Download Fronts /Pressure Systems

Under Pressure
The Highs and Lows…
Modified from various sources by
Tracy Webb Horton High School
Wolfville, NS
Understanding Air Pressure
Air pressure is the pressure exerted by the
weight of air.
► A barometer is a device used for
measuring air pressure.
► When air pressure increases, the mercury in
the tube rises. When air pressure decreases,
so does the height of the mercury column.
Factors Affecting Wind
Wind is the result of horizontal differences in air
pressure. Air flows from areas of higher pressure
to areas of lower pressure.
A pressure gradient is the amount of pressure
change occurring over a given distance.
Closely spaced isobars - lines on a map that
connect places of equal air pressure - indicate a
steep pressure gradient and high winds. Widely
spaced isobars indicate a weak pressure gradient
and light winds.
Isobars –
show areas of same pressure
Pressure Centers and Winds
Cyclones are centers of low pressure. In
cyclones, the pressure decreases from the
outer isobars toward the center.
Anticyclones are centers of high pressure,
and just the opposite is the case—the
values of the isobars increase from the
outside toward the center.
When the pressure gradient and the Coriolis
effect are applied to pressure centers in the
Northern Hemisphere, winds form in very
specific directions.
Low pressure systems have winds that go
counterclockwise - LOWS LOOP LEFT.
Around a high, they go clockwise – HIGHS
ROTATE RIGHT
►
http://www.classzone.com/books/earth_science/terc/content/visualizations/es2
001/es2001page01.cfm?chapter_no=visualization
This brought the storm day of Feb 13, 2006
High and Low Pressure Systems
This is in the southern hemisphere – so what
kind of pressure system is it? ☺
Pressure and Weather
Rising air is associated with cloud formation
and precipitation, whereas sinking air
produces clear skies.
Low-pressure centers can produce bad
weather in any season, while high pressure
centers are associated with fine weather.
WHY?
Weather reports always emphasize the
locations and possible paths of cyclones
(low pressure) and anticyclones (high).
Airflow Patterns, Surface and
Aloft
Normal Pacific Pressures
The Arrival of …
Our claim to weather fame – The
Nor’easter
The
typical
storm
system of
the
western
Atlantic
coast…
Halloween Nor’easter of ‘91
This storm
was associated
with high winds
and BIG waves
♦ The ship the
♦
Andrea Gail
sunk in this
storm
The devastation of this storm reached as far as
Mexico
Satelite picture
by NASA on March
13th, 1993 at 10: 01
♦
Blizzard of 2005 ‘White Juan’
January 22-23, 2005
Dumping Snow on the Atlantic Provinces and North
Eastern United States
Satelite
Picture taken
on Jan. 23rd,
2005 at 9:15
am.
♦
According to NASA, the hottest place in 2004 and 2005 was the Lut
desert of Iran, which reached 70.7 degrees C (159 degrees F). In
2003, Queensland, Australia, was the hottest place on Earth, with a
temperature of 69.3 degrees C (157 degrees F).
Fronts
When two air masses meet, they form a
front, which is a boundary that separates
two air masses.
Types of Fronts
Warm Fronts
A warm front forms when warm air moves
into an area formerly covered by cooler air.
Cold Fronts
A cold front forms when cold, dense air
moves into a region occupied by warmer
air.
http://www.classzone.com/books/earth_science/terc/content/visualization
s/es2002/es2002page01.cfm?chapter_no=visualization
Formation of a warm front
Warm fronts always have a typical cloud
series form – remember “CCANS”
Cirrus - hair like, wispy
Cirrostratus – wispy layers
Altostratus – mid layers
Nimbostratus – rain-bearing layers
Stratus - layers
Guess where this picture was taken – it is within 20 km
from Horton…
Formation of a cold front
Middle-Latitude Cyclone Model
Development of a T-storm
Formation of a Mesocyclone –
otherwise know as a Super Cell
It is estimated that there are around 44,000
thunderstorms that occur around the Earth every day. The
average thunderstorm releases the energy equivalent of a
20 kiloton nuclear weapon, or a small nuclear power plant.
http://sciencereviewgames.com/s
rg/games/ps.php?id=2
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rg/subjects/games.php?id=1