A secularly varying hemispheric climate-signal propagation previously detected in instrumental and proxy data not detected in CMIP3 data base

Abstract

Results of previous studies support the existence of a spatially coherent, secularly varying climate signal, propagating through a network of synchronized climate indices across the Northern Hemisphere during the 20th century. The signal was identified in both instrumental and proxy data sets. In this present study, we seek to detect this same low-frequency signal propagating hemispherically through networks of model-simulated climate indices. These simulated climate indices were reconstructed from a data set generated by models of the third Coupled Model Intercomparison Project (CMIP3). Methods used in the earlier studies on climate-signal propagation guide the strategy for this companion study, for which 60 network analyses were performed. Most analyses focused on 20th century behavior, several on pre-industrial conditions. None succeeded in reproducing a hemispherically propagating signal. In light of previous results, we offer possible reasons for this finding. Among them is speculation on whether mechanisms relevant to signal propagation might be missing from this suite of general circulation models.

On semi‐empirical decomposition of multidecadal climate variability into forced and internally generated components

“…The dynamics of the AMOC and North Atlantic SST signals are still not fully understood, and a large number of different theories are available (Delworth et al ., ; Timmermann et al ., ; Frankcombe et al ., ; Frankcombe and Dijkstra, ; Clement et al ., ; Trenary and DelSole, ). Meanwhile, the simulated signals exhibit a wide spread in their characteristic time scales and amplitudes across CMIP5 models (Zhang and Wang, ; Ba et al ., ), and the climate response mostly confined to the North Atlantic region and its immediate surroundings (Enfield et al ., ; Sutton and Hodson, ; Knight et al ., ), perhaps with an in‐phase (simultaneous) teleconnection to North Pacific (Kravtsov and Spannagle, ; DelSole et al ., ; Wyatt and Peters, ; Kravtsov et al ., ) or tropical Pacific (McGregor et al ., and references therein).…”

“…() argued that the spatiotemporal structure of observed multidecadal climate variability in the 20th century may be even more complex and involves hemispheric propagation of the AMO multidecadal signal, which they termed the ‘stadium wave’. They further noted the absence of the stadium wave in CMIP3 (Wyatt and Peters, ) and some of the CMIP5 models (Kravtsov et al ., ) and argued it to be due to the models' failing to transmit the simulated AMO signal to the overlying atmosphere, which may in turn result from the insufficient atmospheric response to SST or sea‐ice anomalies in model simulations; see Kushnir et al . () and Wyatt and Curry ().…”

“…The dynamics of the AMOC and North Atlantic SST signals are still not fully understood, and a large number of different theories are available (Delworth et al, 1993;Timmermann et al, 1998;Frankcombe et al, 2009Frankcombe et al, ,2010Frankcombe and Dijkstra, 2011;Clement et al, 2015;Trenary and Del-Sole, 2016). Meanwhile, the simulated signals exhibit a wide spread in their characteristic time scales and amplitudes across CMIP5 models (Zhang and Wang, 2013;Ba et al, 2014), and the climate response mostly confined to the North Atlantic region and its immediate surroundings (Enfield et al, 2001;Sutton and Hodson, 2005;Knight et al, 2006), perhaps with an in-phase (simultaneous) teleconnection to North Pacific (Kravtsov and Spannagle, 2008;DelSole et al, 2011;Wyatt and Peters, 2012;Kravtsov et al, 2014) or tropical Pacific (McGregor et al, 2014 and references therein). and Kravtsov et al (2014) argued that the spatiotemporal structure of observed multidecadal climate variability in the 20th century may be even more complex and involves hemispheric propagation of the AMO multidecadal signal, which they termed the 'stadium wave'.…”

Pronounced differences between observed and CMIP5‐simulated multidecadal climate variability in the twentieth century

“…The differences between climate models and observations are, however, not confined to the North Atlantic. Wyatt et al [], Wyatt and Peters [], and Kravtsov et al [] detected considerable mismatches in both the magnitude and spatiotemporal structure of the twentieth century's multidecadal variability—defined via deviations from the long‐term linear trend—in a network of observed and CMIP5 simulated indices characterizing the Northern Hemisphere climate. Assuming that multidecadal discrepancies between the models and observations reflect differences in the observed and simulated internal climate variability, Mann et al [] and Steinman et al [, ] challenged these findings and interpreted them to be an artifact of the linear detrending.…”

The dynamics of the warming hiatus over the Northern Hemisphere

“…The NCEP/NCAR Reanalysis I was from 1948 to present, and the other two products were from 1979 to present. Because the reanalysis products are model-based, the modelled outputs may differ from real observations, especially on decadal-plus time scales (Wyatt and Peters 2012;Kravtsov et al 2014). To access some of the uncertainties in the results based on these reanalysis products, all the results associated with these three products were presented by the ensemble mean of them.…”