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<br />II. THE PHYSICAL BASIS FOR CLOUD SEEDING <br /> <br />Much is still unknown about how some clouds grow, mature and <br />dissipate with the passage of time, especially very severe storms. <br />The following is a much simplified explanation of how convective <br />clouds can form and develop into precipitating systems. During the <br />crop-growing period of the year rapidly growing convective clouds <br />also can quickly become severe (hail-producing) storms, producing <br />highly destructive surface winds and occasionally tornadoes. <br /> <br />In order for precipitating clouds to form,air containing water <br />vapor must first be cooled to condensation. Rising air expands as <br />atmospheric pressure decreases causing air to cool to a temperature <br />at which the water vapor in the air can condense into water. When <br />condensation takes place, it does so upon microscopic particles <br />called cloud condensation nuclei (CeN), CCN particles include dust, <br />smoke and salt crystals---all being found relatively abundantly in <br />the atmosphere, worldwide. When a collection of these water <br />droplets have grown to sufficient size, they are seen as clouds. <br />Some of the mechanisms creating clouds by the lifting and cooling <br />of air in Western Kansas are: <br /> <br />(I) surface heating - returning solar radiation to the <br />atmosphere <br /> <br />(2) intruding cold and warm frontal systems - forcing air to <br />rise over its boundary <br /> <br />(3) relatively cold air in the upper atmosphere sinking into <br />warmer air ahead of it causing warm ~ir to rise <br /> <br />(4) upslope flow of air moving moisture from lower altitudes <br />to the east into the higher altitude areas of western <br />Kansas and eastern Colorado <br /> <br />( 5) regions of convergence created by troughing at the surface <br />or aloft which forces air to rise <br /> <br />(6) upper level low pressure systems (when associated with <br />lower convergence, sinking cold air or upslope effects) <br /> <br />(7) convective scale interaction resulting from thunderstorm <br />outflows digging under warm, humid air acting much like a <br />mini-cold front forcing air ahead of it to lift rapidly; <br /> <br />(B) gravity waves---very small, internal perturbations <br />traveling through the atmosphere, many of which are <br />created randomly and not easily detectable in real-time <br />when forming <br /> <br />5 <br />