Define:
a Evaporation
b. Condensation
c. Precipitation
d Collection
Answers
Answer:
evapo(transpi)ration, condensation, and precipitation
Take away ideas and understandings
Water vapor pressure increases with temperature.
Definitions of evaporation, evapotranspiration, condensation, and precipitation and how these processes relate to saturation water vapor pressure curve.
The presence of condensation nuclei are critical for the formation of clouds.
Mechanisms that result in warm and cold cloud formation.
Processes that form precipitation and distribution of precipitation patterns.
Moisture in the atmosphere
water undergoes huge expansion during evaporation: 1 g of water equals 1 ml volume in liquid form and 42 l as vapor (at 25oC)
gravity concentrates the atmospheric gases near the surface, the pressure drops to 1/e (= 37%) at about 8 km elevation
90% of water vapor content is confined to the lower 6 km
water vapor pressure as a function of temperature (svp = saturation water vapor pressure) (Fig), can explain many phenomena in the atmosphere.
absolute humidity (or water vapor mixing ratio): mass of vapor per unit volume of air, in g m-3
at 30oC, air has a svp of 42.43 hPa (hPa = mbar) and can contain up to 30 g m-3, at 0oC svp is only 4.5 g m-3
relative humidity: actual water vapor pressure / svp in %; or: actual water vapor content / absolute humidity
formation of fog, clouds, mixing clouds, can be understood in the framework of the vapor pressure diagram
Evapotranspiration
evapotranspiration summarizes all processes that return liquid water back into water vapor
water needed and solar energy
of the water taken up by plants, ~95% is returned to the atmosphere through their stomata (Fig)
potential evaporation (PE), i.e. the evaporation rate given an unrestricted water supply - different from actual evaporation
how can the actual evapotranspiratio be measured?
water balance
energy balance
or combination of both
Condensation and Precipitation
Definitions
condensation:transition from vapor phase to liquid phase
precipitation: deposition of liquid water droplets and ice particles that are formed in the atmosphere and grow to a sufficient size so that they are returned to the Earth's surface by gravitational settling. Solid and liquid. Dew and fog do not count as precipitation (can add 5-10% to precipitation in the Pacific Northwest)
Clouds and precipitation
explanantion of processes through the vapor pressure diagram (Fig): air rising => expansion => adiabatical (= no heat exchange with environment) cooling => condensation
at T>0oC: warm cloud process: condensation, gradual growth of water droplets by condensation, collision and coalescence
at T<0oC: cold cloud process: involves also the formation and growth of ice crystals
two extra factors are needed to form precipitation:
sufficient moisture supply
sufficient vertical motion
Warm cloud process
a moisture laiden air parcel rises, cools at dry adiabatic lapse rate (~1oC/100m) until it reaches the dewpoint, at which point condensation occurs. After that, any further rise causes cooling at the moist adiabatic lapse rate (0.5 - 0.9oC/100m), because of the released latent heat. (Fig)
super saturation: relative humidity > 100%
condensation nuclei are needed to increase condensation
most efficient particles: Aitken nuclei (0.01-0.1 micro m)
typical source: dust from land, sea spray (hygroscopic!)
5 million/l air over land, 1 million/l air over the ocean
experiment: salt crystals as condensation nuclei (Fig)
experiment: when a beer bottle is opened, a cloud forms in the neck. If temp. of the bottle is 5oC, temperature drops to ~-36oC when bottle is opened
Cold cloud process
saturation vapor pressure is lower over ice than water => ice crystals grow in favor of liquid droplets
ice crystals are very efficient condensation nuclei
most efficient in mid latitudes (temperatures low enough, but enough instability in the atmosphere)
Precipitation patterns
kinds of precipitation: drizzle, rain, ice pellets, snow, hail
terminal velocity (v) is achieved when gravitational acceleration is counterbalanced by the friction of the air, for 1mm diameter drop: v = 4 m/s
raindrops break up at 5 mm diameter, snow can reach 40mm, and hailstones over 50mm
moisture in atmosphere: 25% condenses, 75% forms ice and snow; only 5% of that falls as snow and ice crystals, the rest melts; a lot of the precipitation re-evaporates before it reaches the ground
most precipitation comes from bordering oceans, but up to 40% can come from local ET.
extremes in US: Kauai: 12,000 mm/y, Death Valley: 40mm/y
dryest place on Earth: Calama in Atacama desert, Chile, rain has never been recorded
average annual precipitation (global (Fig) and US (Fig)) onto the continents is a function of:
(a) latitude (precipitation highest in latitudes of rising air-0° and 60° north and south-and lowest in latitudes of descending air- 30° and 90° north and south);
global circulation patterns in the atmosphere (Fig)
(b) elevation (due to orographic cooling, precipitati
Answer:
1)EVAPORATION - The process of changing water into vapour is called Evaporation.
2)CONDESATION- Water which collects as droplets on a cold surface when humid air is in contact with it.
3)PRECIPITATION- The action or process of precipitating a subtance from solution.
4)COLLECTION- The action or process of collecting someone or something.