Study On Ionospheric Heating Model About Polar Mesosphere Echoes

The objective of this thesis is to study polar mesospheric radar echoes and their temporal behavior after turn-on of artificial radio wave heating. Polar mesospheric radar echoes include summer echoes and winter echoes, named PMSE and PMWE respectively. PMSE is a kind of strong radar echo, which occurs in the summer mesopause between 80 ~ 90 km above the ground. PMWE is also a kind of strong but rarely occurs radar echo, which is observed during the winter months in the mid-mesosphere from around 50 ~80 km altitude at both northern and southern latitudes.These phenomena can greatly help us to understand and to explore the characteristics of polar atmospheric space environment, thus this research field caused massive attention of upper atmosphere physics researchers.Affected by atmospheric circulation, gravity waves, and the influence of air pollution in the polar mesopause region, the water vapor content of this area keeps a relatively high level. Further more,temperature of mesopause is the lowest in the whole atmosphere. Ice crystals are formed under the conditions mentioned above. These ice crystals can be called as dusty particles. Due to the solar ultra-violet rays and x-rays,neutral gas elements are ionized as plasma. Dusty particles are immersed in plasma, we find a new physical form of material called spatial dusty plasma. Many research results have indicated that the regional abnormal radar echoes have a close relationship with spatial dusty plasma. Polar mesopause region is very complex, especially the existence of the charged dusty particles makes the mesopause region of the physical environment more complicated. Study of polar mesospheric echoes is the frontier research field of space physics and dusty plasma.Heating the radar echo area by radio waves based on ground facilities to artificially change the temporal behavior is currently a popular research field. This research method can be utilized in the diagnosis of observing and measuring the change of the related parameters of the dust layer, thus to provide an effective way of having insight on the physical mechanism of polar mesospheric radar echoes.In this paper, we get to know some background knowledge about the atmosphere and the ionosphere, and have a discussion on the details of PMSE phenomenon,statistical variation tendency of PMSE. Observations and analysis of PMWE phenomenon is also within our discussion. Then, we know about general situation of polar mesospheric radio wave heating experiments, bring in the theoretical computational model of PMSE by radio wave heating. On the basis of plasma continuity equation, momentum equation and energy equation, considering the diffusion process and dust charging process which occurs in the dust layer after turn-on of radio wave heating, we have a discussion on the physical mechanism of summer echoes.PMWE research is still at its beginning, so here we pay more attention to the winter echo research. On the basis of PMSE model, we bring in polar mesospheric winter dust layer parameters. Then we conduct numerical simulation of the improved model on radio wave heating, investigating the specific impact of particular winter dust layer parameters on electron irregularities. The results show that:(1) charged dust particles in the mesosphere indeed play an important role in producing PMWE and they are essential factors causing polar mesospheric radar echoes;(2) from the results of numerical simulation, radio waves heating does have a great effect on most of the winter dust layer parameters, and generally coincide with the observation results.During the turn-on of radio wave heating, according to different parameters setting,electron irregularity amplitude rise of different level. In the set range, the lower the frequency of radar, the greater the radius of dust particle, the greater number of the individual dust particle adsorbing electrons, the greater electron density initial value, the higher electron irregularity amplitude peak we get. Electron temperature ratio of after heating to before heating has a relatively complex effect on electron irregularities, when the ratio is set between 6 to 8, we get the peak value;(3) attenuation process of electron irregularity amplitude after turn-on vary. Particularly, attenuation process affected by different number of the individual dust particle adsorbing electrons and different electron density initial value indicate characteristics of consistency.