Colder air masses can warm, warmer air masses can cool. [clarification needed] Atmospheric stability is a measure of the atmosphere's tendency to discourage or deter vertical motion, and vertical motion is directly correlated to different types.
How does moisture affect the stability of air parcels?
The effects of moisture change the lapse rate of the air parcel and, therefore, affects stability. However, the concepts are still the same and we still compare the air parcel temperature to the environmental temperature. We have just one added complication to worry about—we need to know whether the air parcel is dry or moist.
What happens when air is heated from the bottom up?
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. If air is cooled to its dew point, stratus and/or fog forms.
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.
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”.
What happens when an air mass is heated?
As the molecules heat and move faster, they are moving apart. So air, like most other substances, expands when heated and contracts when cooled. Because there is more space between the molecules, the air is less dense than the surrounding matter and the hot air floats upward.
What affects the stability of an air mass?
What makes air stable or unstable? It is the vertical profile of temperature, or lapse rate of the atmosphere, which determines whether an air mass is stable or not. The temperature can be measured using an electronic thermometer attached to a helium-filled weather balloon released from the ground.
Are warm air masses 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.
Which would decrease the stability of an air mass?
The stability of an air mass decreases when its lower layers become warm and sometimes humid, making the mass warmer than its environment and causing it to rise.
Why is warm air unstable?
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.
What causes an unstable air mass?
To be "unstable", the lowest layers of an air mass must be so warm and/or humid that, if some of the air rises, then that air parcel is warmer than its environment, and so it continues to rise.
How do you determine the stability of an air mass?
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.
How is the stability of air determined?
Stability is determined by comparing the temperature of a rising or sinking air parcel to the environmental air temperature. Imagine the following: at some initial time, an air parcel has the same temperature and pressure as its environment.
How can the atmosphere be made more stable more unstable?
Sunlight warms the ground and the air next to it during the day. This steepens the environmental lapse rate and makes the atmosphere more unstable. Cooling air above the ground has the same effect.
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 is stable and unstable air?
An unstable aircraft, when disturbed, continues to move away from a normal flight attitude. So it is with the atmosphere. A stable atmosphere resists any upward or downward displacement. An unstable atmosphere allows an upward or downward disturbance to grow into a vertical or convective current.
How does saturated air that is warmed at the surface lead to an unstable environment in the atmosphere?
The warmth from the forest fire heats the air, causing instability near the surface. Warm, less-dense air (and smoke) bubbles upward, expanding and cooling as it rises. Eventually the rising air cools to its dew point, condensation begins, and a cumulus cloud forms.
What are the factors affecting properties of air masses?
Air masses are characterized by their temperature and humidity properties. The properties of air masses are determined by the the underlying surface properties where they originate. Once formed, air masses migrate within the general circulation.
How can you determine the stability of an air mass?
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 influences the characteristics of an air mass?
An air mass is a large volume of air which travels from one area to another. The weather an air mass brings is determined by the region it has come from and the type of surface it has moved over.
What are characteristics of a stable air mass?
Air mass having a stable stratification in its lower layer, and consequently free from convection, having a low degree of turbulence, and containing either stratiform clouds, fog, or no clouds at all.
How does air pressure affect the temperature of the air parcel?
The higher environmental pressure will push inward on the parcel walls, causing them to compress, and raise the inside temperature.
How to explain instability in the atmosphere?
Instability in the atmosphere is a concept that is intimately connected with thunderstorms, cumulus development, and vertical motion. In order to visualize the concept of stability, you might imagine a boulder sitting at the bottom of a canyon surrounded by steep hills, as depicted in the figure below by the blue circle. If you were strong enough to push the boulder from its initial position partway up one of the hills, it would roll back to the bottom once you let go. Despite exerting a force on the boulder and causing an initial displacement, it would return to its initial position, and the net displacement would be zero. To visualize the concept of instability, imagine the same boulder at the top of a hill (red circle below). If you were able to push the boulder just a little bit in any direction, it would begin to roll downward and accelerate away from its initial position. However, if the same boulder were to be placed on flat ground (green circle below) and you were to push it, it would change position, but remain in its new position. This is an example of neutral stability.
What is the lapse rate of an air parcel?
As long as an air parcel is unsaturated (relative humidity < 100%), the rate at which its temperature will change will be constant. A decrease in temperature with height is called a lapse rate and while the temperature decreases with altitude, it is defined as positive because it is a lapse rate. Recall from chapter 3 that the dry adiabatic lapse rate, Γd, is equal to 9.8 K·km-1 = 9.8 °C·km-1. This drop in temperature is due to adiabatic expansion and a decrease in internal energy.
How to determine if an air parcel is stable?
How do you know if an air parcel will be stable after some initial displacement? Stability is determined by comparing the temperature of a rising or sinking air parcel to the environmental air temperature. Imagine the following: at some initial time, an air parcel has the same temperature and pressure as its environment. If you lift the air parcel some distance, its temperature drops by 9.8 K·km -1, which is the dry adiabatic lapse rate. 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. If the rising air is warmer and less dense than the surrounding air, it will continue to rise until it reaches some new equilibrium where its temperature matches the environmental temperature. In this case, because an initial change is amplified, the air parcel is unstable. In order to figure out if the air parcel is unstable or not we must know the temperature of both the rising air and the environment at different altitudes.
Why is the atmosphere unstable?
The atmosphere is said to be absolutely unstable if the environmental lapse rate is greater than the dry adiabatic lapse rate. This means that a rising air parcel will always cool at a slower rate than the environment, even when it is unsaturated. This means that it will be warmer (and less dense) than the environment, and allowed to rise.
Why do Hawaii have convective clouds?
Convective clouds are clouds where the edges are bumpy and cumuliform, like cauliflower. The clouds are convective because the atmosphere is stable to dry lifting and unstable to moist lifting. Once the air is saturated, instability sets in and vertical motion takes off. This is especially common as air is lifted over our mountainous islands. The forced lifting from the terrain creates clouds and rain right over the mountains! In scientific terms, the initial lifting of the stable low level dry air by the terrain causes the air to adiabatically expand and reach saturation, at which point the environment is unstable to moist lifting and convection is the result.
Why is neutral stability important?
The topic of stability in atmospheric science is important because the formation of clouds is closely related to stability or instability in the atmosphere.
How are air masses modified?
Some ways air masses are modified are: (1) warming from below, (2) cooling from below, (3) addition of water vapor, and (4) subtraction of water vapor:
What happens when cool air moves over a warm surface?
Cool air moving over a warm surface is heated from below, generating instability and increasing the possibility of showers.
When a body of air comes to rest or moves slowly over an extensive area having fairly uniform properties of temperature and moisture?
When a body of air comes to rest or moves slowly over an extensive area having fairly uniform properties of temperature and moisture, the air takes on those properties. Thus, the air over the area becomes somewhat of an entity as illustrated in figure 58 and has fairly uniform horizontal distribution of its properties. The area over which the air mass acquires its identifying distribution of moisture and temperature is its “source region.”
What happens when water is warmer than air?
When the water is warmer than the air, evaporation can raise the dew point sufficiently to saturate the air and form stratus or fog.
How does atmospheric stability affect fires?
For example, winds tend to be turbulent and gusty when the atmosphere is unstable, and this type of airflow causes fires to behave erratically .
How to determine the degree of stability of an atmospheric layer?
The degree of stability or instability of an atmospheric layer is determined by comparing its temperature lapse rate, as shown by a sounding, with the appropriate adiabatic rate. A temperature lapse rate less than the dryadiabatic rate of 5.5°F. per 1,000 feet for an unsaturated parcel is considered stable, because vertical motion is damped. A lapse rate greater than dry-adiabatic favors vertical motion and is unstable. In the absence of saturation, an atmospheric layer is neutrally stable if its lapse rate is the same as the dry-adiabatic rate. Under this particular condition, any existing vertical motion is neither damped nor accelerated.
What are the seasonal effects of solar radiation?
In addition to the seasonal effects directly caused by changes in solar radiation, there is also an important effect that is caused by the lag in heating and cooling of the atmosphere as a whole. The result is a predominance of cool air over warming land in the spring, and warm air over cooling surfaces in the fall.
What is surface high pressure?
In surface high-pressureareas, the airflow is clockwise and spirals outward. This airflow away from a High is called divergence. The air must be replaced, and the only source is from aloft. Thus, surface high-pressure areas are regions of sinking air motion from aloft, orsubsidence.
How is the atmosphere determined?
Atmospheric stability of any layer is determined by the way temperature varies through the layer and whether or not air in the layer it saturated. The adiabatic process is reversible. Just as air expands and cools when it is lifted, so is it equally compressed and warmed as it is lowered.
What is the process of mixing air through turbulent layers?
Turbulence associated with strong winds results in mixing of the air through the turbulent layer. In this process, some of the air near the top of the layer is mixed downward, and that near the bottom is mixed upward, resulting in an adiabatic layer topped by an inversion.
What is the process by which air is lifted in the atmosphere?
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.
Why are air masses important?
Weather can be changed or affected by many factors but air masses is most important factor to controls the weather. We can easily understand about weather changes from air masses by its name .Maritime air masses originate from the Ocean so it produce moist weather.
What is the transition zone between air masses with distinctly different properties?
Long time annual interval patterns of those meteorological conditions — the seasonal fluctuations of rainfall in a given region are known as climate. Fronts Front is the transition zone between air masses with distinctly different properties.
How does convectional lifting affect weather?
convectional lifting. Weather conditions can be changed by moving the air masses vertically known as convectional lifting .here warm air rising and cool sinking, it caused by high absorption of solar radiation by some spot on earth .Moisture air produce big, fluffy and cumulus cloud on its arising, and when it sinks the whole bunch ...
What are the two types of air masses?
2: Polar air masses. Polar air masses a little bit farther from the poles, like in Siberia, Canada and the northern Atlantic and Pacific Oceans. Continental Polar. Cold and dry is originating from high latitudes.
What is the term for the lifting of air masses over mountains?
Orographic lifting. When air masses lifted up over mountains they can also change the weather conditions this way known as orographic lifting. It can be observed the opposite site of mountains. It became cool and expands on rising and this type of cloud produce rain.
What is the temperature of the Arctic?
This air mainly forms when high pressure area become over Eastern. Due to solar radiation and continuous emission of earth surface radiation, on abundant surface of ice the air become colder, temperature reach to -30 to-60 degree,
What is weather and climate?
Weather and climate. Day to day or short time meteorological condition, precipitation, and temperature are known as weather. A thunderstorm along a frontal boundary is an also weather event. E.g. readily observable effects of air masses are mostly in the realm of daily weather.
