Retrospective analysis of ozone
at ECMWF
Rossana Dragani
ECMWF
Acknowledgements to:
D. Tan, A. Inness, E. Hólm,Slide
and
1 D. Dee
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Overview
 Reanalysis activity at ECMWF
 Science application for reanalysis data
 Suitability to assess long-term variability
 Ozone analyses in ERA-40 and ERA-Interim
 Conclusions and remarks
Slide 2
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Reanalysis at ECMWF:
 Reanalysis is based on analysis methods developed to provide
initial states for numerical weather prediction.
 It applies a fixed, modern data assimilation system to multi-year
sets of observations of different types, resulting in more uniform
analysis quality.
ERA-15:
ERA-40:
ERA-Interim:
1979 – 1993
1957 – mid-2002
1989 onwards
ORA-S3:
MACC:
1959 onwards
2003 – 2010
ERA-CLIM:
European Reanalysis of Global Climate Observations
An EU project to help prepare the next ECMWF
Slide 3
reanalysis
ERA-20C: 1900 onwards
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
The ERA data base: www.ecmwf.int
Slide 4
 ERA-Interim reanalysis is continuing in near real-time
 Products are updated monthly
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Science applications that rely on reanalysis data
 “Observations” for verification and diagnosis
- Development of forecast model, climate model; calibration of seasonal
forecasting systems; use of data assimilation increments for identifying
model errors
 Input data for model applications
- for smaller-scales (globalregional; regionallocal), ocean circulation,
chemical transport, …
 Study of short-term atmospheric processes and influences
- Polar vortex dynamics,…
 Providing climatologies
 Assessment of the observing system
- providing feedback on observational quality, bias corrections and a basis for
homogenization studies; contributing to data reprocessing activities
Slide 5
 Study of long-term climate variability and trends
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Suitability to assess long-term changes:
 ERA-40 + ERA-Interim  Mid 1957 to the present
 Analyses are physically coherent and consistent with observations
 A realistic model can propagate information in poorly observed areas
as well as moved forward in time.
MIPAS O3
retrievals:
23 Sep 2002
Ozone fc:
D+6 from
17 Sep 2002
© ESA, 2002.
Ozone analysis:
12Z 23 Sep 2002
Slide 6
Geer, Planet Earth Autumn 2004, www.nerc.ac.uk
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Suitability to assess long-term changes:
From archived weather analyses:
From a retrospective analysis:
 Reanalysis uses a modern, stable and invariant forecasting
/assimilation system to reprocess (re-analyse) past observations:
 Remove artificial changes introduced by model upgrades
 Changes in the observing system and their error characteristics can
also produce shifts and spurious trends.
Slide 7
- ERA-Interim used VarBC for all radiances
- ERA-Clim will also use VarBC for all L2 products (O3, WV)
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Ozone reanalyses at ECMWF:
 Ozone has been reanalysed in ERA-40 and ERA-Interim
-
MACC also reanalysed ozone for the period 2003-2010.
 Long record: ERA-40 until Dec 1988 + ERA-Interim from Jan 1989.
 Main differences between ERA-40 (Cy23r4) and ERA-Interim (Cy31r2):
- Assimilation scheme: ERA-40 used 3D-Var; ERA-Interim used 4D-Var
- Data usage
-
ERA-Interim
ERA-40 for radiances
Variarional Bias Correction (VarBC)
- Upgrades in the ozone model
d O3
dt




 c0  c1  O3   O3  c2 T  T   c3  O3   O3  c4 Cl EQ   O3
2
- Horizontal resolution: T159 (125km, ERA-40)  T255 (80 km, ERA-Interim)
 ERA-40 ozone analyses validated by Dethof
Slide 8and Hólm (2004, QJ).
ERA-Interim ozone analyses validated by Dragani (2011, QJ
submitted).
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Ozone in ERA-40:
Hilo (1992-1995)
JFM
JJA
Dethof & Hólm (2004)
Sonde
ERA-40
Neumayer (1992-1995)
Hohenpeissenberg (1983-1987)
JFM
JJA
Slide 9
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
SO
Ozone in ERA-Interim:
 TCO validated against
 OMI TCO (TOMS-like);
 TCO from Dobson Spectrometers (WOUDC);
 TCO climatology created as a 5-year running mean
from the NASA merged satellite.
 3D O3 analyses (Jan 89-Dec 08) validated against
 WOUDC sondes;
 Satellite data.
V6.2
SAGE:
MLS:
V5
HALOE:
POAM:
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
V2.2
V19
Slide 10
V6
V4
© ECMWF 2011
Validation of the 3D O3 reanalyses:
Sat-An
Sat
 Matching criteria:
 Dt
30 hPa
3 hrs.
 ERA-Interim analyses
were interpolated at
the obs locations.
GOME
SAGE
HALOE
MLS
POAM
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
Slide 11
© ECMWF 2011
Summary of the comparisons: 1989-2008
Lat
30 - 90 N
30S - 30N
30 - 90 S
Lev (hPa)
SAGE
HALOE
MLS
POAM
5
±5%
[0,+5]%
[0,+5]%
[-25,+5]%
10
[-10,+5]%
[-5,+1]%
[-5,+3]%
[-25,+10]%
30
[0,+20]%
[-2,+20]%
[0,+20]%
[-10,+20]%
65
[-20,+10]%
[-2,+10]%
[-20,+10]%
[-20,+10]%
5
±5%
±5%
±5%
10
±10%
±5%
[-5,+8]%
30
[0,+20]%
[0,+20]%
[0,+20]%
65
[-20,+30]%
[-5,+20]%
[+5,+25]%
5
[-8,+5]%
±2%
[-8,+5]%
[-40,+1]%
10
[-10,+5]%
[-8,+1]%
[-10,+3]%
[-40,-5]%
30
[0,+20]%
65
[-20,+20]%
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
Slide 12 [0,+20]%
[0,+20]%
[-20,+10]%
[-2,+20]%
[-20,+20]%
© ECMWF 2011
[0,+20]%
ERA-40 vs. ERA-Interim: Jan 1989 - Aug 2002
UARS MLS
30-90 S
30 S-30 N
30-90 N
HALOE

 RMSO
Slide 13
SAT
3
RMS O
ERA Interim
3
O
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
SAT
3
© ECMWF 2011
ERA40
3
O

ERA-40 vs. ERA-Interim:
Comparisons with ozone sondes
203 soundings
942 soundings
227 soundings
238 soundings
30N – 30S
Jan-Feb-Mar
60 – 90 S
Sep-Oct
ERA-Interim
ERA-40
Pre-GOME
(1989-1995)
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
Slide 14
© ECMWF 2011
GOME
(1996-2001)
Conclusions
 ERA-40 O3 analyses showed general good agreement with
observations, but some problems were seen e.g. at mid-latitudes in
winter, and at high latitudes in the SH in spring.
 ERA-Interim O3 analyses compare well with observations, and show
departures from SAGE, MLS and HALOE ≤10% in the middle
stratosphere, and ≤ 20% in the lower stratosphere.
 ERA-Interim better than ERA-40 in the UTLS region before 1996, and
over the whole stratosphere afterwards (GOME assimilation).
 Planned improvements on ozone:
- Use the Variational Bias Correction (VarBC) scheme with L2 data.
- Revise/improve the assimilation of ozone profiles (e.g. SBUV data)
- Assimilate ozone information from different
Slide 15data type/instruments
(ozone-sensitive radiances, L2 ozone data not yet used, e.g. those
used for validation).
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011
Remarks:
 What can reanalysis deliver?
- Consistent with observations
- Physically coherent
- Complete, with no gaps
- Comprehensive
- Accurate variability and trends
- Meaningful information about uncertainties
 Progress towards climate quality requires open access
to all input data.
Slide 16
 Progress is iterative and needs regular
re-processing.
R. Dragani, SPARC/IOC/IGACO, Geneva, Jan 2011
© ECMWF 2011