Simulation And Statistic Analysis Of Mid-Latitude Sporadic E-Layers

As an anomalous phenomenon, the studies on sporadic E-layers always attractmany experts. The present paper deals with both the statistical study and simulationcalculation of sporadic E-layers at mid-latitude regions. First, statistical analysis isconducted and the main morphological features are described. Then, according to thewidely accepted wind shear theory, simulation for the formation of E_s under the actionof wind fields and electric fields was carried out. The distribution features of temporalvariations caused by the variations of the wind fields and electric fields are found inthe simulation calculation.At first, we confirmed "the Far East Anomaly" advanced by Smith as early 1957by using the f_oF_s data of typical ionosonde stations. Then the seasonal and diurnalvariations are discussed at full length and the temporal variation features are shownthat the sporadic E occurrence is high in summer and peaks in the daytime. Thepre-noon peak predominated at higher latitudes and the post-noon peak at lowerlatitudes.The subsequent simulation work is based on the continuity equation andmomentum equation and method of characteristics curve is adopted. We accomplishsimulating the convergence of metal ions to form a thin layer under reasonabledynamics conditions. The wind field data come from the HWM93 empirical modeland the electric field data from the drift empirical model. The results of simulationconfirm the validity of the wind shear theory indirectly. When changing the inputparameter of the HWM93 empirical model and the drift empirical model, we obtainddifferent results, which make it possible for us to study the reaction of E_s on thediurnal and seasonal variations of the background dynamics conditions. By adjustingthe amplitude of the tidal components of the HWM93 wind model, we draw theconclusion that the tidal wind has an important effect on the diurnal variation of E_s.In addition, this paper studies the correlation between solar activities and the intensity of sporadic E-layers by analyzing the global network data of criticalfrequencies of E_s-layers during the three solar cycle period (1957-1990). It is obtainedthat the yearly averaged values of f_oE_s are correlated with solar activities in daytimeand anti-correlated at night. Meanwhile, the occurrence of sporadic E-layers has apositive correlation coefficient with solar activities in daytime and negative atnighttime. Detailed analysis shows that the discovered strong positive correlation off_oE_s with solar activities in daytime is mainly caused by the contribution of regular Elayers which are deeply controlled by solar activities. When eliminating thecontribution of regular E layers, the intensity of sporadic E-layers is slightlypositively correlated with the yearly averaged sunspots numbers in daytime andnegatively correlated at night. The correlation coefficient has a regular diurnal orsemi-diurnal variation pattern.In conclusion, the paper studies the morphological features of the mid-latitudeE_s by both the data statistic and the theoretical calculation. After a comparison of datastatistic results, the reliable part of the theory is confirmed and its irrationality isdiscussed. By this analysis, we can understand the sporadic E-layers in more detail.