Name: Jessica S.
In an article about water vapor estimates over different land regions I
do not understand the dimensions of evaporotranspiration over a region
which is in mm/yr and for which a mean value is shown. That dimension is
not a unit of volume. Do you know why? I also do not understand the
dimensions of "estimated water vapor" which is expressed in (km3/yr) and
for which a mean value is shown. Is that the average partial pressure of
water vapor broken up into single km cubes or does the value of say 18.3
represent 18.3 cubic kilometers of water vapor?
It is difficult to say how these units might have come about without going
through the derivation. But frequently units are expressed dimensionally. By
that I mean the ratio, R, of a volume V (l^3) per unit area A (l^2) is
sometimes written: V(l^3) / A(l^2) = R(l^1). I think this is misleading and
should be avoided but you find this practice widely in the literature.
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Update: June 2012