Laserfiche WebLink
<br />way to proceed i. to use numerical models capable of simulating the relevant physical <br />processes. These sophisticated numerical models do exist and can provide additional <br />insight in key areas identified above where scientific knowledge is lacking. Following <br />chapters will compare results from numerical simulations and observations collected during <br />1987 over the Mogollon Rim in Arizona, and show how modelling iniormation can be used <br />to unravel the chain of events that proceeds following seeding of these clouds. <br /> <br />!-- <br /> <br />I <br />! . <br />! <br /> <br />Precipitation formation mechamsms can differ dramatically from one location to <br />another and within one location depending on the meteorological setting. Precipitation <br />growth can either take place through coalescence or the ice process or a combination <br />of the two. In clouds with tops warmer than OOC precipitation develops via the <br />coalescence process. However, when cloud tops reach temperatures colder than. OOC ice <br />can develop. Precipitation can then develop via either the coalescence-freezing mechanism <br />(CRG) (Braham, 1986), ice crystal growth by vapor diffusion followed by riming into <br />graupel (mG) mechanism (Silverman, 1986), ice crystals aggregating into precipitation <br />particles (Heymsfield, 1986; Prasad et al., 1989), or a combination of two or more <br />of these mechanisms. The number concentration and size spectrum of cloud droplets <br />can also vary dramatically depending on the cloud condensation nucleus (CCN) size <br />distribution. A maritime droplet spectra will consist of fewer particles but more larger <br />drops than. in a continental spectrum (Pruppa.cher and Klett, 1978). In addition ice <br />crystal concentrations can also vary greatly depending on temperature and whether or <br />not there is an ice multiplication process active. Depending on the temperature at which <br />crystals originate, ice crystals develop with different shapes which in turn have clliFerent <br />riming and aggregation characteristics influencing the precipitation formation mechanism. <br />Recent evidence suggests that the type of hygroscopic chemicals within a drop or ice crystal <br />and electrical efFects both within particles and in the cloud have significant efFects on the <br />development of precipitation (Schlamp et al., 1978; Finnegan. and Pitter, 1988; Pitter <br />and Finnegan, 1990). It is evident that responses to seeding will differ depending on the <br />precipitation mechanism that is operating at the time. <br /> <br />Finally, the present seeding concepts in terms of the static or dynamic seeding mode <br /> <br /> <br />9 <br /> <br />. <br /> <br />. <br /> <br />. <br />