Which phenomenon occurs when the sun crosses the plane of earth's equator

The phenomenon is called an equinox. More specifically when it is September it is called the autumnal equinox ,and when it is March it is called the vernal equinox.  Hope this helped!

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.