Zhengwen Xu

Observations on the irregularities using Kunming VHF radar

Using the data from Kunming(103.7°E, 25.6°N) VHF coherent radar, Low-latitude ionospheric E-region irregularities of primrose season are investigated. The observational results shows that E-region irregularities occur mostly at nighttime, mainly appears in the night, especially in the midnight of LT, the height ranges extensively from 110 to 160km.

Simulation of asymmetry incoherent scatter spectra with the ion acoustic wave

Under the condition of parametric decay instability excitation, the measured up-shifted ion line is higher than downshifted one. We are based on the assumption of the existence of ion acoustic velocity particles, a new ion velocity distribution function and incoherent scatter theory model with the PDI mechanism are build, and the spectra asymmetry characteristic of PDI is simulated successfully, which is consistent with experiments observations. It is great significance to understand the instability mechanism.

The behavior of electron density and temperature during ionospheric heating near the fifth electron gyrofrequency

Published by AGU. Copyright (2017) American Geophysical Union. Source at http://doi.org/10.1002/ 2016JA023121

Validation of super thermal electron induced by nth gyro-harmonic frequency heating

When the gyro-harmonic heating and some other instability happen at the same time, several instabilities interact with each other, which is easier for them to ionize neural gas. It is represented as the huge enhancement of the electron density amplitude, and the scale of enhancement will extend to several hundreds kilometers. Base on the observation results of the heating experiment in polar region, the super thermal electron induced by nth gyro-harmonic frequency heating is validated and the relevant physical process is explained.

Compare of polar ionosphere modification effect with different heating modes

The measured data in polar winter ionosphere heating experiment carried out at Tromso on 24 November 2011 are analyzed here to find out whether the heating modes of O-mode and X-mode have different influences on electron temperature and electron density and what the influences are. It shows that the enhancement of electron temperature under O-mode is more than that under X-mode. Comparing with the O-mode case, the electron density enhance at higher altitudes under X-mode. The results show that the electron temperature can enhance up to 277% maximum and the electron density can enhance up to 53.7% maximum under O-mode, while the data are 71.8% and 54.8% separately under the X-mode.

The analysis of HF-induced abnormal enhancement of plasma line

As an important characterization in ionospheric heating experiments, the disturbed plasma line have been widely studied. On November 23, 2011, a polar winter ionospheric heating experiment with the linearly varied heating frequency was carried out by China. In this experiment, a very interesting feature of HF-enhanced plasma line is observed. When the heating is on, the enhancement of plasma line is tens times larger than that of background in the first 8 minutes. Then the enhancement increases rapidly, and the increase rate can reach thousands or even tens of thousands times. Based on the comparison of the ion acoustic frequency, heating frequency and the frequency of the maximum value of plasma line, and the analysis of the matching height of parametric instability and the matching height of n times gyro-frequency, we infer that the enhanced plasma line in this experiment may be induced by parametric instability and 5 times gyro-frequency resonance.

Ionospheric tomography by using diverse data sources

The computerized ionospheric tomography (CIT) is an under-determined, ill-posed inverse problem. The limited-angle geometry and sparse receivers lead incomplete information in measurements, which affect the precision of the CIT imaging, especially in the vertical dimension. This paper puts forward a new method by combining vertical and oblique sounding data with the total electron content (TEC) retrieved from an assumed tri-band beacon of a planned Chinese satellite for seismological studies transmitting VHF, UHF and L-band frequencies. A ground-based high-resolution ionospheric observation network (GHRION) has been built in northern China in April, 2009. Based on this ground network and the planned satellite, high-resolution ionospheric structures will be reconstructed in real time, for helping monitoring the ionospheric precursors of earthquakes over several large seismic belts in northern China. The initial of the iterative is specified by real sounding data, so it slightly deviates from the real electron density distribution and the CIT result is in high precision. The numerical simulations show that electron density images reconstructed from TEC using three-frequency technique are significantly improved after combining real observation data of the ground-based vertical and oblique ionograms. The results in this paper will help to ensure that the measurements to be made by this solid network will yield their potential.