Dr. Larry O’Neill, Assitant Professor, College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR
Research interests: Air-sea interactions, specifically how ocean temperature affects weather and how weather affects ocean temperature and circulation.
Research highlights: Water is the dominant feature of our planet, and the circulation of water through the ocean and the atmosphere are vital cycles that enable life to exist. However, the amount of water is finite, and only a small percentage of this precious resource is available at a given time as fresh water. One key source of fresh water is precipitation from storms. Knowing why rain falls where it does and how changes in the strength or intensity of ocean currents can impact the distribution of precipitation are two key questions Dr. Larry O’Neill’s research seeks to answer.
As O’Neill points out, interactions between the ocean and the atmosphere can affect circulation patterns in both sea and sky. These circulation patterns also can shift over time in response to changes in global climate. This, in turn, can impact storm formation, storm movement, and precipitation patterns. Given the small amount of fresh water available at any one time, having a better understanding of these air-sea interactions and their effect on weather is critical.
The U.S. Geological Survey estimates that there are over 332,500,000 cubic miles of water on the planet. Most of this water—about 97%—is saline ocean water (about 321,000,000 cubic miles), according to the National Oceanic and Atmospheric Administration. Of the remaining 3% of Earth’s water, only about 1% is readily available fresh water on the surface and not locked up in ice or underground. This fresh water is found in lakes, rivers, and wetland areas or is transported through the atmosphere as water vapor, clouds, and precipitation. As a result, changes in atmospheric and oceanic circulation patterns can impact the formation and track of storms globally, while influencing the amount of fresh water delivered by storms locally.
These air-sea interactions continuously occur through near-surface winds, clouds, rainfall patterns, evaporation, storms, surface waves, and changes in ocean depth. Much of O’Neill’s work centers on regions where these air-sea interactions coincide with very strong and large ocean currents, such as off the U.S. East Coast (the Gulf Stream), the Southern Ocean (the Antarctic Circumpolar Current), and off the east coast of Asia (the Kuroshio Current). Ocean currents in these dynamic regions can be very fast (NASA satellite data indicate that the Kuroshio Current carries warm water northeastward at speeds greater than 4 mph) and the temperature contrast between the core of these currents and nearby surrounding water can be as great as 15 degrees Fahrenheit.
As these currents shift warm water from tropical regions toward the poles, they create their own weather patterns through their impact on evaporation and the resulting storm and cloud development. In fact, O’Neill and his colleagues found that the temperature of the Gulf Stream influences the generation and strength of intermittent storms, creating rain in bursts rather than continuously generating clouds and light rain.
While ocean buoys collect in situ data at specific locations, the ocean is simply too vast for large-scale data collection using conventional measuring devices. Earth observing satellites maintained by NASA and other space agencies provide the large spatial (ocean-wide) and temporal (many years) data that help enable O’Neill’s research.
Of particular use is scatterometer data. A scatterometer is a microwave radar sensor that measures the reflection or scattering of radar waves by wind. Scatterometers are the best remote-sensing system for providing accurate, frequent, high-resolution measurements of ocean-surface wind speed and direction in most weather and cloud conditions and can be mounted aboard aircraft or on space-based platforms (such as a satellite or the International Space Station). Two sources of scatterometer data used by O’Neill are the SeaWinds instrument aboard NASA’s Quick Scatterometer (QuikSCAT) satellite (operational 1999 to 2009) and the Rapid Scatterometer (RapidScat) instrument installed aboard the International Space Station (ISS-RapidScat, operational 2014 to 2016). Data from these instruments are available from the Physical Oceanography Distributed Active Archive Center (PO.DAAC).
For measuring other ocean data, such as sea surface temperature, humidity, and precipitation, an important resource for O’Neill is the Advanced Microwave Scanning Radiometer (AMSR) series of instruments (AMSR, operational 2002 to 2003; AMSR-E, operational 2002 to 2011; and AMSR2, operational 2012 to present). AMSR instruments are passive microwave radiometers that sense energy radiated from Earth, and their near-polar orbits provide frequent sampling of a given location. A key feature of the AMSR instruments is their ability to “see” through clouds, which allows for continuous collection of ocean data. AMSR instrument data also are available from PO.DAAC and are processed to create ocean measurement products including sea surface temperature, surface wind speeds, atmospheric water vapor, cloud liquid water content, and rain rate.
Using a combination of scatterometer and AMSR data supplemented with computer models, O’Neill and his colleagues found that surface winds are affected by contrasts in sea surface temperature and that these surface winds can, in turn, set up a feedback loop that continues to strengthen sea surface temperature contrasts. These surface temperature contrasts contribute to areas of surface convergence and uplift that can result in storm formation. Further research by O’Neill shows that these storms can impact the mean mid-latitude atmospheric circulation and affect the overall transport of water vapor.
Through his research into air-sea interactions, O’Neill is helping to shed light on the complex relationships between ocean and atmospheric circulation and the resulting transport of water that drives our planet. The precipitation that results from these processes helps provide the life-sustaining fresh water necessary for survival. Having a better understanding of where and when this rain might fall is critical information O’Neill’s work attempts to provide.
Representative data products used:
- Data products available through PO.DAAC:
- QuikSCAT ocean surface winds (doi:10.5067/QSX12-L2B01)
- ISS-RapidScat ocean surface winds (doi:10.5067/RSX12-L2C11)
- AMSR instrument sea surface temperature, clouds, humidity, ice extent, and rain data products from multiple satellites:
- AMSR, aboard the Japan Aerospace Exploration Agency, NASA, and French Centre Nationale d’Etudes Spatiales (cnes) Advanced Earth Observing Satellite-2 (ADEOS-II/SeaWinds)
- AMSR-E aboard NASA’s multi-national Aqua Earth observing satellite
- AMSR2 aboard the JAXA Global Change Observation Mission-Water (GCOM-W1) satellite
- Sea surface temperature, clouds, humidity, ice extent, and rain data products from the Global Precipitation Measurement (GPM) Microwave Imager (GMI) aboard the joint NASA/JAXA GPM Core Observatory; GMI data are available through PO.DAAC as well as through the Goddard Earth Sciences Data and Information Services Center (GES DISC)
- Sea surface height data from the joint NASA/CNES Jason series of missions
- GPM and Tropical Rainfall Measuring Mission (TRMM) precipitation data; available through GES DISC
- COAMPS® atmospheric model data; available through the Naval Research Laboratory
Read about the research:
O’Neill, L.W., Haack, T., Chelton, D.B. & Skyllingstad, E. (2017). The Gulf Stream Convergence Zone in the time-mean winds. Journal of Atmospheric Sciences, 74(7): 2383-2412. doi:10.1175/JAS-D-16-0213.1
Wentz, F.J., Ricciardulli, L., Rodriguez, E., Stiles, B., Bourassa, M., Long, D., Hoffman, R., Stoffelen, A., Verhoef, A., O’Neill, L.W., Farrar, T., Vandemark, D., Fore, A., Hristova-Veleva, S., Turk, J., Gaston, R. & Tyler, D. (2017). “Evaluating and Extending the Ocean Wind Climate Data Record.” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10(5): 2165-2185. doi:10.1109/JSTARS.2016.2643641
Gaube, P., Chelton, D.B., Samelson, R.M., Schlax, M.G. & O’Neill, L.W. (2015). Satellite Observations of Mesoscale Eddy-Induced Ekman Pumping. Journal of Physical Oceanography, 45: 104-132. doi:10.1175/JPO-D-14-0032.1
O’Neill, L.W., Haack, T. & Durland, T. (2015). Estimation of time-averaged surface divergence and vorticity from satellite ocean vector winds. Journal of Climate, 28: 7596-7620. doi:10.1175/JCLI-D-15-0119.1
O'Neill, L.W. (2012). Wind speed and stability effects on the coupling between surface wind stress and SST observed from buoys and satellite. Journal of Climate, 25: 1544-1569. doi:10.1175/JCLI-D-11-00121.11
For more information
- Quick Scatterometer (QuikSCAT)
- Rapid Scatterometer (RapidScat)
- Advanced Microwave Scanning Radiometer (AMSR)