Transcript Ch. 12 - Meteorology

Ch. 12 - Meteorology
Weather – current state of the atmosphere.
Climate – long-term variations in weather for a
particular area.
Meteorology – the study of the atmosphere
–Meteor is Greek for “high in the air”.
–Hydormeteors – cloud droplets and forms of
precipitation with water.
–Lithometeors – condensation nuclei – dust, smoke,
haze, etc.
–Electrometeors – thunder and lightning.
–Usually of 30 years or more.
 The Sun’s radiation does not heat the whole
surface for it’s round; it relies on the green
house effect.
 The radiation hits the Earth at angles ranging
from 0 to 90 degrees.
– The continual motion of air and water reallocates
heat energy among Earth’s surface, oceans, and
atmosphere and brings it into balance.
 At what angle does it heat the Earth the most?
– 90 degrees (direct)  illustrate
 Some areas around the equator receive close
to direct radiation at noon all year long.
 During what part of the day is it coolest?
– Just before sunrise
 During what part of the day is it hottest?
– 3:00 to 4:00 Why?
 Cloudy skies trap the heat & clear skies allow it
to release rapidly
– Which would cause a higher risk of sunburn?
 When is it the warmest time of the year in the
Northern Hemisphere?
– June 21
 Southern Hemisphere?
– Dec. 21
 What is the coolest time in the N.H.?
 What is the coolest time in the S.H.?
 Illustrate – tilt of the Earth
 Air Masses - these are huge sections of the
lower troposphere that have the same kind of
weather throughout it.
 They usually maintain the same position for
days or even weeks.
 The weather in an air mass is determined by
the region it originated in. Cold vs. Warm.
– Warm and dry from continental tropic (cT), warm
and humid from maritime tropic (mT), cold and dry
continental polar (cP), cold and humid maritime
polar (mP), and artic (A).
 Fig. 12.3 (pg. 303) & Table 12-1 (pg. 304)
 Video – air masses
Weather Systems
 Coriolis effect – the air coming from the poles moves
to the right in the northern hemisphere and to the left
in the southern hemisphere. This is due to the rotation
of the Earth.
– Trade winds
 Occurs at 30° North & South latitude.
 The air sink, warms and moves toward the equator in a westerly
direction.
 Causes high pressure
– Prevailing westerlies
 Between 30° & 60° north and south latitude in circulation pattern
opposite that of the trade winds.
 Blowing from the west to the east
 Responsible for movement of weather across the U.S.
 Video – Coriolis effect
– Polar easterlies
 Between 60° & the poles.
 Similar to the trade winds
 Jet Streams – narrow bands of fast, highaltitude, westerly winds.
– They strongly influence the temperature and
pressure on either side of the jet stream.
 This causes wind.
– Polar jets stream & Subtropical jet stream fig. 12-6.
– The deeper it dips or the steeper it rises the more
influence it has on temperature changes.
Fronts
 Front is a boundary of different air masses.
– They have different densities due to different temperatures, pressure,
and humidity.
– They can bring big changes in weather.
 1. Cold Fronts – cold, dense air displaces warm air up. As the
warm air rises it cools and condenses – clouds, showers, and
sometimes thunderstorms.
 2. Warm Front – warm air displaces cold air. The warm air
develops a gradual frontal slope unlike a cold front – extensive
cloudiness and precipitation.
 3. Stationary Front – neither air mass advances the other. The
boundary stalls – seldom have extensive cloud and heavy
precipitation.
 4. Occluded Front – cold air mass moves so rapidly that it
overtakes a warm front. The cold air wedges the warm air
upward. Precipitation is common on both sides of the front.
 Video - fronts
Pressure System
 Rising air is associated with low pressure and
sinking air is associated with high pressure.
 High Pressure air sinks and spreads away from
the center. The deflection of the air to the right
caused by the Coriolis effect makes the overall
circulation around a high pressure center move
clockwise in the northern hemisphere and
counter-clockwise in the southern hemisphere.
– Cold air masses are associated with high pressure.
 Low Pressure air rises and must be replaced by
air from outside the system so it flows inward.
The air in a low pressure system turns counterclockwise in the northern hemisphere.
 It is hard for clouds to form when air sinks.
Thus, high-pressure systems are usually
associated with fair weather, while low-pressure
systems are associated with clouds and
precipitation.
 A wave cyclone usually begins along a
stationary front. Some imbalance in
temperature, pressure, or density causes part
of the front to move south as the cold front and
another part of the front to move north as a
warm front. This causes a counterclockwise
rotation.
 Video – weather influences
Gathering Weather Data
 A thermometer is the most common weather
instrument used by meteorologist.
 What measures air pressure?
– Barometer
 At sea level the air pressure is 760 mm or 30 in.
 As air pressure goes up the Hg is forced up in
its measuring column (mercury barometer)
 An aneroid barometer contains a vacuum inside
a metal chamber in which the chamber
contracts or expands with changes in air
pressure.
 Anemometers are used to measure wind
speeds.
 A hygrometer is used to measure relative
humidity.
 Ceilometers may be used to measure the
height of cloud layers and amount of cloud
cover.
 Data must be gathered at the same time at
many different location. Why?
 Our Project Globe weather station needs to be
taken at International time at solar noon, so all
the data collected internationally has
consistency.
 National weather stations use a radiosonde
(weather balloon), which has temperature, air
pressure, and humidity sensors that send back
readings to the ground station. Tracking the
balloon in the upper-level provides accurate
snapshots of atmospheric conditions.
 Doppler Radar – wave frequencies change
speed (energy) as rain & winds caused by a
thunderstorm moves towards or away from the
radar station.
– Accurate wind speeds, precipitation, and storm
intensity can be used by meteorologists.
Weather Analysis
 To record weather data for a particular site at a
particular time a station model is used.
– Fig. 12-15 (pg. 317)
 Isopleths are used to plot nationwide or global data.
The isopleths are lines that connect points of equal or
constant values.
– Lines of equal pressure = isobars (winds)
– Lines of equal temperature = isotherms
 Meteorologist use very sophisticated lab equipment,
computers, & models.
 Meteorologists are very accurate compared to about
15-20 years ago.
 Video – Weather Prediction
 Digital forecasts are highly dependent on the
density of the data available.
 An analog forecast is also used to compare
current weather patterns to past patterns.
 Even high-tech computers cannot predict all
factors that affect the weather.
 Interpreting a Weather Map (pg. 322).
 Video – weather
 Video - predictions