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

ReferencesMarchland, 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.

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

Solar Aureole = Total Hemispheric Irradiance – Observed Partially Occulted Irradiance

2. Design

1. Background and Theory

3. Some Preliminary Observations

1 broadband channel, 6 narrow channels 415, 500, 610, 670, 870 & 940nm

MFRSR Head

Motor Motor

Figure 1

Figure 2a

RMRC0Remote Measurements

& Research

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., 2003Surface 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

Figure 2b

25cm R

10cm R

Testing at BNL

On roof of Radiometer Calibration Facility at SGP, 1/2008Image courtesy of Dan Nelson

Solar Aureole

Total Hemispheric Irradiance

Observed Partially Occulted Irradiance

Thick Cloud Thin Cloud