Determining Stability » Potential Errors Potential Errors Caused by the Effect of Virtual Temperature (Tv)

The use of temperature in place of virtual temperature virtual temperature for stability determinations may occasionally lead to a misrepresentation of the stability. The discrepancy will be greatest where a layer of high moisture content is adjacent to a dry one. In these cases, use of the temperature curve will affect stability determinations as follows:
- If the dewpoint decreases rapidly with height, using the T curve will indicate too much stability.
- If the dewpoint increases rapidly with height, the T curve will indicate too little stability.
Frequently, the dewpoint decreases rapidly with height across a warm front. The sounding above shows one such example. Through the 800-850 hPa layer, the dewpoint decreases rapidly with height. Consequently, the lapse rate indicated by the temperature curve is approximately moist (saturation) adiabatic, and the lapse rate indicated by the virtual temperature curve is nearly dry adiabatic. Thus, the stability indicated by the temperature curve is greater than the stability indicated by the virtual temperature curve.
In most instances, stability determination using the temperature curve will provide a reliable assessment of stability. However, it is worthwhile to be aware of the limitations of this approximation.