ERS 323
What are the typical tracks of coastal cyclones?
1) East Coast cyclones: northeastward along the coast and out to sea northeast of Canada's Atlantic Provinces (2) Gulf Coast cyclones: either eastward along the Gulf Coast and then northward along the Atlantic coastline, or northeastward inland through the Mississippi and Ohio River Valleys.
How does air temperature change with height in the stratosphere?
Increases with height.
What are lines of constant pressure, temperature, and dew point temperature called?
Isobars, isotherms, isodrosotherms
What is geostrophic balance?
balance between the pressure gradient force and the coriolis force.
Between what altitudes is the jet stream typically found?
between 250-500mb
for how many days ahead are medium range forecast models used?
0-15 days ahead
How is atmospheric pressure defined?
force applied by air on a unit area of surface
What are four ways that air parcels can be lifted?
frontal lifting, caused by a cold air mass, lifting along a sea breeze front, lifting by mountains, and local convergence.
What is the relationship between airmasses and fronts?
fronts are the edge of an airmass.
what are the two types of orbits in which weather satellites monitor the earth?
geostationary and low earth orbits
What is latent heat?
hidden heat required for a phase change.
if an air column is cooled thgouh radiative cooling how will the surface pressure change?
high pressure at the surface
What is meant by "conditional instability"?
if a parcel of air will be unstable if saturated and stable if unsaturated, then the atmosphere is conditionally stable.
What are the three main factors that cause NWP model forecasts to degrade as the forecast range lengthens?
inexact equations, errors in the initial weather conditions, inadequate resolution
What is rawinsonde? How frequently does it provide information?
instrument on weather balloons that measures pressure, temperature, dew point temp, wind direction and speed. Provides information twice a day.
What does a computer model consist of?
interconnected set of mathematical equations that represent the atmosphere's behavior. Some predict the future state of the atmosphere based on the current conditions.
What is an adiabatic process?
parcel of air does not mix with it's environment or exchange energy with it's environment.
What is the significance of stability with respect to severe thunderstorms?
stability determine the location and intensity of convective storms in the atmosphere
What units for temperature are used in meteorology in the United States?
the Fahrenheit scale.
What does it mean when we say air is saturated?
the air is holding as much water vapor as it can without forming precipitation.
What is the relative humidity?
the amount of water vapor in the air compared to the amount of water vapor the air can hold.
What is the name of the lapse rate obtained from rawinsonde measurements?
the environmental lapse rate
Coastal cyclones are typically more intense than Rocky Mountain cyclones. Why?
Greater release of latent heat of condensation, more sensible heat from the ocean surface than land, strong thermal contrasts between air over ocean and land along coast, multiple jetstreaks typically present create greater divergence aloft, and less frictional dissipation of low over ocean compared to land.
What is a typical size of an area affected by a mature extratropical cyclone?
1/3 the size of the united states
What is the value of the relative humidity if the dew point temperature equals the air temperature?
100%
What is the value of the average sea level pressure?
1013.25 millibars
For how many days ahead are long range forecast models used?
30 and 90 days
What constant pressure maps might you examine to locate the jet stream?
300, 200, 250 mb maps
for how many days ahead are short range forecast models used?
84 hours
What constant pressure maps might you examine to locate fronts?
850 mb map
What is the importance of the surface high pressure often found over the North Atlantic Ocean during the development of an East Coast cyclone?
Air moving westward south of the high gains heat and moisture as it flows over a large region of the Atlantic Ocean; as it moves westward across the coast, it forces the cold air into a wedge, causing cold air damming and a coastal front. The warm moist air overrides the cold air, producing extensive condensation and precipitation.
New England mariners call some storms "Nor'westers." Where might this terminology come from and what type of weather conditions would you expect to occur over New England during a Nor'wester?
As a Nor'easter tracks to the north of New England, the wind direction shifts from northeast to north to northwest, bringing very cold air into the region.
Describe how a computer model is initialized and run
Begins with the first guess of the state of the atmosphere, typically taken from a previous forecast, these are then corrected by observations, adjusted again to ensure the conditions align with mathematical equations of the atmosphere, then run in five minute intervals to predict the weather.
What is the tropopause?
Boundary layer between troposphere and stratosphere
What is contouring? How does contouring simplify the reading of weather maps?
Contouring connects lines across a map of areas that have the same temp, dew point, or pressure.Contour lines allow you to easily compare weather information across the country.
What are all the possible meteorological conditions that contribute to strong divergence aloft during the initial development of East Coast cyclones?
Curvature effect on eastern side of upper-level trough Jetstreak divergence (jetstreaks in polar and/or subtropical jet streams) Heating of air column by condensation above surface cyclone
How does air temperature change with height in the troposphere?
Decreases with height
What is a wind profiler?
Doppler radar that operates in very high frequency and ultra high frequency radio bands. used to create a vertical profile of the wind.
What is cold air damming? Where does it occur
Onshore flow from the Atlantic forces cold air near the coast into a narrow wedge between the coastline and the Appalachian Mountains. The mountains dam the cold air on their east side, while the warm air coming off the ocean flows up over the trapped cold air.
Which four forces control the movement of air?
Pressure gradient force, coriolis force, gravitational force, frictional force.
How are topographic maps of the earth's surface similar to constant pressure maps of the upper atmosphere?
The closer together the contour lines, the greater the amount of change in a smaller area. Just like steepness on a topography map.
What is the convention for reporting wind direction?
The directions from which the wind is blowing
What is the importance of a dissipating Rocky Mountain cyclone during the early development of cyclones on the East and Gulf Coasts?
The dissipating cyclone provides the necessary environment for the coastal storm to form: Cold air behind its cold front spills over the Appalachians to the East Coast; the polar jetstream above the cold front is displaced southeastward so that it flows across the central Atlantic coast.
How does the altitude of the tropopause affect the eight of clouds in the troposphere?
The higher the tropopause, the higher clouds and storms can go in the troposphere
What is wind?
The movement of air
What do wind barbs represent on a weather map?
The speed of the wind, and the direction
What is the typical range of sea level pressures found in intense coastal cyclones?
The strongest coastal cyclones develop central pressures between 960 and 970 mb.
What is the subtropical jetstream? Where is it typically found? Why does it exist?
The subtropical jetstream is an upper-tropospheric band of strong winds (a jetstream) that forms on the poleward side of the Hadley cell. The poleward- flowing upper branch of the Hadley cell accelerates eastward due to the Coriolis force (conservation of angular momentum); the strong northeastward or eastward airflow is typically found between 20° and 40°N, and near 200 mb in the vertical.
What does a cyclone look like on a satellite image?
a "comma"
What causes the pressure gradient force? In which direction does it act?
a force applied to parcels of air due to differences in pressure. moves perpendicular to isobars, from high pressures to low pressures.
Where will a low-pressure center form at the surface relative to an upper air trough and ridge?
a low will occur on the surface when there is divergence aloft. leading up to a ridge.
What is meant by ensemble forecasting?
a model is run repeatedly but with slight variations, then formatted into a consensus forecast, which will be more accurate than one model alone.
What is the major constraint that prevents mesoscale models from being used for actual forecasting?
a model may take longer to create than the actual weather event would last. they do not include observational data, so you cannot conclude what would happen in a very specific point.
How is the density of an air parcel related to it's temperature and to atmospheric stability?
a parcel of air is less dense than it's environment if it is warmer than the air around it, it an air parcel is warmer of colder, there is a density difference and the atmosphere is unstable.
How does a change in the curvature of airfloww affect the speed of the flow as air flows from a ridge to a trough? A trough to a ridge?
air moves faster from a ridge to a trough, and slower from a trough to a ridge
How does heating of the ground by sunlight affect the stability of the lower atmosphere?
air near the ground becomes warmer than the surrounding air and spontaneously moves up, creating an unstable environment.
How does a mercury barometer measure atmospheric pressure?
air pushes down on the mercury in the vacuum tube. Higher pressures lead to a stronger push on the mercury, which makes it rise in the tube.
where do cold air damming and cold air trapping typically occur?
along mountain chains.
What type of observations are available from automated surface observing systems?
cloud height and amount, visibility, precipitation type, intensity and accumulation, fog, sea level pressure, temperature, dew point temperature, wind direction and speed, and characteristics,
What are the six different kinds of fronts
cold front, warm front, stationary, occluded, dry lines, upper level
What is the dew point temperature?
coldest temperature air can reach before it becomes saturated
How do commercial aircraft contribute to weather data collection?
commercial jets have weather reporting systems on them that transmit data to the national weather service as the fly. Able to transmit info about the jet streams because of their cruising altitude.
What is the approximate value of the dry and moist adiabatic pose rates in the lower atmosphere?
dry 10 C/km, moist 6 C/km
Where do cyclones typically form in North America?
east of the rockies, east of the Canadian rockies, off the coastline of the gulf of the U.S., along the east coast, over the bering sea and the gulf of alaska
How would you identify a dry line on a map of station reports?
finding a sharp gradient in dew point temperature during the daytime, with little to no temperature gradient.
In what units are wind speed reported?
knots
How does a radar determine rainfall rates?
larger drops of rain are associated with heavier rainfall rates. Larger drops of rain scatter more energy back to the radar, so the more energy the radar receives, the higher the rainfall rates.
What important information does the national lightning detection network provide?
lightning strikes across the continental U.S. determining time, location, strength, and polarity of lightning strikes. Could help to prevent forest fires.
If an air column is heated through latent heat release, how will the surface pressure change?
low pressure at the surface
What is a numerical weather prediction?
mathematical equations that predict the behavior of earth's atmosphere done by computers.
How is temperature defined?
measure of the average speed that molecules move in a substance.
What are synoptic measurements?
meteorological measurements made routinely and at the same time around the globe
What units of pressure do meteorologists use?
millibars
In addition to rainfall rates and the elevation and location of precipitation, what else does a doppler radar measure?
movement of a storm's wind field to predict a tornado
What is the jet stream?
narrow band of strong wind that encircles the earth's middle latitudes
What atmospheric variables does a radar monitor?
precipitation
What is the coriolis force? In what direction dose it act in the Northern Hemisphere?
pull on air by the rotation of the earth. Moves to the right, or clockwise in the northern hemisphere.
What is a jet streak?
regions with exceptionally strong winds within the jetstream
What characteristics make a region a good source for airmasses?
relatively flat surfaces with homogenous characteristics.
What is the lifetime of a typical extratropical cyclone?
several days to over a week.
How large and deep is a typical airmass?
several hundred thousand square kilometers, and as thick as the troposphere, or as thin as 1-2km
List at least five variables that can be used to identify the position of fronts on weather maps
sharp temperature gradients, sharp dewpoint temperature gradient, sharp shift in wind direction, pressure troughs, lines of showers and precipitation
Provide two examples of the problems scientists face in developing computer models
snow cover and topography, temperatures change differently base on snow cover, cannot predict the elevations of all regions for localized weather reporting.
What is the difference between the lifting condensation level and the level of free convection?
the lifting condensation level is the level air must reach to caused condensation, seen as the cloud base, the level of free convection is the height at which air first becomes buoyant.
What information does a cross section provide that is different from an upper level map or a surface map?
the vertical structure of fronts, jet streams, and other features
What are three criteria used to classify fronts?
thermal and moisture characteristics, direction in which it is moving, and weather it is touching the ground or is aloft.
Name all of the boundaries that can trigger thunderstorm development south of a low pressure system
upper level front, dry line, and cold front
How are synoptic measurements coordinated?
using utc, must take measurements at the same time everywhere.
What are the tree primary channels used to create weather satellite images?
visible, infrared, and water vapor channels
Where are warm fronts, cold fronts, and dry lines found relative to the center of an extratropical cyclone?
warm moist are is to the south east, warm dry air is to the west, cold dry air to the north, and cold moist air north east
What is hydrostatic balance?
when the upward pressure gradient force equals the force of gravity
What is the role of waves in the jet stream in the development of extratropical cyclones?
when waves in the jet streak lead to a low pressure trough east of the rockies.
What causes friction in moving air? In which direction does the force of friction act?
winds moving at different speeds create friction, which pushes in the opposite direction of the wind.
How does surface friction modify the pressure at the center of low and high pressure systems?
with a low pressure system air will turn inward, with a high pressure system air will spiral outward
