Why does a parcel of air expand as it rises

The air parcel expands as it rises and this expansion, or work, causes the temperature of the air parcel to decrease. When this occurs , cloud droplets begin forming as the excess water vapor condenses on the largest aerosol particles. Furthermore, what determines how much air parcel will cool? As a rising parcel cools , its relative humidity increases. In nature, when air rises, it encounters less pressure, expands, and cools.

The reverse is also true. A rising parcel of air expands because the air pressure falls with elevation. This expansion causes the air to cool. A falling parcel of air contracts because the air pressure increases.

The contraction causes the air to warm. Asked by: Yongfen Davletov asked in category: General Last Updated: 15th March, When a parcel of air is compressed its temperature rises? When an air parcel moves upward, the air temperature in the parcel decreases because it is expanding.

When an air parcel moves down, the air temperature in the parcel increases because it is being compressed. Does rising air warm or cool? Warm air rises up because of the difference in force of gravity between cold and warm air. When it reaches up,the pressure decreases so the saturation temperature of the vapor also decreases at that temperature. When air rises what happens to its water capacity?

Hot air expands, and rises; cooled air contracts--gets denser--and sinks; and the ability of the air to hold water depends on its temperature. Why is rising air important to the process of precipitation? Above this point the cloud droplets grow by condensation in the rising air. If the cloud is sufficiently deep or long lived, precipitation will develop. What happens when air rises into an area of lower pressure?

Air rises in areas where the pressure at the surface is low. As it rises, the air cools and the humidity condenses to form clouds and precipitation.

The centers of all storms are areas of low pressure; therefore, low pressure is often associated with bad weather. Which type of air holds more water vapor? What affects dew point? The higher the dew point rises, the greater the amount of moisture in the air. This continues until the air pressure inside the parcel equals the air pressure outside. If the air pressure on the outside of the parcel pushing inward is less than the air pressure inside the parcel pushing outward , then the parcel will expand outward.

As the parcel expands the air pressure inside starts to decrease. So when an air parcel rises upward in the atmosphere, it must expand because the air pressure surrounding the parcel gets lower See Figure H. This means that the number density of air in the parcel decreases same number of gas molecules but in a larger or expanded volume. The air in the parcel uses energy to expand increase its size , so the temperature of the parcel also decreases. Mathematically, the pressure, number density, and temperature of a gas are related in an equation called the gas law:.

Pressure decreases when a parcel is lifted. From the gas law, the density x temperature must also decrease. Both number density and temperature decrease when a parcel expands. This expression above is the same equation except number density is used instead of volume and number of moles of gas.

Conversely, when an air parcel is lowered in the atmosphere, it is compressed because the air pressure outside the parcel increases. When parcels are lowered the air pressure, number density, and temperature of the gas in the parcel increase.

In this case energy from the surrounding atmosphere is used to compress the parcel decrease its size. This transfer of energy from surrounding environment to parcel acts to increase the parcel temperature. A couple of everyday examples may help you to keep this straight.