Meteorology 1

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9 Terms

1
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Properties of the atmosphere

  • Composed primarily of

    • Nitrogen

    • Oxygen

  • Divided into multiple layers

    • Weather mostly occurs in lowest layer - Troposphere

  • Troposphere varies in height from equator to poles

    • Average height over Europe ~35,000ft

  • Temperature

    • Measures kinetic energy of molecules

  • Density

    • Measures how much mass is in a unit volume

  • Pressure

    • The force applied to a unit area of a surface

  • Related by ideal gas equation of state: P= ρRT

P - Pressure (Pa)

ρ - Density (kgm-3)

R - 287Jkg-1K-1

T - Temperature (K)

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International Standard Atmosphere (ISA)

  • At Sea Level

    • Temperature: 15°C

    • Pressure: 1013.25hPa

    • Density: 1.225kgm-3

  • Height of Troposphere: 12km (~40kft)

  • Within Troposphere

    • Temperature reduces by 6.5°C per kilometre of altitude (~2°C per 1000ft)

    • Pressure reduction is complex

      • At low altitudes approximately linear

      • ~1hPa reduction for every 27ft of altitude

    • Density calculated from ideal gas law

<ul><li><p>At Sea Level</p><ul><li><p>Temperature: 15°C</p></li><li><p>Pressure: 1013.25hPa</p></li><li><p>Density: 1.225kgm<sup>-3</sup></p></li></ul></li><li><p>Height of Troposphere: 12km (~40kft)</p></li><li><p>Within Troposphere</p><ul><li><p>Temperature reduces by 6.5°C per kilometre of altitude (~2°C per 1000ft)</p></li><li><p>Pressure reduction is complex</p><ul><li><p>At low altitudes approximately linear</p></li><li><p>~1hPa reduction for every 27ft of altitude</p></li></ul></li><li><p>Density calculated from ideal gas law</p></li></ul></li></ul><p></p>
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Motion of the atmosphere

  • Solar heating drives global movement of air

  • Tropics get more concentrated heating leading to increased air temperature

  • Higher temperature air is lower density leading to it rising

  • Rising air spreads out toward the poles where it cools increasing density, so it falls

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Coriolis “Force”

  • Not a real force, rather a pseudo force

  • An observer who is stationary in space sees the airflow travelling in a straight line, not acted on by any force

  • But an observer on the surface of the earth sees airflow is deflected to the right (in the norther hemisphere), which would require a force

  • Often useful to consider it as a real force

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Atmospheric circulation

  • Coriolis force disturbs the equator to polar air flow

  • Generates a number of discrete cells

  • Hadley cell

    • 0-30 degrees latitude

  • Ferrel/mid-latitude cell

    • 30-60 degrees latitude

  • Polar cell

    • 60-90 degrees latitude

<ul><li><p>Coriolis force disturbs the equator to polar air flow</p></li><li><p>Generates a number of discrete cells</p></li><li><p>Hadley cell</p><ul><li><p>0-30 degrees latitude</p></li></ul></li><li><p>Ferrel/mid-latitude cell</p><ul><li><p>30-60 degrees latitude</p></li></ul></li><li><p>Polar cell</p><ul><li><p>60-90 degrees latitude</p></li></ul></li></ul><p></p>
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Pressure systems

  • Atmosphere cells drive global weather patterns

  • At local levels weather is driven by pressure systems

  • Characterised by distribution of sea level air pressure

    • Illustrated by isobars

<ul><li><p>Atmosphere cells drive global weather patterns</p></li><li><p>At local levels weather is driven by pressure systems</p></li><li><p>Characterised by distribution of sea level air pressure</p><ul><li><p>Illustrated by isobars</p></li></ul></li></ul><p></p>
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Simple high pressure system

  • Air naturally wants to flow from high pressure to low pressure

  • Without Coriolis force

    • Air flows out radially

  • With Coriolis force

    • Air tends to follow circular path

  • In general airflow is parallel to the isobars

    • Geostrophic wind

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Buys Ballot Law

In norther hemisphere, standing with your back to the wind the Low pressure will be on your Left side. High pressure will be on your Right

<p>In norther hemisphere, standing with your back to the wind the <span style="color: red;"><strong>L</strong></span>ow pressure will be on your <span style="color: red;"><strong>L</strong></span>eft side. High pressure will be on your Right</p>
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Pressure gradient

  • Spacing of isobars illustrates the pressure gradient

  • Close spacing = Steep gradient

  • Steep gradient = Stronger wind

  • Large spacing = Shallow gradient

  • Shallow gradient = Calmer wind

<ul><li><p>Spacing of isobars illustrates the pressure gradient</p></li><li><p>Close spacing = Steep gradient</p></li><li><p>Steep gradient = Stronger wind</p></li><li><p>Large spacing = Shallow gradient</p></li><li><p>Shallow gradient = Calmer wind</p></li></ul><p></p>