'''DEFINITION'''

The medsea_omi_tempsal_sst_anomaly product includes the annual mean Sea Surface Temperature (SST) anomaly map of the Mediterranean Sea in 2019. This OMI is derived from the CMEMS Reprocessed Mediterranean L4 SST satellite product (SST_MED_SST_L4_REP_OBSERVATIONS_010_021, see e.g. the OMI QUID, http://marine.copernicus.eu/documents/QUID/CMEMS-OMI-QUID-MEDSEA-SST.pdf), which provided the SSTs used to compute the SST anomalies over the Mediterranean Sea. This reprocessed product consists of daily (nighttime) optimally interpolated 0.05° grid resolution SST maps over the Mediterranean Sea built from the ESA Climate Change Initiative (CCI) (Merchant et al., 2019) and Copernicus Climate Change Service (C3S) initiatives, including also an adjusted version of the AVHRR Pathfinder dataset version 5.3 (Saha et al., 2018) to increase the input observation coverage. Anomalies are computed against the 1993-2014 reference period. The reference for this OMI can be found in the first and second issue of the Copernicus Marine Service Ocean State Report (OSR), Section 1.1 (Roquet et al., 2016; Mulet et al., 2018).

'''CONTEXT'''

Sea surface temperature (SST) is a key climate variable since it deeply contributes in regulating climate and its variability (Deser et al., 2010). SST is then essential to monitor and characterise the state of the global climate system (GCOS 2010). Long-term SST variability, from interannual to (multi-)decadal timescales, provides insight into the slow variations/changes in SST, i.e. the temperature trend (e.g., Pezzulli et al., 2005). In addition, on shorter timescales, SST anomalies become an essential indicator for extreme events, as e.g. marine heatwaves (Hobday et al., 2018). The Mediterranean Sea is a climate change hotspot (Giorgi F., 2006). Indeed, Mediterranean SST has experienced a continuous warming trend since the beginning of 1980s (e.g., Pisano et al., 2020; Pastor et al., 2020). Specifically, since the beginning of the 21st century (from 2000 onward), the Mediterranean Sea featured the highest SSTs and this warming trend is expected to continue throughout the 21st century (Kirtman et al., 2013).

'''CMEMS KEY FINDINGS'''

A simple and common approach to quantify the magnitude and spatial distribution of the nonseasonal Sea Surface Temperature (SST) variability is to map the SST anomalies (Deser et al., 2010), as shown in the figure. In 2019, the Mediterranean Sea SST basin average anomaly was 0.4 ± 0.2 °C above the 1993-2014 climatology. On average, 2019 was a warm year for the Mediterranean Sea but milder than previous year (2018), which was characterized by a stronger anomaly of about 0.7 °C. The 2019 anomaly spatial pattern indicates positive SST anomalies almost all over the Mediterranean Sea. Stronger positive temperature anomalies (with extremes close to 1.2 °C) characterized the South Adriatic and Ionian cyclonic circulation areas, and the Northern sectors of the Aegean and Levantine basins. Negative anomalies (with extremes close to -0.5 °C) characterized the Alboran Sea.