phy392_lecture10_web_2011

# phy392_lecture10_web_2011 - PHY392S Physics of Climate...

This preview shows pages 1–7. Sign up to view the full content.

PHY392S Physics of Climate Lecture 10 - Web Notes More on Radiative Transfer Terrestrial Fluxes: Schwarzchild’s Equation Revisited The Two-Stream Model PHY392 - Physics of Climate Lecture 10, Page 1

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Schwarzchild’s Equation - Summary The derivative form of Schwarzchild’s Equation: And for local thermodynamic equilibrium: The integral form of Schwarzchild’s Equation, using J = B: J I - dx k dI ν ν ν ν + = ρ ν τ ν ν ν ν τ + τ = 1 ) X ( d B ) X ( ) 0 ( I ) X ( I x k e ) x ( ρ ν ν = τ ρ ν ν ρ ν ν ν ν ρ + = X 0 ' x k X k ' dx e B k e ) 0 ( I ) X ( I PHY392 - Physics of Climate Lecture 10, Page 2 B I - dx k dI ν ν ν ν + = ρ
Consider a laboratory cell containing a gas that absorbs radiation, and for which absorption is the only thing that we need to consider, i.e., we can neglect scattering - valid in the infrared. In this case, J is the blackbody function B and Schwarzchild’s Equation can be written as: X ) 0 ( I ν ) X ( I ν First Example: Lab Gas Cell - 1 Measured with no gas in the cell ( ) X k X k e 1 B e ) 0 ( I ) X ( I ρ ν ρ ν ν ν ν + = Measured with gas in the cell PHY392 - Physics of Climate Lecture 10, Page 3

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
First Example: Lab Gas Cell - 2 At “zero” density (vacuum), a detector at the output of the cell will measure I(0) As the density of the gas (pressure) is increased the measured “exit” intensity will gradually change from I(0) to B In the visible, the emission term is zero (at typical lab temperatures) Beer’s Law In the infrared, the Planck function B becomes important. Three possibilities: hot source, cold cell signal decreases from I(0) to B cold source, hot cell signal increases from I(0) to B isothermal (source T = cell T) no change I(0) ρ I = B ρ ρ I(0) isothermal B B cold target hot target PHY392 - Physics of Climate Lecture 10, Page 4
PHY315S - Radiation in Planetary Atmospheres Lecture 10, Page 5 The Use of Choppers This gas emission complicates infrared lab experiments. One widely used solution is to introduce a chopper that switches rapidly between two values of I(0), and then measure the difference in the output signal. The emission signal does not change because the gas temperature is constant. Thus, the gas transmission term is isolated by eliminating the gas emission term: X k e ) 0 ( I ) X ( I ρ ν ν ν = ) X ( I ν (0) I ν source detector gas cell at uniform T chopper

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Inhomogeneous Paths The real atmosphere is structured in about every physical and chemical manner imaginable in three dimensions, and atmospheric paths are generally inhomogeneous - varying in some parameter(s) such as temperature and pressure.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 24

phy392_lecture10_web_2011 - PHY392S Physics of Climate...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online