[OANNES Foro] Why do Earth's equatorial (Kelvin) waves head east?

[Mario Cabrejos]

Science  24 Nov 2017:
Vol. 358, Issue 6366, pp. 990-991
DOI: 10.1126/science.aaq0469


 


Why do Earth's equatorial waves head east?


1.    Joseph A. Biello, Tudor Dimofte


Summary


Equatorial Kelvin waves occur constantly in Earth's atmosphere and ocean.
They constitute an isolated and powerful component of the observed
atmospheric wave spectrum (1), whereas oceanic Kelvin waves drive up- and
downwelling in the Pacific Ocean thermocline, which affects the El
Niño–Southern Oscillation. In the atmosphere, Kelvin waves are initiated by
and coupled to convective activity (storm systems), mostly over the Indian
and the western Pacific Oceans, whereas in periods of large-scale convective
organization, such as the Madden-Julian Oscillation, equatorial Kelvin wave
activity is suppressed. On page
<http://science.sciencemag.org/lookup/doi/10.1126/science.aan8819> 1075 of
this issue, Delplace et al. (2) attempt to answer the questions of why there
are three equatorially confined waves, and why they all have eastward group
velocity. They propose a fascinating perspective on the existence of
unidirectional, equatorially confined atmospheric waves by developing an
analogy with similar phenomena that occur in electronic materials—in
particular, in quantum Hall states and topological insulators.

 

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Science  24 Nov 2017:
Vol. 358, Issue 6366, pp. 1075-1077
DOI: 10.1126/science.aan8819

 


Topological origin of equatorial waves


1.    Pierre Delplace
<http://science.sciencemag.org/content/358/6366/1075?utm_campaign=toc_sci-ma
g_2017-11-22&et_rid=34815706&et_cid=1680339#aff-1> 1,
<http://science.sciencemag.org/content/358/6366/1075?utm_campaign=toc_sci-ma
g_2017-11-22&et_rid=34815706&et_cid=1680339#corresp-1> *, J. B. Marston
<http://science.sciencemag.org/content/358/6366/1075?utm_campaign=toc_sci-ma
g_2017-11-22&et_rid=34815706&et_cid=1680339#aff-2> 2,
<http://science.sciencemag.org/content/358/6366/1075?utm_campaign=toc_sci-ma
g_2017-11-22&et_rid=34815706&et_cid=1680339#corresp-1> *,  Antoine Venaille
<http://science.sciencemag.org/content/358/6366/1075?utm_campaign=toc_sci-ma
g_2017-11-22&et_rid=34815706&et_cid=1680339#aff-1> 1,
<http://science.sciencemag.org/content/358/6366/1075?utm_campaign=toc_sci-ma
g_2017-11-22&et_rid=34815706&et_cid=1680339#corresp-1> *

·          


Fluid waves with topological origins


Topological effects that arise from material boundaries are well known in
solid-state physics and form the basis for topological insulators. Delplace
et al. describe atmospheric and ocean waves that appear to have a similar
topological origin (see the Perspective by Biello and Dimofte). The waves
exist because of the symmetry-breaking nature of Earth's rotation, which
allows certain fixed topological constraints on the system. These findings
may be useful for understanding a wide variety of geophysical and
astrophysical flows.

Science, this issue p.
<http://science.sciencemag.org/lookup/doi/10.1126/science.aan8819> 1075; see
also p.  <http://science.sciencemag.org/lookup/doi/10.1126/science.aaq0469>
990

 


Abstract


Topology sheds new light on the emergence of unidirectional edge waves in a
variety of physical systems, from condensed matter to artificial lattices.
Waves observed in geophysical flows are also robust to perturbations, which
suggests a role for topology. We show a topological origin for two
well-known equatorially trapped waves, the Kelvin and Yanai modes, owing to
the breaking of time-reversal symmetry by Earth’s rotation. The nontrivial
structure of the bulk Poincaré wave modes encoded through the first Chern
number of value 2 guarantees the existence of these waves. This invariant
demonstrates that ocean and atmospheric waves share fundamental properties
with topological insulators and that topology plays an unexpected role in
Earth’s climate system.

 

 



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