First Observation of Localized F Region Bottom‐Type Scattering Layer by All‐Sky Radar at Low Latitude

Abstract F‐region bottom‐type scattering layers (BSLs) occurring over equatorial and low latitudes may act as the precursor of plasma bubbles, usually observed by narrow‐beam very high frequency radars. However, their spatial features remain unknown due to the radar narrow field‐of‐view. Here we report a case of localized BSL not accompanying plasma bubbles firstly observed by an all‐sky radar at low latitude. Based on radar interferometry over a large field‐of‐view, the BSL was revealed to occur over a limited area northeastward of the radar and did not cause scintillation when Global Navigation Satellite System satellites passed through. The BSL vertical displacement precisely followed the F‐layer bottom fluctuation, without obvious horizontal movement. Interestingly, the localized BSL caused weak spread‐F traces in the ionograms indicating irregularities from specific directions, which are distinct from the satellite traces or range spread F related to plasma bubble development thus could serve as a new signature of BSL in future studies.