LANL MPA Observations

Here are some initial remarks about the observations on the 9th and 10th, including the appearance of a superdense plasma sheet on the 10th (indicating that the magnetospheric "gate" was open, i.e., that IMF Bz was south while the solar wind density was high). They also see evidence of strong magnetospheric currents, including reverse draping of the field near dawn late on the 10th.

April 9, 1997

• No built-up plasmasphere

• Normal convection

• Plasma sheet temperature ordinary

• Plasma sheet density ordinary

• Low levels of penetrating radiation

• Near-earth cross-tail currents normal

• Not much ionospheric upflows into plasma sheet

• Candidate substorms at 3 UT, 4 UT, and 15 UT

• Spacecraft charging modest (<100 volts)

• Candidate compression event begins ~23 UT
  
  

April 10, 1997

• Recovery from apparent compression beginning ~2 UT; long decompression until ~16 UT

• Magnetosphere quiet until ~1800 UT

• No plasmaspheric material seen; plasmaspheric refilling from the ionosphere seen mid-day

• Weak convection until ~1800

• Electron plasma sheet very hot early on 10th; expect spacecraft surface charging

• Ion plasma sheet hot

• Superdense plasma sheet appears suddenly near midnight at ~1800 UT, reaches dusk at ~2030 UT; this indicates that the magnetospheric "gate" was open, i.e., that IMF Bz was south while the solar wind density was high; we believe this is a necessary (but not sufficient) component for strong Dst

• Ion outflow into plasma sheet post-midnight to dawn late in day

• No clear substorm candidates

• Strong near-earth cross-tail currents after 1800 UT

• Strong reverse draping (twist) of magnetic field on dawn side at ~22-24 UT

• Candidate compression event starting ~22 UT

• Penetrating background remains low
  

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  Contacts:
  

  • Michelle Thomsen,
    
  • Joe Borovsky,