Transcript 16-4 - Laconia School District

Chapter 16,section 4
Water in the atmosphere
By Rachel Kalin, Billy Mahoney
Aminata Henderson, Jen Blackey
Words to know
•
Psychrometer: An instrument used to measure relative humidity, consisting
of a wet-bulb thermometer and a dry-bulb thermometer.
• Condensation- The process by which a gas, such as water vapor, changes
to liquid, such as water.
• Dew Point- The temperature at which condensation begins.
• Cumulus- Clouds that form less then 2 kilometers above the ground and
look like fluffy rounded piles of cloth.
• Stratus- Clouds that form in flat layers.
• Cirrus- wispy feathery clouds made mostly of ice crystals that form at high
levels above about a kilometer.
• Humidity- A measure of the amount of water vapor in the air.
• Relative Humidity- The percentage of water vapor in the air compared to the
maximum amount the air can hold at the temperature.
• Evaporation-Evaporation: the act or process of evaporating.
• Evaporating: to change from a liquid or solid state into vapor.
• 1.to give off moisture
• 2.to disappear
Can you explain to me how relative
humidity is measured?
• Relative humidity is measured with a
psychrometer. The psychrometer has two
thermometers, a wet-bulb thermometer and a
dry-bulb thermometer. The bulb of the wet-bulb
thermometer has a cloth covering that is
moistened with thermometers. Because the wetbulb thermometer is cooled by evaporation, its
reading drops below that of the dry-bulb
thermometer. If the relative humidity is high, the
water on the wet bulb will evaporate slowly and
the wet-bulb temperature will not change much.
What is the difference between
relative humidity and humidity?
• Humidity is a measure of the amount of water vapor in
the air and relative humidity is the percentage of water
vapor in the air compared to the maximum amount the
air could hold. Humidity is the amount and relative
humidity is the percentage of water vapor in the air.
• Why are the tops of some mountains almost always
covered by clouds?
• This happens because when wind strikes the side of a
hill or mountain, the air is forced upward. As the air rises
along the slope, the air cools. Rain or snow falls on the
windward side of the mountains, the side facing the
incoming wind.
What instrument is used to measure relative humidity? And how
does it work?
• A psychrometer.
• How does it work?
• A psychrometer is an instrument for determining
atmospheric humidity by the reading of two
thermometers, the bulb of one being kept moist
and ventilated.
How clouds form…
• Clouds of all kinds form when water vapor in the air
becomes liquid water or ice crystals. The process by which
molecules of water vapor in the air become liquid water is
called condensation. How does water condense? As you
know, cold air can hold less water vapor than warm air. As
air cools, the amount of water vapor it can hold decreases.
Some of the water vapor in the air condenses to form
droplets of liquid water. The temperature at which
condensation begins is called the dew point. If the dew
point is below the freezing point, the water vapor may
change directly into ice crystals. When you look at a cloud
you are seeing millions of tiny ice crystals or water droplets.
• Clouds form whenever air is cooled to its dew point and
particles are present. But why does the air cool? If air is
warmed near ground, it becomes less dense and rises in a
convection current.
Why are the tops of mountains almost always covered by
clouds?
• This happens because when wind strikes
the side of a hill or mountain, the air is
forced upward. As the air rises along the
slope, the air cools. Rain or snow falls on
the windward side of the mountains, the
side facing the incoming wind.
What conditions are needed for
clouds to form?
• Clouds of all kinds form when water vapor
in the air becomes liquid water ice
crystals. Clouds form whenever air is
cooled to its dew point and particles are
present.
Three main types of clouds
• Cirrus- a cloud of a class characterized is thin white
filaments or narrow bands and a composition of ice
crystals: of high altitude, about 20,000-40,000 ft.
• Stratus- a cloud of a class characterized by a gray,
horizontal layer with a uniform base, found at a lower
altitude than altostratus, usually below 8000 feet.
• Cumulus- A cloud of class characterized by dense
individual elements in the form of puffs, mounds, or
towers, with flat bases and tops that often resemble
cauliflower: as such clouds develop vertically, they form
cumulonimbus.
Low-level, medium-level, high-level clouds
• Altocumulus- high-level
• Altostratus- medium-level
• Cirrostratus- mediumlevel
• Cirrus- high-level
• Cumulus- low-level
• Fog- low-level
• Nimbostratus- low-level
• Stratus- low-level
THE END!!