Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
B_edi & B_fgm comparisonusing Cluster 200308 data
Lukas Giner (TU‐Graz), Rumi Nakamura (IWF/OeAW)Edita Georgescu (MPS)Edita Georgescu (MPS)
Purpose: try to determine spin‐axis offset from EDI p y pEGD (electron gyrotime data)• Check the stability of the spin‐plane offset (preparation)• Determine spin‐axis offset from EGD assuming FGM spin‐plane offset is correct
Dependence of spin plane –offseton the hours from perigee
•Data set: 200308 data •Calibration: daily cal•Calibration: daily‐cal•X: spin axis, Y, Z: spin‐plane component
•Summary: spin‐plane offset is quite stable <0.1 nTfor the apogee data (low field region) .
•… this curve needs to be more seriously determined for low‐perigee orbit spacecraft like MMS.p g p
FGM spin plane offset evolution from perigeeFGM spin‐plane offset evolution from perigee
C1 C2Y C1 C2 C3
Off set in Y
in Y
OOff set
ZOff set in Z
Hous from perigee
O
Hous from perigee
B edi & B fgm comparisonB_edi & B_fgm comparison
•Data set: 200308 data •Calibration: daily‐calCalibration: daily cal•X: spin axis, Y, Z: spin‐plane component•High (22Hz, 67 Hz) resolution data used
B di f CAA EGD d tB_edi: from CAA EGD data Bx_edi: sqrt (B_edi2 ‐ By_fgm2 –Bz_fgm2)B fgm, Bx fgm, By fgm, Bz fgm: time‐matched data, i.e.B_fgm, Bx_fgm, By_fgm, Bz_fgm: time matched data, i.e.High‐res. data from the closest time of B_edi data.
20030810 20030812acos (Bx/B)
90
20080812
20030810 20030812 90
0 Bx fgm 30 200 Bx fgm 400
•Data 20030810: low field 20030812 hi h fi ld
Bx edi
0 Bx_fgm 30 ‐200 Bx_fgm 40020030812: high field
Bx_edi
0 Bx fgm 30 ‐200 Bx fgm 400
B_edi– B_fgm
0 Bx_fgm 30 200 Bx_fgm 400
B_edi‐B_fgmI diff t d di
0 B_fgm 600 0 B_fgm 600
Is different dependingOn EDI “range”,meaning EDI
Bx_edi– Bx_fgm
meaning EDI code repetition freq.
0 B_fgm 600 0 B_fgm 600
200308 offset Bedi‐Bfgm Bedi/Bfgm
Cluster 1Daily & monthlyaverageg
Using EDI “range”, ie.criteria given in Georgescuet al. paper (PG), daily average for the entire month &
thl
Bxedi‐Bfxgm Bxedi/Bfxgm
monthly average are calculated.
Problem: stdv. Too largeBecause we mix all the days andEDI operate not always as in PG criteria
200308 offset Cluster 2
• Daily & monthlyaverageg
200308 offset Cluster 3
• Daily & monthlyaverageg
20030810 quiet lobe condition (4~9 UT)
D t th bl ti d b f013148 013412
• Due to the problems mentioned before, we select a very quiet lobe day for calbration
20030810 quiet lobe period Cluster 3)<Bedi> = 81 99 stdV 0 13 <Bedi> = 38.83 stdV 0.070 <Bedi> = 38 79 stdV 0 048<Bedi> = 81.99 stdV 0.13
n 1020<Bdfm> = 81.85 stdV 0.12<Bedi‐ Bfgm> = 0 143
Bedi 38.83 stdV 0.070n 727
<Bfgm> = 38.73 stdV 0.082<Bedi ‐ Bfgm> = 0.102
<Bedi> = 38.79 stdV 0.048n 1078
<Bfgm> = 38.69 stdV 0.073<Bedi ‐ Bfgm> = 0.077<Bedi‐ Bfgm> = 0.143
FGM EDIt_edi
g <Bedi Bfgm> 0.077
1/22 s 0 5nT 0 5nT 0 2nT0.5nT82
0.5nT39
0.2nT39
1 s 1 s
001010 001312 080000 080712073224 074030001010 001312 080000 080712• StdV small enough to see clearly the difference (offset). In all three: comparison, i.e.
B:edi and closest –time FGM (top), 22Hz FGH (middle) and 1Hz averaged data (bottom).
Different calibration
CAA calFGM EDI G1 G2
daily cal daily cal + special calFGM EDI G1 G2t_edi
1/22 s 0.5nT
1 s 1 s
001010 001312
For this day, CAA cal. data, have smaller stdv than daily cal, but difference from B_EDI was largerthan for daily‐cal.
angle dependence acos(Bx/B) of offset 20030812 Cluster 1
acos(Bx/B) 90 acos(Bx/B) 50 acos(Bx/B) 20acos(Bx/B)=90<Bedi> = 302.47 stdV 1.06<Bedi> ‐ <Bfgm> = 1.63
FGM EDI
acos(Bx/B)= 50<Bedi> = 324.03 stdV 1.07<Bedi> ‐ <Bfgm> = 1.28
acos(Bx/B)= 20<Bedi> = 329.89 stdV 0.83<Bedi> ‐ <Bfgm> = 1.07
FGM EDIt_edi
1/22 s 2nT
1 s 1 s
005248 005512 013148 013412 015241 015454
Offset v.s. cos b(=Bx/B) for selected periods in 2003 08Try to limit EDI data in the same “range”:32<Bfgm=<61 nT, stdev =< 0.07 n T sigma_EGD =1.5 , t = 5 min n >= 350
ΔB
ΔBx1
ΔBx3
ΔΒ = <Bedi– Bfgm > cosb = <Bfgm_x /B>ΔBx1 = sqrt (ΔΒ2 −2 ΔΒ <Βfgm>+<Βfgm>2cosb 2 ) ‐ <Βfgm>cosbq ( g g ) gΔBx3 = <Bedi_x– Bfgm_x >
As in 20030812 example, offset &stdv varies wit cosb.But, the two lower figure suggest that for cosb > ~0.2, the offset is quite stable
Effect from EDI “range”, i.e. code repetition freqency change
EDI BEDI_BCRF
sigma
• EDI “range” change, ie. change in the code repetition frequency (CRF) or named ”sigma” parameter in the EDI‐CAA file, can happen during the same B value
• That is the stdv can change significantly due to this range change So it is only• That is, the stdv can change significantly due to this range change. So it is only meaningful to use EDI_B data set from the same CRF value.
Special calibrationd il l d il l i l
FGM EDI G1 G2
daily cal daily cal + special cal
FGM EDI G1 G2t_edi
1/22 s 0.5nT
1 s 1 s
001010 001312
• Offset can be better seen with the best FGM cal.