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Ann. Geophys., 22, 25-33, 2004
www.ann-geophys.net/22/25/2004/
© European Geosciences Union 2004
Climatology of ionospheric slab thickness
B. Jayachandran1, T. N. Krishnankutty2, and T. L. Gulyaeva3,4
1Sree Narayana College, Varkala, Trivandrum, Kerala, 695145, India
2Sree Narayana College, Kollam, Kerala, 691001, India
3IZMIRAN, 142190 Troitsk, Moscow Region, Russia
4Space Research Centre, PAS, Bartycka, 18A, Warsaw, Poland
Abstract. The ionospheric slab thickness τ defined as a ratio of the total electron content (TEC) to the F-region
peak electron density (NmF2) has been analysed during the solar maximum (1981) and
minimum (1985) phases of an intense, the 21st, solar cycle. Hourly values of TEC and NmF2
collected at Hawaii (low-latitude), Boulder (mid-latitude) and Goosebay (high-latitude) are
used in the study. Climatology of the slab thickness is described by the diurnal, seasonal, solar
and magnetic activity variations of τ for the different latitude zones. It is found that, for
magnetically quiet days of solar maximum, increased ionization of NmF2 and TEC during the
daytime is accompanied by an increased thickness of the ionosphere compared to the
night-time for non-auroral latitudes. However, the reverse is found to be true during the solar
minimum compensating TEC against a weak night-time ionization of NmF2. For the high-latitude
the night-time slab thickness is higher compared to the daytime for both the solar
phases. Ratios of daily peak to minimum values of slab thickness vary from 1.3 to 3.75 with
the peaks of τ often observed at pre-sunrise and post-sunset hours. The average night-to-day
ratios of τ vary from 0.68 to 2.23. The day-to-day variability of τ, expressed in percentage
standard deviation, varies from 10% by day (equinox, high-latitude) to 67% by night
(summer, mid-latitude) during solar minimum and from 10% by day (winter and equinox, mid-latitude)
to 56% by night (equinox, high-latitude) during solar maximum. A comprehensive
review of slab thickness related literature is given in the paper.
Key words. Ionospheric physics
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