Investigation of low-latitude E and valley region irregularities: their relationship to equatorial plasma bubble bifurcation

Abstract

The low-latitude E, valley and F region 3 m scale irregularities are studied with the Sanya (18.4°N, 109.6°E, dip latitude 12.8°N) VHF coherent scatter radar. The observations show that the E region irregularities (ERIs) often weaken or disappear during the development of postsunset equatorial plasma bubbles (EPBs) in equinoctial months. However, the valley region irregularities (VRIs) are found to occur during the EPB development and show structures with close relation to those of EPBs. The interesting aspect is that the ERI disruption and VRI generation are simultaneously detected. In terms of the electric field coupling from the equatorial F region down to low-latitude E and valley regions, the polarization electric fields (PEFs) associated with the EPB bifurcation are suggested to play key roles in the evolution of ERIs and VRIs. It is shown that the mapping of upward and eastward PEFs generated within the equatorial west tilted bubble would inhibit the occurrence of low-latitude ERIs. However, for the east tilted bubble structure, the associated downward PEFs might map to the low-latitude valley region and play an active role for the development of 3 m scale irregularities through gradient drift instability.