Abstract:
Using the data of the VHF coherent scatter radar in Qujing from March 2016 to February 2018, the morphological characteristics of the ionospheric E-region field-aligned irregularities(FAI) echo are statistically analyzed. The results show that the E-region FAI echoes preferentially occur in three areas, the daytime echoes mainly appear during 07:00-12:00LT at an altitude of 90-105 km, while the two nighttime echoes are clearly visible during 15:00-01:00LT at an altitude of 90-100 km and during 18:00-04:00LT at an altitude of 100-115 km, respectively. Moreover, E-region FAI echoes exhibit distinguishable seasonal variation, i.e., maximum occurrence during May to August, but the minimum occurrence in November and December. The Doppler velocity of these three echoes varies between -85 m/s and 85 m/s with a spectral width of 0-60 m/s, and the mean Doppler velocity is only several m/s which is much smaller than the mean spectral width (20-30 m/s). In addition, we find that the mean Doppler velocity of echoes in the daytime E-region is generally negative, but with a small positive value in the thin layer around the height of 96 km. However, the nighttime E-region is obviously separated by a height of 105 km where the upper are negative, but the lower are positive. The characteristics of E-region FAI in Qujing is typical of type Ⅱ. The generation and evolution process are attributed to ionospheric electron density gradient drift instability in which the meridional wind and low F-region electric field play an important role.