A Review of the Recent Advances in the Investigation of Equatorial Spread F and Space Weather Effects over Indian Sector Using Optical and Other Techniques

Abstract

Observations using a narrow spectral band (0.3 nm) airglow photometer with a narrow field-of-view (3◦) developed recently enabled to capture the impact of space weather events on neutral airglow emission over low latitudes and also opened up new vistas to characterize different plasma structures associated with Equatorial Spread F (ESF). Plasma enhancement structures in buoyancy-dominated altitude region, as predicted by earlier numerical simulation investigation, were identified based on simultaneous VHF radar and airglow observations. A few other varieties of plasma structures that include confined structure in a limited altitude region and fossil plasma bubbles that became active at a later time, had been observed. Moreover, it was also shown that the prompt penetration of interplanetary electric field (IEF) can trigger ESF during post-sunset hours when ionospheric condition is not suitable for the occurrence of ESF. It was also shown that over-shielding effect of IEF can resurrect a plasma plume from a plasma structure confined in a narrow altitude region even during pre-midnight hours. Numerical simulation investigation confirmed that eastward electric field associated with over-shielding electric field is necessary but not sufficient condition for pre-midnight plume event. The importance of pre-seed to pre-midnight plume event in the guise of confined ESF structure developed during post-sunset hours is discussed. An important finding came up in the form of identifying the response of thermospheric OI 630.0 nm airglow emission during nighttime over low latitude corresponding to IEF variations. It was shown that quasi-periodic fluctuations (∼0.5 and 1.0 h) in IEF can affect thermospheric airglow emission over low latitudes. The importance of narrow spectral band airglow variations in bringing out these fluctuations is discussed. Interestingly, these periodicities were also found in the north-south com- ponent of nocturnal magnetic field (H) over the entire Indian sub-continent indicating the current responsible to be of magnetospheric origin. It was also shown during another event that while the fast fluctuations (∼40–45 min) in the vertical drift are governed by IEF during a storm that encompassed multiple sub- storms, the slowly varying component of ionospheric height variations corroborate with the slowly varying component of the variation in the auroral electrojet index, AE. The results discussed in this article highlight the important coupling aspects of ionosphere and thermosphere during quiet and disturbed space weather conditions.