the water content of the atmosphere, at saturation, increases rapidly with increasing temperature.
at any temperature the absolute amount of water in the air, expressed either as mol percent or lb water per lb air, increases with increasing RH.
the atmosphere has a perfectly well-defined -- but quite uneven -- lower boundary, the surface of the land and the oceans.
its upper boundary is not as well-defined; the atmosphere simply becomes thinner and with increasing height until it is as thin as outer space.
one-half of the mass of the atmosphere is within 3.4 miles of the surface; 99 percent is within 20 miles of the surface.
if the atmosphere were peeled off the earth and had its edges stitched together to make a pancake shape, it would have an approximate thickness of 20 miles and a diameter of 16,000 miles
this large width and small depth mean that most of the motions in the atmosphere must be horizontal.
except for very vigorous storms, the vertical motions in the atmosphere are one or two orders of magnitude smaller than the horizontal ones (the vertical component of the wind velocity is one or two orders of magnitude less than the horizontal component of the wind velocity).