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Geol 1350: Exam 4
what are source regions
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regions where air masses originate
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what has to happen in order for a huge mass of air to develop uniform characteristics
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the source region should be generally flat and of uniform composition with light surface winds
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what are ideal source regions
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areas dominated by surface high pressure
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what do ideal source regions include
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ice and snow covered arctic plains in winter and subtropical oceans in summer
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what are the middle latitudes
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where surface temperatures and moisture characteristics vary considerably
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what area is not a good source region
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middle latitudes
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how do we decide what kind of front it is
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from the vantage point of the ground
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what happens if warm air replaces colder air
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the front is a warm front
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what is it called when the cold air replaces warmer air
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the front is a cold
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what happens if the front does not move
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it is a stationary front
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what clouds do not intersect the ground
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occluded fronts
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what are the occluded fronts
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the interface between the air masses is aloft
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What causes surface low pressure to intensify?
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Cyclogenesis
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what initiates "cyclogenesis"
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when upper-level divergence is stronger than lower-level convergence, more air is taken out at the top than is brought in at the bottom. Surface pressure drops, and the low intensifies, or "deepens"
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Based on the trough where is the convergence
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behind
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Based on the trough where is the divergence |
ahead
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What does an upper level divergence initiate?
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Upper level divergence initiates and maintains a surface low.
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what is used to forecast weather
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persistence forecast
trend forecast
analogue forecast
statistical forecast |
what is persistence forecast
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a prediction that future weather will be the same as present weather
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what is forecast
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surface weather systems tend to move in the same direction and at approximately the same speed as they have been moving
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what is analogue forecast
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the future will be like weather that historically occurred when similar conditions were present
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what is statistical forecast
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made routinely of weather elements based on the past performance of computer models
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what are the three stages of an ordinary (air-mass) T-storm in order
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cumulus
mature
dissipation |
what is the cumulus stage
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updrafts dominate throughout the cloud and growth from a cumulus to a cumulonimbus cloud occurs
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what is the mature stage
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heavy rain and possibly small hail, in which downdrafts are found side by side with updrafts
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what is the dissipation stage
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dominated by downdrafts and evaporation
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what is the most intense phase in an ordinary (air-mass) T-storm
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the mature stage
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what are ordinary or air mass T-storms
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localized, short-lived phenomena that dissipate themselves because downdrafts cut off the storm's fuel supply.
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How many T-storms occur annually in US
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100.000
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how many t-storms become severe storms
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10%
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what is the key factor for severe storm
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the existence of strong vertical wind shear
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what is a wind shear
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changes in wind direction and/ or speed between different heights
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what is the diameter for a hurricane
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500 km
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what is the eye of a hurricane
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area of broken clouds at the center
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how are the winds in the eye of the hurricane
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light
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what is the diameter of the eye of the hurricane
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40 km
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what is the surface air pressure for a hurricane
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955 mb
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when do surface winds increase in speed
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they increase when they blow counterclockwise and inward toward this center (NH)
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what is adjacent to the eye
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the eye wall
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what is the eyewall
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a ring of intense thunderstorms that whirl around the storm's center and may extend upward to almost 18 km
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where do we find the heaviest precipitation and the strongest winds
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the eyewall
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what happens when the outflow reaches the storm's periphery
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it begins to sink and warm, inducing clear skies
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what happens in the vigorous convective clouds of the eyewall
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the air warms due to the release of latent heat
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what does the warming in the eyewall cause
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slighter higher pressures aloft, which initiate downward air motion within the eye
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how does air warm when it sinks
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by compression
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what does compression do
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helps to account for the warm air and the absence of thunderstorms in the center of the storm
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where do hurricanes form
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tropical waters where the winds are light
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when do hurricanes form
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when humidity is high in a deep layer extending up through the troposhere
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how warm is the surface water temperature in hurricane
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26.5°C (80°F) or greater over a vast area
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what regions do hurricanes usually form
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over the tropical and subtropical north atlantic and north pacific oceans
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when is hurricane season
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runs form June through November
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what is an air mass
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an extremely large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any given altitude
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how much do air mass cover
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thousands of square km
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how are air mass classified
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by their origin
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what happens when an air mass moves over a large body of water
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its original properties may change considerably
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what happens when cold, dry, and stable air mass moves over the warmer Gulf of Mexico
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surface warm air becomes unstable, rises and forms extensive rows of cumulus cloud streets
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what are fronts
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temp
moisture characteristic
wind direction pressure tendency
precipitation patterns |
what are cylcones
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an area of low pressure around which the winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere
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how do middle-latitude cyclone (wave cyclone) form
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Polar Front Theory
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what is the polar front theory
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stationary
nascent
mature
partially occluded
occluded
dissipated |
what is the lifetime of a typical of a cyclone
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several days to a week
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why is it that some frontal waves develop into huge cyclonic storms, while other dissipate in a day or so
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a low pressure system may develop into a cyclone if the low pressure system intensifies (pressure drops in the center of the low)
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what are comma clouds
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cloud bands associated with mid-latitude cyclone look like a giant comma
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what is a meteogram
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a chart that shows how one or more weather variables has changed at a station over a given period of time
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what is a T-storm
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a cloud or cluster of clouds that produces thunders, lightning, heavy rain, and sometimes hail and tornadoes
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when do T-storms occur
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when warm, moist air rises in an unstable environment, near weather fronts, in advance of upper-level troughs, over mountain slopes
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what is the life span for ordinary T-storms
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short
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what do ordinary T-storms rarely produce
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strong winds or large hails
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how strong are the wind gusts for severe storms
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50 knots
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where are T-storms most common in US
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southeastern
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how long does it take to complete a T-storms life cycle
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one hour
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what is a downburst
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a strong localized downdraft beneath a severe thunderstorm
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what is a microburst
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a downburst less than 4 km wide
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what is a hurricane
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an intense storm of tropical origin, with sustained winds exceeding 64 knots
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