Meteo 465/565 -- The Middle Atmosphere

Pressure and Temperature

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1. Why do we care about Earth's middle atmosphere?

• Stratosphere defines the structure of the lower atmosphere
• Stratospheric ozone blocks cell-damaging UV light
• Climate is influenced by exchange of radiation
• Stratospheric dynamics may influence tropospheric dynamics  --  some kind of trigger mechanism
• The ionosphere influences radio waves
• Drag in the ionosphere affects satellites’ orbits

2. Static pressure in the middle atmosphere

• Ideal gas law and hydrostatic equilibrium:     p = r RT implies that p = p_s exp(-z_lp/H), where H is the scale height
• Geometric heights: Important for lidar and radar measurements
• Hypsometric equation and geopotential:     Z = F(z)/g_o, where F(z) = ò g dz

3. Temperature

• Brassuer and Solomon  (BS) Figure 3.1. Typical vertical temperature profile.
• Definition of the tropopause (WMO):
• The tropopause is the lowest level at which the temperature lapse rate decreases to 2 K per km or less and the lapse rate averaged between this level and any level within the next 2 km does not exceed 2 K per km.
• Potential temperature.
• J = T (p_o/p)^R/cp
• Use as a vertical coordinate (Andrews, Holton, and Leovy, Fig. 9.1)
• Static stability
• Temperature structure at solstice
• Comparison with AHL Figure 1.2, showing the difference between the real atmosphere and one in radiative equilibrium
• The thermal structure near the tropopause -- definition of the overworld and the middleworld.  The middle world is the stratospheric region bounded on top by the potential temperature