scholarly journals Impact of proxies and prior estimates on data assimilation using isotope ratios for the climate reconstruction of the last millennium

2020 ◽  
Author(s):  
Satoru Shoji ◽  
Atsushi Okazaki ◽  
Kei Yoshimura
Keyword(s):  
Data Assimilation ◽  
Isotope Ratios ◽  
Climate Reconstruction ◽  
Last Millennium

scholarly journals Climate reconstruction using data assimilation of water isotope ratios from ice cores

2017 ◽  
Vol 122 (3) ◽  
pp. 1545-1568 ◽  
Author(s):  
Nathan J. Steiger ◽  
Eric J. Steig ◽  
Sylvia G. Dee ◽  
Gerard H. Roe ◽  
Gregory J. Hakim
Keyword(s):  
Data Assimilation ◽  
Ice Cores ◽  
Isotope Ratios ◽  
Climate Reconstruction ◽  
Using Data ◽  
Water Isotope

Comparison of isotopic signatures in ice core and speleothem records to an isotope enabled climate model simulation for the last millennium

2021 ◽  
Author(s):  
Yannick Heiser ◽  
Janica Bühler ◽  
Mathieu Casado ◽  
Kira Rehfeld
Keyword(s):  
Climate Variability ◽  
Climate Model ◽  
Southern Oscillation ◽  
Ice Core ◽  
Ice Cores ◽  
Isotope Ratios ◽  
Last Millennium ◽  
Polar Ice ◽  
Geophysical Research ◽  
Ice Core Records

<div> <div> <div> <p>Stable water isotope ratios (δ18O) measured in e.g. ice-cores or speleothems have long been established as temperature proxies and are used to reconstruct past climate variability but still require more quantification on spatial and temporal scales. The high resolution ice-core archives are mainly found in polar and alpine regions, whereas the speleothem records mostly grow in caves in low to mid-latitudes. To bridge between the archives, models are needed to compare the climate variability stored in both ice-cores and speleothems, which will help to evaluate future projections of climate variability.</p> <p>Here, we compare a transient isotope enabled simulation from the Hadley Center Climate Model version 3 (iHadCM3) [1, 2] to polar ice-core records from the iso2k database [3] for the last millennium (LM, 850-1850 CE). We analyze time-averaged isotope ratios and their variability on decadal to centennial timescales to systematically evaluate the offsets and correlation patterns between simulated and recorded isotopes to specific climatic drivers. For better comparability between speleothem and ice core-archives, we also include non-polar ice core records, as well as monitored precipitation δ18O from a global database.</p> <p>We find the time-averaged δ18O offsets between the simulation and ice-core records to be fairly small for most of the polar ice-core sites, indicating a low simulation climate offset.<br>As expected, we find the simulated δ18O variability to be higher in the polar regions of ice-core locations, compared to the simulated variability at speleothem cave locations. Recorded δ18O variability is also generally higher as stored in ice-cores, compared to that stored in speleothems. Both speleothems and ice-core records show damping effects on decadal time scales, which can in part be attributed to the temporal resolution of the individual records. This comparison of different proxy archives to isotope-enabled GCM output shows a promising way to evaluate the model’s capability to resolve δ18O variability.</p> <div> <div> <div> <p>[1]  Bühler, J. C. et al. Comparison of the oxygen isotope signatures in speleothem records and iHadCM3 model simulations for the last millennium. Climate of the Past: Discussions 1–30 (2020).</p> <p>[2]  Tindall, J. C., Valdes, P. J. & Sime, L. C. Stable water isotopes in HadCM3: Isotopic signature of El Niño-Southern Oscillation and the tropical amount effect. Journal of Geophysical Research Atmospheres 114, 1–12 (2009).</p> <p>[3] Konecky, B. L. et al. The Iso2k database: A global compilation of paleo-δ18O and δ2H records to aid understanding of Common Era climate. Earth System Science Data 12, 2261–2288 (2020).</p> </div> </div> </div> </div> </div> </div>

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.

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

2010 ◽  
Vol 6 (5) ◽  
pp. 627-644 ◽  
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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