Referring to Figure 1 explain why the potential temperature suddenly increases sharply above 13 km altitude; why the daytime potential temperature is (more-or-less) constant with altitude in the lower part of the atmosphere; why nighttime temperatures the lower part of the atmosphere are substantially different from the daytime values and why there are only small differences between daytime and nighttime temperatures above 4 km altitude; explain why the potential temperature () is not equal to the real temperature (T) at the lowest point of this sounding. Here it might be useful to consider how potential temperature is calculated (consider the simple equation, not the one based on pressure). Temperature (C) Temperature (C).