Weather

What is weather? The condition of the air (or atmosphere) at a given location at a given time

Climate “Typical” weather in region; the average weather or the regular variations in weather in a region over a period of years includes temperature, air pressure, humidity, days of sunshine, etc... drastically affected by water & mountains –coastlines have cooler summers and warmer winters –mountains greatly slow down winds and weather

Atmosphere Blanket of air surrounding the earth Air – the mixture of gases, mainly nitrogen and oxygen, that forms the Earth’s atmosphere 78% Nitrogen 21% Oxygen 1% Argon 1% Other stuff : Carbon dioxide, water vapor, ozone, dust, ash, smoke, etc.

Structure of the Atmosphere

Lower Layers Troposphere – the layer of the atmosphere that is closest to the earth’s surface, where all weather phenomenon occurs. 8 km thick at the poles 16 km thick at the equator; (air temperature normally decreases with height) Stratosphere - upper layer of air km to about 50 km and top of the stratosphere contains the ozone layer; almost completely free of clouds.

Middle and Upper layers Mesosphere – the layer of air, 50km to 80km where temperature begins to decrease with height, mainly because ozone in the stratosphere absorbs energy from the sun, principally ultraviolet radiation Thermosphere - where air temperatures can exceed 1000° C (1800° F), 80km to 9600 km, primarily due to oxygen absorbing the sun’s energetic rays

Upper-Upper layers Ionosphere – the region within the atmosphere containing ionized molecules, layers of ionized air in the atmosphere extending from almost 60 km above the surface of the earth to altitudes of 1000 km and more. Exosphere - The region beyond the thermosphere, which extends to about 9,600 km, the outer limit of the atmosphere.

Conditions of the Air Temperature – amount of hotness or coldness relative to something else Thermometer – an instrument that measures relative hotness or coldness Dew Point temperature – The temperature at which air becomes saturated

Heat transfer Conduction – the movement of heat from molecule to molecule Convection – the movement of heat by warm and cold currents Radiation – the release and transfer of energy in wavelengths of heat and light

How is the atmosphere is heated? Draw

Draw on back of notes

Pressure Air pressure - the downward pressure exerted by the weight of the overlying atmosphere or the “weight” of the atmosphere per unit AREA. Barometer – an instrument used to measure air pressure Measured in inches of mercury in a column Or millibars (metricOr millibars (metricconversion) Average air pressureAverage air pressure at sea level is 1013 millibars

Water in the atmosphere Water Vapor Humidity – the amount of water vapor in the air Relative humidity – the actual amount of water vapor in the air compared to the greatest amount the air can hold

Precipitation water or ice that condenses in the air and falls to the ground as: Rain- liquid water that falls to the ground Snow - ice crystal flakes; water vapor in the atmosphere that froze into ice crystals and falls to the ground in the form of flakes Sleet -partially melted grains of ice Hail - pellets made of layers of ice and snow Freezing rain –rain that freezes into ice as it hits the ground

Evaporation the process of changing from liquid to gas; molecules in a liquid state GAIN energy to change into a gaseous state (latent heat energy is the stored in molecules through evaporation) Evaporation DRIVES the water cycle

Condensation the process of changing from gas to liquid; molecules in a gaseous state that LOSE energy to change into a liquid state.

Clouds a visible mass of dense water vapor or ice suspended in the atmosphere; formed by surface heating & convection and/or warm air lifted by rising over mountains

Wind Air moving at a speed fast enough to be notice… Low pressure – air is de-compressed (allowed to expand) and sucks air toward.Low pressure – air is de-compressed (allowed to expand) and sucks air toward. High pressure – air is compressed (contracted) and flows away.High pressure – air is compressed (contracted) and flows away. high pressure moves to low pressure Winds are named by the direction they come FROM Instruments: Weather Vane – measures wind directionWeather Vane – measures wind direction Anemometer – measures wind speedAnemometer – measures wind speed

LOCAL WINDS: Sea breeze

Sea breeze wind blowing from sea to land during the day when the sun warms the land faster and cool air from above the water forces the warm air above the land to rise Draw diagrams

LOCAL WINDS: Land Breeze

wind blowing from land to sea at night because the land cools faster than the sea Draw diagrams

High pressure – air is compressed (contracted) and flows away. Low pressure – air is de-compressed (allowed to expand) and sucks air toward. –Add the Coriolis Effect and you get ‘cyclonic’ and ‘anticyclonic’ flow.

Coriolis Effect the effect of Earth’s rotation on movement of air masses

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Coriolis Effect on a Synoptic Scale Low pressure… air moves: –Up –In –Counter clockwise High pressure … air moves: –Down –Out –Clockwise

Global Winds Draw next page

Air Mass A large region of air with similar properties throughout (ie. temperature, humidity)

Major Air Masses cA – Continental Artic – dry, very cold cP – Continental Polar – dry and cold cT – Continental Tropical – dry and warm mP – Maritime Polar – moist and cold mT – Maritime Tropical – moist and warm Draw next page

Relative Humidity Comparison of the specific humidity and the maximum amount of water vapor that the air can hold at a given temperature and pressure Unit is in percentage = % Relative humidity = specific humidity X 100% maximum capacity 100% Rel. Hum. – saturated air 0% Rel. Hum. – dry air

Psychrometer Dry air - greater evaporation - greater cooling - greater the difference in the 2 temperatures High humidity – no evaporation (saturated air) - temperatures of the 2 bulbs will be the same or very close

Psychrometer  Instrument to measure humidity  Dry bulb – measures air temp.  Wet bulb – has a water soak wick around the bulb – water evaporates – cools the air

Rain Shadow (Orographic Lifting) As a parcel of air rises up the windward side of a mountain range, the water vapor in the air condenses to liquid water and creates clouds and precipitation.

When the air begins to flow over the mountain and down the leeward side of the mountain, it is dry (lost all of its moisture). As the cool air descends, it heats and compresses (increased pressure), reducing its possibility of precipitation.

Front the boundary between two different air masses –Cold front – a front that moves so that cold air replaces a warmer air mass –Warm front – a front that moves so that warm air replaces a cooler air mass –Occluded front – a front formed when a cold front overtakes a warm front –Stationary front – a front that is not moving –Polar front – the low pressure zone where polar and tropical air masses meet

Norwegian Cyclone Model

Manifestation of low pressure:

Jet Stream Jet streams are fast flowing, narrow air currents found in the atmosphere. The main jet streams are located near the tropopause and the stratosphere. en.wikipedia.org/wiki/Jet_stream

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Greenhouse effect the ability of the atmosphere to let much sunlight in, but little infrared radiation (heat) to escape.

Greenhouse effect Greenhouse gasses: carbon dioxide (CO2), water vapor, methane (CH4), nitrous oxide, hydrochlorofluorocarbons, or HCFCs, & chlorofluorocarbons or CFC’s; CFC’s are chemicals used in refrigerators, air conditioners, etc. and aerosol spray cans that destroy ozone molecules

Causes of the Greenhouse effect burning oil, natural gas and coal (increasing CO2 levels) deforestation - burning of cleared forests release more CO2; no trees to convert CO2 to oxygen

Air Pollutant – any harmful matter added to the air Ozone – a three- atom form of oxygen that absorbs ultraviolet sunlight nthly_ htmln

Ocean's Conveyor Belt -- Thermohaline Circulation

Weather Advisories Weather WATCH – predictions about approaching severe weather Weather WARNING – specific severe weather conditions have been actually observed by a person or verified by a computer

The National Weather Service Forecast Office issues the following watches, warnings, and advisories when weather threatens: Watches are issued to allow time for preparation and planning for weather threats. Warnings are issued when a threat is occurring or imminent and action is needed to protect life and property. Advisories are issued when weather conditions impact our lives in ways that are not a direct threat to life and property but ignoring them may lead to hazardous conditions. Can there be a Watch and Warning in effect at the same time? Yes. Watches generally cover longer time periods and highlight the possibility of a threat that may develop at some time in the future. Warnings are issued for specific threats in particular areas as they develop and require immediate action to protect life and property.

Synoptic Map Symbols Synoptic Weather-Weather occurring over aSynoptic Weather-Weather occurring over a wide region on time scales exceeding 12 hours. wide region on time scales exceeding 12 hours. Synoptic Code-Rules and procedures established by the World Meteorological Organization(WMO) for encoding weather observations.Synoptic Code-Rules and procedures established by the World Meteorological Organization(WMO) for encoding weather observations. Synoptic Scale-The spatial scale of the migratory high and low pressure systems of the lower troposphere, with wavelengths of 1000 to 2500 km.Synoptic Scale-The spatial scale of the migratory high and low pressure systems of the lower troposphere, with wavelengths of 1000 to 2500 km. Synoptic Track-Weather reconnaissance mission flown to provide vital meteorological information in data sparse ocean areas as a supplement to existing surface, radar, and satellite data.Synoptic Track-Weather reconnaissance mission flown to provide vital meteorological information in data sparse ocean areas as a supplement to existing surface, radar, and satellite data. Synoptic flights - better define the upper atmosphere and aid in the prediction of tropical cyclone development and movement.Synoptic flights - better define the upper atmosphere and aid in the prediction of tropical cyclone development and movement.

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