What does the 2nd Doppler moment indicate?

The second Doppler moment is indeed associated with the variance of the Doppler spectrum, making it a vital parameter in radar meteorology. This moment provides insights into the distribution of velocity within the sampled volume of precipitation or other targets.

When a radar transmits a signal and receives the returned echoes, the variations in the frequency of these returns can indicate different velocities of particles moving within the radar beam. The first Doppler moment gives an average value of these velocities, commonly referred to as the mean radial velocity. However, the second moment captures the spread or variance of these velocities, elucidating the turbulence or the range of motions occurring within that sample area.

Thus, the second Doppler moment is particularly useful in understanding the microphysical processes within a storm or precipitation event, as it reflects how diverse the motions of hydrometeors—or any particulates—are, providing crucial information for storm interpretation and analysis.