Relationship between refractivity turbulence intensity from MST radar observations and synoptic‐scale vorticity

Abstract

The relationship between the refractivity turbulence structure constant (C_n²) and the synoptic‐scale relative vorticity (ζ) is investigated using observations made with the VHF radar at Vandenberg Air Force Base, California, over the years 2001–2004. During November–April the frequency distributions of the correlation coefficients for C_n² and ζ, C_n² and wind speed, the turbulent kinetic energy (σ_t²) and ζ, and C_n² and σ_t², show a close relationship between C_n² and ζ. Large increases of C_n² occur at about 9–14 km during times of cyclone passages, as expected since C_n² depends strongly on static stability (in dry air), the static stability increases above the tropopause, and the height of the tropopause falls during cyclone passages. The analysis was repeated using distance from the tropopause as the vertical coordinate in order to remove this simple dependence on static stability, and it is found the strong relationship between C_n² and ζ persists in the tropopause‐relative coordinates. When the values of C_n² are averaged into bins based on ζ, the changes in ζ explain over 90% of the variance of mean C_n². A regression model for C_n² by altitude as a function of ζ is developed. The correlation patterns found at Vandenberg AFB are corroborated with the large sets of 50 MHz radar data from White Sands Missile Range, New Mexico, and the Middle and Upper Atmosphere radar near Shigaraki, Japan. Although the three sites are located at similar latitudes, they are in very different topographic and climatic regions, suggesting the results found here are fairly general for midlatitude conditions.