Download Weather instruments and clouds mini lesson

Chapter 21 Section 3: Weather Instruments
Key Ideas
• Identify four instruments that measure lower-atmospheric
weather conditions.
• Describe the conditions that are necessary for clouds to
form.
• Explain the four processes of cooling that can lead to the
formation of clouds.
• Identify the three major types of clouds, noting their
characteristic shapes and the altitudes at which they
generally form.
• Explain how weather stations communicate weather data
(station model).
Gathering Data for Predictions
• From now until the end of the school year, two students will
record the weather conditions displayed on the Vantage
Pro 2 Weather Console.
• Rotation is alphabetical.
• Make sure you are looking at the readout for OUTSIDE
CONDITIONS…. Not inside conditions.
• Students will write down the temperature, pressure, wind
speed, wind direction, and observed cloud cover (if any) in
a station model format in the weather logbook found next
to the weather console.
Station model: Recording Lower-Atmospheric Conditions
• station model a pattern of meteorological symbols that
represent the weather at a particular observing station and
that is recorded on a weather map.
• A simple station model, like the ones you will be recording
in the weather journal, is shown here.
Station model: Air Temperature
• thermometer an instrument that
measures and indicates air
(atmospheric) temperature
• A common type of thermometer uses
a liquid-usually mercury or alcoholsealed in a glass tube to indicate
temperature.
• A rise in temperature causes the liquid
to expand and fill more of the tube
(kinetic theory again). A drop in
temperature causes the liquid to
contract and fill less of the tube.
Station model: Air Temperature
• Another type of thermometer is an electrical thermometer.
• As the temperature rises, the electric current that flows
through the material of the electrical thermometer increases
and is translated into temperature readings.
• A thermistor, or thermal resistor, is a type of electrical
thermometer that responds very quickly to temperature
changes.
Station model – Temp, Relative Humidity, and Dew Point
• Dew point Temperature can be determined using the Air Temperature and
Relative Humidity and the chart below.
Station model – Temp, Relative Humidity, and Dew Point
• The temperature and dew point are plotted to left of
center on the station model and are expressed in
degrees Fahrenheit in the US.
• The dew point indicates how high the humidity of the
air is. When the air temperature drops to the dew point,
condensation forms.
• This knowledge can help determine location of fronts,
where storms and precipitation can occur.
• A front is a boundary separating two masses of air of
different densities.
Station model - Cloud formation/types
• cloud a collection of small water droplets or ice crystals
suspended in the air, which forms when the air is cooled
and condensation occurs
• For water vapor to condense and form a cloud, a solid
surface on which condensation can take place must be
available.
• The lowest layer of the atmosphere, the troposphere,
contains millions of suspended particles of ice, salt, dust,
and other materials that serve as solid surfaces.
• Because the particles are so small—less than 0.001 mm in
diameter—they remain suspended in the atmosphere for a
long time.
Station model - Cloud formation/types
• condensation nucleus a solid particle in the atmosphere
that provides the surface on which water vapor condenses
• In addition, for clouds to form, the air must be “saturated”
with water vapor. When the temperature of the air drops,
condensation occurs more rapidly than evaporation does.
Station model - Cloud formation/types
Adiabatic Cooling – reaching the dew point
• As a mass of air rises, the surrounding atmospheric
pressure decreases.
• The molecules in the rising air move further apart, and
fewer collisions between the molecules happen.
• The resulting decrease in the amount of energy that
transfers between molecules decreases the temperature of
the air.
• adiabatic cooling the process by which the temperature of
an air mass decreases as the air mass rises and expands
Station model - Cloud formation/types
Condensation Level
• When air cools to a temperature that is below the dew point,
net condensation causes clouds to form.
• The altitude at which this net condensation begins is called
the condensation level.
• The condensation level is marked by the base of the clouds.
• Further condensation allows clouds to rise and expand
above the condensation level.
Reading Check
What is the source of energy that warms the air and leads
to cloud formation?
The source of energy that warms the air and leads to cloud
formation is solar energy that is reradiated as heat by
Earth’s surface. As the process continues, latent heat
released by the condensation may allow the clouds to
expand beyond the condensation level.
Station model - Cloud formation/types
• Clouds are classified by their
shape and altitude.
• The three basic cloud forms or
shapes are:
– stratus clouds,
– cumulus clouds, and
– cirrus clouds.
• There are also three altitude groups:
– low clouds (0-2,000 m),
– middle clouds (2,000 to 6,000 m),
“alto”
– high clouds (above 6,000 m)
“cirro”
Station model - Cloud formation/types
Stratus Clouds - gray clouds that have a flat uniform base
and that commonly form at very low altitudes
• Stratus means “sheet-like” or “layered.”
• Stratus clouds form where a layer of warm, moist air lies
above a layer of cool air.
• Stratus clouds cover large areas of sky and often block out
the sun. Usually, very little precipitation falls from most
types of stratus clouds.
Station model - Cloud formation/types
• Three variations of stratus clouds are known as
nimbostratus, altostratus, and cirrostratus.
– Unlike other stratus clouds, the dark nimbostratus clouds
can cause heavy precipitation.
– Altostratus clouds form at middle altitudes and usually
produce very little precipitation.
– Cirrostratus clouds form at higher altitudes and usually
produce very little precipitation.
Station model - Cloud formation/types
(clockwise)
• cirrostratus.
• Altostratus
• Nimbostratus
Station model - Cloud formation/types
Cumulus Clouds are low-level, billowy clouds that commonly
have a top that resembles cotton balls and have a dark, flat
base which represents the condensation level.
• Cumulus means “piled” or “heaped.”
• These clouds form when warm, moist air rises and cools. As
the cooling reaches its dew point, the clouds form.
Station model - Cloud formation/types
• If the base of cumulus clouds begins at higher altitudes, the
clouds are called cirrocumulus clouds.
• If the base of cumulus clouds begins at middle altitudes, the
clouds are called altocumulus clouds.
• Low clouds that are a combination of stratus and cumulus
clouds are called stratocumulus clouds.
Station model - Cloud formation/types
• High, dark storm clouds known as cumulonimbus clouds, or
thunderheads, are often accompanied by rain, lightning,
thunder, and severe weather.
Station model - Cloud formation/types
• cirrus cloud a feathery cloud that is composed of ice crystals
and that has the highest altitude of any cloud in the sky
• Cirro– and cirrus mean “curly.”
• Cirrus clouds form at altitudes above 6,000 m. These clouds
are made of ice crystals because the temperatures are low at
such high altitudes.
• Because these clouds are thin, light can easily pass through
them
Station model - Cloud formation/types
• Cirrocumulus clouds are highaltitude, billowy clouds
composed entirely of ice
crystals. Cirrocumulus clouds
commonly appear just before
a snowfall or a rainfall.
• Long, thin clouds called
cirrostratus clouds form a
high, transparent veil across
the sky.
• A halo may appear around the
sun or moon when either is
viewed through a cirrostratus
cloud.
Station model – Cloud cover and type
• Along with wind direction
cloud cover is one of the
oldest atmospheric
conditions to be coded on a
station model.
• The circle in the middle of
the station model represents
cloud cover.
Station model - Cloud formation/types
Fog - water vapor that has condensed very near the surface
of Earth because air close to the ground has cooled
•
The obvious difference between fog and clouds is that fog
is very near the surface of Earth. However, fog also differs
from clouds because of how fog forms.
Radiation Fog - One type of fog forms from the nightly
cooling of Earth.
•
The layer of air in contact with the ground becomes chilled
to below the dew point, and the water vapor in that layer
condenses into droplets.
•
This type of fog is called radiation fog because it results
from the loss of heat by radiation.
Reading Check
Why are cirrus clouds commonly composed of ice crystals?
because cirrus clouds form at very high altitudes where air
temperature is low
Station model - Air Pressure (barometric pressure)
• Atmospheric pressure is the
force per unit area exerted on a
surface by the weight of
atmosphere above it.
• 1013.25 millibars or hectopascals
= 1 atm (atmosphere)
• barometer an instrument that
measures atmospheric pressure.
•“We live submerged at the bottom of an
ocean of elementary air, which is known by
incontestable experiments to have weight" Evangelista Torricelli, 1644
Station model - Air Pressure (barometric pressure)
Air Pressure (barometric pressure)
• Highest and lowest recorded
– 1,085.7 hPa (32.06 inHg)
– lowest non-tornadic pressure was 870 hPa
• The approach of a front is usually indicated by a drop in
air pressure as surface air is lifted (convected).
Station model - Air Pressure (barometric pressure)
Air Pressure (continued)
• 2 commonly used types of
barometers mercury and aneroid
• Mercury barometers
– A glass tube with a height of at
least 84 cm, closed at one end,
with an open mercury-filled
reservoir at the open end.
Station model - Air Pressure (barometric pressure)
Air Pressure (continued)
• Aneroid barometers (no liquid)
– uses a small, flexible metal box called an aneroid cell
(capsule)
– The evacuated capsule is prevented from collapsing by a
strong spring. Small changes in external air pressure
cause the cell to expand or contract.
Station model - Air Pressure (barometric pressure)
• The atmospheric pressure is plotted on the top right corner
of the model.
• It shows the last two integer digits of the pressure in
millibars, or hectopascals (hPa), along with the first digit
after the decimal.
• For instance, if the pressure at a certain location is 999.7
hPa, the pressure portion of the station model will read 997.
• Most of the time, choosing first digits that would lead to
a value nearest to 1000 works out best.
• The plotting of this value within the station model allows for
the analysis of isobars on weather maps.
Station model – pressure tendency
•The pressure tendency figure is plotted below the pressure will lie and indicates the
pressure change over the past three hours.
•The number depicting the pressure change will usually have two digits and indicate
the pressure change in 0.1 millibar increments.
• Steady rises can indicate improving conditions and approaching high pressure,
and normally occur in the wake of a cold front.
•Steady falls can indicate deteriorating conditions and an approaching low pressure
area, with the largest falls occurring in advance of a surface cyclone and its
attendant warm front.
Station model – Wind speed and direction
Wind Speed
• anemometer an instrument used to measure wind speed
• A typical anemometer consists of small cups that are
attached by spokes to a shaft that rotates freely.
• The wind pushes against the cups and causes them to
rotate. This rotation triggers an electrical signal that
registers the wind speed in meters per second or in miles
per hour.
Station model – Wind speed and direction
Wind Direction
• wind vane an instrument used to determine direction of the
wind
• The wind vane is commonly an arrow-shaped device that
turns freely on a pole as the tail catches the wind.
• Wind direction may be described by using one of 16
compass directions, such as north-northeast. Wind
direction also may be recorded in degrees by moving
clockwise and beginning with 0° at the north.
Station model – wind speed and direction
• The station model uses a wind
barb to show both wind direction
and speed. The wind barb
shows the speed using "flags"
on the end.
– Each half of a flag depicts
five knots
– Each full flag depicts 10
knots
– Each pennant (filled triangle)
depicts 50 knots[4]
• Winds are depicted as blowing
from the direction the flags are
facing.
Station model – weather conditions
• To the left of the cloud
shape in the center of
the station model is
the symbol depicting
present weather.
• The visibility is shown
as a number to the left
of the present weather
symbol. It describes
how far the observer
can see at that time.
A more complete station model.
Station model practice exercises
Global Weather Monitoring
• Weather observers at stations around the world report
weather conditions frequently, often several times per hour.
• The World Meteorological Organization (WMO) sponsors a
program called World Weather Watch to promote the rapid
exchange of weather information.
• This organization helps developing countries establish or
improve their meteorological services and also offers advice
on the effect of weather on natural resource and on human
activities, such as farming and transportation.
Weather Forecasts
• To forecast the weather, meteorologists regularly plot to the intensity
and path of weather systems on maps.
• Meteorologists then study the must recent weather map and compare it
with maps from previous hours.
• By following the progress of weather systems, meteorologist can
forecast the weather.
Severe Weather Watches and Warnings
• One main goal of meteorology is to reduce the amount of destruction
caused by severe weather by forecasting severe weather early.
• A watch is issued when the conditions are ideal for severe weather.
• A warning is given when severe weather has been spotted or is
expected within 24 hours.
END