MHD wave characteristics inferred from correlations between X-rays, VLF, and ULFs at Syowa Station, Antarctica and Tjörnes, Iceland (L∼6)

The Polar Patrol Balloon No. 6 (PPB#6) observed quasi-periodic pulsations of bremsstrahlung X-rays (E 30∼120 keV) in the daytime of 0855 UT (0914 MLT) ∼ 1630 UT (1614 MLT) on January 5, 1993, near Syowa Station, Antarctica (L∼6). The X-ray pulsations near the noon (1208:00 UT (1216 MLT) ∼ 1225:04 UT (1232 MLT)) include a period of about 260 sec, which corresponds to Pc 5 magnetic pulsations. It was found that at Syowa Station and Tjörnes, Iceland, which are both pair locations of the geomagnetic conjugacy, the X-ray pulsations are in correlation with the ULF-D pulsations. Also the Tjörnes VLF (2 kHz) pulsations correlated well with the X-ray pulsations of the period corresponding to Pc 5. It is probable that the VLF- and ULF-associated X-rays or precipitating energetic electrons in the vicinity of the L ∼ 6 shell are in synchronization with the electron-cyclotron resonance. Lastly, the so-called ballooning-mirror instability (the BMI) is a candidate to explain the compressional MHD waves that occur during the short time interval (1216 MLT ∼ 1232 MLT) in which the experimental results were interpreted.