Abstract
Abstract. Since numerical weather prediction (NWP) models are usually used to force ocean circulation models, it is important to investigate their skill in reproducing surface meteorological parameters in open sea conditions. Near-surface meteorological data (air temperature, relative humidity, barometric pressure, wind speed and direction) have been acquired from several sensors deployed on an offshore large spar buoy in the Ligurian Sea (Northern Mediterranean Sea) from February to December 2000. The buoy collected 7857 valid records out of 8040 during 335 days at sea. These observations have been compared with data from NWP models and specifically, the outputs of the ECMWF analysis in the two grid points closest to the buoy position. Hourly data acquired by the buoy have been undersampled to fit the data set of the model composed by values computed at the four synoptic hours. For each mentioned meteorological parameter an analysis has been performed by evaluating instantaneous synoptic differences, distributions, daily and annual variations and related statistics. The comparison shows that the model reproduces correctly the baric field while significant differences result for the other variables, which are more affected by local conditions. This suggests that the observed discrepancies may be due to the poor resolution of the model that probably is not sufficient to appropriately discriminate between land and ocean surfaces in a small basin such as the Ligurian Sea and to take into account local peculiarities. The use of time- and space-averaged model data reduces the differences with respect to the in situ observations, thus making the model data usable for analysis with minor requirements about time and space resolution. Although this comparison is strongly limited and we cannot exclude measurement errors, its results suggest a great caution in the use of the model data, especially at high frequency resolution. They may lead to incorrect estimates of atmospheric forcing into ocean circulation models, causing important errors in those areas, such as the Mediterranean Sea, where ocean circulation is strongly coupled with atmosphere and its high variability. Key words. Oceanography; general (marginal and semiclosed seas; marine meteorology; numerical modelling)
Highlights
Surface meteorological data from numerical weather prediction (NWP) models are widely used for computing surface forcing in ocean models and climate studies
For the first time in the Mediterranean Sea, a comparison has been performed between meteorological surface parameters measured from a fixed offshore buoy and the outputs of the European Centre for Medium Range Weather Forecast (ECMWF) analysis
The buoy is moored in the Ligurian Sea, a peculiar site in the Mediterranean Sea characterised by specific atmospheric and marine phenomena
Summary
Surface meteorological data from numerical weather prediction (NWP) models are widely used for computing surface forcing in ocean models and climate studies. Weller and Anderson (1996) compared near-surface meteorology and air-sea fluxes from a buoy moored near the centre of the COARE-IFA (Coupled Ocean-Atmosphere Response Experiment – Intensive Flux Array) with European Centre for Medium Range Weather Forecast (ECMWF) analysis for the period 15 November 1992 to 15 February 1993. They found significant discrepancies between the model and the observations. Concurrent data from the United States National Centers for Environmental Prediction (NCEP) reanalysis and ECMWF operational analysis This last comparison showed that the model provided realistic surface winds, but failed to replicate other observed surface meteorology and to produce realistic heat fluxes.
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