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 systems Ex: 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 reinforced Negative: if the flow is reduced FEEDBACK AND EQUILIBRIUM EQUILIBRIUM The 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 reinforced Negative: if the flow is reduced Initial condition (matter/energy) causes changes in Another 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 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 21 st ?

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 radiation A 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 – OUTPUT R = ( 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 1 st 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.Insolation 2. Latitude 3. Surface type 4. Coastal vs interior location 5. 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 transpiration cooler surface moist soil evaporation URBAN: dry surfaceinsolationwarmer surface asphalt and roofing (dark surfaces) more absorption (twice the vegetation) warmer surface

GLOBAL PATTERNS OF AIR TEMPERATURE 1.Temperatures decrease from equator to poles 2.Subartic and artic regions have extremely low temperatures in winter 3.Temperatures in equatorial regions change little from January to July 4.Large shift of isotherms (north-south) between January and July over continents in midlatitudes and subartic regions Winter: equatorward Summer: poleward 5. Areas of perpetual ice and snow (Greenland, Antarctica) are always intensely cold

GLOBAL WARMING GREENHOUSE EFFECT The atmosphere traps longwave radiation and returns it to the surface Greenhouse gases (LWR absorbers): CO 2, water vapor Greenhouse liquid: Clouds (tiny water droplets)

Volcanic activityParticles and gases (SO 2 ) 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

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°C was 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 altitudeAir 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 elevation of an air parcel that has NOT reached saturation. Constant, 10°C/1000m WET ADIABATIC RATE: Temperature change with elevation of an air parcel that has reached saturation Variable, 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 /1000m Wet adiabatic lapse rate = 5°C /1000 m What is the temperature at 1500m? What is the Tdew?

PRECIPITATION PROCESSES 1.Orographic precipitation 2.Convectional precipitation 3.Movement of air masses OROGRAPHIC PRECIPITATION warm and dry air Rainshadow: 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