Doppler Weather Radar Research and Development
Other Agency – Enhancement of Radar Retrievals by Use of Higher Moments of the Drop Size Distribution
Funding Agency: U.S. DOE
Objectives
Improve retrievals of cloud and drizzle parameters using information from
Doppler radar.
Accomplishments
Errors of cloud property retrieval formulations based on radar reflectivity,
mean Doppler velocity, and Doppler spectrum width are evaluated under
the controlled framework of the Observing System Simulation Experiments
(OSSEs). Cloud radar parameters are obtained from drop size distributions
generated by the high-resolution CIMMS LES model with explicit microphysics.
We show that in drizzling stratocumulus the accuracy of cloud liquid
water (Ql) retrieval can be substantially increased when information
on Doppler velocity or Doppler spectrum width is included in addition
to radar reflectivity. In the moderate drizzle case (drizzle rate R
of about 1 mm d-1) the mean and standard deviation of errors is of
the order of 10% for Ql values larger than 0.2 g m-3; in stratocumulus
with heavy drizzle (R > 2 mm d-1) these values are approximately
20-30%. Similarly, employing Doppler radar parameters significantly
improves the accuracy of drizzle flux retrieval. The use of Doppler
spectrum width instead of Doppler velocity yields about the same accuracy,
thus demonstrating that both Doppler parameters have approximately
the same potential for improving microphysical retrievals. We note
that our error estimates represent the theoretical lower bound on retrieval
errors, because the actual errors will inevitably increase, first and
foremost, due to uncertainties in estimation contributions from air
turbulence.
This project is completed.
Publications
Kogan, Y. L., Z. N. Kogan, and D. B. Mechem, 2007: Assessing the errors
of microphysical retrievals based on Doppler radar parameters. J.
Hydrometeor.,
GEWEX Special Issue, in press.
Kogan, Y. L., Z. N. Kogan, and D. B. Mechem, 2006: Sensitivity of the retrieval of stratocumulus cloud liquid water and precipitation flux to Doppler radar parameters. 12th Conf. on Cloud Physics, Madison, WI, Amer. Meteor. Soc., CD-ROM P1.17.
The errors of drizzle flux retrieval for the heavy drizzle case. The black and white lines are the one (1P) and twoparameter (2P) retrieval mean errors; the shading areas represent the mean plus/minus one standard deviation. Light/dark gray shading corresponds to the 1P and 2P retrievals, respectively.