Investigation Of Low-frequency Waves In The Solar Wind, Foreshock And Magnetosheath

The magnetosheath and foreshock are the key regions which somewhat mod-ify and then transmit the solar wind variations to the Earth's magnetosphere.Moreover, the waves generated in the foreshock and magnetosheath regions evenunder the quiet solar wind conditions can strongly aflect the near-Earth's en-vironment and their role is very important in all issues related to the"spaceweather". Based on the multiple spacecraft observation such as TC-1, Cluster,Interllball and ACE, this work focuses on the investigation of low-frequency wavesin the solar wind, foreshock and magnetosheath.First we study the characters of the fluctuations in the solar wind and mag-netosheath region by analyzing the data observed by Interball-1 during 01.1997fl10.1998. The results of case and statistical studies show that the level of relativevariations of ion flux and magnetic field magnitude in foreshock is about 3 timeslarger than in undisturbed solar wind. Variations of these parameters in MSHare about two times larger than those in MSH⊥. The fluctuations in the mag-netosheath are strongly controlled by theθBn of upstream bow shock. We alsoanalyze the data observed by Cluster during 01.2001fl01.2003, and compare theresults with those from Interball-1 data analysis. The magnetic field variationsobtained from the diflerent spacecrafts data coincide with each other very wellnot only in quality but also in quantity, even though the spacecraft made theobservations in diflerent time interval of the solar cycle. The fast magnetosonicwaves are found in the foreshock region and the almost compressional waves arefound in the quasi-perpendicular magnetosheath.In order to study the influence of the latitude on the fluctuations in themagnetosheath, we analyzed the data observed by TC-1 and Cluster during 2004in the magnetosheath. Despite the diflerent latitudes of the orbits, the statisticalresults from these two spacecrafts data analysis are very close to each other. Thisshows that there is little dependence of the latitude on the fluctuations. With theincrease of the local plasmaβ, both the magnitude and direction of the magnetic field fluctuate more intensely. There exists an inverse correlation between thelocal temperature anisotropy T⊥/T and the plasmaβ.In order to further investigate the waves in the magnetosheath and theirtransition, we use two methods of mode identification. The first one is to identifythe mirror waves only by the magnetic field data. Using the minimum varianceanalysis, the angleαeB between the maximum variance direction and the meanmagnetic field is calculated. Cooperated with the relative standard deviation(RSD) of the magnetic field, the mirror structures can be identified. We applythis method to the magnetic data observed by TC-1 on 26 February 2004. Themirror structures are found in the inner magnetosheath near the subsolar point.The other method of mode identification is based on a hierarchical deterministicscheme with a tree-root structure. Using this method, we also analyze the caseof TC-1 on 26 February 2004. The preliminary results show that (1) The innermagnetosheath behind a quasi-perpendicular bow shock is dominated by mirrorwaves between 0.01 and 0.06 Hz, which is the same as those from the first method.(2) In the outer magnetosheath that is downstream of a quasi-parallel bow shock,the wave modes between 0.01 and 0.06 Hz are identified as Alfv`en modes. (3)The middle magnetosheath is considered to be the transition region, where theMirror and Alfv`en waves are likely to exist together. There is an apparent modetransition which is probably due to the rotation of the interplanetary field (IMF).