Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 6 2006 10.5194/acpd-6-12701-2006 http://www.atmos-chem-phys-discuss.net/6/12701/2006/ http://www.atmos-chem-phys-discuss.net/6/12701/2006/acpd-6-12701-2006.html http://www.atmos-chem-phys-discuss.net/6/12701/2006/acpd-6-12701-2006.pdf 12701 12728 2006-12-06 3-D polarised simulations of space-borne passive mm/sub-mm midlatitude cirrus observations: a case study C. P. Davis cdavis@staffmail.ed.ac.uk K. F. Evans S. A. Buehler D. L. Wu H. C. Pumphrey Institute of Atmospheric and Environmental Science, University of Edinburgh, UK Dept. of Atmosphere and oceanic Sciences, University of Colorado, USA Department of Space Science, Lulea Technical University, Kiruna, Sweden Jet Propulsion Laboratory, California Institute of Technology, USA Global observations of ice clouds are needed to improve our understanding of their impact on earth's radiation balance and the water-cycle. Passive mm/sub-mm has some advantages compared to other space-borne cloud-ice remote sensing techniques. This paper presents detailed simulated observations for three such instruments, AMSU-B, CIWSIR, and EOS-MLS. The Monte-Carlo radiative transfer code, ARTS-MC, makes proper account of polarisation and uses 3-D spherical geometry. The actual field of view characteristics for each instrument are also accounted for. A 3-D midlatitude cirrus scenario is used, which is derived from Chilbolton cloud radar data and a stochastic method for generating 3-D ice water content fields. Although the main purpose of the work was to demonstrate the capability of accurately simulating observations of this type, the results suggest that cloud inhomogeneity will affect CIWSIR, and EOSMLS low tangent height observations via the beamfilling effect. Also, the results confirm that preferentially oriented ice crystals will produce significant polarisation effects. Davis, C., Emde, C., and Harwood, R.: A 3D Polarized Reversed Monte Carlo Radiative Transfer Model for mm and sub-mm Passive Remote Sensing in Cloudy Atmospheres, IEEE Trans. Geosci. Remote Sensing, 43, 1096–1101, 2005a. Davis, C P., Wu, D L., Emde, C., Jiang, J H., Cofield, R E., and Harwood, R S.: Cirrus Induced Polarization in 122 GHz Aura Microwave Limb Sounder Radiances, Geophys. Res. Lett, 32, L14806, doi:10.1029/2005GL022681, 2005b. Hogan, R J. and Kew, S F.: A 3D stochastic cloud model for investigating the radiative properties of inhomogeneous cirrus clouds, Q. J. R. Meteorol. Soc., 131, 2585–2608, 2005. Houghton, J., Ding, Y., Griggs, D., Noguer, M., van~der Linden, P., Dai, X., Maskell, K., and Johnson, C. A. (Eds.): IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, 2001. Kummerow, C.: Beamfilling Errors in Passive Microwave Rainfall Retrievals, J. Appl. Meteorol., 37, 356–370, 1998. Lafont, D. and Guillimet, B.: Subpixel fractional cloud cover and inhomogenety effects in microwave beam filling error, Atmos. Res., 72, 149–168, 2004. Lynch, D., Sassen, K., Starr, D O., and Stephens, G.: Cirrus, Oxford University Press, 2002. McCollum, J. and Krajewski, W.: Investigations of error sources of the Global Precipitation Climatology Project emission algorithm, J. Geophys. Res., 103, 28 711–28 719, 1998. McFarquhar, G. and Heymsfield, A.: Parametrization of tropical ice crystal size distributions and implications for radiative transfer: Results from CEPEX, J. Atmos. Sci., 54, 2187–2200, 1997. Mishchenko, M.: Calculation of the amplitude matrix for a nonspherical particle in a fixed orientation, Appl. Opt., 39, 1026–1031, 2000. Mishchenko, M. and Travis, L.: Capabilities and limitations of a current FORTRAN implementation of the T-matrix method for randomly oriented, rotationally symmetric scatterers, J. Quant. Spectrosc. Radiat. Transfer, 60, 309–324, 1998. Wilheit, T., Chang, A., Rao, M., Rodgers, E., and Theon, J.: A satellite technique for quantitatively mapping rainfall rates oer the oceans, J. Appl. Meteorol., 16, 551–560, 1977.