Characteristics Of The Far Ultraviolet Radiation Of Auroral Precipitated Particles And Aurora Detection Methods

The auroral ovals around the Earth's magnetic poles in both hemispheres are produced by the collisions between the magnetospheric energetic particles precipitating into the polar region through the Earth's magnetic field lines and the atoms and molecules in the upper atmosphere.Variations of the aurora are closely related to the ionosphere,the magnetosphere,the solar wind,the couplings between them and also the geomagnetic activities.Study on aurora can help us understand not only the varied rules of the solar wind and the geomagnetic field,but also the forecasts of the substorms.The wide-view auroral imager(WAI),onboard the Chinese FY-3 satellite,detects the variations of aurora in Lyman-Birge-Hopfield band(LBH: 140-180nm)at 830 Km from the earth.It provides the real-time data for studying the aurora and the magnetosphere.This dissertation is mainly targeted on the LBH radiation properties of the aurora and constructing algorithms and models to deal with the existing auroral data,and thus to provide basis for the analysis of the WAI images.The methods of theoretical model simulation combined with satellite data analysis are adopted in this dissertation to investigate the FUV radiation properties of the aurora and the dynamic properties between aurora and the solar wind,the interplanetary magnetic field and the geomagnetic activities.The results show that:(1)Introducing and analyzing the structures and the capabilities of four instruments that used to observe the aurora in FUV bands,including POLAR/UVI,IMAGE/WIC,TIMED/GUVI and DMSP/SSUSI.And then,we described the design,framework,and properties of the WAI that was developed by Chinese.The observed window of WAI is 140-180 nm,the resolution ratio in sub-satellite point is 10 Km,and the resolution ration of time is less than 2 minutes which represent 1 frame.The field of view is 130°×130° at an altitude of 830 Km,and these parameters can make sure that the instruments in the lower orbits can acquire the global auroral images.(2)A new method to remove dayglow for auroral observation of the Special Sensor Ultraviolet Spectrographic Imager(SSUSI)aboard the Defense Meteorological Satellite Program(DMSP)F16 in Lyman-Birge-Hopfield(LBH)ranges based on the improved Atmospheric Ultraviolet Radiance Integrated Code(AURIC)algorithm is proposed.This method is developed by determining the relationship between the results calculated by the improved AURIC algorithm and the data from SSUSI in the whole 2005.The least-square polynomials are used to fit our results to the observations and their degrees are set to be 5,7 and 9 in three Ap ranges.The coefficients of the polynomials,divided by Ap indices and solar zenith angles(SZA),can be used to simulate the dayglow intensity in the north polar region at a altitude of 110 Km.The improvements of the new AURIC algorithm include two aspects: 1)update the initial modules and extend the time range of calculation,2)consider the variation of azimuth and solar zenith angle(SZA)along the line of sight(LOS).The fitting precisions and deviations,also the three tested examples demonstrate that this method is feasible and reliable.The proposed method provides us with a useful tool to remove the dayglow from the auroral observation.(3)An automatic auroral boundary determination algorithm is proposed based on the partial auroral oval images from the Global Ultraviolet Imager(GUVI)aboard the Thermosphere Ionosphere Mesosphere Energy and Dynamics(TIMED)satellite and the Special Sensor Ultraviolet Spectrographic Imager(SSUSI)aboard the Defense Meteorological Satellite Program(DMSP F16).This algorithm based on the fuzzy local information C-means clustering(FLICM)segmentation,can be used to extract the auroral oval poleward and equatorward boundaries from merged images with filled gaps from both GUVI and SSUSI.Both extracted poleward and equatorward boundary locations are used to fit the global shape of the auroral oval with a off-center quasi-elliptical fitting technique.Comparison of the extracted auroral oval boundaries with those identified from the DMSP SSJ observations demonstrates that this new proposed algorithm can reliable be used to construct the global configuration of auroral ovals under different geomagnetic activities at different local times.The statistical errors of magnetic latitudes of the fitted auroral oval boundaries were generally less than 3° at 2 sigma and indicate the the fitted boundaries agree better with b2 e and b5 e than b1 e and b6 boundaries.This proposed algorithm provides us with a useful tool to extract the global shape and position of the auroral oval from the partial auroral images.(4)Three auroral models responded to the solar wind,the interplanetary magnetic field,and the geomagnetic indices were constructed.The aurora-Kp model(model 1),was constructed by fitting the auroral data observed by TIMED/GUVI along the MLT lines with Epstein function.The auroral boundary model(model 2),was constructed by fitting the auroral boundaries extracted from POLAR/UVI auroral data with multiple linear regression function.The parameters embedded in model 2 include the velocity of solar wind(Vsw),the density of proton(Nsw),three components of IMF(Bx,By,Bz)and the auroral electrojet index(AE).The auroral model(model 3),was constructed with three parameters including Akasofu's solar wind-magnetosphere coupling function ?=VSWBTsin4(?c/2),the ring current index(SYM-H),and AE.After analyzing the correlations and relations between auroral boundaries and various parameters,the linear fittings between auroral boundaries and ?,SYM-H,AE were adopted to establish the auroral boundary model.The distributions of the average energy and flux of the precipitated particles were also fitted by Epstein function.These models will be useful in a number of applications: global ionosphere/thermosphere simulations,space weather forecasting and nowcasting,and global auroral/ionospheric models.