unit 3 water in the atmosphere
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Unit 3 Water in the Atmosphere. Objectives:. Water vapor and the atmosphere How the system works Different ways to measure water vapor What makes it important Humidity, dew point, frost Fog and other clouds Types of precipitation Instruments used to measure moisture. - PowerPoint PPT PresentationTRANSCRIPT
Objectives:Water vapor and the atmosphere
How the system worksDifferent ways to measure water vaporWhat makes it important
Humidity, dew point, frostFog and other cloudsTypes of precipitationInstruments used to measure moisture
I. Earth’s Hydrologic CycleThe gigantic
system powered by energy from the sun in which the atmosphere that provides a link between the oceans and continents.
Important Components Affecting Weather & ClimateEvaporation – change in state from gas to a liquid.
LOTS of energy gained (2260 J/g)Condensation – change in state from gas to a
liquid. LOTS of energy released (latent heat – 2260 J/g)Transpiration –water vapor released by plantsPrecipitation – liquid or solid water that returns
back to the Earth’s surface in the form of rain, snow, sleet, or hail.
Distribution of Water on Earth
II. Principles of Air & WaterWhen liquid water evaporates, it turns into a
gas called water vapor.Amount of water vapor in the atmosphere is
limited by temperature: warmer air holds more water vapor
Saturation: when air can’t hold any more water
Dry skin and chapped lips in the winter
III. Measurement A. Dew point:
1. The amount of water vapor in the air
2. Often described as the temperature at which air needs to cool to reach saturation (°F or °C)
Table 4-2 Dew Point ThreholdsDewpoint temperature≤ 10°F Significant snowfall is inhibited≥ 55°F Minimum for severe thunderstorms to form ≥ 65°F Considered humid by most people≥ 70°F Typical of the rainy tropics≥ 75°F Considered oppressive by most
Impossible to count the number of water vapor molecules in the air!
Dew PointTemperature
Saturation occurs
Condensation and/or precipitation
occurs
B. Relative Humidity 1. Measure of how close the air is to saturation
2. Saturation occurs at 100% 3. Dependent on temperature and amount of moisture
International Falls, MN14°F
Little water vapor100% R.H.
Phoenix, AZ77°F
Lots of water vapor20% R.H.
Relative Humidity Activity http://cimss.ssec.wisc.edu/satmet/modules/clouds/cloudformation_RH.html
Relative Humidity Activity: Answers
Scenerio Controlling Factor Relative Humidity
Raise thermostat Warmer temps Decrease
Lower thermostat Cooler temps Increase
Take a shower Moisture added Increase
Open the door Cooler temps Increase
Cook Warmer temps Decrease
Throw a BIG party Moisture added Increase
IV. Types of CondensationA. Dew - when the air temperature cools
beyond the dew point temperature, water is squeezed out of the air (condensation – gas to liquid).
Usually happens in the morning or evening when the temperatures are cooling.
B. Frost - same concept as dew, only with ice crystals instead of liquid water (deposition – gas to solid)
Dew point must be 32°F or less Water vapor turns to ice
C. Fog - same process as dew forming, but the dew forms on tiny particles in the air that you cannot see
Types of fog:1. Radiation - thin2. Advection - thick3. Upslope – mountains4. Steam – over water5. Frontal – where precipitation occurs
Need a slight wind to stir particles into air
Radiation fog – Usually forms at night when there are clear skies and fairly high relative humidity (condensation)
Advection fog – warm, moist air moves over a cold surface (condensation)
Upslope fog – air moving up the mountain is forced to cool (condensation)
Steam fog – cool air moves over warm water (evaporation)
Frontal fog – evaporation of rain after cold air moves through
Fun fact: The foggiest location in the U.S. is Cape Disappointment, WA
V. Formation of Clouds
Decrease temperature
100% R.H.D.P. Temp
Clouds form
Growth of precip. begins
A. Clouds are composed of tiny particles of liquid water and ice crystals
B. They form when air cools to the dew point temperature, and relative humidity increases to 100%. Eventually the excess water is dumped and latent heat is released.
C. Condenstion nuclei – particles in which water vapor molecules can attach to
D. Four ways to form clouds by lifting air: 1. Orographic lifting 2. Frontal wedging 3. Convergence 4. Convection c
c c csalt
dust
pollen
Orographic Lifting– air that is forced to rise over a mountain range
Frontal wedging – warmer air moving over a cold pocket of air
Convergence - winds blowing in different directions forces air up
Convection – warm parcels of air rise due to solar heating
VI. Types of CloudsA. Basic Cloud Types: 1. Cirrus – high, wispy 2. Alto – middle 3. Stratus – low, layers 4. Cumulus – cotton-like 5. Nimbus – produce rain
B. Special clouds: 1. Lenticular – formed in mountainous areas
2. Contrails – forms when the humidity starts to increase (bad weather is approaching!)
Fun fact: An average sized cloud contains 13 million gallons of water- enough to fill a small pond!
10,000 km
3,000 km
VII. Types of PrecipitationA. Rain - spherical liquid droplets
B. Snow – aggregates of ice crystals
Ice crystals shapes are based on temperature in which they form
Fun fact: Powdery snow is the result of very low temperatures because the moisture content of air is small.
C. Sleet – frozen raindrops
D. Glaze – rain that freezes when it comes in contact with the ground
Fun fact: The snowiest city in the U.S. is Rochester, NY (avg. of 239 cm per year). Buffalo, NY is a close runner-up.
E. Hail – small to large chunks of ice that are composed of several layers
Fun fact: Largest hailstone ever recorded fell in Aurora, Nebraska in June 2003. It measured 17.8 cm in diameter and weighed 1.5 pounds!
Another fun fact: People used to believe that strong noises- explosions, cannon shots, or ringing church bells- prevented hail formation.
Height Values:
1000mb: 246m
850mb: 1490m
700mb: 3013m
500mb: 5590m
ALL SNOW
Temperature curves are below
freezing
X
X = Probable location of cloud formation (dew point = air temperature)
Height Values:
1000mb: 189m
850mb: 1514m
700mb: 3098m
500mb: 5730m
FREEZING RAIN
Snow
Rain
Shallow freezing layer
X
X = Probable location of cloud formation (dew point = air temperature)
Height Values:
1000mb: 205m
850mb: 1481m
700mb: 3057m
500mb: 5660m
SLEETDeep freezing layer
Rain
Snow ?
X
X = Probable location of cloud formation (dew point = air temperature)
Height Values:
1000mb: 156m
850mb: 1525m
700mb: 3128m
500mb: 5790m
ALL RAINX
X = Probable location of cloud formation (dew point = air temperature)
In case you wanted to know…
VIII. Precipitation Measurement A. Rain gauge: measures rainfall by funneling
liquid into a cylinder or bucket below.
B. Snow: Difficult to measure because the ratio of snow to liquid water varies. Weather spotters!
4:1 (wet
snow)
30:1(fluffy snow)
IX. Hazards & NWS WarningsA. Rain Events: 1. Flood watch/warning –large rivers have
the potential or have exceeded flood stage
2. Urban/small stream watch/warning – local roads may have or already have water running over them
3. Flash flood watch/warning – low-lying areas may have or already have flooded
4. Drought watch/warning – Drought is a deficiency in precipitation over an extended period of time, usually a season or more, resulting in a water shortage causing adverse impacts on vegetation, animals, and/or people.
U.S. Drought Monitor
B. Snow Events: 1. Winter storm watch/warning –
Potential/certainty: 6+ inches or snow (12 hrs) or 8+ inches of snow (24
hrs) Reduced visibility (winds) ¼ inch of ice accumulation
2. Blizzard watch/warning – Potential/certainty:
Wind gusts sustained 35mph or greater for 3+ hrs Falling or blowing snow