Status of the ERA5 reanalysis production

Transcription

1 Status of the ERA5 reanalysis production R. Dragani, H. Hersbach, A. Simmons, D. Shepers, M. Diamantakis, D. Dee and many other colleagues

2 Content Overview of changes and improvements implemented in ERA5 w.r.t. ERA-Interim Production status Preliminary assessment: what works and what does not, and it is currently under investigation* Not an exhaustive account, mostly limited to temperature and ozone.

3 Content Overview of changes and improvements implemented in ERA5 w.r.t. ERA-Interim Production status Preliminary assessment: what works and what does not, and it is currently under investigation* Not an exhaustive account, mostly limited to temperature and ozone.

4 The big picture: ERA5 is a global, atmospheric reanalysis covering the satellite era that will replace ERA-Interim. It is produced by ECMWF on behalf of the EU and as part of the Copernicus Climate Change Service (C3S). USERS Policy Makers & Public & Private, Commercial Different Needs Farming Oil Spill Tracking Air Quality Flood Surveillance Arctic change Examples of areas covered Land Marine Atmosphere Emergency Security Climate 6 Information Services Space Infrastructure In Situ & Infrastructure OBSERVATIONS Sustainable observation capabilities

5 Global reanalyses produced at ECMWF Atmosphere/waves FGGE ERA ERA-40 A 2006 ERA-Interim ERA-CLIM (2) ERA5 Ocean 2006 ORAS ORAS4 Land 2012 EI/Land Atmospheric composition GEMS MACC CAMS

6 ERA5 vs. ERA-Interim ERA-Interim Start of production August 2006 IFS Cy31r2 Model input (radiation and surface) As in operations, currently OSTIA (inconsistent SST) ERA5 2016, reach NRT end before 2017 IFS Cy41r2 Appropriate for climate (CMIP5 includingac&c SPARC ozone, blend HadISST and OSTIA) Analysis method 12h 4D-Var 12h 4D-Var + 10-member EDA (T319, 63km) Spatial resolution 79 km global 60 levels to 10 Pa 31 km global (T639) 137 levels to 1 Pa Output frequency 6-hourly Analysis fields Hourly (three-hourly for the EDA), [Extended list of parameters ~ 5 Peta Byte] Uncertainty estimate from EDA Feedback Archive Time period present 1979 present * Extra Observations Mostly ERA-40, GTS Various reprocessed CDRs Radiative transfer RTTOV7 RTTOV11 + CO2, SSU cell-pressure correction * The period covered spans the period from 1979 onwards, with: prompt operational extension forward in time possible later extension backwards in time

7 Improvements compared to ERA-Interim: forcings Forcings in the radiation scheme of the assimilating ERA5 model follow CMIP5 recommendations for: greenhouse gases solar input ozone aerosols as used in ERA-20CM model simulations and centennial ERA-20C and CERA-20C reanalyses Using the CMIP5 forcing and prescribing SST ensures that the underlying model (as in ERA-20CM) already captures observed trends and low-frequency variability reasonably well; data assimilation should then correct for the remaining deficiencies

8 Lessons learnt from ERA-Interim: data usage Drift due to CO 2 loss in PMR cell Drift due to H 2 O loss Drift due to increase in unadjusted radiosonde data Underestimation by model of Pinatubo warming Assimilation of GPS RO data TIROS-N data poor Poor HIRS spectral response functions Drift due to fixed CO 2 in RTTOV Solar heating change due to orbital drift Drift in data from MSU and early AMSU-A instruments due to frequency shifts of local oscillator Dee and Uppala (2009), Kobayashi et al. (2009), Lu and Bell (2014), Nash and Saunders (2013), Saunders et al. (2013), Simmons et al. (2014)

9 Improved observing system: O 3 in ERA-Interim vs O 3 in ERA5 Level 1b Used / same version Used / new version Never used Level 2 Available from CCI + Ozone variational bias correction

10 Other improvements to input data Other newly reprocessed satellite datasets SSM/I and Meteosat radiances Atmospheric Motion Vectors from Meteosat, GMS, GOES, MTSAT and AVHRR soil moisture from ERS 1/2 and ASCAT-A radio occultation data from Metop, COSMIC, CHAMP, GRACE, SAC-C and TERRASAR-x Newer satellite datasets not used in 2006 system fixed for ERA5 ASCAT, ATMS, CrIS, FY-3, IASI and Himawari Improved usage of data all-sky assimilation of microwave imager data upgraded radiative transfer modelling for simulating observations, including variable atmospheric CO2, and variable CO2-cell pressures for SSU data bias correction of aircraft data and improved correction of radiosonde biases

11 Improvements in the model: e.g. semi-lagrangian departure scheme that enables better forecasts of the Sudden Stratospheric Warmings. Day 5, Random Errors (lat > 65N) New Old Height [km] Std. dev (O-F) [%] OLD NEW Day-5 verification vs GPSRO Courtesy of Michail Diamantakis

12 Technical improvements With hourly analyses, it is possible to better reproduce diurnal cycles, e.g. comparisons of the T2m with independent data. Observations ERA5-like analysis v Courtesy of Clement Albergel Observations ERA5-like analysis

13 Data Production Monitoring tools Effort has been devoted in setting up tools and automatic check facilities to monitor various aspects of the ERA5 production. Observation timeline tool Climate Monitoring Facility

14 Content Overview of changes and improvements implemented in ERA5 w.r.t. ERA-Interim Production status Preliminary assessment: what works and what does not, and it is currently under investigation* Not an exhaustive account, mostly limited to temperature and ozone.

15 ERA-Interim exhibited good continuity between its and production streams ERA5 production streams Current status Current status Current status To be started To be started ERA5 planned releases: v : around the beginning of 2017 v 2017 and subsequent years: in near real time v : beginning of 2018 ERA-Interim production will likely cease in early 2018 ERA5 production for the period prior to 1979 is still to be decided

16 Content Overview of changes and improvements implemented in ERA5 w.r.t. ERA-Interim Production status Preliminary assessment: what works and what does not, and it is currently under investigation* Not an exhaustive account, mostly limited to temperature and ozone.

17 Monitoring impacts of changes in forecasting and observing systems Before 2000, improvements in ops come mainly from better forecasting systems Afterwards, improvements come from better forecasting systems and better (use of) observations ERA5 s forecasts improve more than ERA- Interim s from 2000 onwards, likely due to better and more extensive use of satellite data. Forecast day

18 Monthly global-mean surface air temperatures ERA-Interim shows warming over the period since 1979, and the widely reported exceptional values over the past twelve months ERA5 values for the first three completed years are in good agreement with the adjusted ERA-Interim values Background values are used over sea for both reanalyses, as analysed surface air temperatures are unreliable there

19 The 1998 change from SSU to AMSU-A 1hPa 3hPa 5hPa ERA-Interim suffered of a discontinuity in the temperature fields near the Stratopause caused by the replacement of the SSU radiances with those from AMSU-A in Aug 1998 and the corresponding change in the anchor channels of the variational bias correction. 10hPa Aug 1998

20 The 1998 change from SSU to AMSU-A

21 Differences in zonal means for January 2016 Temperature (K) ERA5 - ERA-Interim pressure (hpa) Contour lines è ERA5 Colours è differences pressure (hpa) Temperature (K) ERA5 - Operations

22 Total column ozone (DU) at the South Pole In many years, ERA-Interim builds up too-high values of ozone near the South Pole in mid to late winter

23 Fit to ozone sondes (RMSE, DU) Jul-Sep 2009 Oct-Dec o -60 o N o -90 o S 42 27

24 Possible causes and preliminary investigation Cariolle scheme? Oct-Dec 2008 Impact from the temperature? Variational Bias Correction (VarBC) v Profiles: SBUV-2, MLS, MIPAS (all used to anchor VarBC) v TCO3: OMI, GOME-2, SCIAMACHY Assimilation? v IR/O3: AIRS (1 ch as anchor), IASI (1 ch as anchor) è Impact assessed for each element individually w.r.t. sondes and MLS (except MLS itself), but not together Impact from other fields (other than temperature)?

25 Conclusions ECMWF is working at the ERA-Interim replacement, ERA5. Effort has been devoted to improve the model, the numerical aspects, and the data assimilation compared to ERA-Interim. The production will be performed in five streams, three of which have already started. The anticipated data availability is as follows: v : around the beginning of 2017 v 2017 and subsequent years: in near real time v : beginning of 2018 v ERA-Interim production will likely cease in early 2018 Preliminary assessment of ERA5 fields shows many improvements compared with ERA-Interim but also some problems currently under investigation: + Temperature discontinuity in summer 1998 seems to be addressed Possible positive temperature trend near Stratopause + Ozone largely improved both in terms of TCO3 and profile at most latitudes and vertical levels Comparisons with sondes degraded in late spring at high latitudes in the SH

26 Extra slides

27 Access to ECMWF reanalysis data access to observation feedback!

28 Geopotential height: 10hPa, JFM 2016 ERA5 ERA-Interim

29 Differences in zonal means for January 2016 Temperature (K) ERA5 - ERA-Interim Temperature (K) ERA5 - Operations Zonal wind (m/s) ERA5 - ERA-Interim Specific humidity (log(kg/kg)) ERA5 - ERA-Interim pressure (hpa) pressure (hpa) Contour lines show ERA5; Colours show differences