Last 160 Ka Paleomagnetic Directional Secular Variation Record from Core MD972151,Southwestern South China Sea

The ground-based magnetic signature of particle precipitation fromthe ring current to low latitude regions during the recovery phase of a geomagnetic storm on 23 December,1995,has been inferred by studying photometric 630.0nm nightglow at a low latitude station,Kolhapur(7.5°N,144.7°E; Geomagnetic,dip latitude 10.6° N) and magnetograms(H,D andZ)of nearby low latitude stations.The maximum optical emission occurredsimultaneously with the maximum positive(north ward)excursions in theH trace of low latitude magnetograms associated with negative H excursions at high latitude observatories.Generally,an increase in Z componentoccurred at all low latitude stations.A large intensity increase of aboutseven times in 630.0nm emission was observed at around 2:15 hrs I.S.T on23 December,1995.The 630.0nm enhancement maximised at the time ofhigh Dst or Kp index during the night.In addition,the ionosonde experiment conducted at Ahmedabad(13.8°N,144.7°E;Geomagnetic)showed theenhancement of peak electron densities in the F-region and sudden lowering of the F layer in the ionosphere.A possible explanation of the effect isgiven in terms of emergence of energetic neutral atoms(Hydrogen or Oxygen) from high energy protons in a typical charge exchange process in thering current depositing energy into the thermosphere-ionosphere system,also possibly due to changes in the composition of the thermosphere-ionosphere during magnetic storms that would enhance the 630.0nm emissions.

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Paleomagnetic Secular Variation ； VGP ； South China Sea ； IMAGES

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