Hands-On, Minds-On Meteorology Description | Programming | Operation Water Collisions Description A brief description of what happens when water vapor / liquid is in ParcelSet* and has the opportunity to either evaporate or condense. Programming Theory The theory for collisions between water elements (vapor and\or liquid) is as follows: If both colliders are water elements and the relative humidity of the parcel is > 100%, they will condense. If the RH = 100%, then a check is made and condensation will only occur when both water elements are themselves already condensed (to conserve the RH) If the RH < 100%, and any condensed water contacts anything, one vapor molecule is evaporated into the air. Assumptions Relative Humidity Collision Possibiilites > 100% = 100% < 100% 1 dry, 1 anything else Bounce Bounce Bounce 1 vapor, 1 vapor Condense* Bounce Bounce 1 vapor, 1 water Condense* Bounce N/A 1 water, 1 water Coalecse Coalecse N/A * Indicates condensation only if it does not drop the RH below 100%, otherwise, it will bounce (see other, below). Equations N/A Other Considering the program only deals with a discrete number of water elements, the addition of one element can increase the RH from less than 100% to more than 100%. In such cases, that is rounded down to 100%. This is what is meant by 100%. Also, even if percentage-wise, there should be 0 molecules, one remains single and the RH = 100%. This only occurs for extremely cold conditions. Also, this process is reversible. Rain never occurs on the reasoning that the liquid water droplets never get large enough. Operation Running the Program This is simply a section of ParcelSet*. Neither this nor ParcelSet* are directly executable. Department of Atmospheric Sciences University of Illinois at Urbana Champaign Created by Dan Bramer: Last Modified 07/27/2004 send questions/comments to bramer@atmos.uiuc.edu