# Three Types of Lapse Rates of Air Temperature

We need to understand different types of lapse rates to satisfy a curious person who might ask for the reason of rainfall. “Why does it rain?”

To answer this simple question, we must understand that the temperature of air declines as it rises from the earth surface towards higher altitude.

The curious mind will again ask, “Why does the rising air cool down? And why does the cooling of air cause rain?

To answer this, we need to understand the three types of lapse rates of temperature i.e. 1) Normal Lapse Rate or Environmental Lapse Rate 2) Dry Adiabatic Lapse Rate and 3) Wet Adiabatic Lapse Rate. Lapse rate means the rate of decline.

## What is an adiabatic change in temperature?

The change in temperature of any parcel of air due to change in pressure is called adiabatic change in temperature. The beginners must read Adiabatic Change in Temperature first before proceeding.

## Normal Lapse Rate or Environmental Lapse Rate

Suppose you are superman! If you fly from the earth’s surface towards clouds, you will feel that the air is becoming cooler and temperature declines. The air is warmer near earth’s surface because the air near earth’s surface is denser and absorbs more outgoing longwave earth radiation. As we fly higher, we will experience that the air becomes less dense and absorbs lesser outgoing earth radiation. Hence, the superman will experience cooler temperatures at higher altitude than the lower altitude. The rate of decline in temperature as we go higher is called Normal/Environmental Lapse Rate. This rate is 6.5°Celsius per kilometer. If the temperature in Delhi is 40°C in May and if the superman flies 2 Kms. up in the air, he will experience 27°C of temperature. This temperature change is purely due to differences in absorption of outgoing earth radiation and density of air between higher and lower altitudes. The Adiabatic cooling of air works differently. There are two types of adiabatic lapse rates i.e. Dry adiabatic and wet adiabatic lapse rates.