In the present paper investigations are made on the lower ionosphere with the help of observed tweek atmospherics at the Indian Antarctic research station Maitri during the second half of austral summer (January–March of 2003 and 2005). The variations in the lower ionospheric reflection height are found to be in correspondence with the sunrise and sunset at Maitri. The results indicate that the tweek atmospherics are helpful in tracking the changes taking place in the lower ionospheric height through the day‐night boundary. The ionospheric reflection height estimated using the cutoff frequency of fundamental (first‐harmonic or first‐mode) tweek atmospherics ranges from ∼64 to ∼79 km with a maximum calculated error of ±2.7 km. The recordings were carried out from 1800 to 0600 UTC. The analysis shows that the average cutoff frequency for the fundamental tweek atmospherics and hence the ionospheric reflection height varies from the months of January to March in accordance with the sunrise and sunset.

This paper presents the effect of geomagnetic storm on geomagnetic field components at Southern (Maitri) and Northern (Kiruna) Hemispheres. The Indian Antarctic Station Maitri is located at geom. long. 66.03 • S; 53.21 • E whereas Kiruna is located at geom. long. 67.52 • N; 23.38 • E. We have studied all the geomagnetic storms that occurred during winter season of the year 2004-2005. We observed that at Southern Hemisphere the variation is large as compared to the Northern Hemisphere. Geomagnetic field components vary when the interplanetary magnetic field is oriented in southward direction. Geomagnetic field components vary in the main phase of the ring current. Due to southward orientation of vertical component of IMF reconnection takes place all across the dayside that transports plasma and magnetic flux which create the geomagnetic field variation.Key words. Dst-vertical component of interplanetary magnetic field and geomagnetic field components.

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