摘要
基于高斯分布的哨声波谱密度分布、偶极子背景磁场模型以及建立在卫星观测数据基础上的半经验电子密度纬度分布模型,对于等离子体层顶以外区域(4≤L≤7),计算了准线性当地及弹跳平均电子共振扩散系数,并估算了与磁层哨声波回旋共振导致的辐射带电子损失及加速时间尺度.结果表明,波粒共振相互作用区域取决于电子能量、波谱分布、电子赤道抛射角以及当地电子密度及背景磁场.哨声波共振频率除了与以上5个参量有关外,还与地磁纬度有关.赤道哨声波主要影响较低能量辐射带电子的加速,中高纬度哨声波主要作用于较高能量辐射带电子的沉降损失.对于较低能量(约200keV)的辐射带电子,磁层哨声波可以在几个小时内使之沉降,对于较高能量(约1MeV)的电子,则需要一到数天;对低能量(约200keV)电子的加热可以在数小时内完成,回旋加速较高能量(约1MeV)电子一般则需要3—4d.电子密度分布的改变能够明显影响电子共振损失时间尺度,但是对电子共振加速时间尺度的作用很小.随着电子密度增强幅度随纬度的上升而增大,电子共振损失时间尺度会随之增大,但是电子共振加速时间尺度基本上不变化.另外,哨声波幅度及频谱随L及纬度的分布也显著影响它对辐射带电子的共振扩散效果,这些作用一般要大于电子密度分布变化带来的影响.
Adopting the dipole geomagnetic field, Gaussian spectral density for the waves, and semi-empirical latitudinal electron density models obtained from available in situ data, this paper has calculated the local and bounce-averaged quasi-linear resonant electron diffusion coefficients due to chorus and then determined the timescales for electron precipitation loss and stochastic acceleration, in the range of 4 ≤ L ≤ 7 outside the plasmapause. The results indicate that the spatial extent where gyroresonance occurs depends on electron energy, equatorial pitch angle, wave spectrum, and the local electron number density and magnetic field. Besides these five parameters, the actual values of resonant frequency rely on magnetic latitude where resonance occurs. The acceleration of radiation belt energetic electrons occurs predominantly due to equatorial chorus, and the mid-latitude chorus preferably contributes to the precipitation loss of relativistic electrons. The timescales for both electron loss and acceleration due to chorus-driven diffusion have been evaluated to be of hours for lower-energy electrons （about 200 keV） and of days for higherenergy electrons （about 1 MeV）. It is also found that variation of latitudinal density distributions contributes importantly to chorus-driven electron resonant diffusion. In general, an increasing latitudinal electron density increases the loss timescales for untrapped electrons with small equatorial pitch angles, but has negligible effect on the acceleration of trapped electrons with large equatorial pitch angles. The variations of chorus wave amplitude and wave spectrum with magnetic latitude and L-shell also make important contributions to the lifetime and acceleration of radiation belt electrons, which are generally greater than the effects of varying latitudinal distribution of cold plasma density.
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2008年第12期7937-7949,共13页
Acta Physica Sinica
基金
国家自然科学基金(批准号:40774100)资助的课题~~
关键词
共振波粒相互作用
地球辐射带
哨声波
回旋共振加速及散射沉降
resonant wave-particle interaction, earth＇s radiation belt, whistler-mode chorus waves, cyclotron resonant acceleration and diffusion precipitation
