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Preliminary Results from the Prototype Thin-Cloud Rotating Shadowband Radiometer

Motor. Motor. MFRSR Head. 1 broadband channel, 6 narrow channels 415, 500, 610, 670, 870 & 940nm. Preliminary Results from the Prototype Thin-Cloud Rotating Shadowband Radiometer. M.J. Bartholomew*, R.M. Reynolds + , A. Vogelmann*, R. Edwards, S. Smith*, and Q.-L. Min^

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Preliminary Results from the Prototype Thin-Cloud Rotating Shadowband Radiometer

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  1. Motor Motor MFRSR Head 1 broadband channel, 6 narrow channels 415, 500, 610, 670, 870 & 940nm Preliminary Results from the Prototype Thin-Cloud Rotating Shadowband Radiometer M.J. Bartholomew*, R.M. Reynolds+, A. Vogelmann*, R. Edwards, S. Smith*, and Q.-L. Min^ *Brookhaven National Laboratory, Upton, NY + Remote Measurements and Research Company, Seattle, WA ^State University of New York, Albany 2. Design 1. Background and Theory Thin clouds prevalent and accuracies are low for their liquid water path (LWP), effective radius (Reff) and cloud optical depth (COD) - At SGP 50% of clouds have LWP less than 100gm-2, mode 40gm-2 - current microwave radiometer LWP retrieval accuracy, +- 20gm-2 - Marchland et al., 2003 Surface irradiance calculations, Figure 1, suggest that a LWP uncertainty of 20gm-2 causes an error of greater than 100W/m2 in total hemispheric irradiance for an atmosphere with a 1 km thick cloud layer (45 degree incidence angle) with 40gm-2 (Min and Duan, 2005) Observations of solar aureole, Figures 2a and b, may lead to simultaneous retrievals of LWP, Reff, and COD with the following expected accuracies LWP, 2gm-2 Reff, 10% COD, 2% - Min and Duan, 2005 Requires a scanning resolution of 1 degree +-15 degrees of the sun 25cm R 10cm R Figure 1 Figure 2a On roof of Radiometer Calibration Facility at SGP, 1/2008 Image courtesy of Dan Nelson Testing at BNL 3. Some Preliminary Observations Figure 2b Total Hemispheric Irradiance Observed Partially Occulted Irradiance References Marchland, R., T. P. Ackerman, E. R. Westwater, S. A. Clough, K. Cady-Periera, and J. C. Liljegren, 2003: An assessment of microwave absorption models and retrievals of cloud liquid water using clear-sky data, J. Geophys. Res, 108(D24), 4773, doi:10.1029/2003JD003843. Min, Q.-L., and M. Duan , 2005: Simultaneously retrieving cloud optical depth and effective radius for optically thin clouds, J. Geophys. Res., 110(D21201), doi:10.1029/2005JD006136. Solar Aureole = Total Hemispheric Irradiance – Observed Partially Occulted Irradiance Solar Aureole Thin Cloud Thick Cloud Future Plans- Complete installation at SGP, make observations there and carry out intercomparisons with other ARM instruments. Acknowledgements- This project received ACRF funding and help from the ARM Operations staff at SGP. We wish to extend a special thank you to SGP Operations staff members Dan Nelson, Craig Webb and Rod Soper RMRC0 Remote Measurements & Research

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