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Level 2a Cloudnet product:

Stratocumulus drizzle (radar/lidar method)

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Summary

Designation
drizzle
Level
2a
Algorithm design/Product maintainer
Institute
University of Reading
Description
Drizzle parameters such as drizzle flux and mean particle size, derived from combined radar and lidar beneath cloud base.
Documentation
See relevant publication
Relevant publication(s)
O'Connor, E. J., R. J. Hogan and A. J. Illingworth, 2005: Retrieving stratocumulus drizzle parameters using Doppler radar and lidar.J. Appl. Meteorol., 44(1), 14-27. PDF
Quicklooks
http://www.met.rdg.ac.uk/radar/cloudnet/quicklooks/
Suggested acknowledgement
We acknowledge the Cloudnet project (European Union contract EVK2-2000-00611) for providing the stratocumulus drizzle retrieval, which was produced by the University of Reading using measurements from [SITE].

Dataset contents

Sample NetCDF file: 20030701_chilbolton_drizzle.nc
Header of sample NetCDF file in ASCII: 20030701_chilbolton_drizzle.cdl

The following is a description of the variables in this product, produced automatically from the metadata in the sample file (using the nc2html unix utility):

Dataset title: Drizzle parameters from Chilbolton

    Institution:Data processed at the Department of Meteorology, University of Reading.
    Software version:1.2

Dimensions and coordinate variables

time
Time UTC
    Units:hours since 2003-07-01 00:00:00 +0:00
    Type:single-precision floating-point vector
height
Height above mean sea level
    Units:m
    Type:single-precision floating-point vector

Variables

latitude
Latitude of site
    Units:degrees_north
    Type:single-precision floating-point scalar
longitude
Longitude of site
    Units:degrees_east
    Type:single-precision floating-point scalar
altitude
Height of radar above mean sea level
    Units:m
    Type:single-precision floating-point scalar
radar_frequency
Radar frequency
    Units:GHz
    Type:single-precision floating-point scalar
Do(time, height)
Drizzle median diameter

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:m
    Type:single-precision floating-point array
    Variable containing the random error in Do:Do_error
    Variable containing the bias in Do:Do_bias
N(time, height)
Drizzle number concentration

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:m-4
    Type:single-precision floating-point array
    Variable containing the random error in N:N_error
mu(time, height)
Drizzle DSD shape parameter

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:
    Type:single-precision floating-point array
    Variable containing the random error in mu:mu_error
S(time, height)
Lidar backscatter-to-extinction ratio, S

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:sr
    Type:single-precision floating-point array
    Variable containing the random error in S:S_error
lwc(time, height)
Drizzle liquid water content

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:kg m-3
    Type:single-precision floating-point array
    Variable containing the random error in lwc:lwc_error
    Variable containing the bias in lwc:lwc_bias
lwf(time, height)
Drizzle liquid water flux

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:kg m-2s-1
    Type:single-precision floating-point array
    Variable containing the random error in lwf:lwf_error
    Variable containing the bias in lwf:lwf_bias
droplet_fall_velocity(time, height)
Drizzle terminal fall velocity

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:m s-1
    Type:single-precision floating-point array
    Variable containing the random error in droplet_fall_velocity:droplet_fall_velocity_error
w(time, height)
Vertical air velocity

    This variable was calculated from the 94-GHz radar reflectivity factor after correction for gaseous attenuation, the Doppler mean velocity, the Doppler spectral width after correction for turbulence using the 30-s standard deviation of the (approximately) 1-s mean radar Doppler velocities and the horizontal winds from a forecast model using the technique of Bouniol et al. (2003, Proc. 31st AMS Conf. on Radar Meteorology, Seattle), the lidar backscatter and temperature taken from a forecast model, using the technique of O'Connor et al. (2004)

    Units:m s-1
    Type:single-precision floating-point array
    Variable containing the random error in w:w_error
Do_bias
Possible bias in drizzle median diameter, one standard deviation

    This variable is an estimate of the possible systematic error (one-standard-deviation) in drizzle droplet median diameter due to the uncertainty in the calibration of the radar and lidar.

    Units:dB
    Type:single-precision floating-point scalar
Do_error(time, height)
Random error in drizzle median diameter, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in drizzle droplet median diameter due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point array
mu_error
Random error in drizzle DSD shape parameter, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in drizzle shape parameter due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point scalar
N_error(time, height)
Random error in drizzle number concentration, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in drizzle number concentration due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point array
S_error(time, height)
Random error in lidar ratio, S, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in the lidar ratio due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point array
beta_corr(time, height)

    This variable provides the attenuation correction applied to the lidar backscatter values calculated using the lidar backscatter-to-extinction ratio, S.

    Type:single-precision floating-point array
lwc_error(time, height)
Random error in drizzle liquid water content, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in drizzle liquid water content due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point array
lwf_error(time, height)
Random error in drizzle liquid water flux, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in drizzle liquid water flux due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point array
droplet_fall_velocity_error(time, height)
Random error in drizzle terminal fall velocity, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in drizzle terminal fall velocity due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point array
w_error(time, height)
Random error in vertical air velocity, one standard deviation

    This variable is an estimate of the one-standard-deviation random error in vertical air velocity due to the uncertainty of the retrieval, including the random error in the radar and lidar parameters.

    Units:dB
    Type:single-precision floating-point array
rainrate(time)
Rain rate

    Converted to rainrate from raingauge c drop counts Original comment: Converted to rainrate from raingauge c drop counts

    Units:mm h-1
    Type:single-precision floating-point vector
drizzle_retrieval_status(time, height)
Drizzle parameter retrieval status

    This variable describes whether a retrieval was performed for each pixel, and its associated quality, in the form of 6 different classes. The classes are defined in the definition and long_definition attributes. The retrieval method is only performed for precipitation below cloud base and is not possible in-cloud due to the severe attenuation of the lidar signal. The most reliable retrieval is for precipitation arising from the warm rain process (drizzle), indicated by the value 1, but can also be performed for light precipitation that may have originated from ice clouds, diagnosed by the presence of a melting layer and indicated by the value 2. The retrieval method is not applicable for precipitation within cloud, indicated by the value 3, while a value 4 indicates the presence of liquid water cloud with no precipitation. No attempt is made to retrieve drizzle parameters when rain reaches the ground; this is indicated by the value 5.

    Type:byte array
    Definition:
    • 0: No liquid present
    • 1: Reliable retrieval
    • 2: Retrieval performed for precipitation that did not arise from the warm-rain process and may be inaccurate
    • 3: Retrieval method is not applicable for precipitation within cloud
    • 4: Warm liquid water clouds present but no precipitation
    • 5: Rain present at the ground so no retrieval performed due to very uncertain attenuation in both radar and lidar

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