Post on 30-Dec-2015
description
Weather
Click HERE for
Discovery ChannelGuide to Extreme Weather
(50 min)
Weather-It’s what’s happening outside NOW!
Weather
All weather is a result of humidity, condensation
and pressure.
Humidity—Water Vapor in the Air
Specific humidity: actual amount of water vapor in the air at a given time & place (grams of vapor per kilogram of air)
Warmer air can hold more water vapor
Humidity
Relative humidity: how close the air is to reaching its maximum capacity of water vapor expressed as a
percentage 100% means it has
reached maximum capacity
Humidity
Measured with a psychrometer
A psychrometer has two thermometers to determine humidity. The dry bulb thermometer measures the room temperature, and wet bulb thermometer is wrapped in a wet cloth. Air is passed through the psychrometer to evaporate moisture on the wet bulb. The readings on the dry bulb thermometer and the wet bulb thermometer are then compared to determine the actual humidity.
CondensationWhen water changes from
a gas to a liquid
Dew point: the temperature at which the air becomes saturated with water vapor & condensation occursIf air cools below the dew point, water starts condensing into a liquid, forming dew or cloud droplets
Condensation
Fog & clouds form only when there are condensation nuclei (like dust particles) for the water to condense on
Air must cool below its dew point
NASA View of Windblown Sands off Coast of Africa
NASA Views of Ash from Volcanic Eruption
NASA Views of Smoke and
Ash from California
Fires
Smog over LA
from car exhaust
Cloud Formation
When warm, wet air from the surface rises, it begins to cool. Eventually, the temperature drops to its dew point, and the water vapor can condense onto the condensation nuclei
Condensation level: the atmospheric level at which condensation occurs
Warm air rises taking the water vapor along with it. Once it cools, it condenses
forming a cloud.
Cloud Types
Classified by altitude
and shape
Explain the process of cloud formation
UFOs or what?What happened?
Cloud Types
Stratus: clouds that form in layers
Cirrus: high, feathery ice clouds
Cumulus: fluffy clouds with flat bases
Nimbus: dark rainclouds
Cloud types
PrecipitationAny form of water that falls
from a cloud to Earth’s surface
Types of Precipitation
Rain
Snow
Sleet: raindrops that refroze on their way to the surface
Freezing Rain: raindrops that only freeze when they hit the surface
Hail: when frozen raindrops are bounced up & down in the cloud until they fall in a huge ball of ice
Types of Precipitationdepend on the temperature of the atmosphere, both at the
surface & on the way down
snow sleet freezing rain
Measuring Precipitation
Rain gauge: measures liquid precipitation
Measuring stick: measures frozen precipitation
Where is Precipitation?
Where is Precipitation?Rain Shadow effect: near a mountain range, the
windward side gets lots of rain and the leeward side gets little/no rain – the rain shadow
Explain the Rain Shadow Effect
Extreme Weather1 minute video
http://science.discovery.com/videos/against-the-elements-mashups-devastating-winds.html
Air Mass
A large body of air in the lower troposphere that has similar characteristics throughout
Temperature & humidity depend on origin and move with the air mass
Types of Air Masses
Continental: dry Polar: cold
Maritime: wet Tropical: warm
Continental polar (cP): cold & dry
Maritime polar (mP): cold & wet
Continental tropical (cT): warm & dry
Maritime tropical (mT): warm & wet
Types of Air Masses
Types of Air Masses
Fronts—boundary between two air masses
FrontsCold Front: boundary between advancing cold air mass & a warmer air mass it is displacing Rising warm air usually produces precipitation if wet Air becomes colder after front passes
FrontsWarm Front: boundary between advancing hot air mass & a colder air mass it is displacing 1st clouds days in advance, then RAIN Air becomes warmer after front passes
FrontsOccluded Front: when cold front ‘catches up’ to a warm front, producing clouds & precipitation
Fronts
Stationary front: when a front stops moving forward, producing clouds & precipitation – causes floods if stationary too long
Station Model
Surface Weather Map
Locating a Front
Wind direction changes
Temperature changes sharply
Dew Point changes sharply
Weather Forecasting
Satellites
Radiosondes
Surface observations
Forecasting
Computer models take current data & plug it into equations to predict weather
Meteorologists take computer models & tweak them to fit their experience with local conditions
ForecastingTrend Method: using past movement of a front &
precipitation to predict future movement
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