Weather and Climate

8th grade science STAAR

What is Weather vs. Climate

• Weather is the current atmospheric conditions, which includes temperature, wind, humidity, etc.

• The average weather in a given area is the climate for that area. – Example: The weather in Lake Dallas, Tx on

June 5th is 95° F and warm, but the climate for the area during summer is hot and dry.

Latitude and Longitude

• What is latitude? Longitude?• Latitude = lines that measure North to

South - go from the poles at 0° to the equator at 90°

• Longitude =is measured from the Prime Meridian with positive values going east and negative values going west. – For example: at the equator what is the

climate like? What about at the north and south poles?

What affects an area’s climate.

• Cycling of water in and out of the atmosphere plays an important role in determining weather and climatic patterns.

• What is the cycling of water in the atmosphere called? WATER CYCLE

• Terms to know: Precipitation, Condensation, Evaporation, Transpiration, Run-off, Groundwater, Surface water

Water Cycle

What affects an area’s climate.• CONVECTION CURRENTS –

– Uneven heating of the Earth's surface that produces weather systems.

• Where hot air rises (less dense) and cooler air sinks (more dense).

Sun’s role in convection currents

• You know that it is warmer at the Equator than at the poles because Earth is tilted!

• Direct rays of sun at the equator and indirect rays at the poles.

• The warmer, lighter air at the Equator moves toward the cooler air at the poles. The cold heavy air at the poles moves toward the Equator. 

• This causes a constant movement of air movement called convection currents.

Convection Currents• Convection currents drive (cause) wind patterns

that affect climate.

Air Masses• Air masses are moved by convection currents• There are two types of air masses; cold and

warm.

– Cold = dry, dense

– Warm = moist, less dense

• Cold air masses come from higher latitudes to lower latitudes. Warm air masses do the opposite. When they meet in the middle some interesting weather happens!

Cold Meets The Warm

• Why is the warm air rising and going on top of the cold air mass?

• Warm air is LESS dense.

Air Masses

• Air masses are classified by TWO letters.

• The first letter shows what the air mass forms over:– Continental (c)- dry air masses that form

over land– Maritime (m) – moist air masses that form

over water.

Air Masses • Second Letter represents the LATITUDE

and the temp.

• Arctic (A) – cold, dry air mass

• Polar (P) – cold dry air mass (not as cold as artic

• Equatorial (E) – warmest air mass

• Tropical (T) – warm air mass (not as warm as equatorial.

Air Masses on Globe

Air Pressure

• This is how scientists measure air pressure.

• Air pressure is the amount of pressure exerted on a surface by the atmosphere above it.– Barometers are used

to measure this with units in millibars (mb).

What is this graph telling us?

• As the altitude increases what happened to the air pressure?– It decreases!

High Pressure System

• The air molecules packed in to the center of a high pressure system doesn’t make the right conditions for cloud and precipitation development

• So weather is generally calm around a high pressure center.

Low Pressure System

• This is an area where air is rising and this fuels weather change. With rising air means rising water vapors which leads to clouds and the rest of the water cycle.

• Hurricanes, cyclones and other storms are associated with low pressure.

Fronts• Fronts- boundaries between two air masses.• they are created when high pressure systems

moves in around low pressure systems. • They bring WEATHER CHANGES!

What Are Main Types of Fronts?

• A cold front forms when a fast cold air mass runs into a slow warm air mass.

• A cold front brings heavy rain or snow.

• After the front passes, cold dry air moves in, skies clear, winds shift, and temperatures drop.

• A warm front forms when a fast-moving warm air mass overtakes a slower-moving cold air mass.

• After the front passes, weather tends to be warmer and more humid.

What Are Main Types of Fronts?

• An occluded front forms when a warm air mass is caught between two cooler air masses.

• Occluded fronts cause weather to turn cloudy and rain or snow may fall.

• A stationary front forms when air masses meet, but neither can move the other.

• Stationary fronts often bring many days of clouds and precipitation.

What Are Main Types of Fronts?

Front Symbols• All symbols are put on an isobar• Isobars are lines that show areas with equal

air pressure

• Cold front –

• Warm front –

• Stationary Front –

• Occluded Front -

Weather Maps

• A weather map can be used to predict temperature and precipitation for several days in a given area

• See if you can find the pressure systems and fronts on the following maps

Can you read the map?

Station Symbols

• You will see symbols like these from weather stations scattered about.

• They tell information about cloud cover, barometric pressure, dew point, temperature, current precipitation, etc.

Station Model

Winds

• Winds move excess heat around the Earth.

• They are caused by air flowing from high pressures to low pressures!– When air moves downward you have HIGH

PRESSURE develop.– When air rises you have LOW PRESSUE

develop.

Winds…

• Winds do not all blow the same direction though they are effected by two main things: – Coriolis Effect – Winds are forced to the right

in the northern hemisphere and to the left in the southern hemisphere

– Convection cells – Heat from the sun powers these.

Wind Directions

Ocean Currents• Ocean currents affect local and global

weather conditions.

• They have a much slower, long lasting effect on climate than winds.

• They move slowly and retain more heat than the atmosphere.

• They are driven by the Sun and the rotation of the earth (Coriolis Effect).

Types of Ocean Currents• Surface Currents – driven by winds, only

10% of water in the ocean- only the top layer.– Gulf Stream – a surface current that travels

along eastern part of the US – causes warmer climates in Europe.

• Deep Water Currents – these are colder (denser) layers that make up 90% of the ocean currents. They are caused by the the change in density causes these currents

El Niño• El Niño is a mass of warm water that moves

eastward as trade winds relax. Originates in the PACIFIC OCEAN.

• El Niño causes warm water brings torrential rains to parts of the world that are not prepared for such weather.

• For reasons that scientists still do not completely comprehend, every few years the trade winds blow less or stop blowing at all. They can also change direction.

• It causes a build-up of warm water off the coast of South America and Africa and causes weather changes all over the globe.

Tracking El Nino

Hurricanes and Cyclones

• A cyclone is a huge revolving storm that is caused by winds blowing around a low pressure area.

• Tornadoes are also a type of cyclone with a tighter, faster spinning vortex of wind.

• Cyclones develop over the oceans near the equator. A cyclone will not develop unless the surface water temperature is at least 26° C (80° F). Warm air rises and creates area of low pressure.

Hurricanes and Cyclones• A hurricane is a huge storm that forms

over warm ocean water! Hurricanes can cause extreme amounts of damage depending on their size and wind speeds.

• The main purpose of a hurricane is to move heat away from the tropics. So the sun is the main energy source for hurricanes.

• Types of damage caused by hurricanes reaching land are strong winds, flooding, storm surge, and tornadoes.

Which would you rather experience?

• Hurricane! • Cyclone!