Download MET 1010 Introduction to Weather

MET 1010
Introduction to Weather
Dr. Arturo Rodriguez
Miami Dade College
North Campus
Chapter 1: The Earth’s
Atmosphere
 Overview of the Earth’s atmosphere
 Vertical structure of the atmosphere
 Weather and climate
Overview of the Earth’s
Atmosphere
• The atmosphere, when scaled to the size of
an apple, is no thicker than the skin on an apple.
The Earth’s Atmosphere
The earth’s atmosphere is a thin gaseous
envelope comprised mostly of nitrogen (N2)
and oxygen (O2), with small amounts of
other gases, such as water vapor (H2O)
and carbon dioxide (CO2).
Almost 99% of the atmosphere lies within a
mere 30 km (about 19 mi) of the earth’s
surface.
The Earth’s Atmosphere
Composition of the Atmosphere.
Table 1.1 shows the various gases present in
a volume of air near the earth’s surface.
Notice that nitrogen (N2) occupies about
78% and oxygen (O2) about 21% of the
total volume of dry air. These percentages
hold up to an elevation of about 80 km (or
50 mi).
Table 1-1, p. 3
The Earth’s Atmosphere
Water vapor is an extremely important gas
in our atmosphere. The concentration of
water vapor varies greatly from place to
place, and from time to time. Close to the
surface in warm tropical locations may
account for up to 4% of the atmospheric
gases, whereas in colder artic areas, its
concentration may dwindle to a mere
fraction of a percent.
The Earth’s Atmosphere
The changing of water vapor into liquid
water is called condensation, whereas the
process of liquid water becoming water
vapor is called evaporation. In the lower
atmosphere, water is everywhere. It is the
only substance that exists as a gas, a
liquid, and a solid at those temperatures
and pressures normally found near the
earth’s surface.
The Earth’s Atmosphere
Water vapor releases large amounts of heat
–called latent heat- when it changes from
vapor into liquid water or ice. Latent heat
is an important source of atmospheric
energy, especially for storms, such as
thunderstorms and hurricanes.
Water vapor is a potent greenhouse gas
because it strongly absorbs a portion of the
earth’s outgoing radiant energy. Thus, water
vapor plays a significant role in the earth’s
heat-energy balance.
The Earth’s Atmosphere
Carbon dioxide (CO2), a natural
component of the atmosphere, occupies
about 0.037% of a volume of air. CO2 enters
the atmosphere mainly from the decay of
vegetation, but it also comes from volcanic
eruptions, the exhalations of animal life,
from the burning of fossil fuels (such as
coal, oil and natural gas), and from
deforestation.
The Earth’s Atmosphere
The removal of CO2 from the atmosphere
takes place during photosynthesis, as
plants consume CO2 to produce green
matter. The CO2 is then stored in roots,
branches and leaves. The oceans act as a
huge reservoir for CO2, as phytoplankton in
surface water fix CO2 into organic tissues.
Estimates are that the oceans hold more
than 50 times the total atmospheric CO2
content.
The Earth’s Atmosphere
Fig. 1.3 reveals that the atmospheric
concentration of CO2 has risen more than
18% since 1958 when it was first measured
at Mauna Loa Observatory in Hawaii. This
increase means that CO2 is entering the
atmosphere at a grater rate than it is
being removed. The increase appears to
be due to the burning of fossil fuels;
however, deforestation also plays a role.
Fig. 1-4, p. 5
The Earth’s Atmosphere
Measurements of CO2 also comes from ice
cores. In Greenland and Antarctica, tiny
bubbles of air trapped within the ice sheets
reveal that before the Industrial
Revolution, CO2 levels were stable at about
280 parts per million (ppm). Since the
early 1800s, however, CO2 levels have
increased by more than 25%.
The Earth’s Atmosphere
With CO2 levels presently increasing by
about 0.4% annually (1.5 ppm/year),
scientists now estimate that the
concentration of CO2 will likely rise from its
current value of about 375 ppm to a value
near 500 ppm toward the end of the XXI
Century.
CO2 is another important greenhouse gas
because, like water vapor, it traps a portion
of the earth’s outgoing energy.
The Earth’s Atmosphere
Mathematical models that predict future
atmospheric conditions estimate that
increasing levels of carbon dioxide (and
other greenhouse gases) will result in a
global warming of surface air between
1.4ºC and 5.8ºC (about 2.5ºF and 10.5ºF)
by the year 2100. Such warming could
result in a variety of consequences.
The Earth’s Atmosphere
Carbon dioxide and water vapor are
not the only greenhouse gases. Other
greenhouse gases include methane,
nitrous oxide and
chlorofluorocarbons.
The Earth’s Atmosphere
The Early atmosphere.
The earth’s first atmosphere (some 4.6
billion years ago) was most likely hydrogen
and helium, as well as methane and
ammonia. A second, more dense
atmosphere, evolved from the gases that
escaped from the earth’s hot interior, mostly
water vapor, carbon dioxide and some
nitrogen.
The Earth’s Atmosphere
Oxygen, probably began an extremely slow
increase in concentration as energetic rays
from the sun split water vapor into hydrogen
and oxygen. This slow increase in oxygen
may have provided enough of this gas for
primitive plants to evolve perhaps 2 to 3
billion years ago.
The Earth’s Atmosphere
Vertical Structure of the Atmosphere.
Air Pressure and Air Density.
Air density is the number of air
molecules in a given space. Air
density is greatest at the surface and
decreases as we move up in the
atmosphere.
Fig. 1-5, p.8
The Earth’s Atmosphere
Air molecules have weight. This weight
act as a force upon the earth. The
amount of force exerted over an area
of surface is called atmospheric
pressure or simply air pressure.
Atmospheric pressure always
decreases with increasing height.
Fig. 1-8, p. 9
The Earth’s Atmosphere
Normal atmospheric pressure is:
14.7 pounds/square inch =
1013 .25 milibars (mb) =
1013.25 hectopascals (hPa) =
29.92 in. Hg
The Earth’s Atmosphere
Layers of the atmosphere.
Both air pressure and density
decrease with height above the earth.
Air temperature however has a more
complicated vertical profile.
Layers of the Atmosphere





vertical temperature profile
troposphere
stratosphere
mesosphere
thermosphere
• Temperatures, winds,
humidity and pressures high
above the ground are
measured twice-daily by
radiosonde.
Fig. 1-7, p.10
The Earth’s Atmosphere
Air temperature normally decreases from
the earth’s surface up to an altitude of about
11km, which is nearly 36,000 feet or 7 mi.
The rate of decrease is called the
temperature lapse rate. The average lapse
rate in the troposphere is about 6.5ºC for
every 1000 meters (m) or about 3.6ºF for
every 1000 ft
The Earth’s Atmosphere
 The layers of the atmosphere are:
Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere
The Earth’s Atmosphere
 The different layers are separated by
boundary regions located at the top of the
layers. They are called:
Tropopause
Stratopause
Mesopause
The Earth’s Atmosphere
 TROPOSPHERE
Is the region located from the surface of the earth
up to approximately 10 to 16 km (6 to 10 mi).
Temperature generally decreases with altitude.
The word troposphere is derived from the Greek
word tropein meaning “to change”. Almost all of
what we normally call weather occurs in this layer,
where 80% of the atmosphere’s mass is located.
The Earth’s Atmosphere
 STRATOSPHERE
Is the region located above the troposphere,
at an altitude near 20 km (12 mi) where
temperature increases with height.
Temperature is increasing because ozone
molecules in the stratospheric ozone layer
are absorbing solar energy near the top of
the stratosphere
The Earth’s Atmosphere
 MESOSPHERE (Middle sphere)
Is the region located above the stratosphere. The
boundary near 50 km (31 mi), which separates
these layers is called the Stratopause, where the
average temperature is close to 0 C. The air
temperature in the mesosphere decreases with
height, a phenomenon due in part to the fact that
there is little ozone in the air to absorb solar
radiation. The temperature reaches a minimum of
about -90 C at the Mesopause.
The Earth’s Atmosphere
 THERMOSPHERE
Is the hot layer above the mesosphere. The
boundary that separates the lower, colder
mesosphere from the warmer thermosphere
is the Mesopause at an average altitude of
about 85 km (53 mi). The temperature
increase, in this layer, is caused by the
absorption of energetic ultraviolet (UV) and
X-Ray radiation from the Sun.
The Earth’s Atmosphere
 IONOSPHERE
The region of the atmosphere above about
80 km is called the ionosphere, since the
energetic solar radiation knocks electrons
off molecules and atoms, turning them into
ions with a positive charge. The ionosphere
reflects and absorbs radio waves.
The Earth’s Atmosphere
 IONOSPHERE
The ionosphere plays a major role in radio
communications. The lower part (called the
D region) reflects standard AM radio waves
back to earth. At night the D region
gradually disappears and AM radio waves
are able to penetrate higher into the
ionosphere (into the E and F regions)
where the waves are reflected back to earth.
Fig. 1-11, p. 13
The Earth’s Atmosphere
 EXOSPHERE
At the top of the thermosphere, about 500
km (300 mi) above the earth’s surface is
located the exosphere, which represents the
upper limit of our atmosphere. It contains
mainly oxygen and hydrogen atoms, but
there are so few that they rarely collide, and
some escape right out into space.
The Earth’s Atmosphere
Weather & Climate
Weather refers to the condition of the
atmosphere at any particular time and place.
Weather is comprised of the elements of:
air temperature
clouds
air pressure
humidity
precipitation
wind
visibility
The Earth’s Atmosphere
Climate represents the accumulation of
daily and seasonal weather events (the
average range of weather) over a long
period of time.
The concept of climate also includes the
extremes of weather – heat waves,
blizzards, hurricanes, etc –that occur in a
particular region. The frequency of these
extremes is what distinguish among climate
that have similar averages.
The Earth’s Atmosphere
A Satellite’s View of the Weather
Longitude. The lines running from pole to
pole are called the meridians. Since the
zero meridian (or prime meridian) runs
through Greenwich, England, the longitude
of any place on earth is simply how far east
or west, in degrees, it is from the prime
meridian. North America is west of Great
Britain and most of the United States lies
between 75º W and 125º W longitude.
The Earth’s Atmosphere
The dotted lines that parallel the equator are
called parallels of latitude. The latitude of
any place is how far north or south, in
degrees, it is from the equator. The line of
the equator is 0º, whereas the latitude of
the North Pole is 90ºN and that of the
South Pole is 90ºS. Most of the United
States is located between latitude 30ºN
and 50ºN, a region commonly referred to as
the middle latitudes.
The Earth’s Atmosphere
A Look at a Weather Map
-The letter L on the map indicates a region
of low atmospheric pressure, often called
a low.
-The letter H represent a region of high
atmospheric pressure, called high or
anticyclone.
-The wind is the horizontal movement of
the air. The wind direction is the direction
from which the wind is blowing, not the
direction toward the wind is moving.
Fig. 1-11, p.17
The Earth’s Atmosphere
The wind blows around the highs and
the lows. The horizontal pressure
differences (pressure gradient) create
a force that starts the air moving from
higher pressure toward lower
pressure. The wind speed is the rate
at which the air is moving due to the
pressure gradient.
The Earth’s Atmosphere
 The new record surface wind gust on Earth
is 253 mph in Barrow Island, 31 miles of
Australia’s NW coast, during the passage of
Tropical Cyclone Olivia on April 10 1996.
The previous record was held by Mt.
Washington (New Hampshire), a wind gust
of 231 mph, set in 1934. There was also, a
new record of 212 mph measured during
2008’s Hurricane Gustav in Pinar del Rio,
Cuba.
The Earth’s Atmosphere
Because the earth’s rotation, the winds are
deflected toward the right in the Northern
Hemisphere –this deflecting force is known
as the Coriolis force. This deflection
causes the winds to blow clockwise and
outward from the center of the highs, and
counterclockwise and inward toward the
center of the low.
The Earth’s Atmosphere
-In regions of high pressure, skies are
generally clear. We can find generally clear
skies and fair weather associated with the
regions of high pressure.
-The boundary that separates the warm and
cold air masses is called a front, across
which there is a sharp change in
temperature, humidity, and wind direction.
The fronts are classified as: cold, warm and
occluded.
The Earth’s Atmosphere
Weather and Climate in Our Lives
Weather and climate play a major role in
our lives. Weather often dictates the type of
clothing we wear, while climate influences
the type of clothing we buy.
Although weather and climate affect our
lives in many ways, their most immediate
effect is in our comfort.