JCOMM Technical Report No. 13, Revision 1 world map
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Advances in the Applications of Marine climatology
The Dynamic Part of the WMO Guide to the Applications of Marine Climatology
- JCOMM TR No. 13 REV. 1 - WMO/TD No. 1081 REV. 1 - June 2005

© Royal Meteorological Society, 2005. Published by John Wiley & Sons.
(see also direct link to the special issue at the journal here)

Article

Authors

Abstract

Text

Editorial

Sergey Gulev

 

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ICOADS release 2.1 data and products

Steven J. Worley, Scott D. Woodruff, Richard W. Reynolds, Sandra J. Lubker, Neal Lott

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Quantifying random measurement errors in Voluntary Observing Ships' meteorological observations

Elizabeth C. Kent, David I. Berry

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Impacts of in situ and additional satellite data on the accuracy of a sea-surface temperature analysis for climate

Richard W. Reynolds, Huai-Min Zhang, Thomas M. Smith, Chelle L. Gentemann, Frank Wentz

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Objective analyses of sea-surface temperature and marine meteorological variables for the 20th century using ICOADS and the Kobe Collection

Masayoshi Ishii, Akiko Shouji, Satoshi Sugimoto, Takanori Matsumoto

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A 1° monthly gridded sea-surface temperature dataset compiled from ICOADS from 1850 to 2002 and Northern Hemisphere frontal variability

Shoshiro Minobe, Atsushi Maeda

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Assessing bias corrections in historical sea surface temperature using a climate model

Chris Folland

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Regime shift in the global sea-surface temperatures: its relation to El Niño-southern oscillation events and dominant variation modes

Sayaka Yasunaka, Kimio Hanawa

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Objective analyses of annual, seasonal, and monthly temperature and salinity for the World Ocean on a 0.25° grid

Timothy Boyer, Sydney Levitus, Hernan Garcia, Ricardo A. Locarnini, Cathy Stephens, John Antonov

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pdf

A seasonally resolved bottom-water temperature record for the period AD 1866-2002 based on shells of Arctica islandica (Mollusca, North Sea)

Bernd R. Schöne, Miriam Pfeiffer, Thomas Pohlmann, Frank Siegismund

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pdf

Climatology, variability and extrema of ocean waves: the Web-based KNMI/ERA-40 wave atlas  

Andreas Sterl, Sofia Caires

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pdf

Methods to homogenize wind speeds from ships and buoys

Bridget R. Thomas, Elizabeth C. Kent, Val R. Swail

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pdf

An overview of the airflow distortion at anemometer sites on ships  

Bengamin I. Moat, Margaret J. Yelland, Robin W. Pascal, Anthony F. Molland

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The effect of instrument exposure on marine air temperatures: an assessment using VOSClim Data  

David I. Berry, Elizabeth C. Kent

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Note: WMO/TD-No. 781 constitutes the static part of the "Guide to the applications of Marine Climatology".

Abstracts

ICOADS release 2.1 data and products

Steven J. Worley (1) (*), Scott D. Woodruff (2), Richard W. Reynolds (3), Sandra J. Lubker (2), Neal Lott (3)

(1) National Center for Atmospheric Research, Boulder, CO, USA
(2) Climate Diagnostics Center, NOAA/OAR, Boulder, CO, USA
(3) National Climatic Data Center, NOAA/NESDIS, Asheville, NC, USA
(*) Correspondence to Steven J. Worley, NCAR/SCD, PO Box 3000, Boulder, CO 80307, USA

The International Comprehensive Ocean-Atmosphere Data Set (ICOADS), release 2.1 (1784-2002), is the largest available set of in situ marine observations. Observations from ships include instrument measurements and visual estimates, and data from moored and drifting buoys are exclusively instrumental. The ICOADS collection is constructed from many diverse data sources, and made inhomogeneous by the changes in observing systems and recording practices used throughout the period of record, which is over two centuries. Nevertheless, it is a key reference data set that documents the long-term environmental state, provides input to a variety of critical climate and other research applications, and serves as a basis for many associated products and analyses.
The observational database is augmented with higher level ICOADS data products. The observed data are synthesized to products by computing statistical summaries, on a monthly basis, for samples within 2° latitude × 2° longitude and 1° × 1° boxes beginning in 1800 and 1960 respectively. For each resolution the summaries are computed using two different data mixtures and quality control criteria. This partially controls and contrasts the effects of changing observing systems and accounts for periods with greater climate variability. The ICOADS observations and products are freely distributed worldwide.
The standard ICOADS release is supplemented in several ways; additional summaries are produced using experimental quality control, additional observations are made available in advance of their formal blending into a release, and metadata that define recent ships' physical characteristics and instruments are available. Copyright © 2005 Royal Meteorological Society

Quantifying random measurement errors in Voluntary Observing Ships' meteorological observations

Elizabeth C. Kent (*), David I. Berry
Southampton Oceanography Centre, Southampton, UK

(*) Correspondence to Elizabeth C. Kent, Southampton Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton, SO14 3ZH, UK

Estimates of the random measurement error contained in surface meteorological observations from Voluntary Observing Ships (VOS) have been made on a 30° area grid each month for the period 1970 to 2002. Random measurement errors are calculated for all the basic meteorological variables: surface pressure, wind speed, air temperature, humidity and sea-surface temperature. The random errors vary with space and time, the quality assurance applied and the types of instrument used to make the observations. The estimates of random measurement error are compared with estimates of total observational error, which includes uncertainty due both to measurement errors and to observational sampling. In tropical regions the measurement error makes a significant contribution to the total observational error in a single observation, but in higher latitudes the sampling error can be much larger. Copyright © 2005 Royal Meteorological Society

Impacts of in situ and additional satellite data on the accuracy of a sea-surface temperature analysis for climate

Richard W. Reynolds (1) (*), Huai-Min Zhang (1), Thomas M. Smith (1), Chelle L. Gentemann (2), Frank Wentz (2)

(1) National Climatic Data Center, NESDIS, NOAA, Asheville, NC, USA
(2) Remote Sensing Systems, Santa Rosa, CA, USA

(*) Correspondence to Richard W. Reynolds, National Climatic Data Center, 151 Patton Avenue, Asheville, NC 28801, USA

Funded by: NOAA Office of Global Programs, and National Climatic Data Center

Additional in situ and satellite data improve the accuracy of a blended (in situ and satellite) sea-surface temperature (SST) analysis using optimum interpolation (OI). Two studies were conducted to evaluate the impacts of in situ and additional satellite data. One study evaluated the adequacy of the recent in situ network. Because of the high coverage of satellite data, in situ data used in the analysis tends to be overwhelmed by satellite data. Thus, the most important role of the in situ data in the analysis is to correct large-scale satellite biases. Simulations with different buoy densities showed the need for at least two buoys on a 10° spatial grid. This will ensure that satellite biases do not exceed 0.5 °C. Using this criterion, regions were identified where additional buoys are needed.
A second study evaluated the impact of satellite SST retrievals from the tropical rainfall measuring mission microwave imager (TMI) on the OI analysis. The present version only uses infrared satellite data from the advanced very high resolution radiometer (AVHRR) instrument. The results of the intercomparisons showed that both AVHRR and TMI data have biases that must be corrected for climate studies. The addition of TMI data clearly improved the OI analysis accuracy without bias correction, but was less significant when bias correction was used. However, there are areas of the ocean with limited in situ data and restricted AVHRR coverage due to cloud cover, and the use of both TMI and AVHRR should improve the accuracy of the analysis in those areas. Copyright © 2005 Royal Meteorological Society

Objective analyses of sea-surface temperature and marine meteorological variables for the 20th century using ICOADS and the Kobe Collection

Masayoshi Ishii (1) (2) (*), Akiko Shouji (3), Satoshi Sugimoto (3), Takanori Matsumoto (3)

(1) Global Warming Research Program, Frontier Research Center for Global Change, Yokohama, Japan
(2) Climate Research Department, Meteorological Research Institute, Tsukuba, Japan
(3) Climate Marine Department, Japan Meteorological Agency, Tokyo, Japan

(*) Correspondence to Masayoshi Ishii, Global Warming Research Program, Frontier Research Center for Global Change, 3173-25 Showamachi Kanazawa-Ku, Yokohama, 236-0001, Japan

Data for the 20th century from the International Comprehensive Ocean and Atmosphere Data Set and the Kobe Collection have been used as input data for global objective analyses of sea-surface temperatures (SSTs) and other marine meteorological variables. This study seeks a better understanding of the historical marine meteorological data and an evaluation of the quality of the data in the Kobe Collection. Objective analyses yield gridded data that are less noisy than observed data, which facilitates handling of historical data. The observed data determine the quality of the objective analyses, and quality control specified for historical data is incorporated into the objective analysis to reduce artificial errors. The objective analyses are based on optimum interpolation and reconstruction with empirical orthogonal functions. The final database produced in this study not only contains analysed values, but also analysis errors and data distributions at each time step of the objective analyses.

The analysis database contains ample information on historical observations, as well as signals of marine climate variations during the century. Time series of global mean marine temperatures and cloud cover include trends linked to global warming, and local peaks appear commonly in all the time series around the 1940s. Sea-level pressure and sea-surface wind fields show significant linear trends at high latitudes and over the North Pacific Ocean respectively. These trends seem to be artificial. An SST analysis used widely in climatological studies was verified against HadISST from the Hadley Centre and an SST analysis derived from satellite and in situ observations. El Niño and southern oscillation indices for the century are successfully reproduced, even though observations in the tropics are much rarer before 1950 than after 1950. Copyright © 2005 Royal Meteorological Society

A 1° monthly gridded sea-surface temperature dataset compiled from ICOADS from 1850 to 2002 and Northern Hemisphere frontal variability

Shoshiro Minobe (*), Atsushi Maeda
Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan

(*) Correspondence to Shoshiro Minobe, Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Sapporo, 060-0810, Japan

Funded by: Ministry of Education, Culture, Sports, Science and Technology, Japan

Using surface marine data collected in International Comprehensive Ocean Atmosphere Data Set (ICOADS) release 2.1, a gridded SST dataset on a monthly, 1° × 1° grid is produced from 1850 to 2002. Some unrealistic features, which are commonly found in the gridded SSTs of ICOADS, are removed by a subjective quality control. Based on the gridded SST data, SST variability associated with the oceanic fronts is investigated for the North Atlantic and North Pacific.

Year-to-year SST variability in the North Atlantic is prominent along the climatological Gulf Stream extension (GSE) in winter and spring. This correspondence is captured better in the present SST dataset than in several widely used datasets. GSE mean SST exhibits multidecadal variability similar to the Atlantic multidecadal oscillation represented by mean SSTs over the North Atlantic.

Year-to-year SST variability in the North Pacific in winter and spring seasons is strong along the subarctic front (SAF) and also in the subtropical front (STF), with weaker amplitudes in the latter. In particular, just east of Japan, the Kuroshio extension appears to be a core of strong variability. Winter and spring averaged SAF and STF exhibit prominent decadal warmings in the 1940s, i.e. these fronts may be two of the action centres for the 1940s climate regime shift and the previously reported 1970s shift. The warming anomalies around the SAF associated with the 1940s shift are distributed more broadly than those with the 1970s shift, and have maximal amplitudes around Japan. Copyright © 2005 Royal Meteorological Society

Assessing bias corrections in historical sea surface temperature using a climate model

Chris Folland (*)
Hadley Centre, Met Office, Exeter EX1 3PB, UK

(*) Correspondence to Chris Folland, Hadley Centre, Met Office, Exeter, EX1 3PB, UK

Funded by: UK Government Meteorological Research Contract, and Department of the Environment, Food and Rural Affairs; Grant Number: PECD/7/12/37

Analyses of simulations of variations in global and large-regional land surface air temperature (LSAT) for 1872-1998 using the HadAM3 atmospheric general circulation model are reported. The analyses are designed to test the accuracy of bias corrections to sea-surface temperature (SST) used in the Hadley Centre's global sea ice and SST (GISST3.1) data set, the more recent Hadley Centre sea ice and SST (HadISST) data set, and in the underlying Met Office historical SST (MOHSST and HadSST1) data sets. The tests are important because SST corrections considerably affect estimates of the magnitude of global warming since the late 19th century. Two ensembles of simulations were created using GISST3.1 as the lower boundary condition. The first ensemble, of six integrations, was forced using GISST with bias-corrections applied from 1871 until 1941, and was continued with no bias corrections to 1998. A second ensemble of four integrations, for 1871 to 1941, was forced with uncorrected GISST data. Simulations with uncorrected GISST show a substantial and often highly significant cold bias in simulated global and large-regional annual mean LSAT changes before 1942 relative to a 1946-65 reference period. By contrast, corrected SST data led to simulations of LSAT changes that are generally insignificantly different from those of observed LSAT in most regions before 1942. Tests on extratropical hemispheric scales generally validate the seasonal variation of the bias corrections, though less clearly before 1890 in some seasons. Issues about the quality of the LSAT data are raised by the results in a couple of regions. Over Australia, the model may have reconstructed LSAT changes using bias-corrected GISST with greater accuracy than the observations before about 1910. © Crown Copyright 2005. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Regime shift in the global sea-surface temperatures: its relation to El Niño-southern oscillation events and dominant variation modes

Sayaka Yasunaka (*), Kimio Hanawa
Department of Geophysics, Tohoku University, Sendai, Japan

(*) Correspondence to Sayaka Yasunaka, Department of Geophysics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan

Funded by: Japan Society for Promotion of Science

Significant changes of mean state appearing widely in the global sea-surface temperature (SST) anomaly field have happened five times from the 1910s to the 1990s: 1925, 1942, 1957, 1970 and 1976. Since the regions of change spread over both hemispheres and/or multiple oceanic basins, they can be considered as global regime shifts. The years of regime shifts are consistent with those of the Northern Hemisphere regime shifts reported by previous studies.

It is also shown that the regime shifts have happened concurrently with El Niño-southern oscillation (ENSO) events, which seems to suggest that the ENSO event acts as a trigger of the regime shift. At the regime shift, the tropical Pacific SSTs change from La Niña (El Niño) to El Niño (La Niña) conditions within 1 year. Further, the ENSO events occur just after the regime shifts begin in the July to September (JAS) season and reach the mature phase in the January to March (JFM) season as a typical evolution of the ENSO events. After that, they continue to at least the next year.

The five regime shifts detected have similar features in their seasonal evolution and persistence of signals. First, the shifts start in the JAS season: an SST change occurs in the eastern and central tropical Pacific, and a change in the mid-latitudes of the North and South Pacific appears with the opposite sign. Then the shifts in the JFM season. The spatial patterns are similar to those of the JAS season, but signals in the North Pacific become remarkable. These features resemble those corresponding to a series of evolutions of ENSO events, but the signals in the North Pacific and the North Atlantic are much stronger than those of the typical ENSO events. After the shifts have happened, the changes in spatial patterns of SST that occurred at the regime shift persist until the next shift. The persistence of signals is more prominent in the JFM season than in the JAS season.
From a review of the dominant variation modes in global SSTs using empirical orthogonal function (EOF) analyses, four modes are identified: the ENSO mode, the Southern Hemisphere trend mode, the North Pacific (NP) mode, and the Arctic oscillation (AO) mode. In the years when regime shifts occur, the ENSO mode, the NP mode, and the AO mode show significant concurrent phase reversals on the global scale as previously shown in the Northern Hemisphere. These findings provide a possible reason why SST changes in the regime shift are similar but not exactly the same pattern as that of ENSO. Furthermore, it can be considered that a simultaneous phase reversal of the NP mode would suppress the growth of anticyclonic (or cyclonic) circulation in the atmosphere over the western tropical Pacific. This suggests that an ENSO event, which begins with a regime shift, would not reverse its condition and last for the following several seasons. Copyright © 2005 Royal Meteorological Society

Objective analyses of annual, seasonal, and monthly temperature and salinity for the World Ocean on a 0.25° grid

Timothy Boyer (1) (*), Sydney Levitus (1), Hernan Garcia (1), Ricardo A. Locarnini (1), Cathy Stephens (2), John Antonov (3)

(1) NODC/NOAA, E/OC5, Silver Spring, MD 20910, USA
(2) US CLIVAR Office, 1717 Pennsylvania Ave NW, Suite 250, Washington, DC 20006, USA
(3) University Corp. for Atmospheric Research, Boulder, CO, USA

(*) Correspondence to Timothy Boyer, Ocean Climate Laboratory/National Oceanographic Data Center NOAA, E/OC5, 1315 East West Highway, Silver Spring, MD 20910, USA

Funded by: NOAA

Objectively analysed climatological mean fields of temperature and salinity have been calculated on a 0.25° grid for the World Ocean for the annual, seasonal, and monthly compositing periods using data from the World Ocean Database 2001. The annual and seasonal fields are calculated at standard levels from the surface to 5500 m. The monthly fields are calculated at standard levels from the surface to 1500 m. In comparison with similarly computed climatologies calculated on a 1° grid, ocean circulation features, such as the Gulf of Mexico Loop Current, are more clearly represented. The new 0.25° climatologies preserve most of the spatial resolution of earlier 0.25° temperature and salinity climatologies, while reducing noise by additional smoothing in horizontal space (geographically at each depth), vertically (along depth at each grid), as well as in time (Fourier filtering). Copyright © 2005 Royal Meteorological Society

A seasonally resolved bottom-water temperature record for the period AD 1866-2002 based on shells of Arctica islandica (Mollusca, North Sea)

Bernd R. Schöne (1) (*), Miriam Pfeiffer (2), Thomas Pohlmann (3), Frank Siegismund (3)

(1) Institute for Geology & Paleontology, INCREMENTS Research Group, J.W. Goethe University, Senckenberganlage 32, 60325 Frankfurt/M., Germany
(2) IFM-GEOMAR, Leibniz-Institute for Marine Sciences, Wischhofstr. 1-3, 24148 Kiel, Germany
(3) Department of Geosciences, Institute for Marine Sciences, University of Hamburg, Bundesstr. 53, 20146 Hamburg, Germany

(*) Correspondence to Bernd R. Schöne, Institute for Geology & Paleontology, INCREMENTS Research Group, J. W. Goethe University, Senckenberganlage 32, 60325 Frankfurt/M., Germany

Funded by: German Research Foundation

Existing studies on recent global warming are almost exclusively based on environmental data from the Earth's surface. Seasonal information on the effects of climate change on subsurface settings of mid to high latitudes is extremely scarce. Here, we present the first temperature proxy record from bottom (c. 50 m) water settings of the North Sea employing the oxygen isotope composition of ocean quahog shells. Results indicate that 18Oaragonite measured across shells of Arctica islandica can provide reliable estimates (±0.25 to ±0.4 °C) of the ambient bottom water temperatures. Over the period AD 1880-2001, warming trends in bottom waters are of the order of 0.042 to 0.138 °C/decade. Apparently, the annual maximum-temperature trend shows a twofold increase over the past four decades (0.236 °C/decade) while the minimum-temperature trend has remained relatively stable (0.042 °C/decade). During the same time interval, however, annual maximum temperatures at the sea surface quadrupled. Shell oxygen-isotope-derived winter temperatures also provide a proxy for the winter North Atlantic oscillation index (WNAO). Some 28 to 50% of the variability in minimum temperatures below the thermocline can be explained by changes of the WNAO. Our new tool enables testing and verification of climate models prior to the 20th century greenhouse forcing. Copyright © 2005 Royal Meteorological Society

Climatology, variability and extrema of ocean waves: the Web-based KNMI/ERA-40 wave atlas  

Andreas Sterl (1) (*), Sofia Caires (1) (2)

(1) Royal Netherlands Meteorological Institute (KNMI), De Bilt, Netherlands
(2) Meteorological Service of Canada, Climate Research Branch, Downsview, Ontario, Canada

(*) Correspondence to Andreas Sterl, Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands

Funded by: INTAS; Grant Number: 01-2206, and EU; Grant Number: KVK2-CT-1999-00027

The European Centre for Medium-Range Weather Forecasts (ECMWF) has recently finished ERA-40, a reanalysis covering the period September 1957 to August 2002. One of the products of ERA-40 consists of six-hourly global fields of wave parameters, like significant wave height and wave period. These data have been generated with the centre's WAM wave model. From these results we have derived climatologies of important wave parameters, including significant wave height, mean wave period, and extreme significant wave heights. Particular emphasis is on the variability of these parameters, both in space and time. Besides being important for scientists studying climate change, these results are also important for engineers who have to design maritime constructions. This paper describes the ERA-40 data and gives an overview of the results derived. The results are available on a global 1.5° × 1.5° grid. They are accessible from the Web-based KNMI/ERA-40 wave atlas at http://www.knmi.nl/waveatlas. Copyright © 2005 Royal Meteorological Society

Methods to homogenize wind speeds from ships and buoys

Bridget R. Thomas (1) (*), Elizabeth C. Kent (2), Val R. Swail (3)

(1) Meteorological Service of Canada, Climate Research Branch, Dartmouth, NS, Canada
(2) Southampton Oceanography Centre, Southampton, UK
(3) Meteorological Service of Canada, Climate Research Branch, Downsview, ON, Canada

(*) Correspondence to Bridget R. Thomas, Meteorological Service of Canada, Climate Research Branch, Dartmouth, NS, Canada

Funded by: Canadian Federal Program of Energy Research and Development

Marine winds reported by Voluntary Observing Ships (VOS) and moored buoys require adjustment to provide a homogeneous record of the marine climate. Known sources of inhomogeneity arise from differences in measurement height and method, averaging method and atmospheric stability; methods are available to correct for these. However, significant differences remain in a paired dataset of ship and buoy winds. Regression methods to remove this remaining inconsistency are discussed, and a ranked regression method chosen as most appropriate to adjust ship wind speeds to yield a similar distribution. We show the factors, such as vessel type, that affect the regression results. The corrections, derived from a high-quality paired dataset with rigorous quality control, are effective at reducing inhomogeneity in monthly mean wind speed distributions derived from the International Comprehensive Ocean-Atmosphere Data Set. Copyright © 2005 Environment Canada. Published by John Wiley & Sons, Ltd.

An overview of the airflow distortion at anemometer sites on ships

Bengamin I. Moat (1) (*), Margaret J. Yelland (1), Robin W. Pascal (1), Anthony F. Molland (2)

(1) National Oceanography Centre, Southampton, UK
(2) School of Engineering Sciences, Ship Science, University of Southampton, Southampton, UK

(*) Correspondence to Bengamin I. Moat, James Rennell Division for Ocean Circulation and Climate, National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK

Funded by: Meteorological Service of Canada, and Woods Hole Oceanographic Institution

Wind speed measurements obtained from ship-mounted anemometers are biased by the presence of the ship itself distorting the flow of air to the anemometer. Recent studies have used numerical models to simulate the flow around very detailed representations of individual research ships in order to quantify the effects of flow distortion at the anemometer locations. Such anemometers are generally in well-exposed positions, typically on a mast in the bows of the ship. In contrast, very little is known about the possible effects of airflow distortion on the wind speed measurements from fixed anemometers on Voluntary Observing Ships (VOS). This is because (1) the several thousand or so merchant vessels vary significantly in shape and size and it would be impractical to study each individual ship, and (2) the anemometer location is not usually known.

This paper describes initial results from a study of flow distortion over typical tankers and bulk carriers. A method to describe the shapes of these VOS and container ships is presented. The influence of distortion on the flow above the bridges of VOS is shown to be significant, with possible biases in the measured wind speed of between +11% and -100%, depending on the anemometer location. Recommendations for the siting of anemometers are made. Copyright © 2005 Royal Meteorological Society

The effect of instrument exposure on marine air temperatures: an assessment using VOSClim Data  

David I. Berry (*), Elizabeth C. Kent
National Oceanography Centre, Southampton, SO14 3ZH, UK

(*) Correspondence to David I. Berry, National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, UK

Observations of marine air temperature (MAT) by Voluntary Observing Ships (VOS) are known to contain significant biases due to solar heating of the sensor environment. MAT and humidity observations are usually made using wet- and dry-bulb thermometers housed in Stevenson screens, or with psychrometers. These instruments are typically mounted in the bridge wings or on the wheel-house top. If not sited carefully then the instruments can be poorly exposed to the undisturbed environmental conditions and have inadequate ventilation, leading to biased observations of both MAT and humidity.

In this paper we use observations collected as part of the VOS Climate (VOSClim) project to investigate the relationship between instrument exposure and heating errors. The heating errors are estimated as the difference between the observed MAT and the collocated output of a numerical weather prediction model. The instrument exposures are assessed from photographs of the instruments. Currently, photographs of the instruments and sufficient observations exist for 17 VOSClim ships.

Two methods of assessing the instrument exposure using the observations are presented. The first method is based on the skewness of the distribution of estimated heating errors for individual ships. The second method is based on a correction developed to correct the heating errors and uses the ratio of the heating to cooling terms in the correction. When ships are ranked both on the skewness and on the ratio of the heating to cooling terms, there is a statistically significant correspondence between the rankings and the visual assessments of instrument exposure. The skewness of the distribution of estimated errors in MAT is proposed as a simple indicator of instrument exposure. Copyright © 2005 Royal Meteorological Society

 
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