The effect of the NAO on sea level and on mass changes in the Mediterranean Sea

Abstract

[1] Sea level in the Mediterranean Sea over the period 1993-2011 is studied on the basis of altimetry, temperature, and salinity data and gravity measurements from Gravity Recovery and Climate Experiment (GRACE) (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)). An observed increase in sea level corresponds to a linear sea level trend of 3.0 AE 0.5 mm/yr dominated by the increase in the oceanic mass in the basin. The increase in sea level does not, however, take place linearly but over two 2-3 year periods, each contributing 2-3 cm of sea level. Variability in the basin sea level and its mass component is dominated by the winter North Atlantic Oscillation (NAO). The NAO influence on sea level is primarily linked with atmospheric pressure changes and local wind field changes. However, neither the inverse barometer correction nor a barotropic sea level model forced by atmospheric pressure and wind can remove fully the NAO influence on the basin sea level. Thus, a third contributing mechanism linked with the NAO is suggested. During winter 2010, a low NAO index caused a basin sea level increase of 12 cm which was almost wholly due to mass changes and is evidenced by GRACE. About 8 cm of the observed sea level change can be accounted for as due to atmospheric pressure and wind changes. The residual 4 cm of sea level change is caused by the newly identified contribution. The physical mechanisms that may be responsible for this additional contribution are discussed.

Improving sea level simulation in Mediterranean regional climate models

“…With improved Atlantic LBCs, the MED12 simulation accounts for both local and large-scale sea level changes from the near-Atlantic. These new LBCs allow a major improvement of the representation of mean Mediterranean sea level, as it was proposed by both Calafat et al (2012) and Tsimplis et al (2013). This result also suggests that previous regional projection of Mediterranean sea level should be considered with caution as none of them considered variable Atlantic sea level conditions.…”

Sea-level variability in the Mediterranean Sea from altimetry and tide gauges

“…This in agreement with Oddo et al (2014) who, looking at the sensitivity of the Mediterranean sea level to atmospheric pressure, observed a large scale zonal gradient, which produces higher sea-level values and a larger variance in the sea-level signal in the Levantine basin. These events have already been observed at the basin scale (Calafat et al 2010(Calafat et al , 2012Tsimplis et al 2013) and defined as non-steric fluctuations due to mass transport through the Strait of Gibraltar driven by wind, occurring during a strong negative phase of the North Atlantic Oscillation (Landerer and Volkov 2013).…”

Impact of the North Atlantic Oscillation on Southern Europe Water Distribution: Insights from Geodetic Data

“…The NAO impact on hydrological or oceanic parameters other than the total water mass has been investigated at local or regional scales. For example, Tsimplis et al (2013), Stanev and Peneva (2001), and Oguz et al (2006) evidenced significant correlations between the NAO index and the sea level of the Black Sea, whereas others (Tsimplis et al 2004;Woolf and Tsimplis 2002) conclude the opposite for the same region. In southeastern Europe (Figure 1), the impact of the NAO on hydrological data such as river flows has also been shown, in particular for the Danube-for example, Rîmbu et al (2002) and I.…”

“…Mares et al (2006, meeting presentation)-where this impact has been linked with interannual precipitation over this basin (Mares et al 2012). Concerning water mass, recent studies have shown a significant NAO impact on the Mediterranean Sea oceanic mass at interannual time scale (Tsimplis et al 2013;Fenoglio-Marc et al 2013). However, up to now, such investigations need to be further extended in order to consider the dynamics of the total oceanic and hydrological system over wider areas.…”