HF absorption enhancements following major geomagnetic storms are analysed, using the superposed epoch method, to examine the geomagnetic latitude limit of the after-effect phenomenon. The absorption data were obtained from one double hop and two single hop A3 transmission paths with ionospheric points at Fgeomag = 3:54oN and ~6. 40oN (15. 40 MHz), Fgeomag ~ 9N (4. 87 MHz), and Fgeomag ~ 11oN (6. 09 MHz) respectively. Presently, the results have shown that enhancement in absorption following major storms could be traced to the low latitude of 3. 54oN.
Gnanalingam S 1974: J. Atmos. Terr. Phys., 36, 1335-1354.