Transcript No Slide Title

• Meteorology Today
• AG2 Vol. 1
• AG2 Vol. 2
• Forecaster’s Handbook
• Cloud Formation
• Heat Transfer in the Atmosphere
• Fronts
• Air Masses
• Global Systems
• Convective Lifting or Convection - ascending
air caused by strong heating at the Earth's
surface.
• Orographic Lifting - air that is forced upward
by mountainous terrain.
• Convergence - air that is forced upward by
convergence of air near the ground. A trough
line, depicted on a weather map as a dashed line,
identifies a line of convergence at the surface.
• Frontal wedging - a process by which air is
forced upward by the displacement of one
airmass by a different airmass. This process
occurs near cold fronts, where cold air displaces
warm air and forces the warm air upward. Near
warm fronts, warm air ascends over cold surface
air that moves relatively little.
CONT.,
Convective Lifting
Some areas of the earth’s surface are better absorbers of solar radiation than others and, so, heat up
more quickly.
•No rising air takes place between the rising air and its surroundings.
•Only a single thermal produces the cumulus cloud.
•The cloud forms when the relative humidity is 100%.
•The rising air in the cloud remains saturated.
The air in contact with with the “hot spots” becomes warmer than its surroundings. A hot bubble
of air (thermal) breaks away from the warm surface & rises, expanding & cooling as it ascends.
As the thermal rises, it mixes w/ the cooler, drier air around it and gradually loses its identity. Its
upward movement now slows. Frequently, before it’s completely diluted, subsequent rising
thermals penetrate it and help the air rise little higher. If the rising air cools to its saturation
point, the moisture will condense, & the thermal becomes visible to us as a cumulus cloud.
•Orographic Lifting
This lifting produces cooling, and, if the air is humid, clouds form. The type of cloud that forms will
depend on the air’s moisture and stability content.
Advection
• Horizontal movement of air, moisture, or heat.
Convection
• Vertical movement of air, moisture, or heat.
Conduction
• Transfer of heat by molecular activity from one substance
another, or through a substance. Transfer is always from
warmer to colder regions.
Radiation
• The transfer of energy through electromagnetic waves.
Latent Heat Transfer
• Heat that is released/ absorbed by a unit mass of a substance
when it undergoes a change of state, such as during evaporation,
condensation, or sublimation.
COLD FRONT
• Leading edge of a cold air mass as that displaces warmer air.
WARM FRONT
• Leading edge of a warm air mass that displaces colder air.
OCCLUDED FRONT
• A transition zone in the atmosphere where an
advancing cold air mass sandwiches a warm air mass between another cold
air mass pushing the warm air into the upper atmosphere.
Boundary between cold and warm air mass that acts like a cold/ warm
front depending on area.
STATIONARY FRONT
• A transition zone in the atmosphere where there is little
movement of opposing air masses and winds blow towards the front
from opposite directions.
The boundary between cold and warm air in which neither air mass is
advancing.
Criteria used to locate a Front on a Surface Weather map:
1. Sharp temp. changes over a relatively short distance.
2. Changes in the air’s moisture content (as shown in marked changes in the dew point)
3. Shifts in wind direction
4. Pressure and pressure changes
5. Clouds and precipitation patterns
An air mass is a body of air extending over a large area.
(1000nm or more)
Air masses originate in areas known as source regions. In order for a
huge mass of air to develop uniform characteristics, its source region
should be flat and of uniform composition, w/ light surface winds. The
longer air remains over its source region, the more it will acquire
properties of the surface below. Most source regions are dominated by
high pressure.
Arctic (A)
Located in the vicinity of the North Pole. In this region, a gentle flow of air over the polar ice fields
allows an arctic air mass to form. This air mass is characteristically dry aloft and very cold and stable
in the lower altitudes.
Antarctic (A)
Anarctica has an intensely cold air masses that have continental characteristics. Coldest surface temp.
in the world.
Continental Polar (cP)
Region covers all land areas effected by the Siberian and Canadian high pressure cells.With the
intense cold and the absence of water bodies, very little moisture is taken into the air in these regions.
(40° to 60°)
Maritime Polar (mP)
Regions consist of the open unfrozen polar sea areas 60°N. and S. latitude.
Continental Tropical (cT)
Regions consist of land areas in the tropics, 25°N and 25° S.
Land in these areas are hot and dry.
Maritime Tropical (mT)
Regions consist of open tropical sea areas.
The air is warm because of the low latitude and can hold considerable moisture.
Equatorial (E)
Region consists of the area 10°N to 10°S.
It’s extremely warm and a high moisture content in this area.
Convergence of the trade winds from both hemispheres and the intense insolation
over this region causes lifting of the unstable, moist air to high levels.
Superior (S)
Region consists south central U.S.
With subsidence effects playing a part, it’s the warmest air mass in N. America.
POLAR CELL
• Three-dimensional atmospheric circulation cell located at roughly 60° to 90° N and S of the
equator.
• Mid-latitude cells in both hemispheres are termed the Ferrel Cells.
• Cold, dense air descends in a polar high-pressure system and moves toward the equator.
FERREL CELL
• Named after the American meteorologist William Ferrel.
• Three-dimensional middle latitude cell located at roughly 30° to 60° N and S of the equator.
• Reverse circulation in these cells results from the air flowing toward the poles from the
subtropical highs which collides with cold air flowing from the Poles.
• The zone of convergence is the polar front.
HADLEY CELL
• Named after the 18th century English meteorologist George Hadley.
• Low latitude air movement toward the equator that with heating, rises vertically, with poleward
movement in the upper atmosphere.
• Forming a convection cell that dominates tropical and sub-tropical climates.
Polar Easterlies
• Shallow body of easterly winds located at high latitudes poleward of the subpolar low.
• Cold air from the poles and behind the polar front is deflected by the Coriolis force, causing the air
to have a NE flow.
Subpolar Front
• Transition zone between the poles and tropics.
• Boundary that seperates tropical air masses from polar air masses.
• A zone of high pressure characterized by ascending air and cloud formation.
Westerlies
• Any semipermanent belt of westerly winds, esp. those that prevail at latitudes lying between the
tropical and polar regions of the earth.
Subtropical Front
• Temperature transition zone over subtropical latitudes.
• Warm air carried poleward by the Hadley cell meets the cooler air of the midlats.
Subtropical High
• Produced by the convergence of air aloft at latitudes near 30°.
• This subsiding air produces clear skies and warm surface temp.
• Over water, the weak pressure gradient in the center of the high produce only weak winds.
Trade Winds
• The trade winds are huge global patterns of wind trend that over the years have been
harnessed for use as trade routes. These winds are a result of the; cold polar regions,
the suns heating and the spin of the earth all combined. To be more specific the Trade
winds are those that blow towards the equator from the subtropics or Horse latitudes.
• In the Northern Hemisphere they are the NE Trade winds.
• In the Southern Hemisphere they are the SE Trade winds.
Intertropical Convergence Zone (ITCZ)
• With the exception of the extreme Western Pacific, the transition between the
northeast and southeast trades usually takes place within a very narrow belt located
several deg. N. of the equator.
• ITCZ is where the NE and SE trades flow together, and are characterized by strong
upward motion and heavy rainfall.
• The ITCZ is most clearly defined over the eastern portions of the Pacific and Atlantic
oceans.
Subpolar Low
• Belt of low pressure between 50° and 70° latitude.
• N. Hemisphere- Aleutian low and Icelandic low
• S. Hemisphere- Around the Anarctic continent area.
Coriolis Effect
• The Coriolis effect was first introduced by a French mathematician named Gaspard Coriolis in
the early 19th century.
• Tendency for any moving body on or above the earth's surface to drift sideways from its course
because of the earth's rotational direction (west to east) and speed, which is greater for a surface
point near the equator than toward the poles.
• In the N. Hemisphere the drift is to the right of the motion, with storms or cyclones rotating
counterclockwise.
• In the S. Hemisphere the drift is to the left of the motion, with storms or cyclones rotating
clockwise.
Jet Stream
• Jet streams are bands of very strong upper level winds
which occur at limited altitudes.
• They can be over 150m wide and 1000m long and can
travel at over 250mph.
• Like most winds they occur where there is a contrast
between hot and cold.
• Jet streams occur around the joins of tropical and
polar air.
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