“…So far, several very diverse paleo-DA schemes have been investigated, including pattern nudging (von Storch et al, 2000), forcing singular vectors (Barkmeijer et al, 2003;van der Schrier and Barkmeijer, 2005), 4D-Var (Paul and Schäfer-Neth, 2005;Kurahashi-Nakamura et al, 2014), particle filters (Annan and Hargreaves, 2012;Dubinkina et al, 2011;Dubinkina and Goosse, 2013;Mathiot et al, 2013;Matsikaris et al, 2015) and ensemble Kalman filter techniques (EnKF; Huntley and Hakim, 2010;Bhend et al, 2012;Pendergrass et al, 2012;Steiger et al, 2014; see Hughes and Ammann, 2009;Widmann et al, 2010;Hakim et al, 2013 for further references).…”