Ocean Observing and Climate
Observational Errors and Uncertainty
High quality surface meteorological observations are only made at a limited number of locations on board research vessels and moored buoys. However, routine meteorological observations are made by merchant ships over much of the global ocean. These observations are collected as part of the Voluntary Observing Ships (VOS) program, coordinated by the World Meteorological Organization (WMO). These observations include all the parameters needed to calculate the surface fluxes such as wind speed, air temperature and humidity and sea surface temperature. The observations also include more descriptive parameters such as the present weather and sea state.
Observations from VOS, and earlier merchant and naval vessels dating back to 1784, have been collated in the International Comprehensive Ocean Atmosphere Data Set (ICOADS). These observations have been used in numerous studies, including studies of climate change, constructing climatologies of the surface marine environment, compiling atlases of surface heat and momentum fluxes, validating satellite parameters and model output validation. VOS observations are also assimilated into Numerical Weather Prediction (NWP) forecast and reanalysis models.
Whilst these observations have been widely used they contain systematic and random errors and need to be handled with care. Part of the research by the Surface Processes sub-group in OOC aims to improve the modern VOS observations through identifying and correcting biases in the observations.
Recent work includes:
- Use of information on observational errors and uncertainty in a new air-sea flux dataset, NOCS v2.0
- An assessment of trends in marine wind speeds from ICOADS. This research showed that standard adjustments for observation height and for biases in the Beaufort Scale used to report some of the observations removed most of the apparent trend in marine winds. A smaller inhomogentiety between wind speed observations made by different methods could not be explained.
- Thomas, B. R., E. C. Kent, V. R. Swail and D. I. Berry, 2008: Analysis of Monthly Mean Marine Winds Adjusted for Observation Method and Height, International Journal of Climatology, 28(6), 747-763.
- Thomas, B. R., E. C. Kent and V. R. Swail, 2005: Methods to Homogenize Wind Speeds from Ships and Buoys, International Journal of Climatology, 25(7), 979-995
- Observing method can have a strong impact on measurements and it is important to gather as much information on observing methods, instruments and practices. A lot of effort has gone into digitising information on historial observing practices and information on observing practice for the period after 1973 is now served alongside ICOADS. This paper describes this observation metadata, including information going back to 1955 which has not yet been incorporated into ICOADS.
- Trends in sea surface temperature (SST) are a crucial part of the global temperature record. Our research has shown that there are differences between measurements made by different methods. These papers describe the different methods of measurement, the sources of error that are expected to occur in each and make an analysis of the biases in a subset of the SST data.
- Kent, E. C., and P. K. Taylor, 2006: Toward Estimating Climatic Trends in SST, Part 1: Methods of Measurement. Journal of Atmospheric and Oceanic Technology, 23(3), 464-475.
- Kent, E. C., and P. G. Challenor, 2006: Toward Estimating Climatic Trends in SST, Part 2: Random Errors. Journal of Atmospheric and Oceanic Technology, 23(3), 476-486.
- Kent, E. C., and A. Kaplan, 2006: Toward Estimating Climatic Trends in SST, Part 3: Systematic Biases. Journal of Atmospheric and Oceanic Technology, 23(3), 487-500.
- Kent, E. C., and P. K. Taylor, 2006: Toward Estimating Climatic Trends in SST, Part 1: Methods of Measurement. Journal of Atmospheric and Oceanic Technology, 23(3), 464-475.
- Air temperature measurements can be biased high if the ship heats up during the day. An adjustment was developed to account for this bias, and an investigation of the effect of instrument exposure on the observations was made.
- Berry, D. I., E. C. Kent and P. K. Taylor , 2004: An analytical model of heating errors in marine air temperatures from ships, Journal of Atmospheric and Oceanic Technology, 21(8), 1198 - 1215.
- Berry, D. I. and E. C. Kent, 2005: The Effect of Instrument Exposure on Marine Air Temperatures: An assessment using VOSClim data, International Journal of Climatology, 25(7), 1007-1022.
- Berry, D. I., E. C. Kent and P. K. Taylor , 2004: An analytical model of heating errors in marine air temperatures from ships, Journal of Atmospheric and Oceanic Technology, 21(8), 1198 - 1215.
- Random uncertainties in the ICOADS observations have been quantified.
- Kent, E. C. and D. I. Berry, 2005: Quantifying Random Errors in Voluntary Observing Ships Meteorological Observations, International Journal of Climatology, 25(7), 843-856.
- Kent, E. C., P. G. Challenor and P. K. Taylor, 1999: A Statistical Determination of the Random Observational Errors Present in Voluntary Observing Ships Meteorological Reports. Journal of Atmospheric and Oceanic Technology, 16(7), 905-914.
