william j. burke boston college: institute for scientific research and air force research...

William J. BurkeBoston College: Institute for Scientific Research

and Air Force Research Laboratory: Space Vehicles Directorate

Electrodynamics of the Equatorial Ionosphere: Messages from the C/NOFS

Satellite

C/NOFS DMSP

C/NOFS Satellite Mission Outline

• Background: (a) Scintillations: A perennial issue(b) Generalized Rayleigh-Taylor instability

(c) Desert Storm: January 1991

(d) Three-pronged approach: SCINDA - C/NOFS - PBMOD

• The Long Wait: 1995 - 2008(a) DMSP as a C/NOFS surrogate

(b) Season-longitude climatology of equatorial plasma bubbles

(c) Stormtime equatorial ionosphere

• Post-C/NOFS launch; April 17, 2008(a) The strange world of deep solar minimum

(b) Season-longitude climatology of deep dawn sector depletions

(c) Revelatory comparison with SCINDA measurements

2

C/NOFS Satellite Mission UHF – L Band Scintillations

Fresnel length = 2 dFor 250 MHz signals with

d = 300 km (altitude of F-layer peak in solar minimum)

Fresnel length is ~ 850 m4S = S

S





• The Long Wait: 1995 - 2008 (a) DMSP as a C/NOFS surrogate



• Post-C/NOFS launch: April 17, 2008(a) The strange world of deep solar minimum



4

C/NOFS Satellite Mission Equatorial Electrodynamics

R-T growth rates are controlled by the variability of E, Un, ΣE, ΣF, veff, and through the flux-tube integrated quantities by the height of the F layer.

0tA A eExponential Growth

GrowthRate

Conductance

Electric Field

Magnetic Field

Log DensityGradient

NeutralWind

Gravity

2

1Fn eff

F E

g NU

B N h

E B

Generalized Rayleigh-Taylor Instability

Linear Stage

Nonlinear Stage


• Background: (a) Scintillations: A perennial issue(b) The generalized Rayleigh-Taylor instability


(d) Three-pronged response: SCINDA - C/NOFS - PBMOD


(b) Season-longitude climatology of equatorial plasma bubble

(c) Comparison with JULIA radar measurements

(d) Stormtime equatorial ionosphere

• Post-C/NOFS launch; April 17, 2008(a) The strange new world of deep solar minimum


(c) Revelatory comparison with SCINDA measurements6

C/NOFS Satellite Mission Desert Storm Experience

• During the lead up to Desert Storm counter offensive radio links between commanders and DOD personnel in theater and the US failed.

• GPS receivers given to front-line soldiers were useless.

• C/NOFS program designed in response to nav / com breakdowns caused by the disturbed ionosphere

• In preparation for the C/NOFS mission we exploited database of equatorial plasma bubble (EPB) encountered by DMSP satellites in the evening local time sector.

Strait of Hormuz

Saudi Arabia











8

C/NOFS Satellite Mission Approach

Mission Response: Ground- and Space-based Measurements

SCINDA = Scintillation Network

Decision Aid

SEVERE MODERATE WEAK

Term

inator

SatelliteLinks

C/NOFS

- Planar Langmuir Probe (PLP)- Vector Electric Field Instrument- Ion Velocity Meter (IVM)- Neutral Wind Meter- GPS Occultation Receiver- RF Radio Beacon

• Pegasus launch • 13 inclination • 850 by 400 km

C/NOFS Satellite Mission Approach

• PBMod snapshots of plasma density by altitude and longitude at five local times in the equatorial plane

• C/NOFS encounters EPBs at all stages of development

• Explains enhanced density C/NOFS observes when flying above rising depletions

Simulated Birth and Growth of Equatorial Plasma Bubbles











11

C/NOFS Satellite MissionThe DMSP Surrogate

12

DMSP Observations of EPBs 1989 - 2006

M-0

M-1

M-2

M-3

South EQ North

EPBs observed by DMSP M - 0 if N 2

M - 1 if 2 < N 10 M - 2 if 10 < N 100 M - 3 if N > 100

Year Spacecraft LT (Hr) Orbits EPBs M-0 M-1 M-2 M-31989 F09 21 5121 1109 297 762 50 0

1990 F09 20.9 5091 1089 289 735 62 3

1991 F09 20.7 5040 1024 304 664 55 1

1991 F10 20 4925 675 218 351 86 20

1992 F10 20.7 5043 755 306 406 41 2

1993 F10 21.3 5092 389 186 191 11 1

1994 F10 21.7 3749 121 53 58 10 0

1994 F12 21.4 1575 42 33 8 1 0

1995 F12 21.4 4976 130 51 71 8 0

1996 F12 21.5 5122 73 35 36 2 0

1997 F12 21.4 3343 47 24 23 0 0

1997 F14 20.6 3104 51 18 32 1 0

1998 F12 21.2 4123 283 106 169 7 11998 F14 20.7 4993 275 129 138 8 0

1999 F12 20.8 4290 431 83 330 13 5

1999 F14 20.8 4839 460 167 285 6 2

2000 F12 20.3 4556 637 85 509 41 2

2000 F14 20.7 4969 821 298 493 26 4

2000 F15 21.3 5060 1034 377 620 30 7

2001 F12 19.8 4557 404 60 305 34 5

2001 F14 20.6 4787 861 174 643 38 6

2001 F15 21.5 5095 1014 292 699 20 3

2002 F14 20.3 4889 781 160 563 55 3

2002 F15 21.5 5113 991 279 672 40 0

2003 F14 19.9 4732 156 37 108 5 6

2003 F15 21.4 5149 385 84 275 15 11

2004 F14 19.6 4777 30 10 14 6 0

2004 F15 21.3 5123 267 63 180 14 10

2004 F16 19.9 5131 77 18 51 7 1

2005 F15 20.8 5139 140 56 68 13 3

2005 F16 20.2 5143 64 27 32 5 0

2006 F15 20.3 5130 51 26 25 0 0

2006 F16 20.2 5122 35 21 13 1 0

Totals 154898 14702 4366 9529 711 96











13

C/NOFS Satellite Mission Season – Longitude Expectation

Terminator alignment with magnetic field in mid-Atlantic

Equinox Winter Solstice

Season-Longitude Variability of Equatorial Plasma Bubbles

2

1Fn eff

F E

g NU

B N h

E B

EPB Occurrence Rates 1989 – 1992 Solar Maximum

During 1989 – 1992 solar maximum, EPBs occurred throughout the year in the Atlantic-Africa sector; rates highest from September to December.

C/NOFS Satellite Mission Season – Longitude Distribution

Pacific America Atlantic Africa India Pacific

LongitudeSAA

{

EPB Occurrence Rates 1999 – 2002 Solar Maximum


LongitudeSAA

{

In 1999 – 2002 solar maximum, EPB occurrence rates are fairly symmetric; high in the America-Atlantic-Africa sector both early and late in the year.


EPB Occurrence Rates 1994 – 1997 Solar Minimum


LongitudeSAA {

During 1994 – 1997 solar minimum, EPB occurrence rates were ~ 5% most of the time.

Highest rates were recorded in the America-Atlantic-Africa sector January to March.


EPB Occurrence Rates 1993 Transition Year


LongitudeSAA

{

During 1993 transition year, EPB occurrence rates were highest in the Atlantic-Africa sector early in the year, January to April.




LongitudeSAA

{

During 1998 transition year, EPB occurrence rates are higher in the America-Atlantic-Africa sector late in the year, September to November.




LongitudeSAA

{

During 2003 transition year, EPB occurrence rates are higher in the America-Atlantic-Africa sector late in the year, September to December.












21

C/NOFS Satellite Mission Stormtime Equatorial Ionosphere

• Vertical lines superposed onto the Dst trace indicate times when DMSP F9 crossed plasma bubbles near magnetic equator - 21:00 LT• CRRES detected dawn-to-dusk E fields earthward of ring current ions at times of all stormtime EPBs [Wygant et al. JGR, 103, 29,527, 1998].• Regular EBP pattern took ~4 days to re-emerge after recovery began.

With solar EUV power ~ 500 GW, why did it take four days to restore pre-storm quiet time EPB rate?











23

C/NOFS Satellite Mission Evening Sector Depletions

This solar min: Nothing yet!

DMSP evening sector EPB climatology

for solar max confirmed Tsunoda’s

[1985] model

Most EPBs were observed

in Atlantic-Africa sector

and when terminator

aligned with magnetic field

Previous solar min: Sparse but consistent


20 January 2010 Orbit 9559 11:45:29 UTC/NOFS PLP: 20 January 2010 Orbit 9558 10:08:35 UT

Orbit 9558: PLP observed wide depletion ~ 10:50 UT at ~240° E, 400 km altOrbit 9559: Narrow, deep depletion at observed ~12:30 UT at ~240° E, 450 km alt

• Between 12 and 19 June 2008 a high-speed stream (HSS) in the solar wind passed Earth

• Interplanetary magnetic field (IMF) compressed and rotated in the corotating interaction region (CIR) at the HSS leading edge

• Excited indicated geomagnetic activity

0

10

20

30

40

200

300

400

500

600

700

800

162 164 166 168 170 172

Den

sity

(#/

cc) |V

SW

| (km

/s)-15

-10

-5

0

5

10

15

162 164 166 168 170 172

BY

-

BZ

(nT

)

0

200

400

600

800

1000

1200

162 164 166 168 170 172

AE

(nT

)

JD 08:

CIR HSS


10

100

1000

104

105

106

20:00 21:00 22:00 23:00 24:00

PLP: 14 June 2008

Ni (

# /

cc)

M

UT

M

PPRev. 878 Rev. 879

0

500

1000

1500

10

100

1000

104

105

106

166:20 166:22 167:00 167:02 167:04 167:06

AE

(n

T) N

i (#/cc)

JD:UT

878 879 880 881 882 883

• PLP measured responses during (Orbit 878) and after (Orbit 879) the CIR excited AE disturbance.

• As time passed, 100 km (EPB) scale structures coalesced into a single large > 1000 km depletion.

• Larger structure co-rotated to dawn meridian and was lost to refilling.

• Not all dawn sector depletions have interplanetary sources but appear “spontaneously” probably due to mi (g × B) currents.

Equatorial Electrodynamics

20 January 2010 Orbit 9559 11:45:29 UTC/NOFS PLP: 20 January 2010 Orbit 9558 10:08:35 UT

Orbit 9558: PLP observed wide depletion ~ 10:50 UT at ~240° E, 400 km altOrbit 9559: Narrow, deep depletion observed ~12:30 UT at ~240° E, 450 km alt

C/NOFS Satellite Mission Dawn Sector Depletions

UTGLonGLatAlt

C/NOFS

F15 F17

UTGLonGLatAlt

UTGLonGLatAlt

Irregularities observed over 40° in latitude and 20°

in longitude

DMSP and C/NOFS: Latitudinal and Longitudinal Extent



DMSP F17 dawn sector EPB rates for 2008 near 5:30 MLT are dramatically different from any evening sector observations. Maximum rates (~ 70%) occur near the June solstice in the America-Atlantic sector. Rates are ~ 30% in the Pacific near the December solstice and < 10% when the dusk terminator aligns with the magnetic field. Dotted lines mark times the dawn terminator aligns with the magnetic field.

C/NOFS Satellite Mission

Power spectral densities and theoretical modeling suggest that density irregularities encountered by C/NOFS at topside altitudes

were conjugate to those responsible for the 250 MHz scintillations.

• During the night of 13 - 14 January 2010, S4 > 0.6 scintillation activity for

250 MHz signals was observed at three SCINDA sites

• Simultaneous measurements by the Planar Langmuir Probe (PLP) and

Ion Velocity Meter (IVM) on C/NOFS suggest that two types of density

irregularities exist at topside altitudes:

– Equatorial plasma bubbles (EPBs): upward drifting depletions

– Upward/downward drifting topside density enhancements / depletions

depletions that map to image depletions / enhancements on the bottomside.

• Consistent with the phase-screen approximation, power spectral densities

from PLP and VEFI data streams indicate significant power at Fresnel

scale.

- For 250 MHz carrier and hmF2 300 km, .

2λd 850SF m

C/NOFS Satellite Mission SCINDA - Satellite Comparison

Intermittent episodes of strong scintillation (S4 > 0.6) recorded at Sao Luis, Brazil, and Cape Verde from 22:00 UT on 13 January

through 04:00 UT on 14 January 2010.

Latitude = 2.6º S

Longitude = 315.8º E

0

0.5

1

1.5

Cape Verde

13 - 14 January 2010

0

0.5

1

1.5

San Luis

0

0.5

1

1.5

20 22 24 26 28 30

Ancon

UT

9462

9464

9466 Latitude = 11.8º S


Latitude = 16.7º N


Ancon

S4:

250

MH

z

Sao Luis Brazil

Cape Verde

Google

Google


Darkness

OrbitMag. Equator

0

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

4 105

-150

-100

-50

0

50

100

150

23.2 23.22 23.23 23.25 23.27 23.28 23.3

13 January 2010 23:12 - 23:18 UT

IonDensity (cm^-3) Vz (km/s)

Ion

Den

sity

(cm

-3)

VZ (km

/s)

23:12 23:13 23:14 23:15 23:16 23:17 23:18

• IVM crossed a sequence of upward drifting density depletions with embedded small scale irregularities

• C/NOFS crossed equatorial plasma bubbles at topside altitudes.

• VEFI data indicate return of PRE.

13 January 2010 Orbit 9462 23:05:05 UT

PLP detected density irregularities near perigee while skimming close to the magnetic equator

Fresnel Scale


Spectral intensity is high at the Fresnel scale (~850 m) inside all depletions.

Densities1 s Resolution

Power at Fresnel scale

Density Variations

Power Spectral Density

13 January 2010 23:10:54 UT

VEFI measurements of low frequency AC fields (top) compared with FFT of 512 Hz PLP data

0200 0230 0300 UT

10.

1.0

0.110.

1.0

0.1

Fre

q. H

zF

req.

Hz

B3AC

E34Fresnel Scale

.75 km

7.50 km

75 km.75 km

7.50 km

75 km

Comparison of VEFI and PLP Observations14 January 2010 Orbit 9464



VEFI measures quasi DC E-fields 1024 s-1 that are reported 16 s-1. - Low pass AC fields < 6 Hz. - High pass AC fields 3 to 8,000 Hz (burst data) - Fresnel scale of 850 m corresponds to a frequency of ~ 8 Hz.

FsFsFs

Both plasma densities and AC electric fields showsignificant power at and near the Fresnel scale.

13 January 2010 23:11:51 UT

IVM measurements indicate local depletions moving

downward with respect to plasma on adjacent flux tubes.

0

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

-100

-50

0

50

100

2.54 2.56 2.58 2.6 2.62 2.64

14 January 2010 02:32 - 02:39 UT

Ion Density (cm^-3) Vz (km/s)

Ion

Den

sity

(cm

-3)

VZ (km

/s)

02:32:24 02:33:36 02:34:48 02:36 02:37:12 02:38:24

14 January 2010 Orbit 9464 02:18:56 UT

Altitude

Density

Darkness

OrbitMag. Equator

C/NOFS perigee north of the magnetic equator

PLP and IVM Measurements

C/NOFS Satellite MissionSCINDA-Satellite Comparison


Densities 1 s Resolution

Fresnel Scale Power

Density Variations


14 January 2010 02:35:48 UT

Spectral intensity at Fresnel scale was high inside depleted flux tubes but decreased sharply as C/NOFS crossed eastern walls.


Darkness

14 January 2010 Orbit 9466 05:32:46 UTAltitude

Density

Orbit

Mag. Equator

• IVM data indicate local density enhancements moving upward with respect to plasma in nearby flux tubes.

• Scintillations at Ancon relatively weak, S4 0.4 AT 05:48 UT.

0

5 104

1 105

1.5 105

-120

-80

-40

0

40

80

120

5.7 5.75 5.8 5.85 5.9 5.95

14 January 2010 05:42 - 5:57 UT

Ni(cm^-3)

Vz

Ion

Den

sity

(cm

-3)

VZ (km

/s)

5:42 5:45 5:48 5:51 5:54 5:57

C/NOFS near perigee, north of the magnetic equator

PLP and IVM Measurements


Spectral intensity at Fresnel scale relatively high within upward moving density enhancement.

Densities:1 s Resolution

Fresnel Scale Power

Density Variations


0

100

200

300

400

500

600

-20 -15 -10 -5 0 5 10 15 20

Alt

itu

de

(km

)

Magnetic Latitude

Map to +/- 7o at F layer peak

(~300 km)

Irregularities C/NOFS observes at magnetic equator at perigee (400 km)

Modeling Considerations

Consider magnetic field as an Earth-centered dipole

Irregularities C/NOFS observes at the magnetic equator near perigee map to +/- 7° at the peak of the F layer (~ 300 km in solar minimum).


Density (cm-3)

Alt

itud

e (k

m)

e- H+O+ Mol+

B

V

E

Unperturbed Bottomside

Perturbed Bottomside

jg = ni M (g B)/B2

jg = ni M (g B)/B2

VA

magnetic equator

B0

B0


Transmission Line Modeling Considerations

C/NOFS Satellite Mission Tentative Conclusions

• Haerendel (1972) argued that the R-T instability responsible for spread F and EPBs involves whole flux tubes rather than just local plasma irregularities.

- Since the seeding irregularities are probably confined in space, we need to ask: How information propagates to tell topside plasma that the bottom irregularities want to change their initially unstable equilibrium configuration? - Alfvén waves are required to transmit energy to topside plasma and maintain field lines near equipotential values (E ≈ E) in regions remote from R-T growth.

• A subset of C/NOFS data are consistent with purely topside irregularities, (i.e. not EPBs) created via polarization E-fields that map to the topside.

- Consistent with Alfvén hypothesis, VEFI detected both E and B perturbations. - Further investigation needed to ascertain role of B and the relationship between E/ B and VA = B0/(0 ρ)½

• If correct, then satellites flying in low-inclination orbits in the lower reaches of the topside ionosphere can remotely sense the presence of scintillation- causing irregularities at conjugate bottomside altitudes through measurements of n, E and/or B irregularity spectra.

william j. burke boston college: institute for scientific research and air force research...

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