Observational Study On The Meso-and Micro-scale Structures In The Solar Wind

In this dissertation, observational study on the magnetic cloud boundarylayers (MCBLs) and the related micro-scale structures are made with emphasis onthe slow shock identification, the global magnetospheric responses to the passagesof MCBLs as well as the plasma waves within MCBLs.The observations of the slow shocks associated with the interplanetary coro-nal mass ejections near 1 AU have seldom been reported in the past severaldecades. Here we report the identification of an interplanetary slow shock ob-served by WIND on September 18, 1997. This slow shock is found to be just thefront boundary of a MCBL. A novel self-consistent method based on the entireRankine-Hugoniot relations is introduced to determine the shock normal. It isfound that the observations of the jump conditions across the shock are in goodagreement with the Rankine-Hugoniot solutions. In addition, the typical interiormagnetic structure inside the shock layer is also analyzed using the 3s time res-olution magnetic field data since the time for the spacecraft traversing the shocklayer is much longer (about 17 s). As a potential explanation to the formationof this kind of slow shock associated with magnetic clouds, this slow shock couldbe a signature of reconnection that probably occurs inside the magnetic cloudboundary layer.A double discontinuity is a rarely observed compound structure composedof a slow shock layer and an adjoining rotational discontinuity layer in the down-stream region. Also we report the observations of a double discontinuity detectedby WIND on May 15, 1997. This double discontinuity is found to be the frontboundary of a magnetic cloud boundary layer. We strictly identify the shocklayer and the rotational discontinuity layer by using the high resolution plasmaand magnetic field data from WIND. The observed jump conditions of the up-stream and downstream region of the slow shock layer are in good agreementwith the Rankine-Hugoniot relations. The magnetic cloud boundary layer ob-served by WIND was also detected by Geotail 48 min later when the spacecraft was located outside the bow shock of the magnetosphere. Whereas, Geotail ob-servations showed that its front boundary was no longer a double discontinuityand the rotational discontinuity layer disappeared. It indicated that this doublediscontinuity was unstable when propagating from WIND to Geotail.The MCBL is a disturbance structure that is located between the magneticcloud and the ambient solar wind. We statistically analyze the characteristicsof the magnetic field Bz component (in GSM) inside MCBLs as well as therelationship between MCBLs and the magnetospheric substorms based on 35typical MCBLs observed by WIND in 1995?2006. It is found that the magneticfield Bz components are more turbulent inside the MCBLs than those insidethe adjacent sheath regions and the magnetic clouds. The substorm onsets areidentified by the auroral breakups that are the most reliable substorm indicatorsby using the Polar UVI image data. The UVI data are available only for 17MCBLs. The statistical analysis indicated that 9 of the 17 events triggered thesubstorms when MCBLs crossed the magnetosphere, and that the southwardfield in the adjacent sheath region is a necessary condition for these triggeringevents. In addition, the"SF"type MCBLs, which are named by their featuresof the Bz components inside MCBLs and adjacent sheath regions, can easilytrigger the substorms during their passage through the magnetosphere."SF"type MCBLs have the characteristics that there are sustaining strong southwardmagnetic fields persisting for at least 30 minutes in the adjacent sheath regionsand the polarity of the Bz component inside the MCBLs changes for at least onetime. 7 out of 8 such type MCBL events triggered the substorm expansion phase,which suggests that the"SF"type MCBLs are another important interplanetarydisturbance source of substorms.The global magnetospheric responses to the passage of one MCBL observedby WIND on November 9 2004 are intensively investigated. An intense geo-magnetic storm main phase is driven by the sustaining strong southward mag-netic field within MCBL. A typical magnetospheric substorm is also triggeredby southward turning after strong southward magnetic field lasting for about30 min. Compared with magnetic cloud body and adjacent sheath region, theMCBL is the enhanced dynamic pressure region which compresses the magneto- sphere into the geosynchronous orbit so that many spacecraft are directly exposedin energetic particles in the solar wind. Furthermore, the front boundary of thismagnetic cloud boundary layer is a rapid dynamic pressure pulse structure whichcan cause global responses of the magnetic field, current, energetic particles inthe magnetosphere and the plasma convection in ionosphere. Most front bound-aries of MCBLs (57%) are rapid strong dynamic pressure pulse structures. Thisexample shows the common characteristics of the magnetospheric responses tosuch dynamic pressure pulse structures. In terms of shue (1998) magnetopausemodel and GOES spacecraft observations, we found MCBLs can intensively com-press the magnetosphere due to the strong dynamic pressure. 8 MCBLs out of 35discussed events even compress the magnetopause into the geosynchronous orbitwhich potentially catastrophic in the point of view of space weather.Two particular types of Langmuir wave activities are found within MCBLs:Langmuir waves enhancement in entire region of MCBLs compared with theadjacent magnetic cloud body and sheath region for majority MCBLs and therapid Langmuir waves burst phenomena associated with broad-band ion-acousticwave activities for a few MCBLs. The analysis by using high resolution electrondistribution data indicates that the bump-on-tail instability resulting from theenergetic electron beam with beam velocity Vb～7×103 km/s is responsible forthe rapid Langmuir waves burst.