Bizarro World: Physics of the Atmosphere
Sometimes I'm pretty sure that I really am living in Bizarro World. I've recently been having a debate, if you can call it that, with a full Professor of Atmospheric Science on another blog who seriously and for real doesn't believe in conservation of momentum. I haven't had the nerve to ask his opinion on whether or not the Earth is flat.
This is not my first bizarro world encounter with meteorologists. I happened to buy a book by a well known pollution modeller once upon a time, and noticed amoung other peculiarities, that he had incorrectly defined temperature, pressure, and even velocity - ok, the velocity thing was almost minor - he called the components of the velocity vector "scalar velocities". A rather famous book on Dynamic Meteorology still had, in its third edition, completely phony derivations of some elementary results - the sort of mistake that would get you a poor grade in Freshman thermodynamics.
I badgered a meteorologist friend about these last two, and his explanation was that meteorolgy was populated mainly by those who found physics too hard, but I think he was joking.
UPDATE: I have been reading some of the sections on energy and momentum transfer in Dr. Pielke's book on Mesoscale Modeling, and thought, incidentally, that the discussion was exceptionally clear. One point he makes is that except at the surface, forces due to molecular viscosity are negligible in the mesoscale. Those forces, though, are the very ones responsible for the ultimate dissipation and conversion of turbulent energy to thermal energy. When that occurs, any net momentum of the turbulent air will either persist in the once turbulent air or have been transferred to waves or the surface. If a model neglects viscous molecular forces though, it will lose track of that momentum and hence, in the model, this negligible amount of net momentum will be lost. With that interpretation, momentum is not conserved *in the model*. A modeler friend tells me most models are like that.
Since momentum is a vector quantity and since turbulence, by definition, has motion in many different directions, the net momentum will always be a lot smaller than the sum of the rms momenta of the parts.
This is not my first bizarro world encounter with meteorologists. I happened to buy a book by a well known pollution modeller once upon a time, and noticed amoung other peculiarities, that he had incorrectly defined temperature, pressure, and even velocity - ok, the velocity thing was almost minor - he called the components of the velocity vector "scalar velocities". A rather famous book on Dynamic Meteorology still had, in its third edition, completely phony derivations of some elementary results - the sort of mistake that would get you a poor grade in Freshman thermodynamics.
I badgered a meteorologist friend about these last two, and his explanation was that meteorolgy was populated mainly by those who found physics too hard, but I think he was joking.
UPDATE: I have been reading some of the sections on energy and momentum transfer in Dr. Pielke's book on Mesoscale Modeling, and thought, incidentally, that the discussion was exceptionally clear. One point he makes is that except at the surface, forces due to molecular viscosity are negligible in the mesoscale. Those forces, though, are the very ones responsible for the ultimate dissipation and conversion of turbulent energy to thermal energy. When that occurs, any net momentum of the turbulent air will either persist in the once turbulent air or have been transferred to waves or the surface. If a model neglects viscous molecular forces though, it will lose track of that momentum and hence, in the model, this negligible amount of net momentum will be lost. With that interpretation, momentum is not conserved *in the model*. A modeler friend tells me most models are like that.
Since momentum is a vector quantity and since turbulence, by definition, has motion in many different directions, the net momentum will always be a lot smaller than the sum of the rms momenta of the parts.
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