Download Chapter 18 Watrer in the atmosphere

Lesson 6 Page 1
Chapter 18 Water in the atmosphere
I Humidity and Condensation
- Water vapor strongly affects the weather
A. Characteristics of water
1.water is the only substance that commonly exists in all 3
states
a. Solid 0 Celsius or lower
b. Liquid between 0 Celsius and 100 Celsius
c. Above 100 Celsius water vapor
2. condensation gas  Liquid - Release heat
3. evaporation liquid gas - absorbs heat
B. Humidity
1. Specific humidity – the actual amount of water vapor
in the air. 20 grams/kilograms of air is very humid
2. Saturated air – rare of evaporation = the rate of
Condensation
3. Warmer air can hold more water vapor
4. Relative humidity – How near the air is to maximum
capacity. 0 - 100%
a
Specific Humidity X 100 % =RH%
Maximum Capacity
5 Measuring Humidity – Psychrometer – wet and dry bulb
tem. If they both read the same – no water is
evaporating 100%
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C. Condensation
1. At Night as air cools it ability to hold water decreases.
If it cools past the point of saturation condensation
occurs, forming clouds, dew, or fog
2. Dew Point - the temperature at which saturation
occurs and condensation begins
3. Cooling and condensation – water vapor must have
something to condense onto once it goes below dew point
4. Condensation nuclei, such as salt, sulfate particles, or
nitrate particles are in the air.
5. Dew vs. Frost – above freezing surface dew will form –
Below freezing frost
6. Formation at Fog – Occurs when cold surfaces cool
warm moist air
a. Slight air movements keep the droplets suspended
7. Advection Fog – warm moist air blows over cool
surface. Northern U.S. Southerly winds blow over
snow
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II Clouds P 396
- Clouds form when air cools to its dew point. Can form at
any altitude in troposphere
A. Types of Clouds – Cloud names are formed from one or more of
the same 5 words
1. Stratus and strato – clouds that form in layers
2. Cumulus and cumulo – describe clouds that grow upward(heap)
Fluffy clouds with flat bases
3. Cirrus and Cirro - Describe feathery clouds(curl of hair) high
feathery ice clouds
4. Alto – between 2000-7000 meters
5. Nimbus and Nimbo – Dark rain clouds
B. Cloud Formation
1. If cloud temp is below -20C cloud is made mostly of ice and
snow
2. As warm air rises it cools. When it reaches a height were it hits
dew point clouds form. – Condensation Level
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3. Unsaturated air cools at a rate of 10C for every kilometer it
rises – dry–adiabatic lapse rate
4. Saturate air cools 5-9C/Km - moist-adiabatic lapse rate
5. The cooling as air rises is due to the expansion of the air
6. Cumulonimbus Clouds - Heat from condensation keeps the
air inside a cumulus cloud less dense that the surrounding
air which makes it grow vertically
7. Meteorologist can predict cloud height if they know:
Temperature of the clouds, dew point and the rate at which
the rising air cools.
8. Layer clouds or stratiform form in stable hair
9. Stable air: If the temp of rising air inside the cloud decrease
more quickly than the temp outside the cloud
Lesson 8 Page 1
III Precipitation
- Any form of water that falls form a cloud to the earth’s
surface
A. How precipitation forms
1. Growth of water droplets in a cloud occurs by bumping
2. Growth of Ice Crystals – temp in the upper clouds are cold
enough to freeze the droplets, as the ice falls it collects more
droplets
3. Kinds of Precipitation
a. Sleet – frozen rain droplets
b. Freezing rain – occurs when rain hits a surface and
freezes – ice sheet or glaze will form
c. Hail – Ball shaped ice from thunderstorms
B. Measuring Precipitation
1. Measured in a rain gauge by 1\100th of an inch
2. Snow is measured by using a ruler or snow stick. 1 inch of rain
is about 10 inches of snow
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C. Weather Modification
1. Dry Ice (frozen CO2) into clouds which cools the cloud
and form ice crystals
2. Artificial nuclei such as a silver iodine is druped into the
cloud for more condensation to occur