Transcript Chapter 18 – Water in the atmosphere

Chapter 18 – Water in the
atmosphere
• Page 388
• How would you describe the cloud in this
photo?
• If you saw this cloud in the sky, what type
of weather would you expect?
• How do clouds form?
• Why do clouds sometimes produce rain?
Chapter 18.1
Humidity and Condensation
• Water vapor strongly affects the weather
Characteristics of water
• water is the only substance that commonly
exists in all 3 states
– Solid 0 Celsius or lower
– Liquid between 0 Celsius and 100
Celsius
– Above 100 Celsius water vapor
• condensation gas  Liquid - Release heat
• evaporation liquid gas - absorbs heat
Humidity
• Specific humidity – the actual amount of water vapor in the air. 20
grams/kilograms of air is very humid
• Saturated air – rare of evaporation = the rate of Condensation
• Warmer air can hold more water vapor
• Relative humidity – How near the air is to maximum capacity. 0 – 100%
• Measuring Humidity – Psychrometer – wet and dry bulb tem. If they
both read the same – no water is evaporating 100%
Condensation
• 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
• Dew Point - the temperature at which
saturation occurs and condensation begins
• Cooling and condensation – water vapor must
have something to condense onto once it goes
below dew point
• Condensation nuclei, such as salt, sulfate
particles, or nitrate particles are in the air.
• Dew vs. Frost – above freezing surface dew
will form – Below freezing frost
• Formation of Fog – Occurs when cold surfaces
cool warm moist air
– Slight air movements keep the droplets
suspended
• Advection Fog – warm moist air blows over
cool surface. Northern U.S. Southerly
winds blow over snow
Discussion – Page 394
• Why would the melting of ice on the fruit
in the morning be a cause for concern?
Chapter 18.2
Clouds P 396
• Clouds form when air cools to its dew point.
Can form at any altitude in troposphere
Types of Clouds – Cloud names are
formed from one or more of the
same 5 words
• Stratus and strato – clouds that form in layers
• Cumulus and cumulo – describe clouds that grow
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upward (heap) Fluffy clouds with flat bases
Cirrus and Cirro - Describe feathery clouds (curl
of hair) high feathery ice clouds
Alto – between 2000-7000 meters
Nimbus and Nimbo – Dark rain clouds
Cloud Formation
• If cloud temp is below -20C cloud is made mostly of
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ice and snow
As warm air rises it cools. When it reaches a height
where it hits the dew point, clouds form –
Condensation Level
Unsaturated air cools at a rate of 10C for every
kilometer it rises – dry–adiabatic lapse rate
Saturated air cools 5-9C/Km - moist-adiabatic lapse
rate
The cooling as air rises is due to the expansion of the
air
• Cumulonimbus Clouds - Heat from
condensation keeps the air inside a cumulus
cloud less dense that the surrounding air which
makes it grow vertically
• Meteorologist can predict cloud height if they
know: Temperature of the clouds, dew point
and the rate at which the rising air cools.
• Layer clouds or stratiform form in stable hair
• Stable air: If the temp of rising air inside the
cloud decrease more quickly than the temp
outside the cloud
Chapter 18.3
Precipitation
• Any form of water that falls form a cloud to
the earth’s surface
How precipitation forms
• Growth of water droplets in a cloud occurs by
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bumping
Growth of Ice Crystals – temp in the upper clouds are
cold enough to freeze the droplets, as the ice falls it
collects more droplets
Kinds of Precipitation
– Sleet – frozen rain droplets
– Freezing rain – occurs when rain hits a
surface and freezes – ice sheet or glaze will
form
– Hail – Ball shaped ice from thunderstorms
Measuring Precipitation
• Measured in a rain gauge by 1\100th of an
inch
• Snow is measured by using a ruler or snow
stick. 1 inch of rain is about 10 inches of
snow
Weather Modification
• Dry Ice (frozen CO2) into clouds which cools
the cloud and form ice crystals
• Artificial nuclei such as a silver iodide is
dropped into the cloud for more condensation
to occur