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Near-surface relative humidity in CCSM4 and CESM1 models

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kimmo.ruosteeno...
Near-surface relative humidity in CCSM4 and CESM1 models
Dear colleagues Within this inquiry, we would like to obtain information about the processing of near-surface relative humidity (variable "hurs" in the monthly and "rhs" in the daily CMIP5 output) in the CCSM4, CESM1-CAM5 and CESM1-BGC models. In our study we have explored the existence of supersaturation (hurs > 100 %) in the published output files of 29 CMIP5 climate models. In the majority of the models (17 out of 29), supersaturated states occur, mainly at high latitudes in winter. Fortunately, it is likely that this is basically a diagnostic problem that does not degrade other aspects of the model output, e.g., temperature and precipitation simulations. All three models belong to the 17 models in which supersaturations occur. The problem is only moderate in CCSM4 and CESM1-BGC but quite severe in CESM1-CAM5. Our manuscript dealing with the supersaturation issue has been submitted to Journal of Geophysical Research and is under revision now. A central review comment was that we should consult the modelling groups to learn their insight on why the supersaturations occur. Accordingly, we would greatly appreciate if you would have time to respond to the following questions: (1) Are you already aware of the occurrence of the near-surface supersaturations in the output of your models? (2) Can you suggest any explanation for how the supersaturations have arisen? (3) Could you briefly explain how near-surface RH (variable "hurs"/"rhs") has been calculated in your models? Is it a prognostic model variable or only determined diagnostically in the post-processing phase? How does the algorithm creating the hurs data function? Even partial responses may help us. Sincerely Kimmo Ruosteenoja Finnish Meteorological Institute Co-authors: Kirsti Jylhä, Jouni Räisänen and Antti Mäkelä PS: Further information will be given by request. Please contact kimmo.ruosteenoja@fmi.fi.

Kimmo Ruosteenoja
Research Scientist
Finnish Meteorological Institute

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