lecture 9 - Formation of Precipitation Requires Cooling of...

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Formation of Precipitation Requires Cooling of air to dew point temperature (requires a lifting mechanism) Condensation of water vapor onto nuclei (dust, ions) to form droplets Growth of droplets so that a) terminal velocity updraft velocity b) sufficient mass of liquid to survive evaporation on way down Importation of water vapor into cloud to replace precipitation and sustain process
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Lifting Mechanisms Three meteorological situations lead to vertical uplift of air masses: uplift due to convergence Nonfrontal convergence of air masses with equal temperature to a low pressure point (i.e. at ITCZ due to convergence of NE/SE tradewinds). Generates moderate rainfall over long duration. Frontal convergence of air masses of different air temperature. Produces cold fronts/warm fronts. uplift due to convection uplift due to orography
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Uplift due to convergence warm front - Occurs when warm air impinges on cold. Two air masses do not mix. Warm moist air is less dense, rises over cold air at relatively gentle slope. Warming occurs gradually resulting in more moderate storms which last longer. See high clouds first. cold front - Cold air impinges on warm air. Again do not mix but cold air moves under warm forcing it upward. Get a steeper sloped interface. Rapid cooling, stronger storms of shorter duration. See low clouds first.
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lecture 9 - Formation of Precipitation Requires Cooling of...

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