Shear in the zonal drifts of 3m irregularities inside spread F plumes observed over Sanya

摘要

abstract_textpIncoherent scatter radars near magnetic equator regularly measured a vertical shear in zonal drifts of the evening background plasma, with westward drifts below the equatorial F region peak and eastward drifts above. We report here observations of a clear shear structure in the zonal drifts of 3m irregularities inside spread F (SF) backscatter plumes measured with a 47.5MHz coherent scatter radar operated at a low-latitude site Sanya (18.4 degrees N, 109.6 degrees E; dip latitude 12.8 degrees N). The radar interferometry analysis on the zonal drifts of the 3m irregularities yields results consistent with that estimated from the irregularity echo Doppler velocity measurements with multiple beams. It is shown that the SF 3m irregularities move westward at the lowest altitudes, while at higher altitudes in the same SF plume structure, the 3m irregularities drift eastward. One interesting point is that the vertical shear of zonal drifts was centered at similar to 300km altitude over Sanya, which maps to an apex altitude of similar to 650km at magnetic equator and is thus apparently higher than the apex altitudes 250-450km where the zonal velocity shear has usually been observed. Analysis of the observations suggests that while the possibility of local generation of the shear flow of the irregularities can exist, the possibility of a plasma vortex appearing at relative high altitudes causing the zonal drift shear of F region 3m irregularities measured over Sanya cannot be totally ruled out./p/abstract_text