Secular Change in Reported Surface Wind Speeds over the Ocean

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: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Trends in ship wind speeds adjusted for observation method and height

Thomas

Kent

Swail

et al. 2007

“…Therefore, 0.5°C is subtracted not only from NAT, but also from daytime AT and DPT observations. Ramage (1987) noted that it can be difficult to identify biases in historical surface wind observations because of mixing in estimated winds from sailing-ship performance and sea surface roughness, and biases in the directly measured anemometer winds. The estimation of sea surface roughness by a number on the socalled Beaufort scale is common in the early decades.…”

Section: Quality Controlmentioning

confidence: 99%

“…However, there were fewer opportunities for reporting winds exceeding 5 m/s during the first half of the century than during the second half of the century. Furthermore, there was no standardized Beaufort scale before World War II (Ramage, 1987;Cardone et al, 1990), which may be a major reason for low wind speeds before 1950. The use of the modified Beaufort scale (Lindau, 1994) yields an increase of about +0.2 m/s in the hemispheric average of the scalar wind before 1950.…”

Section: Slp and Surface Windmentioning

confidence: 99%

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

Ishii¹,

Shouji²,

Sugimoto³

et al. 2005

592

380

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 seasurface 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.

“…We had earlier investigated pre-1950 versions of the MEI in COADS, but found that wind fields in particular had severe problems with respect to changes in measurement techniques, including the shift from sail to motorized ships in the late 19th century, and from sea-state estimates to anemometer measurements in the middle of the 20th century (Ramage, 1987). While reliable homogenized surface wind data appear to be elusive thus far, there have been several successful efforts to create instrumental bias-corrected SST and SLP grids (in particular, Kaplan et al, 1998;Smith and Reynolds, 2003;and Rayner et al, 2003, for the former, and Allan and Ansell, 2006, for the latter) that push the instrumental record back well into the 19th century.…”

Section: Introductionmentioning

confidence: 99%

El Niño/Southern Oscillation behaviour since 1871 as diagnosed in an extended multivariate ENSO index (MEI.ext)

Wolter

Timlin

2011

971

696

El Niño/Southern Oscillation (ENSO) remains the most important coupled ocean-atmosphere phenomenon to cause global climate variability on seasonal to interannual time scales. This paper addresses the need for a reliable ENSO index that allows for the historical definition of ENSO events in the instrumental record back to 1871. The Multivariate ENSO Index (MEI) was originally defined as the first seasonally varying principal component of six atmosphere-ocean (COADS) variable fields in the tropical Pacific basin. It provides for a more complete and flexible description of the ENSO phenomenon than single variable ENSO indices such as the SOI or Niño 3.4 SST. Here we describe our effort to boil the MEI concept down to its most essential components (based on SLP, SST) to enable historical analyses that more than double its period of record to 1871-2005. The new MEI.ext confirms that ENSO activity went through a lull in the earlyto mid-20th century, but was just about as prevalent one century ago as in recent decades. We diagnose strong relationships between peak amplitudes of ENSO events and their duration, as well as between their peak amplitudes and their spacing (periodicity). Our effort is designed to help with the assessment of ENSO conditions through as long a record as possible to be able to differentiate between 'natural' ENSO behaviour in all its rich facets, and the 'Brave New World' of this phenomenon under evolving GHG-related climate conditions. So far, none of the behaviour of recent ENSO events appears unprecedented, including duration, onset timing, and spacing in the last few decades compared to a full century before then.