There exists large-scale lightning in Saturn's water cloud. Based on the powerful moist convection in the water cloud, we establish a thermal-induced convective model to interpret the mechanism for the processes of charge generation and separation. We also estimate the breakdown field of Saturn's atmosphere quantitatively and interpret the discharge process.
Using the east-west geomagnetic disturbance fields observed from stations at mid-latitudes,we investigate the characteristics of field-aligned currents on the nightside during the April 6,2000 superstorm.The results indicate that there is an eastward disturbance on the nightside of Northern Hemisphere during the main phase of magnetic storm,while the interplanetary magnetic field(IMF)is continued southward.The positive disturbances in the postmidnight are larger than that in the premidnight.This suggests that upward field-aligned currents develop on the nightside,when the IMF is directed southward.The peak of upward fieldaligned currents is located in postmidnight,and it will be more obvious at substorm expansion.We get the conclusion that both partial ring current and region-2 field-aligned current shift to dusk sector.The upward region-2 current is decreased at substorm onset,and intensified after it.We also investigate the relationship between the upward field-aligned currents on the nightside and the auroral electrojets at high latitudes.It shows a good correspondence between region-2 current and the westward electrojet in the postmidnight.We suppose that they are both associated with the convection electric field.
WANG YuanHONG MingHuaCHEN GengXiongXU WenYaoDU AiMinZHAO XuDongLIU XiaoCanLUO Hao
Two-dimensional(2-D)and three-dimensional(3-D)hybrid simulations are carried out for mode conversion from fast mode compressional wave to kinetic Alfvn waves(KAWs)at the inhomogeneous magnetopause boundary.For cases in which the incident fast wave propagates in the xz plane,with the magnetopause normal along x and the background magnetic field pointing along z,the 2-D (xz)simulation shows that KAWs with large wave number kxρi～1 are generated near the Alfve′n resonance surface,whereρi is the ion Larmor radius.Several nonlinear wave properties are manifest in the mode conversion process.Harmonics of the driver frequency are generated.As a result of nonlinear wave interaction,the mode conversion region and its spectral width are broadened.In the 3-D simulation,after this first stage of the mode conversion to KAWs with large kx,a subsequent generation of KAW modes of finite ky is observed in the later stage,through a nonlinear parametric decay process.Since the nonlinear cascade to ky can lead to massive transport at the magnetopause,the simulation results provide an effective transport mechanism at the plasma boundaries in space as well as laboratory plasmas.
