Quantifying Structural Uncertainty in Paleoclimate Data Assimilation With an Application to the Last Millennium

2020 ◽  
Vol 47 (22) ◽  
Author(s):  
Daniel E. Amrhein ◽  
Gregory J. Hakim ◽  
Luke A. Parsons
Keyword(s):  
Data Assimilation ◽  
Last Millennium ◽  
Structural Uncertainty ◽  
Paleoclimate Data

scholarly journals Data-assimilation techniques for paleoclimate data

PAGES news ◽  
2009 ◽  
Vol 17 (3) ◽  
pp. 125-126
Author(s):  
Michael Schulz ◽  
◽  
Bette L Otto-Bliesner
Keyword(s):  
Data Assimilation ◽  
Paleoclimate Data

scholarly journals Insights into Atlantic multidecadal variability using the Last Millennium Reanalysis framework

2018 ◽  
Vol 14 (2) ◽  
pp. 157-174 ◽  
Author(s):  
Hansi K. A. Singh ◽  
Gregory J. Hakim ◽  
Robert Tardif ◽  
Julien Emile-Geay ◽  
David C. Noone
Keyword(s):  
Data Assimilation ◽  
Energy Transport ◽  
Atlantic Multidecadal Oscillation ◽  
Spectral Peak ◽  
Shortwave Radiation ◽  
The Arctic ◽  
Last Millennium ◽  
Atlantic Multidecadal Variability ◽  
Multidecadal Variability ◽  
Planetary Albedo

Abstract. The Last Millennium Reanalysis (LMR) employs a data assimilation approach to reconstruct climate fields from annually resolved proxy data over years 0–2000 CE. We use the LMR to examine Atlantic multidecadal variability (AMV) over the last 2 millennia and find several robust thermodynamic features associated with a positive Atlantic Multidecadal Oscillation (AMO) index that reveal a dynamically consistent pattern of variability: the Atlantic and most continents warm; sea ice thins over the Arctic and retreats over the Greenland, Iceland, and Norwegian seas; and equatorial precipitation shifts northward. The latter is consistent with anomalous southward energy transport mediated by the atmosphere. Net downward shortwave radiation increases at both the top of the atmosphere and the surface, indicating a decrease in planetary albedo, likely due to a decrease in low clouds. Heat is absorbed by the climate system and the oceans warm. Wavelet analysis of the AMO time series shows a reddening of the frequency spectrum on the 50- to 100-year timescale, but no evidence of a distinct multidecadal or centennial spectral peak. This latter result is insensitive to both the choice of prior model and the calibration dataset used in the data assimilation algorithm, suggesting that the lack of a distinct multidecadal spectral peak is a robust result.

scholarly journals Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium

2009 ◽  
Vol 5 (5) ◽  
pp. 2115-2156 ◽  
Author(s):  
M. Widmann ◽  
H. Goosse ◽  
G. van der Schrier ◽  
R. Schnur ◽  
J. Barkmeijer
Keyword(s):  
Data Assimilation ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Weather Forecasting ◽  
General Circulation Models ◽  
Last Millennium ◽  
Proxy Data ◽  
Using Data

Abstract. Climate proxy data provide noisy, and spatially incomplete information on some aspects of past climate states, whereas palaeosimulations with climate models provide global, multi-variable states, which may however differ from the true states due to unpredictable internal variability not related to climate forcings, as well as due to model deficiencies. Using data assimilation for combining the empirical information from proxy data with the physical understanding of the climate system represented by the equations in a climate model is in principle a promising way to obtain better estimates for the climate of the past. Data assimilation has been used for a long time in weather forecasting and atmospheric analyses to control the states in atmospheric General Circulation Models such that they are in agreement with observation from surface, upper air, and satellite measurements. Here we discuss the similarities and the differences between the data assimilation problem in palaeoclimatology and in weather forecasting, and present and conceptually compare three data assimilation methods that have been developed in recent years for applications in palaeoclimatology. All three methods (selection of ensemble members, Forcing Singular Vectors, and Pattern Nudging) are illustrated by examples that are related to climate variability over the extratropical Northern Hemisphere during the last millennium. In particular it is shown that all three methods suggest that the cold period over Scandinavia during 1790–1820 is linked to anomalous northerly or easterly atmospheric flow, which in turn is related to a pressure anomaly that resembles a negative state of the Northern Annular Mode.

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