Which type of vortices can contribute to high spectrum width?

High spectrum width in radar meteorology is often related to the presence of small vortices. These small-scale vortices can create significant variations in the radar return signal due to their chaotic and turbulent nature. As these small vortices move through the radar volume, they cause rapid changes in the velocity of scattering particles, leading to a broader range of Doppler velocities detected by the radar. This results in a high spectrum width which is a representation of the spread of velocities in the observed precipitation or atmospheric motion.

In contrast, large vortices or organized vortices might not contribute significantly to high spectrum width because their larger, more structured flows tend to produce more uniform Doppler velocities across the radar beam. Steady-state vortices, by their nature, exhibit little change over time, which would also limit the range of velocities and thus reduce spectrum width. Therefore, it is the small vortices, with their inherent turbulence, that are primarily responsible for increasing the spectrum width measured by radar.