRF). Di tinh toan phdn anh hudng cua trudng cd ngudn gdc ben trong td sd lieu ve tinh CHAMP cho nam 2003, chdng tOi sii dung mO hinh IGRF (nien dai 2003.5). Trong dd, viec lira chgn bac de khai trie'n ham didu hoa cung la mOt viec kha quan trgng, ne'u ta chgn bac qua cao cd the' lam giam tin hieu cdn quan tam va ngugc lai. Qua nhidu tinh toan khac nhau viec sii dung vdi hai didu hoa bae 14 cho sd lieu ve tinh CHAMP la tdi uu.

- Fc : phu thugc vao vj tri do dac va coi nhu khOng ddi trong .sudt thdi gian nghien cdu.

- Fe : ed the' do nhidu ngudn td cac tdng khac nhau nhu tdng dien ly, tu quye'n... vd EEJ .se gay ra mOt trudng nam trong Fe.

Nhu vay, cd the' de dang tach dugc thanh phdn trudng Fp. Tie'p theo, chdng ta phai tach phdn anh hudng eiia EEJ tu Fe va Fe. Tren the gidi, cd nhi^u tdc gia da de cap de'n viec tach trudng do EEJ gay ra [2, 13] tu chudi sd lieu nay. T.J. Sabaka da phat trie'n mO hinh CM3 de' tach, the'nhung mO hinh nay cdn dan gian vi nd chi tinh dugc gia trj trung binh cua mat do ddng tren tdng dien ly ma khOng xac

djnh dugc phdn bd mat dO cua nd. MO hinh CM3 cung ed han che' la dung ham didu hod cdu bac 60 de' loai bd ca trudng chinh va trudng vd, didu nay ddng nghTa vdi viec coi trudng vd se bie'n idi dieu hod theo khOng gian ma thuc te'khOng hdn nhu vay.

Trong bai bao nay, di tach phdn anh hudng ciia EEJ td sir chdng chap ciia cac trudng khac chdng tOi sir dung "bg Igc" la cae da thde ed bac khac nhau ; nhu vay viec dp dung cho eac lat cat sd lieu theo eac kinh tuye'n khac nhau se ddi hdi thdi gian xii ly sd lieu dai hon va phdc tap hon phuang phap cua T.J.

Sabaka nhung cho phep chdng ta loai bd trudng vd Fc mOt each tin cay va chi tie't hon.

3. Tach phin anh hudng cua EEJ

Nhu chdng ta da bie't, phdn trudng tu gay ra bdi he ddng EEJ tren tdng dien ly thu dugc tren ve tinh la rdt nhd so vdi trudng tu tdng (F) ma nd thu dugc, vdi quy dao va dO cao ciia ve tinh CHAMP, phdn trudng anh hudng bdi EEJ chi trong khoang tu 20 nT de'n 70 nT so vdi sd lieu trudng tdng thu dugc vao khoang td 30.000 nT de'n 50.000 nT, them nua nd cdn cd sir chdng chap cua nhieu ngudn khac nhau, do vay viec tach phdn anh hudng cua EEJ la rdt khd khan. Viec dp dung thuat toan tach phdn anh hudng cua EEJ bang da thde cd bae khac nhau khi ta coi :

- Trudng bie'n thien theo thdi gian ghi dugc tren ve tinh cho mOt Idn cat ngang qua xich dao la khOng dang ke' (thdi gian de ve tinh CHAMP bay qua xich dao td chi' khoang 5 phdt tu vy dg 100 deh -100).

- Trudng cua EEJ gay ra ehi trong mOt dai hep kha d6u dan dgc theo xich dao tu va lam giam bien do cua trudng tdng (F) thu dugc tren ve tinh va tao ra phdn "lorn" xudng trong sd lieu cua tung lat cat tren .so lieu ve tinh {hinh 1). Nhu vay, phdn anh hudng cua trudng vd va trudng tren tdng cao hon phdn ndm ngoai vung anh hudng cua EEJ dugc xdp xi bang cac da thuc cd bac cao tuy y de cd the' xdp XI tdt dudng cong thu dugc, cdn phdn trudng trong vung anh hudng cua EEJ, theo kinh nghiem trong qua trinh xii ly sd lieu, chdng tOi su dung da thuc bac tha'p hon. Vi du tren hinh 1, viec sir dung da thde bae thdp vdi phdn anh hudng cua EEJ (vy dg ±10°) se tach ra dugc trudng vd Trai Ddt (dudng manh net lidn) mgt each lien tuc. Ngoai ra, dd dp dung dugc thuat toan tren, chdng ta phai xac dinh dugc be rOng eua EEJ se thu dugc tren quy dao cua ve tinh va lira chgn bac ciia da thuc de' xdp xi.

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Hinh 1. Tach phdn anh hudng eiia EEJ bang cac da thuc a) Do rgng anh hudng cCia EEJ : do EEJ chay

trong dai hep +3° dgc theo xich dao td va qua qua trinh xii ly sd lieu chdng tOi nhan thdy bd rOng anh hudng ciia EEJ tren dg cao ciia ve tinh trong khoang vy do tu -10° de'n 10°. Viec chgn dO rOng ciia EEJ tai do cao ciia ve tinh la ±10° nay la tdi uu khi nd dam bao hdu nhu Id'y he't dugc phdn "1dm" xudng trong trudng cdn lai va thuan tien cho viec viet chuong trinh xii ly sd lieu.

b) Bac cCia da thCtc : bac cua da thde dung dd xdp XI anh hudng de'n dO Idn eua EEJ, nen viec lira chgn bac da thde tdi uu cung rdt quan trgng trong qua trinh xii ly sd lieu. Viec lira chgn bac da thde phu thugc nhilu vao kinh nghiem tinh toan va hinh dang dudng cong sd lieu thu dugc. ThOng thudng, chdng tOi sir dung da thde bac khoang tu 60 de'n 90 cho phdn nam ngoai anh hudng cua EEJ (vy dO dja tu td -40° de'n -10° va tu 10° de'n 40°) cdn phdn nam trong vung anh hudng ciia EEJ (vy dg dja tu tu -10° deh 10°) chdng tgi sii dung da thde bae trong khoang 6 - 1 0 cho mdi lat cdt. COng viec xii ly sd lieu mdt nhidu thdi gian hon cua T.J. Sabaka the' nhung se chinh xac hon khi ta coi trudng vd Fc tai mdi vj tri khac nhau se cd hinh dang dudng cong khac nhau. Cung cdn ndi them, viec lua chon

bde ciia da thde phu thuOc nhilu vao kinh nghiem xii ly sd lieu, viec Idy da thde bac cao qua cd the' lam suy giam tin hieu cdn tach va ngugc lai.

Tren hinh 1, chdng tOi trinh bdy mOt vai vi du vd tach anh hudng ciia EEJ cho sd lieu cae ngay 1, 2 thang 12 nam 2003 tai cac kinh tuye'n khac nhau bang thuat toan tren. Phdn trudng sau khi da loai bd trudng chinh (nhd mO hinh IGRF bac 14, nien dai 2003.5) cdn lai khoang 120 nT dugc bie'u dien bang dudng ddm net lidn bao gdm trudng ciia vd Trai Ddt va trudng ngoai gay ra. Dudng lidn net manh bie'u dien trudng xdp xi bang da thde cd bac tu 6 de'n 10 va dudng net ddt bie'u dien phdn anh hudng ciia EEJ thu dugc.

4. Bien do cua EEJ cho nSm 2003

Tren hinh 2, bie'u didn gia trj bien dO trung binh (Idy gia trj tuyet ddi) eiia EEJ thu dugc cho ca nam 2003 tu ve tinh CHAMP, bao gdm 158 ngay trudng tu yen tinh va 1.345 Idn ve tinh CHAMP cat qua xich dao tai cac kinh tuye'n khac nhau, lua chgn thdi die'm giQa trua tu 10 gid 00 de'n 14 gid 00 (gid dja phuang). Chung ta nhan thdy bien dO ciia EEJ nam trong khoang tu 12 nT de'n 67 nT va tai vung kinh tuye'n 100° (Viet Nam) cd mOt cue tri kha Idn

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(dat 67 nT) so vdi cac kinh tuye'n khac. Chd y tren hinh ve cung cd nhirng khu vuc khOng ed sd lieu, cd nghTa trong khoang thdi gian nay, ve tinh CHAMP khOng bay qua cac kinh tuye'n nay vao giQa trua dja phuong. Vdi gia trj cue dai ciia EEJ nam kha trung vdi dudng tam xich dao tu va bien dO ciia EEJ giam ddn vi hai phia ciia vy tuye'n nen viec lua chgn dO rOng anh hudng ciia EEJ tren quy dao cua ve tinh CHAMP la ±10° la phu hgp.

III. MO HINH EEJ VA AP DUNG CHO SO LIEU CHAMP

/. PhSn bdmSt dd ddng EEJ

Nhu chdng ta da bie't, cudng dO ddng dien xich dao quan sat tai mOt die'm bd't ky se phu thuOc vao kinh do, vy dO va thdi gian (thdi gian dja phuong).

Khi ta coi EEJ nhu mOt dai ddng mdng tdn tai d dO cao cd djnh (cao 105 km so vdi mat dd't) va theo khai trie'n cua O. Fambitakoye va P.N. Mayaud [8|

khi ta coi EEJ nhu mOt dai ddng ddng nha't, su bie'n thien ciia mat dO ddng I(x) ciia EEJ phu thuOc vao vy do (A.) lien he vdi mat dO ddng lo tai tam cua EEJ bie'u dien nhu sau :

/(x) = /o(A) {x-cY a'-

(2) vdi x - khoang each tu tam EEJ de'n die'm quan sat X va dugc xac djnh trong khoang c-a<x<c-va, a - 1/2 \si rOng cua EEJ, c - vj tri cua tam EEJ.

Sir phu thuOc cua thanh phdn trudng nam ngang (AH) tao bdi EEJ vao gid dja phuang dugc mO ta qua ham phan bd Gaussian nhu sau :

G(r) = exp ( r - r ) 2

(3)

vdi T - gid dja phuang khi thanh phdn trudng ndm ngang (AH) gay ra bdi EEJ dat gia trj cue dai (thudng chgn T = 12hOO), tn, - tham .sd hieu chi'nh cua ham phan bd Gauss, phu thuOc vao sir bie'n thien cua thanh phdn nam ngang AH va thanh phdn thing dung AZ, dugc xac djnh bang thuc nghiem, thgng thudng chgn tn, = 4h.

Theo dd, su bie'n thien cua mat dg ddng tai vj tri X bdt ky khi mat dO ddng tai tdm cua EEJ la Io(t) nhu sau:

/()(') = lu^^P (t-T) ^{,2^}

(4)

vdi 112 - gia trj giQa trua dja phuang cua Io(t), nd phu thuOc vao gia trj thanh phdn ndm ngang cua trudng tu (AH^) gay ra bdi EEJ nhu sau :

^ 1 2 = -

AHn 0,4arctg\

(5)

h = 105 km - dg cao eua EEJ. Khi dd ta cd phan bd eua mat dg ddng dien EEJ phu thuOc vao kinh dO, vy do va thdi gian (dja phuang) nhu sau :

l{t,x,A) = l,{A)\^ (x-c)^

.exp ^ ( f - r ) 2 ^ (6) vdi t = tu + {X/\5) , tu - gid qudc td, X - kinh tuye'n nam trong khoang -180°< X <180°.

Td eOng thuc (5), ta hoan toan tinh In lien quan de'n su bie'n ddi thanh phdn ndm ngang AHo, vdi ,sd lieu ve tinh CHAMP ta cd the' thay AH,, bdng phdn trudng anh hudng cua EEJ tach ra td sd lieu trudng tdng (AF). Sau dd, tu (6) cho phep tinh dugc mat dO ddng cua EEJ phu thuOc vao thdi gian dja phuong, kinh dg va vy dg. Kdt qua tinh mat dO ddng eua EEJ cho sd lieu nam 2003 tren toan cdu dugc bie'u dien tren hinh 3, vdi cudng dO manh nhdt tai tam cua EEJ dat khoang 200 A/km va nd cung phu thugc vao kinh do, vy dO, thdi gian (dia phuang) T.

2. Tinh cac thanh phin cua trudng tdgiy boi EEJ

Theo cOng thde khai trie'n bdi O. Fambitakoye (1976), tu cae tham sd c, a, T, t^, \4X). I(t, x, X) ta cd the' tinh thanh phdn eua trudng nam ngang (AH), thanh phdn thdng ddng (AZ) gay ra bdi ddng EEJ tai vj tri xs ba't ky nhu sau :

50 100 A/km 150 Hinh 3. Mat dO ddng dien eua EEJ tinh td CHAMP

150 180

200

AH = 0,2 ^ [(a2 - X2 )2 + (2a2 - 6X2 )h^+h'' \arctgRg - arctgR^) + a^

+ 0,2^[2{a^-X})X,h + 2X,h^]]^n{\ + Rl)-\n{\ + RD\+0,2^'^{Rl-R\)- a^ a* i

-0^4^X,hHRl-Ri)-0,2-^[{2a2 -6X})h^ + h^\R, + R^)

(7)

AZ = -0,l^[(a2_x2)2-h(2a2-6X2)/,2+/,4][in(i + ^2)_in(i + /j2)]+

+ 0,8 ^ [(a2 - X2 )X,/i - X,h^ \arctgR, - arctgR^) _ 0,1 : ^ ^ (7?^ _ /?4) + + 0 , 8 ^ y X,(/?3 _ /e3) + 0,1 i^[(2^2 -6X,2)h2+h^\{Rl-Rl)-

- 0,8 \ X, [{a^-Xj)h + h^]{R,-R^)

vdi c - vj tri cua tam EEJ, h - dg cao cua EEJ tinh Cac ke't qua tinh toan mO hinh ly thuye't cac bang km, lo tinh bdng A/m, AH va AZ tinh bang thanh phdn trudng tu do EEJ gay ra dua vao cOng

thde (7) va (8) dugc bie'u didn tren hinh 4. Tren hinh nay bie'u diln cae thanh phdn eiia trudng tu gay ra bdi EEJ tren toan cdu tai cac thdi gian khac nhau vdi dg cao trung binh cua ve tinh la 400 km so vdi mat ddt. Gia trj dat cue dai cua thanh phdn AH khoang 70 nT (Idy tri tuyet ddi), bien dg cue dai cua AZ vao khoang 40 nT, dudng ddng mdc cho cac hinh ve la 10 nT

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(9)

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Hinh 4a, b. Thanh phdn nam ngang AH (nT) va thanh phdn thdng ddng AZ (nT) tai OhOO UT

Kinh tuyen

Hinh 4c, d. Gia trj cac thanh phdn AH va AZ tai 12h00 UT

Tren hinh 5 bie'u dien gia trj 2 thanh phdn AH do EEJ gay ra tren toan cdu tai cung mOt thdi va AZ tai 12 gid 00 (gid dja phuang) cho tdt ca cac die'm. Tren hinh ve nay, chdng ta nhan thdy ca AH kinh tuye'n khac nhau. Nd cho phep chdng ta cd cai va AZ ed mOt cue trj tai kinh tuye'n 100° va cd mOt nhin tdng thd vd phan bd cua timg thanh phdn trudng cue tidu tai kinh tuydh 50°.

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120 150 180

3. So sanh kit qua tinh md hinh va sd'lieu thu duoc tu CHAMP

Tren hinh 6, hiiu dien viec so sanh giQa EEJ thu dugc td mO hinh va EEJ tinh tu sd lieu ve tinh CHAMP cho nam 2003 tai cac vdng cd kinh tuye'n khac nhau, vdi dudng net ddt la gia trj trudng do EEJ gay ra tinh dugc td mO hinh, dudng net rdi la gia trj trudng tinh dugc tu sd lieu CHAMP cho mdi lat cat sd lieu.

Tren mdi hinh cdn duoc bie'u didn cae tham sd khac

nhu : h la gia trj dO cao ciia ve tinh. Long la kinh tuye'n di qua. Chdng ta nhan thdy eac dudng tinh tu mO hinh va dudng tinh tu sd lieu ve tinh CHAMP la kha trung nhau. Chung tOi da tie'n hanh tinh dO lech binh phuang trung binh (RMS) cho toan bg sd lieu nam 2003. Qua tinh toan nhan thdy gia trj RMS thudng nhd hon 5 nT. Nhu vay viec dp dung mg hinh tren cho sd lieu ve tinh CHAMP la hoan toan cd the' chdp nhan dugc.

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Vy dp dja tir

EEJ tach tu CHAMP EEJ tu mo hinh Long : kinh tuyen h : dp cao quy dao

Hinh 6. So sanh EEJ thu duoc td mO hinh va tinh toan tu sd lieu CHAMP

. KET LUAN

Trong bai bao nay, chdng tOi trinh bdy viec dp dung sd lieu trudng tu thu dugc tren ve tinh de' nghien cdu vd EEJ va da nghien cdu, ap dung phuong phap mdi di tach phdn anh hudng eua EEJ tu sd lieu trudng td thu dugc tren ve tinh CHAMP bdng cac da thde cd bac khac nhau. Sau dd dp dung phuong phap tren cho chudi sd lieu thu dugc bao gdm 1.345 lat cdt sd lieu vdi ngay trudng tu yen tinh thu dugc tu ve tinh CHAMP nam 2003. Td sd lieu bien dg cua EEJ tinh dugc chdng tOi da xay dung mO hinh EEJ cho toan cdu cQng nhu tinh toan cac thanh phdn trudng tu do EEJ gdy ra tai mgt die'm

ba't ky. Qua cac budc tinh toan tren cd mOt sd ke't luan nhu sau :

- DO rOng (theo vy tuye'n) anh hudng cua EEJ tai do cao ve tinh CHAMP bay vao khoang ±10°

(tai mat ddt vao khoang ±3°).

- Bien dg cua trudng td gay bdi EEJ thu dugc tu ve tinh CHAMP bie'n ddi trong khoang td 25 nT de'n 70 nT, tuy thuOc cac kinh tuye'n khac nhau. Tai kinh tuye'n Viet Nam (kinh dO 100°) chdng ta nhan thdy cd 1 cue dai (dat 68 nT), ngudn gdc cua cue trj nay vdn chua bie't, nd cd the' do cae hoat dOng dien dOng lire tren tdng diSn ly, hoac do mat dO cua gid

trung hoa, cung cd the' do dO ddn ciia vd Trai Ddt trong khu vuc ; chdng ta phai nghien cdu sir xudt hien cua cac cue trj nay theo thdi gian de' khang djnh su tdn tai eua nd. Tai kinh tuydn -60°, cd mOt cue tie'u, vdi thanh phdn trudng ndm ngang tai tam EEJ khoang 40 nT.

- Mo hinh vd ddng dien xich dao phu thuOc vao kinh do, vy dO va thdi gian dja phuong bdng mOt ban ddng d dO cao 105 km la kha phu hgp vdi sd lieu quan sat tren ve tinh, cho chdng ta mgt bdc tranh kha hoan chinh ve bien dO, quy luat phan bd, do rgng iinh hudng cua EEJ tren toan cdu, nhd dd chdng ta cd the' cd nhung nghien cdu tie'p theo nhu bie'n thien theo thang, nam, mua...

- MO hinh EEJ thu dugc, vdi dg lech binh phuang trung binh (RMS) nhd hon 5 nTtinh cho toan bg cae kinh tuye'n khac nhau cho chdng ta ed cai nhin tdng the v^ phan bd hinh hgc cung nhu cac tham sd cua EEJ tren toan cdu.

- Viec nghien cuu bie'n ddi cua EEJ theo thdi gian va .so sanh mO hinh nay vdi eac mO hinh su dung sd lieu eua cac ve tinh khac cung nhu td sd lieu mat ddt se de cap trong cac nhien cdu sau nay.

Ldi cam on : cac tac gia chan thanh cam on Ts Yves Cohen vd Ts Amory Mazaudier da ed nhQng y kie'n ddng gdp xac dang trong viec hoan thanh bdi bao. Bai bao dugc hoan thanh vdi phdn sd lieu ve tinh dugc cung edp bdi Vien Vat ly dja cdu Paris trong chuong trinh hgp tac giQa Vien Vat ly dja cdu Ha Ngi, Vien Vat ly dja cdu Paris va Trung tam nghien cdu mOi trudng Trai Ddt va eac Hanh tinh - "Nghien ciru Vat ly dja cdu trong mdi quan he Mat Trdi - Trai Ddt, nghien cdu trudng tu d Viet Nam" (PICS-3366).

TAILIEUDAN

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[2] KW. BEHANNON, N.F, NESS, 1966 : The design of numerical filters for geomagnetic data analysis, NASA Tech, note, D-3341.

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Meteorol. Geophys. Bioclimatol. A4, 368-390.

| 6 | V, DOUMOUYA, J. VASSAL, Y. COHEN, O.

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[101 TRUONG QUANG HAO, LE HUY MINH, 1987 : Mgt .sd dac die'm eua trudng dja tu bie'n thien d Viet Nam, Tap chi Cac khoa hoc ve Trai Ddt. T.

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SUMMARY

The equatorial electrojet model with CHAMP satellite data

The EEJ (Equatorial Electro;et) is a complex current system flowing in the ionospheric E-layer.

Its value changes in space and in local time. The magnetic signature of the EEJ overlaps on the recorded magnetic data and the amplitude of the EEJ magnetic signature is very small with respect to that of the main field. So the separation of the EEJ magnetic is difficult. Today, we have many kinds of data for studying EEJ (ionosonde, rocket, magnetic observatories...). IVIany results of the studies of EEJ were publicated, but these results are with some limit as there are few data from obsevation and the data are no regulady distributed.

The CHAMP satellite has launched from July 15, 2000. It gives the good data for studying the EEJ because of its low orbit and passing along the longitudes, crossing the equator at noon time.

In this paper we introduce the CHAIVIP satellite, its recorded data and give an algorithm for sepa- rating the EEJ magnetic signature from the total magnetic field. We present the application of this method to the data received in 2003, with 158 quiet days, about 1345 values of total field around noon (for local time from 10 to 14 hour) to study the EEJ.

An empirical model of the EEJ, including local time, longitude, latitude is also presented in this paper;

we try to apply the EEJ data for one year 2003 to define some parameters of EEJ around the world.

Ngdy nhdn bdi: 16-10-2009

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