Met 10 Weather ProcessesJeff Gawrych Temperature, Heat Transfer and Earth’s Energy Balance
Lecture Outline • Energy in the atmosphere • Shortwave and longwave radiation • Greenhouse effect • Earth/atmosphere energy balance
Why does the earth heat up? • Incoming solar radiation is absorbed by the surface of the planet. • The amount and intensity of the solar energy received is called insolation. • Some areas get more insolation than others. E.g. The tropics are generally warmer than the polar regions.
Heat • Sensible Heat: he we feel • Latent Heat: The heat energy required to change water from one state to another (e.g. water from vapor to a solid). • “hidden” heat due to phase changes • E.g. Water has 3 phases • 1) Ice 2) Liquid 3) Vapor (gas) • Latent heat of evaporation: • Heat lost to environment • Latent heat of condensation: • Heat released to environment
Earth’s Energy Balance • A balance exists that keeps the planet from getting too hot or cold • Energy entering top of atmosphere must equal Energy leaving top of atmosphere • Energy entering the Earth’s surface must equal Energy leaving Earth’s surface
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.
Electromagnetic radiation l • Radiation is the transfer of energy by rapid oscillations of electromagnetic fields. • The most important general characteristic is its wavelength (), defined as the crest-to-crest distance. • Radiation travels through space at the speed of light (3 x 108 m s-1). • All objects emit radiation!!!! • Amount of radiation absorbed/emitted depends on Temp.
Short and longwave radiation • All objects emit radiation: • Sun emits radiation mostly at shorter wavelengths; ultraviolet (UV) and visible: • Earth emits radiation mostly at longer wavelengths; infrared (IR) • Difference based on temperature of emitting body. • (shortwave or solar radiation) • (Longwave or terrestrial radiation)
Atmospheric Greenhouse Effect • Essential for life as we know it!!! • The atmosphere absorbs some of the Earth’s outgoing longwave radiation. • Atmosphere acts like a blanket • Which atmospheric gases are most responsible for the Greenhouse Effect? Water, Carbon Dioxide (CO2) • Runaway greenhouse effect • The addition of too many greenhouse gases that could possibly lead to large-scale climate change (global warming) • It is analogous to closing a window, in that outgoing radiation cannot escape.
Incoming solar radiation • Each ‘beam’ of incoming sunlight can be either: • Reflected back to space: albedo=reflectivity • Clouds • Atmosphere • Surface • Earth’s Albedo is 30 % • Or absorbed; either by atmosphere (e.g. clouds or ozone) or Earth’s surface. • Or Scattered; This is why the sky is blue, or red, or whatever color. Whichever color you see if the most scattered wavelength (color) of visible light
Earth’s Energy Balance • The earth must stay in balance or else it would forever get hotter or colder. Energy into the Earth/Atmosphere system = Energy out of the Earth/Atmosphere