What is the equivalent-potential temperature?

EQUIVALENT-POTENTIAL TEMPERATURE - represents the amount of heating of air due to condensation of all water vapour contained in it (at a given pressure), followed by adiabatic (without heat exchange with the surroundings) reduction of so heated air to the pressure of 1000 hPa. Te-p isotherms are depicted on a map of the 850 hPa area (altitude approx. 1.5 km above sea level), since the position of atmospheric fronts and the area occupied by Arctic, polar and tropical air can be seen more clearly. The 850 hPa surface map also shows air temperature isotherms, but does not indicate the areas occupied by individual air masses.