Caribbean Sea’s curious ‘whistle’ detected from space

Posted: June 24, 2016 by oldbrew in Ocean dynamics, research



Scientists have detected a mysterious repeating Rossby wave signal in the Caribbean that has links to the Gulf Stream, reports

The murmur of lapping ocean waves and the crash of breaking surf are familiar to any beachgoer. But scientists recently discovered a remarkable ocean sound unlike any other, produced by a unique combination of water movement and underwater geography in the Caribbean Sea.

While the sound is at a frequency inaudible to human ears — about 28 octaves below the lowest note on a piano, according to the researchers — it can be detected in space, from the disruptions it causes in Earth’s gravity field. 

Bounded by South America, Central America and the Caribbean islands, the semi-enclosed basin of the Caribbean Sea acts like the body of a giant whistle, the scientists wrote in the study. And what produces the sound is a recurring but very slow-moving and low-amplitude wave pattern that travels the length of the sea in a 120-day cycle.

Known as a Rossby wave, its motion combines with pressure on the sea bottom to generate an inaudible solo that resonates from the basin, much like how air blown into a whistle produces a melodic toot.

“When you blow a whistle, you hear something because the air oscillates — pulses in and out of the whistle — and radiates a wave,” the study’s lead author Chris Hughes, a researcher at the National Oceanography Centre in Liverpool, in the United Kingdom, told Live Science.

“In this case, the water is pulsing in and out of the Caribbean Sea. As the mass of water changes over time, we can detect that oscillating mass from the impact it has on Earth’s gravity field,” he said.
A cog in Earth’s climate engine

The A-flat note generated in the basin — dubbed the “Rossby whistle” by the scientists — is certainly interesting, but there are more practical applications that could arise from knowing about this wave pattern, such as to help predict sea level change and the risks of flooding, Hughes said.

“Because this oscillation takes 120 days and keeps oscillating over long time scales, it might be possible to predict what sea levels along the South American coast could be doing many months in advance,” Hughes explained. “Quite small changes in what we call “mean sea level” — over a long time scale — can make a big difference in the probability of floods that result from storms and more rapid changes,” he said.

The oscillation could even have implications for Earth’s climate engine, Hughes added.

As soon as the current leaves the Caribbean Sea, it enters the Gulf of Mexico and becomes the current in the Gulf Stream, the fast-moving and powerful Atlantic Ocean current that is a major part of the climate system.

“This whistle effect is sucking energy out of the current as it goes through the Caribbean Sea,” Hughes said. “That might actually have an influence on how the Gulf Stream and the whole climate system operates.”

The findings were published online Sunday (June 19) in the journal Geophysical Research Letters.

Full report: Caribbean Sea’s Curious ‘Whistle’ Detected from Space

  1. oldbrew says:

    A Rossby Whistle: A resonant basin mode observed in the Caribbean Sea

    We show that an important source of coastal sea level variability around the Caribbean Sea is a resonant basin mode. The mode consists of a baroclinic Rossby wave which propagates westward across the basin and is rapidly returned to the east along the southern boundary as coastal shelf-waves. Almost two wavelengths of the Rossby wave fit across the basin, and it has a period of 120 days. The porous boundary of the Caribbean Sea results in this mode exciting a mass exchange with the wider ocean, leading to a dominant mode of bottom pressure variability which is almost uniform over the Grenada, Venezuela and Colombia basins, and has a sharp spectral peak at 120 day period. As the Rossby waves have been shown to be excited by instability of the Caribbean Current, this resonant mode is dynamically equivalent to the operation of a whistle.

  2. Paul Vaughan says:

    120 sounds rounded-off.

    Supposing it was actually 119.9415376 days, look at the slip cycle on the tropical year:

    nearest tropical year harmonic:
    (365.242189) / 3 = 121.7473963 days

    (121.7473963)*(119.9415376) / (121.7473963 – 119.9415376) = 8086.219471 days = 22.1393358 sidereal years = (φ/Φ)/(J+S) ~= 1 / JEV = 1/(3V-5E+2J) = 22.13929985 sidereal years

    (121.7473963)*(119.9415376) / (121.7473963 + 119.9415376) = 60.41886022 days
    (121.7473963)*(119.9415376) / ( (121.7473963 + 119.9415376) / 2 ) = 120.8377204 days

    Aggregated with the year it gives something pretty close to Hale.

  3. oldbrew says:

    Sounds interesting PV. There has to be some reason for a repeating oscillation like that.

    “…might actually have an influence on how the Gulf Stream and the whole climate system operates.”

  4. EG Caldwell says:

    Ah, it’s the Chixulub hole!
    It’s reacting to the tides. 🙂

  5. Paul Vaughan says:

    Core BDO (bidecadal) matches solar Hale but climate BDO better matches J-S (Jupiter-Saturn), so 119.7382779 days is also worth contemplating:

    (121.7473963)*(119.7382779) / (121.7473963 – 119.7382779) = 7255.830751 days = 19.86503587 sidereal years = 1/(J-S)

    The aliasing is incredibly sensitive to the slightest change. This is just exploratory brainstorming.

    Hydrology is nonlinear (latent heat), so I try to stay vigilantly aware that we’re probably extremely ignorant of lots of related aliasing.

    They could look at how “120” changes over time to narrow focus towards whatever’s really going on (aliasing or whatever else).


    Thanks for the interesting report OB.

  6. oldbrew says:

    Maybe there could be a lunar component in the ‘120-day’ oscillation.

    Example: lunar apsidal cycle / 27 = 119.685~ days

  7. Paul Vaughan says:

    While I’m never of the mind that a harmonic or subharmonic by itself is key, I can say broad awareness is good. Nearest-harmonics (there’s only *one* from the infinite population of harmonics) define the spatiotemporal volatility structure — so that’s where I explore. Other exploration is welcome. Different perspectives enrich.

    I’m still waiting for anyone / someone to get serious about the Southern Ocean centennial wave that matches core angular momentum, ENSO volatility, and asymmetric polar volcanic sulfate deposition (SEE SUGGESTIONS 19) — what I’ve been calling “96” for short. That’s some spatiotemporal volatility with confirmed teeth. Why everyone’s so shy about it’s unclear. Maybe it’s because they figure the Southern Ocean and everything else matches AMO.
    Well… it doesn’t!! [ :

    The only person I’ve seen acknowledge a southern centennial oscillation is Bill Illis — one of few relative luminaries enriching discussion at a site that lost its way a few years back and never recovered.

    Well I suppose I could find a little time to keep throwing up an image here and there to keep reminding people. Will something sink in eventually? Eventually, yes.