OceThe OFFiciala MaganZineog OF the Oceanographyra Spocietyhy CITATION D’Asaro, E., P. Black, L. Centurioni, P. Harr, S. Jayne, I.-I. Lin, C. Lee, J. Morzel, R. Mrvaljevic, P.P. Niiler, L. Rainville, T. Sanford, and T.Y. Tang. 2011. Typhoon-ocean interaction in the western North Pacific: Part 1.Oceanography 24(4):24–31, http://dx.doi.org/10.5670/oceanog.2011.91. DOI http://dx.doi.org/10.5670/oceanog.2011.91 COPYRIGHT This article has been published inOceanography , Volume 24, Number 4, a quarterly journal of The Oceanography Society. Copyright 2011 by The Oceanography Society. All rights reserved. USAGE Permission is granted to copy this article for use in teaching and research. Republication, systematic reproduction, or collective redistribution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The Oceanography Society. Send all correspondence to: [email protected] or The Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. doWnloaded From http://WWW.tos.org/oceanography SPECIAL IssUE ON THE OCEANOGRAPHY OF TAIWAN Typhoon-Ocean Interaction in the Western North Pacific Part 1 BY ERIC D’AsARO, PETER BLACK, LUCA CENTURIONI, PATRICK HARR, STEVEN JAYNE, I.-I. LIN, CRAIG LEE, JAN MORZEL, ROSALINDA MRVALJEVIC, PEARN P. NIILER, LUC RAInvILLE, THOMAS SANFORD, AND TsWEN YUNG TANG An oceanographic float is air-deployed out the back of a C130 aircraft by the 53rd Air Force Reserve squadron, “Hurricane Hunters,” during the 2010 Impact of Typhoons on the Ocean in the Pacific (ITOP) program in the western Pacific. Deployments of such instruments in front of typhoons provide a detailed view of the inter- actions between these storms and the ocean. 24 Oceanography | Vol.24, No.4 ABSTRACT. The application of new technologies has allowed oceanographers a comprehensive review. Pun et al. (2011, and meteorologists to study the ocean beneath typhoons in detail. Recent studies in this issue) follow with a more detailed in the western Pacific Ocean reveal new insights into the influence of the ocean presentation of data from the Impact of on typhoon intensity. Typhoons on the Ocean in the Pacific (ITOP) program. InTRODUCTION winds and large waves generated by a The western North Pacific Ocean has typhoon mix these two layers, often THE TYPHOON WAKE the highest concentration of tropical creating a trail of colder water—a Satellite infrared images of the sea cyclones in the world. These strong and typhoon “cold wake”—behind the storm. surface often identify typhoon cold dangerous storms—called hurricanes in More importantly, this wake forms wakes. An image of Typhoon Fanapi the Atlantic Ocean and eastern Pacific underneath the typhoon, decreasing in 2010 (Figure 2) shows a narrow Ocean, cyclones in the Indian Ocean, the sea surface temperature, thereby trail of cold water, 2–3°C colder than and typhoons in the western North reducing the energy supply to the storm the surrounding ocean, that is located Pacific Ocean—draw their energy from and limiting its intensity (Emanuel, 1999; slightly to the north of the storm track. the warm, humid air found over warm Lin et al., 2008, 2009). By the time of this image, the storm had ocean waters. A 150-year compilation Here, we present a brief description moved west and was impacting Taiwan. of tropical cyclone tracks (Figure 1) of these typhoon-ocean interactions and The typhoon is the large masked region shows hurricanes concentrated over the the methods used to study them, using on the west side of the image; the storm warm waters of the subtropical western examples and data from recent scientific clouds prevent this type of satellite Atlantic and Caribbean, and typhoons programs sponsored by the US Office of (infrared radiometer) from sensing the concentrated over the warm waters of Naval Research, the US National Science ocean surface. Satellite microwave radi- the western Pacific. Foundation, and the Taiwan National ometers can see though many clouds, On average, there are 16 typhoons Science Council. This article is intended at reduced spatial resolution, but not per year, about twice the number of to be an introduction to this subject, not through the heavy precipitation within Atlantic hurricanes (Webster et al., 2005). Typhoons can occur in any season, unlike hurricanes, which occur almost entirely from June to November. However, both typhoons and hurri- canes occur most commonly in the late summer and fall. The region of glob- ally highest concentration of storms is the Philippine Sea, east of Luzon and Taiwan. Destructive landfalling storms are common in the Philippines, Taiwan, Japan, Korea, and mainland China, as well as other nearby countries. The typhoons’ strong winds can have TD TS 1 2 3 4 5 a large effect on the underlying ocean under certain conditions. The warm Figure 1. Worldwide tropical cyclone tracks through 2006 from the National Hurricane Center and ocean water that energizes typhoons the Joint Typhoon Warning Center, spanning nearly 150 years. Each track is colored by storm intensity using the Saffir-Simpson storm categoriesT ( ropical Depression, Tropical Storm, and Tropical Cyclone occupies only a relatively thin layer on categories 1 [wind 33–42 m s–1] to 5 [wind > 70 m s–1]). The tracks show that the regions of most top of a colder deep ocean. The strong frequent and intense storms are in the western North Pacific.Image courtesy of NASA Earth Observatory Oceanography | December 2011 25 Satellite SST on 9/20 °C 32 by most of the usual methods. One approach in tropical cyclone oceanog- 31 25°N raphy is to deploy instrumented moor- 30 ings in the regions of most frequent 24°N typhoon activity for several years and 9/19 29 wait for a storm to pass over (Pun et al., 23°N 2011, in this issue). Another approach 28 uses aircraft to both deploy oceano- 22°N = 70 knots graphic instrumentation and measure 27 the properties of the storm itself. Aircraft = 95 knots are the mainstay of meteorological 26 123°E 125°E 127°E 129°E measurements of tropical cyclones. Figure 2. The track (black line) and cold wake (blue stripe) of Typhoon Fanapi on In the Atlantic, “Hurricane Hunter” September 20, 2010. The diameters of the circles along the track are proportional to peak storm winds. The storm traveled along a complex S-shaped path as it aircraft from the US Air Force Reserve strengthened, before heading westward and striking Taiwan. Here, the storm is Command 53rd Weather Reconnaissance centered off the western edge of the image; its cloud mass hides the sea surface Squadron and the National Oceanic and from the satellite. Atmospheric Administration Aircraft Operations Center routinely penetrate the central core of a typhoon. Thus, instruments at the sea surface. hurricanes, providing nearly continuous satellite instruments cannot observe the Oceanographic ships cannot make measurements of the strengths and posi- actual formation of the cold wake nor measurements safely within typhoons. tions of storms that threaten land as well detect the ocean temperature beneath Even if a ship were to unfortunately as supporting research to improve hurri- the core of the storm. These measure- find itself within a typhoon, the severe cane forecasting. Adding aircraft-based ments require aircraft instruments or conditions would prevent measurements oceanographic instrumentation to these operations capitalizes on decades of Eric D’Asaro ([email protected]) is Principal Oceanographer and Professor, experience in tropical cyclone operations Applied Physics Laboratory and School of Oceanography, University of Washington, acquired by the “Hurricane Hunters.” Seattle, WA, USA. Peter Black is Senior Scientist, Naval Research Laboratory Marine Oceanographic profilers deployed Meteorology Division (SAIC), Monterey, CA, USA. Luca Centurioni is Associate Project from aircraft and telemetering data back Scientist, Scripps Institution of Oceanography, La Jolla, CA, USA. Patrick Harr is Professor, to the aircraft have been used for several Naval Postgraduate School, Monterey, CA, USA. Steven Jayne is Associate Scientist, Woods decades in tropical cyclone research Hole Oceanographic Institution, Woods Hole, MA, USA. I.-I. Lin is Professor, Department (Black, 1983; Shay and Elsbery, 1987; of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan. Craig Lee is Sanford et al., 1987). More recently, Principal Oceanographer and Associate Professor, Applied Physics Laboratory and School autonomous floats and drifters, capable of Oceanography, University of Washington, Seattle, WA, USA. Jan Morzel is Research of measuring the ocean throughout the Scientist, Rosetta Consulting, Boulder, CO, USA. Rosalinda Mrvaljevic is a graduate student entire passage of a tropical cyclone, have at the Applied Physics Laboratory and School of Oceanography, University of Washington, been developed. Typically, drifters and Seattle, WA, USA. Pearn P. Niiler (deceased) was Distinguished Emeritus Professor, Scripps floats are deployed about one day in Institution of Oceanography, University of California, San Diego, CA, USA. Luc Rainville is front of the storm. Each instrument is Oceanographer and Affiliate Assistant Professor, Applied Physics Laboratory and School of packed within a wood and/or cardboard Oceanography, University of Washington, Seattle, WA, USA. Thomas Sanford is Principal box that is deployed off the back ramp Oceanographer and Professor, Applied Physics Laboratory and School of Oceanography, of a WC-130J aircraft (see opening- University of Washington, Seattle, WA, USA. Tswen Yung Tang is Professor, Institute of spread photo). A parachute is used to Oceanography National Taiwan University, Taipei, Taiwan. deliver the box to the ocean surface. 26 Oceanography | Vol.24, No.4 Once in the water, the box comes apart, (Figure 3c) showed that this cooling surface to about 200 m depth making a usually through the use of dissolving salt extended across the entire surface full round trip about once an hour and blocks, and the instrument is released. mixed layer, to about 90 m depth.