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J. W. F. Goddard, S. M. Cherry, and V. N. Bringi


Dual-polarization radar measurements of ZH and ZDR, where ZDR = 10 logZH/ZV and ZH, ZV are the radar reflectivity factors for horizontal and vertical polarizations, respectively, are compared with values derived from raindrop-size distributions measured by a Joss-Waldvogel disdrometer. The measurements were made simultaneously, with the radar pulse volume situated 120 m above the ground-based disdrometer.

Despite the difference in size of the respective sampling volumes, agreement between the radar and disdrometer measurements was generally good. The radar estimates of ZH exceeded the disdrometer estimates by 1.6 dB on average, well within the expected experimental error. The disdrometer estimates of ZDR exceeded the radar estimates by 0.3 dB on average. This was somewhat larger than could be accounted for by experimental error, and further analysis suggested that some modification to the theoretical ratios of horizontal and vertical backscattering cross sections was required, for drops of diameter <2.5 mm. An empirical modification to these ratios enabled the difference to be reduced to 0.15 dB on average.

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Continuous Evaluation of Cloud Profiles in Seven Operational Models Using Ground-Based Observations

A. J. Illingworth, R. J. Hogan, E.J. O'Connor, D. Bouniol, M. E. Brooks, J. Delanoé, D. P. Donovan, J. D. Eastment, N. Gaussiat, J. W. F. Goddard, M. Haeffelin, H. Klein Baltink, O. A. Krasnov, J. Pelon, J.-M. Piriou, A. Protat, H. W. J. Russchenberg, A. Seifert, A. M. Tompkins, G.-J. van Zadelhoff, F. Vinit, U. Willén, D. R. Wilson, and C. L. Wrench

The Cloudnet project aims to provide a systematic evaluation of clouds in forecast and climate models by comparing the model output with continuous ground-based observations of the vertical profiles of cloud properties. In the models, the properties of clouds are simplified and expressed in terms of the fraction of the model grid box, which is filled with cloud, together with the liquid and ice water content of the clouds. These models must get the clouds right if they are to correctly represent both their radiative properties and their key role in the production of precipitation, but there are few observations of the vertical profiles of the cloud properties that show whether or not they are successful. Cloud profiles derived from cloud radars, ceilometers, and dual-frequency microwave radiometers operated at three sites in France, Netherlands, and the United Kingdom for several years have been compared with the clouds in seven European models. The advantage of this continuous appraisal is that the feedback on how new versions of models are performing is provided in quasi-real time, as opposed to the much longer time scale needed for in-depth analysis of complex field studies. Here, two occasions are identified when the introduction of new versions of the ECMWF and Météo-France models leads to an immediate improvement in the representation of the clouds and also provides statistics on the performance of the seven models. The Cloudnet analysis scheme is currently being expanded to include sites outside Europe and further operational forecasting and climate models.

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