Thankyou all for your replies,but just after i posted this thread i turned the page of my text book to find that i wasn't looking at what happened on top of the hill after precipitation but what happened when the air mass slid down the other side of the hill!!
I'll learn by this mistake before the exams me thinks!!
p.s.Milt,considering the subject referred to here i think it was quite clear that when saying'moist air is less dense than less moist air' i was referring to the fact that moist air is less dense than dryer air at constant pressure and temperature.I was just trying to make it clearer that 'wetness' had been lost through 'rain' on the hilltop!!
