Study of the morphology of nighttime D-region ionosphere using tweek atmospherics recorded at low latitudes

Abstract:

Recording the tweek atmospherics with a maximum up to eight harmonic using the receiver installed at Tay Nguyen University (12.65^o N, 108.02^o E), Vietnam during January – December 2013, we studied the morphology of the nighttime D-region ionosphere. Tweeks were recorded on 5 quiet nights per month. The occurrence of tweeks with mode number m = 2 - 3 is more dominant. Tweeks with higher modes (m ≥ 4) appear less than other tweeks due to the higher attenuation of wave energy for higher modes reflected at the ionospheric D region. The results show that electron densiy varies from 25.2 – 187.1 cm^-3 corresponding the tweeks with m = 1 - 8 at the reflection height from 81.7– 86.6 km. The variation of tweek reflection hight during the solar maximum year, 2013, could be caused by the hydrogen Lyman-α and Lyman-β emissions from the geocorona, galactic cosmic rays, variations of neutral density, direct lightning coupling to the ionsphere and electron precipitaion. The reference height h’ is low in January – April and high in May – December. The exponential sharpness factor β of electron density profile are higher during summer seasons as compared to those during winter and equinox seasons. The electron density using the tweek method is lower by about 18 – 49 % than those obtained using the IRI-2012 model and shows a good comparision with the IRI-2012 in the altitude range of 83 – 89 km.