Variation of bottom-side profile parameters (B0, B1) over Multan and their comparisons with IRI-2016 during deep solar minimum of solar cycles 23/24

The present study reports the variations in bottom-side thickness (B0) and shape (B1) parameters from ionospheric measurements of Digisonde Portable Sounder, DPS-4 installed at Multan (geog coord 30.18°N, 71.48°E, dip 47.4°) during the deep solar minimum between solar cycles 23/24 i.e., 2008–09 as a continuation to our previous work (Ameen et al., 2018). We have found that B0 has peak values during daytime whereas, B1 exhibits nighttime peaks, with both parameters showing a diurnal pattern. Seasonally, B0 showed annual trend with maximum values during summer and the least values in winter. B1 has the converse seasonal behaviour with respect to B0. These electron density profile parameters have been compared with International Reference Ionosphere (IRI-2016) to check the performance of three available options namely, ‘Gul-1987’, ‘Bil-2000’ and ‘ABT-2009’. The least Root Mean Square Error (RMSE) values with respect to the three options show that ABT-2009 estimated seasonal B0 and B1 with greater confidence as compared to other two options. For day and nighttime values of the parameters, no specific model may be declared the best predicting B0 and B1 for the period under study. Much of the factors that influenced the behaviour of hmF2 over Multan (Ameen et al., 2018) seem to be affecting the magnitude of B0 including the post-sunset peak in winter. The present study may be helpful in updating sub-model ABT-2009 of IRI for better reconstruction of bottom-side profile over Multan.