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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.

This paper investigates the annual cycle in aerosol size distributions in Darwin, Australia, a coastal site in the Tropical Warm Pool where the major aerosol sources are biomass burning and sea salt. We have used radiometer measurements from the Tropical Western Pacific Atmospheric Radiation Measurement facility for March 2002–June 2003. Constrained linear inversion was used to retrieve aerosol size distributions from the aerosol optical thickness (AOT) measurements. A novel technique combining size distribution shape and aerosol optical properties classified the distributions into three classes: biomass burning, mixed/background and marine/sea salt. The biomass burning aerosol was associated with continental winds and only observed during the dry season. The mixed/background aerosol and marine/sea salt occurred throughout the year. The marine class occurred predominantly in the afternoon and was strongly associated with marine winds; the mixed/background aerosol did not show any strong wind dependence or diurnal cycles.

This paper investigates the annual cycle in aerosol optical thickness (AOT) and Angstrom exponent in Darwin, Australia, a coastal site in the Tropical Warm Pool where the major aerosol sources are biomass burning and sea salt. We have used radiometer measurements from the Tropical Western Pacific Atmospheric Radiation Measurement facility for the period March 2002–June 2003. Strong seasonal cycles in AOT and Angstrom exponent were observed, peaking during the burning season (May–November). Investigation of the spectral dependence of optical thickness showed that the Angstrom formula can be satisfactorily fitted to the AOT data during the burning season but not on summer and autumn afternoons due to the presence of sea salt aerosols.