18-2 Flashcards
(25 cards)
what are clouds?
millions of tiny water droplets, so small that they are suspended in air
how do clouds form?
form as humid air is cooled to its dew point and condenses or when more water vapor is added to its air
what is air compression? How does that affect the air temperature?
when air is added it compresses the air making molecules move more, air temperature of compressed air increases. When you take the same amount of air out, the temperature cools the same amount as was heated, so when air expands it cools
what is adiabatic temperature change? when air expands and compresses what does it do?
temperature change that occurs without heat being added or removed; changes due to air pressure changes. When air expands, it cools, when air is compressed, it warms
the higher in the atmosphere what happens to the pressure?
the air pressure drops, fewer and fewer molecules the higher you go. Any time a volume of air moves upward it reaches lower pressure, so air expands and cools
what is dry adiabatic rate?
unsaturated air cools as it ascends while descending air compresses and warms
what is wet adiabatic rate?
the adiabatic rate gets higher and colder or warmer and lower
what is adiabatic cooling?
near surface it cools at dry adiabatic rate, at level it cools to dew point, then condensation forms, from this level or higher it cools at wet adiabatic rate which forms clouds
what are the processes that force air to rise and make clouds?
orographic lifting, frontal wedging, convergence, and localized convective lifting.
what is orographic lifting?
when mountains or elevated terrains act as a barrier and forces air up and over, as air goes up adiabatic cooling creates clouds
how does moisture affect mountain sides
on windward mountain slopes are many rainforest locations, on leeward side moisture is lost
what are fronts?
when warm and cold air masses collide
what is frontal wedging?
colder denser air acts as a barrier over warmer air rises; produces lots of weather
what is convergence?
when air in the lower atmosphere flows together, lifting results. As air flows into each other it has to go up leading to adiabatic cooling (cloud formation)
what are thermals? what is localized convective lifting?
Thermals: localized air pocket that is rising due to heating
Unequal heating of Earth’s surface may cause pockets of air to be warmed more. When warm parcels of air rise above condensation level, clouds form
what is stability?
stable air resists vertical movement when air that was forced up is cooler and more dense than surrounding air sinks back to original position
how do density differences affect rise in altitude in the air? What’s the difference between stable air and unstable air in rising?
if rising air were warmer and less dense than surrounding air it would continue to rise, rise in altitude until temperature becomes equal to surroundings. Stable air tends to remain in original position while unstable air tends to rise
what is the environmental lapse rate?
rate of change of air temperature with height
when is air stable?
when temperature decreases gradually with increasing altitude, even more stable when temperature increases with height
what are temperature inversions? when do they happen?
when air temperature increases with height, happens on cold nights with radiation cooling of Earth’s surface, air next to ground cools more rapidly than air higher above the ground so little vertical air movement
what is unstable air?
when air close to the ground is significantly warmer; large environmental lapse rate, air turns over as warmer air below rises and is displaced by cold air
how does stability relate to daily weather?
stable air has few clouds, if one of the four forces occurs it is forced up forming widespread thin clouds with light rain. unstable air has towering clouds with thunderstorms and tornados
what is condensation?
when water vapor in air changes to liquid by dew, fog, or clouds.Where air becomes saturated, 100% relative humidity, when air is cooled to dew point or when water vapor is added to the air
when is condensation nuclei needed?
needed when water vapor condenses in the air above ground, if absent relative humidity above 100% needed
