As this air heats up, the air parcels begin to rise and expand which creates an area of low pressure .
(this air; heats up; ) (the air parcels; begin; T:As this air heats up) (the air parcels; to rise; ) (the air parcels; to expand; )
this air the air parcels the air parcels the air parcels
heats up begin to rise to expand
T:As this air heats up