Chapter 7 Flashcards
An air mass is a large body of air with generally uniform temp and humidity. How big are air masses? How do they form?
-Air masses are typically larger than 600 Km (1000 mi)
- The formation of air masses is usually associated with what are called source regions (regions of the Earths surface that are particularly well suited to generate air masses). An air mass develops its characteristics when it stagnates for a few days or remains over a uniform land or sea surface (source regions) long enough to acquire the temp, humidity, and stability characteristics of the surface below.
Know characteristics ad source regions of major North American
CP, cT, mP, mT air masses
Air masses classified on the basis of source region…
The latitude of the source region correlates directly with the temp of the air mass, and the nature of the surface strongly influences the humidity within the air mass.
Code cP,
type,
source region,
Source region properties
CP
Continental polar
High latitude plains of Eurasia and North America
Cold, dry, very stable
Code cT,
Type
Source region
Source region Properties
cT
Continental tropical
Low latitude deserts
Hot, very dry, unstable
Code mP
Type
Source region
Source region properties
MP
Maritime polar
Oceans in vicinity of 50-60 N and S latitude
Cold, moist, relatively, unstable
Code mT
Type
Source region
Properties
MT
Maritime tropical
Tropical and subtropical
Warm, moist, of variable stability
Be able to describe the differences (e.g., wind direction and speed, temp, humidity, potential for precipitation) associated with areas that experience the passing of these types of fronts, cold front, warm front, occluded front
Stationary front
Cold front
Warm front
Occluded front
Stationary front:
When neither air mass displaces the other. It is difficult to generalize about the weather along such a front, but often gently rising warm air produces limited precipitation similar to that of a warm front
Cold front:
The combination of steeper slope and faster advance leads to rapid lifting and adiabatic cooling of the warm air ahead of the cold. The rapid often makes the warm air ver unstable, and the result is blustery, violent weather along the cold front. Vertically developed clouds, such as cumulonimbus, are common along with turbulence and showery precipitation. Precipitation is usually more intense but shorter lived than that associated with a warm front.
Warm front:
The slope of a warm front is gentler than that of a cold front. As the warm air pushes against and rises over the retreating cold air, it cools adiabatically, usually resulting in clouds and precipitation. Because the frontal uplift is gradual, clouds form slowly, and turbulence is limited. Precipitation frequently occurs broadly if the rising air inherently unstable, however, precipitation can be showery and violent. —more moderate than cold front
Occluded front:
The occlusion process may result in a short period of intense precipitation and wind until eventually all of the warm air mass is forced aloft, and the ground level pressure enter is surrounded by cool air — a stable condition.
What is mid latitude cyclone?
- Most significant atmospheric disturbance
- Associated primarily with air mass convergence ( CCW in northern hemisphere)
- Wind flow pattern brings together cool air from the north and warm air from the south
- convergence of these two unalike air masses created two fronts 1) Cold front extending to SW from the enter of the cyclone 2) warm extending eastward from the center.
- essentially a vast cell of low-pressure air, with ground level pressure in the center typically between 990 and 1000 milibars
Where is the mid-latitude wave cyclone?
- Throughout the mid latitudes (30-70) degrees
- almost entirely within the band of westerly winds
What is the tropical cyclone?
- Intense, low-pressure disturbances that develop in the occasionally move poleward into mid latitudes
- Associated with trade winds
- Considerably smaller than midlatitude cyclones
- Approximately 100 atmospheric disturbances each year yet only a few strengthen into hurricanes
Where is the tropical cyclone
-tropics
What is the localized severe weather? Where is it?
-Smaller atmospheric disturbance that affect a more restricted area
-Localized
Cyclones are low pressure systems. What happens in cyclogenesis? How do fronts where air masses meet?
-Cyclogenesis is referred to as the “birth” of cyclones
-this is occurs in upper troposphere conditions in the vicinity of the polar front stream.
-Most midlatitude cyclones begin as waves along polar front
-A cyclone is unlikely to develop at ground level unless there is a divergence above it—> convergence of air near the ground must be supported by divergence aloft
-Various ground factors can initiate a wave along the front (such as topographic. Irregularities, temp contrasts between sea and land, or the influence of ocean currents)
In the warm sector. Of a mid-latitude cyclone, winds typically come from the south. Why?
-because of the counter clock wise motion of the winds around he low center.
How does the weather change with the passing of a warm front vs. the passing of a cold front?
We the passing of the cold front, we see a drop in the temp with the warm front it rise
What are the before/after differences in temp, pressure, wind, sky, & precipitation?
-as the cold front passes, temp drops abruptly because the cold front is the boundary between the cold and warm air masses of the storm.
-The trough of low pressure associated with the cold front extends south from the heart of the storm. As the trough along the front approaches, pressure decreases, reaching its lowest point at the front. Then as the cold front passes and the trough moves away, prressure begins to increase steadily.
-due to the overall converging counter clockwise wind pattern, winds is the warm sector come from the south. Once the front passes, winds shift from west to northwest
-The generally clear skies ahead of the cold front are replaced by cloudiness and precipitation at the front. They are generated by the adiabatic cooling of the warm air as it is lifted along the front— and are in turn replaced hours later by clear skies in he cold air mass behind the cold front.
What is an occlusion? Why does it signal the “death” of a mid-latitude wave cyclone?
-an occlusion is the process of he storm dissapating because the cold front overtakes the warm front.
-occlusion creates a stable condition of weather (warm air forced to the top, cool air all at the bottom). This stability weakens the pressure gradient and therefore the storm’s energy. When the storm has no more energy, it dies.
At any given time on average, how many mid-latitude cyclones are swirling in the midlatitudes?
- 5 - 10 midlatitude cyclones
Mid-latitude anticyclones
What are the characteristics of anticyclones high-pressure systems? What weather does it bring?
- Air converges into it from above, subsiding and diverging at the surface (clockwise)
- Contains no fronts
- weather is clear and dry with little or no opportunity or cloud formation
- wind movement is limited near the center of the anticyclone but increases progressively outward (may create very strong winds)
- Move toward the east either at the same rate or. Little slower than midlatitudes cyclones
Stagnation is possible for up to days at a time, this may enhance the likelihood of air pollutants will become concentrated
