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On the Source of Steep TEC Gradients That Impact GPS
E.A. Araujo-Pradere1, T.J. Fuller-Rowell1,
M. Fedrizzi2, M.V. Codrescu1
1 CIRES-University of Colorado, NOAA-Space Environment Center2 Instituto Nacional de Pesquisas Espaciais, Brazil. Now a NRC Research Associate at NOAA-SEC
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SUMMARY
Steep ionospheric gradients:
• Spatial gradients
• Temporal gradients.
Some sources of ionospheric gradients (diverse, mixed and complex):
• Development of the neutral composition bulge
• Equatorial electrodynamics
• Trough and high latitude processes.
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STORM Time Empirical Ionospheric Correction Model
http://sec.noaa.gov/storm/
Gravity Waves
Composition Bulge
Electric Field
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CTIM CTIM mean molecular mass NmF2 depletionmean molecular mass NmF2 depletion
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mean molecular massmean molecular mass latitudinal structurelatitudinal structure
quiet conditions (kp = 2+)
40o
perturbed conditions (kp = 7)
40o
equatorsummer pole winter pole
solar driven circulation, quiet conditions (kp = 0)
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• NOAA CORS (good spatial resolution and geographic coverage)
• 21 storms with ap ≥ 200, 10 days period for each one, average of 250 receivers per storm
• Good seasonal coverage.
Data sources
191 receivers
137 receivers
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2000-07su
mm
er
13
14
15
16
17
18
12
00:00 UT 06:00 UT 12:00 UT 18:00 UT2000 – 07 (GAIM TEC)
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2000 – 07 (GAIM TEC)
ratios
quiet conditions
perturbed conditions
ratio
summer
Combination of downwelling and the
electrodynamics
Upwelling and equatorward
transport of the neutral composition
Possible interpretations:
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March 2001 – TEC vs. Lat.
-60-40-20
0204060
Bz
GS
M (
nT
)
March 30 - A pri l 3 2001
0
1000
2000
AE
(nT
)
U n iversa l T im e
0
3
6
9
Kp
-500-400-300-200-100
0100
SY
M-H
(nT
)
00 06 12 18 00 06 12 18 00 06 12 18 00 06 12 18 00 06 12 18 00 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70
G eographic Latitude (degrees)
0
40
80
120
160
200
TE
C (
TE
CU
)
03/15/2001 03/16/2001 03/31/2001 04/01/2001
Longitude 120 oE - 07:15 U T (15:15 LT)
TE
C (
TE
CU
)
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00:00 UT 06:00 UT 12:00 UT 18:00 UT
24
25
26
27
28
29
23
equ
ino
x1998 - 08
(GAIM TEC)
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quiet conditions
perturbed conditions
ratio
equinox
Combination of the electrodynamics and downwelling
Upwelling and equatorward transport of the neutral composition
Possible interpretations:
“Auroral” processes
1998 - 08 (GAIM TEC)
ratios
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CTIP (physics based model)
Trough: transport of the electron density by the high latitude convection E
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animation window
quiet reference
November 1997
0
1
2
3
4
5
6
7
8
9
10
0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00
Nov-97 (1997/ 11/ 18 - 1997/ 11/ 27)
Intermediate Equ.-Winter (322 - 331)
18 19 20 21 22 23 24 25 26 27
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VTEC ratio vs. time
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CONCLUSIONS
Steep ionospheric gradients can be spatial and temporal gradients. The sources of such gradients are diverse, mixed and complex, including, but not limited to, development of the neutral composition bulge, the equatorial electrodynamics, the trough and high latitude processes.