PHYC Environmental Physics Climate, Climate Change Nuclear Power and the Alternatives

PHYC Environmental Physics PHYC Peter Lynch Meteorology & Climate Centre School of Mathematical Sciences University College Dublin Climate, Climate Change Nuclear Power and the Alternatives

PHYC Environmental Physics The Energy Cycle of the Atmosphere Lecture 2

PHYC Environmental Physics TRANSFER OF ENERGY  CONDUCTION Transfer of energy through matter Transfer of energy through matter Air is a poor conductor Air is a poor conductor Only important at the Earth's surface Only important at the Earth's surface  CONVECTION Transfer of energy by movement of mass Transfer of energy by movement of mass Can only take place in fluids - e.g. Air Can only take place in fluids - e.g. Air Energy transported upward by convective flow Energy transported upward by convective flow Convection on a global scale creates worldwide Convection on a global scale creates worldwide atmospheric circulation atmospheric circulation  ADVECTION Horizontal movement of air Horizontal movement of air  RADIATION

PHYC Environmental Physics Convection

PHYC Environmental Physics Advection

PHYC Environmental Physics Fig. 2-5, p. 33 Phase Changes

PHYC Environmental Physics LATENT HEAT  Latent heat is the heat absorbed or released by unit mass of water when it changes phase.  Latent heat of melting / fusion  Latent of vaporization / condensation  Latent heat of sublimation / deposition All conversions are relevant in atmospheric physics

PHYC Environmental Physics

The EM Spectrum

PHYC Environmental Physics Planck’s Law for blackbody radiation: Wien’s Displacement Law: Stefan-Boltzmann Law:

PHYC Environmental Physics The hotter the object, the higher the curve: Stefan-Boltzmann Law

PHYC Environmental Physics The hotter the object, the shorter the wavelength: Wien’s displacement law

PHYC Environmental Physics Huge difference in the temperature of the Earth and of the Sun. Spectra are effectively disjoint. We speak of short wave radiation (solar) and long wave radiation (terrestrial). Solar Radiation and Terrestrial Radiation

PHYC Environmental Physics Energy Transfer in the Atmosphere

PHYC Environmental Physics

The Solar Constant  The average amount of solar energy reaching the outer limits of the atmosphere.  This “constant” actually varies slightly.  Changes by about 0.1% over the eleven year solar cycle.  Mean value: 1368 W/m².

PHYC Environmental Physics Zenith Angle

PHYC Environmental Physics

THE EARTH’S ORIENTATION  Earth's axis is not perpendicular to the plane of its orbit around the sun.  It is tilted 23.5º from the perpendicular: Inclination of the axis.  Without this inclination we would have no seasons.  This changes the solar zenith angle of the sun, and the area covered by a beam of sunlight.

PHYC Environmental Physics THE EARTH’S ORIENTATION  Area covered by beam of sunlight is proportional to 1/cos of the solar zenith angle  In Belfield, solar zenith angle of the sun is 75º in December and 30º degrees in June.  Ratio of 1/cos of the angles is about 3.3.  Three times as much energy falls on unit area at the ground in Summer as in Winter.

PHYC Environmental Physics Energy Fluxes 4 x 342 = 1368

PHYC Environmental Physics INCOMING SOLAR RADIATION INCOMING SOLAR RADIATION   25% penetrates directly to earth's surface.   26% scattered by atmosphere but then reaches the surface.   Total of 51% reaches surface.   31% reflected back to space by clouds, atmospheric scattering, and reflective surfaces, e.g. snow and ice.   19% absorbed by clouds and atmosphere

PHYC Environmental Physics Energy and Matter  Emission  Absorption  Reflection  Scattering

PHYC Environmental Physics ABSORPTION Gases are excellent absorbers. Gases are excellent absorbers.  When radiation is absorbed, energy is converted into internal molecular motion – temperature rises.  Significant absorbers are: Oxygen and ozone Oxygen and ozone Water vapour Water vapour Carbon dioxide Carbon dioxide

PHYC Environmental Physics REFLECTION - ALBEDO  The fraction of energy that is reflected by a surface is called its albedo.  Albedo of the earth as a whole is ~30%.  Albedo of fresh snow is 80-85%.  Thick cloud - 70 to 80%.  Water - depends on elevation of the Sun, from 50 to 80% near horizon, 3-5% at 90º.  Soil - 10%

PHYC Environmental Physics SCATTERING  Produces diffuse light.  Shorter wavelengths (blue and violet) are scattered more effectively than longer wavelengths (red and orange).  Sky appears blue when viewed at noon.  At sunset, scattering depletes amount of blue light - sky appears reddish.  Scattering more efficient as particle gets larger - aerosols or dust.

PHYC Environmental Physics

LATITUDINAL HEAT BALANCE  The global amount of incoming solar radiation is nearly equal to the outgoing terrestrial radiation.  However is not true at any given latitude.  In general there is a surplus of energy at the equator - i.e. More radiation comes in than goes out.  There is also a deficit of energy at the poles.  Why then do the poles not get colder and the equator hotter?  Because heat is transported from the equator to the poles by ocean currents and by the atmosphere.

PHYC Environmental Physics Fig. 2-20, p. 50

PHYC Environmental Physics Temperature Variations

PHYC Environmental Physics Global Energy Balance

PHYC Environmental Physics Diurnal Temperature Cycle

PHYC Environmental Physics Air Temperature Data  Daily mean temperature is determined by two methods,  (a) average of 24 hourly measurements  (b) the average of the maximum and minimum temperatures for the day.  Daily temperature range is the difference between the max and min temperatures.  Monthly mean temperature is obtained from the average of the daily mean for the month  Annual mean temperature is the average of the monthly means  Annual temperature range is the difference between the coldest monthly mean and the warmest monthly mean

PHYC Environmental Physics Controls on Temperature  Latitude  Surface type  Elevation and aspect  Differential heating of land and water.  Ocean currents.  Cloud cover and albedo

PHYC Environmental Physics Latitudinal Effect

PHYC Environmental Physics Incoming Solar Energy (TOA)

PHYC Environmental Physics Surface Characteristics

PHYC Environmental Physics Effect of Altitude

PHYC Environmental Physics Effect of Aspect

PHYC Environmental Physics Effect of Aspect

PHYC Environmental Physics Differential Heating of Land and Water  As water is heated, convection distributes the heat through a large mass.  In contrast, heat does not penetrate deeply into soil or rock - heat can only be transferred by conduction.  Net result: a relatively thick layer of water is heated to moderate temperatures, while only a thin layer of land is heated to much higher temperatures.  Specific heat is almost three times greater for water than for land

PHYC Environmental Physics Land versus Water

PHYC Environmental Physics Effect of Ocean Currents

PHYC Environmental Physics Effect of clouds on the daytime energy budget at the surface

PHYC Environmental Physics Effect of Cloud Cover

PHYC Environmental Physics Energy in and out

PHYC Environmental Physics DAILY TEMPERATURE CYCLE  Before sunrise, the temperature is controlled by net long-wave radiation from the surface ---- the ground cools.  As sun comes up, solar radiation is absorbed and the temperature of the ground increases.  In general the incoming solar energy is more than the net outgoing thermal energy, so the grounds heats up.  Ground continues to heat up until the amount of incoming solar energy equals the amount of outgoing thermal energy.  This occurs typically at about three in the afternoon.

PHYC Environmental Physics CONTROLS OF TEMPERATURE RANGE  Latitude - determines the intensity of the sun, and the length of the day.  Surface type - land and water contrast, bare soil versus vegetation.  Elevation and aspect.  Relationship to large bodies of water.  Ocean currents.  Cloud cover - reduces the diurnal temperature range.

PHYC Environmental Physics Long-term Temperature Variations

PHYC Environmental Physics Interannual Temperature Variations  Average or normal temperatures  Anomalies  Volcanoes  El Niño / La Niña

PHYC Environmental Physics

Volcanoes

PHYC Environmental Physics Picture from Space Shuttle 3 weeks after the eruption of Mt. Pinatubo

PHYC Environmental Physics Temperature in Spokane and Boise after the eruption of Mount St. Helens

PHYC Environmental Physics Adiabatic Cooling and Warming Effects of Moisture

PHYC Environmental Physics Fig. 3-17, p. 72

PHYC Environmental Physics Fig. 2.7

PHYC Environmental Physics Adiabatic Cooling and Warming  A rising parcel of air always expands  As the parcel expands it will cool  Adiabatic process - no heat energy is gained or lost by the parcel  The rate of cooling with altitude due to this process is called the dry adiabatic lapse rate

PHYC Environmental Physics Adiabatic Cooling and Warming  Usually the air contains water vapour.  As the parcel rises an altitude will be reached when the water vapour condenses.  But this releases latent heat of condensation to the air parcel. Thereafter, the temperaure of the parcel will not fall as much as for dry air.Thereafter, the temperaure of the parcel will not fall as much as for dry air.  Moist adiabatic lapse rate.

PHYC Environmental Physics

Lapse Rates and Stability  Lapse rate is the rate at which the real atmosphere falls off with altitude – the environmental lapse rate  An average value is 6.5 ºC per kilometer  This should be compared with the  This should be compared with the adiabatic lapse rate of 10 ºC.  If the environmental lapse rate is less than 10 ºC, then the atmosphere is absolutely stable  If greater than 10 ºC, it is absolutely unstable

PHYC Environmental Physics (A) (A) Mid-afternoon (B) (B) Evening (C) (C) Sunrise (D) (D) Mid-morning Diurnal Temperature Variation and Nocturnal Temperature inversion

PHYC Environmental Physics TEMPERATURE INVERSIONS  When the temperature profile increases with altitude, this is known as a temperature inversion.  Two main types – subsidence inversion and radiation inversion (nocturnal inversion).  Very important during pollution events – trap pollutants close to the surface.

PHYC Environmental Physics Temperature Inversions

PHYC Environmental Physics Effect of a temperature inversion

PHYC Environmental Physics End of Lecture 2