Transcript global climates & biomes

GLOBAL CLIMATES &
BIOMES
APES CH. 4
Weather vs Climate
 Weather:
The state of the atmosphere at this moment. Scales of
seconds to days.
Can only be predicted (forecast) no more than a few days
into the future.
 Climate:
The average weather that occurs over a region over a long
period, Usually decades to millennia.
Can make general observations regarding temperature &
precipitation. Processes that effect these are: uneven
heating of Earth, convection currents, Earth’s rotation, tilt,
& ocean currents.
Earth’s Atmosphere
Atmospheric Layers
Troposphere:
 Densest layer due to gravity. Air molecules packed
closer to Earth.
 Nitrogen, oxygen & water vapor - gases
 Weather is confined to this layer.
 Air flow is vertically –
 Air rises & falls due to temperature/humidity differences
(in other words density).
 Rising & falling air is called CONVECTION
Warm moist air rises – less dense
Humid air is less dense than dry air
Warm air is less dense than dry air
Cooler dry air sinks – more dense
Dry air is more dense than moist air
Cool air is more dense than warm air
Atmospheric Layers
Stratosphere:
 Temperature inversion – air warms as it increases in
altitude.
 Ozone layer interacting with UV radiation heats this layer.
 Ozone (O3) – absorbs most UV-B & all of UV-C radiation.
 Air flow is horizontal –
 Jet stream – narrow band of high wind that moves W to E
(~ 200 mph)
 Influences weather; approx. three in each hemisphere
Temperature Inversions
 Temperature inversions are when air warms as you
increase in altitude.
 Stratosphere and Thermosphere have temperature
inversions.
 Thermosphere is heated directly by sun’s radiation
 Temperature inversion in the troposphere can occur:
 Traps pollution near surface; affects weather; prevents
mixing of air
Uneven Heating of the Earth
Three Causes of Uneven Heating:
a. Variation of Angle –
 Sun’s rays strike mid-latitudes & polar regions at a more
oblique angle
 Sun’s rays strike the equator (tropics) at perpendicular
(90 degree) angle.
 Causes radiation to travel through more atmosphere at
the poles = loss of solar energy
 more energy reaches the tropics than at the mid-latitude
& polar regions
Earth is Unevenly Heated
Uneven Heating Cont.
b. Surface Area Heated by Sun –
 Perpendicular angle causes energy to be distributed over
a smaller surface area @ equator.
 Thus tropical areas receive more solar energy per square
meter than higher latitudes
Uneven Heating
c. Albedo – the percentage of incoming sunlight is
reflected from a surface.
 The higher the albedo for a surface , more solar energy it
reflects, and less it absorbs.
Properties of Air
 Air has four properties
that determine how air
circulates in the
troposphere:
1. Density
2. Water vapor
capacity
3. Adiabatic heating or
cooling
4. Latent heat release
Density & Water Vapor Capacity
 Density determines the movement:
 Less dense = rises; areas of rising air have low air
pressure
 More dense = sinks; areas of sinking air have high air
pressure
 Water Vapor Capacity is related to temperature:
 Warm air can hold more water vapor than cool air
 Maximum amount of water vapor that can be in the air at
a given temperature is called Saturation Point.
 That given temperature is called Dew point. The
temperature at which water vapor condenses. Humidity
is = 100%
Relative humidity is the amount of
water vapor present in air expressed as
a percentage of the amount needed for
saturation at the same temperature.
Adiabatic Cooling & Heating
 As air rises air pressure decreases, so it expands and
cools.
 As air sinks air pressure increases, so it contracts and
heats.
 These processes are called Adiabatic cooling &
heating respectively.
 The adiabatic lapse rate is a decrease of 3.5°F/1,000 ft
(6.4°C/km) of altitude under normal conditions. Varies.
Dew Point
Latent Heat Release
 Condensation, changing from vapor to liquid, releases
heat (energy).
 This is known as Latent Heat Release:
 Energy released in condensation can warm the air such
as in storms.
Atmospheric Convection Currents
 Global patterns of air movement that are initiated by the
uneven heating of the Earth.
 As air rises at the equator:
1. Density decreases, moisture increases, and air pressure
2.
3.
4.
5.
6.
decreases.
Air reaches saturation point (humidity = 100%)
Condensation occurs and clouds/precipitation form
Condensation releases latent heat which causes air to
expand and rise more rapidly
These processes cause air to continuously rise near
equator forming a river of air upward.
This is considered an area of LOW PRESSURE!!
Atmospheric Convection Currents
 Global patterns of air movement that are initiated by the
uneven heating of the Earth.
 As air is chilled at the top of the troposphere by
adiabatic cooling (Air sinking):
1. Air at this point had little water vapor.
2. It is displaced N or S by the less dense rising moist air
3. Displaced air sinks to about 30° N or S latitude
4. Air contracts and heats up as it sinks due to adiabatic
heating
5. This warm, dry is considered an area of HIGH
PRESSURE!!
High & Low Pressure Systems
Air always moves horizontally across the surface from high
pressure to low pressure = WIND!!!!
High pressure systems are described
as sinking dry air. These are
associated with fair weather because
no condensation is occurring
Low pressure systems are described
as rising, moist air. These are
associated with stormy weather
because condensation occurs.