What is Tropospheric Lapse Rate?

Using the temperature and altitude measurements that you wrote down earlier, graph the temperature profile as a function of altitude. That is, make a graph with the altitude on the x-axis, and the temperature on the y-axis. The slope of this line is the lapse rate.

Tropospheric lapse rate is the rate at which temperature decreases with increasing altitude. Although lapse rate in the troposphere may seem like a foreign concept, you may have experienced this change in temperature with altitude, if you have travelled up a mountain.

Why Does Lapse Rate Exist?

The atmosphere is made up largely of naturally compressible gases – mostly nitrogen (N2) and oxygen (O2). The earth’s gravitational pull on these gases causes them to compress as you approach the surface of the earth. Since compression of gases causes heating, the earth’s atmosphere has a natural temperature profile, getting warmer as you move from the top of the atmosphere to the earth’s surface. There are lots of other effects that come into play (humidity, cloud and dust content etc.) but the overall result is that the atmosphere has a natural drop in temperature from surface to the top of the troposphere and the rate at which this temperature changes is called the tropospheric lapse rate.