地球磁层顶湍动重联的数值模拟

NUMERICAL SIMULATION OF TURBULENT RECONNECTION AT THE MAGNETOPAUSE

用二维磁流体力学数值模拟研究了磁层顶的磁场湍动重联．提出了一个新的磁场湍动重联模型．数值模拟表明，如果磁层顶是一个开放系统并同时存在磁场剪切和流场剪切，当雷诺数和磁雷诺数超过某临界数值时，磁场重联具有很强的湍动特性，可产生许多不同尺度的磁岛和涡旋结构．随着雷诺数和磁雷诺数的增大和减小，大尺度结构能破碎成中小尺度结构，小尺度结构也能合并成大中尺度结构．湍动重联是涡旋诱发重联在一定条件下的过渡．依据本文的模拟结果，我们预言：磁层预可发生准定常重联、瞬时局地重联和湍动重联等多种重联过程；大中小不同尺度的结构都可以存在于磁层顶；湍动重联及其所产生的中小尺度结构在太阳风－磁层的能量、动量和质量耦合过程中可起重要作用．

A 2-D MHD simulation model is presented to study turbulent reconnectlon at the magnetopause. A new turbulent reconnection model is proposed.Numerical simulation shows that, if(1) a sheared flow and a current sheet simultaneously exist at the magnetopause,(2) the magnetopause current sheet Is an open system, and(3)the Reynolds and magnetic Reynolds number(R and Rm) in the transition region are greater than some critical values,the reconnection process possesses a strong turbulent feature,leading to the appearance of irregular meso and small-scale structures (IMSSSs). The larger Rm and R are,the more IMSSSs are produced.The stronger the velocity is, the quicker IMSSSs occur. Large and meso-scale structures can break into meso and small-scale ones as Rm and R are substantially increased. Based on our simulation results, we expect that quasi-steady state reconnection,transient and patchy reconnection,and turbulent reconnection may all take place at the magntopause;large,meso and small-scale structures may all be found there. Turbulent reconnection and meso andsmall-scale structures may play an important role in energy,momentum and mass transport from the solar wind to the magnetosphere.