Anomalous Enhancement of Occurrence of the Preliminary Impulse of Geomagnetic Sudden Commencement (SC) at Low Latitude in the South Atlantic Anomaly (SAA) region

Details Anomalous Enhancement of Occurrence of the Preliminary Impulse of Geomagnetic Sudden Commencement (SC) at Low Latitude in the South Atlantic Anomaly (SAA) region Anomalous Enhancement of Occurrence of the Preliminary Impulse of Geomagnetic Sudden Commencement (SC) at Low Latitude in the South Atlantic Anomaly (SAA) region

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa23b1489s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SA23B-1489

Physics

Plasma Physics

[7836] Space Plasma Physics / Mhd Waves And Instabilities, [7949] Space Weather / Ionospheric Storms, [7954] Space Weather / Magnetic Storms, [7974] Space Weather / Solar Effects

Scientific paper

Occurrence feature of the preliminary impulse (PI) of geomagnetic sudden commencement (SC) at low latitude in the South Atlantic Anomaly (SAA) region was investigated using the long-term magnetic field data obtained from the CPMN [Yumoto and the CPMN group, 2001] and NSWM [Kikuchi et al., 2009] magnetometer networks. At Santa Maria (SMA) located near the center of the SAA region, the preliminary reverse impulse (PRI) dominantly appeared in the daytime sector (08-16 h, MLT) with occurrence probability of 40-80 %. The occurrence probability becomes the maximum around noon and is twice as large as that at Okinawa (OKI) located at the low latitude in the Pacific region. On the other hand, the preliminary positive impulse (PPI) frequently appeared in the nighttime sector (18-06 h, MLT) with its occurrence probability of 60-80 %. This occurrence feature of the PRI and PPI/Stepwise signatures in the SAA region is quite different from that at low latitudes reported by the past studies [e.g., Matsushita, 1962; Araki, 1977]. From the calculation result of the IRI-2007 and MSIS-2000 models, it can be concluded that a significant enhancement of the ionospheric conductivity in the SAA region leads to the anomalous low-latitude PRI and PPI/Stepwise occurrence, compared with that in the Pacific Ocean region. A candidate cause of the enhancement of the ionospheric conductivity is the weakness of the ambient magnetic field intensity in the SAA region.

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