Transcript Chapter 25 - "Weather and Climate"

•Weather and Climate
• Weather is a description of the changeable aspects of the
atmosphere, the temperature, rainfall, pressure, and so forth,
at a particular time. These changes usually affect your daily
life one way or another, but some of them seem more
inconvenient than others.
• Clouds and Precipitation
• Introduction
– Hydrological Cycle – 4 main parts
• Evaporation of water from the oceans
• Transport of water vapor in the atmosphere
• Condensation and precipitation
• Return of water to ocean by rivers and streams
• The main events of the hydrologic cycle are: (1) The
evaporation of water from the ocean, (2) the transport of
water vapor through the atmosphere, (3) condensation and
precipitation of water on the land, and (4) return of water to
the ocean by rivers and streams.
• Cloud-forming Processes
– Upward Air Movement
• Convection resulting from differences in temperature
• Barriers such as mountain ranges which provide lift to
air masses
• Meeting of moving air masses with different densities.
– Adiabatic Cooling
• Decrease in temperature of an expanding gas
– Adiabatic Heating
• Heating of a gas as it undergoes compression
– Dry Adiabatic Lapse Rate
• Rate of cooling in the absence of condensation
• About 10 OC for each increase or decrease of 1 km
(5.5OF/1,000 ft)
• As a parcel of dry air is moved upward, it expands
and cools according to the dry adiabatic lapse rate.
This graph compares the temperature of a rising and
adiabatically cooling parcel of dry air with the
average temperatures of the surrounding atmosphere
when the temperature at the surface is 30OC (86O F).
– Atmospheric Stability
• Stability
– When the atmospheric lapse rate is less that the dry
adiabatic lapse rate
• Instability
– When the atmospheric lapse rate is greater than the
dry adiabatic lapse rate.
• If a parcel of air is moved up or down, it will cool or warm
according to the dry adiabatic lapse rate. In a state of
atmospheric stability, the parcel of air will always be cooler,
and therefore more dense, than the surrounding air at any
altitude. It will, therefore, return to the original level when
the upward force is removed.
• In a state of atmospheric instability, a parcel of air
will always be warmer, and therefore less dense,
than the surrounding air at any altitude. The parcel
will, therefore, continue on in the direction pushed
when the upward force is removed.
– Wet Adiabatic Lapse Rate
• The lapse rate for a parcel of air at a slow rate and
releasing the temperature equal to its latent heat of
vaporization
– Supersaturated
• When the air contains more water vapor than is the
normal amount of water vapor
• When the dew point temperature is reached in a rising
parcel of air, the latent heat of vaporization is released as
water vapor condenses. This release of heat warms the air,
decreasing the density and accelerating the ascent. The new
lapse rate from the release of latent heat is called the wet
adiabatic lapse rate.
• Origin of Precipitation
– Processes of precipitation formation
• Coalescence
– When water droplets merge with millions of other
water droplets.
• Growth of ice crystals
– Ice crystals can capture other water molecules and
grow to enormous sizes.
– Supercooled
• If water remains in the liquid state after the
temperature is below the freezing point.
– Ice-forming nuclei
• Solid particles on which the ice forms
• Precipitation is water in the liquid or solid form that returns
to the surface of the earth. The precipitation you see here is
liquid, and each raindrop is made from billions of the tiny
droplets that make up the clouds. The tiny droplets of clouds
become precipitation by merging to form larger droplets or
by the growth of ice crystals that melt while falling.
• Weather Producers
• Introduction
– There is a shift in weather during the changes of the
seasons that is related to:
• Movement of air masses
• Leading fronts of air masses
• high and low pressure areas
• Air Masses
– Polar air mass
• An air mass that moves from a cold region
– Tropical Air Mass
• An air mass that moves from a warm region
– Continental Air Mass
• Moves in from a land mass
– Maritime Air Mass
• Moves in from over an ocean
– Major types of air masses
• Continental Polar
– Cold
– Dry
• Maritime Polar
– Cold
– Moist
• Continental Tropical
– Warm
– Dry
• Maritime tropical
– Warm
– Moist
• The general movement of the four main types of air masses
that influence the weather over the contiguous United
States. The tropical air masses visit most often in the
summer, and the polar air masses visit most often during the
winter. During other times, the polar and tropical air masses
battle back and forth over the land.
• This satellite photograph shows the result of a polar air
mass moving southeast over the southern United States.
Clouds form over the warmer waters of the Gulf of Mexico
and the Atlantic Ocean, showing the state of atmospheric
instability from the temperature differences.
– Air mass weather
• When the weather in an area is under the influence of
an air mass.
• Weather Fronts
– Front
• A boundary between two different air masses
– Cold Front
• When a cold air mass moves into a warmer area,
displacing the warm air mass
• Provides lift to adiabatically cool the warm air,
resulting in towering cumulus and thunderclouds.
• (A)A cold air mass is
similar to a huge,
flattened bubble of
cold air that moves
across the land. The
front is the boundary
between two air
masses, a narrow
transition zone of
mixing. (B) A front is
represented by a line
on a weather map,
which shows the
location of the front at
ground level.
• An idealized cold front, showing the types of clouds that
might occur when an unstable cold air mass moves through
unstable warm air. Stable air would result in more stratus
clouds rather than cumulus clouds.
– Warm Front
• When a warm air mass moves into an area, displacing
the cold air mass
• A gently sloping front as the Warm air moves over top
of the cooler air.
– Stationary Front
• When the edge of a front ceases to advance
• An idealized warm front, showing a warm air mass
overriding and pushing cold air in front of it. Notice that the
overriding warm air produces a predictable sequence of
clouds far in advance of the moving front.
• Waves and Cyclones
– Occluded Front
• One that has been lifted completely off the ground
• Has s low pressure center and cyclonic activity
– Cyclone
• a low pressure area with winds moving into the low
pressure area and being forced upward.
• Friction and the Coriolis effect cause the air to move
to the right of the direction of movement.
– Anticyclone
• A high pressure center
• The development of a low-pressure center, or cyclonic
storm, along a stationary front as seen from above. (A) A
stationary front with cold air on the north side and warm air
on the south side.
• (B) A wave develops, producing a warm front
moving northward on the right side and a cold front
moving southward on the left side.
• (C) The cold front lifts the warm front off the
surface at the apex, forming a low-pressure center.
• (D) When the warm front is completely lifted off the
surface, an occluded front is formed.
• (E) The cyclonic storm is now a fully developed
low-pressure center.
• Cyclonic storms usually follow principal storm tracks across
the continental United States in a generally easterly
direction. This makes it possible to predict where the lowpressure storm might move next.
• Air sinks over a high-pressure
center that moves away from
the center on the surface,
veering to the right in the
Northern Hemisphere to create
a clockwise circulation pattern.
Air moves toward a lowpressure center on the surface,
rising over the center. As air
moves toward the low-pressure
center on the surface, it veers
to the left in the Northern
Hemisphere to create a
counterclockwise circulation
pattern.
• Major Storms
– Thunderstorms
• Conditions
– Uplift of air
– Cumulus clouds
• Frontal Thunderstorms
– Move with the front that produced them
• Stages
– Cumulus
» Air is lifted and cools adiabatically to the dew point and
a cumulus cloud develops.
» Heat of vaporization is released and accelerates the
uplift.
– Mature
» When the moisture that is produced reaches the surface
of the Earth
» This series of updrafts, downdrafts, and precipitation
release electrical charges which become the lightening
associated with the storm
– Final
» All of the updrafts are cut off and only downdrafts exist.
• Lightening
• Thunder
• hail
• Three stages in the life of a thunderstorm cell. (A) The
cumulus stage begins as warm, moist air is lifted in an
unstable atmosphere. All the air movement is upward in this
stage.
• (B) The mature stage begins when precipitation
reaches the ground. This stage has updrafts and
downdrafts side by side, which create violent
turbulence.
• (C) The final stage begins when all the updrafts have been
cut off, and only downdrafts exist. This cuts off the supply
of moisture, and the rain decreases as the thunderstorm
dissipates. The anvil-shaped top is a characteristic sign of
this stage.
• Different parts of a thunderstorm cloud develop centers of
electric charge. Lightning is a giant electric spark that
discharges the accumulated charges.
• These hailstones fell from a thunderstorm in Iowa,
damaging automobiles, structures, and crops.
– Tornados
• Most violent, focused storm on Earth
• Speeds in excess of 300 km/hr (200 mi/hr)
– Hurricanes
• A hurricane is a violent storm that is produced over the
warm tropical ocean near the equator.
• Tropical Cyclone
• Typhoon
• A tornado might be
small, but it is the
most violent storm
that occurs on the
Earth. This
tornado, moving
across an open
road, eventually
struck Dallas,
Texas.
• This is a satellite
photo of
hurricane John,
showing the eye
and
counterclockwise
motion.
• Cross section of
a hurricane.
• Weather Forecasting
• Weather predictions are based on information about air
masses, fronts, and associated pressure systems in an area.
• This information is used to produce a model of behavior for
weather using a computer.
– Many models are used and then summarized when the
different models agree fairly closely to a model of the
weather.
• Supercomputers make routine weather forecasts possible by
solving mathematical equations that describe changes in a
mathematical model of the atmosphere. This "fish-eye"
view was necessary to show all of this Cray supercomputer
at CERN, the European Center of Particle Physics.
• This weather map of the United States shows a cold front
running from Houston, Texas, to near Raleigh, North
Carolina, where it becomes a stationary front that runs in a
northeasterly direction. Note the areas of showers and the
temperature predictions.
• Climate
• Introduction
– Climate is a generalized pattern for weather over a
period of time
– Weather describes the changes that occur to the
atmospheric conditions over short periods of time.
• The climate determines what types of plants and animals
live in a location, the types of houses that people build, and
the life-styles of people. This orange tree, for example,
requires a climate that is relatively frost-free, yet it requires
some cool winter nights to produce a sweet fruit.
• Major Climate Groups
– Factors Determining Weather
• Temperature
• Moisture
• Movement of Air
– Low Latitudes
• Have vertical solar radiation at noon some times of the
year
– High Latitudes
• Have no vertical solar radiation at noon some times of
the year.
– Middle Latitudes
• Between high and low latitudes.
• Latitude groups based on incoming solar radiation. The low
latitudes receive vertical solar radiation at noon some time
of the year, the high latitudes receive no solar radiation at
noon during some time of the year, and the middle latitudes
are in between.
– Tropical Climate Zone
• Near the equator and receives the greatest amount of
sunlight throughout the year.
– Polar Climate Zone
• The Sun never sets during the summer and never rises
during the winter.
– Temperate Climate Zone
• Average temperatures that are between the two
extremes
• The principal climate zones are defined in terms of yearly
temperature averages, which are determined by the amount
of solar radiation received at the different latitude groups.
• A wide
variety of
plant life
can grow
in a
tropical
climate, as
you can
see here.
• Polar climates
occur at high
elevations as
well as high
latitudes. This
mountain
location has a
highland polar
climate and
tundra
vegetation, but
little else.
• This
temperatureclimate
deciduous
forest responds
to seasonable
changes in
autumn with a
show of color.
• Regional Climate Influence
– Altitude
• Higher altitudes radiate more energy back into
space.
• Temperature decreases with altitude
– Mountains
• Decreasing temperature with altitude
• Uplifting effect on air masses
– Large Bodies of Water
• high specific heat and loses energy by
evaporation.
• This has the effect of keeping the temperatures
more constant from night to day on a land mass
near a large body of water
– Ocean Currents
• Currents move large amounts of water from
different parts of the world.
• Can warm or cool land depending upon the
origin of the current
• Ocean currents can move large quantities of warm or cool
water to influence the air temperature of nearby landmasses.
• Describing Climates
– Major Climate Zones
• Maritime Climate
– Influenced by air masses from the ocean
• Continental Climate
– Influenced by air masses from land
• Arid
– dry
– Less than 25 cm (10 in) of rain per year
• Humid
– Moist
– More than 50 cm (20 in) of rain per year
• Semiarid
– Between arid and humid
– 25 – 50 cm (10 – 20 in) of rain per year
• The idealized
general
rainfall
patterns over
the earth shift
with seasonal
shifts in the
wind and
pressure areas
of earth's
general
atmospheric
circulation
patterns.
– Local Climates
• Cities
– Materials used to build cities have a higher heat
holding capacity that natural materials.
– Also change wind direction and speeds
• Microclimates
– A local pattern of climate influenced greatly by the
local conditions.
• This map highlights the approximate location of the major
types of climates in North America.