The Response Of The Mesospheric/Lower Thermospheric Metallic Layered Phenomena To Thunderstorms In The Lower Atmosphere

Metal sodium(Na)is one of the major meteoric materials existing as layers of metal atoms in the Mesosphere/Lower Thermosphere(MLT)region at altitudes between 80 and 105 km and atomic ions at altitudes between 90 and 130 km.The MLT region is the boundary between neutral and ionized atmosphere.It can be affected by the mesoscale convective weather and thunderstorms/lightning from lower atmosphere and also can be exposed to solar high energy particles from upper atmosphere.Therefore,the char?acteristics of atmospheric dynamical and photochemical processes in the MLT region are very complex.The variation of neutral atomic sodium density is controlled by atmospheric com?position,the atmospheric temperature and the vertical wind shear.The neutral sodium atom layer can be measured by the sodium resonance fluorescence lidar which is the tracer for exploring the variation of the atmospheric properties,the dynamical processes and chemical processes in the MLT region.The ionospheric sporadic E(Es)layer is usually composed of metallic ions such as Fe+,Na+ and its variation was attributed to the influence of solar activity,geomagnetic activity,and atmospheric composition.Recently,tropospheric thunderstorms and lightning are found to affect the lower iono?sphere.There exists an insufficient observational capability in the MLT region,especially in the neutral atmosphere observations.In the last several years,China has established its new chains of geospace environment monitoring stations across China mainly along 120°E longitude and 30°N latitude.It is called the Meridian Space Weather Monitoring Project(Chinese Meridian Project).In this study,we investigate the metallic sodium ions and atoms in the MLT region on the basis of the Chinese Meridian Project observa-tions.The metallic layered phenomena are particularly studied to explore the coupling of the lower atmosphere and upper atmosphere.Furthermore,the previous studies of the coupling between the sporadic E layers and the sporadic sodium layer could be proved.The main works and results are listed as follows:Firstly,on the basis of the Constellation Observing System for Meteorology,'Iono-sphere,and Climate(COSMIC)GPS radio occultation(RO),a global map of the inten-sity of Es layer between 90 and 130 km is retrieved.The general morphologies of the Es layer are studied for the period from 2006 to 2014.It is found that the distribution of Es layer is associated with the geomagnetic field.Besides,the Es layer also shows a seasonal dependence with a summer hemisphere maximum,similar to the seasonal variation of the occurrence of the Es layer.Secondly,we analyze the World-Wide Lightning Location Network(WWLLN)lightning data and the ionospheric Es observation observed by ionosondes at Sanya and Beijing stations in the Chinese Meridian Project.The changes in ionospheric electron density in the Es layer above thunderstorms in response to lightning events are exam-ined.A statistically significant enhancement of the critical frequency,?foEs and a de-crease in the virtual height,?foEs are identified at Sanya station after lightning during thunderstorms.It is found that the lightning-associated enhancement of the Es layer is dependent on the lightning stroke energy,which is predominantly attributed to hight-energy lightning.The lightning-generated gravity waves(GWs)could be the potential mechanism which inject the energy to reinforce the Es layer.Thirdly,a new phenomenon of the coupling of the mesospheric neutral metal sodium(Na)layer and thunderstorms is presented.We use the Haikou sodium lidar observa-tion and the WWLLN lightning data to investigate the influences of thunderstorms on the mesospheric sodium layers.The atomic sodium density and the column density are extremely enhanced 19 h after lightning during thunderstorms.It is first revealed that the thunderstorms could affect the metal layer at altitude of around 90 km based on a robust analysis of a very large data set.Finally,the cases of the enhancement of sodium layers during thunderstorms si-multaneously with the enhanced Es layer are further analysed,to study the possible mechanism responsible for these metallic layered coupling phenomena during thun-derstorms.The mesospheric Na chemistry are considered in a Na chemistry model to study the chemical processes of the lightning-associated enhancement of Na layer and Es layer.A thunderstorm-ionosphere model is also used to investigate the changes of electron density in the ionosphere E layer during thunderstorms.The thunderstorm-generated electric field and thunderstorm-generated GWs could be the mechanism for the enhancement of the neutral atomic sodium densitiy and Es layer after lightning.The mesospheric metal Na layer and the ionospheric sporadic E layer undergo a significant response to lightning above intense thunderstorms.These lightning-associated metallic layered phenomena show evidence that the lower atmosphere and upper atmo-sphere are tightly coupled.These coupling processes from the lower atmosphere to the upper atmosphere would affect the whole atmospheric dynamical and chemical pro-cesses as well as the atmospheric properties.Therefore,the influence of thunderstorms on the metal layers in modelling and observation should be further investigated.