Wikipedia:Sandbox

DEFINITION
The CMEMS BLKSEA_OMI_seastate_extreme_var_swh_mean_and_anomaly OMI indicator is based on the computation of the annual 99th percentile of Significant Wave Height (SWH) from hourly mean model data. Two different CMEMS products are used to compute the indicator: The Multi Year Product (MYP) and the Analysis product (NRT).

• Mediterranean sea MYP product: MEDSEA_HINDCAST_WAV_006_012
  
• Mediterranean sea NRT product: MEDSEA_ANALYSIS_FORECAST_WAV_006_017
  

Two different indicators constitute the product:

• Map of the 99th mean percentile: It is obtained from the MYP product, the annual 99th percentile is computed for each year of the product. The percentiles are temporally averaged in the whole period (1992-2016).
  
• Anomaly of the 99th percentile in 2018: The 99th percentile of the year 2018 is computed from the NRT product. The anomaly is obtained by subtracting the percentile in 2018 and the mean percentile.
  

CONTEXT
The SEASTATE SWH extreme variability indicator is based on the computation of the 99th percentile (that represent approximately the 1% highest values of SWH) from model results, following the same approach applied by Woodworth and Blackman (2004) to extreme sea levels. This method determines changes in the frequency distribution of the measured variables.
The indicator is defined following the steps of other indicators oriented to monitor the variability of extreme events (Pérez Gómez et al., 2016; Pérez Gómez et al., 2018, Staneva et al., 2014). More details and full scientific evaluation can be found in the CMEMS Ocean State Report 3 (OSR3, Alvarez Fanjul et al., 2019).

CMEMS KEY FINDINGS
The highest values (up to 6 m) of the mean annual 99th percentile extend from the Gulf of Lion to southwestern Sardinia through the Balearic Sea. They result from northerly winds that are accelerated by orography and act over a large area. Northerly winds are responsible for most high waves in the Mediterranean (e.g. Chronis et al. 2011; Menendez et al. 2014). In 2018, the positive anomalies in the east (up to 0.9 m) can be associated with the Mediterranean hurricane “Zorbas” (27/9 – 01/10) which formed in the Ionian sea and propagated northeastwards affecting the Central Mediterranean, Greece and Turkey. Extended positive anomalies are also observed in the Tyrrhenian Sea and offshore from France. The strongest negative anomalies (up to -0.9 m) coincide with the region of maximum mean annual values.

REFERENCES

• Álvarez Fanjul E, Pascual Collar A, Pérez Gómez B, De Alfonso M, García Sotillo M, Staneva J, Clementi E, Grandi A, Zacharioudaki A, Korres G, Ravdas M, Renshaw R, Tinker J, Raudsepp U, Lagemaa P, Maljutenko I, Geyer G, Müller M, Çağlar Yumruktepe V. Sea level, sea surface temperature and SWH extreme percentiles: combined analysis from model results and in situ observations, Section 2.7, p:31. In: Schuckmann K, Le Traon P-Y, Smith N, Pascual A, Djavidnia S, Gattuso J-P, Grégoire M, Nolan G, et al. 2019. Copernicus Marine Service Ocean State Report, Issue 3, Journal of Operational Oceanography, 12:sup1, S1-S123, DOI: 10.1080/1755876X.2019.1633075
  

• Chronis T, Papadopoulos V, Nikolopoulos EI. 2011. QuickSCAT observations of extreme wind events over the Mediterranean and Black Seas during 2000-2008. Int J Climatol. 31: 2068–2077.
  

• Menendez M, García-Díez M, Fita L, Fernández J, Méndez FJ, Gutiérrez JM. 2014. High-resolution sea wind hindcasts over the Mediterranean area. Clim Dyn. 42:1857–1872.
  

• Pérez-Gómez B, Álvarez-Fanjul E, She J, Pérez-González I, Manzano F. 2016. Extreme sea level events, Section 4.4, p:300. In: Von Schuckmann K, Le Traon PY, Alvarez-Fanjul E, Axell L, Balmaseda M, Breivik LA, Brewin RJW, Bricaud C, Drevillon M, Drillet Y, Dubois C , Embury O, Etienne H, García-Sotillo M, Garric G, Gasparin F, Gutknecht E, Guinehut S, Hernandez F, Juza M, Karlson B, Korres G, Legeais JF, Levier B, Lien VS, Morrow R, Notarstefano G, Parent L, Pascual A, Pérez-Gómez B, Perruche C, Pinardi N, Pisano A, Poulain PM , Pujol IM, Raj RP, Raudsepp U, Roquet H, Samuelsen A, Sathyendranath S, She J, Simoncelli S, Solidoro C, Tinker J, Tintoré J, Viktorsson L, Ablain M, Almroth-Rosell E, Bonaduce A, Clementi E, Cossarini G, Dagneaux Q, Desportes C, Dye S, Fratianni C, Good S, Greiner E, Gourrion J, Hamon M, Holt J, Hyder P, Kennedy J, Manzano-Muñoz F, Melet A, Meyssignac B, Mulet S, Nardelli BB, O’Dea E, Olason E, Paulmier A, Pérez-González I, Reid R, Racault MF, Raitsos DE, Ramos A, Sykes P, Szekely T, Verbrugge N. 2016. The Copernicus Marine Environment Monitoring Service Ocean State Report, Journal of Operational Oceanography. 9 (sup2): 235-320. http://dx.doi.org/10.1080/1755876X.2016.1273446
  

• Pérez Gómez B., De Alfonso M., Zacharioudaki A., Pérez González I., Álvarez Fanjul E., Müller M., Marcos M., Manzano F., Korres G., Ravdas M., Tamm S. 2018. Sea level, SST and waves: extremes variability. In: Copernicus Marine Service Ocean State Report, Issue 2, Journal of Operational Oceanography, 11:sup1, Chap. 3.1, s79–s88, DOI: https://doi.org/10.1080/1755876X.2018.1489208
  

• Woodworth PL, Blackman DL. 2004. Evidence for systematic changes in extreme high waters since the mid-1970s. Journal of Climate: 1190–1197