Interferometry Observations of the Gravity Wave Effect on the Sporadic E Layer

On the basis of interferometry measurement made with the Chung-Li VHF radar, we investigated the effects of upward propagating gravity waves on the spatial structures and dynamic behavior of the 3 m field-aligned irregularities (FAIs) of the sporadic E (Es) layer. The results demonstrate that the quasi-periodic gravity waves oscillating at a dominant wave period of about 46.3 min propagating from east-southeast to west-northwest not only modulated the Es layer but also significantly disturbed the Es layer. Interferometry analysis indicates that the plasma structures associated with gravity wave propagation were in clumpy or plume-like structures, while those not disturbed by the gravity waves were in a thin layer structure that descended over time at a rate of about 2.17 km/h. Observation reveals that the height of a thin Es layer with a thickness of about 2-4 km can be severely modulated by the gravity wave with a height as large as 10 km or more. Moreover, sharply inclined plume-like plasma irregularities with a tilted angle of about 55 & DEG; or more with respect to the zonal direction were observed. In addition, concave and convex shapes of the Es layer caused by the gravity wave modulations were also found. Some of the wave-generated electric fields were so intense that the corresponding E x B drift velocities of the 3 m Es FAIs approximated 90 m s(-1). Most interestingly, sharp Doppler velocity shear as large as 68 m/s/km of the Es FAIs at a height of around 108 km, which bore a strong association with the result of the gravity wave propagation, was provided. The plausible mechanisms responsible for this tremendously large Doppler velocity shear are discussed.