Predicted and measured bottomside total electron content under high and moderate solar activity conditions over New Delhi

Abstract

Digital ionosonde measurements at a low-middle latitude station, New Delhi (28.6ºN, 77.2ºE, dip 42.4ºN) are used to derive bottomside total electron content (BTEC) for a period of high (2001-2002) and moderate (2003) solar activity periods. These observations are then used to evaluate the predictability of the latest available IRI-2001 model using both the options, i.e. (<i style="">B</i>₀ Tab. and Gulyaeva). The study reveals that for both the solar activity periods, the diurnal variations of BTEC show more or less similar trend during all the seasons (i.e. maximum around daytime and minimum around midnight) and BTEC exhibits a large day-to-day variability at any given local time. Comparison of BTEC with those predicted by the IRI model using both the options during moderate solar activity reveals, in general, good agreement, except for post-noon hours during summer and equinox. However around noontime, IRI (<i style="">B</i>₀ Tab.) option shows somewhat better agreement with the observations than by IRI (Gulyaeva) option. During high solar activity, a comparative analysis shows that discrepancies do exist during winter and equinox during daytime with both the options of the IRI, however the agreement between the IRI (<i style="">B</i>₀ Tab.) and observations is reasonably good for summer during daytime, whereas IRI (Gul.) option overestimates the BTEC. Solar activity variations of observed median BTEC show that the peak content in general increases by a factor of more than two from moderate to high solar activity.