Wind Tunnel Evaluation of PAM II Pressure Ports

Abstract

The Portable Automated Mesonet II (PAM II) is a network of automated remote weather stations developed by the National Center for Atmospheric Research (NCAR) for measuring wind speed and direction, atmospheric pressure, temperature, humidity, and precipitation. The atmospheric pressure is measured with a pressure transducer connected to the central opening of a round disk?the pressure port. Wind tunnel tests were conducted to determine wind effects an the atmospheric pressure measured with this port. Three port designs were tested in the wind tunnel and their performances were compared. It was found that the two with symmetric edges performed the best at high wind speeds. The expected pressure errors were evaluated for normal PAM II operation and were generally found to be less than the rms error in the pressure transducers. For special circumstances where these pressure errors cannot be neglected, the wind tunnel data and the procedures discussed here can be used to make appropriate corrections if the horizontal and vertical components of the wind velocity at the height of the pressure port are measured. Results of this study should be of value to those who intend to use PAM II or other systems to make measurements in severe storms such as tornadoes, hurricanes, downbursts, or mountain downslope winds.