Transcript Scattering
Part 1. Energy and Mass Chapter 3. Energy Balance and Temperature Introduction Atmospheric Influences on Solar Insolation Solar radiant energy is absorbed, reflected, scattered or transmitted by the atmosphere and the Earth’s surface Absorption of EM radiation Gases, liquids, and solids absorb EM energy, which increases their heat Reflection of EM radiation Redirection of EM energy with no increase in heat (amount of reflected sunlight) Albedo = (total amount of incoming sunlight) Scattering of EM radiation Scattered energy diffuses radiation, reducing its intensity (no heat absorbed) • There are two types of atmospheric scattering Rayleigh Scattering --Small molecules scatter the energy in all directions --Shorter wavelength electromagnetic radiation is scattered --Blue visible light preferentially scattered, causing the sky to appear blue Mie Scattering --Larger objects like aerosols scatter mostly in the forward direction --All wavelengths across visible spectrum • Hazy, grayish skies are caused by Mie scattering • Red sunrises and sunsets are caused by Mie scattering At sunrise or sunset, Rayleigh scattering removes the blue wavelengths, while Mie scattering allows the red wavelengths through the atmosphere. Nonselective Scattering Very large scattering agents (water) Scatter across the visible spectrum • White or gray appearance No wavelength especially affected Transmission of EM radiation EM energy transmitted through objects (such as a gas or transparent solid like glass) What happens to incoming solar shortwave (SW) radiation? It is reflected, scattered or absorbed in the atmosphere or at the Earth’s surface. For 100 units of incoming solar electromagnetic shortwave radiation: About 1/2 of the Sun’s radiation makes it to the Earth’s surface. Shortwave (SW) radiation -- UV and visible Surface Emission of Longwave (LW) EM Radiation Much is absorbed by atmospheric “greenhouse” gases, especially H2O and CO2 Absorption by atmosphere increases air temperature Longwave (LW) radiation -- IR IR absorption bands IR “window” The Earth’s surface temperature causes it to radiate with a blackbody radiation spectrum with its peak at 10 mm, but its atmospheric greenhouse gases absorb most of this terrestrial longwave radiation, except in the IR window between 8 and 15 mm IR “window” for Earth Earth’s LW Cooling This shows the fate of LW radiation from the Earth’s surface Net LW radiation loss This shows the fate of LW radiation from the Earth’s atmosphere Because clouds absorb virtually all LW radiation, cloudy nights are warmer than clear nights Earth’s SW and LW Radiation Balance These two columns show the fate of SW radiation from the Sun Net SW+LW radiation Net LW absorption (plus) and loss radiation loss (minus) for the Earth for the Earth Convection Heat transfer by fluid flow (motions usually circular) Convection from Free convection • Warmer, less dense fluids rise; colder, more dense fluid sink Forced convection • Initiated by eddies and disruptions to uniform airflow Warm air rising Cool air sinking Free Convection The circular motion in convection is called a convection cell. Forced Convection Heat content of substances Sensible Heat Readily detected heat energy transferred by convection and conduction Related to object’s specific heat and mass Latent Heat Energy which induces a change of state (usually in water) Redirects some energy which would be used for sensible heat Latent heat of evaporation is stored in water vapor and released during condensation Earth’s EM and Sensible/Latent Heat Balance These two columns show the EM radiation balance for the Earth and its atmosphere These two columns show the sensible and latent heat balance for the Earth and its atmosphere Annual Average Net Radiation at Different Latitudes Between 38oN and S = net energy surpluses Poleward of 38o = net energy deficits Winter hemispheres have net energy deficits poleward of 15o, but mass advection neutralizes energy imbalances Ocean Circulation Because of the high specific heat of water, ocean currents carry a major amount of latent heat to different parts of the Earth. For example, the northward Gulf Stream carries warm water toward Ireland, giving it a relatively mild climate. Average winter and summer temperatures are affected by latitude, altitude, humidity, and location relative to large water bodies and land masses. Average winter and summer temperature differences are largest over higher latitude land masses and lowest along equatorial oceans. The Greenhouse Effect The effect of greenhouse gases on the Earth’s climate Greenhouse gases absorb LW EM radiation from the Earth’s surface, warming the atmosphere • Major greenhouse gases: H2O, CO2, and CH4 Without the greenhouse effect, the average Earth temperature would be -18oC (0oF) Human activities play a role in producing greenhouse gases in the atmosphere A true greenhouse stems convection SW radiation can get in, but LW radiation cannot get out. Sensible and latent heat stays within the system. Localized Temperature Effects Elevation effects on the heating and cooling of the atmosphere Atmospheric Circulation Latitudinal temperature and pressure differences cause large-scale advection Contrasts between Land and Water Continentality versus maritime effects Warm and Cold Ocean Currents Western ocean basins are warm Eastern ocean basins are cold Local Conditions Small spatial scale features impact temperatures South-facing slopes have more vegetation The role of vegetation in a local energy balance Daily and Annual Temperature Patterns Diurnal temperatures lag energy receipt Surface cooling rate is lower than the warming rate • Due to stored surface energy Winds moderate temperature ranges • Transfer energy through large mass of air Diurnal energy Global Extremes Greatest extreme temperatures in continental interiors • World record high = 57oC (137oF) at Azizia, Libya, 1913 • World record low = -89oC (-129oF) Antarctica, 1960 Thermodynamic diagrams • Depict temperature and humidity with height • Stuve diagrams plot temperatures as a function of pressure levels – Important for forecasting Simplified Stuve Diagram