Magnetic Reconnection And Local Heating In Magnetic Cloud Boundary Layers

Magnetic Clouds(MCs)are large transient structures originated from the Sun.A boundary layer(BL)would form as a result of the interaction between the MC and the ambient solar wind,with turbulent magnetic field and heated plasma inside.In this dissertation,observational studies on magnetic reconnection(MR)and turbulence inter-mittent heating in the MCBLs as well as a preliminary study of turbulence intermittent heating in the MC sheath are carried out.Magnetic reconnection is prevalent in the solar wind.The direct evidence of inter-planetary magnetic reconnection is a pair of back-to-back Alfvénic outflow jets based on Petschek reconnection model.However,the slow shock pair bounded the exhaust,as an observational evidence for Petschek-type reconnection,has been rarely observed.We report a slow shock pair associated with a reconnection exhaust(RE)in the MCBL observed by WIND spacecraft on June 2nd,1998.Both shocks are in great agreement with the characteristics of slow shocks:(1)the intermediate Alfvén Mach numbers were both below unit in the up/downstream region;(2)the slow Mach number was above unit in the upstream side but below unit in the downstream side.Rankine-Hugniot relations are also satisfied for both shocks.Our work confirms that a Petschek-type exhaust could form in the collisionless solar wind.In turn,magnetic reconnection process could be a source generating interplanetary slow shocks.Interplanetary REs are considered to be not as common in the MCBLs as in the low-?solar wind.A pair of back to back REs are identified in the front BL of a heavily studied MC observed by WIND spacecraft on October 18th,1995.Except for the two REs indentified in our study,at least two other REs have been identified in another seperate study,suggesting the abundance of MR processed in the MCBLs.The abundant MR processes in the MCBL may affect the power spectrum density(PSD)of magnetic field.The PSD in the leading sheath shows a Kolmogorov-like power law with a slope of-1.67 in the inertial range,but is flattened in the MCBL.Intermittent structures in the solar wind are found to be associated with local en-hancements of ion temperature.A statistical study of intermittent structures in 74 MCs revealed that BLs are more intermittent than adjacent sheath regions,and they con-tain a greater concentration of strong intermittencies.These strong intermittencies are accompanied by local enhancements of the proton temperature.Since the strong inter-mittencies are associated with MR processes according to previous studies,these results indicate that MR processes may account for the local heating in the MCBLs to a large extent.Meanwhile,the proton heating effects around the intermittent structures within the turbulent sheath regions of MCs are investigated.It is found that the proton temperature enhancement near coherent structures in the MC sheath is not as remarkable as in the solar wind.Significant temperature increase only exist near coherent structures with great directional changes(>45~?)in magnetic field or intensity changes(?10%of the mean magnetic field magnitude),which merely account for 13%of the total 12426identified intermittent events in the 71 studied MC sheaths.The temperature increment is more evident near strong current sheets with great directional changes(>45~?)at smaller scales than those at larger scales.It suggests that the heating effects in the MC sheath regions are likely to be highly localized.In addition,a brief review of theoretical models of three-dimensional magnetic reconnection is given in Chapter 6.