Part 1. Energy and Mass Chapter 3. Energy Balance and Temperature.
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Part 1. Energy and Mass Chapter 3. Energy Balance and Temperature
Atmospheric Influences on Solar Insolation Solar radiant energy is absorbed, reflected, scattered or transmitted by the atmosphere and the Earth’s surface Introduction
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 Albedo = Scattering of EM radiation Scattered energy diffuses radiation, reducing its intensity (no heat absorbed) There are two types of atmospheric scattering (amount of reflected sunlight) (total amount of incoming sunlight)
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
At sunrise or sunset, Rayleigh scattering removes the blue wavelengths, while Mie scattering allows the red wavelengths through the atmosphere. 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
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 H 2 O and CO 2 Absorption by atmosphere increases air temperature IR absorption bands IR “window” Longwave (LW) radiation -- IR
The Earth’s surface temperature causes it to radiate with a blackbody radiation spectrum with its peak at 10 m, but its atmospheric greenhouse gases absorb most of this terrestrial longwave radiation, except in the IR window between 8 and 15 m for Earth IR “window”
Because clouds absorb virtually all LW radiation, cloudy nights are warmer than clear nights This shows the fate of LW radiation from the Earth’s surface This shows the fate of LW radiation from the Earth’s atmosphere Net LW radiation loss Earth’s LW Cooling
Earth’s SW and LW Radiation Balance These two columns show the fate of SW radiation from the Sun Net SW+LW radiation absorption (plus) and loss (minus) for the Earth Net LW radiation loss 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
Free Convection Forced Convection Warm air rising Cool air sinking The circular motion in convection is called a convection cell.
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
These two columns show the EM radiation balance for the Earth and its atmosphere Earth’s EM and Sensible/Latent Heat Balance These two columns show the sensible and latent heat balance for the Earth and its atmosphere
Annual Average Net Radiation at Different Latitudes Between 38 o N and S = net energy surpluses Poleward of 38 o = net energy deficits Winter hemispheres have net energy deficits poleward of 15 o, but mass advection neutralizes energy imbalances
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. Ocean Circulation
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 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: H 2 O, CO 2, and CH 4 Without the greenhouse effect, the average Earth temperature would be -18 o C (0 o F) Human activities play a role in producing greenhouse gases in the atmosphere The Greenhouse Effect
A true greenhouse stems convection SW radiation can get in, but LW radiation cannot get out. Sensible and latent heat stays within the system.
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