What is energy? The ability to do work Energy is always conserved Potential Energy Represents the potential to do work (stored) PE = mgh Kinetic Energy Energy associated with motion KE = 1/2 mv 2 The temperature of the air is a measure of its average kinetic energy or it is a measure of the average speed of the atoms and molecules. Internal Energy Sum of all stored energy in molecules
Potential vs. Kinetic Energy At any moment in its flight, the ball has exactly the same energy it had at the start (energy is conserved). The energy is divided between potential and kinetic, but the total energy stays the same. What kind of energy does the ball have as it leaves your hand? As the ball goes higher, does it gain or lose potential energy? All potential energy Mostly kinetic energy Half potential, Half kinetic
What do we mean by heat? Heat is energy in the process of being transferred from one object to another because of the temperature difference between them. The transfer of energy goes from higher temperatures to lower temperatures. In the atmosphere, heat is transferred by conduction, convection, and radiation.
Transfer of Energy Conduction Molecules transfer energy to other molecules they come in contact with Ex: The sun warms the ground, and this heats a thin layer of air above the surface Convection Energy transfer by the motion of matter from one location to another Ex: Warm, less dense parcel of air rising Radiation Energy transfer not requiring contact between bodies or a fluid between them Ex: The sun warms the earth from 91 million miles away
Sensible Heat: the heat we can feel, “sense”, and measure with a thermometer Latent Heat: the heat energy required to change a substance, such as water, from one state to another
Radiation Radiation travels in the form of electromagnetic waves that release energy when they are absorbed by an object. All things, no matter how big or small, emit radiation. The wavelengths emitted depend primarily on the object’s temperature Higher temperature faster vibration of electrons shorter wavelengths of emitted radiation As the temperature of an object increases, more total radiation is emitted each second (Stefan-Boltzmann Law):
Wien’s Displacement Law The wavelength of maximum emission from an object is related to the temperature by a simple expression: λ max = 2897 [μm·K] / T Sun: max = 0.5 m Earth: max = 10 m
What happens to radiation in the atmosphere? Reflection Albedo is a percentage of incident radiation that is immediately reflected back Absorption Everything that emits radiation also absorbs radiation Some things are better at absorbing than others Scattering EM waves can be scattered off in all directions when they come in contact with particles in the atmosphere The reason why the sky is blue and sunsets are red Transmission Waves also may simply pass directly through an object
Why is the sky blue and why are sunsets red? Blue sky: During the day, Rayleigh scattering preferentially scatters shorter wavelengths (blue/green) towards the observer, so the sky appears blue. Red sunsets: When the sun is low in the sky, it has a thicker atmosphere to travel through. Blue and green light is completely depleted by Rayleigh scattering and therefore, only red light (longer wavelengths) is left to reach the observer.
Greenhouse Effect Greenhouse gas molecules (and clouds) absorb outgoing infrared radiation, keeping the Earth from cooling without end. Greenhouse gases are carbon dioxide, water vapor, methane These same absorbers radiate as well, slightly less though since they are a lower temperature than the surface. Water vapor and CO 2 absorb and radiate IR energy and act as an insulating layer around the earth net effect is warming of the earth.
Surface Analysis: Contouring Isotherms: contour lines connecting locations of equal temperature Reminder: temperature is the top left number on a station plot Be sure to label isotherm lines with a temperature In class example 72