View
- Term
- Definition
- Both Sides
Study
- All (55)
Shortcut Show
Next
Prev
Flip
GEOG 111: TEST 3
Circumpolar vortex
|
Large cyclone of cold air over the high latitudes. Low pressure at the center (because it's a cyclone), lots of day to day variability.
|
Jet Stream
|
Happens where the north/south temp. gradient is the strongest, so the isoheights are closest together. Usually friction pulls it to flow west --> east. It's where the winds are blowing the fastest and the air north of it is cold, south of it is warm. Most extreme weather happens in the vicinity of the jet stream or when it's in unusual position.
|
Circumpolar vortex in winter/early spring
|
When the winds in the CPV are the fastest and the cyclone is the most expansive (I.E., the diameter is largest) -- this pushes the Jet stream farthest south that it gets. See lots of variation in NC weather because it's far enough down to be over us, but day-to-day variations mean sometimes it's north of us and other times it's south of us.
|
Circumpolar vortex in Summer/early fall
|
Winds are the weakest they will get. The cyclone is as small as it gets (the jet stream is over Canada), leads to very consistent weather over NC, because the pressure is really consistent over large swaths of land in the southern half of the US.
|
What features do you see coming out of troughs and why?
|
Cyclones, because the air is lifting coming out of troughs and that creates a cyclonic flow with low pressure at the surface.
|
Continental polar air mass
|
Cold, dry (because it's continental) air masses that form over Canada
|
Cold Front
|
cold air mass advances on warm air mass dense cold air stays at surface, less dense warm air mass rises, often short-lived localized high intensity precipitation
|
Conditions that favor creation of continental polar air masses
|
Prolonged negative values of net radiation (more radiation leaving than coming in). The absence of vertical mixing in the air (causes the cold air to sit on the surface and just keep getting colder rather than mix with the warm air above it and warm up some -- happens when you have calm anticyclonic conditions over the source region).
|
Ingredients for cold air outbreaks
|
Once a continental polar air mass develops and has the strong inversion (really cold bottom air under warm top air) you need a cold advection pattern to blow the cold air south (either a strong anticyclone or cyclone). And you also need an absence of air modification (you need the cold air mass to not interact with the other surface air as it moves south because that would warm it up. Positive net radiation and no snow are things which can cause rapid modification).
|
Cold air advection over water
|
The warm moist air directly above the water mixes with the super cold air and condenses, leading to fog called and stratus/stratocumulus clouds.
|
lake effect snowfall
|
Lake effect snows occur when a mass of sufficiently cold air moves over a body of warmer water, creating an unstable temperature profile in the atmosphere which leads to lots of warm moist air moving upward and then the water condenses and freezes and it snows.
|
Snowbelts
|
The areas where the lake effect snowfall lands. For the great lakes these tend to be on the southeast sides, because the air is usually coming from the northwest.
|
Freezing rain
|
rain that falls when surface temperatures are below freezing
raindrops become supercooled while passing through a sub-freezing layer of air many hundreds of feet above the surface, and then freeze upon impact with any object they encounter
|
Sleet |
When a liquid raindrop freezes while falling to the ground. Different than hail.
|
Synoptic situation
|
When you have a wave cyclone and the precipitation out in front of it goes from rain to freezing rain to sleet to snow as you get farther out.
|
Warm nose
|
When there is a section of the vertical air column that is warmer than the area above and below it where snow melts and becomes rain. Then once the rain goes past that section, depending on how high it is, it becomes super cooled or re-frozen and leads to either freezing rain or sleet
|
Conditions associated with freezing rain development
|
Snow in the high altitudes, a warm nose where the snow melts completely (which is a cooling process) and then a cold wedge beneath that supercools the water so that it freezes when it hits the ground (which is a warming process -- causes freezing rain to be self limiting). Sometimes though either dry air causing evaporation or just an influx of cold air can cool off the warm nose and lead to snow from freezing rain rather than the freezing warming up the air and causing normal rain.
|
Ice accretion
|
Depends on the temperature of the surface prior to the icing (colder the area is, whether it's in the shadows most of the day or it's been cloudy or it's just low albedo, the more ice accretion you'll get). The wind speed (faster wind takes heat away from the surface and strong winds out of the north indicate a strong anticyclone) and the rainfall rate and duration (sustained light rainfall allows the rain to freeze before a bunch more falls on it and it lasts a long time).
|
Ingredients for the "perfect ice storm"
|
1. strong anticyclone to north that produces a replenishing supply of cold, dry air
2. slow-moving wave cyclone that moves south of the area and provides persistent warm and moist air advection over the wedge of cold air
|
Isothermal vertical temperature profile
|
When it's just a little above freezing at the surface and it's snowing higher up. Then the snow melting before it lands cools the column enough that it's below freezing all the way down.
|
What determines snowfall accumulation?
|
High rate and/or long duration leads to lots of accumulation. The wetness of the snow matters as well (generally 10" of snow = 1" of water, dry snow is 20:1 and wet snow is 5:1). Third the antecedent (prior) temperature of the surface its landing on affects accumulation levels.
|
What determines a snows wetness
|
It's set by the amount of moisture within the system the snow is coming from.
|
What are the ingredients for the "perfect snow storm"
|
A wave cyclone to the south of you (pushes the precipitation up toward you), strong anticyclone pulling in cool dry continental air from the north, no warm advection in the middle of the column creating a warm nose.
|
What are the basic parts of a thunderstorm?
|
overshooting top with strong vertical motion penetrating the equilibrium level, anvil is the cirrus later formed when rising air has nowhere to go so it spreads out, updraft is fast upward moving air that gives the storm heat and moisture, downdraft is rapidly sinking air accompanied by rain and hail
|
What limits thunderstorm growth
|
Since thunderstorms thrive off instability, once air parcels (air lifted by the updraft) are lifted and reach the stratosphere,they are no longer warmer than the environmental temperature. Above this levelthe atmosphere becomes stable, which is where the stratosphere resides and thus caps the thunderstorms vertical growth.
|
Stages in Development of a Thunderstorm
|
1) Cumulus Stage: cloud is dominated by strong updrafts that act to build the storm/ updrafts keep water droplets & ice crystals suspended in the cloud. Rainfall does NOT occur at cumulus stage
2) Mature stage: Lasts about 30 minutes. When you get heavy rain and lightning and all that. Still building from updrafts.
3) Dissipation stage: No longer getting updrafts, cloud dissipates and light rain.
Storms last 1-2 hours, dissipation can last several
|
Air mass thunderstorms
|
Usually happen when cold downdrafts outflow from another storm and hit some moist warm air and they convect up and mix, causing the air to become saturated and developing a new storm. Tend to be pretty light and are late afternoon/evening kinds of storms. Really common in the summer when the bermuda high is pulling in a lot of moist air.
|
Squall line
|
An organized line of thunderstorm cells that work together and are reasonably predictable. The cells will all be moving in basically the same direction and their outflow creates new cells in front of the dissipating ones -- called the gust front. Typically impact large areas for 6-12+ hours even though individual cells only last the typical 1-2 hours. The line typically moves to the right of the cells, even though the cells themselves are usually moving on a diagonal to the northeast, because the line is outflow.
|
Gust Front
|
Leading edge of the squall line -- the newly forming cells to the southeast of the mature cells. Typically forming on to the southeast of the cells when the cells are moving to northeast. Really dark rolling clouds with lots of air mixing happening. Move in quickly, typically don't bring thunder and rain but bring lots of wind. First sign that mature cells are developing overhead and the squall line is coming at you.
|
Where do squall lines typically form?
|
Tend to form in an atmosphere where the wind speed increases a lot as you move up the air column. This sends the anvil way downstream and stops it from expanding upstream at all. Always have a really sloped updraft coming in and downdraft leaving the cloud.
|
Thunder Days
|
Central colorado and florida get the most thunder days (days where you can hear thunder at least once). Florida because the unstable moist climate leads to lots of air mass thunderstorms, Colorado because lots of convection up the mountains gives you really elevated heat sources that can easily become thunderstorms. Varies in NC (western is Colorado-ish). Coastal Cali. and New England have very few because the climate is very stable in Cali -- lots of marine air -- and lots of continental air in NE
|
lightning formation
|
-result from separation of charges, charge separation increases with rain and ice collision, top of cloud- positive charge, bottom of cloud/ground- negative charge, negative attracts positive -- resistance in air cannot keep them apart. Have cloud to cloud, cloud to ground, and bolt from the blue (comes out the back of the storm, travels horizontally and then goes toward the ground). Lightning is most likely to hit the tallest conductive object it can -- fastest path to the ground.
|
Thunder
|
Compression wave (sound wave) created by the intense heat of the lightning and rapid expansion of the air. 5 second difference between strike and thunder for each mile of distance between you and the storm. Sound and loudness controlled by how many muffling things there are in the area. Fog and snow are both things that muffle the sound of thunder, low clouds can also muffle things. Your elevation (proximity to the cell itself) can also affect how it sounds.
|
Microbursts
|
A very localized column of sinking air producing damaging and straight line winds at the surface.
Usually located in a strong downdraft area and produces extremely strong straight line winds. Don't last long (< 5 mins), but the strength of the winds and the turbulence as it curls back up in all directions will do things like jerk planes coming in for landing straight up.
|
Hail |
Develop as chunks of ice from above the freezing line in a cloud fall, but get blown back up by updrafts. Freeze some more and get bigger, fall a little farther, get blown back up.. rinse & repeat until heavy enough to fall. Size of the stones is determined by the strength of the updrafts and the height of the freezing level (lower it is the more likely the hail is to get to the ground without melting).
|
Wave cyclone
|
Occur when you have a warm front with a cold front trailing behind it. Basically, when you have a boundary where the air masses are so different they can't mix. The warm zone is underneath the warm front and in front of the cold front, everything in front of the warm front and behind the cold front is relatively colder. The air sinks in front of the cold front (trough) and lifts coming out over the warm front (ridge).
|
Wave cyclone precipitation zones
|
Overruning: right in front of the warm front, rain right in front and can slowly get closer to snow until it is actually snow as it gets farther from the front.
Cold Frontal: the area right in front of the cold front, behind the warm front. See thunderstorms here.
Wrap around: An area where the cyclone carries some of the precipitation around the axis that the fronts are spinning on.
|
Stages of wave cyclone development
|
Start off along a pre-existing stationary front where all the cold air is on one side and all the warm on the other. Something happens which creates a bump in the front and low pressure starts to develop around that bump. Then as the cyclone forms around that low pressure core the fronts separate and move clockwise with the cyclone. Eventually the cold front overtakes the warm front and the wave cyclone is donezo.
|
How does Jet stream position affect wave cyclones?
|
It basically follows the jet stream, if it's north of NC then we are in the warm sector of the wave cyclone and if it's south we're in the cold.
|
Three general tracks of wave cyclones
|
Alberta Clipper.
Texas low.
The gulf-atlantic coast
|
Alberta Clipper
|
fast moving, light precipitation near the cyclone's track. Goes south into the top of the US and curves back north around the great lakes and finished in Maine. NC is in the warm, dry part.
|
Texas Low
|
Draws moisture from Gulf of Mex. so there's heavy precip. around the track and to the north of it. Can get severe thunderstorms, starts in Texas and goes to Maine. NC is in the cool sector, then it passes us and we're in the warm.
|
The gulf-atlantic coast
|
Starts in Texas, goes over the gulf, above Florida through the Carolinas and over the ocean toward Maine. Heavy precipitation along the north of the track, NC stays in the cool the whole time and sometimes gets frozen precip, Generally get the most precip, in NC
|
Tornadoes infrastructure
|
Generally at the back of a thunderhead, cyclonic updrafts spinning up into the rear at really high speeds. If it's large enough the sinking air in the center can create an eye-of-the-storm like thing where you can see blue at the top. Lifting is so strong that no precipitation comes out unless it's REALLY heavy hail -- only get precipitation at the front of the cell. Appear white if light is hitting from the front, if it's behind the tornado it looks dark grey.
|
Funnel clouds
|
Happen because as the air converges and lifts at the ground there's a really fast drop in pressure and the air cools dramatically and condenses into a cloud, which takes on the shape of the fast spinning and lifting cyclone. It's possible to have an invisible tornado if no cloud appears, it would have to pick up debris for you to see it.
|
Where in cells do tornadoes happen?
|
They happen at the wrap-around point of the wave cyclone in super cell thunderstorms. There's basically a hook and at the tip of it you see tornadoes start to form. The reason the hook is there is because there's a lot of updraft that's stopping precipitation in the zone between the spot where the tornado might form and the rest of the cell.
|
Super cell thunderstorms
|
Rotating circular/oval shaped thunderstorms where the lightest precipitation is on the edge and the heaviest is in the center. Sometimes they have hail, see lots of them in the midwest.
Super cell thunderstorms
|
Wind shear
|
Very fast change of speed (speed sheer) or direction (directional sheer) as you move up the super cell, this is responsible for the rotation that ends up forming tornadoes. Low level winds come in and turn clockwise as they move up.
|
Mesocyclone
|
The hook of the supercell, it's a small rotating cloud that the tornadoes come out of.
|
Typical tornado direction
|
They usually move SE -- > NW, but locally their movement is erratic. Sometimes they can turn and move back in the direction they just came from, for example.
|
Strength ratings for tornadoes
|
F0-F6. With 6 being the strongest. Generally only get up to F5, and there are only a few 4's and 5's a year. 0's and 1's the most common. Stronger tornadoes last longer, have more diameter, and occur less often. Strength is determined by the updrafts -- which are responsible for the storms height. The taller the storm the stronger.
|
Multiple vortex tornadoes
|
Usually F4's and F5's have multiple suction vortices within the tornado.
|
Capping inversion
|
stable layer of warm dry air that holds rising warm, moist air beneath it. Eventually the air builds enough for the cap to break and the air really quickly rises and forms thunderheads which are likely to produce tornados.
|
How does speed shear cause tornado genesis?
|
Creates a horizontal rolling effect as the upper level winds blow faster than the lower level ones. Important for forming mesocyclones.
|
Why does the US have the most tornadoes and where do they happen?
|
Because it's a huge continent with a large swath of land where cool, dry air coming off the rockies hits warm, moist from the gulf of Mexico and creates lots of storms over the great plains and midwest in general, north of texas and just east of the rockies.
|