test 3 Flashcards
Primary circulation
General worldwide atmospheric circulation
Secondary circulation
This consists of migration of high and low pressure systems
Air mass thunderstorms
They are short lived and rarely produce severe weather
Super cell thunderstorms
produces hail at least 3/4 of an inch in diameter and has surface wind gusts of 58 mph, or creates a tornado
Why are surface winds generated?
When two regions have different temperatures, they soon begin to have different air pressures as well. Differences in air pressure allows air molecules to move from one place to another (which is what wind is)
synoptic scale: Across two latitudes
regional scale: Between two surface
What is pressure gradient force?
wind speed proportional to the pressure difference between high and low pressure regions. The greater the PDF, the greater the wind flow
What is the corolis force?
This is the way that the wind flows due to the fact that it spins on an access..it does not have an effect on wind flows
why is the corolis force stronger at the poles than at the equator?
Because at the poles it is perpendicular to the earths surface but it is parallel at the poles
How does the corolis force affect the direction of the wind?
Wind is deflected to the right in the Northern hemisphere and to the left in the Southern hemisphere
What is a geostrophic wind and how is it created?
This is when the wind has reached a constant flow. It is created by the pgf that acts on an air parcel and deflects it to the right. As the air parcel increases in speed, it gets closer and closer to the pgf. This is the point at which it is balanced and becomes constant
Free atmosphere
This occurs when wind flow is above the level of friction . On average this is reached at about 1000m. Creates a geostrophic wind
What is the impact of friction on wind flow?
Reduces wind speed and it alters the direction of the wind. The deflection of wind flow on the ocean is about 8 degrees while it is about 25 degrees on land
Poleward air flow (western side)
air flow carries a lot of moisture. This affects continental margins of the US. Creates adibiatic cooling and condensation
Equatorward air flow
air carries dryness because of strong air subsidence. This air cannot cool and condense. Many of the deserts are located on the eastern side of the subtropical high cells because of this
polar front
the boundary between continental polar air mass (cold/dry) and tropical maritime air mass (warm/moist)… where frontal precipitations can take place. It seperates the polar easterlies from the westerlies
The westerlies
they are generated from substropical high pressure cells They take place between 30 degrees and 60 degrees and are more active in the southern hemisphere than in the northern because of the unbroken belt of oceans
what happens when tropical air mass carried by the westerlies collides with the polar front?
condensation, development of mid latitude cyclones, and frontal precipitation
Polar easterlies
cold and dry wind flow moving from the polar regions. They have a greater velocity of Antarctica because of the strong polar high that develops at the south pole
Upper air circulation
It controls the movement of air masses at the surface and is responsible for the development of mid latitude cyclones
zonal flow
fast moving wind from west to east. maintains air masses from within their natural boundaries
Meriodinal flow
slow moving flow moving across the latitudes in both directions. allows very cold air from the arctic to move toward lower latitudes. also very warm air from the tropics to move north ward
What is air mass
a large body of air whose physical properties (e.g., density, temperature, moisture) are more or less
uniform horizontally for hundreds of kilometers.
Why is weather variable in the mid latitude regions
It has to do with the traveling air masses and how they interact with one and other
mE
maritime equtorial. warm oceans in the equatorial zone. warm and very moist
mT
maritime tropical. warm oceans in tropical zone. warm and moist
cT
Continental tropical. Subtropical deserts. warm and dry
mP
maritime polar. Midlatitude oceans. cool and moist
cP
contiental polar. Northern continental interiors. cold and dry
cA
Continental arctic. Regions near north and south pole. very cold and very dry
what happens when an air mass starts to move?
it will gain (or lose) heat and gain (or lose) moisture
Secondary air masses
these are created because of thermodynamic and dynamic changes.
Thermodynamic change
Takes place when a cold air mass is moving south over areas where the land mass is warmer
dynamic change
Takes place when an air mass has to go over a topographic barrier
mid latitude wave cyclone
a common situation along the polar front in the continental United States
3 phases of mid laittude wave cyclone
- ) Frontogenesis and cyclogenesis stage
- ) Mature (or open) stage
- ) Occluded (or dying) stage
frontogensis
this is the first stage that refers to the creation of fronts delimiting air masses with different physical properties
stationary front
develops at the surface when two air masses remain in the same place. (typical of zonal flow conditions aloft)
Frontal waves
Frontal waves at the surface indicate that the upper air flow is starting to enter a meridional phase. Warm air mass is starting to move above the ground
warm front
created when warm air mass starts to glide on top of the cool air
cold front
created when the cold air mass is pushing warm air aloft
Cyclogenesis
adiabatic cooling takes place, condensation is reached, and a low pressure forms at the apex of the two fronts. (creation of mid latitude cyclones)
The Mature stage
The storm is fully developed and precipitations are generated. Cold front travels faster than the warm front as it is pushing the warm front aloft. intense rain is happening near the front
What happens with frontal passage?
Changes in temperature, wind speed, wind direction, cloudiness, and moisture take place
what is overrunning?
this occurs when the air is very moist and unstable, and if the vertical rise of the warm air mass to the horizontal distance is 1km to 100km (or less)
What are the weather conditions associated with an occluded front?
it is often the most intense part of the storm. (as far as rainfall is concerned) but there is no longer any warm or moist air. As the storm continues, central air pressure starts to rise.
When does a storm dissipate when talking about an occluded front?
when all the warm air that is used at the surface is moved aloft
Cold-type occlusion
In this type of occlusion, the cold front is catching up to the warm front and eventually takes over. eventually the warm air is moved aloft
warm-type occlusion
This occurs mostly on the western side of the United States. The cold air mass coming from the pacific overruns the colder air mass which is pushed upward
What are hurricanes?
A large scale storm (500-600 miles in diameter) that have speeds from 75 to 200 mph
When is hurricane season in the Atlantic?
June through November
What are the 6 conditions required for a tropical storm to turn into a hurricane?
- Warm sea surface temps (81%)
- Westward trajectory maintaining the storm over warm water
- No topographic obstacles islands?
- Creation of spinning cortex
- Little or no vertical wind shear
- Divergence of air aloft must exceed the convergence of air at the surface
Why does the water need to be warm for the development of a hurricane?
this allows there to be sufficient convective motion and latent energy transfer
why does there need to be no vertical wind shear in order for there to be a hurricane?
This allows there the be eye wall formation
The eye of a hurricane
The eye of the equator is where air subsidence takes place. Usually reaches a span of about 30-50 miles wide
Saffir-Simpson scale
This is the scale that explains that weak hurricanes are category and strong are category 5.
- wind speeds of 74-95 mph
- wind speeds greater than 155 mph
Storm surge
a lot of sea water pushed inland by strong winds that is associated with a hurricane during landfall
Where is the most dangerous part of a hurricane upon landfall?
The right front quadrant
why does a hurricane lose strength after hitting land?
It no longer has the latent heat flux that is available over the warm ocean surface
Can tornados form within a hurricane?
yes. they are very common and happen a lot in the right front quadrant of a hurricane
What is the difference between a hurricane watch and warning?
issued when a hurricane will make landfall within the next 24 hours while a hurricane watch is when there is a possibility that a hurricane could hit land in the next 24-48 hours
What three landscape settings are most at risk with hurricanes?
- ) Densely populated deltas
- ) Isolated Island groups
- ) Highly populated coasts in highly populated countries
Why must warm air be moist in order to form a thunderstorm?
That way condensation (latent heat transfer) can be reached more quickly
What are the main physical mechanisms that can generate a thunderstorm?
Frontal lifting 1 2 and 3. And non frontal generated thunderstorms
Front lifting one
this occurs because of a cold front
frontal lifting 2
occurs due to overrunning
frontal lifting 3
Moisture front (dry line) lifitng
Why is the frequency of Thunderstorms higher in Southeastern USA. Why is it low on the West coast?
availability of warm and moist air from the gulf of Mexico all year around…Stagnant anticyclonic conditions are common
Air Mass Thunderstorms
These are short thunderstorms that have an individual storm cell. There are three distinct stages of development
Cumulus stage (initial stage)
The cloud grows and moist air continues to be lifted and the growing cell expands vertically and horizontally. The process of collision and coalescence is active
Mature stage
This is the stage where rain begins to fall and the most intense part of the storm. The top of the cloud is anvil shaped. The downdraft is cutting the updraft in half which means the storm dissipates quickly
Dissipating stage
starts about 15-30 minutes after the Mature stage starts. This stage happens because the downdrafts dominates the updraft and clouds start to disappear
Severe thunderstorms
a thunderstorm that produces hail of 3/4 diameter and has surface winds that are 58 mph or greater
Oridnary thunderstroms…
tend to form in a region where there is limited vertical wind shear. (wind speed and direction do not abruptly change with increasing height above the surface)
What is overshooting?
This happens in super cell thunderstorms where updrafts are strong enough to push into the lower stratosphere. (60,000 ft)
What is gust front?
The out-flowing boundary that forces warm moist air into the thunderstorm
What is a shelf cloud?
This is a cloud that forms as warm moist air rises along the forward edge of the gust front
What is a Multi-cell thunderstorm?
Thunderstorms that are composed of several individual single-cell storms. All in different stages of development
What is a squall line thunderstorm?
composed of thunderstorms arranged in a line or a band. They occur along a boundary of unstable air and is a form of a multi-cell thunderstorm
Mesoscale convective complex
A number of individual multicell thunderstorms occasionally grow in size and organize into a large circular convective weather system. They are not fronts
When/How do Mesoscale convective complex happen?
In the summer and in regions where upper winds are weak and where intense heating at the surface favors strong convection
What is dryline thunderstorms?
These are a lot like squall line thunderstorms except they are aligned along a moisture front and not a thermal front.
What air mass is involved in dryline thunderstorms?
cT airmass
Why does moist air rise above dry air?
Moist air has a lot of water vapor it. And water vapor is a light gas which will rise above a dry gas
What is thunder
it is formed because of lightning that causes expand explosity. This creates a shock wave
Sheet lightning vs cloud to ground lightning
Sheet: diffuse illumination of the parts in the cloud that a flash happened
cloud to ground: It accounts for 20% of the lightning and takes place when an electrical discharge occurs between the cloud and the earth’s surface
where are tornados most common in the world and in the US?
The US is the most common place in the world for tornado activity.
When is tornado season?
April to July
What is a mesocycle
The updraft of a thunderstorm rotating. Which causes a tornado. As it starts stretching vertically, it shrinks horizontally. This accelerates the spinning motion
What are multi vortex tornadoes?
These are tornadoes that have smaller swirls that rotate within the tornado
What are the 5 stages to a tornado?
- Dust-Whirl stage
- Organizing stage
- Mature stage
- Shrinking stage
- Rope Stage
Dust whirl stage
1st stage of a nado. Dust swirling upward from the ground indicates that the tornado has touched down
organizing stage
2nd stage of the tornado. Funnel cloud has hit the ground and is picking up intensity
Mature stage
This is the 3rd stage. the greatest damage is encountered during this stage
Shrinking stage
4th stage of tornado. overall decrease in funnel’s width and the funnel starts to tilt. still capable of a lot of damage
Rope stage
this is the final stage of a tornado. It is stretched into the shape of a rope and eventually dissipates
Tertiary circluation
These are local winds
Sea breeze vs Land Breeze
Sea breeze: happens during the day
Land breeze: happens at night
