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OceanTe h Official Magazineog of the Oceanographyraphy Society

CITATION May, P.W., J.D. Doyle, J.D. Pullen, and L.T. David. 2011. Two-way coupled atmosphere- modeling of the PhilEx Intensive Observational Periods. Oceanography 24(1):48–57, doi:10.5670/ oceanog.2011.03.

COPYRIGHT This article has been published inOceanography , Volume 24, Number 1, a quarterly journal of The Oceanography Society. Copyright 2011 by The Oceanography Society. All rights reserved.

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downloaded from www.tos.org/oceanography Philippine Straits Dynamics Experiment

By Paul W. May, James D. Doyle, Julie D. Pullen, and Laura T. David two-Way Coupled Atmosphere-Ocean Modeling of the PhilEx Intensive Observational Periods

Abstract. High-resolution coupled atmosphere-ocean simulations of the primarily controlled by topography and show the regional and local nature of atmospheric patterns and ocean geometry, and they act to complicate response during Intensive Observational Period cruises in January–February 2008 and obscure an emerging understanding (IOP-08) and February–March 2009 (IOP-09) for the Philippine Straits Dynamics of the interisland circulation. Exploring Experiment. Winds were stronger and more variable during IOP-08 because the time the 10–100 km circulation patterns period covered was near the peak of the northeast monsoon season. Distinct wind jets of the Philippines, particularly of the between islands and wakes behind islands are common northeast monsoon features surface winds and upper-ocean currents, that are controlled by winds interacting with island topography. The modeled upper- requires many observations and the ocean flow associated with Philippine straits during IOP-08 exhibits large (> 1 m -1s ) interpretive assistance of high-resolution westward mean flow through Suriago Strait and highly variable flow through numerical modeling. Strait. The model shows prominent eddies in the and Cuyo East Pass that The Naval Research Laboratory were also observed during the field experiment. A high-resolution nested simulation (NRL) contributed to the Philippine of the Passage finds local wind-driven upwelling that is confirmed Straits Dynamics Experiment (PhilEx) by shipboard sea surface temperature measurements and satellite observations of Intensive Observational Period research chlorophyll concentration. cruises in 2008 and 2009 (IOP-08 and IOP-09) by supplying the shipboard Introduction western Pacific Ocean to the east, with team with real-time atmospheric and The Philippine Archipelago is an intri- its nearby North Equatorial, Kuroshio, oceanic forecasting, and with addi- cate array of islands, straits, and semi- and currents. Observational tional retrospective two-way coupled enclosed whose broad atmospheric and numerical studies of these global- numerical hindcasts. The forecasts circulation is governed by the rhythm scale phenomena abound (Qu et al., provided information to scientists at of the East Asian monsoon and steady 2009), but within the island archipelago, sea both for general operations and Pacific trade winds. Philippine oceanic there are finer scales at play in both as guidance for developing underway circulation is dominated by the posi- the atmosphere and ocean that have sampling strategies. The more carefully tion of the island chain between the not received as much attention. These controlled, a posteriori simulations offer to the west and the smaller-scale winds and currents are important insights into complex regional

48 Oceanography | Vol.24, No.1 kinematics and dynamics. Although graupel (snow pellets). In the two-way oceanic and atmospheric COAMPS there are other numerical studies of coupling scheme, the atmospheric forecasts were supplied to researchers on the region (e.g., Metzger and Hurlburt, model passes parameterized surface the cruises in real time (see Pullen et al., 1996; Han et al., 2009), the NRL coupled momentum, heat, and moisture fluxes 2011, for details of how the model guid- atmosphere-ocean model is a unique through ESMF to the ocean model. ance was used in ship-track planning). tool for simultaneous high-resolution The ocean, which also uses a Mellor- Additional simulations, using two-way studies of both the meteorology and Yamada level 2.5 turbulent boundary coupled COAMPS with higher ocean oceanography of a region. layer mixing scheme, completes the resolutions were run later for the time two-way coupling by returning the sea period that encompassed the IOP-08. Coupled Air-Sea Model surface temperature through ESMF to From these simulations, a 60-day period NRL numerical simulations for the act as a lower boundary condition to covering January through February 2008 Philippines used the Coupled Ocean/ the atmosphere. The coupled model and a 40-day period covering February Atmosphere Mesoscale Prediction supports grid nesting, which permits through March 2009 were selected for System (COAMPS), which consists progressively higher resolution with comparison here. For the 2008 time of an atmospheric model coupled each grid refinement—typically imple- period, nested atmospheric grid meshes with the Navy Coastal Ocean Model mented at a 3:1 ratio. Further details of 27, 9, and 3 km ran above nested (NCOM). The atmospheric model is of the parameterizations, nesting, and ocean grids of 3 and 1 km. There were nonhydrostatic with a terrain-following coupling in COAMPS may be found 40 vertical levels in both the atmosphere vertical coordinate (Hodur, 1997), while in Chen et al. (2010). and ocean models. After initializing the ocean model features hydrostatic Regional forecast models require with NOGAPS and gNCOM fields on dynamics, generalized curvilinear external information in the form of January 1, 2008, the coupled model horizontal coordinates, a bathymetry- initial conditions, lateral boundary was run for 60 days with atmospheric following vertical coordinate, and a free conditions, and timely observations. The data assimilation cycles every 12 hours. surface (Barron et al., 2006). Air-to- atmospheric data assimilation of quality- For 2009, nested atmospheric grids of ocean two-way coupling is accomplished controlled upper-air sounding, surface, 27 and 9 km were used with a 9-km through the community-based Earth commercial aircraft, and satellite data is ocean grid. In the 2009 model, hori- System Modeling Framework (ESMF; achieved with the use of a Multivariate zontal spatial domains differed slightly Earth System Modeling, 2010), which Optimum Interpolation (MVOI) from those in 2008, reflecting a ship allows each model to use flexible, scheme. Ocean observations, which course that was further south. Also, generalized grids and a configurable include floats, drifters, moorings, satellite because of the coarser resolution (9 km) air-sea coupling interval, typically every sea surface temperatures (SST), conduc- of the ocean model run during the 2009 10 to 15 minutes. Atmospheric physical tivity-temperature-depth/expendable field experiment, it is not considered parameterizations for surface fluxes use bathythermograph (CTD/XBT) profiles, in the comparisons. In all the cases bulk aerodynamic formulae based on and satellite altimetry, are assimilated by presented here, NCOM ran without tidal the TOGA-COARE (Tropical Ocean the MVOI-based NRL Coupled Ocean boundary forcing. Global Atmosphere-Coupled Ocean Data Assimilation System (Cummings, Atmosphere Response Experiment) 2005). The initial state and lateral Atmospheric Forcing algorithms (Fairall et al., 1996), a boundary conditions for the outermost During IOP-08 and IOP-09 level 2.5 Mellor-Yamada boundary atmospheric and oceanic nests are from Surface wind is an important forcing layer representation, short- and the 1° Navy Operational Global Analysis mechanism for the upper ocean on both long-wave radiation parameteriza- and Prediction System (NOGAPS) and global and local scales, and is particu- tion, and moist processes, including the operational 1/8° Global NCOM larly evident in circulation patterns in explicit microphysical equations for (gNCOM) forecast fields, respectively. and around the Philippine Archipelago. rain, snow, cloud water, cloud ice, and During IOP-08 and IOP-09, daily In nearby and surrounding waters,

Oceanography | March 2011 49 large-scale stresses from the Pacific trade Sea (7°N, 120°E). A series of wind-speed consequence of the partial blocking of winds are responsible for the North maxima and minima are noticeable cross-island monsoon flow by the moun- Equatorial Current and the resulting sea features on the leeward or downwind tains (e.g., Gabersek and Durran, 2004). level differences between the western side of the Philippine Archipelago (see Downstream wakes form from air Pacific and the South China Sea. Figure 1a in Gordon et al., 2011, for descent, acceleration, wave breaking, and Seasonal monsoon winds are also known locations of major islands and passages). potential vorticity generation that occur to modulate circulation in the adjacent The most prominent wind jets occur over the islands (Smith et al., 1997). South China Sea (Metzger and Hurlburt, (from north to south) at Verde Island Wakes can be long and straight when the 1996; Qu, 2000). But, local-scale winds Passage (13°30'N, 120°50'E), which sepa- mountain-generated potential vorticity also drive important interisland circula- rates and Mindoro islands, and and Coriolis force are weak (e.g., at low tions. These local wind characteristics (12°20'N, 121°40'E), which latitudes; Smith et al., 1997; Burk et al., during PhilEx are described by consid- separates Mindoro and . In Tablas 2003). In other situations, with stronger ering the mean and variability of the Strait, mean winds exceed 12 m s-1 and forcing, vortex shedding can ensue atmospheric model’s 10-m wind. The the jet extends nearly 200 km to the (Smolarkiewicz and Rotunno, 1989). variability of vector quantities (winds southwest. There are prominent wind Island wakes and wind jets in ocean and currents) is concisely summarized maxima or tip jets (Doyle and Shapiro, straits are not uncommon and have by using the eigenvalues and eigen- 1999) at the northern and southern been observed in the Hawaiian Islands vectors of the vector component’s covari- flanks of Mindoro Island. Wind jets are (Smolarkiewicz et al., 1988; Yoshida ance matrix (Emery and Thompson, also present in the / et al., 2010), Caribbean (Smith et al., 1998), which define two principal axes of Strait (10°20'N, 122°20'E) and Dipolog 1997); Tsushima Straits (Shimada and variability. In this scheme, the axis in the Strait (8°50'N, 123°10'E), which lies Kawamura, 2008), Aleutians, Sandwich direction of greatest variance, the major between the islands of Mindanao and Islands, Madagascar, and numerous principal axis, has a magnitude equal to . Minima in the mean wind veloc- other island regions. the standard deviation of the wind or ities occur on the downwind side of each It is remarkable that wind variability current in that direction. The minor axis of the islands: Luzon, Mindoro, Panay, (Figure 1b) is largest in the wake regions, is the magnitude and direction of vari- Negros, and Mindanao. These wind jets where unsteady conditions may exist. ability that is orthogonal or uncorrelated and associated leeside wakes are caused By contrast, wind variability has relative with the major axis variability. by the airflow over the mountainous minima in the wind jet regions where Mean 10-m winds from the 9-km terrain of the Philippine Archipelago. the flow is less influenced by topography COAMPS forecasts for January through Along this mountainous island chain, and hence less turbulent. In the two most February 2008 (Figure 1a) clearly several peaks in the Cordillera Central prominent wake regions, those down- show the influence of the northeasterly on Luzon exceed 2700 m in elevation, wind from Luzon and Mindoro islands, (winter) monsoon, which is normally and the highest point in the Philippines, the largest variability is nearest the strongest at this time of year (Chang, Mount Apo on Mindanao, is more than western coast, and the major axis of vari- 2004). The mean winds range from 2900 m above sea level. The enhanced ability is oriented in a distinctly onshore 10–12 m s-1 in (20°N, wind flow in the straits is driven by direction, which likely is associated with 121°E) to 5–6 m s-1 in the southern Sulu along-gap pressure gradients that are a strong but intermittent downslope winds that penetrate to the ocean surface and Paul W. May ([email protected]) is Research Scientist, Computer Science interrupt the wake signature. Another Corporation, Monterey, CA, USA. James D. Doyle is Head, Mesoscale Modeling obvious area of large variability is the Section, Marine Meteorology Division, Naval Research Laboratory, Monterey, CA, USA. region to the northwest of Luzon where Julie D. Pullen is Director, Maritime Security Laboratory, Stevens Institute of Technology, the monsoon winds are channeled into Hoboken, NJ, USA. Laura T. David is Professor, Marine Science Institute, University of the the South China Sea through Luzon Philippines Diliman, City, Philippines. Strait. In this region, the largest wind

50 Oceanography | Vol.24, No.1 a b

c d

Figure 1. The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) 10-m mean wind (left panels) and mean variability (right panels) from the 9-km computational grids for the two Intensive Observational Periods (IOPs). Every fifth wind vector and variability cross is plotted. (a) Wind vectors with color-shaded wind speed (m s-1) for January to February 2008. (b) Variability vectors with color-shaded variability magnitude (m2 s-2) for 2008. (c) Wind vectors plotted over color-shaded wind speed (m s-1) for February to March 2009. (d) Variability vectors plotted over color-shaded variability magnitude (m2 s-2) for 2009.

variability is associated with strong mean direction is relatively unchanged, but the mean wind direction. winds, and the orientation of the vari- preferred wind variability orientation The mean 10-m winds and wind ability is parallel to the wind. Further trends in the alongshore direction where variability from the COAMPS forecasts south along Luzon, the mean wind it is, in some cases, at right angles to the that cover the PhilEx IOP-09 period are

Oceanography | March 2011 51 averaged over a 40-day period from the the weakest winds behind Mindoro island passage jets and highest variability middle of February through the end of and the Cordillera Central in the wake in mountain wakes. Variability in the lee March 2009 (Figure 1c). During this regions. Wind jets over Panay Gulf and of the mountains has the same distinct time, the winds are significantly weaker through Dipolog Strait are stronger onshore-offshore orientation and, as in than those of 2008, indicating a drop in relative to 2008. Again, well-defined 2008, the variability in orientation near the intensity of the seasonal monsoon. wind maxima along the lee slopes of Luzon Straits shifts directions, possibly Besides being weaker, the wind direc- the mountain ridges are clearly evident, an adjustment of the northeast monsoon tion has more of an easterly component. which is consistent with the presence of to the Luzon island wake. Wind jets and wakes are still apparent mountain-wave-induced wakes. Wind Synthetic aperture radar (SAR) to the west of the Philippines, with the variability during IOP-09 (Figure 1d) is surface wind speeds (Figure 2a), derived strongest winds again through Verde also uniformly lower than that in 2008, from a European Space Agency Envisat Island Passage and Tablas Strait, and but still shows the lowest variability in Advanced SAR (ASAR) image on

a b

Figure 2. (a) Surface wind speeds derived from an Envisat Advanced Synthetic Aperture Radar (ASAR) image using the Johns Hopkins University APL/NOAA SAR Wind Retrieval System (ANSWRS) for 0144 UTC 31 January 2008. Image courtesy of NOAA/NESDIS/ORA/STAR and Christopher Jackson, Global Ocean Associates. (b) The COAMPS 10-m winds from the 3-km COAMPS nested grid at 0300 UTC on the same date. Modeled wind vectors are displayed every 18 km or every sixth grid point. The SAR image, with wind vectors from the Navy Operational Global Analysis and Prediction System (NOGAPS) model, shows sharply delineated wind velocity gradients (jets) at the ends of Mindoro, Panay, and Negros islands that have close counterparts in the COAMPS model winds.

52 Oceanography | Vol.24, No.1 January 31, 2008, verify the presence shear lines along the jet flanks. In Ocean Model Surface of wind jets and wakes (see Thompson particular, the wind jet emanating from Circulation During IOP-08 and Beal, 2000, for an explanation of the southwest corner of Panay is readily Mean surface (0–50 m) currents from how SAR measures wind stress) in the identifiable in the SAR image for more the 3-km resolution ocean model Philippines during IOP-08. Although than 300 km into the . Another during IOP-08 and their associated vari- the image is a snapshot, it agrees with difference is that the SAR wind maxima ability (Figure 3) illustrate the primary the general patterns that are apparent in are stronger and more concentrated. The modeled circulation characteristics of the mean 9-km model winds shown in strongest winds in the SAR image, for the upper ocean across the region. In the Figure 1a. As in the model, the strongest example, are just to the west of Verde western Pacific, the North Equatorial winds, nearly 20 m s-1, are in Verde Island (13°35'N, 120°55'E) where the Current is clearly evident (Figure 3a) Island Passage and across the southern flow is constricted by the topography as it divides into the poleward-flowing tip of Mindoro through Tablas Strait. bordering the passage, whereas the Kuroshio and the equatorward-flowing A suggestion of trapped mountain lee strongest winds in the model are near Mindanao currents. A mean flow of waves may be discerned at the northwest Calavite Point (13°30'N, 120°15'E) where more than 1 m s-1 enters the Philippine corner of Panay (11°40'N, 121°55'E) in the passage opens to the South China Archipelago through Strait the SAR image. Surface winds from the Sea. These differences may relate to (10°15'N, 125°25'E) and the 3-km COAMPS at almost the same time mismatches in the exact timing of atmo- and flows out to the Sulu Sea through (Figure 2b) are similar in magnitude spheric mesoscale features or may reflect Dipolog Strait as a strong jet along the and pattern, though the SAR winds are the SAR product’s higher resolution. coast of Mindanao. A much weaker more coherent downwind, with sharper (12°35'N,

a b

Figure 3. Navy Coastal Ocean Model (NCOM) near-surface (0–50 m) mean velocity and sea surface height from the 3-km ocean model. Sixty-day averages are from January through February 2008. (a) Surface velocity vectors with color-shaded velocity magnitude (m s-1). (b) Surface velocity variability vectors drawn over color-shaded variability magnitude (m2 s-2).

Oceanography | March 2011 53 124°10'E) flow winds through the The greatest interisland upper- Springer (2005) as a peak region of , enters Tablas Strait north ocean velocity variability (Figure 3b) is marine biological diversity and has been of , and eventually transits concentrated in a band from the South designated as a priority marine conser- to the Sulu Sea along the western edge China Sea through to the vation site by the Philippine govern- of Cuyo East Pass (11°00'N, 121°30'E) eastern Sulu Sea. This strip of high vari- ment (Ong et al., 2002; Conservation west of Panay. Strong currents in these ability includes the junction (11°30'N, International, 2009). In this biologically two straits were also observed during 121°40'E) of Mindoro and Tablas productive region, atmospheric forcing IOP-08 with underway acoustic Doppler straits with Cuyo East Pass, an area of may contribute to marine ecosystem current profilers (ADCP; Gordon et al., complex bathymetry and channeling dynamics through wind-induced 2011) and are seen in other numerical where currents may branch or converge upwelling (Villanoy et al., 2011). models of the region (Han et al., 2009). from three different directions. Most For most of IOP-08, winds blew A moderately strong southward flow of this modeled nontidal variability is a steadily from east to west over Verde (0.3–0.4 m s-1) through Mindoro Strait consequence of strong southward flow Island Passage. On several occasions partially recirculates along the western past the islands and shallow banks in during January 2008, the easterly wind side of the strait. The remainder of the Mindoro Strait where eddies are formed briefly intensified (e.g., Pullen et al., southerly surface flow through Mindoro and shed frequently, while some is due 2011). Figure 4a shows details of the Strait does not clearly connect with the to occasional fluctuations of the wind vector wind field in the passage and flow through Tablas Strait, but flows into that advect surface waters into and out of along the northern coast of Mindoro the Sulu Sea through the shallow Cuyo the connected channels. The region with Island on January 31 (at the same time as West Pass (11°20'N, 120°30'E). the most upper-ocean current variability the SAR image in Figure 2a), following Several eddies are clearly evident is found in the eastern Sulu Sea. Here, one of the periods of increased wind. In in the 60-day mean surface circula- interacting currents entering and exiting this figure (an enlargement of the model tion pattern. The most prominent is a the area from Cuyo East Pass and from fields from Figure 2b), winds reach a cyclonic eddy in the South China Sea the Bohol Sea through Dipolog Strait maximum of ~ 12 m s-1 along the north west of Mindoro. This feature may be produce a series of energetic transitory coast of Mindoro and over 15 m s-1 off artificially enhanced by its proximity eddies. These shallow eddies, which can the northwest shore of Mindoro. The to the open model boundary, but it is be either cyclonic or anticyclonic, are strong, steady winds along the north also seen in studies with larger domains confined to the deeper southern Sulu Sea coast of Mindoro are a manifestation of and more distant boundaries. The loca- basin by a submarine ridge associated the topographic tion and vorticity of the eddy suggests with the Island chain (9°30'N, wind jet and favor offshore Ekman spin-up by the atmospheric wind jet 121°10'E). The current variability ellipses transport with subsequent nearshore emanating from Verde Island Passage do not exhibit much directional prefer- upwelling of deeper water. (Pullen et al., 2008; Wang and Chen, ence in the deeper parts of the East Sulu As an indication of an upwelling 2008). Another cyclonic circulation that Sea but are oriented along the bathym- response to increased surface wind, is visible in Cuyo East Pass between etry near the Cagayan Islands, Negros surface waters along the north coast of Panay and Cuyo islands was identified in Island, and coastal Mindanao. Mindoro cooled noticeably on January 26 the ship survey (Gordon et al., 2011) and in the 1-km resolution ocean model. The is frequently observed in radar-derived Wind-Driven Upwelling cooler temperatures are evident along the surface currents. A third cyclonic eddy, in Verde Island Passage coast for several days following the wind which Gordon et al. (2011) call the The narrow Verde Island Passage pulse. The minimum temperature, 1°C Iligan Bay Eddy (11°50'N, 124°05'E), (13°30'N, 121°5'E) separates Luzon colder than ambient, was found between is apparent in the southwestern Bohol and Mindoro islands and connects the January 27 and January 29 in the model Sea where it was observed during South China Sea to the Sibuyan Sea. It (Figure 4c). SST data collected during all PhilEx cruises. has been identified by Carpenter and IOP-08-1 for January 30–31 clearly

54 Oceanography | Vol.24, No.1 show that the ship is sailing through the in situ SST. Additional evidence for (Figure 4b). Vertical temperature profiles cooler water along the northern coast upwelling in the passage during IOP-08 from the model, which are in reason- of Mindoro (Figure 4d). The zonal comes from MODIS Aqua satellite able agreement with CTD measure- temperature gradient in the observa- ocean color (Pacific Islands Fisheries ments in the area, suggest that the tions is located to the east of that in the Science Center, 2010). A composite upwelling is confined to the upper 60 m model, and observed temperatures along image of chlorophyll a concentration of the water column. the ship’s track are 0.5–1.0°C warmer for January 25–31, 2008, highlights the Elevated chlorophyll concentra- than the model, but the basic pattern influence of upwelling on the phyto- tions are frequently seen in Verde of colder temperatures is reinforced by plankton biomass north of Mindoro Island Passage and other Philippine

Figure 4. (a) Atmospheric model winds from 3-km nest on January 31, 2008. (b) January 25–31, 2008, MODIS Aqua composite chlorophyll a image (mg m-3). (c) Ocean model sea surface temperature (SST) on 12 UTC January 28, 2008, from 1-km nest. (d) Underway shipboard SST from IOP-08-1 from January 30–31, 2008.

Oceanography | March 2011 55 straits during the northeast monsoon Conclusions The structure of upper-ocean current (e.g., Figure 5a), indicating increased Coupled modeling of the atmosphere fluctuations indicates areas where the biological productivity and suggesting and ocean during IOP-08 and IOP-09 surface currents are most dynamic, that cooler, nutrient-rich water is being find that surface winds and upper-ocean including a band that extends from the transported upward into the euphotic currents during IOP-08 were stronger west coast of Mindoro through Mindoro zone by upwelling. Studies of marine life and more variable than those of IOP-09. Strait and along Panay to Dipolog Strait. (Dolar et al., 2006; Deocadez et al., 2008) Prominent, topographically generated Observations support the presence of a also find greater species richness and wind jets in the gaps between the islands dynamic regime along this corridor. The larger local populations of cetaceans and and wakes downwind of the islands mean near-surface ocean flow features pelagic fish in these regions. A short time are persistent features of the northeast agree with the seasonal Regional Ocean history of surface temperature, in the monsoon in both 9-km and 3-km atmo- Modeling System (ROMS) simulations form of a Hovmöller diagram along the spheric model grids. Wind variability that used coarser atmospheric (~ 50 km) 120°50'E meridian (Figure 5b), shows is greatest in the island wake regions forcing and ocean (~ 5 km) grids (Han that cooler water is present close to the and least in the jets. Some aspects of et al., 2009). However, local details of northern shore of Mindoro Island during the coarser 3-km ocean model flow are the ocean response to wind jets and the entire month of January 2008. It also validated by IOP-08 field study data. wakes and the local pattern of upwelling shows that the upwelling is modulated The “Panay Eddy,” the “Iligan Bay Eddy,” in Verde Island Passage are attained in by the increasing (January 3 and 26) and and strong flow through San Bernardino the ocean model due to the finer 3-km decreasing (January 12) speed of the and Surigao straits were observed by atmospheric and 1-km ocean model Verde Island wind jet. shipboard ADCP at this time and appear grids. The presence of upwelling and in the model as prominent features. nutrient-rich surface water is supported a b

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26.2 Figure 5. ( a) Chlorophyll concentration (mg m-3) along a ship’s transit of Verde Island 16JAN2008 Passage a few days after the wind intensification in early January 2008. (b) Hovmöller 26.0 diagram of SST along 120°50'E (temperature as a function of time and latitude) 25.8 showing time and spatial extent (offshore) of upwelling in Verde Island Passage. 11JAN2008 25.6

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13.50°N 13.55°N 13.60°N 13.65°N

56 Oceanography | Vol.24, No.1 by the increased chlorophyll concen- Sea, Philippines. Pp. 999–1,003 in Proceedings Pullen, J., J. Doyle, P. May, C. Chavanne, P. Flament, of the 11th International Coral Reef Symposium and R. Arnone. 2008. Monsoon surges trigger trations seen in satellite imagery and 7–11 July 2008. International Society for Reef oceanic eddy formation and propagation in in situ measurements. Studies, Ft. Lauderdale, FL. the lee of the Philippine Islands. Geophysical Dolar, M.L.L., W.F. Perrin, B.L. Taylor, Research Letters 35:7–10. G.L. Kooyman, and M.N.R. Alava. 2006. Pullen, J.D., A.L. Gordon, J. Sprintall, Acknowledgements Abundance and distributional ecology of C.M. Lee, M.H. Alford, J.D. Doyle, and J. Doyle and P. May were supported by cetaceans in the central Philippines. Journal of P.W. May. 2011. 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