Term
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Definition
when total # of H2O molecules evaporating from body/bodies of water is in equilibrium with condensing
-no net loss or gain of liquid molecules
**more likely to occur in cool air than in warm** |
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Term
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Definition
-microscopic bits of dust, smoke, and salt upon whose surfaces condensation of water vapor begins in the atmosphere
-in cold air, molecules move more slowly and are more apt to stick to these nuclei
-when billions condense onto this nuclei, cloud droplet forms |
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Term
| humidity and measures of it |
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Definition
-refers to any of a number of ways of specifying air's water vapor amount
-in hot/humid air... up to 4% volume
1)absolute humidity-water vapor density: compares mass of water vapor with volume of air.... g/m^3
2)specific humidity - compare mass of water vapor with total mass of all air (including vapor).. g/Kg
3)mixing humidity- compare mass of water vapor to mass dry air
4)actual vapor pressure - total pressure of air with relation to amount of vapor (1% vapor in 1000 millibars equals 10mb of actual vapor pressure)
5)saturation vapor pressure - describes how much water vapor is necessary to make the air saturated at any given T
6)relative humidity - ratio of amount of water vapor in the air to the max amount of water vapor required for saturation of that particular temperature...given as a percent.. 100%=supersaturated
-RH = AVP/SVP.... can be changed by vapor content or T |
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Term
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Definition
-the temperature TO WHICH air would have to be cooled with no change in air pressure/moisture content for saturation to occur.
-this is a good indicator of air's actual water vapor content
***high dew point = high H2O vapor content
-it is difficult to measure, but easy to calculate if you already have Tw
-hydrometeoric (snow/sleet/hail/rain/etc) and atmospheric (clouds/fog) all result because T is cooled to dewpoint
-high dew points result in violent storms
****when air temp and dew point are equal, air is saturated and RH is 100% (though air may still be considered dry... it is a relative measure) |
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Term
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Definition
-wet-bulb temperature is the lowest T(@ saturation) that can be reached by evaporating water into the air... it is a good way to measure how cool skin can become
-when it exceeds skin T... no evap occurs
-usually lower than skin temp |
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Term
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Definition
| -apparent temp- what air T feels like to person |
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Term
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Definition
-instruments used to measure humidity
-most common is psychrometer... 2 thermometers... one wet and one dry... wet bulb depression is the difference in temp between the two |
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Term
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Definition
-tiny visible specks of water that form when water vapor condenses when ground cools at night
-cloudy/windy weather that inhibits rapid cooling near earth often signifies approach of rain-system |
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Term
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Definition
-crystals formed be deposition
-must reach "frost point" |
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Term
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Definition
| -layer of particles dispersed through a portion of atmosphere |
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Term
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Definition
-cloud resting near the ground
-forms either by cooling to below saturation point or evaporation
Types:
-radiation fog
-advection fog
-upslope fog
-evaporation fog |
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Term
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Definition
-(ground fog) - produced by earth's radiational cooling
-most common late fall and winter (longer nights)
-ideal is a light breeze... small amount of mixing but not blowing away
-forms normally in low-lying areas (cold air sinks)
-fog usually dissipates by afternoon
-radiation causes air to cool below dew point |
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Term
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Definition
-formed when warm and moist air moves across cold surface such as pacific coast in summer
-always involves movement of air |
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Term
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Definition
| -fog that forms as moist air flows up elevated plain/hill/mountain |
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Term
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Definition
-like moist air from your mouth on cold day
-fog that forms from two unsaturated masses of air
-also when cold air moves over warm water (steam fog)
-steam fog is very short lived |
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Term
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Definition
| -air from ocean bends into headlands and lifts, bringing up fog |
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Term
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Definition
Lv-latent heat of vaporization... nearly 600calories/g
-released when you get Lc below Td
**DEW warms environment... Temp rarely cools below dewpoint
Lf= latent heat of fusion... 80cal/g
-freezing releases Lf
*when it snows you get Lv plus Lf |
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Term
| Howard's latin for clouds |
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Definition
-stratus... sheet-like
-cirrus... wispy - 'a curl of hair'
-cumulus .... 'heap'
-nimbus ... 'violent rain'
Abercrombie and Hildebrondsson have current system of classification |
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Term
| High, Med, Low, and VD clouds |
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Definition
High... cirrus/cirrocumulus/cirrostratus
-above 20000ft (6km)... mostly ice crystals
Med... Altocumulus/Altostratus
-bases b/w 2000-7000m... mostly water
Low... Nimbostratus/stratocumulus/stratus
-bases below 2000m...all water
VD... cumulus/cumulonimbus |
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Term
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Definition
-most common high cloud- thin and whispy... 'mares tails'
-white patch with feathery wisp at a tail
-no precip
-formation high level ascent |
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Term
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Definition
-small rounded white puffs
-occur individually or in rows... rippling appearance
-resemble scales of fish... no precipitation
-formation through convection-internal instability |
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Term
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Definition
-thin and sheetlike... often cover entire sky
-can see sun/moon through them... halo effect
-typically indicate advance of storm
-no precip
-formation through widespread upper level ascent |
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Term
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Definition
-gray puffy masses... sometimes parallel waves or bands
-one part of cloud is darker than other
-appear larger that cirrocumulus
-precip is virga or light showers
-formation through convection and wave flow near mountins |
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Term
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Definition
-bluegray or gray cloud that often covers entire sky
-sun may be dimly visible as a round disk
-dif from cirrostratus in grayness, height, and dimness of sun
-also will never get a halo; you won't see your shadow
-rain or snow may form
-widespread ascent formation |
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Term
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Definition
-dark, gray wet looking cloud layer... associated with continuous rain or snow
-precip usually light or moderate
-formation widespread ascent |
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Term
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Definition
-low and lumpy cloud layer... rows or patches
-light to dark gray... usually scattering cumulus cloud
-bigger elements that altocumulus and have lower base
-blue sky visible between them, yet they are closer together than cumulus
-light rain/drizzzle/snow |
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Term
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Definition
-uniform grayish cloud... often covers entire sky
-resembles fog that does not reach ground
-usually no precip-but sometimes light drizzle
-occurs near coastal waters in summer
-formation low level ascent |
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Term
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Definition
-piece of floating cotton with sharp outlines and flat base...different from stratocumulus in that they are very detached
-showers of rain or snow
-formation from convection (surface heating or instability) |
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Term
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Definition
-thunderstorm cloud with anvil top
-all kinds of precip |
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Term
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Definition
-cumulus humilis - only slight vertical growth... associated with fair weather
-cumulus fractus - small and appear as broken fragments with ragged edges
-cumulus congestus - towering cumulus, with head resembling head of cauliflower.... almost cumulonimbus |
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Term
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Definition
-lenticular - shape of lens... formed due to mist air crossing mountain barrier forming waves (stack of pancakes or hovering spaceship)
-pileus - cap clouds- usually resembles a silken scarf capping a towering cumulus cloud
-contrail - cirrus like trail of condensed vapor formed by jets flying at high altitudes... due to heat exhaust with cold air... stay for hours if RH high
-nacreous clouds - soft pearly clouds above troposphere... form in stratosphere @ 30+ km
-noctilucent clouds - upper mesosphere 75+km.. appear bright against darker background... tiny ice crystals... water from dissolved meteors |
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Term
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Definition
| -when air parcel expands/cools or compresses/warms with no exchange of heat with outside surroundings |
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Term
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Definition
-only applies to unsaturated air
-10C/km (1C/100m)
-if rising air cools to dew point, further lifting beyond this point results in condensation |
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Term
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Definition
-lesser rate than 10C as condensation offsets this cooling
-approx 6C, but fluctuates a lot depending upon amount of vapor density
-** rate at which rising or sinking saturated air changes T is less than dry adiabatic rate |
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Term
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Definition
-rising air is colder than environment (resists upward displacement)
-clouds in stable environment are all 4 stratus cloud types... flat clouds
-atmosphere is stable when environmental lapse rate is small (gets cold slowly going up)
-atmosphere generally most stable at sunrise...due to ground cooling... nighttime radiational cooling, influx of cold surface wind, air moving over a cold surface
-stable air tends to form excellent conditions for high pollution |
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Term
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Definition
-rising air is warmer (less dense) than surroundings
-associated with severe weather & thunderstorms
-very large lapse rate (air T decreases rapidly)
-usually occurs during very warm periods (summertime, not winter)
-unstable air tends to be very well mixed |
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Term
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Definition
| -inversion formed by slow sinking air |
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Term
| 3 kinds of atmospheric conditions |
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Definition
1)stable atmosphere
2)unstable atmosphere
3)conditionally stable atmosphere (dry and moist adiabatic lapse rates.... rising air may or may not overcome stable area) |
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Term
| instability on different scales |
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Definition
-convection - 5km - pops up to cumulus cloud
-orographic uplift - 150km - topography lifts
-low pressure - 500km - convergence of air
-along fronts - 1500km - over cold fronts (lifts) |
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Term
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Definition
| another term for environmental lapse rate |
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Term
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Definition
-forced up at first (stable) but breaks barrier at moist lapse rate so instability occurs higher up
AVERAGE GLOBAL LAPSE RATE IS 6C/KM
***EXISTS WHENEVER THE ENVIRONMENTAL LAPSE RATE IS IN BETWEEN MOIST AND DRY LAPSE RATES |
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Term
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Definition
-lapse rate when environmental lapse rate exceeds dry lapse rate
-leads to unstable conditions |
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Term
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Definition
| -level in atmosphere where air parcel becomes warmer than the air surrounding it (the switching spot in a conditionally stable atmosphere) |
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Term
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Definition
side of mountain range where rain shadow exists
-lenticular clouds may form on this side
-rotor clouds form here as well |
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Term
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Definition
-any form of water that falls from a cloud and reaches the ground
-typical raindrop is 100X diameter of a cloud droplet, and 10000X condensation nucleus |
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Term
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Definition
-above freezing temperatures at all levels
- |
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Term
| factors for rain droplet formation |
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Definition
-liquid water content
-cloud thickness
-range of droplet sizes
-updrafts of cloud
-electric charge of droplets and electric field in cloud |
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Term
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Definition
-also called ice-crystal process
-proposes that both ice crystals and liquid cloud droplets must coexist in clouds at temperatures below freezing
-these are COLD CLOUDS
-if not many ice nuclei exist, clouds in freezing areas are mostly water
******the saturation vapor pressure just above water surface is greater that saturation vapor pressure above ice surface.... this causes vapor molecules to move from droplet to ice crystal |
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Term
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Definition
-process of ice crystals growing larger as they collide with super-cooled cloud droplets
*a snowflake is an aggregate of the crystals |
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Term
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Definition
-introduction of artificial substance into a cloud for the purpose of either modifying its development or increasing precipitation
-silver iodide is a good seeder- c
natural seeding may occur as ice crystals fall from cirrus clouds into cumulus and act as nuclei |
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Term
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Definition
rain-diameter greater than 0.5mm
drizzle-diameter less than 0.5mm
virga-tiny evaporating streaks of precipitation
shower-rain in a downdraft
cloudburst-excessively heavy shower |
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Term
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Definition
-fallstreaks- ice crystals/snowflakes that fall from high cirrus clouds .....large snowflakes associated with moist air and T near freezing
-dendrite - fernlike branch shape snowflake... most common
-flurries - snow falling from developing cumulus clouds
-snow squall - more intense snow shower
-sleet - tiny transparent ice pellet... occurs when snowflake melts and then refreezes
-freezing rain - rain that freezes immediately upon contact
-rime - white/milky granular ice formed when supercooled cloud/fog droplets strike on object whose T is below freezing
-snow grains - solid equiv of drizzle
-snow pellets - white opaque grains of ice about the size of an average raindrop - are brittle, crunchy, and bounce |
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Term
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Definition
-pieces of ice ... largest up to 7 inches
-produced in cumulonimbus when graupel acts as nuclei for accretion
-must remain in cloud for 5-10 minutes to get golf-ball sized stone
-hailstreaks are long and narrow bands where clouds deposit hail
-efforts to prevent hail include introducing many nuclei (seeding) |
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Term
| ways of measuring precipitation |
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Definition
1)standard rain gauge- funnel shaped collector attached to measuring tube
2)tipping bucket - more accurate... loses a little rainfall during each tip
3)weighing type - extremely accurate... weighs rainfall |
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Term
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Definition
| -generally 10 inches snow will melt to 1 inch water... though this varies GREATLY |
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Term
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Definition
-used to analyze inside of a cloud
-returning echo received when pulse hits 'target'
-doppler has capacity to measure speed at which rain is moving
-radar beam travels in straight line, but earth curves away
-polarimetric radar makes it easier to determine if falling precipitation is rain or snow |
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