h Pa ▁or ▁m bar ], ▁▁ ▁is ▁standard ▁reference ▁pressure ▁( 1 0 0 0 ▁h Pa ), ▁▁ ▁is ▁the ▁water ▁v apor ▁pressure ▁( to ▁obtain ▁ ▁for ▁dry ▁air ), ▁▁ ▁is ▁the ▁ratio ▁of ▁the ▁specific ▁gas ▁constant ▁to ▁the ▁specific ▁heat ▁of ▁dry ▁air ▁at ▁constant ▁pressure ▁( 0 . 2 8 5 4 ), ▁▁ ▁is ▁mixing ▁ratio ▁of ▁water ▁v apor ▁mass ▁per ▁mass ▁[ kg / kg ] ▁( s ometimes ▁value ▁is ▁given ▁in ▁[ g / kg ] ▁and ▁that ▁should ▁be ▁divided ▁by ▁ 1 0 0 0 ). ▁ ▁A ▁little ▁more ▁theoretical ▁formula ▁is ▁commonly ▁used ▁in ▁literature ▁like ▁Hol ton ▁( 1 9 7 2 ) ▁ ▁when ▁theoretical ▁explanation ▁is ▁important : ▁ ▁Where : ▁▁ ▁is ▁s atur ated ▁mixing ▁ratio ▁of ▁water ▁at ▁temperature ▁, ▁the ▁temperature ▁at ▁the ▁s atur ation ▁level ▁of ▁the ▁air , ▁▁ ▁is ▁lat ent ▁heat ▁of ▁ev ap oration ▁at ▁temperature ▁ ▁( 2 4 0 6 ▁k J / kg ▁{ at ▁ 4 0   ° C } ▁to ▁ 2 5 0 1 ▁k J / kg ▁{ at ▁ 0   ° C }), ▁and ▁▁ ▁is ▁specific ▁heat ▁of ▁dry ▁air ▁at ▁constant ▁pressure ▁( 1 0 0 5 . 7 ▁J /( kg · K )). ▁ ▁Further ▁more ▁simplified ▁formula ▁is ▁used ▁( in , ▁for ▁example , ▁St ull ▁ 1 9 8 8 ▁§ 1 3 . 1 ▁p