chapter 5 weather and climate

chapter 5 weather and climate - Chapter 5 -As clouds form...

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Chapter 5 -As clouds form vast quantities of heat are released into the atmosphere -clouds help regulate the earth’s energy balance by reflecting and scattering solar radiation and by absorbing the earth’s infrared energy -without clouds there would be no precipitation -clouds are also significant because they visually indicate the physical processes taking place in the atmosphere -Atmospheric Stability -most clouds form as air rises, expands, and cools -when talking about atmospheric stability it means a condition of equilibrium -air is in stable equilibrium when after being lifted or lowered it tends to return to its original position, it resists upward and downward air motions -air that is in unstable equilibrium will when given a little push move farther away from its original position, it favors vertical air currents -a balloon like blob or air is called an air parcel -when an air parcel rises, it moves into a region where the air pressure surrounding it is lower -this allows the air molecules inside to push outward on the parcel walls, expanding it -as the air parcel expands, the air inside cools -if the same parcel is brought back to the surface the increasing pressure around the parcel squeeze (compresses) it back to its original volume and the air inside warms -a rising parcel of air expands and cools while a sinking parcel is compressed and warms -if a parcel of air expands and cools or compresses and warms with no interchange of heat with its outside surrounding this situation is called an adiabatic process -as long as the air in the parcel is unsaturated the rate of adiabatic cooling or warming remains constant and is 10*C for every 1000 meters of change in elevation -since this rate of cooling or warming only applies to unsaturated air, it is called the dry adiabatic rate -as the rising air cools, its relative humidity increases as the air temp approaches the dew point temp -if the rising air cools to its dew point temp the relative humidity becomes 100 percent -because the heat added during condensation offsets some of the cooling due to expansion the air no longer cools at the dry adiabatic rate but at a lesser rate called the moist adiabatic rate -the rate at which rising or sinking saturated air changes temp the moist adiabatic rate is less than the dry adiabatic rate -the dry adiabatic rate is constant, but the moist adiabatic rate isn’t and instead varies with temp and with moisture content, as warm saturated air produces more liquid water than cold saturated air -the moist adiabatic rate is much less than the dry adiabatic rate when the rising air is quite warm, and the two rates are nearly the same when the rising air is very cold -Determining Stability -we determine the stability of the air by comparing the temp of a rising parcel to that of its surrounding -if the rising air is colder than its environment it will be more dense and tend to sink back to its original level -the air is stable because it resists upward displacement -if the rising air is warmer and therefore less dense, then the surrounding air, it will continue to rise until it
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This note was uploaded on 04/10/2008 for the course ATM OCN 100 taught by Professor Martin during the Fall '08 term at Wisconsin.

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chapter 5 weather and climate - Chapter 5 -As clouds form...

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