fredag 21 maj 2010
The Atmosphere as Air Conditioner
In Atmosphere as Air Conditioner we argue than a planetary atmosphere partly acts like an air conditioner or refrigerator, transporting heat from the planet surface to the top of the atmosphere in a cyclic thermodynamic process of air rising-expanding-cooling and descending-compressing-warming. The "engine" driving this process is gravitational bouyancy forcing hot light air to rise and cool dense air to descend. Ocean circulation is driven similarly.
We identify two extreme hydrostatic base solutions depending on height, one isentropic with
zero turbulent dissipation and with constant maximal temperature gradient/lapse rate, and one with maximal turbulent dissipation and with constant temperature/zero lapse rate.
We observe that the real lapse rate of - 6 C/km lies between these extremes of -10 (dry adiabatic lapse rate) and 0.
This analysis indicates that the main aspect of global climate of a temperate Earth surface
of 15 C connected to a tropopause at - 55 C, results from thermodynamics and
The lapse rate in the troposhere is - 6 C/km, and changes sign in the stratosphere to reach
0 C at the stratopause thus with a climb of 55 C, with the stratosphere being heated by ozon absorbing radiation from the Sun. Without this effect the Earth surface temperature might have been 55 + 15 = 70 C. The ozon in the stratosphere thus may have a cooling effect on the Earth surface.
The 0 C in the stratopause fits with blackbody radiation, which is also the effective blackbody temperature of an Earth without an atmosphere.
An Earth with atmosphere without radiation can thus be expected to be at 70 C. The absorption in the stratosphere by the ozon appears to have a major cooling effect, while the warming effect of a small amount of CO2 in the troposphere may be small.
We make a connection to the Joule experiment of a gas expanding-cooling under warming from turbulent dissipation, which we analyze in Mathematical Simulation Technology, Chap 166 The Secret of Thermodynamics.