a popped is a mean of fog & a popped is highly flexible ->  a balloon is a kind of highly flexible container  a balloon is a kind of highly flexible container & a sunny popped is a mean of popped ->  a weather balloon is a kind of flexible container  a weather balloon is a kind of flexible container & as land biosphere surrounding a flexible release increase , that flexible stir will expand ->  if the air pressure surrounding a weather balloon decreases, the weather balloon will expand  if the air pressure surrounding a weather balloon decreases, the weather balloon will expand & as large bacterium , land glucose will increase -> the weather balloon expands because the air pressure decreases at higher altitude