Simplify the following text for a Grade 10 native English-speaking person.
Original: A polar cyclone is a low pressure weather system usually spanning 1,000 -- 2,000 kilometers ( 620 -- 1,240 miles ) in which the air is circulating in a counter-clockwise fashion ( in the northern hemisphere ) .
Simplified: Polar cyclones are usually 1,000 to 2,000 kilometers wide in which the air is moving in a spiral counterclockwise fashion in the northern hemisphere .