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Details Title: Earth Science - Chapter 17 Description: Moisture, Clouds, and Precipitation Total Flash Cards: 30 Created: 04/23/2006 20:26:37	To study from this set of flash cards, or to create your own your own study flash cards, register HERE. If you are already a registered user, CLICK HERE.
Cards Term relative humidity Definition the ratio of the actual water content of the air to that amount of water that the air "can hold" at that temperature Term dew-point temperature Definition temperature at which air must be cooled in order to reach saturation if the temp falls below the dew point, the atmosphere becomes supersaturated and fog or rain will form temp vs. dew point relates to how comfortable we feel - closer = muggier, greater = drier Term measuring humidity Definition hair hygrometer hair lengthens with increased humidity conductivity salt's ability to conduct electricity increases w/humidity electronic hygrometers using lithium chloride salt crystals Term mixing ratio Definition mass of water vapor in a unit of air vs. remaining mass of dry air dependent on total air pressure (greater at pressures) Term humidity Definition the general term for the amount of water vapor in air Term stable air Definition temperature of a parcel of air is the same as its surroundings density is the same resists vertical movement clouds are widespread and have little vertical thickness requires some mechanism to initiate vertical mixing of air Term unstable air Definition temperature of a parcel of air is different from its surroundings Denser air (cooler) sinks Less dense air (warmer) rises rises or falls because its density is higher or lower than the surrounding environment Clouds are towering accompanied by heavy precipitation Term Absolute Stability Definition Environmental lapse rate is less than the wet adiabatic rate Temperature inversion Temperature in a layer of air increases with altitude night due to radiative cooling Warmer air at altitude acts as a lid, preventing vertical mixing of air Term Conditional Instability Definition Moist air has an environmental lapse rate between the dry and wet adiabatic rates Air unstable for an unsaturated parcel of air, but stable for a saturated parcel of air Conditional since the air must be forced upward before it becomes unstable and rises under its own buoyancy Term processes that lift air Definition orographic lifting frontal wedging convergence Term orographic lifting Definition air rises to cross mountains rising air expands and cools adibatically at dew point temperature, it condenses and forms clouds continued condensation may produce rain or snow Term Frontal Wedging Definition Occurs when cool air acts as a barrier over which warmer, less dense air rises Weather producing fronts are part of the middle-latitude cyclones: the “Lows” that you see on weather maps Produce a high proportion of the precipitation in mid-latitude regions Term Convergence Definition Occurs when air masses flow together Results in a general upward movement of air A major contributor to stormy weather associated with mid-latitude cyclones and hurricanes Term Condensation Definition must be a surface upon which the water can condense Dew - objects at or near the ground Fog and clouds - Suspended particulate matter Condensation nuclei - small particles in air If missing, relative humidity >> 100% for clouds to form Term Cirrus Definition High, white and thin clouds Term Cumulus Definition Globular, individual masses Term Stratus Definition Sheets or layers that cover most of the sky Term Mechanisms of Cloud Formation Definition Formed when air is saturated Saturation caused by: Cooling .Adiabatic Ascent ..Buoyant (Unstable) ..Forced (Orographic or Frontal) .Contact with the earth’s surface (Fog) Moisture Gain Mixing Term high clouds Definition cirro- base normally above 6000 meters usually no precipitation mostly ice crystals Term middle clouds Definition base 2000-6000 associated with infrequent light snow or drizzle mixture of supercooled water droplets and ice crystals Term low clouds Definition base below 2000 meters usually water droplets (little or no ice) <0 droplets are supercooled Term Precipitation Definition any form of water that falls from the atmosphere and reaches the ground raindrops fall slowly, most evaporate cloud droplets must coalesce in order to form droplets that can reach the ground explained by bergeron process & collision coalescence process excludes: dew, frost, water vapor, cloud droplets Term Bergeron Process Definition Dominant process is “cold clouds” Pure water drops do NOT freeze at 0°C it needs to be colder (“supercooled”) bigger water drops will freeze at warmer temperatures than smaller drops smaller water drops require colder temperatures to freeze more smaller drops than larger drops higher in the cloud During ice crystal process, ice crystals grow at the expense of water droplets Ice crystals fall and collide with supercooled water droplets. Term Collision/Coalescence Definition Cloud droplet growth by collision Dominant process for precipitation formation in warm clouds Some cloud droplets will grow large enough and will start to fall in the cloud Since the bigger drops fall faster than the smaller drops, they will "collect" the smaller drops - the bigger drop grows Droplet fall speed is called it's terminal velocity Need droplets of different sizes for this process to really work. factors promoting c/c: different drop sizes, thicker clouds, stronger updrafts Term sleet Definition tiny ice pellets that are transparent if a deep freezing layer exists at low levels, sleet may form Term Rime Definition Supercooled drops in fog/cloud that freeze onto objects on ground Term hail Definition Usually formed in strong storms by accretion of super-cooled water onto graupel, or other frozen particles Term adiabatic cooling and heating Definition occurs whenever air is compressed or allowed to expand compression - heating expansion - cooling does not require the addition of heat Term Dry adiabatic rate Definition Air pressure decreases with altitude Any parcel of air that rises will expand and cool A parcel of air that descends will undergo compression and HEAT UP Term Wet Adiabatic Rate Definition If air rises high enough, temperature will lower to the Dew Point. If air continues to rise, stored latent heat (of condensation) will be released to the surroundings. Thus the released heat causes a slower rate of cooling