William J. Burke Boston 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: (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 For 250 MHz signals with d = 300 km (altitude of F-layer peak in solar minimum) Fresnel length is ~ 850 m

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: (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 4

C/NOFS Satellite Mission Equatorial Electrodynamics R-T growth rates are controlled by the variability of E, U n, Σ E, Σ F, v eff, and through the flux-tube integrated quantities by the height of the F layer. Exponential Growth Growth Rate Conductance Electric Field Magnetic Field Log Density Gradient Neutral Wind Gravity Generalized Rayleigh-Taylor Instability Linear Stage Nonlinear Stage

C/NOFS Satellite Mission Outline Background: (a) Scintillations: A perennial issue (b) The generalized Rayleigh-Taylor instability (c) Desert Storm: January 1991 (d) Three-pronged response: SCINDA - C/NOFS - PBMOD The Long Wait: (a) DMSP as a C/NOFS surrogate (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 (b) Season-longitude climatology of deep dawn sector depletions (c) Revelatory comparison with SCINDA measurements 6

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

C/NOFS Satellite Mission Outline Background: (a) Scintillations: A perennial issue (b) The generalized Rayleigh-Taylor instability (c) Desert Storm: January 1991 (d) Three-pronged approach: SCINDA - C/NOFS - PBMOD The Long Wait: (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 8

C/NOFS Satellite Mission Approach Mission Response: Ground- and Space-based Measurements SCINDA = Scintillation Network Decision Aid SEVEREMODERATEWEAK Terminator Satellite Links 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

C/NOFS Satellite Mission Outline Background: (a) Scintillations: A perennial issue (b) The generalized Rayleigh-Taylor instability (c) Desert Storm: January 1991 (d) Three-pronged approach: SCINDA - C/NOFS - PBMOD The Long Wait: (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 11

C/NOFS Satellite Mission The DMSP Surrogate 12 DMSP Observations of EPBs M-0 M-1 M-2 M-3 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

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: (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 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

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 PacificAmericaAtlantic Africa IndiaPacific Longitude SAA {

EPB Occurrence Rates 1999 – 2002 Solar Maximum PacificAmericaAtlanticAfricaIndiaPacific Longitude SAA { 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. C/NOFS Satellite Mission Season – Longitude Distribution

EPB Occurrence Rates 1994 – 1997 Solar Minimum PacificAmericaAtlantic Africa IndiaPacific Longitude SAA { 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. C/NOFS Satellite Mission Season – Longitude Distribution

EPB Occurrence Rates 1993 Transition Year PacificAmericaAtlanticAfricaIndiaPacific Longitude SAA { During 1993 transition year, EPB occurrence rates were highest in the Atlantic-Africa sector early in the year, January to April. C/NOFS Satellite Mission Season – Longitude Distribution

EPB Occurrence Rates 1998 Transition Year PacificAmericaAtlantic Africa IndiaPacific Longitude SAA { During 1998 transition year, EPB occurrence rates are higher in the America-Atlantic-Africa sector late in the year, September to November. C/NOFS Satellite Mission Season – Longitude Distribution

EPB Occurrence Rates 2003 Transition Year PacificAmericaAtlanticAfricaIndiaPacific Longitude SAA { During 2003 transition year, EPB occurrence rates are higher in the America-Atlantic-Africa sector late in the year, September to December. C/NOFS Satellite Mission Season – Longitude Distribution

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: (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 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?

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: (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 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

C/NOFS Satellite Mission Equatorial Electrodynamics 20 January 2010 Orbit :45:29 UTC/NOFS PLP: 20 January 2010 Orbit :08:35 UT Orbit 9558: PLP observed wide depletion ~ 10:50 UT at ~240° E, 400 km alt Orbit 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 CIR HSS C/NOFS Satellite Mission Equatorial Electrodynamics

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 m i (g × B) currents. Equatorial Electrodynamics

C/NOFS Satellite Mission Outline Background: (a) Scintillations: A perennial issue (b) The generalized Rayleigh-Taylor instability (c) Desert Storm: January 1991 (d) Three-pronged response: SCINDA - C/NOFS - PBMOD The Long Wait: (a) DMSP as a C/NOFS surrogate (b) Season-longitude climatology of equatorial plasma bubbles (c) Comparison with JULIA radar measurements (d) 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 28

20 January 2010 Orbit :45:29 UTC/NOFS PLP: 20 January 2010 Orbit :08:35 UT Orbit 9558: PLP observed wide depletion ~ 10:50 UT at ~240° E, 400 km alt Orbit 9559: Narrow, deep depletion observed ~12:30 UT at ~240° E, 450 km alt C/NOFS Satellite Mission Dawn Sector Depletions

UT GLon GLat Alt C/NOFS F15 F17 UT GLon GLat Alt UT GLon GLat Alt Irregularities observed over 40° in latitude and 20° in longitude DMSP and C/NOFS: Latitudinal and Longitudinal Extent C/NOFS Satellite Mission Dawn Sector Depletions

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 Outline Background: (a) Scintillations: A perennial issue (b) The generalized Rayleigh-Taylor instability (c) Desert Storm: January 1991 (d) Three-pronged response: SCINDA - C/NOFS - PBMOD The Long Wait: (a) DMSP as a C/NOFS surrogate (b) Season-longitude climatology of equatorial plasma bubbles (c) Comparison with JULIA radar measurements (d) 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 32

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 January 2010, S 4 > 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 h m F 2  300 km,.

C/NOFS Satellite Mission SCINDA - Satellite Comparison Intermittent episodes of strong scintillation (S 4 > 0.6) recorded at Sao Luis, Brazil, and Cape Verde from 22:00 UT on 13 January through 04:00 UT on 14 January Latitude = 2.6º S Longitude = 315.8º E Latitude = 11.8º S Longitude = 282.9º E Latitude = 16.7º N Longitude = 337.1º E Ancon S4: 250 MHz Sao Luis Brazil Cape Verde Google

C/NOFS Satellite Mission SCINDA - Satellite Comparison Darkness Orbit Mag. Equator 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 :05:05 UT PLP detected density irregularities near perigee while skimming close to the magnetic equator Fresnel Scale

C/NOFS Satellite Mission SCINDA - Satellite Comparison Spectral intensity is high at the Fresnel scale (~850 m) inside all depletions. Densities 1 s Resolution Power at Fresnel scale Density Variations Power Spectral Density 13 January :10:54 UT

VEFI measurements of low frequency AC fields (top) compared with FFT of 512 Hz PLP data UT Freq. Hz B3AC E34 Fresnel Scale.75 km 7.50 km 75 km.75 km 7.50 km 75 km Comparison of VEFI and PLP Observations 14 January 2010 Orbit 9464 C/NOFS Satellite Mission SCINDA - Satellite Comparison

VEFI measures quasi DC E-fields 1024 s -1 that are reported 16 s 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. FsFs FsFs FsFs Both plasma densities and AC electric fields show significant power at and near the Fresnel scale. 13 January :11:51 UT

IVM measurements indicate local depletions moving downward with respect to plasma on adjacent flux tubes. 14 January 2010 Orbit :18:56 UT Altitude Density Darkness Orbit Mag. Equator C/NOFS perigee north of the magnetic equator PLP and IVM Measurements C/NOFS Satellite Mission SCINDA-Satellite Comparison

Equatorial Electrodynamics Densities 1 s Resolution Fresnel Scale Power Density Variations Power Spectral Density 14 January :35:48 UT Spectral intensity at Fresnel scale was high inside depleted flux tubes but decreased sharply as C/NOFS crossed eastern walls.

Equatorial Electrodynamics Darkness 14 January 2010 Orbit :32:46 UT Altitude 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, S 4  0.4 AT 05:48 UT. C/NOFS near perigee, north of the magnetic equator PLP and IVM Measurements

C/NOFS Satellite Mission SCINDA - Satellite Comparison Spectral intensity at Fresnel scale relatively high within upward moving density enhancement. Densities: 1 s Resolution Fresnel Scale Power Density Variations Power Spectral Density

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). C/NOFS Satellite Mission SCINDA - Satellite Comparison Density (cm -3 ) Altitude (km) e- H+ O+  Mol+

BB VV EE Unperturbed Bottomside Perturbed Bottomside j g = n i M (g  B)/B 2 VAVA magnetic equator B0B0 B0B0 C/NOFS Satellite Mission SCINDA - Satellite Comparison 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 V A = B 0 /(  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.