Comparison of COADS Release 1a Winds with Instrumental Measurements in the Northwest Atlantic

Swail

et al. 2007

Globally averaged wind speeds from archived ship reports show an increasing trend since the 1940s, which previous studies attributed to the gradual shift from visually estimated to anemometer-measured winds, and an increase in mean anemometer height. To test this hypothesis, adjustments to account for these changes were applied to individual ship wind observations in the International Comprehensive Ocean-Atmosphere Data Set (ICOADS). Annual means calculated from adjusted reports were compared to reanalysis near-surface winds in consistently well-sampled regions for the period 1958-2002.The adjustments to individual ship wind reports for known biases improve the homogeneity over the entire period and remove trends, prior to the early 1980s. However, for the 21-year period 1982-2002, trends remain in the annual mean spatially averaged adjusted winds, of 0.4 ms −1 decade −1 (6% decade −1 ) for estimated speeds, and of 0.2 ms −1 decade −1 (3% decade −1 ) for measured speeds. In contrast, co-located reanalysis near-surface wind speeds show little change, 1% decade −1 or less. Anemometers were installed on increasing numbers of ships during the period of study, even as many of these ships continued to report estimated winds. Part of the trend in estimated wind speeds is probably spurious, most likely a result of observers being increasingly influenced by readings from anemometers located well above 10-m. This influence is indicated by the gradual reduction in the tendency to underestimate nighttime marine winds. Results confirm earlier findings that reanalysis near-surface winds were biased low. The paper summarizes methods that could be employed to account for remaining inhomogeneities and thereby improve the quality of the marine wind climate record.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Trends in ship wind speeds adjusted for observation method and height

Thomas

Swail

et al. 2007

“…We did not account for a possible high bias in visual averages of an analogue anemometer dial. Errors in calculating true winds from platform relative winds could introduce consistent differences if shipping lanes are aligned with prevailing winds (Gulev, 1999). New logging systems mean that the occurrences of such errors should reduce over time.…”

Section: Possible Sources Of Residual Inhomogeneitymentioning

confidence: 99%

“…Inhomogeneities occur for many reasons, including: different observing methods (Quayle, 1980;Peterson and Hasse, 1987;Cardone et al, 1990;Wilkerson and Earle, 1990;Kent et al, 1993Kent et al, , 1998Lindau 1995a;); systematic changes in measurement height (Cardone et al, 1990); airflow distortion over the ship (Dobson, 1981;Yelland et al, 2002;Moat et al, 2005); different averaging times and methods (Dobson, 1981;Pierson, 1983;Gilhousen 1987;Taylor et al, 2002); and the effect of environmental conditions (Dobson, 1981;Kent et al, 1993). Other sources of observational error include: differences from nominal observing time; the anemometer type, calibration, and location; errors in calculation of true wind from the relative wind (Kent et al, 1993;Gulev, 1999;Smith et al, 1999); rounding artefacts; and for Beaufort winds, the stage of development of the waves. Researchers have studied the relationship between Voluntary Observing Ship (VOS) winds and pressures and have concluded that in some cases the pressure and wind trends are consistent (Inoue and Bigg, 1995) and in some cases inconsistent (Posmentier et al, 1989;Ward and Hoskins, 1996).…”

Section: Introductionmentioning

confidence: 99%

Methods to homogenize wind speeds from ships and buoys

Thomas¹,

Swail³

2005

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.

Quantifying random measurement errors in Voluntary Observing Ships' meteorological observations

Berry

2005

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.