▁impact ▁on ▁air ▁quality . ▁ ▁Cloud s ▁▁ ▁We ather ▁and ▁climate ▁model ▁grid box es ▁have ▁sides ▁of ▁between ▁ ▁and ▁. ▁ ▁A ▁typical ▁cum ulus ▁cloud ▁has ▁a ▁scale ▁of ▁less ▁than ▁, ▁and ▁would ▁require ▁a ▁grid ▁even ▁fin er ▁than ▁this ▁to ▁be ▁represented ▁phys ically ▁by ▁the ▁equations ▁of ▁fluid ▁motion . ▁ ▁Therefore , ▁the ▁processes ▁that ▁such ▁clouds ▁represent ▁are ▁parameter ized , ▁by ▁processes ▁of ▁various ▁s oph istic ation . ▁ ▁In ▁the ▁earliest ▁models , ▁if ▁a ▁column ▁of ▁air ▁in ▁a ▁model ▁grid box ▁was ▁un stable ▁( i . e ., ▁the ▁bottom ▁war mer ▁than ▁the ▁top ) ▁then ▁it ▁would ▁be ▁over turn ed , ▁and ▁the ▁air ▁in ▁that ▁vertical ▁column ▁mixed . ▁ ▁More ▁s oph istic ated ▁schemes ▁add ▁enh anc ements , ▁recogn izing ▁that ▁only ▁some ▁port ions ▁of ▁the ▁box ▁might ▁con ve ct ▁and ▁that ▁ent rain ment ▁and ▁other ▁processes ▁occur . ▁ ▁We ather ▁models ▁that ▁have ▁grid box es ▁with ▁sides ▁between ▁ ▁and ▁ ▁can ▁explicitly ▁represent ▁con ve ct ive ▁clouds , ▁although ▁they ▁still ▁need ▁to ▁parameter ize ▁cloud ▁micro physics . ▁ ▁The ▁formation ▁of ▁large - scale ▁( str atus - type ) ▁clouds ▁is ▁more ▁phys ically ▁based : ▁they ▁form ▁when ▁the ▁relative ▁hum id ity ▁reaches ▁some ▁pres cribed ▁value . ▁ ▁Still , ▁sub ▁grid ▁scale ▁processes ▁need ▁to ▁be ▁taken ▁into ▁account . ▁ ▁R ather ▁than