Gathering Weather DataGathering Weather Data““Know yourself and know your Know yourself and know your

enemy, and victory is enemy, and victory is guaranteed. Know the terrain guaranteed. Know the terrain

and know the weather, and and know the weather, and you will have total victory.” you will have total victory.”

Chinese philosopher Sun Tzu, 4th Chinese philosopher Sun Tzu, 4th century BCcentury BC

• DoctorsDoctors– TemperatureTemperature– Blood PressureBlood Pressure– WeightWeight– HeightHeight– PulsePulse– RespirationRespiration– Skin/surfaceSkin/surface

• MeteorologistsMeteorologists– TemperatureTemperature– Air pressureAir pressure– WindWind– Relative humidityRelative humidity– CloudsClouds– RainRain

Gathering Weather DataGathering Weather Data

Surface DataSurface Data

• Both Doctors and Meteorologists use Both Doctors and Meteorologists use many different instruments to gather many different instruments to gather informationinformation

• Two most important factors in Two most important factors in weather forecastingweather forecasting– Accuracy of dataAccuracy of data– Density of data (amount of data Density of data (amount of data

available)available)

ThermometersThermometers• Temperature measures how Temperature measures how

fast/slow particles are movingfast/slow particles are moving• Fast=high temp; slow=low tempFast=high temp; slow=low temp• Mercury or alcohol basedMercury or alcohol based• Liquid in bulb is heatedLiquid in bulb is heated• It expandsIt expands• Forced up the columnForced up the column

BarometersBarometers• Measure air pressureMeasure air pressure

• A rising barometer means sunny and dry conditions, while A rising barometer means sunny and dry conditions, while a falling barometer means stormy and wet conditions. a falling barometer means stormy and wet conditions.

• An Italian scientist named Torricelli built the first An Italian scientist named Torricelli built the first barometer in 1643.barometer in 1643.

• PSI (pounds per square inch) or millibarsPSI (pounds per square inch) or millibars

• Two typesTwo types– MercuryMercury– AneroidAneroid

Mercury Mercury barometerbarometer

• Changes in Changes in pressure indicated pressure indicated by changes in by changes in height of column height of column of mercuryof mercury

Aneroid Aneroid BarometerBarometer• Contains vacuum in Contains vacuum in

metal chambermetal chamber• Chamber expands or Chamber expands or

contracts with changes contracts with changes in pressurein pressure

AnemometerAnemometer

• Measures wind speedMeasures wind speed

• Cupped arms that rotate as wind Cupped arms that rotate as wind blowsblows

HygrometerHygrometer• Measures relative humidityMeasures relative humidity

• Wet- and dry-bulb typeWet- and dry-bulb type– Sling psychrometerSling psychrometer

• As water evaporates from the As water evaporates from the wet bulb, the bulb cools, wet bulb, the bulb cools, creating a temperature creating a temperature difference between the wet difference between the wet bulb and the dry bulbbulb and the dry bulb

• The temperature difference is The temperature difference is used with a relative humidity used with a relative humidity chart to determine atmospheric chart to determine atmospheric relative humidity p. 915relative humidity p. 915

Automated Surface Automated Surface Observing System (ASOS)Observing System (ASOS)

• To make accurate forecasts, The different variables To make accurate forecasts, The different variables of Weather data must be gathered at the same of Weather data must be gathered at the same moment, several times a day, at many different moment, several times a day, at many different locationslocations

• The National Weather Service (NWS) has a network The National Weather Service (NWS) has a network of approx. 1700 official weather observing sites to of approx. 1700 official weather observing sites to measure and record data at least every hourmeasure and record data at least every hour

• The ASOS collects all this information using the The ASOS collects all this information using the instruments we talked about in addition to rain instruments we talked about in addition to rain gauges and ceilometersgauges and ceilometers

Automated Surface Observing System (ASOS) - The National Weather Service (NWS), Federal Aviation Administration (FAA) and Department of Defense operate this network of 967 stations located throughout the United States [Arkansas (16), Kansas (17), Louisiana (18), Missouri (19), Oklahoma (15), Texas (60)]. The data generally available from ASOS stations includes hourly (and special) observations of air temperature, dew point, wind speed, wind direction, cloud cover, visibility, present weather, and precipitation. The hourly and special observations are included within many data archives. Additionally, data with up to one minute temporal resolution can be obtained from the ASOS stations via modem (password required for access). The most recent 12 hours of 1-minute observations are kept at the stations.

CeilometersCeilometers

• Measure Measure cloud cloud height and height and cloud covercloud cover

• Uses laser Uses laser pulsespulses

Cloud Observations - Ground-based  

Ground-Based Description of Sky Conditions

Description ASOS (NWS) Human Meaning

Clear (CLR or SKC) 0to 5% 0 No Clouds

Few >5 to <25% 0 to 2/8 Few clouds visible

Scattered (SCT) > 25 to <50% 3/8 to 4/8 Partly cloudy

Broken (BKN) > 50 to <87% 5/8 to 7/8 Mostly cloudy

Overcast (OVC) > 87 to 100% 8/8 Sky is covered by clouds

Sky obscured NA NASky is hidden by surface-based phenomena, such as

fog, blowing snow, smoke and so forth, rather than by cloud cover

Rain gaugeRain gauge • Measures amount Measures amount of precipitationof precipitation

Upper Level DataUpper Level Data

• More complex technology is needed More complex technology is needed to collect data from the upper to collect data from the upper tropospheretroposphere

• Remember: changes in the upper Remember: changes in the upper atmosphere changes weather at atmosphere changes weather at Earth’s surfaceEarth’s surface

RadiosondeRadiosonde• Balloon-borne Balloon-borne

instrumentinstrument

• Contains sensors to Contains sensors to collect upper level collect upper level variables such as variables such as relative humidity, relative humidity, temperature, wind temperature, wind speed and direction, speed and direction, and air pressureand air pressure

• Radio signal Radio signal transmits info to transmits info to ground stationground station

Weather radarWeather radar

• Used to predict areas of Used to predict areas of precipitationprecipitation

• Transmitter emits Transmitter emits electromagnetic waves thru electromagnetic waves thru antennaeantennae

• When waves hit water droplets, When waves hit water droplets, they are reflected, making an they are reflected, making an echo picked up by receiving echo picked up by receiving antennaeantennae

• Elapsed time between Elapsed time between transmission and echo reception transmission and echo reception is used to determine where rain is used to determine where rain is fallingis falling

• Radar systems have range 400 Radar systems have range 400 km in diameterkm in diameter

Doppler RadarDoppler Radar• Similar to radar systems but with added advantage: measure wind speeds Similar to radar systems but with added advantage: measure wind speeds

associated with stormsassociated with storms

• Based on Doppler effectBased on Doppler effect– Change in wave frequency that occurs as source of waves moves Change in wave frequency that occurs as source of waves moves

towards or away from the observertowards or away from the observer– Ex. Ambulance sirenEx. Ambulance siren

• High pitched as it approaches and low pitch as it leavesHigh pitched as it approaches and low pitch as it leaves

• By plotting echos of radar signals, meteorologists can determine speed at By plotting echos of radar signals, meteorologists can determine speed at which rain drops are moving towards or away from the receiving antennaewhich rain drops are moving towards or away from the receiving antennae

Weather SatellitesWeather Satellites• Orbit high enough above the surface and transmit images Orbit high enough above the surface and transmit images

to Earth’s weather stationsto Earth’s weather stations

• VisibleVisible– Picture of cloudsPicture of clouds

• InfraredInfrared– Does not need light…uses infrared radiation istead of Does not need light…uses infrared radiation istead of

visible light to make imagevisible light to make image– tells you the temperature of what the satellite is sensing, tells you the temperature of what the satellite is sensing,

whether its the ground or the tops of cloudswhether its the ground or the tops of clouds– very useful for determining the height of the cloud (low, very useful for determining the height of the cloud (low,

middle, high)middle, high)– Low clouds=warmLow clouds=warm– High clouds=coldHigh clouds=cold– Good for detecting thunderstorms high up in atmosphereGood for detecting thunderstorms high up in atmosphere

VisibleVisible

Infrared ImageryInfrared Imagery