Scale-Dependent Reconstruction of the NAO Index

Timm, O. Elison; Ruprecht, Eberhard; Kleppek, Sabine

doi:10.1175/1520-0442(2004)017<2157:srotni>2.0.co;2

Cited by 53 publications

(17 citation statements)

References 76 publications

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“…The proxy time series were linearly interpolated onto an equidistant time step of 10 yr. Next, the maximum overlap discrete wavelet transform (Percival and Walden 2000;Whitcher et al 2000;Timm et al 2004) was applied as a low-pass filter with a nominal cutoff period at 5120 yr. The same filter is applied to the SIM2b temperatures.…”

Section: B Local Proxy-model Comparisonsupporting

confidence: 64%

Simulation of the Last 21 000 Years Using Accelerated Transient Boundary Conditions*

2007

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The earth system model of intermediate complexity ECBilt-CLIO has been used for transient simulations of the last deglaciation and the Holocene. The forcing effects of the ice sheets, greenhouse gas concentrations, and orbital configurations are prescribed as time-varying boundary conditions. In this study two key aspects of the transient simulations are investigated, which are of broader relevance for long-term transient paleoclimate modeling: the effect of using accelerated boundary conditions and of uncertainties in the initial state. Simulations with nonaccelerated boundary conditions and an acceleration factor 10 were integrated. These simulations show that the acceleration can have a significant impact on the local climate history. In the outcropping regions of the high southern latitudes and the convective regions in the North Atlantic, the acceleration leads to damped and delayed temperature response to the boundary conditions. Furthermore, uncertainties in the initial state can strongly bias the climate trajectories in these areas over 500-700 model years. The affected oceanic regions are connected to the large heat capacities of the interior ocean, which cause a strong delay in the response to the forcing. Despite the shown difficulties with the acceleration technique, the accelerated simulations still reproduce the large-scale trend pattern of air temperatures during the Holocene from previous simulations with different models. The accelerated transient model simulation is compared with existing proxy time series at specific sites. The simulation results are in good agreement with those paleoproxies. It is shown that the transient simulations provide valuable insight into whether seasonal or annual signals are recorded in paleoproxies.

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Section: B Local Proxy-model Comparisonsupporting

confidence: 64%

Simulation of the Last 21 000 Years Using Accelerated Transient Boundary Conditions*

2007

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“…Figure 8 shows the running correlation between the smoothed series (11-years moving average) of three different NAO index reconstructions (Glueck and Stockton 2001;Cook et al 2002;Luterbacher et al 2002) and the regional inferred precipitation series. The divergences between NAO index reconstructions have been already subject of different analysis (Schumtz et al 2000;Timm et al 2004). In this case we want to point out the decoupling signal between Luterbacher et al (2002Luterbacher et al ( , 2004 reconstruction and the Cuenca regional time series during two long periods such as 1610-1680 and 1800-1850.…”

Section: Analysis Of the Climate Signalmentioning

confidence: 99%

Reconstruction of annual winter rainfall since A.D.1579 in central-eastern Spain based on calcite laminated sediment from Lake La Cruz

et al. 2011

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We present the first winter (December to March) rainfall reconstruction based in a novel proxy, the thickness of annual calcite laminations preserved in Lake La Cruz (central-eastern Spain). A previous calibration analysis between laminae thickness and the instrumental data series (1950 to present) indicated a highly significant correlation with winter rainfall. Therefore this study attempts the winter rainfall reconstruction since the onset of laminations (1579 a.d.) by means of the calibration function previously developed. The verification analysis between inferred annual values and earlier instrumental data confirms the suitability of this novel proxy and the reliability of the series reconstructed. The reconstructed series show the fluctuating character of winter rainfall in the western Mediterranean area; interdecadal dry periods alternated with wetter periods following, in a board sense, the pattern recorded by documentary sources in other regions of the Iberian Peninsula. At present times regional winter rainfall anomalies are highly correlated with the phase of the North Atlantic Oscillation (NAO). However the time series analysis showed the dominance of nonstationary components at high frequencies of the climate signal over the last four centuries suggesting that the connection between

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“…For better understanding of the modeled relationship between proxy and instrumental data, wavelengthdependent calibration was performed (e.g., Guiot 1985;Osborn and Briffa 2000;Rutherford et al 2005;Timm et al 2004), that is, predictor and predictand were decomposed into high-and low-pass components using a 20-yr smoothing spline. Linear regression was separately performed on both frequency bands.…”

Section: Calibration and Verificationmentioning

confidence: 99%

Summer Temperature Variations in the European Alps, a.d. 755–2004

et al. 2006

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Annually resolved summer temperatures for the European Alps are described. The reconstruction covers the A.D. 755-2004 period and is based on 180 recent and historic larch [Larix decidua Mill.] density series. The regional curve standardization method was applied to preserve interannual to multicentennial variations in this high-elevation proxy dataset. Instrumental measurements from high-(low-) elevation grid boxes back to 1818 (1760) reveal strongest growth response to current-year June-September mean temperatures. The reconstruction correlates at 0.7 with high-elevation temperatures back to 1818, with a greater signal in the higher-frequency domain (r ϭ 0.8). Low-elevation instrumental data back to 1760 agree with the reconstruction's interannual variation, although a decoupling between (warmer) instrumental and (cooler) proxy data before ϳ1840 is noted. This offset is larger than during any period of overlap with more recent high-elevation instrumental data, even though the proxy time series always contains some unexplained variance. The reconstruction indicates positive temperatures in the tenth and thirteenth century that resemble twentieth-century conditions, and are separated by a prolonged cooling from ϳ1350 to 1700. Six of the 10 warmest decades over the 755-2004 period are recorded in the twentieth century. Maximum temperature amplitude over the past 1250 yr is estimated to be 3.1°C between the warmest (1940s) and coldest (1810s) decades. This estimate is, however, affected by the calibration with instrumental temperature data. Warm summers seem to coincide with periods of high solar activity, and cold summers vice versa. The record captures the full range of past European temperature variability, that is, the extreme years 1816 and 2003, warmth during medieval and recent times, and cold in between. Comparison with regional-and large-scale reconstructions reveals similar decadal to longer-term variability.

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Scale-Dependent Reconstruction of the NAO Index

Cited by 53 publications

References 76 publications

Simulation of the Last 21 000 Years Using Accelerated Transient Boundary Conditions*

Simulation of the Last 21 000 Years Using Accelerated Transient Boundary Conditions*

Reconstruction of annual winter rainfall since A.D.1579 in central-eastern Spain based on calcite laminated sediment from Lake La Cruz

Summer Temperature Variations in the European Alps, a.d. 755–2004

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