Level 3 Cloudnet product:

Evaluation statistics of RACMO model ice water content

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Summary

Designation: iwc-Z-T-racmo-grid-stats
Level: 3
Algorithm design/Product maintainer
Institute: University of Reading and the Royal Dutch Meteorological Institute (KNMI)
Description: This product consists of evaluation statistics for the ice water content of the KNMI Regional Atmospheric Climate Model (RACMO), including means, PDFs and skill scores.
Documentation: None yet available
Relevant publication(s): Pending
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 evaluation statistics of RACMO model ice water content, which was produced by the University of Reading and the Royal Dutch Meteorological Institute (KNMI) using measurements from [SITE].

Dataset contents

Sample NetCDF file: 200304_chilbolton_iwc-Z-T-racmo-grid-stats.nc
Header of sample NetCDF file in ASCII: 200304_chilbolton_iwc-Z-T-racmo-grid-stats.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: Evaluation of KNMI RACMO ice water content at Chilbolton during Apr 2003

This dataset contains statistics on the performance of KNMI RACMO ice water content, including means as a function of height, probability density function, skill scores and the contingency table to allow other skill scores to be calculated.

Institution:

Dimensions and coordinate variables

height
Height above ground

Units:

Type:

height_raw
Mean height of model levels above ground

Units:

Type:

height_coarse
(No coordinate variable)

iwc_bin
(No coordinate variable)

Variables

height_coarse_min(height_coarse)
Height above ground of the bottom of each range used for PDFs

Units:

Type:

height_coarse_max(height_coarse)
Height above ground of the top of each range used for PDFs

Units:

Type:

time_resolution
Temporal resolution of model

Units:

Type:

iwc_bin_min(iwc_bin)
Ice water content bin minimum

This variable provides the ice water content thresholds for the contingency tables and the skill scores, and the minimum of the bins used in the ice water content probability density functions.

Units:

^-3

Type:

iwc_bin_nominal_centre(iwc_bin)
Ice water content nominal bin centre

This variable provides the nominal centres of the bins used in the ice water content probability density functions, evenly spread in logarithmic space. It therefore does not strictly correspond to the centre of the first bin (which has a minimum at 0) or the last bin (which has a maximum at infinity).

Units:

^-3

Type:

forecast_time_min
Minimum time since forecast initialization

The hourly model forecasts evaluated in this file are from a range of different forecast lead times. This variable is the minimum forecast lead time.

Units:

Type:

forecast_time_max
Maximum time since forecast initialization

The hourly model forecasts evaluated in this file are from a range of different forecast lead times. This variable is the maximum forecast lead time.

Units:

Type:

mean_observed_iwc(height)
Mean observed ice water content

This variable is the mean ice water content versus height as determined by the radar and lidar. Only data coincident with the model were used, and measurements above any surface rain were not used due to the possibility of strong attenuation leading to an underestimate of ice water content. A missing value indicates that in this height range there were no simultaneous model and observational data.

Units:

^-3

Type:

mean_model_iwc(height)
Mean model ice water content

This variable is the mean model ice water content versus height. Only data with coincident observations were used, and data above any observed surface rain have not been used due to the possibility of bias in the observations leading to an unfair comparison. A missing value indicates that in this height range there were no simultaneous model and observational data.

Units:

^-3

Type:

mean_mod_model_iwc(height)
Mean model ice water content modified to remove undetectable cloud

This variable is the mean model ice water content versus height, after modification to remove ice clouds that are deemed to be below the radar sensitivity threshold. This was done by converting the known minimum detectable radar reflectivity as a function of height into a minimum detectable ice water content. Rather than simply setting the model ice water content to zero when the model ice water content falls below this threshold, the Hogan and Illingworth (2003, J. Atmos. Sci., 60, 756-767) formula has been used to estimate the PDF of ice water content to be expected in the model grid box. This modified ice water content is also used in the calculation of skill scores. The user is advised to compare this variable with the unmodified mean_model_iwc to see at which heights this modification has had a significant effect. Only data with coincident observations were used, and data above any observed surface rain have not been used due to the possibility of bias in the observations leading to an unfair comparison. A missing value indicates that in this height range there were no simultaneous model and observational data.

Units:

^-3

Type:

mean_observed_iwc_raw(height_raw)
Mean observed ice water content on model grid

This variable is the same as mean_observed_iwc except that it was calculated on the original model grid.

Units:

^-3

Type:

mean_model_iwc_raw(height_raw)
Mean model ice water content on model grid

This variable is the same as mean_model_iwc except that it was calculated on the original model grid.

Units:

^-3

Type:

mean_mod_model_iwc_raw(height_raw)
Mean model ice water content on model grid, modified to remove undetectable cloud

This variable is the same as mean_mod_model_iwc except that it was calculated on the original model grid.

Units:

^-3

Type:

mean_modmax_model_iwc_raw(height_raw)
Mean model ice water content on model grid, modified to remove undetectable cloud assuming radar 3 dB more sensitive than best estimate

This variable is the same as mean_mod_model_iwc_raw except that in removing undetectable cloud the radar has been assumed to be 3 dB more sensitive. In combination with mean_modmin_model_iwc_raw, this variable provides an estimate of the uncertainty in the procedure of removing undetectable clouds.

Units:

^-3

Type:

mean_modmin_model_iwc_raw(height_raw)
Mean model ice water content on model grid, modified to remove undetectable cloud assuming radar 3 dB less sensitive than best estimate

This variable is the same as mean_mod_model_iwc_raw except that in removing undetectable cloud the radar has been assumed to be 3 dB less sensitive. In combination with mean_modmax_model_iwc_raw, this variable provides an estimate of the uncertainty in the procedure of removing undetectable clouds.

Units:

^-3

Type:

mean_all_model_iwc_raw(height_raw)
Mean model ice water content on model grid, including when no observations were available due to uncorrected attenuation

This variable is the mean model ice water content for all periods that the radar was operating, including those for which no retrieval was possible due to uncorrected attenuation by rain, melting ice, and liquid cloud with unknown liquid water path. By comparison with the variable mean_model_iwc_raw, this variable indicates how much of the total ice mass for the period has not been characterised by the observations.

Units:

^-3

Type:

foo_observed_raw(height_raw, iwc_bin)
Mean observed frequency of occurrence on model grid

This variable is the mean observed frequency of occurrence of ice water contents above a range of different values, as indicated by the iwc_bin_min variable.

Units:

Type:

foo_model_raw(height_raw, iwc_bin)
Mean model frequency of occurrence on model grid

This variable is the mean model frequency of occurrence of ice water contents above a range of different values, as indicated by the iwc_bin_min variable.

Units:

Type:

foo_mod_model_raw(height_raw, iwc_bin)
Mean model frequency of occurrence on model grid, modified to remove undetectable cloud

This variable is the mean model frequency of occurrence of ice water contents above a range of different values, as indicated by the iwc_bin_min variable. The model has been modified to remove undetectable cloud, as described in the comment of the mean_mod_model_iwc variable.

Units:

Type:

foo_modmax_model_raw(height_raw, iwc_bin)
Mean model frequency of occurrence on model grid, modified to remove undetectable cloud assuming radar 3 dB more sensitive than best estimate

This variable is the same as foo_mod_model_raw except that in removing undetectable cloud the radar has been assumed to be 3 dB more sensitive. In combination with foo_modmin_model_raw, this variable provides an estimate of the uncertainty in the procedure of removing undetectable clouds.

Units:

Type:

foo_modmin_model_raw(height_raw, iwc_bin)
Mean model frequency of occurrence on model grid, modified to remove undetectable cloud assuming radar 3 dB less sensitive than best estimate

This variable is the same as foo_mod_model_raw except that in removing undetectable cloud the radar has been assumed to be 3 dB less sensitive. In combination with foo_modmax_model_raw, this variable provides an estimate of the uncertainty in the procedure of removing undetectable clouds.

Units:

Type:

foo_all_model_raw(height_raw, iwc_bin)
Mean model frequency of occurrence on model grid, including when no observations were available due to uncorrected attenuation

This variable is the mean model frequency of occurrence of ice water contents above a range of different values, as indicated by the iwc_bin_min variable. The ice water content distribution included all periods that the radar was operating, including those for which no retrieval was possible due to uncorrected attenuation by rain, melting ice, and liquid cloud with unknown liquid water path. By comparison with foo_model_raw, this variable indicates how well the radar-derived statistics represent the whole distribution of ice water content.

Units:

Type:

awp_observed_raw(height_raw, iwc_bin)
Mean observed amount when present on model grid

This variable is the mean observed ice water content when it exceeds a range of different values, as indicated by the iwc_bin_min variable.

Units:

^-3

Type:

awp_model_raw(height_raw, iwc_bin)
Mean model amount when present on model grid

This variable is the mean model ice water content when it exceeds a range of different values, as indicated by the iwc_bin_min variable.

Units:

^-3

Type:

awp_mod_model_raw(height_raw, iwc_bin)
Mean model amount when present on model grid, modified to remove undetectable cloud

This variable is the mean model ice water content when it exceeds a range of different values, as indicated by the iwc_bin_min variable. The model has been modified to remove undetectable cloud, as described in the comment of the mean_mod_model_iwc variable.

Units:

^-3

Type:

awp_modmax_model_raw(height_raw, iwc_bin)
Mean model amount when present on model grid, modified to remove undetectable cloud assuming radar 3 dB more sensitive than best estimate

This variable is the same as awp_mod_model_raw except that in removing undetectable cloud the radar has been assumed to be 3 dB more sensitive. In combination with awp_modmin_model_raw, this variable provides an estimate of the uncertainty in the procedure of removing undetectable clouds.

Units:

^-3

Type:

awp_modmin_model_raw(height_raw, iwc_bin)
Mean model amount when present on model grid, modified to remove undetectable cloud assuming radar 3 dB less sensitive than best estimate

This variable is the same as awp_mod_model_raw except that in removing undetectable cloud the radar has been assumed to be 3 dB less sensitive. In combination with awp_modmax_model_raw, this variable provides an estimate of the uncertainty in the procedure of removing undetectable clouds.

Units:

^-3

Type:

awp_all_model_raw(height_raw, iwc_bin)
Mean model amount when present on model grid, including when no observations were available due to uncorrected attenuation

This variable is the mean model ice water content when it exceeds a range of different values, as indicated by the iwc_bin_min variable. The ice water content distribution included all periods that the radar was operating, including those for which no retrieval was possible due to uncorrected attenuation by rain, melting ice, and liquid cloud with unknown liquid water path. By comparison with awp_model_raw, this variable indicates how well the radar-derived statistics represent the whole distribution of ice water content.

Units:

^-3

Type:

pdf_observed_iwc(height_coarse, iwc_bin)
PDF of observed ice water content

This variable is the probability density function of observed ice water content in four height ranges, with bin minima indicated by the iwc_bin_min variable. Only data with coincident model and observations were used, and missing values indicate height ranges where no such data were available.

Units:

Type:

pdf_model_iwc(height_coarse, iwc_bin)
PDF of model ice water content

This variable is the probability density function of model ice water content in four height ranges, with bin minima indicated by the iwc_bin_min variable. Only data with coincident model and observations were used, and missing values indicate height ranges where no such data were available.

Units:

Type:

pdf_mod_model_iwc(height_coarse, iwc_bin)
PDF of model ice water content modified to remove undetectable cloud

This variable is the same as pdf_model_iwc, except that the model data have been modified to exclude undetectable cloud, as described in the comment of the mean_mod_model_iwc variable.

Units:

Type:

pdf_all_model_iwc(height_coarse, iwc_bin)
PDF of model ice water content including when no observations were available due to uncorrected attenuation

This variable is the probability density function of model ice water content in four height ranges, with bin minima indicated by the iwc_bin_min variable. Unlike pdf_model_iwc, it includes all periods that the radar was operating, including those for which no retrieval was possible due to uncorrected attenuation by rain, melting ice, and liquid cloud with unknown liquid water path. By comparison with the pdf_model_iwc it indicates what part of the distribution of ice mass for the period has not been characterised by the observations.

Units:

Type:

num_samples(height)
Number of samples used

This variable contains the number of samples at each height used in calculating the contingency table and the skill scores. Each sample is one hour apart in the original data.

Units:

Type:

num_samples_raw(height_raw)
Number of samples used for variables on model grid

This variable contains the number of samples at each height used in calculating the contingency table and skill scores reported on the model grid. Each sample is one hour apart in the original data.

Units:

Type:

num_samples_all_raw(height_raw)
Number of samples used for mean_model_all_raw

This variable contains the number of samples at each height used in calculating the the variable mean_model_all_raw.

Units:

Type:

num_samples_coarse(height_coarse)
Number of samples used for PDFs

This variable contains the number of samples in the four coarse height ranges used in calculating the probability density functions of ice water content.

Units:

Type:

num_samples_all_coarse(height_coarse)
Number of samples used for pdf_all_model_iwc

This variable contains the number of samples in calculating the variable pdf_all_model_iwc.

Units:

Type:

A(height, iwc_bin)
Number of samples with cloud in model and observations

This variable is used with "B", "C" and "D" to calculate various skill scores. It has been calculated for the full range of ice water content thresholds (indicated by the iwc_bin_min variable). Thus for a threshold of 1e-08 kg m-3, this variable is the number of samples with ice water content greater than 1e-08 kg m-3 simultaneously in the model and the observations. Note that the modified model ice water content was used in the comparison, as described in the comment of the mean_mod_model_iwc variable. Skill scores for multiple months should be calculated by first summing the values of A, B, C and D for those months.

Units:

Type:

B(height, iwc_bin)
Number of samples with cloud in model but not observations

See the comment of the "A" variable.

Units:

Type:

C(height, iwc_bin)
Number of samples with cloud in observations but not model

See the comment of the "A" variable.

Units:

Type:

D(height, iwc_bin)
Number of samples with cloud in neither model nor observations

See the comment of the "A" variable.

Units:

Type:

ETS(height, iwc_bin)
Equitable threat score

This variable is a measure of the skill of the forecasts calculated as ETS=(A-E)/(A+B+C-E), where E is the number of hits that occurred by chance, given by E=(A+B)*(A+C)/(A+B+C+D). A perfect forecast would have an ETS of 1 and a random forecast an ETS of 0.

Units:

Type:

Q(height, iwc_bin)
Yule's Q skill score

This variable is a measure of the skill of the forecasts calculated as Q=(A*D-B*C)/(A*D+B*C). It is closely related to the odds ratio, but ranges from -1 to 1.

Units:

Type:

ETS_all(iwc_bin)
Equitable threat score for all heights

This variable is calculated from A, B, C and D at all heights.

Units:

Type:

Q_all(iwc_bin)
Yule's Q skill score for all heights

This variable is calculated from A, B, C and D at all heights.

Units:

Type:

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