Geomagnetic observations and ionospheric response during storm on 14 April 2006

71-79 A study of the intense geomagnetic storm on 14 April 2006 has been done using ionospheric data obtained from ionosonde station located in the American sector. The results indicate appearance of positive storm before the beginning of geomagnetic disturbance in the mid latitudes and occurrence of strong negative phase at the equator. It was observed that magnetospheric process, responsible for Dst decrease, was the enhancement of the plasma sheet and appeared to be caused by the combined effect of large intense proton density at 1400 hrs UT, southward turning of Bz at 1800 hrs UT and enhancement of speed stream at 1400 hrs UT on 13 April. The ionosonde stations located at American sectors are: College (64.9°N), Gakoma (62.4°N), Goose bay (53.3°N), Boulder (40.0°N), Dyess (32.2°N), Eglin AFB (30.4°N) and Puerto Rico (18.5°N). The present results were obtained using critical frequency foF2. The peak height of F2 layer hmF2 showed that the stations had some degree of simultaneity in the depletion of foF2 between 2000 hrs UT on 14 April and 0100 hrs UT on 15 April and that of hmF2 between 1600 and 1900 hrs UT on 15 April.