Double Coherent Scatter Radars Observations of the Daytime F-Region Irregularities in Low-Latitudes on 29 May 2017

In the morning on 29 May 2017, the Sanya very-high-frequency Radar and the Hainan COherent Scatter Phased Array Radar (HCOPAR) at Fuke were cooperated with similar operating frequencies to investigate the dissipation of the daytime F-region Field-Aligned Irregularities (FAIs). The two radars are located on south and north sides of the Hainan island of China, and the distance between them is about 140 km. The Sanya VHF radar recorded the FAIs between 00:12 and 02:42 UT (07:12 and 09:42 LT), and the FAIs observed by the HCOPAR appeared more than 10 min later at lower altitudes and suffered severe dissipation. The echoes emerged in all the beams simultaneously, and their Doppler velocities were close to zero, implying that the daytime FAIs were traveling along the magnetic field lines downward and northward with almost no zonal velocity. The front and bottom edges of the irregularities decayed earlier, and the parts in the FAIs with steeper density gradient lasted longer. The dissipation mechanism is attributed primarily to the photoionization and diffusing across the geomagnetic field in different period and gradient of the irregularities.