Observations and Station Models

AOS 101 Discussion Sections 302 and 303

www.westcoastweathervanes.com

Observations What do we mean by observations?

Collecting data through various instruments

Importance of observations Assess current state of atmosphere Also aid in predicting future weather

Can be taken by people or automated sensors Examples

Buoys Ships Commercial aircraft (ACARS) Satellites www3.sympatico.ca

noaanews.noaa.gov

Types of Observations

Air temperature Dew point

temperature Air pressure Humidity Wind speed and

direction Cloud cover Ocean salinity Etc…

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Air Temperature Air temperature is measured by a

thermometer

www.faqs.org

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www.weatherconnect.com

Dew Point Temperature

Dew point temperature The temperature at which water

precipitates out of the air Can be measured by a hygrometer Can be calculated by using

observations from a wet bulb thermometer or psychrometer

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www.edupic.net

Wet Bulb Temperature Measured with a thermometer

that has a moist cloth over the glass bulb The wet-bulb temperature is

reached when the air temperature is high enough to evaporate the water from the cloth

A simpler way to think of it The temperature you feel when

your arm is exposed to moving air

Can also be measured by a psychrometer

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Pressure

Units Hectopascals (hPa) Millibars (mb) Inches of mercury (inHg)

Why is pressure important? Low pressure systems

indicate cooler or stormy weather

High pressure systems indicate warmer or drier weather

Measured by a barometer

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Wind Speed and Direction Wind speed is measured by an anemometer

Weather vanes and wind socks tells us wind direction

www.greensvanes.co.uk

www.sportys.com

www.bom.gov.au

Air Pollution The concentration of pollutants can be

measured by an aerosol monitor

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blog.lib.umn.edu

www.industrysearch.com.au

Heat Index The “apparent temperature”

How hot it really feels when relative humidity is taken into account with air temperature

Wind Chill

A description of “coldness” The discomfort

or danger resulting from wind and air temperature

Values found by calculation

Radiosonde A balloon-borne instrument platform

that transmitts its observations via radio Radio – radio transmitter Sonde – messenger in Old English

What does it measure? Air Temperature Pressure Humidity Wind Speed (indirectly)

It reaches a height of ~30km and at that height the balloon swells to a 30 foot diameter!

www.ucar.edu

Radiosonde Instrumentation

Thermistor (Temperature) Hygristor (Humidity)

Can be used to find dew point Aneroid Barometer

(Pressure) Can be used to detect

different atmospheric layers Radio Transmitter & GPS Balloon & Parachute

Radiosondes cost approximately $300 and most of the time the instruments are never found

artemis.rsmas.miami.edu

www.plymouth.edu

Sounding Diagramrap.ucar.edu

Main Cloud Name Elements Alto

High Cirrus

Thin and wispy

Cumulus Fluffy

Nimbus Raincloud

Stratus Layer or

spread-out

Low-Level Clouds (~5,000 ft) Stratus

Form in low horizontal layers having a frayed or uniform base

Stratocumulus Puffy clouds that form following a cold front Can produce light rain

www.colby.edu

Stratus

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Stratocumulus

Low-Level to Mid-Level Clouds Cumulus

Fair weather clouds, fluffy From below ~6,500 ft to ~10,000 ft

Nimbostratus Constant precipitation and low visibility Above ~6,500 ft

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Cumulus

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Nimbostratus

Mid-Level Clouds (~15,000 ft) Altostratus

Occurs when a when an air mass is lifted to the point where it condenses

Usually produces rain or snow Altocumulus

Formed by mid-level convective instability

Altostratus

www.victoriaweather.ca

Altocumulus

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High-Level Clouds Cirrostratus

Occurs when moist air cools to saturation at a high altitude

Made of ice crystals Cirrocumulus

Same as cirrostratus, but has convective instability

Cirrus Happens at the highest

part of the tropopause Usually means a storm is

approaching

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Cirrostratus

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Cirrocumulus

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Cirrus

Vertically Developed Clouds Cumulonimbus

Develop from cumulus when the air mass is highly unstable

Usually forms thunderstorms

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Cumulonimbus

Aerosol Clouds Nacreous Clouds

Also known as “Mother of Pearl” Clouds

Made of sulfuric acid (H2SO4) drops

Formed in the stratosphere

Noctilucent Clouds Glows at night, observed as

waves Made of parts of meteorites Formed in the mesosphere

www.sflorg.com Nacreous

Clouds

Noctilucent Clouds

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Station Observation Maps Surface observation map

http://aos.wisc.edu/weather/wx_obs/Surface.html Flash animation

http://www.rap.ucar.edu/weather/surface/displaySfc.php?region=cod&endDate=20110123&endTime=-1&duration=24

Station Observations

Air Temperature

Dew Point Temperature

Current Weather

Cloud Cover

Pressure

Wind Speed & Direction

• Cloud Cover: 75% Cloud Coverage - Broken• Pressure: 1002.7 mb• Wind Speed: 15 Knots (~7.5 m/s)• Wind Direction: Out of the South-East (Northwestward)

• Temperature: 64 °F• Dew Point: 58 °F• Current Weather: Thin Fog

Most scientists measure temperature (T) in Celsius (°C) or Kelvin (K)

Temperature

Current Weather

Cloud Cover

Pressure If less than 500

Place 10 on the left and divide by 10 Examples

027 becomes 1002.7 mb 184 becomes 1018.4 mb

If greater than 500 Place 9 on the left and divide by 10 Examples

867 becomes 986.7 mb 642 becomes 964.2 mb

Wind Speed & Direction Wind direction points in the direction that the

wind is coming from (Ex: out of the SE)

• 1 knot = 1.151 mph• 1 knot = 0.514 m/s

Practice Online Examples

Example 1 Example 2 Example 3 Example 4 Example 5

In-class Examples