Earth Systems, Structure and Processes

Introduction to Weather and Weather Stations

Vocabulary

• What do these words mean?• Atmosphere• Weather• Weather forecasting• Meteorology• Meteorologist• Climate • Weather station

Weather Vocabulary – take 1

• Atmosphere– The air surrounding the

earth

• Weather– The condition or state of

atmosphere at a given time and place

• Weather Forecasting

– Predicting of future weather conditions

Meteorology and Meteorologists

• Meteorology –

– The study of atmosphere and its weather

• Meteorologist

– A person who studies the atmosphere and its weather

• Climate

– The average temperature over a long period of time

• Weather Station

– A place for recording and displaying data that has been collected.

Forecast• a scientifically derived

prediction of the upcoming weather at any given time.

Weather Instruments

• What is air pressure?– When air pushed down on the Earth’s surface

What is a Barometer?– An instrument that measures air pressure.

What is convection?

– Differences in air pressure causes convection. Energy moves through troposphere because of the rising and sinking of air. Warm air rises and cold air moves in to takes its place. This moving air is called WIND.

• What is a wind vane?• A wind vane shows wind direction. The wind

vain points in the direction the wind is blowing from.

• What is an Anemometer?• An anemometer measures wind speed. There

are little cups on the top and the faster they spin the faster the wind is blowing.

• Why is there water vapor in the atmosphere?– The water on the Earth is heated and it evaporates

and forms a gas in the air.• Describe humidity.– It is the amount of water vapor in the air.

• What is a hygrometer?– It is a weather instrument that measures

humidity.

• Describe Relative Humidity?– It compares the amount of water vapor in the air

with the greatest amount that could be in the air at that temperature and pressure. It the hygrometer reads 50%, then that means there is half of the mount of water vapor in the air that could be there.

• What is precipitation?– It is any form of water falling from the clouds to

the Earth.

What is a weather balloon used for?

• Weather balloons collect information from high in the atmosphere. The balloons rise through the air and has an instrument panel hanging from it. It holds weather instruments which measures temperature, air pressure, wind speed and humidity.

Collecting Weather Data

• Beaufort Scale – Is a scale used to rate the force and speed of the wind on a scale from 0-12 and relates to the observable effects. For example: The more intense the wind – indicates a storm is approaching. The decreasing speed of the wind indicates calmer weather is approaching.

• Rain Gauge – an instrument that collects rain to determine the amount of rain that has fallen to the Earth.

Air Pressure

• Air Pressure – is measured in terms of weight of air per unit of area. The air pressure on an object is equal to the amount of pressure exerted on an object in all directions.

• A vacuum is a space that has no air pressure.

What does air pressure have to do with the weather?

• Temperature and air pressure are related. Cold air is dense, so, when it pushes down on the earth, it creates high air pressure. Warm air is less dense and does not exert as much pressure. In areas with warm air, the air pressure is lower.

What do you think causes wind?

• Air moves from areas of higher pressure to areas of lower pressure. The greater the difference in air pressure, the stronger the movement of air; consequently, the stronger the wind blows.

How does the change in barometric pressure change the weather?

• A falling barometer reading and warm temperatures precede stormy weather and some sort precipitation.

• A rising barometer reading and cooler temperatures indicate fairer weather and probably dry conditions.

• Typically, areas of high pressure press down on warm, moisture-filled air, preventing it from rising and forming clouds, so the weather is usually dry.

• Areas of low pressure allow the moisture-filled air to rise, forming clouds and then precipitation. There are always exceptions.

Vocabulary

• Barometer- an instrument to measure barometric pressure or air pressure.

• Aneroid barometer – uses mercury to measure air pressure instead of liquid.

• Millibars – The inner scale that gives the metric equivalent of inches of barometric pressure. A millibar is a unit of pressure that is related to the actual weight of air pressing on a 1 square centimeter area.

Look at a weather map

• http://www.weather.com/maps/maptype/currentweatherusnational/uscurrentweather_large.html

Station Model

Weather Fronts

• Air mass –a term used to describe a vast body of air in which temperature / humidity is basically the same.

• Front – is the boundary where air masses of different temperatures and humidities collide. ( they are called weather changers)

Four different types of Fronts

• Cold Front – Forms when a cold air mass advances to display masses of warm air.

• Warm front - Forms when a warm air mass advances and rises over a retreating mass of cold air. *As it rises, the warm air cools. If the warm air is also moist, layered clouds and precipitation may form. Hot, humid weather usually follows.

Fronts - continued

• Occluded Front – Occurs when a cold front, closely following a warm front, finally overtakes the warm front. The dense, cool airlifts the less-dense warm air off the ground. As the warm air is pushed upward, it also cools, producing clouds and precipitation. Occluded fronts produce less extreme weather than cold or warm fronts.

• Stationary Front – If a warm air mass encounters a cold air mass and no movement occurs, a stationary front forms.

Fronts

• What would happen if the warm air contained a lot of moisture? (As the moist, warm air rose up higher into the atmosphere, any water vapor would be cooled, causing it to condense and turn into a liquid.)

• • What kind of weather does a warm front bring? Why?

(Clouds and rain. Warm fronts slide slowly above the cold air, so more air cools, causing condensation and precipitation. Because the warm air is the mass that moves in, storms, are usually followed by hot and humid weather.)

Fronts

• What kinds of weather does a cold front bring? Why? (The denser the cold air dives under the warm air, pushing it upward. Again, the warm air cools, and any water vapor condenses. This time, however, it is the cold front that is moving in, so rain is followed by cooler weather.)

• What kinds of weather does occluded fronts bring? Why? (In an occluded front, the warm air mass, being lighter, is pushed above the two cold masses. Up high, the air becomes cooler and its water vapor condenses. So occluded fronts usually bring clouds and rain, but less extreme conditions than cold fronts bring. )

Fronts

• What kind of weather does a stationary front bring? Why? (With a stationary front, neither the cold nor the warm air is advancing, and widespread clouds can form on both sides of the frontal boundary. Since the clouds are barely moving, a stationary front often brings lengthy periods of precipitation.)

• What direction do weather fronts typically move? ( they move typically from west to east; however, some will push down from the north or up from the south)

Isobars – areas of same atmospheric pressure can be connected on a weather map by lines

called isobars

Isotherms – are lines drawn to connect areas of the same atmospheric temperature at a given

time.

What happens when the sun heats the earth and water condenses?

• Convection – As the sun heats the surface of the earth, whether it be land or a body of water, water at the surface evaporates as water vapor. This water vapor is carried up from the surface by rising warm air is a process called convection.

• Condense - Water vapor goes higher and higher and it gets cooler and cooler. The cool air cannot hold as much water as warm air so water vapor condenses to form droplets of liquid water.

How do clouds form?

• For clouds to form, more is needed that just air and water vapor. The water vapor needs tiny particles around which to condense. We call these tiny particles nuclei. They can be any type of small airborne materials, including dust and smoke particles. Then the water molecules attach. If enough water vapor condenses round the nuclei, a cloud forms.

Cirrus Clouds

Cirrus – clouds appear wispy and form at very HIGH altitudes.

• Since they form where the temperature is always far below freezing they are almost always complete made up of ice crystals.

Cumulus - billowing white or dark grey cloud associated with rising air currents

• Clouds appear puffy or piled up and form throughout much of the cloud layer

Cumulonimbus-

• tall and dense and usually dark.

• A Cumulonimbus forms if a cumulous cloud produces precipitation.

Nimbus - they are typically gray and heavy and present just before and during a storm.

Nimbostratus-• dark, low-level clouds with

precipitation • Nimbostratus are dark, low

level clouds accompanied by light to moderately falling precipitation.

• A stratus cloud that forms precipitation. Nimbus is Latin for “rainstorm”

Stratus – clouds appear layered form at levels below 6500 feet

• Stratus clouds are low-lying, uniform clouds that blanket the sky. They are often a dullish white to gray in color, and they are generally the sort of clouds that appear when people talk about a cloudy day. Stratus clouds are not generally associated with poor weather, although they can be accompanied by drizzle, and at higher altitudes, they can be an indicator that rain is on the way.

Fog- stratus clouds that are formed on the surface of the Earth.

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Tornado• Tornado- Tornados can be

even more destructive than hurricanes; however, they follow a narrower path. It does not last as long but has violent rotating , narrow columns of air. The wind speeds are between 50-300 mph. They usually develop in cumulonimbus clouds but is not officially called a tornado unless it looks like a funnel.

Hurricanes• Hurricane- are largest storm

on the earth for the sheer size. It is a rotating wind system that originates over warm ocean water in low pressure areas. Hurricanes extend for several miles/kilometers and can last for days. They have severe winds that can be up to 200 mph. The eye of the hurricane is the calm center (the eye of the storm). The eye averages about 20 miles wide.

Other Severe Weather

• What causes a thunderstorm? (warm moist air quickly rising along a cold front)

• What type of air pressure do you find in a tornado? (very low)

• How can you tell a thunderstorm is approaching? (anvil shape cloud with a dark bottom is approaching)

Jet Streams

• The jet stream is a fast flowing, river of air found in the atmosphere at around 12 km above the surface of the Earth just under the tropopause.

• They form at the boundaries of adjacent air masses with significant differences in temperature, such as of the polar region and the warmer air to the south.

• Because of the effect of the Earth's rotation the streams flow west to east, in a serpentine or wave-like manner at lower speeds than that of the actual wind within the flow.

Jet stream

What are the global wind patterns?

• The equator receives the Sun's direct rays. • Here, air is heated and rises, leaving low pressure

areas behind. • Moving to about thirty degrees north and south of

the equator, the warm air from the equator begins to cool and sink.

• Between thirty degrees latitude and the equator, most of the cooling sinking air moves back to the equator. The rest of the air flows toward the poles.

Global Wind Patterns

What are the trade winds?

• What are the trade winds?The trade winds are just air movements toward the equator.

• They are warm, steady breezes that blow almost continuously.

• The Coriolis Effect makes the trade winds appear to be curving to the west, whether they are traveling to the equator from the south or north.

What are the doldrums?

• The doldrums is an area of calm weather. • The trade winds coming from the south and

the north meet near the equator. • These converging trade winds produce general

upward winds as they are heated, so there are no steady surface winds

What are the prevailing westerlies?

• Between thirty and sixty degrees latitude, the winds that move toward the poles appear to curve to the east.

• Because winds are named from the direction in which they originate, these winds are called prevailing westerlies.

• Prevailing westerlies in the Northern Hemisphere are responsible for many of the weather movements across the United States and Canada.

What are the polar easterlies?

• At about sixty degrees latitude in both hemispheres, the prevailing westerlies join with the polar easterlies to reduce upward motion.

• The polar easterlies form when the atmosphere over the poles cools.

• This cool air then sinks and spreads over the surface.

• As the air flows away from the poles, it is turned to the west by the Coriolis effect. Again, because these winds begin in the east, they are called easterlies.

El NinoIntroduction• El Niño refers to the irregular warming in the sea

surface temperatures from the coasts of Peru and Ecuador to the equatorial central Pacific.

• This causes a disruption of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe.

• This phenomenon is not totally predictable but on average occurs once every four years. It usually lasts for about 18 months after it begins.

What are the effects of El Nino?

• Effects show up most clearly during wintertime• Linked with drought not just in parts of Latin

America but in southeastern Africa, South Asia, Indonesia and Australia.

• El Niño usually brings a warm winter to the northern USA from the Pacific Northwest across to the Midwest and sometimes the Northeast

• Reduction in the number of hurricanes that form over the Atlantic Ocean, especially strong ones

La Nina

• La Nina is the name given to the slight cooling of the surface waters of the Pacific Ocean.

• As the ocean is one of the biggest influences on our weather, this change in the surface temperature has a dramatic effect on the weather around the world.

Causes of La Nina

• What is known is that during a La Nina event the prevailing winds strengthen.

• These winds blow towards the west, so the warm surface waters are blown away from the coast of South America, towards Indonesia.

• This causes cold waters from the depth of the ocean to well-up along the coast of Peru and Ecuador.

Affects of La Nina

• La Nina - as the water near the coast of Peru and Ecuador is cooler than usual, it makes sense that the weather in the region is also cooler than usual.

• If the waters around Indonesia are warmer than usual, then this part of the world will be wetter than usual.

• As the warmer water will heat the air, and warmer air can hold more moisture than cooler air.