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WEATHER

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Title: WEATHER


1
WEATHER
2
  • Meteorology is the study of the atmosphere and
    its phenomena
  • Aristotle wrote a book on natural philosophy (340
    BC) entitled Meteorologica
  • Sum knowledge of weather/climate at time
  • Meteors were all things that fell from the sky or
    were seen in the air
  • meteoros Greek word meaning high in air

3
WEATHER VS. CLIMATE Weather is NOW and is
comprised of a) air temperature b) air pressure
c) humidity d) clouds e) precipitation f)
visibility g) wind Climate represents long-term
(e.g. 30 yr) averages of weather.
4
  • Invention of weather instruments
  • 1500s Galileo invented water thermometer
  • 1643 Torricelli invented mercury barometer
  • 1667 Hooke invented anemometer
  • 1719 Fahrenheit developed temp scale based on
    boiling/freezing water
  • 1735 Hadley explained how the earths rotation
    influences winds in tropics
  • 1742 Celsius developed the centigrade temp scale

5
  • 1787 Charles discovered relationship between temp
    and volume of air
  • 1835 Coriolis used math to demonstrate the effect
    that the earths rotation has on atmosphere
  • 1869 first isobars were placed on map
  • 1920 concepts of air masses and weather fronts
    were formulated in Norway
  • 1940s upper air balloons
  • 3-D view of atmosphere
  • 1950s high speed computers
  • 1960 Tiros 1 first weather satellite

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Air Pressure
  • the weight of the air above you from where you
    are to the top of the atmosphere.

12
Air is compressible -
  • Half of all air molecules are below 18,000 feet
    of altitude 3/4 are below 36,000 feet, etc.
  • At sea level air exerts a force of about 14
    pounds per square inch

13
Air pressure is measured with a barometer
14
Air Pressure in the News -
15
Cold air has higher pressure
  • Cold air is more dense, so it sinks down and
    pushes harder.
  • Barometer goes?
  • Hot air expands, becomes less dense, rises, and
    exerts less pressure.
  • Barometer goes?

16
Wind movement of air
  • Wind goes from an area of high pressure toward an
    area of lower pressure.
  • Wind direction is described by where the air
    comes from - a west wind blows from west toward
    the east.

17
Local Winds-Which way would the wind blow?
What time of day is shown in this picture?
18
More Local Winds-Which way would the wind blow?
What time of day is shown in this picture?
19
How do meteorologists predict wind direction?
20
Coriolis Effect
  • Because the Earth rotates on its axis, things
    moving from North to South or from South to
    North are deflected.
  • In the Northern Hemisphere, the deflection is to
    the right.
  • In the Southern Hemisphere, the deflection is to
    the left.

21
Winds Around Pressure Systems
22
Lets take one more look at that map.
23
A Low Pressure System Over Iceland
24
Why dont high pressure systems show up on
satellite photographs?
25
The summer Monsoon
  • During July, August and half of September,
    precipitation comes from thunderstorms associated
    with the summer monsoon
  • Convection occurs in moist southerly flow
  • Because of its high intensity/short duration,
    most summer rainfall runs off quickly and/or
    evaporates
  • Less replenishment of soil moisture and
    recharging of aquifers than winter precip

26
Winds shift to a southerly or southeasterly
direction. This produces a change in moisture.
Together with daytime heating causes the Arizona
monsoon.
27
The recipe for monsoon precipitation in Arizona
Middle-level flow
Westerlies well to the north
High pressure belt moves north of AZ, bringing
mid-level easterly flow to AZ
H
H
Mid-level Gulf moisture enters AZ from the east
Low-level surge of warm, moist air
Convection breaks out over AZ
28
Physical Ingredients for a Monsoon
  • Land-Sea differences land and water have
    different heating capacities water can store
    more heat because it is a fluid and can mix heat
    down for future release
  • Planetary rotation introduces swirl and much
    stronger winds
  • Moisture water vapor, collected over oceans
    through evaporation, condenses over land and
    marginal seas releasing vast quantities of heat
  • Orography acts as elevated heat source which
    intensifies flow also conducts flow.

29
Winter Rains Air circulation pattern is called
the Pacific/North America or PNA pattern. It is
characterized by Warm, dry weather in the
western half of the country (dominated by a ridge
of high pressure). Cold, wet weather in the
eastern half of the country (dominated by a
trough of low pressure).
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