Summary of The Hypohydrostatic Rescaling and Its Impacts on Modeling of Atmospheric
Convection by Pauluis, Frierson, Garner, Held and Vallis, which appears
in Theoretical and Computational Fluid Dynamics.
Primary arguments:
- Hypohydrostatic (AKA DARE, RAVE) rescaling is not an ideal strategy for
cloud resolving modeling: a reduction of updraft speeds is unavoidable with
this scaling, which negatively affects cloud ice distributions and other
features when compared with coarse resolution simulations.
Discussion:
In this paper we evaluate the usefulness of a rescaling strategy that may
be useful for modeling convection at a lower resolution than is usually
needed. The strategy is something that Kuang, Blossey and Bretherton
came up with in a GRL paper and called DARE, for Diabatic Acceleration
and Rescaling; Olivier was working on a similar idea independently
(although Kuang et al beat us to publication by far!). Essentially the
strategy is to multiply the nonhydrostatic terms in the vertical
motion by a constant larger than one. This makes convective motions
happen on larger scales, so convection is therefore more easily resolved
in a numerical model.
However, this improvement in resolvability doesn't come
for free (surprise, surprise!). Along with the increase in scale of
convection, there's also an increase in the convective overturning time,
i.e., convection becomes more sluggish. So, it's not clear that the
strategy will actually improve simulations, as compared to low-resolution
simulations without the rescaling (Pauluis and Garner showed that coarse
resolution cloud resolving simulations can do surprisingly well).
Using high resolution cloud resolving model simulations as the "truth",
we compare coarse resolution simulations with hypohydrostatic simulations
at the same resolution. Although there are strengths and weaknesses of
each approach, the hypohydrostatic simulations perform worse than their
non-rescaled counterparts, particularly with respect to cloud ice
distributions, and vertical velocity PDFs. This work therefore suggests
that this innovative idea may not be very useful in simulating convection.
We have a companion paper to this study, Garner et al. While in
this study we focused on the pragmatic question of is the
hypohydrostatic rescaling useful for cloud resolving modeling, in the Garner
et al paper we use the hypohydrostatic rescaling as a tool for understanding
the general circulation of the atmosphere.
The figure above shows cloud ice fractions for hypohydrostatic and
coarse resolution cloud resolving model simulations, a key diagnostic
in which the coarse resolution simulations outperform the analogous
hypohydrostatic simulations.
Full citation:
Pauluis, O. M., Frierson, D. M. W., Garner, S. T., Held, I. M. and G. K.
Vallis. The Hypo-hydrostatic Rescaling and Its Impacts on Modeling of
Atmospheric Convection. Theoretical and Computational Fluid Dynamics, 20,
485-499, 2006.
The official journal link can be found here.
A PDF download of the full paper can be found here.
This download is courtesy of Springer, who owns sole rights to it.
The download is subject to copyright laws and statutes. For more
information, please visit the Springer website.
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