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Interview with Scientists

Interview with Dr. Luca Centurioni

Drifting Buoys: Disasters and Developments
June 27th, 2014
By Sonja Hartmann

Q: Can you define your role in the development and deployment of drifting buoys?

A: The Global Drifter Program is a scientific project in which I work with colleagues at NOAA (National Oceanic and Atmospheric Administration) to define the scientific direction and goals of the project. We determine which scientific questions to ask about ocean currents for climate science and understanding the interactions between the ocean surface and the atmosphere.

Within the Global Drifter Program, my general focus is on what the observations [gathered by GDP instruments] teach us [about climate science]. From Scripps [Institution of Oceanography], I oversee the technical development [of drifting buoys]. I work in labs with engineers to improve and expand the capabilities of drifting buoys. We create new sensors and find new ways to collect measurements.

Drifters are deployed by whoever is first scheduled to travel to the area where drifters are needed, sometimes by cargo vessels or research ships.

Q: In an interview with CNN, you demonstrated the ways that a drifter may potentially be able to aid the process of finding the missing Malaysia Airlines Flight 370 by explaining the structure and function of a drifting buoy. Were NOAA drifters used in the investigation for Malaysia Airlines Flight 370?

A: Drifter data are available worldwide and in real time to anyone with access to the GTS [Global Telecommunication  System] of the World Weather Watch, i.e. operational marine and meteorological forecast centers. Data transmitted include location and time (from which surface velocity can be computed), SST [Sea Surface Temperature] and air pressure.

Information gathered from drifters and other instruments can be used to constrain and/or validate numerical models. I am not directly involved in the search [for Malaysia Airlines Flight 370], but I think it is highly likely that drifter data were used directly or indirectly through assimilation into numerical models that simulate and forecast ocean currents. If objects floating on the ocean’s surface were spotted their path could be reconstructed or modelled with information from drifters and satellites, if a drifter was in the same area as debris at the same time, but that is very unlikely. It is much harder to retrace the path of an object and find its origin, which is what must be done in this plane search, than it is to follow it in real time with a drifting buoy. This incident was such a messy process with the search areas changing rapidly that it is hard to target a drifter’s dataset. When objects are found in the ocean, it is not uncommon to mark them so that they can later be relocated, or to deploy a drifter near the debris to track the object’s path. Investigators use all possible information from drifter data and measurements from other equipment to make an educated guess at the answer to their question, or develop numerical models to do so. Drifter information helps scientists make estimates, but doesn’t directly locate debris.

Problems such as this are why it is so important to maintain an adequate array of drifters, so that as many parts of the world as possible are covered, because even if debris from the plane is located, it is unlikely that there will be a drifter in that specific spot to inform others of the material’s path, even with the currently existing array of more than 1,250 drifters.

Q: How were drifters useful in the process of predicting effects of the Fukushima Nuclear Crisis? Were predictions made by drifter data accurate?

A: Drifters were used to give a ballpark estimate of when tsunami debris could be expected to wash ashore on the US west coast. The issue with nuclear meltdowns and the fate of radioactive water that leaked into the ocean is of different nature.

I took drifters near Fukushima and tracked their progress towards the North American West Coast to estimate the travel of  debris from the tsunami. My prediction that the drifting debris would take between one-and-a-half and two-and-a-half years to reach North American coast ended up being correct, as debris reached the coasts of Oregon and Alaska. Debris from this tsunami would not reach the coast of California because very often it is protected by upwelling currents that tend to move floating debris offshore. Although this information couldn’t contain the spread of the debris, the scientific interest helps agencies plan for their reactions and solutions to such problems. The government understands the need to have these instruments in place and to fund programs such as the GDP to develop infrastructure so that by planning ahead they can act quickly and deploy drifters or other equipment when situations occur.

Radiation is a different issue and the information from the drifters are of limited application there. Radioactive water can also mix vertically, not only horizontally along the surface as drifters track. Understanding mixing water over the entire North Pacific ocean requires more knowledge about dispersion and vertical movement than the drifters provide.

Q: Were drifters deployed in anticipation of Hurricane Sandy? What useful information did they supply and how was that information applied?

A: No, the problem there was that we stage the drifters at Keesler Air Force Base [in Biloxi, Mississippi] and it was not possible for us to deploy drifters from there using the C130-J [because the storm was located too far from this base]. This is way we are now developing a more compact drifter that can also be stored at multiple locations and deployed from a P-3 (i.e., a smaller plane).

To deploy hurricane drifters, “Hurricane Hunters” airdrop boxes containing drifters from a C130-J aircraft approximately 24 hours head of a storm, the trck of which is determined and forecasted by the National Hurricane Center . The planes that deploy these drifters are safe if they fly high inside of the storm, but not down low in front of the storm because. That is just is too dangerous. In deployment, hurricane drifters are set up along a 300 to 500 km-long line intercepting the forecasted track of the hurricane. These drifters are unique because they have a 150-meter tether [that extends down into the ocean] with temperature sensors along the cable. They measure vertical changes in temperature of the ocean’s surface, which helps the forecaster to better predict the intensification of the storm  based on how much heat is near the surface. The air pressure and wind speed data collected often come from near the center of the storm, and this information is also very useful understand the nature of the torm and contrain the numerical models. Although a variety of instruments are used to collect as much information as possible about hurricanes, drifters are unique in their ability to measure subsurface ocean temperature and atmospheric components as in-situ instruments. Additional measurements come from other floats and aircraft. The more observations that can be made the better, because hurricanes change rapidly and move very fast.

Q: How useful were drifters in tracking Hurricane Isaac in 2012?

A: I can’t quantify the value of drifters in Hurricane Isaac because that is a very technical question, but the National Hurricane Center seemed to be very pleased with the data, as they were able to successfully receive wind data in real time.

Q: How important were drifter data in tracking the spread of oil after the Deepwater Horizon oil spill?

A: In my mind that was very important because it allows the validation of numerical simulation of dispersion. Private companies also deployed drifters to track the oil.

Q: What do you see as the greatest need in terms of drifter development?

A: The GDP is the only global array that collects in-situ observations of surface velocity, SST (temperature) and SLP (pressure). We need to improve the temporal lag between data collection and data availability, especially for air pressure data for forecast purposes. We are uniquely positioned to measure upper ocean processes and air-sea interaction physics. We need to expand the sensor suite. Coming along in the short term are wave and pH sensors.

Q: Would these be used for disaster relief, other research, or both?

A: New sensor developments would have a variety of climate science and practical applications. PH sensors could ground truth important information about CO2 concentration in the ocean, which would have numerous implications for the understanding of climate change. The goal is to come up with sensors that can be used on a drifting buoy to better understand interactions between the ocean’s surface and the atmosphere. Wave sensors are new, inexpensive developments that have practical applications, to inform traveling ships of rough waters by measuring the energy and direction of surface gravitywaves. Another area of interest is lowering the cost of salinity sensors, as they are especially important to climate science. Also, more compact, air-deployable hurricane drifters.

Q: Could new developments affect the number of drifters or the location of drifter deployments?

A: Absolutely yes. The tendency is for drifters to last longer and to carry more sensors. This may require some repositioning of the array, for example at high latitudes where the melting ice is exposing unexplored stretches of the ocean.

The size of the global drifter array   is dictated by the need to to constrain the bias of of SST measurements from space with in-situ measurements from drifters.. If the scope of the GDP  is expanded to get more drifters to cover other aspects [of of oceanography and climate science], then there may be a need for more drifters. I like this question because the number of drifters in the array, now 1250, may change with developments, like the wave sensor, but currently, SST measurements dictate the number in the array.

10.  Is there anything else that you would like to share in regards to drifting buoys?

A: It is a great project and it is extremely rewarding to be involved in such activity. The drifters are extremely central for science, climate and day-to day applications (search and rescue, emergency response and weather forecast) and offer an incredible infrastructure to exploit new sensors and technologies to monitor the surface ocean and the way it interacts with the atmosphere. Also I would like to acknowledge the vision of Peter Niiler who started this project and the fundamental support of NOAA and of the US Office of Naval Research.


Drifters: Disaster and Developments

Data from drifting buoys, also known as drifters, are used in a variety of ways by scientists and operational agencies all around the world. Information from drifting buoys has been helpful not only in understanding ocean currents and temperatures, but in solving problems that arise when hurricanes, oil spills, tsunamis, and other ocean-related disasters occur. Today, scientists continue to develop new uses for drifters, as well as new technology to make these applications possible. With the combination of improving technology and the occurrence of events that demand information from drifting buoys, drifters have become an indispensable tool in oceanic and atmospheric research.

Dr. Luca Centurioni plays a significant role in the drifting buoy community. The Global Drifter Program (GDP) is a scientific project in which he works alongside colleagues at the National Oceanic and Atmospheric Administration (NOAA) to define the scientific direction and goals of the program. Dr. Centurioni poses insightful scientific questions about the ocean’s currents for the benefit of the oceanographic, meteorological and climate science communities and the better understanding of the interactions between the ocean’s surface and the atmosphere. Within the GDP, Centurioni has several resposabilities, including  finding out what the observations gathered by GDP instruments teach us about ocean circulation and climate. Centurioni also oversees the development of drifters at the Scripps Institute of Oceanography (SIO). Dr. Centurioni directs a lab where engineers work to improve and expand the capabilities of drifting buoys in the exploration of new sensors and measurements of ocean currents.

With his highly qualified background and current position, Dr. Centurioni was able to provide an immense amount of insight into the recent uses and developments of drifting buoys, specifically in detailing the involvement of drifters in response to several major ocean-related disasters of the past decade.

According to Dr. Centurioni, special hurricane drifters have been air-deployed by the 53rd Weather Reconnaissance Squadron “Hurricane Hunters” in more than ten hurricanes and typhoons since 2003. The “Hurricane Hunters” are part of an Air Force squadron that flies into hurricanes to take measurements and deploy scientific equipment, like drifting buoys, before a storm. Hurricane drifters are unique in their structure as they have a series of temperature sensors that extend down into the ocean to provide information about how hurricanes affect the temperature of the ocean’s surface which in turn can affect the intensification of the storm. Although a variety of instruments are used to collect as much information about hurricanes as possible, drifters are unique in their ability to measure temperature and atmospheric components as in-situ instruments. With the combination of hurricane drifting buoys’ measurements and that of other scientific instruments and sensors comes an invaluable ability to understand and track these rapidly changing, fast-moving storms.

Hurricane drifters have proven to be sources of information that are integral to the understanding of tropical storms. For Hurricane Isaac in 2012, drifters were able to successfully collect wind data in real time for the first time, making accurate measurements more accessible than ever before. However, NOAA hurricane drifters cannot be used in every hurricane, as, in some cases, they are limited by their location at Keesler Air Force Base in Mississippi. Because deployment of hurricane drifters require a special aircraft, a C130-J, a storm like Hurricane Sandy, that hit along the Northeastern seaboard, may be too far away for the drifters to be efficiently and effectively deployed. For this reason, engineers are working on developing more compact, air-deployable drifters that could be released by smaller, more accessible aircraft.

Aside from studying ocean currents and the interaction of hurricanes with the ocean, drifting buoy data have also helped scientists solve problems related to oil spills, tsunamis, and other ocean-related crises. Following the Deepwater Horizon Oil Spill in 2010, drifters were used to track the spread of oil as they revealed information about currents in and around the Gulf of Mexico. The buoys allow scientists to verify simulations of potential outcomes, in this case anticipating the spread of oil. Similarly, drifting buoys were used to validate predictions about the path of debris that was floating in the ocean after the Japanese tsunami and Fukushima Nuclear Crisis happened in 2011.

Drifters have even offered information in cases of disaster like that of the missing Malaysia Airlines Flight 370 in the spring of 2014. Had the investigation been able to identify debris from the plane, assuming it crashed in water, ideally such evidence could have assisted the process of locating the crash by retracing the ocean currents’ paths. However, the likelihood of a drifter being in the same area of suspect debris is very slim, so, theoretically, more drifters would be necessary in different parts of the ocean to prepare for investigations like this.

What can be learned from drifting buoys is ever expanding as technology improves. Aside from the aforementioned plan to make hurricane drifters more compact in order to ease the process of deployment, developments are underway to release wave and pH sensors in the near future, according to Dr. Centurioni. Wave sensors measure the energy in the water, and this information can be used in practical ways such as informing sailors of rough waters ahead. By measuring the amount of certain substances in the ocean, such as carbon dioxide, scientists can use pH sensors to understand more about the interactions between the sea’s surface and the atmosphere.

As with any useful equipment, the structure and application of drifting buoys are constantly evolving and adapting. Even the optimal number of drifters in the global array is subject to change from 1,250 buoys. This is because the array is currently determined by a demand for SST (Sea Surface Temperature) measurements, which are used to verify the information being collected by satellites and to do so in near-real time. As drifter technology becomes more capable and last longer, fewer buoys may need to be deployed each year; however, the melting ice that is exposing unexplored regions of the ocean may lead to an increase in drifter demand. Clearly, the array of drifters is subject to fluctuate as the abilities of drifting buoys change as well.

Ultimately, Dr. Centurioni asserts that the Global Drifter Program is an extremely rewarding project with which to be involved. Drifters are important for science, climate, and daily applications such as search and rescue, emergency response, and weather forecasting. This system offers “incredible infrastructure to exploit new sensors and technologies to monitor the ocean surface and the way it interacts with the atmosphere.” Thanks to the vision of Peter Niiler, the founder of the GDP, and with the primary support of NOAA and of the US Office of Naval Research, this project has become a significant source of cutting-edge information regarding our oceans’ surfaces and their impact on climates around the world.