88．Now，scientistshave data from satellites and ground—based observations from which we know that the auroral brilliance isan immense electrical discharge similar to that occurring in a neon sign．

(介词提前的定语从句：from which，which指前面的data)

如今，科学家们根据来自卫星和陆基观察的数据得知，极光是发光原理类似于霓虹灯的巨大的电流释放。

解析：

主句：scientistshave data from satellites and ground—based observations

从句1：from which we know

从句2：the auroral brilliance is animmense electrical discharge

从句3：similar to that occurring in a neonsign

从句1修饰主句中的data

从句2作为从句1的宾语从句，表示科学家从data中的得知的内容

从句3修饰从句2整句