The results show that electron density varies from cm-3, corresponding to the tweeks with m = 1-8 at the reflection height from km. The reference height h’ and electron density gradient β are higher during summer seasons as compared to those during winter and equinox seasons. The mean values of h’ and β are km and km-1, respectively. The electron density using the tweek method is lower by about 11-38 % than those obtained using the IRI2012 model. | Vietnam Journal of Earth Sciences, 38(4), 327-338, DOI: Vietnam Academy of Science and Technology Vietnam Journal of Earth Sciences (VAST) Study of the morphology of the low-latitude D region ionosphere using the method of tweeks observed at Buon Ma Thuot, Dak Lak Le Minh Tan*1, Nguyen Ngoc Thu2, Tran Quoc Ha3, Nguyen Thi Thao Tuyen4 1 Faculty of Natural Science and Technology, Tay Nguyen University Geophysical Center, South Vietnam Geological Mapping Division 3 Ho Chi Minh City University of Education 4 Department of Geophysics, Ho Chi Minh city Uiniversity of Science 2 Received 13 October 2015. Accepted 12 October 2016 ABSTRACT Tweek is the electromagnetic waves at Extremely Low Frequency (3 - 3000 Hz) and Very Low Frequency (330 kHz) bands, which originates from lightning discharges and propagates about thousands of kilometers in the Earth-Ionosphere waveguide. Recording the tweeks with a maximum up to eighth harmonics using the receiver installed at Tay Nguyen University (, ), Buon Ma Thuot, Dak Lak, during January - June 2013, we have studied the morphology of the low-latitude D region ionosphere in the nighttime. 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 density varies from cm-3, corresponding to the tweeks with m = 1-8 at the reflection height from km. The reference height h’ and electron density gradient β are higher during summer seasons as compared to those during winter and equinox seasons. The mean values of h’ and β are km and km-1, respectively. The electron density using the tweek method is lower by about 11-38 % than those obtained using the IRI2012 model. Keywords: The morphology of the D-region ionosphere, tweek, .
