SYSTEMS IN PHYSICAL GEOGRAPHY

1. Open flow systems: inputs and outputs of energy and matter

2. Closed flow systems: NO inputs or outputs

Natural Flow systemsEx: • Flow of energy from Sun to Earth (energy)•River system (matter)

A system is a set of relationships between features, processes or phenomena

Positive: if the flow is reinforcedNegative: if the flow is reduced

FEEDBACK AND EQUILIBRIUM

EQUILIBRIUMThe flow rates remain about the same

FEEDBACK: When flow (matter/energy) in a pathway acts either to reduce or increase the same flow in another pathway

The amounts of energy and matter within the system are constant.

Positive: if the flow is reinforcedNegative: if the flow is reduced

Initial condition (matter/energy)

causes

changes inAnother variables

causes changes in

Initial condition MODIFIED(matter/energy)

LOW TEMPERATURE

MORE SNOW

MORE ALBEDO

LESS SOLAR RADIATION

LOWER TEMPERATURE

Example:

THE SUN-EARTH RELATIONSHIP

SOLSTICE/ EQUINOX CONDITIONS AND SEASONS

SOLSTICE: One of the poles is tilted away from the Sun

EQUINOX:The Earth’s axial tilt is neither toward nor away from the Sun

SOLSTICE CONDITIONS

One of the poles is tilted away from the Sun

• Observe the circle of illumination at different latitudes: because the tilt toward the Sun, we only have equal halves in Equator.

JUN 21-22 DEC 21-22

EQUINOX CONDITIONS

The Earth’s axial tilt is neither toward nor away from the Sun

•The circle of illumination has equal halves in all latitudes

INSOLATION AND SUN ANGLE

The angle of the Sun’s rays determines the intensity of insolation on the ground

This is controlled by the latitude of the location and the time of the year.

DAILY INSOLATION OVER THE YEAR AT VARIOUS LATITUDES (NORTH

HEMISPHERE)

THE SUN-EARTH RELATIONSHIP

Location with 12 hours of day and 12 hours of night along all year?Location with 24 hours of night on March 21st?

ENERGY FLUXES

•Radiation: Shortwave (SWR), Longwave (LWR)•Heat fluxes (Sensible and Latent heat)

Short waves (warmer temperatures)

Long waves (cooler temperatures)

TEMPERATURE

Less energy

More energy

RADIATION (LONGWAVE AND SHORTWAVE)

NET RADIATION = INPUT – OUTPUT

SOLAR RADIATION (short wave radiation, SWR)

•As solar radiation passes through the atmosphere, is affected by absoption and reflection

Albedo: An important property of a surface. It measures how much solar energy will be reflected:A surface with high albedo (snow, ice) reflects most of the solar radiationA surface with low albedo (black pavement) absorbs most of incoming solar radiation

INCOMING LWR

LONG WAVE RADIATION (LWR)

The atmosphere, land and ocean also emit energy in the form of long wave radiation

INCOMING LWR The Earth’s surface emits energy to the atmosphere that is absorbed by the atmosphere and radiated back down to Earth’s surface

R = INPUT – OUTPUTR = ( SWR + LWR) – ( SWR + LWR)

INCOMING LWR

NET RADIATION (RADIATION BUDGET)

It is the difference between total upward and downward radiation fluxes and is a measure of the energy available at the ground surface.

THE ENERGY BALANCE AT SURFACE

Net Radiation + Sensible Heat + Latent Heat + Ground Heating = 0

1st LAW OF THERMODYNAMICS (CONSERVATION OF ENERGY):Energy only changes from one form to another. It cannot be created or destroyed.

SENSIBLE AND LATENT HEAT

SENSIBLE HEAT:•Heat sensed by touching or feeling (measured by a thermometer)

•Sensible heat transfer (Ex: conduction, convection)

LATENT HEAT:•Hidden heat, stored in the form of a molecular motion when a change of state takes place (solid to liquid, liquid to gas, solid to gas)

SENSIBLE HEAT

LATENT HEAT

THE AIR TEMPERATURE

Factors that influence air temperature:

1.Insolation2. Latitude3. Surface type4. Coastal vs interior location5. Elevation

WORLD LATITUDE ZONES

Temperature at surface is determined by the balance among energy flows:

1. Net radiation (positive at day, negative at night)2. Sensible heat transfer 3. Latent heat transfer

URBAN-RURAL DIFFERENCES

RURAL:

vegetation

transpirationcooler surface

moist soil evaporation

URBAN:

dry surface

insolation warmer surface

asphalt and roofing(dark surfaces)

more absorption(twice the vegetation)

warmer surface

GLOBAL PATTERNS OF AIR TEMPERATURE

1. Temperatures decrease from equator to poles2. Subartic and artic regions have extremely low temperatures

in winter3. Temperatures in equatorial regions change little from January

to July4. Large shift of isotherms (north-south) between January and

July over continents in midlatitudes and subartic regions Winter: equatorward Summer: poleward5. Areas of perpetual ice and snow (Greenland, Antarctica) are

always intensely cold

GLOBAL WARMING

GREENHOUSE EFFECTThe atmosphere traps longwave radiation and returns it to the surface

Greenhouse gases (LWR absorbers):CO2, water vapor

Greenhouse liquid:Clouds (tiny water droplets)

Volcanic activity

Particles and gases (SO2)into stratosphere (aerosols)

Strong winds spread throughout the entirely layer

Aerosols reflect income radiation (cooling effect)

Aerosols : suspension of fine solid or liquid particles (smoke from fires, volcanic activity, air pollution)

COOLING EFFECT

GLOBAL DIMMING

The gradual reduction in the amount of global sun radiation at Earth’s surface

Gerald Stanhill (Israel):

Solar Radiation observations: 22% decrease (1950s-1980s)

Beate Liepert (Germany):Similar pattern in Alps

1950-1990 decrease of solar energy:• 9% Antartica•10% USA•30% Rusia

Antartic

Arctic

SEPTEMBER 12, 2001 (USA):

Near-total shutdown of air traffic during the three days

US climate absent from the effect of contrails (visible trails of condensed water vapor).

During this period, an increase in temperature over 1°Cwas observed in some parts of the U.S.

PRECIPITATION

What do we need to have precipitation?

•Water vapor (humidity)•Cooling of water vapor (for condensation)

•Formation of clouds (collision and coalescence)

Key concepts:• dew point•lifting condensation level

ADIABATIC COOLING

atmospheric pressure decreases with altitude

Air parcel expands and cools

ADIABATIC PROCESS: Heating or cooling process as result of pressure change

ADIABATIC RATE: Temperature change with elevation

10°C/1000m (each 1000m temperature drops 10°C)

ADIABATIC COOLING

As the parcel of air continues rising, the air is cooled to its dew point temperature. Then, condensation starts (lifting condensation level), and we have saturated air

DRY ADIABATIC RATE: Temperature change with elevationof an air parcel that has NOT reached saturation. Constant, 10°C/1000m

WET ADIABATIC RATE: Temperature change with elevationof an air parcel that has reached saturationVariable, most 5°C/1000m

EXERCISE: Estimating the lifting condensation level

EXERCISE: Estimate the temperature at the lifting condensation level

To=20.0°C

Dry adiabatic lapse rate = 10°C /1000mWet adiabatic lapse rate = 5°C /1000 m

What is the temperature at 1500m?What is the Tdew?

PRECIPITATION PROCESSES

1. Orographic precipitation2. Convectional precipitation3. Movement of air masses

OROGRAPHIC PRECIPITATION

warm and dry airRainshadow: a belt of dry climate

CONVECTIVE PRECIPITATION

Convection:

• The upward motion of a parcel of heated air

MOVEMENT OF AIR MASSES

1.An area of warm air meets and area of cold air.

2.The warm air is forced over the cold air

3.Where the air meets the warm air is cooled and water vapor condenses.

4. Clouds form and precipitation occurs.

THUNDERSTORMS: CONVECTION IN UNSTABLE AIR

•The air parcel rising, is warmer and less dense that surrounding air

•While it remains warmer than surrounding air, it continues rising

•As it rises, it is cooled adiabatically, and condensation takes place (cumulus cloud formation)

• Normally, this cloud evaporates (mix of winds)

THUNDERSTORMS: CONVECTION IN UNSTABLE AIR

However, sometimes convection continues

Dense cumulonimbus cloud

Thunderstorms (heavy rain)

SO, WHAT DO WE NEED TO HAVE THIS CONDITION?

1. Very warm and moist air

2. A big environmental lapse rate : temperature of surrounding decreases faster with elevation (compared to dry and wet adiabatic lapse rate)

UNSTABLE AIR

See Figure 4.13, page 113