scholarly journals Development and evaluation of a system of proxy data assimilation for paleoclimate reconstruction

2017 ◽  
Vol 13 (4) ◽  
pp. 379-393 ◽  
Author(s):  
Atsushi Okazaki ◽  
Kei Yoshimura
Keyword(s):  
Data Assimilation ◽  
Ice Cores ◽  
Observation System ◽  
Proxy Data ◽  
Paleoclimate Reconstruction ◽  
Past Climate ◽  
Temperature And Precipitation ◽  
Low Latitudes ◽  
Proxy Models ◽  
Isotopic Proxies

Abstract. Data assimilation (DA) has been successfully applied in the field of paleoclimatology to reconstruct past climate. However, data reconstructed from proxies have been assimilated, as opposed to the actual proxy values. This prevented full utilization of the information recorded in the proxies. This study examined the feasibility of proxy DA for paleoclimate reconstruction. Isotopic proxies (δ18O in ice cores, corals, and tree-ring cellulose) were assimilated into models: an isotope-enabled general circulation model (GCM) and forward proxy models, using offline data assimilation. First, we examined the feasibility using an observation system simulation experiment (OSSE). The analysis showed a significant improvement compared with the first guess in the reproducibility of isotope ratios in the proxies, as well as the temperature and precipitation fields, when only the isotopic information was assimilated. The reconstruction skill for temperature and precipitation was especially high at low latitudes. This is due to the fact that isotopic proxies are strongly influenced by temperature and/or precipitation at low latitudes, which, in turn, are modulated by the El Niño–Southern Oscillation (ENSO) on interannual timescales. Subsequently, the proxy DA was conducted with real proxy data. The reconstruction skill was decreased compared to the OSSE. In particular, the decrease was significant over the Indian Ocean, eastern Pacific, and the Atlantic Ocean where the reproducibility of the proxy model was lower. By changing the experimental design in a stepwise manner, the decreased skill was suggested to be attributable to the misrepresentation of the atmospheric and proxy models and/or the quality of the observations. Although there remains a lot to improve proxy DA, the result adequately showed that proxy DA is feasible enough to reconstruct past climate.

scholarly journals Development and evaluation of a system of proxy data assimilation for paleoclimate reconstruction

2016 ◽  
Author(s):  
Atsushi Okazaki ◽  
Kei Yoshimura
Keyword(s):  
Data Assimilation ◽  
Southern Oscillation ◽  
Ice Cores ◽  
Observation System ◽  
Proxy Data ◽  
Paleoclimate Reconstruction ◽  
Temperature And Precipitation ◽  
Reconstructed Temperature ◽  
Low Latitudes ◽  
Isotopic Proxies

Abstract. Data assimilation (DA) has been successfully applied in the field of paleoclimatology to reconstruct past climate. However, data reconstructed from proxies have been assimilated, as opposed to the actual proxy values. This banned to fully utilize the information recorded in the proxies. This study examined the feasibility of proxy DA for paleoclimate reconstruction. Isotopic proxies (δ18O in ice cores, corals, and tree-ring cellulose) were assimilated into models: an isotope enabled general circulation model (GCM) and forward proxy models, using offline data assimilation. First, we examined the feasibility using an observation system simulation experiment (OSSE). The analysis showed a significant improvement compared with the first guess in the reproducibility of isotope ratios in the proxies, as well as the temperature and precipitation fields, when only the isotopic information was assimilated. The accuracy for temperature and precipitation was especially high at low latitudes. This is due to the fact that isotopic proxies are strongly influenced by temperature and/or precipitation at low latitudes, which, in turn, are modulated by the El Niño-Southern Oscillation (ENSO) on interannual timescales. The proxy temperature DA had comparable or higher accuracy than the reconstructed temperature DA. The proxy DA was compared with real proxy data. The reconstruction accuracy was decreased compared to the OSSE. In particular, the decrease was significant over the Indian Ocean, eastern Pacific, and the Atlantic Ocean where the reproducibility of the proxy model was lower. By changing the experimental design in a stepwise manner, the decrease in accuracy was found to be attributable to the misrepresentation of the models. In addition, the accuracy was also dependent on the number and/or distribution of the proxies to be assimilated. Thus, to improve climate DA, it is necessary to enhance the performance of models, as well as to increase the number of proxies.

scholarly journals Wavelet analysis reveals periodic oscillations in a 1700 year ice-core record from Guliya, China

2006 ◽  
Vol 43 ◽  
pp. 132-136 ◽  
Author(s):  
Meixue Yang ◽  
Tandong Yao ◽  
Xiaohua Gou ◽  
Huijun Wang ◽  
Thomas Neumann
Keyword(s):  
Wavelet Analysis ◽  
Ice Core ◽  
Ice Cores ◽  
Past Climate ◽  
Ice Caps ◽  
The Past ◽  
Ice Cap ◽  
Temperature And Precipitation ◽  
Temperature Records ◽  
Precipitation Records

AbstractIce cores contribute important records of past climate changes. As one of the thickest ice caps in central Asia, the Guliya ice cap (35°17′ N, 81°29′ E) provides valuable information for this critical region about the past climate and environment changes. We used wavelet analysis to examine periodic temperature and precipitation oscillations over the past 1700 years recorded in the Guliya ice core. The results show non-linear oscillations in the ice-core records, with multiple timescales. Temperature records indicate persistent oscillations with periodicities of approximately 200, 150 and 70 years. Precipitation records show significant periodicities at 200, 100, 150 and 60 years. However, the amplitude modulation and frequency vary with time. Wavelet analysis can explore these time series in greater detail and furnish additional useful information.

scholarly journals Temperature and precipitation signal in two Alpine ice cores over the period 1961–2001

2014 ◽  
Vol 10 (3) ◽  
pp. 1093-1108 ◽  
Author(s):  
I. Mariani ◽  
A. Eichler ◽  
T. M. Jenk ◽  
S. Brönnimann ◽  
R. Auchmann ◽  
...  
Keyword(s):  
Meteorological Data ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Global Network ◽  
Proxy Data ◽  
Altitude Effect ◽  
Temperature And Precipitation ◽  
Precipitation Regimes ◽  
Combining Data

Abstract. Water stable isotope ratios and net snow accumulation in ice cores are commonly interpreted as temperature or precipitation proxies. However, only in a few cases has a direct calibration with instrumental data been attempted. In this study we took advantage of the dense network of observations in the European Alpine region to rigorously test the relationship of the annual and seasonal resolved proxy data from two highly resolved ice cores with local temperature and precipitation. We focused on the time period 1961–2001 with the highest amount and quality of meteorological data and the minimal uncertainty in ice core dating (±1 year). The two ice cores were retrieved from the Fiescherhorn glacier (northern Alps, 3900 m a.s.l.), and Grenzgletscher (southern Alps, 4200 m a.s.l.). A parallel core from the Fiescherhorn glacier allowed assessing the reproducibility of the ice core proxy data. Due to the orographic barrier, the two flanks of the Alpine chain are affected by distinct patterns of precipitation. The different location of the two glaciers therefore offers a unique opportunity to test whether such a specific setting is reflected in the proxy data. On a seasonal scale a high fraction of δ18O variability was explained by the seasonal cycle of temperature (~60% for the ice cores, ~70% for the nearby stations of the Global Network of Isotopes in Precipitation – GNIP). When the seasonality is removed, the correlations decrease for all sites, indicating that factors other than temperature such as changing moisture sources and/or precipitation regimes affect the isotopic signal on this timescale. Post-depositional phenomena may additionally modify the ice core data. On an annual scale, the δ18O/temperature relationship was significant at the Fiescherhorn, whereas for Grenzgletscher this was the case only when weighting the temperature with precipitation. In both cases the fraction of interannual temperature variability explained was ~20%, comparable to the values obtained from the GNIP stations data. Consistently with previous studies, we found an altitude effect for the δ18O of −0.17‰/100 m for an extended elevation range combining data of the two ice core sites and four GNIP stations. Significant correlations between net accumulation and precipitation were observed for Grenzgletscher during the entire period of investigation, whereas for Fiescherhorn this was the case only for the less recent period (1961–1977). Local phenomena, probably related to wind, seem to partly disturb the Fiescherhorn accumulation record. Spatial correlation analysis shows the two glaciers to be influenced by different precipitation regimes, with the Grenzgletscher reflecting the characteristic precipitation regime south of the Alps and the Fiescherhorn accumulation showing a pattern more closely linked to northern Alpine stations.

scholarly journals Greenland temperature and precipitation over the last 20 000 years using data assimilation

2020 ◽  
Vol 16 (4) ◽  
pp. 1325-1346
Author(s):  
Jessica A. Badgeley ◽  
Eric J. Steig ◽  
Gregory J. Hakim ◽  
Tyler J. Fudge
Keyword(s):  
Data Assimilation ◽  
Spatial Patterns ◽  
Climate Model ◽  
Ice Core ◽  
Ice Sheet ◽  
Proxy Data ◽  
Model Simulations ◽  
Temperature And Precipitation ◽  
Climate Model Simulations ◽  
Paleoclimate Data

Abstract. Reconstructions of past temperature and precipitation are fundamental to modeling the Greenland Ice Sheet and assessing its sensitivity to climate. Paleoclimate information is sourced from proxy records and climate-model simulations; however, the former are spatially incomplete while the latter are sensitive to model dynamics and boundary conditions. Efforts to combine these sources of information to reconstruct spatial patterns of Greenland climate over glacial–interglacial cycles have been limited by assumptions of fixed spatial patterns and a restricted use of proxy data. We avoid these limitations by using paleoclimate data assimilation to create independent reconstructions of mean-annual temperature and precipitation for the last 20 000 years. Our method uses oxygen isotope ratios of ice and accumulation rates from long ice-core records and extends this information to all locations across Greenland using spatial relationships derived from a transient climate-model simulation. Standard evaluation metrics for this method show that our results capture climate at locations without ice-core records. Our results differ from previous work in the reconstructed spatial pattern of temperature change during abrupt climate transitions; this indicates a need for additional proxy data and additional transient climate-model simulations. We investigate the relationship between precipitation and temperature, finding that it is frequency dependent and spatially variable, suggesting that thermodynamic scaling methods commonly used in ice-sheet modeling are overly simplistic. Our results demonstrate that paleoclimate data assimilation is a useful tool for reconstructing the spatial and temporal patterns of past climate on timescales relevant to ice sheets.

scholarly journals Testing the Fidelity of Methods Used in Proxy-Based Reconstructions of Past Climate

2005 ◽  
Vol 18 (20) ◽  
pp. 4097-4107 ◽  
Author(s):  
Michael E. Mann ◽  
Scott Rutherford ◽  
Eugene Wahl ◽  
Caspar Ammann
Keyword(s):  
Tree Rings ◽  
Climate Changes ◽  
Ice Cores ◽  
Data Networks ◽  
Proxy Data ◽  
Climate History ◽  
Past Climate ◽  
Climate Proxy ◽  
The Past ◽  
Statistical Approaches

Abstract Two widely used statistical approaches to reconstructing past climate histories from climate “proxy” data such as tree rings, corals, and ice cores are investigated using synthetic “pseudoproxy” data derived from a simulation of forced climate changes over the past 1200 yr. These experiments suggest that both statistical approaches should yield reliable reconstructions of the true climate history within estimated uncertainties, given estimates of the signal and noise attributes of actual proxy data networks.

scholarly journals Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM

2009 ◽  
Vol 5 (3) ◽  
pp. 1297-1336 ◽  
Author(s):  
M. Heinemann ◽  
J. H. Jungclaus ◽  
J. Marotzke
Keyword(s):  
Temperature Difference ◽  
Radiative Forcing ◽  
Co2 Concentration ◽  
The Arctic ◽  
Balance Model ◽  
Proxy Data ◽  
Reference Simulation ◽  
Low Latitudes ◽  
Planetary Albedo ◽  
Temperature Proxy

Abstract. We investigate the late Paleocene/early Eocene (PE) climate using the coupled atmosphere-ocean-sea ice model ECHAM5/MPI-OM. The surface in our PE control simulation is on average 297 K warm and ice-free, despite a moderate CO2 concentration of 560 ppm. Compared to a pre-industrial reference simulation (PR), low latitudes are 5 to 8 K warmer, while high latitudes are up to 40 K warmer. This high-latitude amplification is in line with proxy data, yet a comparison to sea surface temperature proxy data suggests that the Arctic surface temperatures are still too low. To identify the mechanisms that cause the PE-PR temperature difference, we fit a zero-dimensional energy balance model to the ECHAM5/MPI-OM results. Doubled pCO2 in PE compared to PR, increased atmospheric water vapour, and a slightly increased longwave cloud radiative forcing together cause about 2/3 of the PE-PR temperature difference; planetary albedo changes cause about 1/3. Our results support the hypothesis that local radiative effects as well as topographic changes, rather than increased meridional heat transports, were responsible for the "equable" PE climate.

scholarly journals Evaluation of Regional Aircraft Observations Using TAMDAR

2010 ◽  
Vol 25 (2) ◽  
pp. 627-645 ◽  
Author(s):  
William R. Moninger ◽  
Stanley G. Benjamin ◽  
Brian D. Jamison ◽  
Thomas W. Schlatter ◽  
Tracy Lorraine Smith ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Data Assimilation ◽  
Meteorological Data ◽  
Time Range ◽  
Observation System ◽  
Vertical Resolution ◽  
Commercial Aircraft ◽  
Aircraft Observation ◽  
Aircraft Observations ◽  
High Vertical Resolution

Abstract A multiyear evaluation of a regional aircraft observation system [Tropospheric Aircraft Meteorological Data Reports (TAMDAR)] is presented. TAMDAR observation errors are compared with errors in traditional reports from commercial aircraft [aircraft meteorological data reports (AMDAR)], and the impacts of TAMDAR observations on forecasts from the Rapid Update Cycle (RUC) over a 3-yr period are evaluated. Because of the high vertical resolution of TAMDAR observations near the surface, a novel verification system has been developed and employed that compares RUC forecasts against raobs every 10 hPa; this revealed TAMDAR-related positive impacts on RUC forecasts—particularly for relative humidity forecasts—that were not evident when only raob mandatory levels were considered. In addition, multiple retrospective experiments were performed over two 10-day periods, one in winter and one in summer; these allowed for the assessment of the impacts of various data assimilation strategies and varying data resolutions. TAMDAR’s impacts on 3-h RUC forecasts of temperature, relative humidity, and wind are found to be positive and, for temperature and relative humidity, substantial in the region, altitude, and time range over which TAMDAR-equipped aircraft operated during the studied period of analysis.

scholarly journals Revisions and Extension of the Hohenheim Oak and Pine Chronologies: New Evidence About the Timing of the Younger Dryas/Preboreal Transition

Radiocarbon ◽  
1998 ◽  
Vol 40 (3) ◽  
pp. 1107-1116 ◽  
Author(s):  
Marco Spurk ◽  
Michael Friedrich ◽  
Jutta Hofmann ◽  
Sabine Remmele ◽  
Burkhard Frenzel ◽  
...  
Keyword(s):  
Calibration Curve ◽  
Younger Dryas ◽  
Ice Cores ◽  
Early Holocene ◽  
Proxy Data ◽  
The Past ◽  
Varve Chronology ◽  
New Evidence ◽  
Radiocarbon Calibration

Oak and pine samples housed at the Institute of Botany, University of Hohenheim, are the backbone of the early Holocene part of the radiocarbon calibration curve, published in 1993 (Becker 1993; Kromer and Becker 1993; Stuiver and Becker 1993; Vogel et al. 1993). Since then the chronologies have been revised. The revisions include 1) the discovery of 41 missing years in the oak chronology and 2) a shift of 54 yr for the oldest part back into the past. The oak chronology was also extended with new samples as far back as 10,429 BP (8480 BC). In addition, the formerly tentatively dated pine chronology (Becker 1993) has been rebuilt and shifted to an earlier date. It is now positioned by 14C matching at 11,871-9900 BP (9922–7951 BC) with an uncertainty of ±20 yr (Kromer and Spurk 1998). With these new chronologies the 14C calibration curve can now be corrected, eliminating the discrepancy in the dating of the Younger Dryas/Preboreal transition between the proxy data of the GRIP and GISP ice cores (Johnsen et al. 1992; Taylor et al. 1993), the varve chronology of Lake Gościąż (Goslar et al. 1995) and the pine chronology (Becker, Kromer and Trimborn 1991).

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