DOCSLIB.ORG

Final Report to the NOAA Joint Hurricane Testbed (JHT) Program

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Final Report to the NOAA Joint Hurricane Testbed (JHT) Program Final Report To the NOAA Joint Hurricane Testbed (JHT) Program Project Title: Improving the Hurricane WRF-Wave-Ocean Coupled System for Transition to Operations Award Period: 08/01/2007 - 07/31/2009 Principal Investigator: Isaac Ginis Graduate School of Oceanography The University of Rhode Island December, 2009 Executive Summary The primary goal of this project was to improve the operational hurricane predictive capabilities at the NOAA’s Environmental Modeling Center/National Centers for Environmental Prediction by transitioning recent improvements in the air-sea momentum flux parameterizations and the ocean model initialization made by the URI research group into to the Hurricane WRF (HWRF) modeling system. This work was conducted in close collaboration with our EMC colleagues, building directly upon our successful joint EMC/GFDL/URI coupled model research program. We also collaborated with scientists at NOAA/ESRL on the implementation of the NOAA/ESRL sea-spray parameterization scheme into the HWRF model. The following major tasks were conducted: • Implementing and testing the URI wave boundary layer in the HWRF coupled system. • Improving air-sea momentum and heat flux parameterization in the HWRF model by including the effects of wave breaking, sea-spray, and wave-current interaction. • Improving ocean initialization in the HWRF coupled system by implementing new methods for assimilating satellite and in-situ measurements. This report summarizes the main work accomplishments and the results. Tasks completed: I. Implementing the URI wave boundary layer model into the HWRF a) Improving drag coefficient formulation We have implemented an improved drag coefficient parameterization into the operational version of HWRF by upgrading the wave boundary layer (WBL) model of Moon et al. (2007). The WBL model is based on the theoretical model of Moon et al. (2004a-c) and derived from coupled wave-wind (CWW) model simulations of ten tropical cyclones in the Atlantic Ocean during 1998-2003. The upgraded WBL model incorporates the observational results from the CBLAST field experiment (Black et al., 2007) and the estimations of drag coefficient distribution based on GPS sonde wind profiles by Powell (2007). In the improved WBL model, a new formulation for the nondimensional surface roughness (Charnock coefficient) has been derived in order to better match the model results with the observations. Fig. 1 shows Cd vs. wind speed at various sections relative to the storm center. These sections represent composite distributions based on simulations of Hurricanes Noel (2007), Helene and Florence (2006), Katrina, Rita, Emily, Dennis (2005), Ivan and Frances (2004), and Isabel and Fabien (2003). The HRD wind analyses available at every 6 hours were used as the wind input into the model. The new parameterization is now more consistent with the Powell (2007) results but still cannot reproduce the extreme high and low values of Cd in his estimations. We speculate that one possible reason for the observed low values of Cd is related to the sea spray effect, which is not included in this WBL model. Recent studies (e.g., Andreas et al. 2004) suggest that sea sprays may significantly reduce the drag coefficient at very high wind speeds. The sea spray effect is now being implemented in the new coupled wind-wave- current framework as discussed below. Figure 1. Drag coefficient (Cd) vs. wind speed. Left panel shows Cd in 8 sectors relative to the storm center. Each sector is 45o where the zero degree direction is aligned with the storm movement vector. Right panel shows Cd in 3 sectors with the sizes corresponding to those in Powel (2007). Powell’s data are shown for comparison. The WBL model was recently upgraded further by implementing the coupled wind and wave formulation of Kukulka and Hara (2008a,b) that includes the enhanced form drag of breaking waves. Breaking and non-breaking waves induce air-side fluxes of momentum and energy in a thin layer above the air-sea interface within the constant flux layer (the wave boundary layer). By imposing momentum and energy conservation in the wave boundary layer and wave energy conservation, Kukulka and Hara (2008a,b) have derived coupled nonlinear advance-delay differential equations governing the wind speed, turbulent wind stress, wave height spectrum, and the length distribution of breaking wave crests. The system of equations is closed by introducing a relation between wave dissipation (due to breaking waves) and the wave height spectrum. Wave dissipation is proportional to nonlinear wave interactions, if the wave curvature spectrum is below the threshold saturation level. Above this threshold, however, wave dissipation rapidly increases, so that the wave height spectrum is limited. The improved model was first applied for fully-grown seas and then applied for a wide rage of wind-wave conditions from laboratories to the open ocean. Kukulka and Hara (2008a,b) investigated the effect of air flow separation due to breaking waves on the air- sea momentum flux and concluded that the contribution of breaking waves is increasingly important for younger seas under higher wind speeds. However, the precise effects of surface breaking waves on the drag coefficient are still under investigation and are not yet explicitly calculated in our model. Since the effects of surface breaking waves and sea sprays on the drag coefficient are still uncertain, we instead introduced two purely empirical parameterizations of the drag coefficient based on the recent observations, as shown in Fig. 2. These new formulas are now being tested in the HWRF model. Figure 2. Three sea state independent drag coefficient formulae (C1: parameterization implemented into the operational HWRF and GFDL model; C2: proposed drag formula to saturate at high winds, C3: proposed drag formula to decrease at high wind) are compared with previous observations (symbols with error bars). Different symbols of Powel (2003) indicate estimates from different wind profile ranges. b) Improving momentum flux parameterization in WW3 for hurricane conditions It has been known that the WAVEWATH III (WW3) wave model overestimates the significant wave height under very high wind conditions in strong hurricanes (Tolman et al., 2005; Chao et al., 2005). Moon et al. (2008) suggested that one of the reasons for the overestimation of the significant wave height is due to overestimation of the drag coefficient in high wind conditions. In preparation for coupling of WW3 with HWRF, we have implemented the Moon et al. (2007) drag coefficient formulation into WW3. The effect of wave-current interaction in WW3 was also introduced and investigated under a tropical cyclone wind forcing (Fan et al. 2009a). The model results were compared with field observations of the surface wave spectra from a scanning radar altimeter, NDBC data and satellite altimeter measurements in Hurricane Ivan (2004) (Fig. 3). The results suggest that WW3 with the original drag coefficient parameterization tends to overestimate the significant wave height and the dominant wave length, and it produces a wave spectrum that is higher in wave energy and narrower in directional spreading. When an improved drag parameterization is introduced and the wave-current interaction is included, the model yields an improved forecast of significant wave height and wave spectral energy, but it underestimates the dominant wave length (Figs. 4 and 5). (msï1) 75 30 42040 42039 70 28 42041 26 65 42001 42003 24 60 N) o 22 Sept. 14ï15 55 20 50 Latitude ( 18 Sept. 09 45 16 Sept. 12 40 14 12 35 10 30 ï90 ï85 ï80 ï75 ï70 ï65 Longitude (oW) Figure 3. Left: Hurricane Ivan track from Sept. 6 0:00 UTC to Sept. 10 12:00 UTC. The color and size of the circle represent the maximum wind speed. Black lines represent the flight tracks during the SRA measurements. Right: Swath of maximum significant wave heights produced by WW3 using the original WW3 parameterization (Exp. A), the new parameterization (Exp. B), and the new parameterization with the wave-current interaction (Exp. C). When a hurricane moves over mesoscale ocean features (warm- and cold-core rings, Loop Current), the current response can be significantly modulated by the non-linear interaction of the storm-induced and pre-existing strong currents in the mixed layer. We investigated the role of pre-existent currents due to mesoscale ocean features on wave predictions. Hurricane Ivan in 2004 crossed the Loop Current (LC) and a warm-core ring (WCR) in the Gulf of Mexico. Fortunately, during that time, detailed SRA wave spectra measurements were collected by NASA through a joint effort between the NASA/Goddard Space Flight Center and NOAA/HRD. These observations were used to investigate whether inclusion of the effect of pre-existent currents may improve the wave predictions using WW3. x10ï4msï1 200 4 300 100 2 ) o 200 HRA 0 0 Exp. A Exp. B Direction ( Exp. C ï100 ï2 100 Distance to eye (km) 2msï1 ï200 ï4 0 ï200 ï100 0 100 200 0 100 200 300 Distance to eye (km) spectrum number 15 400 300 10 200 5 100 dominant wave length (m) Significant wave height (m) 0 0 0 100 200 300 0 100 200 300 spectrum number spectrum number Figure 4. Upper left: WW3 wave field divergence in the run with the new flux parameterization and wave-current interaction at Sept. 9 18:00UTC. The color scale indicates significant wave height in meters; arrow length represents mean wave length, and arrow direction shows mean wave direction. Upper right, bottom right, and bottom left: wave direction, dominant wave length, and significant wave height, respectively. We used the Colorado Center for Astrodynamics Research (CCAR) altimetry map on September 12, 2004 (Fig. 6a) to identify the position and structure of the LC and the WCR in the Gulf of Mexico. The feature-based modeling procedure of Yablonsky and Ginis (2008) was used to assimilate the altimetry observations into the ocean model (Fig.
Load more

Recommended publications
  • Intensity Forecast Experiment of Hurricane Rita (2005) with a Cloud-Resolving, Coupled Hurricane–Ocean Modelling System
    Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. 137: 2149–2156, October 2011 B Intensity forecast experiment of hurricane Rita (2005) with a cloud-resolving, coupled hurricane–ocean modelling system Xin Qiu,a,b Qingnong Xiao,b,c Zhe-Min Tana* and John Michalakesb aKey Laboratory of Mesoscale Severe Weather/MOE, and School of Atmospheric Sciences, Nanjing University, China bMesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, Colorado, USA cCollege of Marine Science, University of South Florida, St Petersburg, Florida, USA *Correspondence to: Z.-M. Tan, School of Atmospheric Sciences, Nanjing University, Nanjing 210093, China. E-mail: [email protected] A cloud-resolving, coupled hurricane-ocean modelling system is developed under the Earth System Modeling Framework using state-of-the-art numerical forecasting models of the atmosphere and the ocean. With this system, the importance of coupling to an eddy-resolving ocean model and the high resolution of the atmospheric model for the prediction of intensity change of hurricane Rita (2005) is demonstrated through a set of numerical experiments. The erroneous intensification in the uncoupled experiments could be eliminated when taking account of the negative feedback of sea-surface temperature cooling. Moreover, the deepening rate of Rita becomes larger with higher resolution of the atmospheric model. Nevertheless, the horizontal resolution of the atmospheric model with grid spacing at least less than ∼4 km is required in order to predict the rapid intensity changes of hurricane Rita in the fully coupled experiment. This strong dependence is found to arise from the potential interaction between the ocean coupling and internal processes of Rita, thus indicating that both high resolution and the ocean coupling are indispensable for the future improvement of hurricane intensity prediction.
    [Show full text]
  • The Vertical Structure of a Loop Current Eddy 10.1029/2018JC013801
    Journal of Geophysical Research: Oceans RESEARCH ARTICLE The Vertical Structure of a Loop Current Eddy 10.1029/2018JC013801 T. Meunier1 , E. Pallás-Sanz1 , M. Tenreiro1 , E. Portela1 , J. Ochoa1 , A. Ruiz-Angulo2 , Key Points: 1 • The thermohaline and kinematic and S. Cusí vertical structure of a recently 1 2 detached Loop Current Eddy is Departamento de Oceanografía, CICESE, Ensenada, B.C., Mexico, UNAM, Ciudad de México, CDMX, Mexico revealed in details • This structure results from conservative advection of Caribbean Abstract The vertical structure of a recently detached Loop Current Eddy (LCE) is studied using in water below 200 m and surface fluxes situ data collected with an underwater glider from August to November 2016. Altimetry and Argo data are and mixing above • Heat and salt excess carried by the analyzed to discuss the context of the eddy shedding and evolution as well as the origin and transformation eddy requires important heat fluxes of its thermohaline properties. The LCE appeared as a large body of nearly homogeneous water between and fresh water input for balance to 50 and 250 m confined between the seasonal and main thermoclines. A temperature anomaly relative be reached in the Gulf of Mexico to surrounding Gulf’s water of up to 9.7∘ C was observed within the eddy core. The salinity structure had a double core pattern. The subsurface fresh core had a negative anomaly of 0.27 practical salinity unit, while Correspondence to: T. Meunier, the deeper saline core’s positive anomaly reached 1.22 practical salinity unit. Both temperature and salinity [email protected] maxima were stronger than previously reported.
    [Show full text]
  • Eurico J. D'sa, Dept. of Oceanography and Coastal Sciences, Coastal
    P2.9 COMPARISON OF SEA SURFACE HEIGHTS DERIVED FROM THE NAVY COASTAL OCEAN MODEL WITH SATELLITE ALTIMETRY IN THE GULF OF MEXICO Eurico D’Sa1*, Dong-Shan Ko2, and Mitsuko Korobkin1 1Department of Oceanography and Coastal Sciences, Coastal Studies Institute, Louisiana State University, Baton Rouge, LA 2Naval Research Laboratory, Stennis Space Center, MS 1. INTRODUCTION The Gulf of Mexico (GOM) is a semi-enclosed sea that connects in the east to the Atlantic ocean through the straits of Florida, and in the south to the Caribbean Sea through the Yucatan channel. The GOM is rich in natural resources and supports a large fisheries and oil and gas industry. The region is also impacted by natural events such as hurricanes necessitating a better understanding of the physical and biogeochemical processes in the region. Numerous field, remote sensing and numerical modeling studies have provided greater insights into various processes in the GOM, especially the Loop Current (LC) and its eddy field that is a dominating feature in the GOM (Maul 1997; Vukovich and Maul 1985; Sturges and Leben 2000; Welsh and Inoue 2000; Oey et al. 2005). Numerical models such as the NRL Layered Ocean Model (NLOM) (Hurlburt and Thompson 1980), the Navy Coastal Ocean Model (NCOM) (Barron et al. 2006), the Hybrid Coordinate Ocean Model (HYCOM) (Chassignet et al. 2005), the University of Colorado version of the Princeton Ocean Model (CUPOM) (Kantha et al. 2005) and remote sensing from altimeters (Leben et al. 2002; Leben 2004) have provided better insights into the LC, its eddies and its interaction with the waters of the GOM.
    [Show full text]
  • Sramsoe295ocr.Pdf
    76° 75° 74° 73° ,., .. ~[_ ,I / / / / ()?.~.,.) ·....1 ~ ••..' .,. r"" ("'\ _. .., '-' \ i·.. J -·. \,.•. .. / \ DAVID B. EG LESTON ) I / _.i SEPTE BER 1988 , : -· .~.I' .= 1s• 75° 74° 73° SRAMSOE No. 295 of the Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062. Remote Sensing of Offshore Water Mass Features: Present and Potential Benefits to Virginia's Recreational Fishery for Marlin and Tuna David B. Eggleston Virginia Institute of Marine Science School of Marine Science College of William and Mary Gloucester Point, Virginia 23062 September 1988 SRAMSOE No. 295 of the Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062. 2 INTRODUCTION The distribution, abundance, and catchability of pelagic recreational fishes such as billfishes (Istiophoridae and Xiphidae) and tunas (Scombridae) are markedly influenced by known optimum temperatures and hydrographic frontal zones (Squire, 1962, 1974; Uda, 1973; Mather, et al. 1975; Laurs and Lynn, 1977; Magnuson, et al. 1980, 1981; Rockford, 1981; Shingu, 1981; Sund, et al. 1981; Laurs, et al. 1984). Environmental temperature directly inf·luences fish metabolism which in turn affects life processes such as growth, development, and swimming speed (Laevastu and Hayes, 1983). Temperature effects on the movement, distribution, and nervous system response of fishes are summarized by Sullivan (1954). Sullivan (1954) stated tlhat fish select a certain optimium temperature because of the effect of the same on their movement (activity, sensu Laevastu and Hayes, 1983), and concluded temperature change may act on a fish: 1) as a nervous stimulus, 2) as a modifier of metabolic processes and 3) as a modifier of bodily activity.
    [Show full text]
  • The Gulf Stream Structure and Strategy W.Frank Bohlen Mystic, Connecticut [email protected]
    The Gulf Stream Structure and Strategy W.Frank Bohlen Mystic, Connecticut [email protected] January, 2012 For the Newport-Bermuda racer the point at which the Gulf Stream is encountered is often considered a juncture as important as the start or finish of the Race. The location, structure and variability of this major ocean current and its effects presents a particular challenge for every navigator/tactician. What is the nature of this challenge and how best might it be addressed ? The Gulf Stream is a portion of the large clockwise current system affecting the entire North Atlantic Ocean. Driven by the wind field over the North Atlantic and the associated distributions of water temperature and salinity, the Gulf Stream is an energetic boundary current separating the warm waters of the Sargasso Sea from the cooler continental shelf waters adjoining New England. The resulting thermal boundary represents one of the most striking features of this current and one that is most easily measured. From Florida to Cape Hatteras the Gulf Stream follows a reasonably well defined northerly track along the outer limits of the U.S. continental shelf. Beyond, to the north of Hatteras, Stream associated flows proceed along a progressively more northeasterly tending track with the main body of the current separating gradually from the shelf. Horizontal flow trajectories in this area, which includes the rhumb line to Bermuda, become increasingly non-linear and wavelike with characteristics similar to those observed in clouds of smoke trailing downwind from a chimney. The resulting large amplitude meanders in the main body of the Stream tend to propagate downstream, towards Europe, and grow in amplitude.
    [Show full text]
  • The Interaction of Supertyphoon Maemi (2003) with a Warm Ocean Eddy
    SEPTEMBER 2005 L I N E T A L . 2635 The Interaction of Supertyphoon Maemi (2003) with a Warm Ocean Eddy I-I LIN AND CHUN-CHIEH WU Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan KERRY A. EMANUEL Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, Massachusetts I-HUAN LEE Institute of Marine Geology and Chemistry, National Taiwan Sun Yat-Sen University, Kaohsiung, Taiwan CHAU-RON WU AND IAM-FEI PUN Department of Earth Science, National Taiwan Normal University, Taipei, Taiwan (Manuscript received 28 September 2004, in final form 2 March 2005) ABSTRACT Understanding the interaction of ocean eddies with tropical cyclones is critical for improving the under- standing and prediction of the tropical cyclone intensity change. Here an investigation is presented of the interaction between Supertyphoon Maemi, the most intense tropical cyclone in 2003, and a warm ocean eddy in the western North Pacific. In September 2003, Maemi passed directly over a prominent (700 km ϫ 500 km) warm ocean eddy when passing over the 22°N eddy-rich zone in the northwest Pacific Ocean. Analyses of satellite altimetry and the best-track data from the Joint Typhoon Warning Center show that during the 36 h of the Maemi–eddy encounter, Maemi’s intensity (in 1-min sustained wind) shot up from 41 msϪ1 to its peak of 77 m sϪ1. Maemi subsequently devastated the southern Korean peninsula. Based on results from the Coupled Hurricane Intensity Prediction System and satellite microwave sea surface tem- perature observations, it is suggested that the warm eddies act as an effective insulator between typhoons and the deeper ocean cold water.
    [Show full text]
  • Impact of Ocean Warm Layer Thickness in ECCO Ocean State Estimates
    1 Impact of ocean warm layer thickness on the intensity of hurricane Katrina in a regional coupled 2 model 3 4 Hyodae Seo1 and Shang-Ping Xie2 5 1 Physical Oceanography Department, Woods Hole Oceanographic Institution 6 2Scripps Institution of Oceanography, UC San Diego 7 8 Corresponding Author and Address: 9 Hyodae Seo, 266 Woods Hole Road, MS#21, Woods Hole, MA 02543 10 Email: [email protected], Tel: 508-289-2792, Fax: 508-457-2181 11 12 13 Abstract 14 The effect of pre-storm subsurface thermal structure on the intensity of hurricane Katrina (2005) 15 is examined using a regional coupled model. The Estimating Circulation and Climate of Ocean 16 (ECCO) ocean state estimate is used to initialize the ocean component of the coupled model, and 17 the source of deficiencies in the simulation of Katrina intensity is investigated in relation to the 18 initial depth of 26°C isotherm (D26). The model underestimates the intensity of Katrina partly 19 due to shallow D26 in ECCO. Sensitivity tests with various ECCO initial fields indicate that the 20 correct relationship between intensity and D26 cannot be derived because D26 variability is 21 underestimated in ECCO. A series of idealized experiments is carried out by modifying initial 22 ECCO D26 to match the observed range. A more reasonable relationship between Katrina’s 23 intensity and pre-storm D26 emerges: the intensity is much more sensitive to D26 than to sea 24 surface temperature (SST). Ocean mixed layer process plays a critical role in modulating inner- 25 core SSTs when D26 is deep, reducing mixed layer cooling and lowering the center pressure of 26 the Katrina.
    [Show full text]
  • Stalling of Near-Inertial Waves in a Cyclone L.-Y
    GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L12604, doi:10.1029/2008GL034273, 2008 Click Here for Full Article Stalling of near-inertial waves in a cyclone L.-Y. Oey,1 M. Inoue,2,3 R. Lai,4 X.-H. Lin,1 S. E. Welsh,3 and L. J. Rouse Jr.2,3 Received 8 April 2008; accepted 2 May 2008; published 20 June 2008. [1] Observations at the edge of the Loop Current after A numerical model is used to estimate the eddy field which hurricane Katrina show inertial energy amplified at a depth is then used to calculate energy paths by ray-tracing. of approximately 600700 m. Ray-analysis using the eddy field obtained from a numerical simulation with data 2. Data assimilation suggests that the amplification is due to inertial motions stalled in a deep cyclone. Citation: Oey, [4] The LSU (Louisiana State University) mooring con- L.-Y., M. Inoue, R. Lai, X.-H. Lin, S. E. Welsh, and L. J. Rouse sists of two ADCPs, one upward-looking set at 140 m and Jr. (2008), Stalling of near-inertial waves in a cyclone, Geophys. the other downward-looking set at 3200 m at (87°W, Res. Lett., 35, L12604, doi:10.1029/2008GL034273. 25.5°N; Figure 1) in water of 3356 m where the bottom is relatively flat. Additional Aanderra current meters were deployed between the two ADCPs to sample the entire 1. Introduction water column. The top ADCP measured near-surface [2] Near-inertial waves generally have frequencies above currents up to z = À60 m, while the bottom ADCP 1/2 feff = f(1 + &/f) f + &/2 for small Rossby number = sampled near-bottom currents; the bottom-most currents &/f in (background) flow with non-zero vorticity & [Mooers, were measured at z = À3340 m.
    [Show full text]
  • The Interaction Between Hurricane Opal (1995) and a Warm Core Ring in the Gulf of Mexico
    MAY 2000 HONG ET AL. 1347 The Interaction between Hurricane Opal (1995) and a Warm Core Ring in the Gulf of Mexico XIAODONG HONG,*,@ SIMON W. C HANG,+ SETHU RAMAN,* LYNN K. SHAY,# AND RICHARD HODUR+ * North Carolina State University, Raleigh, North Carolina 1 Naval Research Laboratory, Monterey, California # Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida (Manuscript received 2 October 1998, in ®nal form 27 April 1999) ABSTRACT Hurricane Opal (1995) experienced a rapid, unexpected intensi®cation in the Gulf of Mexico that coincided with its encounter with a warm core ring (WCR). The relative positions of Opal and the WCR and the timing of the intensi®cation indicate strong air±sea interactions between the tropical cyclone and the ocean. To study the mutual response of Opal and the Gulf of Mexico, a coupled model is used consisting of a nonhydrostatic atmospheric component of the Naval Research Laboratory's Coupled Ocean±Atmosphere Mesoscale Prediction System (COAMPS), and the hydrostatic Geophysical Fluid Dynamics Laboratory's Modular Ocean Model version 2 (MOM 2). The coupling between the ocean and the atmosphere components of the model are accomplished by conser- vation of heat, salt, momentum, as well as the sensible and latent heat ¯uxes at the air±sea interface. The atmospheric model has two nests with spatial resolutions of 0.68 and 0.28. The ocean model has a uniform resolution of 0.28. The oceanic model domain covers the Gulf of Mexico basin and coincides with a ®ne-mesh atmospheric domain of the COAMPS. The initial condition for the atmospheric component of COAMPS is the archived Navy Operational Global Atmospheric Prediction System operational global analysis, enhanced with observations.
    [Show full text]
  • The Consequences of Eddies on Biological Productivity
    ___________________________________________ The Consequences of Eddies on Biological Productivity: Western versus Eastern Boundary Currents ___________________________________________ Joshua Coupe Dynamics of Marine Ecosystems 12/7/15 An eddy is a result of the turbulent transfer of momentum of a fluid through time and space, which in the ocean can have physical, biological, as well as chemical consequences. To catalogue the effect of eddies in oceans around the world, this paper will summarize studies on biological productivity in eddies in and around the Gulf Stream, Kuroshio Current, East Australian Current, California Current, and Peru Current. In high energy ocean regions such as the Gulf Stream, Kuroshio current, other western boundary or eastern boundary currents, eddies are commonplace when meanders break off from the dominant current (Chen et al., 2014). In the northern hemisphere, an eddy breaking off a western boundary current and propagating towards the west-northwest is an anticyclonic eddy (warm core ring) and an eddy propagating towards the west-southwest is a cyclonic eddy (cold core ring). In the formation of a cyclonic eddy, the thermocline arranges itself in a bell-like shape pointing towards the surface, and the sea surface itself depresses downwards in response (Kumar et. al, 2007). The rising of the thermocline induces colder waters to upwell, which can also shift the nutricline upwards towards the surface (Kumar et. al, 2007). Anticyclonic eddies would have the opposite arrangement. Exceptions to this rule exist but are few and characterized by exceptionally unique dynamics beyond the scope of this paper. Warm core or cold core rings are distinguished by their relative temperature departure compared to their surroundings, which occurs as a result of the shifting of temperature gradients.
    [Show full text]
  • Warm Spiral Streamers Over Gulf Stream Warm-Core Rings
    NOVEMBER 2020 Z H A N G A N D M C G I L L I C U D D Y 3331 Warm Spiral Streamers over Gulf Stream Warm-Core Rings WEIFENG (GORDON)ZHANG AND DENNIS J. MCGILLICUDDY JR. Applied Ocean Physics and Engineering Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts (Manuscript received 5 February 2020, in final form 31 August 2020) ABSTRACT: This study examines the generation of warm spiral structures (referred to as spiral streamers here) over Gulf Stream warm-core rings. Satellite sea surface temperature imagery shows spiral streamers forming after warmer water from Downloaded from http://journals.ametsoc.org/jpo/article-pdf/50/11/3331/5016945/jpod200035.pdf by MBL/WHOI Library, Weifeng Zhang on 11 November 2020 the Gulf Stream or newly formed warm-core rings impinges onto old warm-core rings and then intrudes into the old rings. Field measurements in April 2018 capture the vertical structure of a warm spiral streamer as a shallow lens of low-density water winding over an old ring. Observations also show subduction on both sides of the spiral streamer, which carries surface waters downward. Idealized numerical model simulations initialized with observed water-mass densities reproduce spiral streamers over warm-core rings and reveal that their formation is a nonlinear submesoscale process forced by mesoscale dynamics. The negative density anomaly of the intruding water causes a density front at the interface between the intruding water and surface ring water, which, through thermal wind balance, drives a local anticyclonic flow. The pressure gradient and momentum advection of the local interfacial flow push the intruding water toward the ring center.
    [Show full text]
  • Fishery Bulletin/U S Dept of Commerce National Oceanic
    THE POSSIBLE INFLUENCE OF WARM CORE GULF STREAM RINGS UPON SHELF WATER LARVAL FISH DISTRIBUTION G. R. FLIERL' AND J. S. WROBLEWSKI2 ABSTRACT We propose a simple one-dimensional model for examining the impact of warm core rings upon the larval fish distribution and abundance over the continental shelf off the northeastern United States. The model in­ cludes (in a cross-shelf averaged sense) the loss of larvae due to biological causes of mortality, the advective transport of larvae due to the mean down-shelf currents, and the changes in larval density produced by the on-shelf or off-shelf flows occurring when a ring approaches the shelf-slope front. The results of this highly idealized model indicate that the decreases in larval abundance caused by cross-shelf flows may be as large as those caused by biological factors and, furthermore, the effects are strongly dependent upon the rate of motion of the ring. A stationary ring may cause a 20 to 50% drop in abundance, depending on the strength and size of the ring and on the longshore velocity in the shelf water. When the ring is slowly moving, the im­ pact can be even greater: a patch of larvae being advected downshelf by the longshore current could, when catching up to the back side of an eddy, essentially be swept off the shelf, decimating the patch. Model predictions are compared with historical MARMAP data of larval cod and haddock density in the Georges Bank area. There does appear to be a relationship between the frequency of ring interaction with Georges Bank and the subsequent year-class strength of cod and haddock stocks.
    [Show full text]