measuring and forecasting weather

ccc 2nd year geography

what is weather

state of the atmosphere at any given time

what is a weather station

a facility that uses equipment and instruments to measure and observe the weather

how weather is gathered

through satellites and weather stations

what data is gathered

atmospheric pressure

temperature

precipitation

wind direction and speed

humidity

sunshine

what is atmospheric pressure measured by

weight of the atmosphere pushing down on the earth, measured in millibars(mb) by a barometer

barometer

a very sensitive vacuum chamber inside the barometer responds to atmospheric pressure

the the main needle on the face moves clockwise when pressure increases and anticlockwise when it decreases

the second needle is used as a marker to check back and see what the atmospheric pressure was later

barograph

a barometer that records its readings on a moving graph used in weather stations

the barometer is squeezed as air pressure increases and expands when pressure decreases

levers transfer its movements to a pen which draws on the paper

isobars

lines on map that measure atmospheric pressure

H = high atmospheric pressure

L = low atmospheric pressure

Low atmospheric pressure

wind is quite strong

significant cloud cover

high levels of precipitation

High atmospheric pressure

light wind

little cloud cover

little or no precipitation

what is temperature measured with

degrees celsius/centigrade using a thermometer - maximum and minimum thermometer

maximum and minimum thermometer

u shaped glass tube

alcohol is on the minimum side and empty space on the maximum side with mercury in between

metal makers on either side of the mercury

when temp. decreases alcohol contracts causing the metal marker to go up on min. side

when temp increases alcohol expands causing metal marker to go up on max. side

what is precipitation measured with

milimeters measured using a rain gauge

rain gauge

an outer cylinder and a funnel that directs water into a measuring cylinder, is partially buried in ground

water cycle

1. precipitation

2. surface run off

3. groundwater

4. evaporation

5. transpiration

6. condensation

types of rain

relief

convectional

frontal

relief rain

• warm moist air travels over a large body of water

• it reaches a mountain, rises and cools and condenses forming clouds and bringing rain

• once it passes over the mountain the air begins to dry up again and forms a rain shadow

convectional rain

1. occurs during warm weather when land is heated

2. this creates warm air which rises which is known as a convection current

3. as warm air rises it cools and condenses forming large clouds

frontal rain

1. this rain occurs when a warm front of air meets a cold front

2. the heavier cold air will sink to the ground and the warm air will rise above it

3. when the air rises it cools and condenses

4. clouds form bringing rain

what is a front

a boundary between two different types of air

rainfall on maps

lighter shade of blue = less rain

darker shade of rain = more rain

climate graphs

used to illustrate avg. temp. and precipitation of an area over 12 months of the year

line shows the temperature

bars show precipitation

cloud types

cirrus

cumulus

stratus

cirrus

above 8000m

thin and wispy

tiny ice crystals not water droplets

cumulus

below 5000m

base is flat rounded top

white = fair weather

black = heavy rain

stratus

below 200m

large thick heavy grey

long spells of precipitation

what is wind direction measured with

a wind vane

what is wind speed measured with

km/h with anemometer

wind vane

anemometer

three cups rotate when the wind blows

stronger wind = faster they move

beufort scale

scale used to measure wind force

what is humidity measured with

amount of water vapour in the air using a hygrometer shows relative humidity

wet and dry hygrometer

one thermometer measures the air temp.

the other bulb is kept wet by a cloth that is dipped in water

the difference between the two indicates relative humidity

what is sunshine measured with

a campbell-stokes recorder

campbell-stokes recorder

a solid glass ball concentrates the suns ray onto a removable strip of card which is placed behind the ball

the card is marked at hourly intervals as the sun shines through the ball it scorches a mark on the paper