On the Spatial Structure and Zonal Drift of Low Latitude E Region Irregularity Patches Over Hainan

All-sky radar measurements provide a unique capability to resolve the spatial structure of E region irregularities over a large zonal region. With the all-sky radar interferometry observations at Ledong (18.4 & DEG;N, 109.0 & DEG;E) in Hainan, China, the spatial structure and zonal drift of low latitude E region field-aligned irregularities (FAIs) over a large region are statistically investigated for the first time. It is revealed that the E region FAIs, including both the continuous and quasi-periodic (QP) types shown in radar range-time-intensity maps, occurred most frequently in summer. The continuous type was observed being generated locally without obvious zonal drift. The QP type generally covered & SIM;40-500 km zonally, and consisted of up to 9 (peaking at 3-4) FAI patches separated by & SIM;20-130 km (peaking at & SIM;60 km). The spatially separated FAI patches predominantly drifted westward at the speed & SIM;50-200 m/s. Besides the Kelvin-Helmholtz instability, gravity waves were surmised to be a major source for causing the spatial structures of low latitude QP type E region FAIs. Neutral wind was suggested to play an important role for their zonal drifts. Plain Language Summary The characteristics of E region field-aligned irregularities (FAIs) were traditionally investigated by using narrow beam radars, which direct the majority of power into a narrow direction perpendicular to the geomagnetic field. Due to the limited field-of-view of narrow beam radars, the spatial structure and dynamics of E region FAIs over a large zonal region (e.g., a few hundred kilometers) were seldom explored. It is not clear, in a statistical behavior, how the E region FAIs behave over a large region. In this study, with all-sky radar interferometry measurements at low latitudes, the spatial morphology of E region FAIs over a large zonal field-of-view spanning hundreds of kilometers, including the number of FAI structures, their separation and spatial coverage, and the zonal drift were statistically investigated. Periodic FAI structures, which consisted of multiple (with a maximum number up to 9) FAI patches, were observed covering up to 500 km or more in the zonal direction. The separations between adjacent structures centered around 60 km. The drift of the FAI patches was mainly westward at the speed similar to 50-200 m/s. In combination with other kinds of collocated measurements, the major driving sources responsible for the spatial structure and zonal drift of E region FAI patches are discussed.