The Study Of Ionospheric Irregularities Associated With Scintillations Over The Polar Region

The polar ionosphere is an important part and key layer in the whole solar-terrestrial coupling system,where the Earth' s magnetic field lines are extremely convergence and vertical in and out.Therefore,the variety of dynamic processes of solar wind-magnetosphere-ionosphere couplings are directly mapping to the polar ionosphere through these connected field lines,which are hence driving the large-scale convection cell and also producing particle precipitation in this region,consequently generating a large number of ionospheric irregularities in dif-ferent scales,such as storm-enhanced density(SED),tongue of ionization(TOI),polar cap patch,auroral oval and high-latitude trough,etc.During the evo-lutions of these newly formed irregularities,they are probably structuring into smaller pieces through the combined effects of plentiful instability mechanisms and then possibly inducing ionospheric scintillations,therefore making the polar ionosphere as one of the regions of high occurrence of scintillations on Earth.Re-cently,as increasing of our space activities and expanding of the navigation and communication systems,there is a rapidly growing requirement to comprehen-sively monitor and forecast the disturbances of the polar ionosphere and also the activities of ionospheric scintillations.Consequently,they are urgently putting on the agenda to monitoring and investigating and simulation the evolution of large-scale structures associated with ionospheric scintillations in a widely polar region.In this paper,we are mainly focusing on the investigation of the large-scale irregularities in the polar ionosphere as well as the corresponding effects of ionospheric scintillations.We have developed a method named by Total Elec-tron Content(TEC)keogram from TEC maps to continuously and conveniently tracking the large-scale structures in the polar ionosphere along three different directions,and then constructed the comparison tool between the mentioned ir-regularities and scintillations in a broad zone,as well as comprehensively explored the characteristics of ionospheric irregularities in the F layer and E layer of the polar ionosphere,as well as the related behaviours of scintillations,respectively.Morevoer,we also continued the study of scintillation theory as well as initially modelling.The detailed contents are as follows:1.Created the TEC keogram to tracking the large-scale structures extracted from global TEC maps,and applying to the case and statistical studies of polar cap patchesWith a growing number of navigation satellites and ground-based receivers,the global coverage of TEC data is getting better and better,which is released and updated on time by the madrigal online website since more than 10 years,providing us a unique way to monitoring the whole polar ionosphere.To fully taking advantage of this yearly denser TEC data,a tool named by TEC keogram has been developed to tracking the formation and evolution of large-scale struc-tures continuously in the polar ionosphere,which is basically following three well defined directions.Hence,it is expectantly help to carrying out case study easily and also performing statistical study conveniently.Moreover,to further validate the newly released tool,a comparison between TEC keogram and SuperDARN observation had been launched,briefly conclud-ing that the catched polar cap patches by the TEC keogram were corresponding to the structured backscatter of SuperDARN radar one by one,as well as with similar speeds measured by these two ways.According to the motion of these observed irregularities,the averaged speeds of their movements could be roughly estimated,which are also indicating the convection speeds,as well as the evolu-tion period and also life time.Furthermore,based on a large number of revealed polar cap patches from TEC keogram in the whole year of 2015,a statistical study had been carried out,suggesting that the occurrences of these patches on the months and UTs,respec-tively,were fundamentally consistent with previous studies and also founding that the mean time of all polar cap patches moving from dayside segmented re-gion to reaching nightside auroral oval was around 2 hours.In addition,from the statistical study,the dayside magnetopause reconnection is probably the main mechanism on creating polar cap patches because most of patches occurred with the southward IMF conditions under which the magnetopause reconnection is favored,when southward stronger the averaged speed faster.2.Established a widely comparison tool to investigating the large-scale irregularities and also the corresponding scintillations simultaneously,as well as discussing possible mechanismsBased on the global TEC data,which was downloaded from the madrigal database,and the vast scintillations in Canadian sector of arctic using by CHAIN,a comparison tool had been firstly proposed by mapping the scintillations on a previously created TEC map and following their IPPs at an assumed altitude of 350km,which is offering us a good chance to continuously monitoring a great number of large-scale irregularities associated with scintillations over an extensive region in the polar ionosphere.Regarding this tool,a case study has been started on 27 Feb 2014.During this interval,a moderate storm had been produced by a reached Coronal Mass Ejection(CME),consequently creating the high-density structures like storm enhanced density(SED)or tongue of ionization(TOI).Meanwhile,these irreg-ularities had also been segmented into a series of polar cap patches.From the TEC map and also TEC gradients,several types of irregularities could be clearly identified,at least including SED/TOI,middle-latitude trough,polar cap patch,auroral oval.Referring to the scintillation measurement simultaneously,the pe-culiar behaviours of scintillations occurred around at different irregularities or regions.According to this unique scintillation phenomena,the polar ionosphere can be roughly divided into four characterized regions:SED segmented region,middle-latitude trough region,polar cap and auroral oval.Based on this specific event,it could be simply concluded that the phase scintillations were increasing along with the stronger or reversal flows in the SED segmented region and also the equatorward of middle-latitude trough region without the amplitude scintilla-tion,and in the polar cap both of the scintillations were weak,while in the auroral oval a particular phenomenon had been found that the amplitude scintillation was stronger than the phase scintillation,which was the first time to reporting in high latitude,possibly caused by the particle precipitation structured the polar cap patch exiting from polar cap into auroral oval.3.Comprehensively explored the characterize of Es layers in the polar iono-sphere and also the induced TEC variations and scintillations,enriching our knowledge of Es layersMost of the large-scale irregularities we focused on are usually appearing in the F layer of ionosphere.However,in the E layer,there are also high-density structures.Es layers is just a common irregularity in this lower layer.But due to the limitation of observations,until now the understanding of Es layers was also little especially in the polar region.Fortunately,Resolute Bay station provides us a unique opportunity to inves-tigate Es layers in detail using by the joint observations of multiply instruments(CADI,ISR-N incoherent scatter radar,ground-based GPS receiver),founding that the Es layers is probably a band-like structure in horizontal and extending more than 200km,one sector is moving from dayside to nightside which is pos-sibly driven by the strong E field,however,another one is keeping still which is likely regarding to the gravity wave.Moreover,the TEC variations caused by Es layers had also been determined as that the pulse-like variations followed by rapid but smaller fluctuations with peak TEC variation no more than 2TECu(normally 0.5TECu).Furthermore,the scintillations regarding to Es layers were firstly reported that the mean spectral slope of amplitude scintillation(-1.10)and phase scintillation(-1.25)in power spectral density,generally weaker than the scintillations from F layer irregularities and also auroral particle precipitations.4.Firstly validated the severe dependence of phase scintillation index on plasma flows through the observation measurements,strongly challenging the application of this index in the polar regionThe firstly experimental evidence had been presented to determining that the dependence of phase scintillation index is obviously higher than amplitude scintillation index on the plasma flows in the polar ionosphere using by Super-DARN radars and GPS receivers in CHAIN,questioning the reliability of phase scintillation index especially when applied to the polar ionosphere.Decades,this traditional phase scintillation index are always used to study-ing the polar ionosphere,which was originated from the precedent one in the low latitude region.However,this index is possibly not good enough to adapting the high latitude conditions particulary undescintillation r strong or variable convection flows because it is easily producing the popular phenomenon of "Phase without am-plitude" scintillations that the phase index is growing obviously but not the amplitude scintillation index.In order to figuring out this specific issue,the theory of phase screen scintillation has been carried out,probably pointing to that under stronger flow conditions the fresnel frequency,attaining to scintilla-tion window,is drifting to higher sector,as well as many quantification analyses.After that,the phase scintillation index is consequently getting greater,which is also calculated by the same way with a fixed cutoff frequency.But referring to the amplitude scintillation index,it is not much sensitive to the moving of fresnel frequency like the phase scintillation index due to the existed filter effect at around the fresnel frequency.Unluckily,this well explanation from theory is always lacking powerful support from observation measurements directly.5.Introduced a preliminary empirical scintillation model at high latitudes,basically applying to forecast/nowcast over the polar regionWe are always trying to modify the scintillation model to making better forecast/nowcast.However,until now most of these models are just providing climatic prediction.To better investigating ionospheric scintillations in the arctic beyond the previous ones,an empirical scintillation model was introduced as a function of B-spline in order to outputting a finely scintillation map using by ground-based GPS receiver at Svalbard,which was then checked by the results from linear interpolation method.Moreover,to improving the performance of application and service in the near future,more data from a large number of ground-based GPS receivers in the polar region could also be adopted by this scintillation model.In conclusion,in this paper the research results can fully extend our knowl-edge of large-scale irregularities associated with scintillations in the polar iono-sphere,establishing the tools of TEC keogram to tracking irregularities in F layer of polar ionosphere and also a widely comparison map between structures and scintillations,comprehensively expanding the understanding of Es layers in the polar cap,initially starting an empricial scintillation model at high latitudes to improving the potential ability to give out better nowcast and/or forecast of ionospheric scintillations,and then expecting to making better qulity of commu-nications and navigations over the polar region.