Atlantic warming turbocharges Pacific trade winds

Tropical beach (stock image). Rapid warming of the Atlantic Ocean, likely caused by global warming, has turbocharged Pacific Equatorial trade winds, according to new research. Credit: © michaelfitz / Fotolia

New research has found rapid warming of the Atlantic Ocean, likely caused by global warming, has turbocharged Pacific Equatorial trade winds. Currently the winds are at a level never before seen on observed records, which extend back to the 1860s.

The increase in these winds has caused eastern tropical Pacific cooling, amplified the Californian drought, accelerated sea level rise three times faster than the global average in the Western Pacific and has slowed the rise of global average surface temperatures since 2001.

It may even be responsible for making El Nino events less common over the past decade due to its cooling impact on ocean surface temperatures in the eastern Pacific.

"We were surprised to find the main cause of the Pacific climate trends of the past 20 years had its origin in the Atlantic Ocean," said co-lead author Dr Shayne McGregor from the ARC Centre of Excellence for Climate System Science (ARCCSS) at the University of New South Wales.

"It highlights how changes in the climate in one part of the world can have extensive impacts around the globe."

The record-breaking increase in Pacific Equatorial trade winds over the past 20 years had, until now, baffled researchers.

Originally, this trade wind intensification was considered to be a response to Pacific decadal variability. However, the strength of the winds was much more powerful than expected due to the changes in Pacific sea surface temperature.

Another riddle was that previous research indicated that under global warming scenarios Pacific Equatorial Trade winds would slow down over the coming century.

The solution was found in the rapid warming of the Atlantic Ocean basin, which has created unexpected pressure differences between the Atlantic and Pacific. This has produced wind anomalies that have given Pacific Equatorial trade winds an additional big push.

"The rapid warming of the Atlantic Ocean created high pressure zones in the upper atmosphere over that basin and low pressure zones close to the surface of the ocean," said Prof Axel Timmermann co-lead and corresponding author from the University of Hawaii.

"The rising air parcels, over the Atlantic eventually sink over the eastern tropical Pacific, thus creating higher surface pressure there. The enormous pressure see-saw with high pressure in the Pacific and low pressure in the Atlantic gave the Pacific trade winds an extra kick, amplifying their strength. It's like giving a playground roundabout an extra push as it spins past."

Many climate models appear to have underestimated the magnitude of the coupling between the two ocean basins, which may explain why they struggled to produce the recent increase in Pacific Equatorial trade wind trends.

While active, the stronger Equatorial trade winds have caused far greater overturning of ocean water in the West Pacific, pushing more atmospheric heat into the ocean, as shown by co-author and ARCCSS Chief Investigator Prof Matthew England earlier this year. This increased overturning appears to explain much of the recent slowdown in the rise of global average surface temperatures.

Importantly, the researchers don't expect the current pressure difference between the two ocean basins to last. When it does end, they expect to see some rapid changes, including a sudden acceleration of global average surface temperatures.

"It will be difficult to predict when the Pacific cooling trend and its contribution to the global hiatus in surface temperatures will come to an end," Prof England said.

"However, a large El Niño event is one candidate that has the potential to drive the system back to a more synchronized Atlantic/Pacific warming situation."

Source: University of New South Wales

Long-running Jason-1 ocean satellite takes final bow

Artist's concept of the joint NASA/CNES Jason-1 ocean altimetry satellite. During its 11-1/2-year life, Jason-1 helped create a 20-plus-year climate record of global ocean surface topography, providing new insights into ocean circulation, tracking our rising seas and enabling more

The curtain has come down on a superstar of the satellite oceanography world that played the "Great Blue Way" of the world's ocean for 11-1/2 years. The successful joint NASA and Centre National d'Etudes Spatiales (CNES) Jason-1 ocean altimetry satellite was decommissioned this week following the loss of its last remaining transmitter.

Launched Dec. 7, 2001, and designed to last three to five years, Jason-1 helped create a revolutionary 20-plus-year climate data record of global ocean surface topography that began in 1992 with the launch of the NASA/CNES Topex/Poseidon satellite. For more than 53,500 orbits of our planet, Jason-1 precisely mapped sea level, wind speed and wave height for more than 95 percent of Earth's ice-free ocean every 10 days. The mission provided new insights into ocean circulation, tracked our rising seas and enabled more accurate weather, ocean and climate forecasts.

"Jason-1 has been a resounding scientific, technical and international success," said John Grunsfeld, associate administrator of NASA's Science Mission Directorate in Washington. 

"The mission met all of its requirements, performed an extended mission and demonstrated how a long-term climate data record should be established from successively launched satellites. Since launch, it has charted nearly 1.6 inches (4 centimeters) of rise in global sea levels, a critical measure of climate change and a direct result of global warming. The Jason satellite series provides the most accurate measure of this impact, which is felt all over the globe."

During parts of its mission, Jason-1 flew in carefully coordinated orbits with both its predecessor Topex/Poseidon and its successor, the Ocean Surface Topography Mission/Jason-2, launched in 2008. These coordinated orbit periods, which lasted about three years each, cross-calibrated the satellites, making possible a 20-plus-year unbroken climate record of sea level change. These coordination periods also doubled data coverage.

Combined with data from the European Space Agency's Envisat mission, which also measured sea level from space, these data allow scientists to study smaller-scale ocean circulation phenomena, such as coastal tides, ocean eddies, currents and fronts. These small-scale features are thought to be responsible for transporting and mixing heat and other properties, such as nutrients and dissolved carbon dioxide, within the ocean.

"Jason-1 was an exemplary and multi-faceted altimeter mission and contributed so much to so many scientific disciplines," said Jean-Yves Le Gall, CNES president in Paris. "Not only did Jason-1 extend the precise climate record established by Topex/Poseidon, it made invaluable observations for mesoscale ocean studies on its second, interleaved orbit. Even from its 'graveyard' orbit, Jason-1 continued to make unprecedented new observations of the Earth's gravity field, with precise measurements right till the end."

The in-orbit Jason-2 mission, operated by the meteorological agencies of the United States and Europe (the National Oceanic and Atmospheric Administration and EUMETSAT, respectively) in collaboration with NASA and CNES, is in good health and continues to collect science and operational data. This same U.S./European team is preparing to launch the next satellite in the series, Jason-3, in March 2015.

Contact was lost with the Jason-1 satellite on June 21 when it was out of visibility of ground stations. At the time of the last contact, Jason-1 and its instruments were healthy, with no indications of any alarms or anomalies. Subsequent attempts to re-establish spacecraft communications from U.S. and French ground stations were unsuccessful. Extensive engineering operations undertaken to recover downlink communications also were unsuccessful.

After consultation with the spacecraft and transmitter manufacturers, it was determined a non-recoverable failure with the last remaining transmitter on Jason-1 was the cause of the loss of contact. The spacecraft's other transmitter experienced a permanent failure in September 2005. There now is no remaining capability to retrieve data from the Jason-1 spacecraft.

On July 1, mission controllers commanded Jason-1 into a safe hold state that reinitialized the satellite. After making several more unsuccessful attempts to locate a signal, mission managers at CNES and NASA decided to proceed with decommissioning Jason-1. The satellite was then commanded to turn off its magnetometer and reaction wheels. Without these attitude control systems, Jason-1 and its solar panels will slowly drift away from pointing at the sun and its batteries will discharge, leaving it totally inert within the next 90 days. The spacecraft will not reenter Earth's atmosphere for at least 1,000 years.

"Like its predecessor Topex/Poseidon, Jason-1 provided one of the most comprehensive pictures of changes in the tropical Pacific Ocean, including the comings and goings of El Nino and La Nina events," said Lee-Lueng Fu, Jason-1 project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "These Pacific Ocean climate cycles are responsible for major shifts in sea level, ocean temperatures and rainfall every two to five years and can sometimes be so large that worldwide weather patterns are affected. Jason-1 data have been instrumental in monitoring and predicting these ever-changing cycles."

In the spring of 2012, based on concern over the limited redundancy of Jason-1's aging control systems, NASA and CNES moved the satellite into its planned final "graveyard" orbit, depleted its extra fuel and reconfigured the mission to make observations that will improve our knowledge of Earth's gravity field over the ocean, in addition to delivering its oceanographic data products.

The first full 406-day marine gravity mission was completed on June 17. The resulting data have already led to the discovery of numerous small seamounts, which are underwater mountains that rise above the deep-sea floor. The data also have significantly increased the resolution of Earth's gravity field over the ocean, while increasing our knowledge of ocean bathymetry, which is the underwater depth of the ocean floor.

JPL manages the U.S. portion of the Jason-1 mission for NASA's Science Mission Directorate. CNES manages the French portion of the mission.

Source: NASA/Jet Propulsion Laboratory

Likely near-simultaneous earthquakes complicate seismic hazard planning for Italy

Before the shaking from one earthquake ends, shaking from another might begin, amplifying the effect of ground motion. Such sequences of closely timed, nearly overlapping, consecutive earthquakes account for devastating seismic events in Italy's history and should be taken into account when building new structures, according to research published in the September issue of the journal Seismological Research Letters (SRL).

"It's very important to consider this scenario of earthquakes, occurring possibly seconds apart, one immediately after another," said co-author Anna Tramelli, a seismologist with the Istituto Nazionale di Geofisica e Vulcanologia in Naples, Italy. "Two consecutive mainshocks of magnitude 5.8 could have the effect of a magnitude 6 earthquake in terms of energy release. But the effect on a structure could be even larger than what's anticipated from a magnitude 6 earthquake due to the longer duration of shaking that would negatively impact the resilience of a structure."

Historically, multiple triggered mainshocks, with time delays of seconds to days, have caused deadly earthquakes along the Italian Apennine belt, a series of central mountain ranges extending the length of Italy. The 1997-98 Umbria-March seismic sequence numbered six mainshocks of moderate magnitude, ranging M 5.2 -- 6.0. The 1980 Irpinia earthquakes included a sequence of three events, occurring at intervals within 20 seconds of each other. The 2012 Emilia sequence started with an M 5.9 event, with the second largest mainshock (M 5.8) occurring nine days later, and included more than 2000 aftershocks.

In this study, Tramelli and her colleagues used the recorded waveforms from the 2012 Emilia seismic sequence to simulate a seismic sequence that triggered end-to-end earthquakes along adjacent fault patches, observing the affect of continuous ruptures on the resulting ground motion and, consequently, its impact on critical structures, such as dams, power plants, hospitals and bridges.

"We demonstrated that consecutively triggered earthquakes can enhance the amount of energy produced by the ruptures, exceeding the design specifications expected for buildings in moderate seismic hazard zones," said Tramelli, whose analysis suggests that the shaking from multiple magnitude 5.0 earthquakes would be significantly greater than from an individual magnitude 5.0 event.

And back-to-back earthquakes are more than theoretical, say the authors, who note that this worst-case scenario has happened at least once in Italy's recent history. Previous studies identified three sub-events at intervals of 20 seconds in the seismic signals recorded during the 1980 Irpinia earthquake sequence, whose shared ground motion caused more than 3000 deaths and significant damage to structures.
A "broader and modern approach" to seismic risk mitigation in Italy, suggest the authors, would incorporate the scenario of multiple triggered quakes, along with the present understanding of active fault locations, mechanisms and interaction.

Source: Seismological Society of America

The Gas-charged fluids creating seismicity associated with a Louisiana sinkhole

Natural earthquakes and nuclear explosions produce seismic waves that register on seismic monitoring networks around the globe, allowing the scientific community to pinpoint the location of the events. In order to distinguish seismic waves produced by a variety of activities -- from traffic to mining to explosions -- scientists study the seismic waves generated by as many types of events as possible.

In August 2012, the emergence of a very large sinkhole at the Napoleonville Salt Dome in Louisiana offered University of California, Berkeley scientists the opportunity to detect, locate and analyze a rich sequence of 62 seismic events that occurred one day prior to its discovery.

In June 2012, residents of Bayou Corne reported frequent tremors and unusual gas bubbling in local surface water. The U.S. Geological Survey installed a temporary network of seismic stations, and on August 3, a large sinkhole was discovered close to the western edge of the salt dome.

In this study published by the Bulletin of the Seismological Society of America (BSSA), co-authors Douglas Dreger and Avinash Nayak, evaluated the data recorded by the seismic network during the 24 hours prior to the discovery of the sinkhole. They implemented a waveform scanning approach to continuously detect, locate and analyze the source of the seismic events at the sinkhole, which are located to the edge of the salt dome and above and to the west of the cavern near the sinkhole.

The point-source equivalent force system describing the motions at the seismic source (called moment tensor) showed similarities to seismic events produced by explosions and active geothermal and volcanic environments. But at the sinkhole, an influx of natural gas rather than hot magma may be responsible for elevating the pore pressure enough to destabilize pre-existing zones of weakness, such as fractures or faults at the edge of the salt dome.

Source: Seismological Society of America