The presence of water vapor in the air influences the temperature, pressure, and density of the air. Meteorologists substitute the virtual temperature (Tv) for the actual temperature (T) when making calculations in which temperature is a variable. Though the formula for computing the virtual temperature can take on many forms, one that meteorologist's often use looks like this:
Use theJavascript calculator on the right to compare the effects of varying amounts of water vapor on the virtual temperature. You can also use this calculator to solve for any variable in the equation, given known values for all others.
Sample values are supplied to give you a feel for what a "normal" value might be for the variables on the right hang side of the equation. You can go ahead and click on "CALCULATE" to compute the virtual temperature with the default values. Or, by using the "Reset Values", "Clear Field", and "Clear All" buttons, you can solve for any of the variables listed in the table. Just one note, to ensure an accurate computation, be sure to field of the variable you wish to solve is clear ("Clear Field") before you click on "CALCULATE".
The virtual temperature represents the temperature to which a sample of dry air must be heated in order to have the same density as a sample of moist air at the same pressure. This calculator automatically converts temperatures from Celsius to Kelvin, so when solving for other variables, be sure enter the virtual temperature in degrees Celsius. Refer to the temperature converter if you need to convert between degrees Fahrenheit, Celsius, and Kelvin.
The mixing ratio represents the amount of water vapor in the air and is normally given in grams of water vapor per kilogram of dry air (g/kg). Normally, when using the mixing ratio in computations, you should convert the grams of water vapor to kilograms of water vapor to keep the units consistent and in agreement with SI units. When using this Javascript calculator, the conversions are done for you. So enter the mixing ratio in the units of g/kg. These are the units in which the mixing ratio is normally reported.
Here, temperature refers to the actual measured air temperature. As in the case of virtual temperature described above, enter the temperature in units of degrees Celsius. Refer to the temperature converter if you need to convert between degrees Fahrenheit, Celsius, and Kelvin.