Daytime E region field-aligned irregularities observed during a solar eclipse

The driving mechanism of the midlatitude field-aligned irregularities (FAIs) has been in dispute for many years. The experimental observations were carried out during the solar eclipse of 22 July 2009 in Wuhan, China, to study the possibility of the wave-driven irregularities. A high-frequency coherent scatter radar was used to detect the E region irregularities. An ionosonde was applied to record the trace of gravity waves in ionosphere. The E region FAIs occurred at the end of the solar eclipse with fluctuant Doppler. At the same time, the oscillations on the fE(s) (maximum reflecting frequency of E-s) curve and in the Doppler velocity of the echoes from the E-s layer were also recorded. The data analysis and comparison show that the gravity waves and the FAIs occurred at the same time with the in-phase variations in amplitude and phase. Thus, the solar eclipse and the gravity waves may play important roles in the occurrence of the irregularities. A schematic diagram of one-period gravity wave is used to explain the possible gravity wave-driven mechanism and the Doppler fluctuation in the irregularities. The daytime FAI in midlatitude is a rare phenomenon, even in the condition of solar eclipse. There are only four cases of the E region FAIs observed during a solar eclipse, including our observations. The unique feature of our observations is the synchronized oscillations in the irregularities and in the E-s layer, which will help address the outstanding question of the source of the midlatitude E region FAIs.