© Crown copyright Met Office The EN4 dataset of quality controlled ocean temperature and salinity profiles and monthly objective analyses Simon Good

© Crown copyright Met Office

The EN4 dataset of quality controlled ocean temperature and salinity profiles and monthly objective analysesSimon Good


What is the EN series of datasets?

• Climate datasets of ocean temperature and salinity profiles.• Include:

1. The observed profiles with quality flags.

2. Monthly objective analyses formed from the data.

• Data are in NetCDF files.

• Freely available for scientific research and private study.

• www.metoffice.gov.uk/hadobs


Contents

• History of the dataset

• The EN4 dataset

• Objective analysis uncertainty estimates

• Ensemble of opportunity

• Conclusions


History of the dataset


How did they originate?

• The first version of the dataset was produced for the ENACT project (ENhanced ocean data Assimilation and Climate predicTion) for global ocean data assimilation.

• Data were collected from a number of sources.• To get consistent quality control, all flags were

discarded from the source.• Then, all data were run through the Met Office

quality control system.• The system was shared with real time systems –

necessary to have good automated checks.


Updates to EN2 and EN3

• A new version was produced for the ENSEMBLES project (EN2; Ingleby and Huddleston, 2007, Journal of Marine Systems, 65).• Changes were updated data from sources; tweaks to

quality control checks; updated background error covariances.

• EN3 (with various subversions) followed.• Updated data again.• Revised climatology.• Tweaks to quality control checks again.• Added some manual rejects.


Update to EN4

• Targeted development of a duplicate check and new quality control checks to solve specific issues with the dataset.• Work done for the ERA-CLIM project (European

Reanalysis of Global Climate Observations; http://www.era-clim.eu/).

• Uncertainty estimates produced to accompany the objective analyses.

• Good et al. (2013), JGR-Oceans, 118.


The EN4 dataset


Input data

• Profiles obtained from • WOD• ASBO (Arctic Synoptic Basinwide Observations)• Argo• GTSPP

• Argo and GTSPP are used for monthly updates.

• Duplicate check applied to remove the multiple versions of profiles.• Based on Gronell and Wijffels (2008), JAOT, 25.


Number of profiles


Thinning of levels

CTD profile

50.9°W, 58.2°N

July 1995

Original profile: 3596 levels

EN3 version: 127 levels(~5m spacing near surface)

EN4 version: 390 levels(~1m spacing near surface)

Thinned profiles have (if available)

EN3: 5m spacing near surface

EN4: 1m spacing near surface


Monthly processing cycle

Quality control

Analysis

Persistence forecast

Output as NetCDF file

One month of observations

processed per cycle

Output as NetCDF file

Available from Met Office

website

Observations


Quality control tests

Manual exclusions

Track check

Profile check (spikes etc.)

Thinning (informational)

Stability check

Background checks

Buddy checkMulti level check

Argo delayed mode flags

Argo grey list

Argo altimetry quality control

External quality information

Automatic quality checks

Bathymetry check

Measurement depths check

Waterfall check

Near surface and deep BTs

Range check


Background check

Quality control examples

Measurement depths check


Quality control examples

Track check

Waterfall check

Spike check


Objective analysis system

• Uses a iterative scheme equivalent to optimal interpolation.• But no need to subselect a limited number of

observations close to a grid box.

• Monthly.• Potential temperature and salinity.• 1 degree grid, 42 levels in the vertical.• Uses a persistence forecast as background.• Relaxes to a climatology in the long term

absence of observations.


Example fields – March 2014 at 5 m


Objective analysis uncertainty estimates


Method

• The scheme used to produce the objective analyses makes it impossible to calculate uncertainty using the optimal interpolation equations.• These are only valid if background error covariances are well

known.

• Use an analysis quality method instead where observation values are set to 1 and background values to 0 (based on Donlon et al. 2012, Remote Sensing of Environment, 116).

• All other aspects of the analysis are the same except length scales are shortened.

• Result is linearly related to analysis error variance.


Example of observation influence



Dots are the locations of observations








Linear relationship between ‘observation influence’ and analysis error variance

• Using simulated data points it is possible to show this relationship.

• Length scales have to be shortened by a factor 1.75 to get a linear relationship.

Simulations

Line fit


Coefficients of the linear relationship• For EN4 I developed an empirical scheme to do

this.• The observations are split into two groups and

analyses made from each.• The differences between analyses allow the

uncertainty to be estimated.• The method also allows some checks to be

done:• Intercept should match the background error

variance – method can even be used to improve this• Gradients should be negative – some issues with the

EN4 analyses were identified


Gradients of the linear relationship


Example uncertainty estimates


Ensembles of opportunity


Uncertainty in construction of an ocean dataset• There are a number of global ocean profile

databases:• WOD• GTSPP• CORA• EN4• Etc.

• These are constructed differently, e.g.• Different quality control.• Different choices about which profiles to include.• Bias adjustments.

• This tells us about the uncertainty in the data.


Example

• From Lyman et al. (2010), Nature, 465.


Conclusions


Conclusions

• The EN series of datasets were originally started for global ocean data assimilation.

• This has been incrementally updated to the latest version EN4.

• It is available freely for scientific research and private study from www.metoffice.gov.uk/hadobs.

• The new version includes objective analysis uncertainty estimates produced using an ‘observation influence’ method.


Questions and answers

Documents

© Crown copyright Met Office The EN4 dataset of quality controlled ocean temperature and salinity profiles and monthly objective analyses Simon Good