the "Stadium Wave"
The 'stadium wave' is a hypothesized, multi-decadally varying climate signal that propagates across the Northern Hemisphere (Wyatt, Kravtsov, and Tsonis 2012). Its role in the Southern Hemisphere is suspected, but not yet tested. It sequentially travels through a network of oceanic, ice, and atmospheric indices, hence, the allusive term - 'stadium wave'. As the stadium-wave signal propagates, it scripts the multi-decadal component of the Northern Hemisphere surface average temperature. Climate regimes -- multi-decadal intervals of prevailing surface average temperature trend -- evolve in four stages as the hypothesized signal propagates through the climate-index network (Wyatt and Curry 2014). Tempo of variability in North Atlantic Ocean temperatures governs the stadium-wave signal tempo. A warm North Atlantic promotes a multiple-decade trend of cooling hemispheric surface average temperatures. A cool North Atlantic triggers a multiple-decade interval of warming hemispheric surface average temperatures. West Eurasian Arctic sea ice plays a key role in converting the initial ocean signature into an oppositely signed atmospheric one. The West Eurasian shelf sea region is unique. Only here is Arctic sea ice exposed to the open ocean in winter. Thus, the polarity of the North Atlantic Ocean temperatures strongly influences winter inventory of sea ice. Sea ice inventory regulates escape of ocean heat, which exerts dominant influence on wintertime Arctic surface temperatures, and by extension, on the polar-equatorial temperature gradient (PETG). In turn, the PETG dictates equator-to-pole transport of heat, converting the initial ocean signal-polarity to the oppositely signed atmospheric signature. As the signal continues to propagate, atmosphere-ice-ocean interactions feed back positively onto the prevailing temperature trend; while Pacific-centered processes negatively feed back onto the North Atlantic's salinity balance, effectively nudging a polarity reversal of Atlantic Ocean temperatures, thereby promoting a climate-regime reversal (See figure of stadium wave below).
Instrumental records for the collection of stadium-wave-network indices are temporally limited to the 20th and early 21st centuries. The signal emerges clearly in this data base, with climate-regime intervals persisting for approximate 30-year stretches. But there are other data that capture traces of the 'wave': anomalies in fish populations, Earth's rotational-rate record, isotopic ratios in various media, foraminifera-accumulations in sediment, and the like. Records for these data include and pre-date the 20th century, enabling a peek further into the signal's past. Analyses of these data suggest the 'stadium wave' has been in existence for at least 300 years (Wyatt 2012). And while instrumental and proxy data capture the consistent propagation sequence that characterizes the 'stadium wave'; model-generated data derived from the CMIP3 data base do not (Wyatt and Peters 2012). Reasons for this remain unclear. Ocean-stratosphere-troposphere coupling, geographically shifting atmospheric and oceanic centers-of-action, ocean-atmosphere coupling at western-boundary currents and their extensions, sea-ice dynamics, and network interactions are thought to be fundamental links in the stadium-wave propagation. Improved representation of these features may enhance model simulation of the multi-decadal natural component of climate variability.
A topic ripe for further study is external forcing. What is its role in the stadium-wave ? Solar is suspected as a player (Wyatt 2012) - its tempo and magnitude of variability at the helm. Exactly how, remains the question. On the other hand, while the natural multi-decadal component - i.e. the stadium-wave signal - may dampen or enhance the longer-term increasing linear temperature trend; the reverse does not appear to be true. The character of the 'wave' signal exhibits remarkable consistency since at least 1850, seemingly unaffected by the co-occurring centennial-scale increasing linear trend. Prior to 1850, minor modifications of amplitude and frequency emerge in analysis (present research).
Current debate regarding climate variability focuses on relative roles of external forcing versus internally generated (or intrinsic) variability. Similar debate is worth considering in context of the stadium-wave signal. Is the signal externally forced, intrinsically generated, or a combination of both. While authors of the hypothesis concur that the propagation of the signal across the Northern Hemisphere is likely tied to internally generated variability (see Wyatt and Curry 2014), the tempo of this propagation is set by variability in the North Atlantic (Atlantic Multidecadal Oscillation (AMO)). External forcing - natural, anthropogenic, or both - of AMO variability is presumed; although the extent of that contribution to the observed pattern of variability remains a topic of active research. In brief, internally generated and interacting processes likely are responsible for the stadium-wave's propagation through a hemispherically spanning network of geophysical indices; while external forcing (natural and anthropogenic likely) is at least a contributing factor to the signal's tempo of oscillation, via the influence of external forcing on the temporal behavior of the AMO.
The 'stadium wave', if it has been correctly interpreted, illuminates some previously unrecognized details of Earth's machinery. In addition, if the stadium-wave signal has, indeed, captured the multi-decadal component of climate variability correctly, and if this signal behavior remains consistent in its propagation sequence, the hypothesis holds potential for: 1) attribution - allowing climate behavior to be better placed in context; 2) for predictive capacity - possibly allowing prediction of decadal-scale trend shifts in precipitation, drought distribution, wind-regimes, sea ice extent, and temperature; and 3) for facilitating improvements in model design via the identification of critical elements involved in stadium-wave dynamics that may be absent or poorly resolved in computer simulations, assuming these dynamics indeed contribute to the multi-decadal component of the overall Northern Hemisphere surface average temperature.
