Winds hide Atlantic variability from Europe’s winters

Posted: March 15, 2016 by oldbrew in Ocean dynamics, research, wind

Out in the Atlantic Ocean [image credit: NASA]

Out in the Atlantic Ocean [image credit: NASA]

Researchers claim to have ‘discovered a cycle of heating and cooling at the surface of the ocean’ in the North Atlantic which is modulated – so to speak – by winds, although they are also quick to make the obligatory nod in the direction of assumed future ‘global warming’.

Shifting winds may explain why long-term fluctuations in North Atlantic sea surface temperatures have no apparent influence on Europe’s wintertime temperatures.

The findings, published in Nature Communications, could also have implications for how Europe’s climate will evolve amid global warming. In the mid-1990s, scientists assembled the first century-long record of North Atlantic sea surface temperatures and quickly discovered a cycle of heating and cooling at the surface of the ocean. Each of these phases lasted for decades, even as temperatures warmed overall during the course of the century.

Since this discovery, these fluctuations in ocean temperature have been linked to all manner of Northern Hemisphere climate disturbances, from Sahel drought to North Atlantic hurricanes. Research also linked European climate variability to the temperature swings of its neighboring ocean in the spring, summer and fall. Surprisingly, however, no imprint of the ocean’s variability could be found in Western Europe’s wintertime temperature record. This absence was especially puzzling in light of the fact that Europe’s mild winters are a direct consequence of its enviable location downwind of the North Atlantic.

Now, a study by researchers at McGill University and the University of Rhode Island suggests that the answer to this puzzle lies in the winds themselves. The fluctuations in ocean temperature are accompanied by shifts in the winds. These wind shifts mean that air arrives in Western Europe via very different pathways in decades when the surface of the North Atlantic is warm, compared to decades when it is cool.

Paths of virtual particles traced

The researchers studied the winds and their interaction with the ocean in a recently developed reconstruction of 20th century climate. Their main approach was to launch virtual particles into the winds, and trace their journey for ten key days leading up to their arrival in Western Europe. They repeated this procedure using the wind field for each winter of the last 72 years, a period for which the winds of the North Atlantic have already been carefully documented and validated.

The new research reveals that, in decades in which North Atlantic sea surface temperatures are elevated, winds deliver air to Europe disproportionately from the north. In contrast, in decades of coolest sea surface temperature, swifter winds extract more heat from the western and central Atlantic before arriving in Europe. The researchers suggest the distinct atmospheric pathways hide the ocean oscillation from Europe in winter.

Ongoing debate

Whether the atmosphere is the tail to the ocean’s dog or vice versa remains up for debate. “There is an ongoing argument about whether the ocean circulation sets the slow temperature fluctuations at its surface, or the atmosphere is the more important agent,” says University of Rhode Island professor Jaime Palter, one of the authors. report: Winds hide Atlantic variability from Europe’s winters

Graphic: Winds hide Atlantic variability from Europe’s winters
Caption: The map reflects how the winds blowing towards Europe shift with fluctuations in North Atlantic sea-surface temperature. During decades when the sea is cool (associated with blue colors), the prevailing winds are more likely to flow across the Atlantic from North America, keeping western European air temperatures mild. In periods when the ocean surface warms (associated with red), the prevailing winds are more prone to sweep down from the north. Credit: Ayako Yamamoto

  1. oldbrew says:

    Related: Dueling climate cycles may increase sea level swings

    ‘Tony Song of NASA’s Jet Propulsion Laboratory, Pasadena, California, and colleagues looked at the correlations of tropical Pacific sea level with different phases of two important climatic cycles: the Pacific Decadal Oscillation (PDO) and El Niño/Southern Oscillation.

    Song and his team found that the phases of these cycles can either reinforce or dampen each other, directly affecting the variability of sea level across the Pacific.’

  2. E.M.Smith says:

    Megatons of water at high specific heat vs kilograms of air with low specific heat and no phase change. Which is more influential? Decisions decisions….

    I’ll go with “water”…

  3. peterazlac says:

    Hang on! Didn’t someone called Hubert Lamb develop the link between wind patterns in the Atlantic and the weather in the UK and Europe?

  4. oldbrew says:

    ‘Whether the atmosphere is the tail to the ocean’s dog or vice versa remains up for debate.’

    The answer is blowin’ in the wind – Bob Dylan.

  5. erl happ says:

    This is a variant of an old story re-discovered. Its called the Arctic Oscillation or the North Atlantic Oscillation or more recently the Northern Annular Mode. Wind flows from centres of high surface pressure to low surface pressure. In mid to high latitudes surface pressure is a function of the ozone content of the upper part of the atmospheric column. Low pressure zones have a lower tropopause with more ozone aloft giving rise to polar cyclones that engender lower pressure. Its the ozone that activates and drives the ascending circulation. As an absorber of the Earth’s radiation ozone warms the air aloft……..the cause of the warmth of the stratosphere.

    It follows that to understand the phenomenon we need to look not at the ocean but at the stratosphere.

  6. Erl.

    I am certain that low pressure containing warm rising air pushes the tropopause up and high pressure containing cold descending air allows the tropopause to descend.

    As regards convection, that is a consequence of uneven surface heating causing density differentials in the horizontal plane, nothing to do with ozone.

    Ozone has its effect exclusively above the tropopause.

  7. ren says:

    Distribution of ozone is very important in winter because it blocks the polar vortex.

    Lock in the stratosphere brings about a blockade in the troposphere on the eastern side.

  8. ren says:

    The low below Greenland will be quite durable and will continue cooling the Atlantic.

    “Thus, the data in Fig.2 suggest a ~60-year periodicity in SA/GCR effects on tropospheric pressure, as
    well as in the vortex development, the transitions between its different states occurring in the 1950s, 1980s
    and apparently near the 2010s. These transitions coincide with those between cold and warm epochs in the
    Arctic detected in surface temperatures [Gudkovich et al., 2009]. As Fig.2 shows, the sign reversals of
    SA/GCR effects coincide well with the transitions between the different states of the vortex. When the vortex
    is strong (~1980-2010) meridional processes in the troposphere intensify and GCR increase is accompanied
    by an enhancement both of cyclonic activity at middle latitudes and anticyclone formation at polar ones.
    When the vortex is weak (~1950-1980) the meridional circulation weakens and GCR effects change the sign.
    Thus, the ~60-year variation of the amplitude and sign of SA/GCR effects on troposphere pressure seem to
    be closely related to the vortex state and the corresponding changes in the evolution of the large-scale
    atmospheric circulation. It should also be stressed that at the present time the vortex seems to change its state
    (see Fig.2c, d), so we could expect a reversal of those correlations which were observed between dynamic
    processes in the lower atmosphere and SA/GCR characteristics during the last thirty years.”

  9. ren says:

    Jumping galactic radiation within a month.

  10. ren says:

    Temperatura północnego Atlantyku spada.

    4. Sea Surface Temperature (SST) Anomaly

    SUMMARY: CRW’s SST Anomaly is produced by subtracting the long-term mean SST (for that location in that time of year) from the current value. A positive anomaly means that the current sea surface temperature is warmer than average, and a negative anomaly means it is cooler than average. The spatial resolution is 0.5-degree (50-km), and the data and images are updated twice-weekly. Animations of the most recent SST Anomaly images are also available online.

    CRW’s near-real-time global SST Anomaly product makes it possible to quickly pinpoint regions of elevated SSTs throughout the world oceans. It is especially valuable for the tropical regions where most of the world’s coral reef ecosystems thrive. It is also very useful in assessing ENSO (El Niño-Southern Oscillation) development, monitoring hurricane “wake” cooling, observing major shifts in coastal upwellings, etc.

    A twice-weekly SST anomaly at a 0.5-degree (50-km) grid is calculated by subtracting the daily climatological SST of the last day of the twice-weekly period at that grid from the corresponding twice-weekly SST (described in Sea Surface Temperature Section). The formula for obtaining the anomaly is

    SST_anomaly = SST – Daily_SST_climatology

    The color range of temperature anomalies displayed on the SST Anomaly charts is -5.0 to +5.0 °C (or Kelvin). Areas with SST anomaly values less than -5.0 °C are displayed as -5.0 °C, and areas with values greater than +5.0 °C are displayed as +5.0 °C. Note that these anomalies are somewhat less reliable at high latitudes where more persistent clouds limit the amount of satellite data available for deriving accurate SST analysis fields and climatologies.

    Data and images of both near-real-time and archived SST anomalies are available from the CRW website, along with the operational 0.5-degree monthly mean SST climatologies. Animations of SST Anomaly images for the past six months are also available.

    Charts of the retrospective 1984-1998 monthly mean SST anomalies are available online at 36-km resolution.

  11. oldbrew says:

    Dog wags tail, or was it the other way round – or both?

    Report: Variability of major oceanic currents driven by climate change

    ‘Thermohaline circulation moves energy and matter around the globe and drives the planet’s climate, but it also responds to changing climate conditions.’

    ‘…an international collaborative of researchers has now investigated the effects of climate change on AMOC-IV amplitude and time scale.’

  12. ulriclyons says:

    The temperatures tend to move in phase with solar cycles when the AMO is warm, and anti-phase when the AMO is cold. The AMO itself does the complete reverse.