Regional ionospheric disturbances during magnetic storms. John Foster

Transcription

1 Regional ionospheric disturbances during magnetic storms John Foster

2 Regional Ionospheric Disturbances John Foster MIT Haystack Observatory

3 Regional Disturbances Meso-Scale (1000s km) Storm Enhanced Density (SED): Plumes of enhanced plasma stretching poleward from the mid-latitude ionosphere in the afternoon sector. Related to SAPS electric field. Mid-latitude TEC enhancement inside the PBL. Source population for SED plumes Equatorial low-lat lat plasma redistribution. Deep TEC depletions over SAA. Enhanced, spread equatorial anomaly peaks.

4 Storm Enhanced Density Ionospheric signature of the plasmasphere erosion plumes imaged from space. Serves as tracer of disturbance electric fields [ExB motion] Links mid to polar ionosphere and plasmasphere to magnetotail with enhanced fluxes of heavy ions during disturbed conditions Responsible for SPW effects at mid, auroral, and polar latitudes Workshop Hypothesis: Predictable tracer of Ring Current Expansion (?) [Poleward Edge of SED = SAPS = Ring Current Tracer] Inner Edge of SAPS motion related to Penetration E Field

5 Meteorological Space Weather Storm Front Observations at at km km Altitude Storm Enhanced Density (SED) Mid-Latitude Ionosphere

6 Schematic Relationship Millstone Hill IS Radar 5.5 DMSP F 13 RPA May 30, :35 UT DMSP Effect: SED log Density (cm 3) 5 SED electron precipitation Cause: Electric Field Source:??? Velocity (m/s) RC Ions DMSP IDM SAPS Geographic Latitude

7 GPS samples the ionosphere and plasmasphere to ~20,000 km. Dual-frequency Faraday Rotation Observations give TEC (Total Electron Content) Hundreds of Ground-Based Receivers ~30 satellites in High Earth Orbit TEC is a measure of integrated density in a 1 m 2 column 1 TEC unit = electrons m -2 TEC Sampled Continuously along Each Satellite- Receiver Path

8 Visualizing the Ionospheric Storm Front: GPS TEC

9 20 Nov :45:00 UT M Global Phenomenon: SED Plume is carried through the Cusp and forms the Polar Tongue of Ionization S GPS TEC Map 60 November 20, :45 UT log TEC E Geographic Latitude Merged SuperDARN/DMSP Convection Longitude Common projection: 350 km alt [Foster et al., JGR 2005]

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12 Millstone Hill Azimuth Scan April 12, 2001 UT Westward Ion Velocity SAPS Peak Polarization Stream L=2 L=4 Plasmasphere Trough Gradient Parameters Tabulated for 1400 Radar Scans: Latitude of SAPS Peak Magnitude of Peak Width of SAPS Channel Date UT and MLT Kp

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14 Sub-Auroral Polarization Stream DMSP F15 6 April 2000 Plasmapause Trough 21 MLT A Strong Electric Field forms in the Low-Conductivity Region between the Inner Edge of the Plasmasheet Precipitation and the Plasmapause Plasmapause Plasmasheet SAPS 2-Cell Convection

15 Disturbed Ring Current drives Magnetic Field- Aligned Currents into the Sub-Auroral Ionosphere REGION 1 REGION 2 Equatorward Motion of SAPS indicates Penetration of Ring Current to Lower Latitudes And Enhancement of Penetration E Field (Slide courtesy D. Mitchell) EXTENDING TO PLASMASHEET

16 noon

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18 SAPS Low-Altitude Datasets Align Closely

19 MHR

20 Conclusion: We can use the steep Density / TEC gradient at the poleward edge of the SED to locate the equatorward extent of the strong SAPS channel. Conclusion: The SAPS, SED, and TEC-gradient boundaries appear to behave in a regular (predictable) fashion as functions of disturbance level and MLT. next Mid-Latitude TEC Enhancement or Where Does the SED Come From?

21 Prompt Dayside Enhancement of TEC (19-21 UT)

22 Mid-Latitude TEC Enhancement at Base of SED Plume

23 TEC Enhancement at Base or Erosion Plume Corotates over US East Coast March 31, deg N Latitude TEC [20,100] TECu UT hour March 31, Longitude

24 Low-Latitude Latitude Ionosphere & Plasmasphere: Effects of Sub-Auroral Disturbance Electric Fields Undershielded eastward electric field: Strong uplift at equator redistributes plasma to higher latitudes Mid-Latitude TEC: Spread EA & Bulge: Downwelling & poleward/sunward plasma transport increase TEC at low & mid latitudes SED/TEC plumes & plasma tails: SAPS overlaps outer plasmasphere (PBL) carrying thermal plasma sunward

25 Bubbles TEC hole [References: Greenspan et al. (March 1989 storm); Basu et al. (July 2000 storm)]

26 Key West TEC Hole Guiana Poleward SAPS Electric Field Strips Away Outer Layers of Plasmasphere Equatorial GPS Samples Anomalies Ionosphere/Plasmasphere Spread Poleward TEC

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28 Another Example - Similar Structure

29 21 UT May 29/30, 2003

30 Watch for formation of Bulge at 19:30 UT (6 hours later Bulge remains at 285 E longitude)

31 Space-Based View of May 2003 Event

32 May 29/30, 2003

33 October 30, 2003 Plasma Redistribution TEC hole Similar Structure

34 21 UT

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36 Bz, nt November 20

37 Merged Foster-Vo SAPS model with Millstone 2-cell 2 convection (SAPS is associated only with the DUSK convection cell)