Interannual changes in mass consistent energy budgets from ERA-Interim and satellite data



[1] Diagnostic comparisons and evaluations of the global atmospheric energy and water budgets have been carried out with the new ERA-Interim reanalysis product and with satellite-derived fluxes. In the first part of this paper, we address time discretization, mass imbalance, and spin-up effects, which affect diagnostics from analysis and forecast fields in reanalysis. We discuss two ways of calculating vertically integrated horizontal energy and moisture flux divergence: (1) direct computation using analyzed fields and (2) indirectly from forecast model fluxes and vertically integrated tendencies. The spatial divergence patterns from the indirect method are found to be more realistic than those from direct computation from 6-hourly analyses since they are much less affected by temporal sampling errors, but corrections were nevertheless necessary to ensure mass consistency. The second part of this paper is focused on the interannual variability of ERA-Interim vertical fluxes and on comparisons with satellite flux data. Time series of vertically integrated energy/moisture tendencies and the corresponding analysis increments are also investigated, since shifts in these important quantities indicate artificial jumps in ERA-Interim, and relationships with vertical fluxes indicate internal consistency of the budgets. All data agree in that the most prominent changes in global budgets are internally forced (El Niño–Southern Oscillation). Broad agreement is found in ERA-Interim and Hamburg ocean atmosphere parameters and fluxes from satellite data (HOAPS-3) on a trend in the surface turbulent energy fluxes. Some of this trend may be caused by artificial shifts in ERA-Interim and especially HOAPS-3 in 1992 and possibly 2007. A strong increase in tropical land precipitation during the past decade is found in ERA-Interim and Global Precipitation Climatology Project 2. While large improvements have been made in terms of temporal homogeneity compared with ERA-40, especially with regard to precipitation, the homogeneity issue still needs to be carefully addressed when interpreting surface flux data from reanalyses or other sources.