Diurnal and seasonal variations of <i>hm</i>F2 deduced from digitalionosonde over New Delhi and its comparison with IRI 2001

• Main Authors: N. K. Sethi, R. S. Dabas, V. K. Vohra
• Format: Article
• Language: English
• Published: Copernicus Publications 2004-01-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/22/453/2004/angeo-22-453-2004.pdf
• ISSN: 0992-7689; 1432-0576

Using digital ionosonde observations at a low mid-latitude station, New Delhi (28.6°N, 77.2°E, dip 42.4°N), we have derived hourly monthly values of <i>hm</i>F2 (the real height corresponding to the peak electron density in the F2-region), employing both the Dudeney&nbsp;(1983) and Bilitza&nbsp;(1990) empirical formulations for the period from January 2001 to August 2002. The diurnal and seasonal variations of <i>hm</i>F2 are analyzed. Further, to assess the predictability of the latest available model, International Reference Ionosphere, (IRI-2001), we have obtained the median values of <i>hm</i>F2 derived from M(3000)F2 for each hour during different seasons and compare these with the model. Our results show that both the Dudeney&nbsp;(1983) and Bilitza (1990) formulations reveal more or less a similar diurnal trend of <i>hm</i>F2, with higher values around midnight and lower during sunrise, in all the seasons. It is also noted that the <i>hm</i>F2 shows a larger variability around midnight than by daytime, in all the seasons. Further, the study shows that median values of observed <i>hm</i>F2, using both formulations, are somewhat larger than those predicted by the IRI, in all seasons and at all local times. During summer, the IRI values agree comparatively well with the observations, especially during daytime. Major discrepancies occur when the IRI underestimates observed <i>hm</i>F2 for local times from about 14:00&nbsp;LT to 18:00&nbsp;LT and 04:00&nbsp;LT to 05:00&nbsp;LT during winter and equinox, where the percentage deviation of the observed <i>hm</i>F2 values with respect to the IRI model varies from 15 to 25%. The difference between the model and observations, outside this time period, remains less than 20% during all the seasons.<br><br> <b>Key words.</b> Ionosphere (modelling and forecasting; equatorial ionosphere)