The Spectral Dimension of Relative Humidity Feedbacks in the CMIP5 Experiments

Spectrally resolved relative humidity (RH) feedbacks for 16 GCMs that participated in the CMIP5 were derived using the spectral radiative kernel technique. Examining spectral and spatial details of these RH feedbacks leads to three findings. First, while the global average of broadband RH feedbacks are close to zero in all GCMs, there are wide discrepancies in the spectral details among the GCMs. Second, the spatial pattern of RH feedbacks varies with spectral frequency; for a given frequency, the spatial feedback pattern correlates well with the spatial pattern of RH changes at the pressure level that the top-of-atmosphere spectral flux at the same frequency is sensitive to. Third, the nearly zero broadband RH feedback is a result due to spatial and spectral compensations. The spectral RH feedbacks were further analyzed using the radiative RH kernels, in order to infer the corresponding changes of RH vertical profiles. It is demonstrated that the spectral details of RH feedbacks can provide us useful information about vertical profiles of RH changes, which cannot be provided by the broadband feedbacks.