Study of low-latitude ionospheric D-region negative ion profile during an M-class solar flare using VLF propagation effects

We dealt with the negative ion contents of the lower ionospheric D-region during an M-class solar flare. We did a generalized study of the variation of the λ-parameter both with D-region height and time. In this purpose, we numerically solved the D-region electron continuity equation, where, we supplied the N_e-profile calculated from Long Wave Propagation Capability code results. The results generally agree with those present in the literature, namely, the effect on the negative ion density during that flare due to photo-electron detachment and photo-dissociation processes. However, for our VLF propagation path of interest, we found that the negative ions exist till somewhat higher altitudes (~ 73-74 km) than the high-latitude D-region heights. Other workers did model study on Cl ions and its complex compounds at night-time in high latitude ionosphere. They reported that, though negative ions are less abundant in daytime, in lower latitudes its availability increases, which supports our results.