An ensemble-based approach to climate reconstructions

Abstract

Abstract. Data assimilation is a promising approach to obtain climate reconstructions that are both consistent with observations of the past and with our understanding of the physics of the climate system as represented in the climate model used. Here, we investigate the use of ensemble square root filtering (EnSRF) -a technique used in weather forecasting -for climate reconstructions. We constrain an ensemble of 29 simulations from an atmosphere-only general circulation model (GCM) with 37 pseudo-proxy temperature time series. Assimilating spatially sparse information with low temporal resolution (semi-annual) improves the representation of not only temperature, but also other surface properties, such as precipitation and even upper air features such as the intensity of the northern stratospheric polar vortex or the strength of the northern subtropical jet. Given the sparsity of the assimilated information and the limited size of the ensemble used, a localisation procedure is crucial to reduce "overcorrection" of climate variables far away from the assimilated information.

Towards the assimilation of tree-ring-width records using ensemble Kalman filtering techniques

“…2a). This situation, where a DA method presents TA analysis skill for averaging periods where the TA forecasting skill is completely lost, has been previously observed in studies applying EnKF techniques on TA quantities (Huntley and Hakim 2010;Bhend et al 2012;Pendergrass et al 2012;Steiger et al 2014). DA performed under these circumstances is currently labeled as "offline".…”

“…To date, several very diverse DA schemes have been tested on climate models-such as pattern nudging (von Storch et al 2000), forcing singular vectors (Barkmeijer et al 2003), adjoint method (Kurahashi-Nakamura et al 2014), particle filter Mathiot et al 2013) and ensemble Kalman filter (Bhend et al 2012;Pendergrass et al 2012)-providing very encouraging results regarding the potential constraint of the inter-annual internal variability. As for the observations employed in these experiments, the dominant approach has been to use either pseudo-proxies or statistically reconstructed climate Abstract This paper investigates the applicability of the Vaganov-Shashkin-Lite (VSL) forward model for treering-width chronologies as observation operator within a proxy data assimilation (DA) setting.…”

Climate windows for Polynesian voyaging to New Zealand and Easter Island

“…A signal-to-noise ratio of 0.33 was added to each pseudoproxy to simulate realworld uncertainty (after ref. 38). The 1,200-y model simulation was then reconstructed at 20-y resolution using the multivariate data assimilation approach to select climate state analogs from the unforced 10,000-y simulation (see Methods) based only on the climate signals from the pseudoproxy network.…”

On-line and off-line data assimilation in palaeoclimatology: a case study

“…The off-line approach of DA was advanced by Bhend et al (2012), through the assimilation of proxy data into a high-resolution general circulation model (GCM). The ensemble square root filter (EnSRF), a variant of the ensemble Kalman filter, was used to update the ensembles with climate proxy information.…”