Warming the Earth and Atmosphere Dr Craig Clements San Jos State University MET 10 Chapter 2 Is the measure of the average speed or Temperaturethermal energy of the particles in a substance How fast the atoms molecules are moving Three temperature scales Kelvin Celsius K C 273 Fahrenheit What does 0 K mean Absolute zero molecules would posses minimum amount of energy and no thermal motion Heat is energy in the process of being transferred from one object to another because of the temperature difference between them Latent Heat Hidden Warmth Water vapor is an invisible gas that becomes visible when it changes into larger liquid or solid particles such as ice This process of transformation is known as a change of state or phase change The heat energy required to change a substance such as water from one state to another is called latent heat Latent Heat Hidden Warmth Example cooling produced by evaporating water Examine a small drop of water At drop s surface water molecules are constantly escaping evaporating Because the more energetic fast moving molecules escape most easily the average motion of all the molecules left behind decreases Since temperature is a measure of the average molecular motion the slower motion suggests a lower water temperature Evaporation is a cooling process Latent Heat Hidden Warmth Evaporation is a cooling process because the energy needed to evaporate the water to change its phase from liquid to a gas comes from the water The energy lost during evaporation can be thought of as carried away by the water vapor molecule The energy is thus stored or hidden and we call this latent heat Condensation Opposite of evaporation is condensation Condensation is a process where a gas changes into a liquid Is condensation a cooling process or warming process Warming Phase changes Latent Heat Latent heat is an important source of atmospheric energy Once the vapor molecules become separated from the earth s surface they are transported by the wind Rising to high altitudes where the air is cold the vapor changes into liquid and ice cloud particles During these processes a tremendous amount of heat energy is released into the environment Energy transmission There are three modes of energy transmission in the atmosphere Conduction the transfer of energy in a substance by means of molecular excitation without any net external motion Convection the transfer of energy by mass motions within a fluid or gas resulting in actual transport of energy Radiation the propagation of electromagnetic waves through space Conductio n Convection In meteorology the vertical exchange of heat is called convection During the process of convection bubbles of air form at the surface and rise These vertical currents are known as thermals The horizontal motion of air wind carries properties of the air temperature moisture etc with it This is called advection The sport of paragliding is dependent on thermals Photographer unknown The Rising and Sinking Air Game Take an invisible blob called an air parcel This air parcel is wrapped with imaginary elastic plastic like a balloon The parcel can expand and contract freely But neither external air nor heat is able to mix with the air inside Also as the air parcel moves it does not break apart but remains as a single unit At the earth s surface the parcel has the same temperature and pressure as the surrounding air The Rising and Sinking Air Game Suppose we lift the parcel Remember air pressure always decreases as we move up into the atmosphere As the parcel rises it enters a region where the surrounding air pressure is lower To equalize the pressure the parcel molecules inside push the parcel walls outward expanding it The molecules use some of their own energy to expand the parcel This energy loss shows up as slower molecular speeds lower parcel temperature Air that rises always expands and cools The Rising and Sinking Air Game The Rising and Sinking Air Game If the parcel is lowered it returns to a region where the air pressure is higher The higher outside pressure squeezes compresses the parcel back to its original smaller size Because the air molecules have a faster rebound velocity after striking the sides of the a collapsing parcel the average speed of the molecules goes up This increase in molecular speed represents a warmer parcel temperature Therefore Air that sinks always warms by compression Electromagnetic radiation Radiation is the transfer of energy by rapid oscillations of electromagnetic fields The most important general characteristic is its Defined as the crest to crest distance wavelength Radiation travels through space at the speed of light 3 x 108 m s 1 or 670 616 630 MPH Radiation What emits radiation All objects with a temperature greater than 0 K emit some type of radiation energy Examples Radiation laws Warmer objects emit more intensely than cold objects Stefan Boltzmann Law Warmer objects emit a higher proportion of their energy at short wavelengths than cold objects Wien s Law Wien s Law w T maximum wavelength m w constant 0 2897 m K T temperature of the object K Stefan Boltzmann Law E T4 E radiation emitted W m 2 Stefan Boltzmann constant 5 67 x 10 8 W m 2 K 4 T temperature of the object K Review questions Considering the previous discussion Which object would emit more intensity radiation Earth or Sun Sun If you were examining the radiation emitted by both the Sun and Earth which would have a longer wavelength Earth What wavelength radiation are you emitting right now infrared Solar Radiation Sunlight Sunlight is primarily made up of the following Visible Light 44 Infrared Radiation 48 Ultraviolet Radiation 7 Unit 1 m 0 000001 m Terrestrial or Longwave Radiation Planets mainly emit infrared radiation Radiation emitted by planets occurs mainly at longer wavelengths than those contained in solar radiation Solar Radiation Shortwave Terrestrial Radiation Longwave Solar vs Terrestrial Radiation The sun is much hotter than planets therefore sunlight consists of shorter wavelengths than planetary radiation Thus Energy from the Sun Obviously the Sun provides the Earth with it s energy The question is how much of the Sun s energy does the Earth get Sun s energy is either Scattered reflected away or Absorbed Scattering happens by bouncing off Particles in the atmosphere Earth s surface Absorption happens when certain gases absorb the energy The reality is the only certain gases absorb certain wavelengths Absorption of radiation