Study on The Bottom-Type Back Scattering Layer Precursor to The Equatorial Plasma Bubble

Abstract The bottom-type scattering layer precursor to the equatorial plasma bubble is named by its belt feature in the temporal record of the coherent scattering radar. Its spatial structure is rarely studied and has not been clearly described so far. Through the data observed by the coherent scattering radar and digisonde at Fuke observatory, we argued that the shape of the bottom-type scattering layer in space should be a plasma structure of a quasi-circular cross-section extending along the geomagnetic field with the quasi-static velocity feature. Such a plasma structure along the geomagnetic field line at the F region bottom has the characteristics of a waveguide. Based on this derived result, it’s proposed the possible origination of the equatorial plasma bubble. On the condition that the state of plasma density in the waveguide greater than that of the background reversed, the transverse bipolar electric field of the hybrid electric eigen-mode in the waveguide excited by resonance break out of the boundary, and the equatorial plasma bubble will generate. Electromagnetic disturbances such as Alfven wave and ULF wave etc. may be the source of exciting the hybrid electric eigen-modes of plasma waveguide.