透過ISEE-1衛星上Hot Plasma Composition Experiment（HPCE）儀器的電漿量測與AMPTE衛星的Charge Composition Explorer磁場觀測，我們發現太陽風粒子在地球船頭波前方與進入磁鞘區後的特性顯著不同。統計HPCE資料顯示經過船頭波加熱後，磁鞘區粒子的非均向性（anisotropy）溫度分布為：(1) He2+與H+的非均向性（T/T||）比值(T/T||(He2+))/(T/T||(H+))=1.240.12；(2)平行磁場方向的熱速度比為Vth||(He2+)/Vth||(H+)=0.890.09；(3) He2+離子與H+離子的溫度（T=(2T+T||)/3）比值T(He2+)/T(H+)=3.770.63，略小於其質量比；(4)垂直磁場的溫度分量比值T(He2+)/T(H+)=3.950.68。我們認為這些性質主要是緣於船頭震波直接對粒子的加熱作用。本文應用混合粒子碼模擬，以實際太陽風（96% H+ and 4% He2+）的粒子組成及測試的O+粒子，探討高馬赫數船頭（MA=4~10）震波對H+離子與重離子（He2+, O+）的加熱。
　　在船頭波前方的太陽風粒子具有相同熱速度的狀態下，我們以（MA=8, =1, =80）之上游參數來模擬快震波加熱，分析得出下列結果: (1)He2+與H+的非均向比值(T/T||(He2+))/(T/T||(H+))=1.31 0.44；(2) Vth||(He2+)/Vth||(H+) =0.860.10；(3)T(He2+)/T(H+)~3.53；(4) T(He2+)/T(H+)~3.71。進一步累計MA=4, 6, 8, 10與=50, 60, 70, 80各種不同強度震波的統計結果顯示﹕(1)He2+與H+的非均向比值(T/T||(He2+))/(T/T||(H+))=1.200.35；(2)Vth||(He2+)/Vth||(H+)=0.920.09；(3)T(He2+)/T(H+)~3.74；(4)T(He2+)/T(H+)~3.89。這些模擬數據皆與HPCE觀測值相當吻合，我們的研究顯示船頭快震波的直接加熱可有效地改變太陽風粒子的溫度分布特性。

　　ISEE-1/HPCE and AMPTE/CCE observations in 1984 showed that the thermal temperatures of protons (H+) and helium ions (He2+) are anisotropic in the magnetosheath. Statistical analysis shows the anisotropy (T/T||) and temperature ratio between protons (H+) and helium ions (He2+) are: (1) the anisotropy ratio is (T/T||(He2+))/(T/T||(H+))=1.240.12; (2) the ratio of parallel thermal velocities is Vth||(He2+)/Vth||(H+)=0.890.09; (3) temperature (T=(2T+T||)/3) ratio is T(He2+)/T(H+)=3.770.63; (4) perpendicular temperature ratio, T(He2+)/T(H+)=3.950.68, is very close to the mass ratio. We suggest these properties are mainly resulted from the particle heating by Earth’s bow shock, where other post heating processes behind bow shock (i.e., in the magnetosheath) can be neglected. We applied hybrid simulations to study the anisotropic heating of H+, He2+ and O+ ions by Earth’s bow shock with various value of Alfvén Mach number MA=4~10. In simulations, the particle distributions consist of realistic solar wind with 96% H+ and 4% He2+, and additional test O+ particles which do not feedback to the variations of density and current in the simulation system.
　　We first set the typical parameters upstream of bow shock with MA=8, =1, =80. We assume H+ and He2+ ions in the upstream of shock have same thermal velocities. The simulation results show that (1) (T/T||(He2+))/(T/T||(H+))=1.310.44; (2) Vth||(He2+)/Vth||(H+)=0.860.10; (3) T(He2+)/T(H+)~3.53; (4) T(He2+)/T(H+)~3.71. In spite of this single case analysis, we also simulate cases with different Mach numbers (MA=4, 6, 8, 10), plasma betas (=0.5, 1, 1.5) and shock normal angles (=50, 60, 70, 80). The average values obtained from simulations show: (1) (T/T||(He2+))/(T/T||(H+))=1.200.35; (2) Vth||(He2+)/Vth||(H+) =0.920.09; (3) T(He2+)/T(H+)~3.74; (4) T(He2+)/T(H+)~3.89. It is found that the average values are closer to the spacecraft measurements than one typical case. Our study shows that the solar wind temperature anisotropy can be effectively generated by the Earth’s bow shock heating. The shock heating mechanism can explain the temperature observations for H+ and He2+ ions in the magnetosheath.

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