32(1), 48-57 Tap chi CAC KHOA HOC VE T R A I BAT 3-2010
MO HINH DONG DIEN XICH DAO Ttr SO LIEU VE TINH CHAMP
LE TRUdNG THANH, DOUMOUYA VAH, LE HUY MINH, H A DUYEN C H A U
I. Md DAU
Hien tugng tang ba't thudng bien dd ngay dem thdnh phdn nam ngang ciia trudng dja tir trong mOt dai hep+3° khoang dgc theo xich dao tir gay bdi mdt he ddng dien hudng vl phia ddng chay trong ldp E eiia tdng dien ly, duge Chapman [5 ] ggi Id ddng dien xich dao (Equatorial Electrojet - EEJ).
Tren the gidi da cd rdt nhilu nghien ciru vl EEJ hay md hinh ly thuylt vl EEJ dugc cdng bd 11, 6, 7, 14, 18] nhdt la tir khi thilt lap dugc tram ghi sd lieu gdn xich dao tir tai Huancayo (Peru) va nhilu dai quan sat dja ttr vl ca hai phia ciia xich dao tir.
Ngay nay, viee nghien curu EEJ cung da dua tren nhilu loai sd lieu khac nhau nhu sd lieu ttr cae tram radar, ten liia [4, 18], ttr nhilu ve tinh khac nhau (POGO, Orsted, Magsat, CHAMP...[ 1, 121).
Mgt sd md hinh ly thuylt vl EEJ cila A.D. Rich- mond [14], T.J. Sabaka [15[, R.J. Stening [16] xay dung da gdp phdn giiip chiing ta hie'u rd hon vl co chi hinh thanh, thdi gian xudt hien, cudng dd cung nhu cae kich thudc hinh hgc (dO cao, bl rOng...) ciia EEJ. Sau nay, nhd cd chudi sd lieu vdi thdi gian dai hon cila cdc tram gdn xich dao tir, cho phep xay dung nhu'ng md hinh phiic tap han (Agu [ 1 ]).
Viec nghien cim vl EEJ ciing dugc nhilu nha nghien cim dja tii Viet Nam quan tam [9,10,11,17], trong hdu hit cac cdng trinh nay cac tac gia da sii dung sd lieu ttr cac tram dja ttr tren mat ddt cila Viet Nam (Bac Lieu) va cila mdt sd nudc khac tren thi gidi (An Dd, Peru...). Tuy nhien, viec sir dung sd lieu trudng dja ttr cila cac tram tren mat ddt cd han che' do viec phan bd cdc tram khdng ddng diu, va nha't la viec khdng cd .so lieu d cac dai duong, nen xay dung md hinh EEJ theo .so lieu mat ddt thudng khdng chinh xac. Tai Viet Nam chua cd mdt nghien ciru nao vl EEJ dua tren sd lieu thu dugc tir cac ve tinh, trong bai bao nay chiing tdi sii dung sd lieu
trudng tu ghi tren ve tinh CHAMP de nghien cioi vl EEJ tren toan cdu nhd dp dung phuong phap mdi dl tach phdn anh hudng cila EEJ ttr sd lieu trudng tu thu dugc. Dua vdo bien dd EEJ tinh dugc, chimg tdi da xay dung md hinh phan bd cila EEJ tren toan cdu cung nhu tinh toan cac thanh phdn trudng tir do EEJ gay ra, tao co sd ban ddu cho nghien cim vl EEJ mdt each he thd'ng .se tie'n hanh sau nay nhu tim hilu vl EEJ d vting Viet Nam, so sanh EEJ thu dugc tren ve tinh va .sd lieu mat ddt hay nghien cim bie'n thien theo thdi gian ciia EEJ.
II. TIN HIEU EEJ TLT SO LIEU VE TINH CHAMP /. Gioi thieu ve ve tinh CHAMP
ve tinh CHAMP dugc thilt k l va chi tao bdi Trung tam Khoa hgc Qudc gia Dire vdi trgng lugng 750 kg, dugc phdng ttr be phdng COSMOS ciia Nga, bdt ddu cho sd lidu lien tuc ttr ngay 15-7-2000 din nay. Tren boong ve tinh cd nhieu thilt bj cho phep thu dugc nhilu loai sd lieu khac nhau nhu trudng trgng luc, ndng dd khi oxy, khi nita, thdi gian chudn (dung ddng hd thach anh), djnh vj GPS, trudng tir (trudng tdng F, va ba thanh phdn X, Y, Z, vdi dO phan giai 0,01 nT). Vdi thilt kidac thti dl nghien ciru vimg xich dao ttr, nen ve tinh CHAMP cd dd cao bay kha thdp d khoang 390 - 450 km so vdi be mat Trai Ddt, quy dao gdn nhu vudng gdc vdi xich dao dja ly (nghieng 87.3°). Trung binh, mdt ngay ve tinh CHAMP bay qua xich dao ttr khoiing 30 ldn (bay 90 phiit cho mdt vdng quanh Trai Dd't), nhung cd nhiing thdi gian khdng bay qua xich dao vao giira trua (gid dja phuong) va quy dao cung nhu dd cao dugc dilu khiln tuy theo muc dich nghien ciru nen cdn phai chu y trong qua trinh xii ly sd lieu.
2. Xuly sd'lieu
Trong bai bao nay chiing tdi siir dung mdt tdp hgp sd lieu trudng tdng (F) ca nam 2003 thu dugc
ttr ve tinh CHAMP (sd lieu do Vien Vat ly Dja cdu Paris cung edp), bao gdm 158 ngay trudng ttr yen tTnh (chgn nhirng ngdy ed chi sd am < 20 nT [13]).
Vdi hon 2 trieu dilm do cho 1.345 ldt cdt sd lieu ve tinh ngang qua xich dao vdo giira trua dja phuong (ttr 10 de'n 14 gid dja phuang), quy udc mdt lat cat sd lieu la tap hgp sd lieu khi quy dao eua ve tinh bay qua xich dao ttr theo mdt kinh tuyln bdt ky.
Cdng viec ddu tien cila qua trinh xii ly sd lieu la loai bd nhilu trong qua trinh do dac, do td'c dd Idy mdu tren ve tinh Id 1 Hz nen trong chudi sd lieu ghi dugc thudng xudt hien nhilu do dac, viec Igc nhilu dugc thuc hien nhd cae bd Igc khac nhau, trong bai bao nay chiing tdi sii dung bd lgc la cac da thirc bac rdt cao (bac trong khoang 60-90) trong qua trinh tinh todn dl loai bd nhirng gia tri ndm ngoai quy luat. Tilp theo, chung ta phai tach dugc phdn anh hudng ciia EEJ ttr sd lieu do dac.
Nhu chiing ta da bilt, trudng tdng (F) do dac tai mdt dilm bdt ky tren mat ddt cung nhu tren ve tinh dugc ddng gdp bdi 3 phdn chinh : trudng ttr chinh cd ngudn gdc ben trong nhan Trai Ddt (Fp), trudng ciia vd Trai Ddt (Ec), trudng tir cd ngudn gdc ben ngoai (Fe) va :
F - Fp + Fe + Fe (1)
- Fp : cd thi tinh dugc nhd md hinh trudng ttr chudn qudc tl (IGRF). Di tinh toan phdn anh hudng ciia trudng cd ngudn gd'c ben trong tir sd lieu ve tinh CHAMP cho nam 2003, chiing tdi sir dung md hinh IGRF (nien dai 2003.5). Trong dd, viec lira chgn bac dl khai tril'n ham dilu hod cung la mdt viec kha quan trgng, niu ta chgn bac qua cao cd thi lam giam tin hieu cdn quan tam vd ngugc lai. Qua nhilu tinh toan khac nhau viec sii dung vdi hai dilu hod bac 14 cho sd lieu ve tinh CHAMP la td'i uu.
- Fc : phu thudc vao vi tri do dac va coi nhu khOng ddi trong sudt thdi gian nghien ciru.
- Fe : cd thi do nhieu ngudn ttr cac tdng khac nhau nhu tdng dien ly, ttr quyin... vd EEJ se gay ra mOt trudng ndm trong Fe.
Nhu vay, cd thi dl dang tach duge thdnh phdn trudng Fp. Tilp theo, chimg ta phai tach phdn anh hudng cila EEJ tir Fe va Fc. Tren thi gidi, cd nhieu tac gia da di cap din viec tach trudng do EEJ gay ra [2, 13[ tir chudi sd lieu nay. T.J. Sabaka da phat tril'n md hinh CM3 dl tach, the nhung mO hinh nay cdn don gian vi nd chi tinh dugc gid trj trung binh ciia mat dd ddng tren tdng dien ly ma khdng xac
djnh dugc phan bd mat dd cila nd. Md hinh CM3 ciing cd han chi la dimg ham dieu hod cdu bac 60 dl loai bd ca trudng chinh va trudng vd, dieu nay ddng nghTa vdi viec coi trudng vd se biln ldi dilu hoa theo khdng gian ma thirc t l khong hdn nhu vay.
Trong bdi bao nay, dl tdch phdn anh hudng ciia EEJ ttr sir chdng chap cila cac trudng khac chiing tdi sir dung "bd lgc" la cdc da thirc cd bac khac nhau ; nhu vay viec dp dung cho cac lat cdt sd lieu theo cac kinh tuyln khac nhau .se ddi hdi thdi gian xii ly sd lieu dai han va phirc tap han phuang phap cila T.J.
Sabaka nhung cho phep chung ta loai bd trudng vd Fc mdt each tin cay vd chi tilt hon.
3. Tich phin anh huong cua EEJ
Nhu chiing ta da bilt, phdn trudng ttr gay ra bdi he ddng EEJ tren tdng dien ly thu dugc tren ve tinh la rdt nhd so vdi trudng ttr tdng (F) ma nd thu dugc, vdi quy dao va dd cao cila ve tinh CHAMP, phdn trudng anh hudng bdi EEJ chi trong khoang ttr 20 nT de'n 70 nT so vdi sd lieu trudng tdng thu dugc vao khoang ttr 30.000 nT din 50.000 nT, them niia nd cdn cd sir chdng chap ciia nhilu 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 ciia EEJ bang da thirc cd bac khac nhau khi ta coi :
- Trudng biln thien theo thdi gian ghi dugc tren ve tinh cho mdt ldn cat ngang qua xich dao la khdng dang kl (thdi gian de ve tinh CHAMP bay qua xich dao ttr chi khoang 5 phiit ttr vy dd 100 din -100).
- Trudng cila EEJ gay ra chi trong mdt dai hep kha diu dan dgc theo xich dao tir vd lam giam bien dd eua trudng tdng (F) thu dugc tren ve tinh va tao ra phdn "ldm" xud'ng trong sd lieu cila tirng lat cdt tren sd lieu ve tinh {hinh 1). Nhu vay, phdn anh hudng ciia trudng vd va trudng tren tdng cao hon phdn nam ngoai viing anh hudng ctia EEJ dugc xdp XI bang cac da thirc cd bac cao tuy y dl ed thi xdp xi td't dudng cong thu dugc, cdn phdn trudng trong vung anh hudng cua EEJ, theo kinh nghiem trong qua trinh xii ly sd lieu, chiing tdi sir dung da thuc bac thdp hon. Vi du tren hinh 1, vifc sii dung da thirc bac thdp vdi phdn anh hudng cila EEJ (vy do ±10°) se tach ra dugc trudng vd Trai Ddt (dudng manh net liln) mdt each lien tuc. Ngoai ra, dl dp dung dugc thuat toan tren, chiing ta phai xdc djnh dugc bl rdng cila EEJ se thu dugc tren quy dao cila ve tinh vd lua chgn bac cua da thirc dl xdp xi.
-.55
<
c
1 1
••.= 43< i m
""t"^.
f ~ 1
7 i
*
%-
Vy do dja tir Vy dp dia tir Vy do dja tir
u. „
<
0
r.' 3 5 ^ w , Lorvj; - ' •=
^
t> i.ii srr I Lonj: g 'E
I ""-r'"'" ; \
-40 .23 0 2.; «
Vy do dja tir Vy dp dja tir
' s = 4 : •
—
•<r. ! U r f ; : se "E
—<cp'-f\
100
c
j^^r:-'\Z KIT , Lo?.3: 15-0 • =
T-^VT/'- i
I \ \l. \
Vy dp dja tir
Tri/dng sau khi trir trudng chinh Xap xl bSng da thtfc
Phan anh hi/dng cCia EEJ Long : l<inh tuyen
h : dp cao quy dao Vy dp dja tir ' " Vy dp dja tir
Hinh 1. Tach phdn anh hudng ciia EEJ bdng cac da thirc a) Do rang anh hudng cua EEJ : do EEJ chay
trong dai hep +3° dgc theo xich dao ttr va qua qua trinh xii ly sd lieu chiing tdi nhan tha'y bl rdng anh hudng ciia EEJ tren dd eao cila ve tinh trong khoang vy dd tir -10° din 10°. Viec chgn dd rdng ciia EEJ tai dd cao eiia ve tinh la ±10° nay la td'i uu khi nd dam bao hdu nhu Idy hit dugc phdn "ldm" xud'ng trong trudng cdn lai vd thuan tien cho viec vie't chuong trinh xii ly sd lieu.
b) Bac cQa da thifc : bac cua da thiic diing dl xdp XI anh hudng din dd ldn cua EEJ, nen viec lira chgn bac da thiic tdi uu ciing rdt quan trgng trong qua trinh xii ly .so lieu. Viec lira chgn bac da thiie phu thudc nhilu vdo kinh nghiem tinh toan va hinh dang dudng cong sd lieu thu dugc. Thdng thudng, chung tdi sii dung da thirc bac khoang ttr 60 din 90 cho phdn nam ngoai anh hudng cua EEJ (vy dd dja tiir tiir -40° din -10° va ttr 10° din 40°) edn phdn nam trong vting anh hudng cila EEJ (vy dd dja ttr ttr -10° de'n 10°) chiing tdi sii dung da thiic bac trong khoang 6 - 1 0 cho mdi lat cdt. Cdng viec xii ly sd lieu mdt nhilu thdi gian hon ciia T.J. Sabaka thi nhung se chinh xac hon khi ta coi trudng vd Fc tai mdi vi tri khac nhau se cd hinh dang dudng cong khac nhau. Cung cdn ndi them, viec lira chgn
bdc cila da thiic phu thudc nhilu vao kinh nghiem xur ly .sd lieu, viec la'y da thiic bac cao qua cd thi lam suy giam tin hieu cdn tach va ngugc lai.
Tren hinh 1, ehimg tdi trinh bdy mdt vai vi du vl tach anh hudng cila EEJ cho sd lieu cac ngay 1, 2 thang 12 nam 2003 tai cac kinh tuye'n khac nhau bang thuat todn tren. Phdn trudng sau khi da loai bd trudng chinh (nhd md hinh IGRF bac 14, nien dai 2003.5) cdn lai khoang 120 nT dugc bilu diin bang dudng ddm net liln bao gdm trudng cua vd Trdi Ddt va trudng ngoai gay ra. Dudng liln net manh bilu diin trudng xdp xi bang da thiic cd bac ttr 6 de'n 10 va dudng net diit bilu diin phdn anh hudng ciia EEJ thu dugc.
4. Bien dp cua EEJ cho nSm 2003
Tren hinh 2, bilu diin gia trj bien dd trung binh (Id'y gia trj tuyet ddi) cila EEJ thu dugc cho ca nam 2003 ttr ve tinh CHAMP, bao gdm 158 ngay trudng ttr yen tTnh va 1.345 ldn ve tinh CHAMP cdt qua xich d^o tai cac kinh tuyln khac nhau, lira chgn thdi dilm giiia trua ttr 10 gid 00 de'n 14 gid 00 (gid dja phuang). Chung ta nhan thdy bien dd ciia EEJ ndm trong khoang ttr 12 nT din 67 nT va tai viing kinh tuye'n 100° (Viet Nam) cd mdt cue tri kha ldn
40
20
-20
-40
Kfc"
.
^JSItL i
.iJm^^^^^
\
k
^
. ^ ^ M |
^ ^ ^ ^ ^ ri^w^^^^^^^^^K^
Xich dao
'^WMWf.'iifW,:'' •iW. •
4-
WmOmai
-180 -140 100 -60 -20 20
Kinh tuyen
60 100 140 180
1
10 20 30 40 50
Hinh 2. Bien dd ciia EEJ tinh theo sd lieu nam 2003
60 nT
(dat 67 nT) so vdi cac kinh tuyln khac. Chu y tren hinh ve cung cd nhiing khu vuc khdng cd sd lieu, cd nghTa trong khoang thdi gian nay, ve tinh CHAMP khdng bay qua cac kinh tuyln nay vao giira trua dja phuang. Vdi gia trj cue dai cila EEJ nam khd triing vdi dudng tam xich dao ttr va bien dd cda EEJ giam ddn vl hai phia ciia vy tuyln nen viec lira chgn dd rdng anh hudng ciia EEJ tren quy dao ciia ve tinh CHAMP Id +10° la phu hgp.
III. MO HINH EEJ VA AP DUNG CHO SO LIEU CHAMP
/. PhSn bd'mit dp dong EEJ
Nhu chiing ta da bie't, cudng dd ddng dien xich dao quan sat tai mdt dilm bdt ky se phu thudc vao kinh dd, vy dd vd thdi gian (thdi gian dja phuong).
Khi ta coi EEJ nhu mdt dai ddng mdng tdn tai d dd cao cd djnh (cao 105 km so vdi mat ddt) va theo khai tril'n cua O. Fambitakoye va P.N. Mayaud [8[
khi ta coi EEJ nhu mdt dai ddng ddng nha't, sir biln thien ciia mat dd ddng I(x) ciia EEJ phu thudc vao vy dd {X) lien he vdi mat dd ddng Io tai tam cila EEJ bilu diin nhu sau :
/(x) = /o(A) 1 {x-cy a^
(2) vdi X - khoang each ttr tam EEJ de'n dilm quan sat X va dugc xae djnh trong khoang c-a<x<c + a, a - 1/2 bl rdng cila EEJ, c - vj tri cua tdm EEJ.
Su phu thudc ciia thanh phdn trudng nam ngang (AH) tao bdi EEJ vao gid dja phuang dugc md ta qua ham phdn bd Gaussian nhu sau :
G{t) = exp (r-7-)2
(3)
vdi T - gid dja phuong khi thanh phdn trudng nam ngang (AH) gay ra bdi EEJ dat gid tri cue dai (thudng chgn T = 12h00), tm - tham sd hieu chinh cila ham phan bd Gauss, phu thude vao sir biln thien cua thdnh phdn nam ngang AH va thanh phdn thing dirng AZ, dugc xdc dinh bdng thue nghiem, thdng thudng chgn tm = 4h.
Theo dd, su biln thien ciia mat dd ddng tai vj tri X bdt ky khi mat dd ddng tai tam ciia EEJ la Io(t) nhu sau :
/(,(;) = / , 2 e x p (t-T) 2\
(4)
vdi li2 - gia trj giira trua dia phuang cila Io(t), nd phu thudc vao gia tri thanh phdn ndm ngang cua trudng tir (AH^) gay ra bdi EEJ nhu sau :
/ , 2 = A//„
0,4a;Trg -
(5)
h = 105 km - dd cao ciia EEJ. Khi dd ta cd phan bd cila mat dd ddng dien EEJ phu thudc vao kinh dd, vy dd vd thdi gian (dja phuang) nhu sau :
l{t,x,A) = lo{A)\\ ( A - - C ) 2
.exp
{t-T)^]
(6) vdi t = tu + {X/\5) , tu - gid qud'e tl, X - kinh tuyln nam trong khoang -180°< X <180°.
Ttr cdng thirc (5), ta hoan toan tinh 112 lien quan de'n sir bie'n ddi thanh phdn ndm ngang AHo, vdi sd lieu ve tinh CHAMP ta cd thi thay AH,, bdng phdn trudng anh hudng ciia EEJ tdch ra tir sd lieu trudng tdng (AF). Sau dd, ttr (6) cho phep tinh dugc mat dd ddng cila EEJ phu thudc vao thdi gian dja phuong, kinh dd va vy dd. Kit qua tinh mat dd ddng cila EEJ cho sd lieu ndm 2003 tren toan cdu dugc bilu diin tren hinh 3, vdi cudng dd manh nhdt tai tam ciia EEJ dat khoang 200 A/km va nd cung phu thudc vao kinh dd, vy dd, thdi gian (dia phuang) T.
2. Tinh cac thanh phin ciia trudng tir giy boi EEJ
Theo cdng thirc khai tril'n bdi O. Fambitakoye (1976), ttr cac tham sd c, a, T, \^, \o{X), I(t, x, X) ta cd thi tinh thanh phdn cua trudng ndm ngang (AH), thanh phdn thdng dirng (AZ) gay ra bdi ddng EEJ tai vj tri xs bdt ky nhu sau :
-180 -150 -120 -30 0 30
Kinh tuye'n
60 90 120 150 180
50 100 A/km 150 Hinh 3. Mat dd ddng dien cila EEJ tinh ttr CHAMP
200
AH = 0 , 2 ^ [(a2 - X2 )2 + (2a2 - 6X2)/i2 + /i4 ](arcfg7?B - arcrgT?^) + a'^
+ 0,2^[2(a2-X2)X,/i + 2X,/,3][ln(l + /?2)-ln(l + / ? 2 ) ] + 0 , 2 ^ ^ ( / ? 3 - 7 ? 3 ) . -0,4-^X,7r3(/?2-7?2)_o,2^[(2a2-6X2)/i2+/,4](^^+^j
(7)
AZ = - 0 , l - ^ [ ( a 2 - X 2 ) 2 - H ( 2 a 2 - 6 X 2 ) / l 2 - | - / ; 4 ] [ l n ( l - h / ? 2 ) _ l n ( i + ; j 2 ) l ^
a''
+ 0 , 8 ^ [(a2 - X2 )X,/i - X,/r3 ](a,rrg/;^ - arcrg/f J - 0,1 ^ ^ (7?^ - 7?^) + a^ • a* 2
+ 0 , 8 ^ ^ X , ( 7 ? 3 -/?3) + 0,l^[(2a2 -6X,2)/,2 -^/,4](/?2 - / ? 2 ) _ a4 3 a4
- 0 , 8 ^ X, [(^2 - X} )h + /r3 ]{R^ - R^ )
(8)
vdi c - vj tri ciia tam EEJ, h - dd cao cila EEJ tinh Cac kit qua tinh toan md hinh ly thuylt cac bang km, lo tinh bdng A/m, AH va AZ tinh bang thanh phdn trudng ttr do EEJ gay ra dua vdo cdng nT.
Xi; = XS -C
/?.
7?« Xs+a
(9)
thirc (7) vd (8) dugc bieu dien tren hinh 4. Tren hinh nay bilu diin cac thanh phdn cila trudng tir gay ra bdi EEJ tren todn cdu tai cac thdi gian khac nhau vdi dd cao trung binh cua ve tinh la 400 km so vdi mat ddt. Gia trj dat cue dai cila thdnh phdn AH khoang 70 nT (Idy tri tuyet ddi), bien dO cue dai cila AZ vao khoang 40 nT, dudng ddng miic cho cac hinh ve la 10 nT.
Kinh tuyen
:^
?' Zf
• ^ f x
'^
Kinh tuye'n
Hinh 4a, b. Thanh phdn ndm ngang AH (nT) va thanh phdn thang dirng AZ (nT) tai OhOO UT
.30 0 30
Kinh tuyen
Hinh 4c, d. Gia trj cac thanh phdn AH va AZ tai 12h00 UT
Tren hinh 5 biiu diin gia tri 2 thanh phdn AH do EEJ gay ra tren toan cdu tai ciing mdt thdi va AZ tai 12 gid 00 (gid dja phuang) cho tdt ca cdc dilm. Tren hinh ve nay, chung ta nhan thdy ca AH kinh tuyln khac nhau. Nd cho phep chiing ta cd cai vd AZ ed mdt cue trj tai kinh tuyln 100° va cd mdt nhin tdng thi vl phan bd cila ttrng thanh phdn trudng cue tilu tai kinh tuyln 50°.
AH (nT)
g -
-30 0 30
Kinh tuyen AZ (nT)
BO 90 120 550 leo
-180 -150 -120 -90 -60 -30 0 3 )
Kinh tuyen 60 90 120 150 1H3
Hinh J. AH va AZ Tai 12h LT
3. So sanh kei qua tinh md hinh va sd'lieu thu duac tu CHAMP
Tren hinh 6, bilu diin viec so sanh giiia EEJ thu dugc ttr md hinh va EEJ tinh ttr sd lieu ve tinh CHAMP cho nam 2003 tai cac viing cd kinh tuyln khac nhau, vdi dudng net dirt la gia trj trudng do EEJ gay ra tinh dugc ttr md hinh, dudng net rdi la gia trj trudng tinh dugc ttr sd lieu CHAMP cho mdi lat cdt sd lieu.
Tren mdi hinh cdn duoc bilu diin cac tham sd khac
nhu : h Id gid tri dd cao ciia ve tinh. Long la kinh tuyln di qua. Chiing ta nhan thdy cdc dudng tinh ttr md hinh va dudng tinh ttr sd lieu ve tinh CHAMP la khd triing nhau. Chiing tdi da tie'n hanh tinh dd lech binh phuang trung binh (RMS) cho todn bd sd lieu nam 2003. Qua tinh toan nhan thdy gid tri RMS thudng nhd han 5 nT. Nhu vay viec dp dung mO hinh tren cho sd lieu ve tinh CHAMP la hoan toan cd thi chdp nhan dugc.
l!=4C4 Lis(ig;-16S*E
-iO -20 0 20 Vy dp dja tir
5
h=3.S kni 1 Lciig:-7 'E
-y-r~"
1 i
-20 0 20 Vy dp dja ti/
h=4li tm
1 \
Lciig:86 'E
/ \
-20 0 20 Vy dp dja tir
h=39. km ; Lc^g:-t•^6'E
V
; ; .^
Lotis:-11S'E
-40 -20 0 20 <0 -40 -20 0 20 40 Vy dp dia ttr Vy dp dja ttr
LokgiS'E h=-05.km 1 Lc65;66'E
i " ^ ' \
\ i
-40 -20 0 20 40 Vy dp dja tir
h=3S: km
V—
Lcig;1£G'E
;
-20 _ C 20
Vy dp dja tir
EEJ tach tir CHAMP EEJ tir m o hinh
Long : kinh tuyen h : dp cao quy dao
-40 -20 0 20 Vy dp dja fir
Hinh 6. So sdnh EEJ thu duoc tir mO hinh vd tinh toan ttr sd lieu CHAMP
KET LUAN
Trong bdi bao nay, chiing tdi trinh bdy viec dp dung sd lieu trudng ttr thu dugc tren ve tinh d l nghien ciru v l EEJ vd da nghien ciru, dp dung phuang phdp mdi di tach phdn anh hudng ciia EEJ ttr sd lieu trudng tir thu dugc tren ve tinh CHAMP bang cac da thirc cd bac khac nhau. Sau dd dp dung phuang phap tren cho chudi sd lieu thu dugc bao gdm 1.345 lat cdt sd lieu vdi ngdy trudng ttr yen tTnh thu dugc ttr ve tinh CHAMP nam 2003. Ttr sd lieu bien dd ciia EEJ tinh dugc chimg tdi da xay dung md hinh EEJ cho toan cdu ciing nhu tinh todn cdc thanh phdn trudng ttr do EEJ gay ra tai mdt dilm
bdt ky. Qua eac budc tinh todn tren cd mOt sd kit luan nhu sau :
- Dd rdng (theo vy tuyln) anh hudng cila EEJ tai dd cao ve tinh CHAMP bay vao khoang ±10°
(tai mat ddt vdo khoang ±3°).
- Bien dd ciia trudng ttr gay bdi EEJ thu dugc tir ve tinh CHAMP biln ddi trong khoang tir 25 nT de'n 70 nT, tuy thudc cac kinh tuyln khac nhau. Tai kinh tuyln Viet Nam (kinh dd 100°) chiing ta nhan thdy cd 1 circ dai (dat 68 nT), ngudn gdc cila cue trj nay vdn chua bilt, nd cd thi do cdc hoat ddng dien ddng lire tren tdng dien ly, hodc do mat dd cila gid
trung hod, cung cd t h i do dd ddn cila vd Trai Dd't trong khu vuc ; chiing ta phai nghien ciru su xud't hien cila cdc cue tri nay theo thdi gian d l khdng djnh sir tdn tai ctia nd. Tai kinh tuye'n -60°, cd mdt cue tilu, vdi thanh phdn trudng ndm ngang tai tam EEJ khoang 40 n T
- Md hinh vl ddng dien xich dao phu thudc vao kinh dd, vy dd va thdi gian dja phuong bang mdt ban ddng d dd cao 105 km la kha phii hgp vdi .sd lieu quan sat tren ve tinh, cho chiing ta mdt buc tranh kha hoan chinh ve bien dd, quy luat phan bd, dd rdng anh hudng cua EEJ tren todn cdu, nhd dd chiing ta cd t h i cd nhu'ng nghien ciiu tie'p theo nhu bie'n thien theo thang, nam, mtia...
- Md hinh EEJ thu dugc, vdi dd lech binh phuang trung binh (RMS) nhd han 5 nTtinh cho toan bd cac kinh tuyln khac nhau cho chiing ta cd cai nhin tdng t h i v l phan bd hinh hgc cung nhu cdc tham .sd cila EEJ tren toan cdu.
- Viec nghien cim bie'n ddi ciia EEJ theo thdi gian va so sanh md hinh nay vdi cac md hinh sii dung sd lieu cila cae ve tinh khac ciing nhu tir sd lieu mat ddt se de cap trong cac nhien ciru sau nay.
Ldi cam an : cdc tie gia chan thanh cam an Ts Yves Cohen vd Ts Amory Mazaudier da cd nhiing y kie'n ddng gdp xac dang trong viec hoan thdnh bdi bdo. Bai bao dugc hodn thanh vdi phdn sd lieu ve tinh dugc cung edp bdi Vien Vat ly dia cdu Paris trong chuong trinh hgp tac giira Vien Vat ly dja cdu Ha Ndi, Vien Vat ly dja cdu Paris vd Trung tam nghien ciru mdi trudng Trai Ddt vd cac Hanh tinh - "Nghien cim Vat ly dja cdu trong md'i quan he Mat Trdi - Trai Ddt, nghien cim trudng ttr d Viet Nam" (PICS-3366).
TAJ UEU DAN
| 1 | CE. AGU, CA. ONWUMECHILI, 1981 : Comparision of the POGO satellite and ground measurement of the magnetic field of the equa- torial electrojet. J. Atmos. and Terr Phys, 43, 801-807.
[21 K.W. BEHANNON, N.F. NESS, 1966 : The design of numerical filters for geomagnetic data analysis, NASA Tech, note, D-3341.
[3] B.N. BHARGAVA, N.S. SASTRI, B.R.
ARORA and R. RAJARAM, 1980 : The afternoon counter-electrojet phenomenon, Ann. Geophys., 2,6,231-240.
[4] H. CHANDRA, H.S.S. SINHA, R.G. RASTOGI, 2000 : Equatorial electrojet studies from rocket and ground measurements. Earth Planets Space, 52, 111-120.
[5] S. CHAPMAN, 1951 : The equatorial electrojet as detected from the abnormal electric current distri- butions above Huancayo, Peru and elsewhere. Arch.
Meteorol. Geophys. Bioclimatol. A4, 368-390.
| 6 | V. DOUMOUYA, J. VASSAL Y COHEN, 0.
FAMBITAKYOYE, M. MENVIELLE, 1998 : Equatorial electrojet at african longitudes : first results from magnetic measurements, Ann. Geophysics, 16, 658-676.
171 V. DOUMOUYA, Y COHEN, 2003 : Local time and longitude dependence of the equatorial electrojet magnetic effects, J. Atmos. Sol. Terr.
Phys., 65,1265-1282.
| 8 | O. FAMBITAKOYE, P.N. MAYAUD, 1976 : The Equatorial Electrojet and Regular Daily Varia- tion SK : - I. A Determination of the Equatorial Electrojet Parameters, Joumal of Atmospheric and Terrestrial Physics, 38,1-17.
[9] TRUONG QUANG HAO, 1998 : Xac djnh mdt vai thdng sd cua ddng dien xich dao d Viet Nam. Tap chi Cac Khoa hgc v l Trai Ddt, 7,12-19.
jlOl TRUONG QUANG HAO, LE HUY MINH, 1987 : Mdt sd dac dilm ciia trudng dja ttr biln thien d Viet Nam, Tap chi Cac khoa hoc vl Trai Ddt. T.
9 , 1 , 7 - 7 5 .
1111 LE HUY MINH, 1998 : Biln thien ttr tai Viet Nam va ddng dien ngugc xich dao. Tap chi Cac khoa hgc v l Trai Da't, T. 20, 3,189-199.
[121 A. PATRIC, M. STEFAN, 2002 : Spatio- temporal characterization of the equatorial electrojet from CHAMP, Orsted and SAC-C satellite magnetic measurements. Geophys. J. Int., 112,1-10.
[131 G.K. RANGARAJAN, 1973 : Indices of Geomagnetic Activity. In Geomagnetism, Volume 3 Edited by J.A. Jacobs.
[141 A.D. RICHMOND, 1973 : Equatorial electro- jet-I. Development of a model including winds and electric field. Joumal of Atmospheric and Terrestrial Physics 35, . / 0 S i - 7 ; 0 i .
115] T.J. SABAKA, N. OLSEN and R.A. LANGEL 2002 : A comprehensive model of the quite-time
near Earth magnetic field: phase 3, Geophys. J.
Int., 32-68.
1161 R.J. STENING, 1985 : Modeling the equatorial electrojet. Journal of Geophysical Research, 90, 1705-1719.
1171 N G U Y I N THI KIM THOA, NGUYEN VAN GIANG va nnk, 1990 : Dac trung biln thien cila trudng dja ttr dudi anh hudng cila vdng dien xich dao quan sat dugc tren lanh thd Viet Nam, Tap chi a c Khoa hgc v l Trai Ddt, T 12, 2, 33-42.
[181 B.T. VIKRAMKUMAR, K.S. VISWANATHAN and P.B. RAO, 1984 : VHF backscatter radar obser- vations of the equatorial electrojet irregularities, Ann. Geophys., 2, 295-310.
1191 M. YANAGISAWA and M. KONG, 1985 : Mean ionospheric field correction for Magsat data, J. Geophys. Res., 90., B3, 2527-2536.
SUMMARY
The equatorial electrojet model with CHAMP satellite data
The EEJ (Equatorial Electrojet) is a complex current system flov\/ing 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...). Many 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 regularly 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 CHAMP 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.
Ngciy nhdn bdi: 16-10-2009
Vien Vdt ly dia cdu