D region effects of the 17–19 March 2015, a St Patrick's Day super geomagnetic storm (Dst = −223 nT), using a navigational transmitter very low frequency (VLF) signal (NWC, 19.8 kHz) recorded at a low‐latitude Indian station, Allahabad (geomag. lat., 16.45°N), have been analyzed and compared with similar strength of the 22–25 June 2015 storm (Dst = −204 nT). During the March storm, NWC signal amplitude decreased on 17 March (main phase of the storm) and recovered on 27 March, which is 1 day after the recovery of the storm, whereas for the June storm, VLF amplitude decreased for 2 days only during its recovery phase. The decrease in the amplitude was pronounced during evening terminator for both the storms. The modeling of VLF signal anomaly on 17 March and on 25 June using Long‐Wave Propagation Capability code shows an increase in the D region reference height (h′) by ~2.6 km and ~2.5 km, for March and June storms, respectively. The D region electron density (N_e) determined using storm time h′ and sharpness factor β shows a decrease in the N_e during the main phase followed by a slow recovery during the recovery phase of the March storm, whereas June 2015 storm showed a decrease in the N_e only on 25 and 26 June. Morlet Wavelet analysis of the amplitude for both the storms shows a presence of strong wave‐like signatures, suggesting propagation of atmospheric gravity waves/traveling ionosphere disturbances to the low latitude D region due to the Joule heating at high latitudes.

Particulate matter (PM) concentrations and aerosol optical depth (AOD) are measured and correlated simultaneously using a high-volume sampler and a MICROTOPS-II Sunphotometer, respectively. The present work deals with the characteristics of particulate matter (PM₁, PM_2.5, and PM₁₀) over Varanasi, from April 2019 to March 2020. Daily variation, as well as seasonal variation, reveals the dominancy of fine-mode particles over the Varanasi region in the winter season and the dominancy of coarse-mode particles in the summer season, which was further confirmed by calculating the ratio between particulate matter (PM₁/PM₁₀ and PM_2.5/PM₁₀). This ratio was discovered to be lowest in the summer and highest in the winter. Annual mean concentrations of PM₁, PM_2.5, and PM₁₀ are found to be 93.91, 111.34, and 180.70 μgm⁻³, respectively. The seasonal variation shows relatively a higher concentration of PM₁, PM_2.5, and PM₁₀ in the winter season, which may be due to stable meteorological conditions and increased biomass burning in winter. Diurnal and seasonal variations in AOD were also studied during this period. A large and small value of AOD represents the dominancy of fine particles over coarse particles. At 500 nm, maximum (1.17) and minimum (0.44) AODs were measured in December and August of 2019, respectively. There was a statistically significant correlation between PM particles (PM₁, PM_2.5, and PM₁₀) and AOD. Elemental analysis shows that fluorine and carbon are the major elements that were observed in selected samples during the post-monsoon and winter season using SEM-EDX analysis.