Why does positive charge accumulate on the upper clouds and negative charge on the lower ones? How do we knoe about what charge is accumulated where??

Hi Kanika!

As the water vapour moves upward, it collides with the ice crystals to form a soft, ice-water mixture called graupel. The collision results in slight positive charge in ice crystals and slight negative charge in graupel. Different materials have different capacity in holding the electrons. The ice crystals lose electrons while the graupel gains them. As the ice crystals are less dense compared to the graupel, they accumulate at the top of the cloud. This is the reason that the upper part of cloud to be positively charged and lower part to be negatively charged.