How Do We Measure and Describe Weather?

Despite the weather reporter's sentiments in the clip above, most of us would agree that Milwaukee's weather is the best in the country.  Regardless, her description of the weather as "sucking" leaves something to be desired for us as Earth Scientists.  In this unit we we go into the complicated symphony of variables that come together to create the experience we call weather.  By the end of this unit you will be able to take simple measurements to give a much better report than the one above.

What is Weather?

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WEATHER IS THE CONDITION OF THE ATMOSPHERE AT ONE LOCATION, AT ONE MOMENT IN TIME.

As we know weather is extremely fickle, varying a great deal from place to place and minute to minute.  What we experience as weather is the result of interactions between dozens of different variables, each of which we can measure and describe.

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Weather Variables and Instruments:

  • Temperature - measured with a thermometer
  • Humidity - measured with a psychrometer
  • Air pressure - measured with a barometerWind speed - measured with a anerometer
  • Wind direction - measured with a wind vein
  • Precipitation - measured with a ain guage, ruler
  • Dew Point  - measured with a  psychrometer
  • Visibility - miles
  • Cloud cover

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CLIMATE:

CLIMATE IS A DESCRIPTION OF THE AVERAGE WEATHER CONDITIONS FOR A REGION OVER A PERIOD OF DECADES

In contrast to weather,  climate covers a much larger area and a much longer period of time.  It is slower to change, and plays a larger role in effecting life on Earth.

 

THE ATMOSPHERE

THE ATMOSPHERE IS A THIN LAYER OF GASSES SURROUNDING THE EARTH STRETCHING ABOUT 300 KM ABOVE THE EARTH'S SURFACE.

AIR IS A MIXTURE OF GASSES

  • Nitrogen 78%
  • Oxygen 21%
  • The remaining 1% is a mix of lots of stuff but mostly CO2 and Argon.

As you go higher up in the atmosphere the air thins, or becomes less dense but the composition remains the same.  About 99% of the atmosphere’s weight is concentrated within 32 km of the Earth’s surface, so almost the whole thing is in the troposphere.

THE LAYERS OF THE ATMOSPHERE

TROPOSPHERE

  • THE BOTTOM LAYER OF THE ATMOSPHERE
  • 99% OF ALL OF THE AIR IS IN THE TROPOSPHERE
  • THIS LAYER CONTAINS ALL OF THE WATER VAPOR
  • THIS LAYER CONTAINS ALL OF THE WEATHER
  • TEMPERATURE DECREASES WITH ALTITUDE
  • The top of the troposphere is called the tropopause.

Within the Troposphere three important trends exist in relation to altitude:

  1. As altitude increases temperature decreases
  2. As altitude increases air pressure decreases
  3. As altitude increases humidity decreases

STRATOSPHERE

  • SECOND LAYER OF THE ATMOSPHERE
  • THIS IS WHERE THE OZONE LAYER THAT PROTECTS US FROM UV RADIATION IS LOCATED
  • TEMPERATURE INCREASES WITH ALTITUDE
  • The top of the stratosphere is called the stratopause.

MESOSPHERE AND THERMOSPHERE

  • THE THIRD AND FOURTH LAYERS OF THE ATMOSPHERE
  • IN THE MESOSPHERE THE TEMPERATURE DECREASES WITH ALTITUDE
  • IN THE THERMOSPHERE THE TEMPERATURE INCREASES WITH ALTITUDE
  • NOTHING REALLY IMPORTANT HAPPENS HERE

EXOSPHERE

Beyond the thermosphere is the Exosphere, which is very ionized or charged, and sometimes called the ionosphere.  The ionosphere is really important for communications on Earth.  Layers of ions and electrons in the ionosphere reflect radio waves.  Radio waves travel in straight lines, so they should go straight out into space, but because the ionosphere reflects them they get bounced back towards Earth.  Because the radio waves are bounced back which means radio stations can be heard over wide areas. 

 The ionosphere is also effected by solar events.  Solar flares and sun spots send massive amounts of radiation out which disrupts radio signals.  They also send out a stream of ions called the solar wind.  Because these ions are charged Earth’s magnetic field deflects the ions towards the N and S pole.  There the ions interact with the air to create auroras, which are colorful moving lights in the night sky.