Evaluation of
Microphysical Parameterizations
Investigators:
J. M. Straka, M. S. Gilmore, K. Kanak, and E. N. Rasmussen
Equations that will represent the
Gamma drop spectrum distribution changes more physically are being
derived, by allowing certain parameters to vary which have formerly
been assumed to be constant. We are working on a set of equations
and their theoretical solutions that will allow the distribution
spectrum to vary with diffusional (e.g., evaporation/condensation),
collection and other growth processes in a more realistic manner.
We will also develop discretized forms of these equations to be
incorporated in numerical models.
The equations that represent two microphysical processes, for which
total number concentration (Nt) should be conserved, are integrated
over sizes of hydrometeor diameters (D) for one- and two moment
methods. The gamma distribution function is assumed and incorporates
total mixing ratio q, Nt, and mean diameter, Dn,
(inverse of the
distribution slope λ). In all of the methods, the slope intercept (no),
is diagnosed or specified but not predicted. The moment methods
explored include:
• The one-moment method where q is predicted, no is specified, and Nt
and Dn are diagnosed,
• The one-moment method where q is predicted, Dn is specified, and Nt
and no are diagnosed,
• The two-moment method where q and Nt are predicted, and no and Dn are
diagnosed, and
• The two-moment method where q and Dn are predicted, and Nt and no are
diagnosed.
To more easily discern the strengths and weaknesses of each
moment-method, two processes are considered: vapor diffusional growth
and continuous collection growth, and in both cases there is no
introduction of new particles (dNt/Dt = 0). It is demonstrated for the
processes examined that all of the schemes fail to conserve Nt and have
other unphysical attributes, except the two-moment method where q and
Nt are predicted.
Publications on this topic:
- Straka, J. M., K. M. Kanak, and M. S. Gilmore: 2007:
The behavior of number concentration tendencies for conservative
microphysical growth equations using bulk one-, and two-, moment
schemes. J.
Appl. Meteor. and Climatology, 46, 1264-1274.
- Straka, J. M., M. S. Gilmore, K. M. Kanak and E. N Rasmussen,
2005: A comparison of the conservation of number concentration for the
continuous collection and vapor diffusion growth equations using one-
and two- moment schemes. J.
Appl. Meteor., 44, 1844-1849.
- Straka, J. M., K. M. Kanak, and M. S. Gilmore: 2006:
The behavior of number concentration tendencies for conservative
microphysical growth equations using bulk one-, and two-, moment
schemes. 12th Conference
on Cloud Physics, 10-14 July, Madison, WI, AMS.
- Straka, J. M. , M. S. Gilmore, E. N. Rasmussen, and K. M.
Kanak, 2004: A Comparison of conservation properties of
microphysical parameterizations: continuous gamma distribution function
with fixed shape parameter. Preprints,
Fourteenth International Conference on Clouds and Precipitation,
July 19-23, Bologna, Italy.
This research is supported by the
National Science Foundation (NSF) Grants
ATM-0340639, ATM-0339519, ATM-9986672, ATM- 0003869, and ATM-0119398.
Partial funding for this research was provided by the National Severe
Storms Laboratory under NOAA–OU Cooperative Agreement NA17RJ1227. K.
Kanak is supported by the Cooperative Institute for Mesoscale
Meteorological Studies (CIMMS) under Award NA17RJ1227 from the NOAA,
U.S. Department of Commerce, and NSF ATM-0135510.
Return to K. Kanak home page
Return to J. Straka home page
Any opinions, findings, and
conclusions or recommendations expressed in this material are those of
the author(s)
and do not necessarily reflect the views of the National Science
Foundation.