Air at the equator is warm and has a density, which creates in comparison to the air at the poles.

Lower, low pressure

Explanation:

The temperature at equator are mostly higher than at the poles almost all times of year. This high temperature causes air at the equator to warm up quickly and thus, the air density reduces and it becomes lighter. Now, light air rises upwards. Thus, creating a low pressure region at equators. This low pressure causes the air near the poles gush towards the equator.

Hence, the blanks will be filled with the words

Lower, low pressure.

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.