virtual temperature derivations

1. virtual temperature from temperature

   symbol	description	unit	variable name
   \(M_{air}\)	molar mass of total air	\(\frac{g}{mol}\)	molar_mass {:}
   \(M_{dry\_air}\)	molar mass of dry air	\(\frac{g}{mol}\)
   \(T\)	temperature	\(K\)	temperature {:}
   \(T_{v}\)	virtual temperature	\(K\)	virtual_temperature {:}

   The pattern : for the dimensions can represent {vertical}, {latitude,longitude}, {latitude,longitude,vertical}, {time}, {time,vertical}, {time,latitude,longitude}, {time,latitude,longitude,vertical}, or no dimensions at all.

   \[T_{v} = \frac{M_{dry\_air}}{M_{air}}T\]