Weather Instruments
Barometers - aneroid
measured in? hectapascals or millibars
vacuumed container made of steel or berylium which compresses or
expands according to the air pressure.
expands - low pressure
compresses - high pressure
decreasing pressure - Low pressure indicates approaching rain
Temperature
thermometers contain either mercury or alcohol
why - expands when heated and contracts when cooled
true reading needs to be in a shelter or shaded area
Stevenson screen - louvered box with free flowing air, painted
white, 4 ft. above ground on grass and 32 ft. away from other buildings
Wind speed - cup anemometer
describe - 4 half cups on rotating arms that spin around.
Timed # of rotations / min. x 6 x .02
Wind direction - instrument is wind vane or wind sock
Humidity -varies with temperature (warm holds more water vapor)
instrument is psychrometer - wet and dry bulb
works? - water evaporates from cotton ball in dry air,
lowering temp.
Electronic instruments
radiosonde is small helium filled balloon that measures air
pressure,
temp., humidity in upper atmosphere
radar - sends out radio signals and measures how much is reflected
back. Good for plotting precipitation and storms, rain & snow
Satellites
-meteosate weather- infrared images of earth’s atmosphere every 30 min
-infrared radiometers measures cloud top temperatures
-microwave radiometers best measure under cloudy conditions
-NOAA - measures temperature of ice and snow
-ERS 1 & ERS 2 - carries radar equipment and measures ocean wave
height
and ocean currents, wind speeds, polar ice caps
Clouds
Basic cloud shapes - cumulus (puffy cottonball), stratus (sheets, layers),
cirrus (feathery, wispy)
Cloud prefixes indicate the level – strato - low; alto - middle; cirro –
high
Type
stratus
level
low
stratocumulus
weather
light drizzle / snow
low
none
cumulus humilis,
or mediocris,
low
none - early sign of thunderstorm
pyrocumulus
low/med
showers/ storms
cumulonimbus
wind/hail
low/ high
moderate to heavy
rain/ strong
altostratus
med
extensive rain or snow
altocumulus
med
light rain if thick otherwise approaching
front
approaching front
altocumulus mackerel
sky
med
cirrus
high
shows moisture in upper atm.,
if a lot approaching front
otherwise a sign of decayed thunderstorm
cirrostratus
high
indicates ice crystals (lifted moist air mass)
shows iridescence or haloes.
cirrocumulus
high
contrails
high
most spectacular clouds across entire sky
moisture from exhaust of aircraft