Factors that affect weather Air pressure, humidity, temperature, precipitation

The Water Cycle Take out a clean sheet of paper. Number your paper 1-7 leaving half of the page for a picture. Write the 7 definitions on the following slide. Wait for Mrs. Couch to draw the picture (Yes you have to draw the picture)

The Parts of the Water Cycle Evaporation Condensation Precipitation Deposition Sublimation Infiltration Percolation Surface Run off Transpiration Urination Accumulation

Important parts of the water cycle Evaporation – liquid to gas Condensation – gas to liquid Precipitation – any form of water falling from the clouds to the ground Transpiration – plant sweat Surface Run off – water moving over land from higher to lower ground Infiltration – Water fills the space between particles of soil

The water cycle – cont. Percolation – Ground water moving below earth’s surface Accumulation – a big pile of water, pond, puddle, ocean, river etc. Urination – liquid waste – yuk Sublimation – Water vapor freezes into a solid – makes snow Deposition – Solid that vaporizes – skips the liquid phase

Humidity

Humidity and Relative Humidity Humidity – the amount of water vapor in the atmosphere Relative Humidity = The actual amount of water vapor in the air divided by the maximum amount of water vapor the air can hold

Measured with A sling psychrometer Made of 2 thermometers A wet bulb A dry bulb

How it works 2 – the wet bulb is cooled by evaporation 1 – sling it over your head for 20 seconds so air blows over the thermometers 2 – the wet bulb is cooled by evaporation 3 – therefore the temperature of the wet bulb is < the dry bulb 4 – use the chart to compare the temperatures

Dew Point Dew Point = The temperature at which air would have to cool to reach saturation (all of the water vapor it could hold) The dew point will never be greater than the temperature!! BUT if it is equal – humidity = 100% - causes condensation  fog, clouds, precipitation Check out the Dew point Calculator!

How do clouds form? Remember: **Warm air holds more water than cold air **As air rises it cools Condensation: occurs when there is enough water vapor in the air tiny particles must be present for the water to stick to Dew Point: The temperature at which condensation occurs Clouds form when warm air rises and the water vapor the air holds is cooled to the dew point Let’s put this in your own words!!!

Important Cloud Vocabulary Cirro – curly or whispy Nimbus – rain Stratus - layer Alto – middle Cumulo - heaped

3 Ways to Identify Clouds Altitude Shape The weather they bring Let’s look at some examples:

Cumulo (heap/pile) Fair weather 2 – 18 km

Cirrus (curly/whispy) Above 6 km – very high in the sky Made of ice crystals

Stratus (layer – spread out) Cover all or most of the sky Thicker – brings rain/snow/drizzle

Other Clouds Nimbo – Rain Alto – middle 2 – 6 km Fog – stratus clouds low to the ground Cumulonimbus – Thunderheads Contrails – Jet trails

Factors that affect weather Air pressure, humidity, temperature, precipitation

Remember … Air has mass and takes up space. Air pressure – the mass of the air being pulled down on an area of the earth’s surface. It pushes in all directions - it does not crush objects

2 things that affect air pressure Temperature The amount of air above it

Air moves? Yes – air moves from areas of high pressure to low pressure quickly

Weather Indicators Falling Air Pressure Storms Rising Air Pressure Good Weather

Measuring Air Pressure – Barometer Mercury - glass tube open at the bottom In a glass dish of mercury Measured in inches Aneroid Barometer – air tight metal chamber The wall flex in and out with the changes in air pressure. Measured in millibars 1 inch = 33.87 mb

Cheat sheet Elevation Pressure Pressure Density

Precipitation

Any form of water that falls from the clouds to the ground What is precipitation? Any form of water that falls from the clouds to the ground

Rain The most common Must be at least .5mm in diameter Any smaller =mist or drizzle Which falls from nimbostratus clouds

Sleet Occurs when rain falls through a layer of air below freezing Freezes into solid ice before it hits the ground Smaller than 5 mm

Freezing Rain Falls as rain and freezes when it touches a surface below freezing Does not freeze in the air

Hail Ice > than 5 mm in diameter ONLY from cumulonimbus clouds Adds layers from up and down drafts in the cloud Can damage property

Snow Water vapor that turns directly into ice (not frozen liquid water) Each snowflake has six sides and is different

How is it measured? Liquid Precipitation – rain is measured with a rain gauge Snow is measured with a ruler

Long periods of unusually low precipitation Drought Long periods of unusually low precipitation

Other Terms: Drought: long period of low precipitation Cloud Seeding: dropping tiny crystals of dry ice (solid CO2) and silver iodide sprinkled into clouds from planes. May be used to clear fog at airports.