Estimating uncertainty of reanalyses using energy budget diagnostics Michael Mayer Michael Mayer - April 2012

Aim of this work Michael Mayer - April 2012 Evaluation of climatology, anomalies and trends of the atmospheric energy budget Data: Reanalyses: ERA-Interim, MERRA, CFSR Additionally: CERES, ISCCP, GPCP Changes in the budgets: True climate signal? Changes in the observing system?

Divergence of horizontal energy transport Calculation of the divergence from u, v, q, T Analysed fields with 6-hourly resolution Problems with mass consistency Michael Mayer - April 2012 Direct methodIndirect method Calculation of the divergence as a residual Use of 12-hourly accumulated vertical fluxes Energy tendency from 12-hourly forecasts No problems with time resolution Mass inconsistencies as well

Mass budget in ERA-Interim Systematically deficient surface pressure forecasts (Up to -600hPa/year!) Instantaneous mass flux divergence also erroneous Mass correction is necessary!

Climatology at TOA Michael Mayer - April 2012 Too little energy input in the Tropics Too weak meridional Rad TOA gradient

Mean poleward energy transport Michael Mayer - April 2012 Much too weak total poleward energy transport (atmosphere + ocean) Atmospheric transport in better agreement with reference estimate

Variability: Zonal mean budget (20N/20S) Michael Mayer - April 2012 Tropical energy export is varying very weakly Direct/Indirect method show different anomalies

Michael Mayer - April 2012 Radiative fluxes quite stable in time Trends in latent heat flux are compensated by trends in energy tendency forecasts Fluxes at TOA and at the surface

Analysis increments Michael Mayer - April 2012 Defined as the difference between the analyzed and the forecasted state of the model, using 12-hourly forecasts Total energy tendency analysis increments: Increments can change in time due to Changes in the observation system Imperfectly forecasted changes of the atmospheric circulation

Analysis increments in the Tropics Michael Mayer - April 2012 Strong shifts in analysis increments Precipitation and moist analysis increments highly correlated

Michael Mayer - April 2012 Strongest shifts related to SSM/I in 1992 and 2008 Apparently relatively weak anomalies related to climate anomalies On overall, no improvement over time Zonal mean latent heat analysis increments

Michael Mayer - April 2012 Zonal structure of tropical moisture flux divergence

Michael Mayer - April 2012 Use different climatologies to get rid of inhomogeneities Simple algorithm reducing RMS-value of analysis increments ENSO-related anomalies Zonal structure of tropical latent heat analysis increments

Michael Mayer - April nd iteration: remove either 2008 shift or stripes Further reduce inhomogeneities

Michael Mayer - April 2012 Result: fairly homogeneous anomaly timeseries

Trends in zonal mean transport Michael Mayer - April 2012 IPCC AR4 models predict increase in total poleward energy transport + stronger Hadley cell Indirect ERA-I estimate shows opposite trends Held and Soden (2006): Indirect estimate ΔF [PW]

Michael Mayer - April 2012 Direct estimate slightly more stable in time Both estimates show unrealistically strong trends Reliable trend estimation of energy transports not possible Direct estimate Held and Soden (2006): ΔF [PW]

Conclusions Michael Mayer - April 2012 Reanalyses have too weak mean meridional Rad TOA gradient and thus too weak poleward total energy transports Weak variation in zonal mean budgets, true climate anomalies hard to identify Strong increase of evaporation over time -> compensated by analysis increments For investigation of interannual variability split of climatologies is helpful 30-year trends in zonal mean poleward transport are too strong and in disagreement with climate models

Michael Mayer - April 2012

Indirect method Correction methods I

Correction methods II Michael Mayer - April 2012 Direct method

Mass budget in ERA-Interim II Michael Mayer - April 2012 Time-averaged mass flux divergence unrealistic Indirect estimation from mass tendency and E-P much better

Michael Mayer - April 2012 Mass budget in ERA-Interim Up to -600hPa/year! Forecast error: Systematically deficient surface pressure forecasts ()

Results so far – Direct method Michael Mayer - April 2012 Many important climatological features, but noisy

Indirect method Michael Mayer - April 2012 Much clearer and less noisy

Poleward energy transports– different results Michael Mayer - April 2012 FT08…Fasullo und Trenberth (2008) Mass correction reduces cross-equatorial energy transports

Interannual variations of the transports Which anomalies are true climate signals (e.g. due to ENSO)? Which anomalies are artefacts? Michael Mayer - April 2012

Changes in the observing system affect analysis increments D. Dee(2009) COSMIC SSM/I AMSU-A AIRS

Next steps Understanding the different lags of moist and dry anomalies Michael Mayer - April 2012 Negative lag of total export anomalies ~Zero lag (moist/dry/total) Positive Lag of total export anomaly

Next steps Fast propagating anomalies (continous blue) in agreement with Trenberth et al We find a much larger pattern (dashed blue) Slowly propagating anomalies (red) linked to ENSO? -> Reproducibility with other datasets? -> Objective method for determining phase speed of the transient features required (e.g. wavelets) -> propagating SLP anomalies in Peterson and White (1998) – connection? Michael Mayer - April 2012

Next steps Reliable ‚independent‘ datasets are required ISCCP is being reprocessed More homogeneous datasets expected Michael Mayer - April 2012

Next steps Prolongation of the ERA-Interim-datasets back to 1979 is being produced – extension of the study period – Long-term transport trend estimates become possible – Try to verify expected increase of poleward energy transports (Held and Soden, 2006) Employment of a GCM to – Study varying partition between moist and dry anomalies – Study effects of El Niño on energy transports without data inhomogeneities – verify features found in the reanalysis data Michael Mayer - April 2012

Summary – Scientific goals A new estimate of the poleward atmospheric energy transport A better understanding of the interannual variability of the energy transports Understanding of the mechanisms leading to the observed eastward moving anomaly patterns Feedback regarding data homogeneity and consistency to the producers of the used datasets Michael Mayer - April 2012

Work plan and financing 1 st year: Visit CAS at NCAR (02/ /2011) -> access to new datasets (GCM output, reprocessed satellite data, ocean data) and expertise of the group 2 nd year: access to extended ERA-Interim dataset and investigation of long-term trends 3 rd year: Employment of GCM results and investigation of the described questions Thesis work is funded within FWF project “Global historic in situ upper air data for climate change research” (running at least until 06/2012) Stay at NCAR mainly funded by ASP Michael Mayer - April 2012 Thank you for your attention

Literature Michael Mayer - April 2012