air is rising to a colder region
thermals is rising_currents_of_warm_air. air is not region. air is region. tops_of_mountains is not colder_than_surrounding_countryside. winter is not colder_than_summer. air is thinner_at_higher_altitudes. winter is colder_than_summer. air is not thinner_higher_go. air is thinner_higher_go. tops_of_mountains is colder_than_surrounding_countryside.