An algorithm based on sea-level pressure fluctuations to identify major Baltic inflow events

Abstract

A B S T R A C T Major Baltic inflows are an important process to sustain the sensitive steady state of the Baltic Sea. We introduce an algorithm to identify atmospheric variability favourable for major Baltic inflows. The algorithm is based on sea-level pressure (SLP) fields as the only parameter. Characteristic SLP pattern fluctuations include a precursory phase of 30 days and 10 days of inflow period. The algorithm identifies successfully the majority of observed major Baltic inflows between 1961 and 2010. In addition, the algorithm finds some occurrences which cannot be related to observed inflows. In these cases with favourable atmospheric conditions, inflows were precluded by contemporaneously existing saline water masses or strong freshwater supply. Moreover, the algorithm clearly identifies the stagnation periods as a lack of SLP variability favourable for MBIs. This indicates that the lack of inflows is mainly a consequence of missing atmospheric forcing during this period. The only striking inflow which is not identified by the algorithm is the event in January 2003. We demonstrate that this is due to the special evolution of SLP fields which are not comparable with any other event. Finally, the algorithm is applied to an ensemble of scenario simulations. The result indicates that the number of atmospheric events favourable for major Baltic inflows increases slightly in all scenarios.

Sensitivity of the overturning circulation of the Baltic Sea to climate change, a numerical experiment

“…For these reasons we distance our analysis strategy from that taken by Matthäus (2006) or Schimanke et al (2014): instead of analyzing MBIs, or any salt inflow that reaches the lower layers of the Baltic Sea, as discrete or quantified phenomena, we perform our analysis on the resulting circulation which is directly driven by MBIs, that is the Baltic Sea haline conveyor belt as defined by Döös et al (2004). Döös et al (2004) define a meridional stream function in the Baltic Sea, which can be viewed along meridional and depth axis.…”

“…The work done by Schimanke et al (2014) identified atmospheric patterns related with MBIs. In their study, they used observed salinities following the protocol defined by Matthäus (2006) in order to identify MBIs.…”

“…We set in total four simulations using the same atmospheric forcing that are used by Schimanke et al (2014). Based on two global climate models (EC-EARTH and MPI) driving the RCA4 atmospheric configuration (Samuelsson et al 2011), we have access to the simulated atmospheric circulation for the control period , and for two emission scenarios (RCP 4.5 and RCP 8.5) for the period 2005-2100.…”

“…The purpose of this article is to provide a broader answer in terms of changes in the MBI process by combining the latest climate scenarios used by Schimanke et al (2014) with the use of a Baltic Sea ocean model. In particular, we aim to understand what are the effect of changes in direct atmospheric forcing (wind forcing, temperature) on the Baltic Sea thermo-haline structure and how these changes affect the baroclinic circulation.…”

“…The amount of river runoff delivered to the Baltic Sea, and its narrow connection to the North Sea through 1 3 their decrease. Lately, one can cite (Schimanke et al 2014) who used a EOF decomposition of atmospheric pressure over Northern Europe to identify the atmospheric patterns that create MBIs. Based on this decomposition and using five different climate scenarios (Samuelsson et al 2011), they have forecasted an increase of MBIs in the Baltic Sea towards the end of the 21st century.…”