Download Chapter 12-Meteorology

Chapter 12-Meteorology
1
I. Causes of Weather
A. Meteorology is the study of
atmospheric phenomena.
1. Clouds, raindrops, snowflakes, fog,
dust and rainbows are all types of
atmospheric meteorology.
2
3
4
B. Weather and climate
1. Weather is the current state of the
atmosphere.
2. Weather is referred mainly to short-term
variations in the atmosphere.
3. These variations could occur over minutes,
hours, days, weeks, or months.
5
4. Long term variations in weather for
a particular area make u the climate of
that area.
5. Climate is usually averaged over the
course of 30 years or more.
6
Weather
7
Climate
8
C. A question of balance
1. The sun’s rays are spread out all
over the earth.
2. There are some areas that have high
amounts of the sun’s rays and some
areas that have low amounts of the
sun’s rays.
9
10
D. Air masses
1. Air mass is a large body of air that
takes on the characteristics of the area
over which it forms.
2. Air masses form over land or water.
3. Air masses are classified according
to their regions.
11
12
4. All five main types of air masses can
be found in North America because of
the continent’s proximity to the source
regions associated with each air mass.
5. Air masses do not stay in one place
indefinitely. They move.
13
Air mass
14
II.
Weather systems
A. Global wind systems.
1. Trade winds occur at 30 degrees
north and south latitude.
2. There, air sinks, warms and moves
toward the equator in a westerly
direction.
15
16
3. The second wind system, the
prevailing westerly, flows between 30
degrees and 60 degrees north and
south latitude in a circulation pattern
opposite that of the trade winds.
17
4. The polar easterlies lies between 60
degrees latitude and the poles.
5. Similar to the trade winds, the polar
easterlies flow from the northeast to the
southwest in the northern hemisphere.
18
B. Jet Streams
1. Narrow bands of fast, high-altitude,
westerly winds called jet streams flow at
speeds up to 185 km/h.
2. Disturbance form along jet streams and
give rise to large-scale weather systems that
transport surface cold air toward the tropics
and surface warm air toward the poles.
19
20
3. A front is the
narrow region
separating the two
air masses of
different densities.
21
4. Cold fronts –
dense air displaces
warm air and forces
the warm air up
along a step front.
22
5. Warm frontsAdvancing warm air
displaces cold air.
23
6. Stationary fronttwo air masses meet
and neither
advanced into the
other’s territory.
24
7. Occluded frontsCold air mass moves
so rapidly that it
overtakes a warm
front.
25
26
C. Pressure systems
1. High-pressure systems, air sinks, so
that when it reaches Earth’s surface, it
spreads away form the center.
2. Low-pressure systems, air rises.
27
HIGH PRESSURE
28
LOW PRESSURE
29
III. Gathering weather data
A. Surface data
1. One of the most common weather
instruments is a thermometer, a
device used to measure temperature.
30
2. Barometers measure
air pressure.
3. In a mercury
barometer, changes in
air pressure are
indicated by changes in
the height of a column
of mercury.
31
32
4. An anemometer is used to measure
wind speed.
33
34
5.
Hygrometer measures relative
humidity.
35
36
6. Ceilometers measure the height of
cloud layers and estimates the amount
of sky covered by clouds.
37
38
7. The instrument of choice gathering upper –level
data is a balloon- born package of sensors called a
radiosonde.
39
B. Weather radar
1. The Doppler
effect is the change
in wave frequency
that occurs in
energy, such as
sound or light as the
energy moves
toward or away from
an observer.
40
IV. Weather analysis
A.
Surface Analysis
1. Station models provide information for
individual sits.
2. To plot data nationwide or globally,
meteorologists use isopleths, which are
lines that connect points of equal or
constant values.
41
3. Digital forecasting is the main
method used by modern
meteorologists.
4. It is highly dependent on the density
of the data available, basically, the more
data, the more accurate the forecast.
42
5. Another type of forecast, an analog
forecast, involves comparing current
weather patterns to patterns that took
place in the past.
6. Long term forecasts involving
months and seasons are based largely
on patterns or cycles.
43
The end
44