1. Evaluation of the MERRA-2 Assimilated Ozone Product
Gordon Labow
Krzysztof Wargan
Stacey Frith
Steven Pawson
Gary Partyka
September, 8, 2016

2. Based on the GEOS-5 assimilation system
What is MERRA-2?
MODERN-ERA RETROSPECTIVE ANALYSIS FOR RESEARCH AND APPLICATIONS
Based on the GEOS-5 assimilation system
Input:
Ozone profiles & total column (SBUV, MLS/OMI), winds, temperature, pressure (from radiosondes, aircraft, satellite radiances, GPS)
Ozone Output:
-72 vertical layers (about 1km in stratosphere)
-576 x 360 gridded data (0.625 x 0.5 degree)
-Ozone profile (every 3 hours)
-Total Ozone (every hour)
-1980 to present
-Global daily maps (pole to pole)
present

3. Some issues with the SBUV input:
Nadir only (80N to 80S)
Drifting orbits
No data in Polar night
SBUV JULY 1st, 2003
MLS resolves many of these issues
MLS JULY 1st, 2013
OMI +
MLS

4. Delauney Interpolation Longitude 10/25/1988 Column Ozone at 40 North 1
TOMS Ozone
Total Ozone (DU)
SBUV measurement
Delauney
Interpolation
Longitude

5. Longitude 10/25/1988 Column Ozone TOMS Total Ozone (DU) MERRA-2
(every 2 hours)
Longitude

6. Longitude 10/25/1988 Column Ozone at 40 South TOMS Total Ozone (DU)
MERRA-2
(every 2 hours)
Longitude

7. MERRA-2
TOMS minus MERRA-2
N7-TOMS
EP-TOMS
OMI

8. TOMS – MERRA2

9. MERRA-2 compared to SAGE II
hPa column
( km)
MERRA= Red
MERRA-2 = Green

10. Comparisons to Ozonesondes
2003
(SBUV)
2003
2005
(MLS)
2005
Statistical comparisons of MERRA-2 ozone against global ozonesondes available in 2003
(a-b) and 2005 (d-e). All data are interpolated to the tropopause-based vertical coordinate.
Ozone sondes (black) and MERRA-2 (green). Standard deviation of ozonesonde measurements (red).

11. UARS MLS ( )
MIPAS ( )

12. A case study:
(a) Color background: MERRA-2 ozone between 30°N and 90°N at 10 hPa on 21 December 1993 at 6Z.
UARS MLS observations made between 1:30Z and 10:30Z are shown as filled circles color-coded by the
retrieved mixing ratios. The highest latitude observed by SBUV around the same day (51°N) is marked by
black dots. (b) a scatter plot of all UARS MLS observations at 10 hPa.

13. MERRA-2 biased low Longitude 10/25/1988 Column Ozone at 10 North TOMS
Total Ozone (DU)
MERRA-2
(every 2 hours)
MERRA-2 biased low
Longitude

14. A difficult case: The South Pole
MERRA=Red
MERRA-2=Green
The time series of total ozone at the South Pole derived from individual ozonesondes (black)
and collocated reanalysis: MERRA (red) and MERRA-2 (green).
(b) reanalysis minus ozonesonde differences divided by sonde total ozone

15. Comparisons have been made with:
Total ozone: TOMS & OMPS (Mid latitudes) Bias= -1.4%
Ozone profile: SAGE II V7 (Midlatitudes) Bias
4.3 hPa ±4.4%
10.1 hPa ± 6.1%
42.7 hPa ± 4.4%
MIPAS V6 (Global)
4.6 hPa ± 6.2%
9.4 hPa ± 4.3%
39.8 hPa ± 10.3%
UARS MLS V5 (Midlatitudes)
4.3 hPa ± 5.5%
10.1 hPa ± 4.7%
42.7 hPa ± 9.4%
Ozone sondes (Midlatitudes)
10.0 hPa ± 16%
50.0 hPa ± 21%
500 hPa ± 32%

16. What’s MERRA-2 good for?
-Great for: high resolution (temporal & spatial) total ozone maps,
regional studies, stratospheric vertical ozone distribution,
lower stratosphere studies, a-priori profiles for retrievals.
Possibly good for:
Filling in ozone values in polar night
Not recommended for:
- Long-term ozone trends
- Lower tropospheric ozone studies
MERRA-2 data are available at MDISC, managed by the NASA Goddard Earth Sciences (GES)
Data and Information Services Center (DISC).