Transcript Ch 18 Water in Atmx

Chapter 18: Water in the Atmosphere
H2O basics
• Liquid range: 0°C-100°C
• Solid: 0°C- and below
• Gas: 100°C and above
• Review the characteristics
and terms for water as it changes
state.
• Review energy requirements!
Humidity
• Specific humidity: number of grams H2O vapor
per kilogram of air.
– More H2O vapor in air, more humid it feels.
– Limit to how much H2O
– Condensation = evaporation, air is saturated.
– Warm air hold more H2O
• Capacity doubles for every 11°C rise in temp.
• Relative humidity: how close the air is to its
maximum capacity for holding H2O.
– Expressed as percent:
RH = specific humidity x 100
max capacity
• Measured with psychrometer
– Wet bulb & dry bulb
– Tables of values used
condensation
• At night: air cools, holds less H2O.
– Dew point: temp when saturation occurs and
condensation begins.
• Measure of amt. of H2O vapor in air.
• Condensation requires two things:
1. Condensation nuclei (dust, salt, particulates)
2. Air temps below dew point (caused by radiant heat
loss, mixing with colder air, thermal loss by
expansion, contact with colder surfaces)
• Frost: deposition when air temp below 0°C.
– Killing frost: air temp near ground below -2°C for
hours destroying plant cells.
• Fog: cloud on the ground.
– cold surface, warm, moist air above.
– Common near water, in valleys
Clouds
• Form when air cools to dew point.
• Any altitude in troposphere.
– Height measured from ground, NOT sea level.
– Water at lower altitudes & higher temps
– Below freezing: snow crystals & supercooled water.
– Below -20°C, snow, ice crystals.
Types
• Stratus: Low, layered
• Cumulus: puffy with flat bases
• Cirrus: feathery and thin, high altitude.
Cloud descriptors
• alto: clouds btwn
2000-7000 m.
• cirrus/cirro: curly,
above 7000 m
• stratus/strato: layered
• cumulus/cumulo:
growing upward
• nimbus/nimbo: rain
Cloud types by height
• Low (<2000 m): stratus
nimbostratus
stratocumulus
• Medium (2000-7000m): altostratus
altocumulus
• High (>7000m): cirrus
cirrostratus
cirrocumulus
What commonalities do you see within the names?
Formation
• Condensation level: atmospheric level when
condensation occurs.
– Warm air rises, cools at altitude
• Adiabatic lapse rate: rate air cools when
rising.
– Dry adiabatic lapse rate: cooling due only to
expansion of air as it rises. Faster cooling.
– Wet adiabatic lapse rate: saturated air, rate is
ranges from 5-9°C per km.
•
rate of cooling is lower creating larger clouds
predicting
• Knowing condensation level needed for
forecasting.
– Cumulonimbus: warm, moist air rises until dew
point reached. Need stead supply of moist air.
Grows until reaching stable air.
– Layer clouds form in stable air, so they spread
horizontally.
Precipitation
• Any form of water falling from a cloud.
– Collisions allow drops to grow.
– High altitudes allow drops to freeze.
• Types of precip:
– Rain
• Freezing rain: becomes
supercooled when hitting
a cold surface
– Snow
– Sleet: rain freezes as it falls.
– Hail: frozen rain that up and down cycles within a
cloud growing in size. Layered development
Measuring precip
• Rain gauge.
• Measuring stick
(snow)
– Depth of snow
does not indicate
moisture level.
– Rain equivalent
determined
during melting.
Annual averages for rainfall plus snowfall
Days
Place
Inches
mm
61
Albuquerque
9.5
240
65
Clovis
19.1
486
69
Taos
12.8
324
83
El Morro National Monument
15.1
385
76
Gallup
11.6
294
55
Alamogordo
11.7
298
57
Grants
10.5
266
80
Las Vegas
18.1
458
71
Pecos National Monument
17.2
437
66
Santa Fe
14.2
360
54
Socorro
10.3
261
65
Tucumcari
17.1
434
http://www.currentresults.com/Weather/New-Mexico/average-yearly-precipitation.php
Where in the world?
• Mountain effect
– Windward side
receives more
precip
• Equatorial warm air rises, sinks near poles.
– Low pressure: moist air = tropical rain forest
– High pressure: 30°N & 30°S dry air present=deserts
– Polar regions: cold air = little H2O vapor