Atlantic And Pacific Blob Pattern May Be Linked To Warming In The Arctic And Tropics

[bluewave]

https://www.ess.uci.edu/~yu/PDF/Liang+Yu.et al.blob.JCLI-2017.pdf

ABSTRACT
During 2013–15, prolonged near-surface warming in the northeastern Pacific was observed and has been referred to as the Pacific warm blob. Here, statistical analyses are conducted to show that the generation of the Pacific blob is closely related to the tropical Northern Hemisphere (TNH) pattern in the atmosphere. When the TNH pattern stays in its positive phase for extended periods of time, it generates prolonged blob events primarily through anomalies in surface heat fluxes and secondarily through anomalies in wind-induced ocean advection. Five prolonged ($24 months) blob events are identified during the past six decades (1948–2015), and the TNH–blob relationship can be recognized in all of them. Although the Pacific decadal oscillation and El Niño can also induce an arc-shaped warming pattern near the Pacific blob region, they are not responsible for the generation of Pacific blob events. The essential feature of Pacific blob generation is the TNH-forced Gulf of Alaska warming pattern. This study also finds that the atmospheric circulation anomalies associated with the TNH pattern in the North Atlantic can induce SST variability akin to the so-called Atlantic cold blob, also through anomalies in surface heat fluxes and wind-induced ocean advection. As a result, the TNH pattern serves as an atmospheric conducting pattern that connects some of the Pacific warm blob and Atlantic cold blob events. This conducting mechanism has not previously been explored.

Summary and discussion
This study argues that the TNH pattern is the princi- ple atmospheric circulation pattern involved in the generation of the Pacific warm blob. Prolonged warm blob events occurred together with extended episodes of positive phases of this atmospheric circulation pattern. The TNH–blob relationship is verified by performing statistical analyses and case studies of the five prolonged Pacific warm blob events during the analysis period (1948–2015). This study also finds that the shift from a GOA warming pattern to an ARC warming pattern is not a necessary feature of Pacific blob generation. This shift occurs if an El Niño develops during a Pacific blob event, such as during the 2013–15 Pacific warm blob event. The core part of the Pacific warm blob is the GOA warming pattern, which is closely tied to the TNH forcing. EOF analysis demonstrated that the Pacific warm blob is not part of the PDO or ENSO and is a separate dynamical entity.
This study further shows that the cross-basin structure of the TNH pattern enables it to force SST variability inboth the Pacific blob and Atlantic blob regions. As a result, some of the Pacific warm blob events occurred together with some of the Atlantic cold blob events. This connection between the Pacific warm blob and Atlantic cold blob appears as a leading covariability mode in the North Pacific–Atlantic sector. Three of the five prolonged Pacific warm blob events were accompanied by prolonged Atlantic cold blob events. It is important to note that the TNH contribution to the generation of the Pacific warm blob is larger than its contribution to the generation of the Atlantic cold blob. Factors other than the TNH pattern, such as the NAO, the AMOC, and Greenland ice sheet melting, are also important in the generation of Atlantic cold blob events. These fac- tors may weaken the apparent connection between the Pacific and Atlantic blobs. The connection can be better revealed if we focus on the TNH pattern and its asso- ciated oceanic covariability.
This study raises a number of unanswered questions. For example, what causes the TNH pattern to stay in its positive phase for an extended period of time? Previous studies have suggested the TNH (or TNH-like) pattern may be triggered by tropical forcing mechanisms, such as the El Niño (Mo and Livezey 1986; Barnston et al. 1991; Yu et al. 2012; Yu and Kim 2011; Yu and Zou 2013; Zou et al. 2014), the quasi-biennial oscillation (Barnston et al. 1991), the propagation of the wave activity initi- ated from the western tropical Pacific Ocean (Wang17 LIANG ET AL. 9055
et al. 2014; Lee et al. 2015; Seager and Henderson 2016; Hu et al. 2017), and the internal dynamics in the atmo- sphere (Kumar et al. 2013; Seager et al. 2014; Xie and Zhang 2017). Also, recent warming in the Arctic regions has been suggested to exert strong impacts on mid- latitude weather and climate by altering large-scale at- mospheric circulation patterns (Cohen et al. 2012, 2014; Kim et al. 2014; Peings and Magnusdottir 2014; Deser et al. 2015; Lee et al. 2015; Overland et al. 2015, 2016; Yu et al. 2017). Thus, forcing related to certain tropical Pacific Ocean or polar conditions may be potential fac- tors for the phase-locking of the TNH pattern. Extensive investigations on the underlying dynamics of the TNH pattern are clearly warranted in future research, given its importance as a mechanism for connecting the climate of the North Pacific and Atlantic Oceans. In addition, we notice that the linear trends for the Pacific and Atlantic blob indices, when calculated using the nondetrended SST anomalies, are 0.0078Cyr21 and 20.0048Cyr21, respectively. The trends, although small, may produce cumulative warming large enough to affect the charac- teristics of the Pacific and Atlantic blobs or their re- lationships with large-scale atmospheric circulation patterns in recent decades. This possibility also needs to be explored in the future.

 

More details on the new SST records that continue to be set by the blob pattern.

https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century

https://alaskapacificblob.wordpress.com/

 

 

 

[NegativeEPO]

Can't wait for more cold, miserable springs around the Great Lakes region!!!

[etudiant]

Very interesting paper.

It suggests that the phenomenon is a quite frequent occurrence, with 5 such events of over 24 months duration during the past 60 years. Do any of the atmospheric models show the TNH pattern that the researchers suggest is driving this? 

[bluewave]

1 hour ago, etudiant said:

Very interesting paper.

It suggests that the phenomenon is a quite frequent occurrence, with 5 such events of over 24 months duration during the past 60 years. Do any of the atmospheric models show the TNH pattern that the researchers suggest is driving this? 

This recent event dwarfed all other episodes. Best guess is that it may be a combination of Tropical Pacific and Arctic warming. The remarkable part is how synchronized Pacific side was with the Atlantic. This new regime began with the rapid warming of the Pacific in 2013 along with the Atlantic cold pool emerging south of Greenland. This has been the dominant Northern Hemisphere 500 mb and SST pattern since then. 

The 2013–15 event has the highest mean TNH value (1.09), followed by the 1961–63 (0.65), the 1985–87 (0.57), the 1989–95 (0.56), and the 1956–58 (0.16) events. 

There was also another recent paper which reproduced a similar pattern which linked the Tropical Pacific and Arctic.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL077325

Fast Response of the Tropics to an Abrupt Loss of Arctic Sea Ice via Ocean Dynamics

 

Whereas previous modeling studies have examined the equilibrium coupled climate response to projected Arctic sea ice loss, we have investigated aspects of the transient adjustment to an abrupt loss of Arctic sea ice, with a particular focus on the tropics and the role of ocean dynamics. To study the relative roles of dynamical versus thermodynamic air‐sea interaction, we conducted identical sets of experiments with CCSM4 in the full‐depth ocean model (FOM) and slab ocean model (SOM) configurations. The SOM response is dominated by a quasi‐steady interhemispheric SST contrast (warming in the NH and little change in the SH), accompanied by a northward shift of the ITCZ and Hadley Circulation. The FOM response is more complex, with distinctive patterns that evolve over time. The tropical SST response is characterized by a distinct equatorial Pacific maximum, which develops within approximately 20 years, accompanied by an equatorward intensification of the ITCZ and Hadley Circulation. These structures amplify with time and are in marked contrast to the SOM response. A heat budget analysis for the upper 100 m of the eastern equatorial Pacific indicates the importance of anomalous vertical advection, which is tied to a monotonic warming at depth (below 200 m). Although further diagnostics and experiments are needed to understand the origins of this subsurface warming, it appears to be qualitatively consistent with the adjustment of the global thermohaline circulation to a density perturbation in the North Atlantic, in this case induced by a freshening and warming of the subpolar gyre due to sea ice melt.

In addition to distinctive tropical responses, FOM and SOM also exhibit some differences in their NH midlatitude atmospheric circulation responses. In particular, FOM shows an increase in lower tropospheric westerlies over the North Pacific, a response that strengthens over time. This aspect is very weak and shifted poleward in SOM compared to FOM. In addition, SOM shows reduced westerlies farther south, a feature that is lacking in FOM. These distinctions in the midlatitude circulation responses between FOM and SOM, apparent even within the first 25 years, can be traced to differences in their tropical Pacific SST responses and affect the precipitation response along the west coast of North America among other regions.

In summary, the coupled ocean‐atmosphere response to an abrupt loss of Arctic sea ice is rapidly (within 20–30 years) and markedly modified by dynamical ocean processes. To what extent our results depend on the particular model used and the experimental design remains to be ascertained.