Level 2b Cloudnet product:

Ice water content (radar-temperature method) on ECMWF model grid

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Summary

Designation: iwc-Z-T-ecmwf-grid
Level: 2b
Algorithm design
Product maintainer
Institute: University of Reading and ECMWF
Description: This product consists of ice water content calculated from the observations on grid of the ECMWF model.
Documentation: None yet available
Relevant publication(s): Hogan, R. J., M. P. Mittermaier and A. J. Illingworth, 2004: The retrieval of ice water content from radar reflectivity factor and temperature and its use in the evaluation of a mesoscale model. Submitted to J. Appl. Meteorol., September 2004. 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 ice water content on ECMWF model grid data, which was produced by the University of Reading and ECMWF using measurements from [SITE].

Dataset contents

Sample NetCDF file: 20031001_chilbolton_iwc-Z-T-ecmwf-grid.nc
Header of sample NetCDF file in ASCII: 20031001_chilbolton_iwc-Z-T-ecmwf-grid.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: Ice water content at Chilbolton averaged to the ECMWF Integrated Forecast System (IFS) grid

This dataset contains ice water content derived using radar reflectivity and temperature, averaged on to the grid of a forecast model. It also contains the ice water content from that model, so may be used to calculate statistics quantifying the model performance.

Institution:

Software version:

Dimensions and coordinate variables

time
Hours UTC

Units:

Type:

height
Height above ground

Units:

Type:

Variables

horizontal_resolution
Horizontal resolution of model

Units:

Type:

altitude
Height of radar above mean sea level

Units:

Type:

forecast_time(time)
Time since initialization of forecast

For each profile in the file this variable contains the time elapsed since the initialization time of the forecast from which it was taken. Note that the profiles in this file may be taken from more than one forecast.

Units:

Type:

height(time, height)
Height above ground

The heights have been calculated using pressure, temperature and specific humidity.

Units:

Type:

latitude
Latitude of site

Units:

Type:

longitude
Longitude of site

Units:

Type:

iwc(time, height)
Observed mean ice water content, 1 hour sampling

This variable is the observed mean ice water content derived from radar reflectivity factor and temperature using an empirical formula derived using aircraft data, averaged onto the model grid with height, and 1 hour in time. The formula has been applied where the "categorization" data has diagnosed that the radar echo is due to ice, but note that the phase of pixels is sometimes misdiagnosed. Where microwave radiometer liquid water path was available it was used to correct the radar for liquid attenuation when liquid cloud occurred below the ice, but there is some uncertainty in this prodedure. This variable does not include ice water content retrievals in situations of uncorrected attenuation (due to liquid water clouds beneath the ice cloud but no microwave radiometer data; rain and melting ice beneath the ice cloud; attenuation due to wetting of the radome when the rain reaches the surface); ice clouds being detected only by the lidar. In these situations the ice water content will be assigned "missing_value".

Units:

^-3

Type:

iwc_adv(time, height)
Observed mean ice water content, 40 km.

This variable is the same as the observed mean ice water content, iwc, except that model winds were used to estimate the time taken to advect the cloud a distance equivalent to the model's horizontal resolution of 40 km (max 1 hour, min 10 minutes).

Units:

^-3

Type:

iwc_inc_att(time, height)
Observed mean ice water content (including attenuated profiles), 1 hour sampling

This variable is the same as the observed mean ice water content, iwc, except that profiles with uncorrected attenuation of the radar reflectivity were included (although profiles with rain at the surface were still excluded) and should therefore only be used when the effect of attenuation is being studied.

Units:

^-3

Type:

iwc_adv_inc_att(time, height)
Observed mean ice water content (including attenuated profiles), 40 km.

This variable is the same as the advected observed mean ice water content, iwc_adv, except that profiles with uncorrected attenuation of the radar reflectivity were included (although profiles with rain at the surface were still excluded) and should therefore only be used when the effect of attenuation is being studied.

Units:

^-3

Type:

iwc_inc_rain(time, height)
Observed mean ice water content (including attenuated and raining profiles), 1 hour sampling

This variable is the same as the observed mean ice water content including attenuation, iwc_inc_att, except that profiles with rain at the surface were also included. It should only be used when the effect of attenuation is being studied. Radome attenuation is a serious problem for some of these profiles.

Units:

^-3

Type:

iwc_adv_inc_rain(time, height)
Observed mean ice water content (including attenuated and raining profiles), 40 km.

This variable is the same as the advected observed mean ice water content including attenuation, iwc_adv_inc_att, except that profiles with rain at the surface were also included. It should only be used when the effect of attenuation is being studied. Radome attenuation is a serious problem for some of these profiles.

Units:

^-3

Type:

model_iwc(time, height)
Model ice water content

Units:

^-3

Type:

model_snow_iwc(time, height)
Model ice water content including snow

The ECMWF model treats ice cloud and snow separately, with snow not contributing to cloud fraction or ice water content. This variable is model ice water content but with the contribution of model snow added. See Hogan et al. (2001, J. Appl. Meteorol., 40, 513-525) for further discussion.

Units:

^-3

Type:

model_iwc_filtered(time, height)
Model ice water content with undetectable cirrus removed using best guess of radar sensitivity

This variable is model ice water content, filtered to remove ice cloud deemed to be too tenuous to be detected by the radar. The best guess of the radar sensitivity has been used, and the spread of IWC across the grid box assumed to be described by a gamma distribution (Hogan and Illingworth, 2003, J. Atmos. Sci., 60, 756-767).

Units:

^-3

Type:

model_iwc_filtered_min(time, height)
Model ice water content with undetectable cirrus removed assuming radar 3 dB less sensitive than best guess

This variable is the same as "model_iwc_filtered" except that the sensitivity of the radar is taken to be 3 dB worse. It therefore provides an approximate estimate of the uncertainty associated with the removal of undetectable ice clouds from the model.

Units:

^-3

Type:

model_iwc_filtered_max(time, height)
Model ice water content with undetectable cirrus removed assuming radar 3 dB more sensitive than best guess

This variable is the same as "model_iwc_filtered" except that the sensitivity of the radar is taken to be 3 dB better. It therefore provides an approximate estimate of the uncertainty associated with the removal of undetectable ice clouds from the model.

Units:

^-3

Type:

model_snow_iwc_filtered(time, height)
Model ice water content with snow added and undetectable cirrus removed using best guess of radar sensitivity

This variable is the same as "model_iwc_filtered" but with snow added in the same way as in "model_snow_iwc".

Units:

^-3

Type:

model_snow_iwc_filtered_min(time, height)
Model ice water content with snow added and undetectable cirrus removed assuming radar 3 dB less sensitive than best guess

This variable is the same as "model_iwc_filtered_min" but with snow added in the same way as in "model_snow_iwc".

Units:

^-3

Type:

model_snow_iwc_filtered_max(time, height)
Model ice water content with snow added and undetectable cirrus removed assuming radar 3 dB more sensitive than best guess

This variable is the same as "model_iwc_filtered_max" but with snow added in the same way as in "model_snow_iwc".

Units:

^-3

Type:

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