Observations of clear air turbulence and winds with the Millstone Hill radar

Abstract

The Millstone Hill 440 MHz radar at Westford, Massachusetts, has been upgraded for studies of turbulence and winds in the troposphere and lower stratosphere. Useful data have been obtained up to 20 km altitude. The radar has been operated with a peak pulse power of 1–1.5 MW, a pulse length of 10 μs and a pulse repetition of 500 Hz. The 150‐foot diameter steerable antenna has been used differently in three types of experiments, (1) Antenna azimuth scans with fixed elevation, (2) elevation scan with fixed azimuth, and (3) fixed antenna. Azimuth scan experiments can obtain both the horizontal and the vertical wind components. Antenna elevation scans have been used to investigate the horizontal structure of turbulence. The fixed antenna experiments provide maximum time resolution and are useful for studying the occurrence of waves. Waves in both the velocity and Cn2, the refractive index turbulence structure constant, have been frequently observed at heights near the tropopause and below. The waves have periods 10–20 min and have been interpreted as internal gravity waves. The largest amplitude waves have been found to occur (1–2 km) below the level of a velocity shear. Waves generally persist for several cycles. By using the antenna elevation scan method, the level of turbulence (as measured by the Cn2 value) has been measured at points separated by 10–20 km. Horizontal patches of turbulence have been found that appear to move with the wind.