# Presentation: 000165

## Modern biases in in situ SST measurements

**Modern biases in *****in situ *****SST measurements**

- John Kennedy, Nick Rayner, Philip Brohan, David Parker, Chris Folland, et al.

## Summary	

- SST measurement methods.
- Introduction to the SST record.
- Biases associated with each method.
- Impacts of measurement method on climate monitoring.

**Notes:**
Mention HadSST2 and ICOADS

## Measurement Methods

**Notes:**
Buckets insulated, uninsulated, wooden. Buckets cool, sensible and latent heat losses. Sample surface layer ~top 1m
ERI biased warm or cold depending. Warm because ships are bigger and thus water must travel further. Cold because they sample deeper water. Atlantic modern day cooling.
XBT, CTD. Profilers sampling the water column. Observations taken in the top 4m are used.
Moored Buoys. TOGA TAO, US buoys (Discus, Nomad)
Drifting Buoys

## Relating Measurement Method to Bias.

**Notes:**
Comparison between NMAT and uncorrected and corrected SST. Global annual average.
Assumptions – Wooden bucket –> canvas bucket –> (insulated bucket, ERI, Hull contact sensors) -> all this + buoys

## SST (60 ̊N-60 ̊S) and uncertainties

**Notes:**
Things to note: No bias uncertainties after 1941.
TEENY-TINY ERRORS since 1941 – much smaller than the inter-annual variability

## Japanese and Dutch SSTs

**Notes:**
Global annual average SST anomalies
Dutch and Japanese data using un-insulated buckets it seems.

## American SSTs

**Notes:**
Biased warm!
US ships mostly ERI measurements.

## The changing balance

- US

- Japanese

- Dutch

- German

- UK

- Russian

- Misc

**Notes:**
Smoothed data.
Misc: international compilations and contributions from many countries (including UK) for which there are only a few observations
UK, German: Insulated buckets
Dutch: un-insulated buckets
Japanese: buckets – ERI in the later data.
Russian: Buckets
US: ERI

Data sources come and go abruptly -> correlation in time of biases as well as in space
Also implies jumpy biases.
Currently lack the necessary metadata to crack this nut.

## Modern period 1970-2005

- Metadata on measurement methods from
- WMO publication 47 (1972-2005)
- ICOADS.
- VOSClim
- WMO Pub. 47 being digitized back to 1953.
- Kent, E. C., S. D. Woodruff and D. I. Berry, 2005:  WMO Publication No. 47 Metadata and an Assessment of Observation Heights in ICOADS. *Submitted to the Journal of Atmospheric and Oceanic Technology*
- Kent, E. C., and A. Kaplan, 2005:  Towards Estimating Climatic Trends in SST, Part 3: Systematic Biases. *Journal of Atmospheric and Oceanic Technology, in press*

**Notes:**
Metadata (at last) from ICOADS and WMO Publication 47.
Details on measurement methods, ship lengths, heights, instrumentation, country of registration, captains shoe-size.
Use this to make datasets which are enriched in buckets or ERI measurements.

## Buckets v ERI

**Notes:**
ERI warmer than buckets but cooling in the north Atlantic
Too few hull contact observations to say anything meaningful

## Drifting Buoys vs Ships

**Notes:**
Free floating truly in situ often considered to be ground truth.
May be true, but in that case not homogeneous.
Nothing like them in the record
What compensates for them?
Nothing
Nice plot of cool buoys.

## A Plague of Buoys

- Ships

- Drifters

- Moorings

**Notes:**
1980: ~no buoys
2005: 76% of observations from buoys
Explain about large numbers of observations from moorings and geographically restricted nature of their distribution
Drifters have greater gridbox coverage than ships – not just more observations.

## Implications

**Notes:**
Difference is almost 0.1 degrees on a global annual average.
Difference is larger than random error bounds.
Difference is significant after about 1992.
Underestimate of recent warming. Difference between 1998 being the warmest year for SST and 2003 being it.

## SSTdrifter-SSTship (average 1990-2005)

**SST****drifter****-SST****ship**** (average 1990-2005)**

**Notes:**
Hawaiian and Mediterranean features are due to dodgy ships.

## Seasonal Cycle

- Drifting Buoys

- Ships

**Difference (**** ̊C****)**

## Conclusions

- There are biases in modern SST measurements
- Current monitoring system is potentially good – random errors are small...
- ... but, errors due to biases are larger than random errors.
- Predominance of buoys in recent data may be leading to an underestimate of warming.

## Further Work

- (A)ATSR instruments 1991-2005

- Buoy/Ship matchup database

- 1.3 Million ship-buoy pairs

- Use VOSClim data

**Notes:**
AATSR = good because independent of insitu measurements (validated against insitu radiometers, but self calibrating)
Investigate reasons for buoy ship differences
Extend metadata back (WMO publication 47)
Digitization of new obs esp. WWII
Satellite data

## Questions and Answers

**Questions and Answers**