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Advanced method to derive the IMF direction near Mars from cycloidal proton distributions

机译：根据摆线质子分布推导火星附近IMF方向的先进方法

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In a previous paper, we showed a method for deriving the interplanetary magnetic field (IMF) orientation from the velocity distribution of ring-like distributed ions as measured by the Ion Mass Analyser (IMA) on board Mars Express (MEX). This method has been improved so that one can derive the IMF orientation from a very limited portion of the ring distributions, i.e., only the highest energy portion of the ring distribution. This method uses the maximum variance direction L instead of the minimum variance direction N, which are derived from manually selected ring data. Because IMA's count rate for a semi-persistent ring distribution is nearly proportional to energy squire, L is most likely aligned to the tangential direction of the ring distribution at its highest energy, and this tangential direction is parallel or anti-parallel to the electric field. A vector product of L and the solar wind direction (X) gives the IMF orientation projected to the Y-Z plane. The tilt angle of IMF toward the X direction from the Y-Z plane is the same as the angle between the X direction and the ring plane, and is obtained from two methods when the initial speed of the ring ions is estimated to be much smaller than the solar wind speed: (1) angle between the velocity of ring's maximum energy portion and the solar wind vector, and (2) energy ratio between the solar wind and the maximum energy of the ring. The present method is applied to the IMA data from 3 June 2005 (0605-0640 UT) when the Mars Global Surveyor (MGS) magnetometer data are available. Using these data, we also tried to determine the sign of the IMF direction by estimating the evolution direction of the ring ions.
机译：在先前的论文中，我们展示了一种方法，该方法可通过由Mars Express（MEX）上的离子质量分析仪（IMA）测量的环状分布离子的速度分布来推导行星际磁场（IMF）方向。对该方法进行了改进，以便可以从环分布的非常有限的部分（即仅环分布的最高能量部分）得出IMF方向。该方法使用最大方差方向L代替最小方差方向N，后者是从手动选择的圆环数据中得出的。因为IMA对于半永久性环分布的计数率几乎与能量需求成正比，所以L最有可能在其最高能量下与环分布的切线方向对齐，并且该切线方向与电场平行或反平行。 L与太阳风向（X）的矢量乘积给出了投影到Y-Z平面的IMF方向。 IMF从YZ平面向X方向的倾斜角度与X方向与环平面之间的角度相同，并且当估计环离子的初始速度远小于环离子的初始速度时，可以通过两种方法获得太阳风速：（1）环的最大能量部分的速度与太阳风矢量之间的夹角，以及（2）太阳风和环的最大能量之间的能量比。当火星全球测量师（MGS）磁力计数据可用时，将本方法应用于2005年6月3日（0605-0640 UT）开始的IMA数据。使用这些数据，我们还尝试通过估计环离子的演化方向来确定IMF方向的符号。

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