Copernicus Marine In Situ TAC - Ocean Monitoring Indicator OMI_EXTREME_SST_BALTIC_sst_mean_and_anomaly_obs

DEFINITION The OMI_EXTREME_SST_BALTIC_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 Baltic Sea has showed in the last two decades a warming trend across the whole basin with more frequent and severe heat waves (IPCC, 2022). This trend is significantly higher when considering only the summer season, which would affect the high extremes (e.g. Høyer and Karagali, 2016).
COPERNICUS MARINE SERVICE KEY FINDINGS The mean 99th percentiles showed in the area go from 19.6ºC in Tallinn station to 21.4ºC in Rohukula station, and the standard deviation ranges between 1ºC and 5.4ºC reached in the Estonian Coast. Results for this year show either positive or negative low anomalies in the Coast of Sweeden (-0.7/+0.5ºC) within the standard deviation margin and a general positive anomaly in the rest of the region. This anomaly is noticeable in Rohukula and Virtsu tide gauges (Estonia) with +3.9ºC, but inside the standard deviation in both locations. In the South Baltic two stations, GreifswalderOie and Neustadt, reach an anomaly of +2ºC, but around the standard deviation.
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