| 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) |