David L. Mitchell

Associate Research Professor
Division of Atmospheric Sciences

Dr. Mitchell's research has focused on the following areas: (1) theoretical understanding and modeling of the microphysical evolution within cirrus and frontal clouds, especially with regard to particle size spectra and ice production; (2) understanding and modeling the radiative properties of ice clouds; (3) satellite remote sensing of cloud properties; (4) understanding and predicting the onset, strength and extent of the Mexican monsoon.

Accomplishments regarding (1) include the development of two models successfully predicting the evolution of ice particle size spectra. The input for one model consists of the ice water content and temperature profiles, while the other is driven by changes in super-saturation. These models are computationally efficient, utilizing analytical solutions for ice particle growth by vapor diffusion and aggregation.

Regarding (2), the optical properties of ice clouds have been successfully described by parameterizing the absorption and scattering processes and rigorously treating their dependence on cloud microphysics. This treatment, the Modified Anomalous Diffraction Approximation (MADA), was formulated in terms of the size distribution and ice particle shape, and agrees with explicit electrodynamic solutions of ice crystal single scattering properties within 15%. These developments, along with parameterizing the asymmetry parameter for various crystal shapes, have lead to a new treatment of ice cloud radiative properties which is used in (i) the GCM and operational forecast model at the Hadley Centre/U.K. Meteorological Office, (ii) in the new NCAR GCM (CCSM4), (iii) in the Colorado State University GCM, (iv) in the Regional Atmospheric Modeling System (RAMS) at CIRES, and (v) in the Rapid Radiation Transfer Model (RRTM) at Atmospheric and Environmental Research (AER), Inc.

Regarding (3), a new method for estimating the amount of ice contained in clouds (i.e. the ice water path, or IWP) from satellite- or ground-based platforms has been developed, based on the heat emitted by the earth at discrete wavelengths. The method considers the details of the size distribution and ice particle shape and delivers IWP estimates accurate to within ± 15%.

RESEARCH AREAS:

• Cloud Microphysics, Cloud Radiative Properties (especially ice clouds), Remote Sensing of Cloud Physical Properties, Climate Dynamics, Large-Scale and Mesoscale Dynamic Meteorology, Precipitation Scavenging .

SELECTED PUBLICATIONS:

Mitchell, D.L., A.J. Brown, W.P. Arnott, and C. Schmitt, 2006:

Testing and comparing the modified anomalous diffraction approximation. Accepted for publication in J. Atmos. Sci.

Mitchell, D.L., A. Huggins and V. Grubisic, 2006:

A new snow growth model with application to radar precipitation estimates. Atmos. Research, in press.

Mitchell, D.L. and A.J. Heymsfield, 2005:

Refinements in the treatment of ice particle terminal velocities, highlighting aggregates. J. Atmos. Sci., 62, 1637-1644.

Mitchell, D.L., R.P. d'Entremont, D.H. DeSlover, and W.P. Arnott, 2003:

Multispectral thermal retrievals of size distribution shape, effective size, ice water path, optical depth and photon tunneling contribution. 12th Conf. on Satellite Meteorology and Oceanography, AMS Annual Meeting, Long Beach , California, 9-13 Feb. 2003.

Mitchell, D.L., 2002:

Effective diameter in radiation transfer: General definition, applications and limitations. J. Atmos. Sci., 59, 2330-2346.

Mitchell, D.L., D. Ivanova, R. Rabin, K. Redmond, and T.J. Brown, 2002:

Gulf of California sea surface temperatures and the North American monsoon: Mechanistic implications from observations. J. Climate, 15, 2261-2281.

Ivanova , D.C. , D.L. Mitchell, W. Patrick Arnott and M. Poellot, 2001:

A GCM parameterization for bimodal size spectra and ice mass removal rates in mid-latitude cirrus clouds. Atmos. Res., 59, 89-113.

Mitchell, D.L., 2000:

Parameterization of the Mie extinction and absorption coefficients for water clouds. J. Atmos. Sci., 57, 1311-1326.

Mitchell, D.L., 1996:

Use of mass- and area-dimensional power laws for determining precipitation particle terminal velocities. J. Atmos. Sci., 53, 1710-1723.

Mitchell, D.L., A. Macke, and Y. Liu, 1996:

Modeling cirrus clouds. Part II: Treatment of radiative properties. J. Atmos. Sci., 53, 2967-2988.

Mitchell, D.L., 1994:

A model predicting the evolution of ice particle size spectra and the radiative properties of cirrus clouds. Part I: Microphysics. J. Atmos. Sci., 51, 797-816.

Mitchell, D.L. and W.P. Arnott, 1994:

A model predicting the evolution of ice particle size spectra and the radiative properties of cirrus clouds. Part II: Dependence of absorption and extinction on ice crystal morphology. J. Atmos. Sci., 51, 817-832.