- Cool air moving over a warm surface is heated from below, generating instability and increasing the possibility of showers.
- Warm air moving over a cool surface is cooled from below, increasing stability. ...
- Evaporation from water surfaces and falling precipitation adds water vapor to the air. ...
- Water vapor is removed by condensation and precipitation.
How does the path an air mass follows affect stability?
The path an air mass follows determines the stability in the upper levels of the air mass. The flow of an air mass around the subpolar lows decreases stability which enhances weather because of the upward vertical motion. It is given stability indicator of “u”.
How does a lifted layer of air become more stable?
A lifted layer of air stretches vertically, with the top rising farther and cooling more than the bottom. If the layer is initially stable, it becomes increasingly less stable as it is lifted. Similarly, a subsidizing layer becomes more stable.
What are the effects of a modification of the air mass?
The effects of a modification of the air mass can be observed on the leeside of the lake. Cyclones fall and winter, result in intense vertical mixing and convective clouds. 6,000 feet thick, can result in significant rain or snow showers over the crossing the Great Lakes during Clouds, typically only 5,000 to lakes and adjacent shores.
How do atmospheric forces affect an air mass?
There are several atmospheric forces that effect an air mass as it moves from its source region. These forces show up as the air mass is being modified and can determine the severity of the weather associated with the air mass. Warm air wants to rise and cold air want to sink due to the different densities.
What increases the stability of an air mass?
Warm air moving over a cool surface is cooled from below, increasing stability.
What does the stability of an air mass depend on?
To determine the stability of an air parcel, one compares its temperature to the temperature of the surrounding air mass. If the air parcel's temperature is less than the temperature of the surrounding air mass, it is denser than the surrounding air and therefore has a tendency to sink.
What would decrease the stability of an air mass?
Warming from below decreases the stability of an air mass. Unstable air forced upward will cause clouds with considerable vertical development and associated turbulence.
Which air mass is more stable?
If a parcel is warmer than the surrounding air, it will rise and this is unstable. If warm air is over cold air, this is stable. If cold air is over warm air this is unstable. For this reason, tropical air masses are usually less stable than polar air masses.
What affects air stability?
Three characteristics of the sounding then determine the stability of the atmospheric layer in which the parcel of air is embedded. These are: (1) The temperature lapse rate through the layer; (2) temperature of the parcel at its initial level; and (3) initial dew point of the parcel.
What conditions cause a stable air mass CAX?
Due to their static nature, stable air masses are characterized by certain atmospheric conditions.Cloud Cover. Because stable air masses are, by nature, calm and free of violent disturbances, they are often marked by the appearance of stratiform clouds or fog. ... Smooth Air. ... Uninterrupted Precipitation. ... Low Visibility.
What conditions cause a stable air mass quizlet?
Warm air rises when the air above is cooler. Cooling from below: surrounding air is warmer, which would increase the stability of an air mass.
What would decrease the stability of an air mass quizlet?
Clouds with considerable vertical development and associated turbulence. What would decrease the stability of an air mass? Warming from below.
What are four characteristics of stable air?
What are the characteristics of stable air? A—Good visibility; steady precipitation; stratus clouds. B—Poor visibility; steady precipitation; stratus clouds.
How is stable air formed?
If the air parcel is colder than the environment in its new position, it will have higher density and tend to sink back to its original position. In this case, the air is stable because vertical motion is resisted.
Are high pressure systems stable or unstable?
In high-pressure systems or anticyclones, air may be descending, compressing and gaining energy, such that temperature at altitude rises, thereby increasing atmospheric stability.
What are the causes of unstable air?
Air is considered unstable, in the lowest layers of an air mass when the air is warmer and or more humid than the surrounding air. When this occurs the air will rise, as that air parcel is warmer than the air surrounding it. In an unstable environment, the weather can change suddenly and can be violent.
Sections
Stability Determinations
Layer Stability
- Many local fire-weather phenomena can be related to atmospheric stability judged by the parcel method. Equally important, however, are weather changes that occur when whole layers of the atmosphere of some measurable depth and of considerable horizontal extent are raised or lowered. Here again, it is necessary to employ some assumptions with respect to conservation …
Lifting Processes
- A common process by which air is lifted in the atmosphere, as is explained in detail in the next chapter, is convection. If the atmosphere remains stable, convection will be suppressed. But we have seen that surface heating makes the lower layers of the atmosphere unstable during the daytime. Triggering mechanisms are required to begin convective action, and they usually are pr…
Diurnal and Seasonal Variations in Stability
- Stability frequently varies through a wide range in different layers of the atmosphere for various reasons. Layering aloft may be due to an air mass of certain source-region characteristics moving above or below another air mass with a different temperature structure. The inflow of warmer (less dense) air at the bottom, or colder (more dense) air a...
Subsidence
- Air that rises in the troposphere must be replaced by air that sinks and flows in beneath that which rises. Local heating often results in small-scale updrafts and downdrafts in the same vicinity. On a larger scale, such as the up-flow in low-pressure systems, adjacent surface high-pressure systems with their divergent flow normally supply the replacement air. The outflow at t…
Local Indicators of Stability
- The continent-wide network of weather stations that make regular upper-air soundings gives a broad general picture of the atmospheric structure over North America. These soundings show the major pressure, temperature, and moisture patterns that promote stability, instability, or subsidence, but they frequently do not provide an accurate description of the air over localities a…
Summary
- In this chapter we have seen how the distribution of temperature vertically in the troposphere influences vertical motion. A large decrease of temperature with height indicates an unstable condition which promotes up and down currents. A small decrease with height indicates a stable condition which inhibits vertical motion. Where the temperature increases with height, through a…