Mesoscale & Microscale Meteorology Division Science Plan:
2.3 Fundamental Research on Precipitation Processes, with an Emphasis on their Improved Representation in Numerical Models
Goal: To understand the microphysical development of precipitation in cloud, including ice and liquid phases and their interactions, and to determine improved methods of representing precipitation formation in very high resolution numerical models.
It is well known that the structure and evolution of precipitating weather systems depend strongly on the microphysics and, in particular, on the conversion of water to ice and vice versa. Such microphysical processes affect the dynamics of systems through their influence on the strength of updrafts, downdrafts, and cold outflows; they also directly affect important forecast parameters such as precipitation type and amount. Quantitative precipitation forecasts, which are a critical societal requirement, are highly sensitive to these microphysical properties and processes. Despite this, precipitation formation processes are currently not adequately represented in both weather and climate models. Especially uncertain is the treatment of water and ice phases and precipitation development. Physically based improvements to the model physics must be developed, particularly for the ice formation that accounts for much of the deficiency.
As the dynamic representation of convection in models improves through higher
resolution and improved parameterizations, uncertainties in the microphysical
processes will become an increasingly crucial hurdle to improving quantitative
precipitation forecasts. Further, detailed understanding of cloud physics
are of importance to understanding the contributions of the radiative and
other properties of clouds to global climate.
A comprehensive study of microphysical processes within precipitation systems,
ranging from tropical cyclonic systems, to mid-latitude mesoscale convective
systems, to wintertime snowstorms, will be conducted. This study will use
data gathered from a number of field campaigns involving aircraft and multi-parameter
radar observations. A particular focus will be improved understanding of
heterogeneous ice nucleation, which is a serious current deficiency and characterizing
primary and secondary ice formation processes in layer and convective clouds.
Of specific interest and needs are the role and potential use of cloud condensation
nuclei in forecast applications, and better understanding of the factors
that control downdraft and outflow characteristics. These efforts will be
conducted in cooperation with EOL and RAL to enable development of new observing
capabilities and field campaigns. In particular, NCAR’s new HIAPER
platform will be extremely important in providing in-situ measurements in
cirrus and as a long range remote sensing platform.
In December 2004 and January 2005 MMM scientists participated in the Rain
in Cumulus over the Ocean (RICO) program. RICO focused on shallow maritime
cumulus convection over the tropical oceans and included processes occurring
on the broad range of scales characteristic of this regime, from the microphysical/cloud
scale to the cloud-interaction scale and the ensemble cloud field scale.
The development of warm rain, together with the related scale interactions,
will be important aspect to be pursued in the analysis of the RICO data set.
The results of this research will be incorporated into WRF and other models
to test new microphysics parameterizations and QPF forecasts. Inconsistencies
in the treatment of cloud microphysical representations will be identified
and solutions developed. Careful consideration also will be given to the
manner in which microphysics interact with other parameterized physics within
the WRF modeling system. These model improvements will benefit the academic
research and operational users of WRF.