  In the theory of protoplanetary disk turbulence, a widely adopted
\emph{ansatz}, or assumption, is that the turnover frequency of the largest
turbulent eddy, $\Omega_L$, is the local Keplerian frequency $\Omega_K$. In
terms of the standard dimensionless Shakura-Sunyaev $\alpha$ parameter that
quantifies turbulent viscosity or diffusivity, this assumption leads to
characteristic length and velocity scales given respectively by
$\sqrt{\alpha}H$ and $\sqrt{\alpha}c$, in which $H$ and $c$ are the local gas
scale height and sound speed. However, this assumption is not applicable in
cases when turbulence is forced numerically or driven by some natural processes
such as Vertical Shear Instability. Here we explore the more general case where
$\Omega_L\ge\Omega_K$ and show that under these conditions, the characteristic
length and velocity scales are respectively $\sqrt{\alpha/R'}H$ and
$\sqrt{\alpha R'}c$, where $R'\equiv \Omega_L/\Omega_K$ is twice the Rossby
number. It follows that $\alpha=\alphat/R'$, where $\sqrt{\alphat} c$ is the
root-mean-square average of the turbulent velocities. Properly allowing for
this effect naturally explains the reduced particle scale heights produced in
shearing box simulations of particles in forced turbulence, and may help with
interpreting recent edge-on disk observations; more general implications for
observations are also presented. For $R'>1$ the effective particle Stokes
numbers are increased, which has implications for particle collision dynamics
and growth, as well as for planetesimal formation.
