Profiling the Atmosphere Part 1.

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Every day, atmospheric balloons (often referred to as “soundings”) are launched all over the world to help determine the state of the atmosphere and to provide forecast models with much needed data.  For simplistic sake, you can think of these as large and expensive pibals.  Worldwide, there are nearly 900 sites which sample the atmosphere regularly.  A network of sites which launch balloons are scattered across the United States, separated by approximately 300 miles. In the continental US, 69 National Weather Service Offices launch these balloons a minimum of twice a day. A few offices in the Midwest that makes these launches include La Crosse WI, Davenport IA, Minneapolis MN, Omaha NE and Aberdeen, SD. Each balloon costs nearly 300.00 to launch, which is why there are specified locations which perform these launches. 

           

Balloon launches across the United States are performed at as close to the same time as possible, to provide an accurate picture of the atmosphere at a specific across the United States.  Each balloon is made out of a stretchy latex material, and is most generally filled with hydrogen.  Initially, the balloon that is launched is nearly six feet in diameter, but by the time the balloon bursts, the atmospheric pressure around the balloon has reduced significantly so that the balloon has expanded to a size of approximately thirty feet in diameter. 

           

During the balloons flight, three main types of weather observations are made directly by an instrument pack (called a “rawindsonde”) carried by the balloon. These observations are then transmitted back to the launch site in nearly real time.  Ten observations per minute are made of pressure, temperature and relative humidity.  Wind information is also computed using a simple geometry.  A satellite dish is used to track the radio signal from the rawindsonde, and using the position of the balloon, an accurate wind speed and direction can be computed. 

           

Each balloon ascends at a rate of around 1000 feet per minute, and rises to a height around 100,000 feet before bursting.  At this height, the balloon has traversed the entire depth of the troposphere, and has generally sailed into part of the mesosphere (where the temperature increases with height).  When the balloon bursts, the rawindsonde falls back to the earth slowly with the help of a parachute.  During a flight, radiosondes can drift more than 125 miles from the original launch site.  A mailbag also accompanies the rawindsonde in case it is recovered after a flight.  The rawindsonde may then be able to be sent in for reconditioning, and then used again on a future flight.  

           

By now, you may be wondering what type of information can be obtained, especially at that kind of price tag.  The rawindsonde may be the single most important meteorological tool available, and can be used for many purposes including aviation and for verification of satellite observations.  For example, one of the most important pieces of information is a temperature profile of the entire troposphere (where most to all of the weather as we know it occurs).  This allows for analysis of the atmosphere that helps determine the stability of the various layers and the depth and strength of an inversion to name just a few.  Wind information (both speed and direction) can be helpful in determining the location of the jet stream and in determining storm motion prior to the storm formation.  Moisture information for a large depth of the troposphere is also recorded, which along with the wind data and temperature data, can be helpful in determining the type of storms that would occur if they were to form.

           

 

In the next article, we will begin to learn how to read and interpret the data from a sounding.

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