SP11%20Ch5%20Cloud%20Development%20_%20Precipitation -...

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Chapter 5 Cloud Development and Precipitation ¾ Stability in the atmosphere depends on the change of temperature in a moving parcel relative to its surroundings. ¾ In a stable atmosphere, a parcel which is given an upward push will become colder and denser than its surroundings and will resist further upward motion. ¾ Clouds which form in a stable atmosphere tend to develop horizontally and have a layered structure. ¾ In an unstable atmosphere, a rising air parcel will become warmer and less dense than its surroundings and will continue to move upward on its own, often forming cumuliform clouds. ¾ The rising air motions that are needed to form clouds can be produced in a variety of ways including convection, topographic uplifting, convergence, and lifting at frontal boundaries. ¾ A variety of factors can affect atmospheric stability such as warming or cooling at the ground and the influx of warm or cold air at upper levels. ¾ Adiabatic processes : change in temperature without giving or removing heat; a process in which an air parcel expands and cools, or compresses and warms, with no interchange of heat with its surroundings. ¾ During a moist adiabatic process the heat added during condensation offsets some of the cooling due to expansion, so the air no longer cools at the dry adiabatic rate but at a lesser rate called the moist adiabatic rate. ¾ The atmosphere tends to become more stable as the air aloft warms or the surface air cools. If the air aloft is being replaced by warmer air (warm advection), and the surface air is not changing appreciably, the environmental lapse rate decreases and the air becomes stable. Similarly, if the surface air cools and the aloft air temperature remains relatively constant, the air becomes more stable. ¾ Conditional instability means that if the atmosphere is unsaturated it is stable, but if it is saturated it is unstable. ¾ Sinking air between the clouds compensates for the rising air beneath the clouds. ¾ Cumulus clouds form as hot, invisible air bubbles detach themselves from the surface, then rise and cool to the condensation level. ¾
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This note was uploaded on 09/25/2011 for the course 670 201 taught by Professor Hopey during the Spring '11 term at Rutgers.

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SP11%20Ch5%20Cloud%20Development%20_%20Precipitation -...

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