1. Pilot Balloon Radiosonde Upper Air Measurements

2. Pilot Balloon: Pibal A pilot balloon can be tracked visually with a single theodolite that measures the azimuth, relative to True North, and the elevation angle. If the balloon ascent rate is known (assumed from balloon and gas specifications), position of the balloon can be determined and the wind velocity inferred from successive balloon positions. The procedure is to track the balloon optically with the theodolite and measure the azimuth and elevation angles at 1 min or 30 s intervals. Height, z, is determined from the known or assumed ascent rate.

3. Z S Φ θ ElevationAzimuth X Z Pilot Balloon: Single Theodolite Geometry x = S sin θ y = S cos θ z = R sin Φ s = R cos Φ Solve for x and y: X = zcot Φ sin θ Y = zcot Φ cos θ X and y define the horizontal position of the balloon relative to the theodolite, S is the distance from the theodolite to balloon, R is slant range to the balloon

4. Pilot Balloon: Single Theodolite Geometry u = (x n -x n-1 )/30 v = (y n -y n-1 )/30 For 30 s intervals Horizontal wind speed = (u 2 +v 2 ) 1/2 Wind direction is computed following Appendix E.

5. Assignment: Due Tuesday May 5: Calculate the wind profiles from the theodolite lab. Each student needs to digitize their lab book data and input the data into either Excel or a text file. Send these files to the instructor and the files will be put onto the course website. Once the profiles are calculated: Plot the profiles in two plots: 1. wind speed vs. z 2. wind direction vs. z Comment on the wind structure.

6. Radiosonde What are the advantages of a radiosonde?