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<br />~ <br />I <br />I <br />I <br />I <br />j <br />I <br />I <br />, <br />I <br />I <br />I <br />I <br />I <br />, <br />I <br />I <br />, <br />I <br /> <br />II. THE PHYSICAL BASIS FOR CLOUD SEEDING <br /> <br />Although a vast amount of knowledge is knOM! generally about clouds, there is still much <br />unknoM! about those rapidly growing convective clouds which can quickly become severe, <br />produce highly destructive hail and surface winds, destroy crops and property, cause flooding and <br />produce occasional tornadoes. What follows is a simplified explanation of how convective clouds <br />grow to become severe storms and presents a general theory supporting the feasibility of seeding <br />to reduce hail and/or to increase rainfall, <br /> <br />A convective cloud forms when rising air containing water vapor cools by adiabatic <br />expansion reaching a temperature at which condensation occurs to form water droplets, <br />Condensation begins first upon the relatively abundant microscopic atmospheric aerosols, or <br />particles, called cloud condensation nuclei (CCN) which include dust, smoke and salt particles, <br />Clouds become visible when a collection of water droplets have grown to sufficient size, The <br />primary mechanisms in Western Kansas causing air to rise and form into convective clouds are: <br /> <br />(1) surface heating <br /> <br />(2) advancing cold and warm frontal systems <br /> <br />(3) relatively cold air in the upper atmosphere sinking into warmer air ahead of it causing <br />warm, moist air to be displaced upward <br /> <br />(4) upslope air flow moving moisture from lower altitudes in Eastern Kansas into higher <br />altitude areas of Western Kansas and Eastern Colorado, usually a post-frontal <br />condition <br /> <br />(5) regions of horizontal convergence created by troughing at the earth's surface, or aloft <br /> <br />(6) Elevated convection---or at least one form of it <br /> <br />(7) upper level low pressure systems (most often associated with low-level convergence, <br />sinking cold air and/or upslope effects) <br /> <br />(8) convective scale interaction resulting from thunderstorm outflows digging under <br />warm, humid air, often forcing a rapid lifting above it into a more unstable <br />atmosphere. <br /> <br />(9) gravity waves---very small, internal perturbations traveling through the atmosphere, <br />many of which are created randomly and not easily detectable in real-time. Such <br />waves act much like the effects seen from convective scale interaction, <br /> <br />o <br />.J <br />