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

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.

STORM Time Empirical Ionospheric Correction Model

http://sec.noaa.gov/storm/

Gravity Waves

Composition Bulge

Electric Field

CTIM CTIM mean molecular mass NmF2 depletionmean molecular mass NmF2 depletion

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)

• 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

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)

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:

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

)

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)

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

CTIP (physics based model)

Trough: transport of the electron density by the high latitude convection E

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

VTEC ratio vs. time

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.