Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Transpiration Measuring
Name: Jessica S.
Status: other
Age: 17
Location: N/A
Country: N/A
Date: 5/5/2004


Question:
2 questions: 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?


Replies:
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.

Vince Calder



Click here to return to the Botany Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory