AOS 100: Weather and Climate Instructor: Nick Bassill Class TA: Courtney Obergfell

Miscellaneous Homework Reminder Note takers

Review of September 15th: Heat and Heat Transfer Heat can be thought of as a form of energy transfer The amount of heat gained by one object is equal to the amount lost by the other object Heat transfer is why certain objects feel warm or cold Specific heat is a measure of the heat energy needed to heat 1 g of an object 1º C This is why water changes its temperature less during the day then the air

Review Continued There are four primary mechanisms of heat transfer in the atmosphere: - Conduction, convection, advection, and radiation Conduction is the transfer of heat through an object molecule by molecule Heat Conductivity is a measure of the effectiveness of different materials at conducting heat This is one reason that 40º F water “feels” colder than 40º F air, even though they are the same temperature Convection is heat transfer by the movement of fluids (gases and liquids) in the vertical (along gravity) Less dense (i.e. warmer) fluids tend to rise and more dense fluids (i.e. colder) tend to sink

Review Continued The lapse rate is simply a measure of the rate of change of temperature with height If the temperature decreases by 15ºC in 2000 meters, you would say that the lapse rate is 7.5ºC/km Advection is the transfer of heat through the horizontal movement of a fluid

Radiation Unlike Conduction, Convection, and Advection … Radiation does not need a medium to travel through (i.e. it can travel through empty space) Radiation carries energy in the form of electromagnetic waves This is how the Earth receives energy from the sun All objects emit and receive radiation

Radiation Continued As objects emit radiation, they cool (i.e. lose energy), unless they are being warmed by some other process Radiation can be – Emitted (such as from the sun) Absorbed (like sunlight on your face) Reflected (visible light off a mirror) Scattered (visible light as seen in a rainbow)

Wien’s Law The emitted wavelength of radiation depends on the temperature of the object Hotter objects emit radiation with a shorter wavelength Shorter wavelengths are more energetic This means that there is more energy in the radiation that hot objects emit The wavelength of maximum emitted radiation (λ, in nm) is approximately: λ=2897/T (in Kelvin)

λ=2897/T

Stefan-Boltzmann Law This law essentially states that warmer objects emit (transfer) more energy than colder objects However, this isn’t a linear relationship The amount of energy emitted is proportional to the temperature to the fourth power Energy emitted = σ * T4 where σ is a constant (5.67 x 10-8 W m-2 K-4) Really, we can think of it as E~ T4 (In Kelvin)

The Spectrum of the Sun’s Emittance Notice that the largest component of the Sun’s emittance falls in the visible spectrum

A Comparison of Emittances From:www.csulb.edu/~rodrigue/geog140/sunwavelength.gif

Albedo The albedo of an object is a measure of the amount of sunlight it reflects For example, snow, ice, and clouds have a much higher albedo than grass, water, or dirt The average albedo of the planet is about .3, which means on average the planet reflects 30% of the incoming solar radiation This varies strongly from location to location (i.e. the arctic vs. forests or the ocean)

The atmosphere absorbs some radiation However, this doesn’t happen uniformly for all wavelengths Since the Sun’s radiation and the Earth’s radiation are almost completely separate wavelengths, these variations are important! Much more of the Earth’s radiation is absorbed by the atmosphere than the Sun’s