A Statistical Determination of the Random Observational Errors Present in Voluntary Observing Ships Meteorological Reports

Abstract

The random observational errors for meteorological variables within the Comprehensive Ocean?Atmosphere Dataset (COADS) have been determined using the semivariogram statistical technique. The error variance has been calculated using four months of data, spanning summer and winter months and the start and end of the dataset. The random errors found range from 1.3 to 2.8 m s?1 for 10-m-corrected wind speed, 1.2 to 7.1 mb for surface pressure, 0.8° to 3.3°C for 10-m air temperature, 0.4° to 2.8°C for sea surface temperature, and 0.6 to 1.8 g kg?1 for 10-m specific humidity. The air temperature and specific humidity random observational errors contain a dependence on their mean values, but correlations between errors and mean values are low for the other variables analyzed. The accuracy of the error estimates increases with the number of observational data pairs used in the analysis. Wind speed random observational errors were reduced by height correction and by the use of the Lindau Beaufort Scale. Taken over the latitude range 45°S?75°N, the mean random observational errors are 2.1 ± 0.2 m s?1 for 10-m-corrected wind speed, 2.3 ± 0.2 mb for surface pressure, 1.4° ± 0.1°C for 10-m air temperature, 1.5° ± 0.1°C for sea surface temperature, and 1.1 ± 0.2 g kg?1 for 10-m specific humidity.