))As air descends or sinks from a level of low pressure to a level of higher pressure, the temperature of the sinking air rises (see Equation of State). Because the actual temperature and virtual temperature of an individual parcel are continuously changing as the air moves from one pressure level to another, meteorologists often refer to the potential temperature of a parcel of air. The potential temperature is the temperature an unsaturated parcel would have if lowered (or raised) to a level of 1000 mb (100 kPa). The potential temperature is conserved, or remains the same, for a parcel of air that is unsaturated and remains unsaturated as it rises and sinks.
The formula for computing the potential temperature is derived from Poisson's Equation. The formula we will use looks like this:
The Javascript calculator to the right will allow you to experiment with the relationships between the variables in the equation above.
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 potential temperature for a parcel of air 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 clear the field ("Clear Field") of the variable you wish to solve before you click on "CALCULATE".
NOTE: Normally, the original temperature must be converted to degrees Kelvin. Here, we have made this conversion for you. Also note that this form of the equation requires that you convert pressure to kilopascals and returns potential temperature as degrees Kelvin.
The potential temperature is the temperature an unsaturated parcel would have if lowered (or raised) to a level of 1000 mb (100 kPa). The potential temperature is conserved, or remains the same, for a parcel of air that is unsaturated and remains unsaturated as it rises and sinks. This calculator will returns the value for potential temperature in units of degrees Kelvin. Be sure to enter the potential temperature in degrees Kelvin if you are using the calculator to solve for another variable. Refer to the temperature converter if you need to convert between degrees Fahrenheit, Celsius, and Kelvin.
The temperature refers to the actual temperature of parcel, in degrees C, at the pressure level it originally resides, before raising or lowering the parcel to 1000 mb (100 kPa). Using this calculator you can solve for the temperature an unsaturated parcel would have at any pressure level if you know its potential temperature. Refer to the temperature converter if you need to convert between degrees Fahrenheit, Celsius, and Kelvin.
The pressure refers to the original pressure of parcel before raising or lowering the parcel to 1000 mb (100 kPa). Using this calculator you can solve for the pressure of an unsaturated parcel at any temperature, if you know its potential temperature. Note:Unlike the other calculators in this course, this one requires that you enter pressure in units of millibars (mb). Refer to the pressure converter if you need to convert between millibars, kiloPascals, and Pascals.
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