'''DEFINITION'''

The OMI_EXTREME_SST_NORTHWESTSHELF_sst_mean_and_anomaly_obs indicator is based on the computation of the 99th and the 1st percentiles from in situ data (observations). It is computed for the variable sea surface temperature measured by in situ buoys at depths between 0 and 5 meters. The use of percentiles instead of annual maximum and minimum values, makes this extremes study less affected by individual data measurement errors. The percentiles are temporally averaged, and the spatial evolution is displayed, jointly with the anomaly in the target year. This study of extreme variability was first applied to sea level variable (Pérez Gómez et al 2016) and then extended to other essential variables, sea surface temperature and significant wave height (Pérez Gómez et al 2018).

'''CONTEXT'''

Sea surface temperature (SST) is one of the essential ocean variables affected by climate change (mean SST trends, SST spatial and interannual variability, and extreme events). In Europe, several studies show warming trends in mean SST for the last years (von Schuckmann, 2016; IPCC, 2021, 2022). An exception seems to be the North Atlantic, where, in contrast, anomalous cold conditions have been observed since 2014 (Mulet et al., 2018; Dubois et al. 2018; IPCC 2021, 2022). Extremes may have a stronger direct influence in population dynamics and biodiversity. According to Alexander et al. 2018 the observed warming trend will continue during the 21st Century and this can result in exceptionally large warm extremes. Monitoring the evolution of sea surface temperature extremes is, therefore, crucial.

The North-West Self area comprises part of the North Atlantic, where this refreshing trend has been observed, and the North Sea, where a warming trend has been taking place in the last three decades (e.g. Høyer and Karagali, 2016).

'''KEY FINDINGS'''

The mean 99th percentiles showed in the area present a range from 14ºC in the Northwest of the British Isles, 18ºC in the English Channel to 20-21ºC around Denmark (Helgoland Bight, Skagerrak and Kattegat Seas). The standard deviation ranges from 0.5ºC in the English Channel and 0.8in the Northwest of the British Isles to 1.0 in the buoys around Denmark, reaching 3ºC in Helgoland Bight.

Results for this year show either positive (+1ºC) or negative (-0.1) anomalies around their corresponding standard deviation in all the area, except in Hornbaek station in the South of Kattegat Sea where the positive anomaly reaches +2.0ºC, over the 1.3ºC of standard deviation, in concordance with the positive anomalies found in the Zealand Region in the Baltic OMI.

'''DOI (product):'''

https://doi.org/10.48670/moi-00274