INSTRUCTIONS ON HOW TO ANALYZE THE PIBAL LAB DATA

• Strip Chart Interpretation
• Wind Calculations

Strip Chart Interpretation

Refer to the diagram to the right for how to interpret the strip chart.

• The horizontal axis is temperature.  Each major line (1 cm) is equal to 5 degrees Celsius.
• The vertical axis is time or height.  Each major line (also 1 cm) is equal to 30 seconds of time.  Assuming an ascent rate of 600 feet per minute, then each major line is also 300 feet.
• T₀ is the initial temperature at the time and place the pibal was launched.  The temperature scale is then set relative to the value of T₀ .

Wind Calculations

•  To calculate the horizontal winds, the three-dimensional position of the balloon must be known at given times. 
• The vertical height of the balloon is known relative to the launch time since this particular size of pibal ascends at 600 feet per minute.
• The horizontal positions of the balloon can be found through trigonometry.  Refer to the diagram to the below.

• The above diagram assumes that the azimuth and elevation angles are in meteorological coordinates.  Make sure your angles are also in meteorological coordinates.
• Once U,V are known at a given level, then compute the wind speed and direction.  Remember that the wind speed will be in feet per second.
• In meteorological coordinates, the wind direction can be found using

  DIR = 57.2957795*ARCTAN(U/V)+180.