Study On The Echo Characteristics Of Polar Mesosphere Summer Echoes

Recently, considerable attention has been paid to the anomalously high power radar echoes from the mesosphere at high latitude in summer: the polar mesosphere summer echoes (PMSE). PMSE considerable relate to the charged dust particles in polar mesopause. Much research on PMSE has been done since it was first found by Ecklund and Balsley as a fascinating phenomenon in 1979. On the basis of theoretical research on electromagnetic wave propagation in dusty plasma, the generation mechanism is studied with layered media theory. The effect of heating on PMSE is discussed and the ionosonde is used to analyze PMSE. The main topics and results of the study are as follows:Firstly, the basic knowledge of PMSE is introduced; the data of ECT-02 only occurring PMSE are given. The data provide a good base to study various features of PMSE. By analyzing the data, one can find that the region in polar summer mesopause where charged dust particles exist should be studies with dusty plasma theory. The variable disturbance of electron density is used to explain PMSE.Secondly, by statistically analyzing the volume reflectivities of PMSE at different time, stations and frequencies, the relation between the volume reflectivity and the work frequency is obtained. The differential scattering cross section obtained with Born approximation in dusty plasma is also derived, the same result is obtained. Others, the relation between the volume reflectivity and frequency occurring PMSE is studies using the small scale structure of electron density caused by charged dust particles. A theoretical expression for the radar volume reflectivity is derived and shows that the statistical result agrees with the theoretical results. When studying the generation mechanism of PMSE, the charged dust particles must be considered. The theory of dusty plasma may be a useful tool to investigate the generation mechanism of PMSE.Thirdly, the data obtained from sounding rocket campaigns indicate that radar echo power, electron density and dust charge density of polar mesosphere in summer are obvious layered structures. Based on the theory of wave propagation in layered media, the reflection coefficient and radar signal to noise ratio (SNR) at 53.5 MHz at each layer in polar mesosphere is studied. The agreement of the SNR calculated with the theoretical results and the measured results are good. Others, the theory of wave propagation in layered media are also used to study the reflection coefficient at other frequencies. The intensity of the radar echoes reflected by layered structure decreases greatly with the frequency increasing. So the phenomenon of PMSE may mainly be caused by the reflection of the layered structure. Combining dusty plasma theory, the attenuation of L2 carrier frequency of Global Positioning System (GPS) traverses in PMSE layer is studied with the layered media theory. One find that the signals attenuate greatly in PMSE layer, so the PMSE layer can affect communication.Fourthly, PMSE have obvious layered structures, the overshoot can be caused by artificial electron heating experiments during PMSE conditions. Since 2006, we have carried out the heating campaign for three years. Based on the data from 2006 to 2008, the different layered structures are observed, the number of layer change very quickly. The overshoot characteristic curve (OCC) is obtained in our heating campaign too. Others, the echo power changing with height and time are also got. The heating campaign may be the found of studying PMSE in the future.Finally, the ionosonde is used to study PMSE at MF and HF bands. Using the ionograms detected by ionosonde at Troms? Station, Arctic and Zhongshan Station, Antarctica, PMSE are studied with data observed by a Digisonde Portable Spunder-4 ionosonde. By analyzing the irregular characteristics of E and Es layers in ionograms, the PMSE-Es may be observed at MF and HF bands. The phenomena of irregular E and Es layer are called PMSE-Es (Polar Mesosphere Summer Echoes-Es). The occurrence rate variations of PMSE-Es exhibit similarity to those of PMSE, such as: seasonal variation, diurnal variation, and semidiurnal variation. Others, in order to compare the seasonal variation of the Arctic PMSE'occurrence rate from 1999 to 2003, a new statically method is used to obtain the PMSE-Es'seasonal variation. Both occurrence rates of PMSE in Arctic and that of PMSE-Es in Antarctica occurrence rates are relatively lower in 2002. At the same time, the occurrence rate of PMSE-Es in the other four years is nearly consistent with that of PMSE. The results show that PMSE-Es should have some relations with PMSE. The ionosonde in Arctic and Antarctica may be used to detect PMSE with the phenomenon of PMSE-Es at MF and HF bands.