Yalin Fan - Academia.edu (original) (raw)
Papers by Yalin Fan
The barotropic version of the 3-dimensional, finite element Dartmouth circulation model called Qu... more The barotropic version of the 3-dimensional, finite element Dartmouth circulation model called Quoddy has been used to simulate the response of the Gulf of Maine to wind forcing at 1/16 M2 tidal cycle (0.78 hr) increments in near real-time. Model forcing consists of predicted M2 tidal sea level around the open ocean boundary and surface wind stress derived from NDBC buoy-measured winds at severl sites in the region. Nontidal sea level forcing along the Scotian shelf transect is inferred from a wind-forced statistical model. Nowcast model products include 3-D currents and sea level at the model resolution of about 10 km in the Gulf of Maine and 5 km along the coastalines. A comparison of model and observed M2 tidal sea level results at 49 sites show average rms differences of 9 cm and 7 degrees for amplitude and phase, respectively. The nontidal results of the model, which are consistent with observed Gulf-wide response to wind forcing, will be presented.
The 3-D QUODDY barotropic model tests were run for the period of February 7 - 18, 1987 with both ... more The 3-D QUODDY barotropic model tests were run for the period of February 7 - 18, 1987 with both a time-space constant drag coefficient Cd and a time-space variable Cd. The constant Cd QUODDY test captured more than 60% of the observed variance, as compared to the 31% of the variance captured by the linear harmonic finite element model FUNDY. Thus the use of a constant Cd thus represents an improvement in coastal modeling effects. However, there still were large differences between model results and observations in or around the times of intense storms (e.g. February 9 th to 13 th ). The QUODDY tests with a variety of realistic Cd values did not improve model results significantly. Neither did the use of time and space variable Cd. The model behavior was most sensitive to the specification of surface wind stress forcing. Thus, we expect that model improvements may come with a better understanding of the wind stress calculation in the Gulf, perhaps a more detailed understanding of th...
ABSTRACT Ocean surface wave climate change is one of the eight main climate drivers affecting the... more ABSTRACT Ocean surface wave climate change is one of the eight main climate drivers affecting the coast (Hemer, et al 2010). In recent years, several dynamic projections of regional wave climate have been carried out, where downscaled Atmosphere/Ocean Global Climate Model (GCM) projections are used to force regional wave models. But bias could arise in the simulated wave climate from the low level of confidence in the projected circulation changes from GCMs. The European Centre for Medium-Rage Weather Forecasts (ECMWF) ERA-40 reanalysis (T159) produced global wave information at 1.5° resolution. Even though it captures the variability of the true wave height very well on all time scales, due to the relatively coarse resolution of the atmospheric model and its limited ability to resolve storm systems, high wave heights were severely underestimated (Hemer, 2010). We have developed a high resolution global simulation system by coupling the operational wave model developed at the National Centers for Environmental Prediction/Environmental Modeling Center, to GFDL's prototype Global Cloud-Resolving Model (HiRAM). A free-run 29-year (1980 to 2009) AMIP-type wave climatology was generated using this coupled system. Prescribed SSTs from the Met Office Hadley Center Sea Ice and SST version 1.1 model (HadISST 1.1; Ryner et al. 2003) was used as the lower boundary condition for the atmospheric model. During the model simulation period, the well-mixed greenhouse gases and both tropospheric and stratospheric ozone vary from year to year, following the procedure used in the CM2.1 historical simulations in the CMIP3 database (Delworth et al. 2006). Model evaluation against NDBC buoy data, satellite measurements, and ERA-40 reanalysis shows good agreements. The linkage between wave climate change and some climate indices (ENSO, North Atlantic Oscillaiton, NPAC index, and Southern Annular Mode) was explored and the global trend analysis for both significant wave height and mean wave length will be presented as well. Delworth, T. D., and Coauthors, 2006: GFDL's CM2 global coupled climate models. Part I: Formulation and simulation characteristics. J. Climate, 19, 643-674. Hemer, M. A., X. L. Wang, J. A. Church, and V. R. Swail, 2010: Coordinating global ocean wave climate projections. BAMS, 451-454.
Nature Climate Change, 2013
Future changes in wind-wave climate have broad implications for the operation and design of coast... more Future changes in wind-wave climate have broad implications for the operation and design of coastal, near-and off-shore industries and ecosystems, and may further exacerbate the anticipated vulnerabilities of coastal regions to projected sealevel rise 1,2 . However, wind waves have received little attention in global assessments of projected future climate change. We present results from the first community-derived multi-model ensemble of wave-climate projections. We find an agreed projected decrease in annual mean significant wave height (H S ) over 25.8% of the global ocean area. The area of projected decrease is greater during boreal winter (January-March, mean; 38.5% of the global ocean area) than austral winter (July-September, mean; 8.4%). A projected increase in annual mean H S is found over 7.1% of the global ocean, predominantly in the Southern Ocean, which is greater during austral winter (July-September; 8.8%). Increased Southern Ocean wave activity influences a larger proportion of the global ocean as swell propagates northwards into the other ocean basins, observed as an increase in annual mean wave period (T M ) over 30.2% of the global ocean and associated rotation of the annual mean wave direction (θ M ). The multi-model ensemble is too limited to systematically sample total uncertainty associated with wave-climate projections. However, variance of wave-climate projections associated with study methodology dominates other sources of uncertainty (for example, climate scenario and model uncertainties).
This was a test of a near real-time operational application of the Dartmouth 3-dimensional finite... more This was a test of a near real-time operational application of the Dartmouth 3-dimensional finite-element circulation model QUODDY designed to nowcast the meteorologically-forced response of the Gulf of Maine region in the presence of the strong semidiurnal tide. The model is forced along the open ocean boundaries with a predicted M2 tidal sea level and at the surface with wind stress derived by an optimal interpolation of an array of NOAA National Weather Service/ National Data Buoy Center measure ments that were obtained in near real-time . In this application, the model is run every 1/16 M2 tidal period (i.e., 0.77625 hours) in near real-time. Because each calculation runs faster than real time, subsequent calculations are delayed until real time catches up with model time, when the model sea level results are output. A model/observation comparison of tidal sea level results at 49 observation stations throughout the Gulf indicated that M2 tidal sea level amplitude differences wer...
Northeastern Naturalist, 2006
A simple heat budget has been constructed for Mount Hope Bay (MHB) for two one-month periods: win... more A simple heat budget has been constructed for Mount Hope Bay (MHB) for two one-month periods: winter 1999 (February-March) and summer 1997 (August-September). The box model considered here includes the heat contributions to MHB from the Brayton Point Power Station (BPPS), the exchange across the airwater interface, the Taunton River, and the tidal exchange between MHB and both Narragansett Bay and the Sakonnet River (NB/SR). Comprehensive measurements of MHB temperature fields by Applied Science Associates, Inc., and meteorological data from T.F. Green Airport (Warwick, RI) were used to estimate the different heat flux component contributions. The box model results for winter show that the BPPS heating is balanced (within the uncertainty of the estimates) by air-water cooling alone. The simple winter balance does not hold during the summer, when heat losses due to tidal exchanges between MHB and NB/SR are important. The summer heat budget of MHB-including BPPS heating, air-water cooling and tidal exchange cooling-can be balanced (within the uncertainty of the estimates) by assuming that 3% of the colder NB/SR tidal input water is exchanged with the warmer MHB water during each tidal cycle. The air-water cooling accounts for 84.4% of the total cooling, and the tidal exchange accounts for 15.6% of the total cooling. Taunton River contributions to the heat budget were negligible in both seasons. Analyses show that the model temperature is most sensitive to uncertainty in the measurements used to estimate the air-water heat fluxes-the relative humidity in particular. Thus, local MHB measurements are important for accurate monitoring of the MHB heat budget in the future.
Journal of Physical Oceanography, 2009
In this paper, the wind-wave-current interaction mechanisms in tropical cyclones and their effect... more In this paper, the wind-wave-current interaction mechanisms in tropical cyclones and their effect on the surface wave and ocean responses are investigated through a set of numerical experiments. The key element of the authors' modeling approach is the air-sea interface model, which consists of a wave boundary layer model and an air-sea momentum flux budget model. The results show that the time and spatial variations in the surface wave field, as well as the wave-current interaction, significantly reduce momentum flux into the currents in the right rear quadrant of the hurricane. The reduction of the momentum flux into the ocean consequently reduces the magnitude of the subsurface current and sea surface temperature cooling to the right of the hurricane track and the rate of upwelling/downwelling in the thermocline. During wind-wave-current interaction, the momentum flux into the ocean is mainly affected by reducing the wind speed relative to currents, whereas the wave field is mostly affected by refraction due to the spatially varying currents. In the area where the current is strongly and roughly aligned with wave propagation direction, the wave spectrum of longer waves is reduced, the peak frequency is shifted to a higher frequency, and the angular distribution of the wave energy is widened.
Journal of Physical Oceanography, 2010
In coupled ocean-atmosphere models, it is usually assumed that the momentum flux into ocean curre... more In coupled ocean-atmosphere models, it is usually assumed that the momentum flux into ocean currents is equal to the flux from air (wind stress). However, when the surface wave field grows (decays) in space or time, it gains (loses) momentum and reduces (increases) the momentum flux into subsurface currents compared to the flux from the wind. In particular, under tropical cyclone (TC) conditions the surface wave field is complex and fast varying in space and time and may significantly affect the momentum flux from wind into ocean. In this paper, numerical experiments are performed to investigate the momentum flux budget across the air-sea interface under both uniform and idealized TC winds. The wave fields are simulated using the WAVE-WATCH III model. The difference between the momentum flux from wind and the flux into currents is estimated using an air-sea momentum flux budget model. In many of the experiments, the momentum flux into currents is significantly reduced relative to the flux from the wind. The percentage of this reduction depends on the choice of the drag coefficient parameterization and can be as large as 25%. For the TC cases, the reduction is mainly in the right-rear quadrant of the hurricane, and the percentage of the flux reduction is insensitive to the changes of the storm size and the asymmetry in the wind field but varies with the TC translation speed and the storm intensity. The results of this study suggest that it is important to explicitly resolve the effect of surface waves for accurate estimations of the momentum flux into currents under TCs.
Journal of Physical Oceanography, 2009
The performance of the wave model WAVEWATCH III under a very strong, category 5, tropical cyclone... more The performance of the wave model WAVEWATCH III under a very strong, category 5, tropical cyclone wind forcing is investigated with different drag coefficient parameterizations and ocean current inputs. The model results are compared with field observations of the surface ...
Grant and Madsen (1979) showed that the nonlinear interaction between steady near bottom currents... more Grant and Madsen (1979) showed that the nonlinear interaction between steady near bottom currents and oscillatory surface wave currents can produce enhanced bottom stress relative to what a quadratic drag law formulation would indicate. A numerical study of this process has been conducted by combining a bottom boundary layer model (BBLM) with the Dartmouth one-dimensional (1-D) finite element dynamic model called NUBBLE. This model system is forced to dynamic equilibrium by typical Gulf of Maine storm-related 12-second surface waves and prescribed steady geostrophic currents. The results of a suite of sensitivity tests show that: (1) the combined wave and current influence on bottom stress calculations is very important in water depth less than 80 m; (2) the equivalent drag coefficient (Cd) associated with the combination of wave and current interactions is larger than that due to either forcing process alone; and (3) the quadratic drag law is practical for simulating the bottom str...
Journal of Geophysical Research, 2005
The storm response of the Gulf of Maine/Georges Bank region was investigated using the barotropic... more The storm response of the Gulf of Maine/Georges Bank region was investigated using the barotropic version (i.e. uniform density) of the Dartmouth 3-D nonlinear, finite element coastal ocean circulation model with quadratic bottom stress called QUODDY. A suite of model hindcast experiments for the period 4 -18 February 1987 was conducted, in which the model was forced at the open ocean boundaries by the M 2 semidiurnal tidal sea level and in the interior by realistic surface wind stresses featuring a strong 9-11 February nor'easter. Results for a reference model run with a time-space constant drag coefficient C d of 0.005 captured more than 60% of the observed sea level variance, but left large unexplained model/observed sea level differences, particularly during the storm. Model sensitivity testing to a realistic range of constant C d values did not improve model results significantly. However, when atmospheric pressure was added to the surface forcing, significant reductions in the model/observed sea level differences were realized.
Journal of Climate, 2013
ABSTRACT Surface wind (U10) and significant wave height (Hs) response to global warming are inves... more ABSTRACT Surface wind (U10) and significant wave height (Hs) response to global warming are investigated using a coupled atmosphere-wave model by perturbing the sea surface temperatures (SSTs) with anomalies generated by WGCM CMIP-3 coupled models that use the IPCC/AR4/A1B scenario late in the 21st century. Several consistent changes were observed across all four realizations for the seasonal means: robust increase of U10 and Hs in the Southern Ocean for both the austral summer and winter due to the poleward shift of the jet stream; a dipole pattern of the U10 and Hs with increases in the northeast sector and decreases at the mid-latitude during the boreal winter in the North Atlantic due to the more frequent occurrence of the positive phases of NAO; and strong decrease of U10 and Hs at the tropical western Pacific Ocean during the austral summer, which might be caused by the joint effect of the weakening of the Walker circulation and the large hurricane frequency decrease in the South Pacific. Changes of the 99th percentile U10 and Hs are twice as strong as changes in the seasonal means, and the maximum changes are mainly dominated by the changes in hurricanes. Robust strong decreases of U10 and Hs in the South Pacific are obtained due to the large hurricane frequency decrease, while the results in the Northern Hemisphere basins differ among the models. An additional sensitivity experiment suggests that the qualitative response of U10 and Hs is not affected by using SST anomalies only and maintaining the radiative forcing unchanged (using 1980 values) as in this study.
Journal of Climate, 2014
The impacts of parameterized upper-ocean wave mixing on global climate simulations are assessed t... more The impacts of parameterized upper-ocean wave mixing on global climate simulations are assessed through modification to Large et al.'s K-profile ocean boundary layer parameterization (KPP) in a coupled atmosphereocean-wave global climate model. The authors consider three parameterizations and focus on impacts to highlatitude ocean mixed layer depths and related ocean diagnostics. The McWilliams and Sullivan parameterization (MS2000) adds a Langmuir turbulence enhancement to the nonlocal component of KPP. It is found that the Langmuir turbulence-induced mixing provided by this parameterization is too strong in winter, producing overly deep mixed layers, and of minimal impact in summer. The later Smyth et al. parameterization modifies MS2000 by adding a stratification effect to restrain the turbulence enhancement under weak stratification conditions (e.g., winter) and to magnify the enhancement under strong stratification conditions. The Smyth et al. scheme improves the simulated winter mixed layer depth in the simulations herein, with mixed layer deepening in the Labrador Sea and shoaling in the Weddell and Ross Seas. Enhanced vertical mixing through parameterized Langmuir turbulence, coupled with enhanced lateral transport associated with parameterized mesoscale and submesoscale eddies, is found to be a key element for improving mixed layer simulations. Secondary impacts include strengthening the Atlantic meridional overturning circulation and reducing the Antarctic Circumpolar Current. The Qiao et al. nonbreaking wave parameterization is the third scheme assessed here. It adds a wave orbital velocity to the Reynolds stress calculation and provides the strongest summer mixed layer deepening in the Southern Ocean among the three experiments, but with weak impacts during winter.
Journal of Climate, 2012
ABSTRACT This study describes a 29-yr (1981-2009) global ocean surface gravity wave simulation ge... more ABSTRACT This study describes a 29-yr (1981-2009) global ocean surface gravity wave simulation generated by a coupled atmosphere wave model using NOAA/GFDL's High-Resolution Atmosphere Model (HiRAM) and the WAVEWATCH III surface wave model developed and used operationally at NOAA/NCEP. Extensive evaluation of monthly mean significant wave height (SWH) against in situ buoys, satellite altimeter measurements, and the 40-yr ECMWF Re-Analysis (ERA-40) show very good agreements in terms of magnitude, spatial distribution, and scatter. The comparisons with satellite altimeter measurements indicate that the SWH low bias in ERA-40 reanalysis has been improved in these model simulations. The model fields show a strong response to the North Atlantic Oscillation (NAO) in the North Atlantic and the Southern Oscillation index (SOI) in the Pacific Ocean that are well connected with the atmospheric responses. For the NAO in winter, the strongest subpolar wave responses are found near the northern Europe coast and the coast of Labrador rather than in the central-northern Atlantic where the wind response is strongest. Similarly, for the SOI in the Pacific Ocean, the wave responses are strongest in the northern Bering Sea and the Antarctic coast.
Journal of Climate, 2014
The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface grav... more The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface gravity wave climatology produced using a coupled atmosphere-wave model. The swell energy fraction analysis shows that swell dominates most of the World Ocean basins for all four seasons, and the Southern Ocean swells dominate swell in the global ocean. The swells are loosely correlated with the surface wind in the midlatitude storm region in both hemispheres, while their energy distribution and propagation direction do not show any relation with local winds and vary significantly with season because of nonlinear interactions. The same coupled system is then used to investigate the projected future change in wind-sea and swell climate through a timeslice simulation. Forcing of the coupled model was obtained by perturbing the model sea surface temperatures and sea ice with anomalies generated by representative Working Group on Coupled Modelling (WGCM) phase 3 of the Coupled Model Intercomparison Project (CMIP3) coupled models that use the IPCC Fourth Assessment Report (AR4) A1B scenario late in the twenty-first century. Robust responses found in the wind seas are associated with modified climate indices. A dipole pattern in the North Atlantic during the boreal winter is associated with more frequent occurrence of the positive North Atlantic Oscillation (NAO) phases under global warming, and the wind-sea energy increase in the Southern Ocean is associated with the continuous shift of the southern annular mode (SAM) toward its positive phase. Swell responses are less robust because of nonlinearity. The only consistent response in swells is the strong energy increase in the western Pacific and Indian Ocean sector of the Southern Ocean during the austral winter and autumn.
The barotropic version of the 3-dimensional, finite element Dartmouth circulation model called Qu... more The barotropic version of the 3-dimensional, finite element Dartmouth circulation model called Quoddy has been used to simulate the response of the Gulf of Maine to wind forcing at 1/16 M2 tidal cycle (0.78 hr) increments in near real-time. Model forcing consists of predicted M2 tidal sea level around the open ocean boundary and surface wind stress derived from NDBC buoy-measured winds at severl sites in the region. Nontidal sea level forcing along the Scotian shelf transect is inferred from a wind-forced statistical model. Nowcast model products include 3-D currents and sea level at the model resolution of about 10 km in the Gulf of Maine and 5 km along the coastalines. A comparison of model and observed M2 tidal sea level results at 49 sites show average rms differences of 9 cm and 7 degrees for amplitude and phase, respectively. The nontidal results of the model, which are consistent with observed Gulf-wide response to wind forcing, will be presented.
The 3-D QUODDY barotropic model tests were run for the period of February 7 - 18, 1987 with both ... more The 3-D QUODDY barotropic model tests were run for the period of February 7 - 18, 1987 with both a time-space constant drag coefficient Cd and a time-space variable Cd. The constant Cd QUODDY test captured more than 60% of the observed variance, as compared to the 31% of the variance captured by the linear harmonic finite element model FUNDY. Thus the use of a constant Cd thus represents an improvement in coastal modeling effects. However, there still were large differences between model results and observations in or around the times of intense storms (e.g. February 9 th to 13 th ). The QUODDY tests with a variety of realistic Cd values did not improve model results significantly. Neither did the use of time and space variable Cd. The model behavior was most sensitive to the specification of surface wind stress forcing. Thus, we expect that model improvements may come with a better understanding of the wind stress calculation in the Gulf, perhaps a more detailed understanding of th...
ABSTRACT Ocean surface wave climate change is one of the eight main climate drivers affecting the... more ABSTRACT Ocean surface wave climate change is one of the eight main climate drivers affecting the coast (Hemer, et al 2010). In recent years, several dynamic projections of regional wave climate have been carried out, where downscaled Atmosphere/Ocean Global Climate Model (GCM) projections are used to force regional wave models. But bias could arise in the simulated wave climate from the low level of confidence in the projected circulation changes from GCMs. The European Centre for Medium-Rage Weather Forecasts (ECMWF) ERA-40 reanalysis (T159) produced global wave information at 1.5° resolution. Even though it captures the variability of the true wave height very well on all time scales, due to the relatively coarse resolution of the atmospheric model and its limited ability to resolve storm systems, high wave heights were severely underestimated (Hemer, 2010). We have developed a high resolution global simulation system by coupling the operational wave model developed at the National Centers for Environmental Prediction/Environmental Modeling Center, to GFDL's prototype Global Cloud-Resolving Model (HiRAM). A free-run 29-year (1980 to 2009) AMIP-type wave climatology was generated using this coupled system. Prescribed SSTs from the Met Office Hadley Center Sea Ice and SST version 1.1 model (HadISST 1.1; Ryner et al. 2003) was used as the lower boundary condition for the atmospheric model. During the model simulation period, the well-mixed greenhouse gases and both tropospheric and stratospheric ozone vary from year to year, following the procedure used in the CM2.1 historical simulations in the CMIP3 database (Delworth et al. 2006). Model evaluation against NDBC buoy data, satellite measurements, and ERA-40 reanalysis shows good agreements. The linkage between wave climate change and some climate indices (ENSO, North Atlantic Oscillaiton, NPAC index, and Southern Annular Mode) was explored and the global trend analysis for both significant wave height and mean wave length will be presented as well. Delworth, T. D., and Coauthors, 2006: GFDL's CM2 global coupled climate models. Part I: Formulation and simulation characteristics. J. Climate, 19, 643-674. Hemer, M. A., X. L. Wang, J. A. Church, and V. R. Swail, 2010: Coordinating global ocean wave climate projections. BAMS, 451-454.
Nature Climate Change, 2013
Future changes in wind-wave climate have broad implications for the operation and design of coast... more Future changes in wind-wave climate have broad implications for the operation and design of coastal, near-and off-shore industries and ecosystems, and may further exacerbate the anticipated vulnerabilities of coastal regions to projected sealevel rise 1,2 . However, wind waves have received little attention in global assessments of projected future climate change. We present results from the first community-derived multi-model ensemble of wave-climate projections. We find an agreed projected decrease in annual mean significant wave height (H S ) over 25.8% of the global ocean area. The area of projected decrease is greater during boreal winter (January-March, mean; 38.5% of the global ocean area) than austral winter (July-September, mean; 8.4%). A projected increase in annual mean H S is found over 7.1% of the global ocean, predominantly in the Southern Ocean, which is greater during austral winter (July-September; 8.8%). Increased Southern Ocean wave activity influences a larger proportion of the global ocean as swell propagates northwards into the other ocean basins, observed as an increase in annual mean wave period (T M ) over 30.2% of the global ocean and associated rotation of the annual mean wave direction (θ M ). The multi-model ensemble is too limited to systematically sample total uncertainty associated with wave-climate projections. However, variance of wave-climate projections associated with study methodology dominates other sources of uncertainty (for example, climate scenario and model uncertainties).
This was a test of a near real-time operational application of the Dartmouth 3-dimensional finite... more This was a test of a near real-time operational application of the Dartmouth 3-dimensional finite-element circulation model QUODDY designed to nowcast the meteorologically-forced response of the Gulf of Maine region in the presence of the strong semidiurnal tide. The model is forced along the open ocean boundaries with a predicted M2 tidal sea level and at the surface with wind stress derived by an optimal interpolation of an array of NOAA National Weather Service/ National Data Buoy Center measure ments that were obtained in near real-time . In this application, the model is run every 1/16 M2 tidal period (i.e., 0.77625 hours) in near real-time. Because each calculation runs faster than real time, subsequent calculations are delayed until real time catches up with model time, when the model sea level results are output. A model/observation comparison of tidal sea level results at 49 observation stations throughout the Gulf indicated that M2 tidal sea level amplitude differences wer...
Northeastern Naturalist, 2006
A simple heat budget has been constructed for Mount Hope Bay (MHB) for two one-month periods: win... more A simple heat budget has been constructed for Mount Hope Bay (MHB) for two one-month periods: winter 1999 (February-March) and summer 1997 (August-September). The box model considered here includes the heat contributions to MHB from the Brayton Point Power Station (BPPS), the exchange across the airwater interface, the Taunton River, and the tidal exchange between MHB and both Narragansett Bay and the Sakonnet River (NB/SR). Comprehensive measurements of MHB temperature fields by Applied Science Associates, Inc., and meteorological data from T.F. Green Airport (Warwick, RI) were used to estimate the different heat flux component contributions. The box model results for winter show that the BPPS heating is balanced (within the uncertainty of the estimates) by air-water cooling alone. The simple winter balance does not hold during the summer, when heat losses due to tidal exchanges between MHB and NB/SR are important. The summer heat budget of MHB-including BPPS heating, air-water cooling and tidal exchange cooling-can be balanced (within the uncertainty of the estimates) by assuming that 3% of the colder NB/SR tidal input water is exchanged with the warmer MHB water during each tidal cycle. The air-water cooling accounts for 84.4% of the total cooling, and the tidal exchange accounts for 15.6% of the total cooling. Taunton River contributions to the heat budget were negligible in both seasons. Analyses show that the model temperature is most sensitive to uncertainty in the measurements used to estimate the air-water heat fluxes-the relative humidity in particular. Thus, local MHB measurements are important for accurate monitoring of the MHB heat budget in the future.
Journal of Physical Oceanography, 2009
In this paper, the wind-wave-current interaction mechanisms in tropical cyclones and their effect... more In this paper, the wind-wave-current interaction mechanisms in tropical cyclones and their effect on the surface wave and ocean responses are investigated through a set of numerical experiments. The key element of the authors' modeling approach is the air-sea interface model, which consists of a wave boundary layer model and an air-sea momentum flux budget model. The results show that the time and spatial variations in the surface wave field, as well as the wave-current interaction, significantly reduce momentum flux into the currents in the right rear quadrant of the hurricane. The reduction of the momentum flux into the ocean consequently reduces the magnitude of the subsurface current and sea surface temperature cooling to the right of the hurricane track and the rate of upwelling/downwelling in the thermocline. During wind-wave-current interaction, the momentum flux into the ocean is mainly affected by reducing the wind speed relative to currents, whereas the wave field is mostly affected by refraction due to the spatially varying currents. In the area where the current is strongly and roughly aligned with wave propagation direction, the wave spectrum of longer waves is reduced, the peak frequency is shifted to a higher frequency, and the angular distribution of the wave energy is widened.
Journal of Physical Oceanography, 2010
In coupled ocean-atmosphere models, it is usually assumed that the momentum flux into ocean curre... more In coupled ocean-atmosphere models, it is usually assumed that the momentum flux into ocean currents is equal to the flux from air (wind stress). However, when the surface wave field grows (decays) in space or time, it gains (loses) momentum and reduces (increases) the momentum flux into subsurface currents compared to the flux from the wind. In particular, under tropical cyclone (TC) conditions the surface wave field is complex and fast varying in space and time and may significantly affect the momentum flux from wind into ocean. In this paper, numerical experiments are performed to investigate the momentum flux budget across the air-sea interface under both uniform and idealized TC winds. The wave fields are simulated using the WAVE-WATCH III model. The difference between the momentum flux from wind and the flux into currents is estimated using an air-sea momentum flux budget model. In many of the experiments, the momentum flux into currents is significantly reduced relative to the flux from the wind. The percentage of this reduction depends on the choice of the drag coefficient parameterization and can be as large as 25%. For the TC cases, the reduction is mainly in the right-rear quadrant of the hurricane, and the percentage of the flux reduction is insensitive to the changes of the storm size and the asymmetry in the wind field but varies with the TC translation speed and the storm intensity. The results of this study suggest that it is important to explicitly resolve the effect of surface waves for accurate estimations of the momentum flux into currents under TCs.
Journal of Physical Oceanography, 2009
The performance of the wave model WAVEWATCH III under a very strong, category 5, tropical cyclone... more The performance of the wave model WAVEWATCH III under a very strong, category 5, tropical cyclone wind forcing is investigated with different drag coefficient parameterizations and ocean current inputs. The model results are compared with field observations of the surface ...
Grant and Madsen (1979) showed that the nonlinear interaction between steady near bottom currents... more Grant and Madsen (1979) showed that the nonlinear interaction between steady near bottom currents and oscillatory surface wave currents can produce enhanced bottom stress relative to what a quadratic drag law formulation would indicate. A numerical study of this process has been conducted by combining a bottom boundary layer model (BBLM) with the Dartmouth one-dimensional (1-D) finite element dynamic model called NUBBLE. This model system is forced to dynamic equilibrium by typical Gulf of Maine storm-related 12-second surface waves and prescribed steady geostrophic currents. The results of a suite of sensitivity tests show that: (1) the combined wave and current influence on bottom stress calculations is very important in water depth less than 80 m; (2) the equivalent drag coefficient (Cd) associated with the combination of wave and current interactions is larger than that due to either forcing process alone; and (3) the quadratic drag law is practical for simulating the bottom str...
Journal of Geophysical Research, 2005
The storm response of the Gulf of Maine/Georges Bank region was investigated using the barotropic... more The storm response of the Gulf of Maine/Georges Bank region was investigated using the barotropic version (i.e. uniform density) of the Dartmouth 3-D nonlinear, finite element coastal ocean circulation model with quadratic bottom stress called QUODDY. A suite of model hindcast experiments for the period 4 -18 February 1987 was conducted, in which the model was forced at the open ocean boundaries by the M 2 semidiurnal tidal sea level and in the interior by realistic surface wind stresses featuring a strong 9-11 February nor'easter. Results for a reference model run with a time-space constant drag coefficient C d of 0.005 captured more than 60% of the observed sea level variance, but left large unexplained model/observed sea level differences, particularly during the storm. Model sensitivity testing to a realistic range of constant C d values did not improve model results significantly. However, when atmospheric pressure was added to the surface forcing, significant reductions in the model/observed sea level differences were realized.
Journal of Climate, 2013
ABSTRACT Surface wind (U10) and significant wave height (Hs) response to global warming are inves... more ABSTRACT Surface wind (U10) and significant wave height (Hs) response to global warming are investigated using a coupled atmosphere-wave model by perturbing the sea surface temperatures (SSTs) with anomalies generated by WGCM CMIP-3 coupled models that use the IPCC/AR4/A1B scenario late in the 21st century. Several consistent changes were observed across all four realizations for the seasonal means: robust increase of U10 and Hs in the Southern Ocean for both the austral summer and winter due to the poleward shift of the jet stream; a dipole pattern of the U10 and Hs with increases in the northeast sector and decreases at the mid-latitude during the boreal winter in the North Atlantic due to the more frequent occurrence of the positive phases of NAO; and strong decrease of U10 and Hs at the tropical western Pacific Ocean during the austral summer, which might be caused by the joint effect of the weakening of the Walker circulation and the large hurricane frequency decrease in the South Pacific. Changes of the 99th percentile U10 and Hs are twice as strong as changes in the seasonal means, and the maximum changes are mainly dominated by the changes in hurricanes. Robust strong decreases of U10 and Hs in the South Pacific are obtained due to the large hurricane frequency decrease, while the results in the Northern Hemisphere basins differ among the models. An additional sensitivity experiment suggests that the qualitative response of U10 and Hs is not affected by using SST anomalies only and maintaining the radiative forcing unchanged (using 1980 values) as in this study.
Journal of Climate, 2014
The impacts of parameterized upper-ocean wave mixing on global climate simulations are assessed t... more The impacts of parameterized upper-ocean wave mixing on global climate simulations are assessed through modification to Large et al.'s K-profile ocean boundary layer parameterization (KPP) in a coupled atmosphereocean-wave global climate model. The authors consider three parameterizations and focus on impacts to highlatitude ocean mixed layer depths and related ocean diagnostics. The McWilliams and Sullivan parameterization (MS2000) adds a Langmuir turbulence enhancement to the nonlocal component of KPP. It is found that the Langmuir turbulence-induced mixing provided by this parameterization is too strong in winter, producing overly deep mixed layers, and of minimal impact in summer. The later Smyth et al. parameterization modifies MS2000 by adding a stratification effect to restrain the turbulence enhancement under weak stratification conditions (e.g., winter) and to magnify the enhancement under strong stratification conditions. The Smyth et al. scheme improves the simulated winter mixed layer depth in the simulations herein, with mixed layer deepening in the Labrador Sea and shoaling in the Weddell and Ross Seas. Enhanced vertical mixing through parameterized Langmuir turbulence, coupled with enhanced lateral transport associated with parameterized mesoscale and submesoscale eddies, is found to be a key element for improving mixed layer simulations. Secondary impacts include strengthening the Atlantic meridional overturning circulation and reducing the Antarctic Circumpolar Current. The Qiao et al. nonbreaking wave parameterization is the third scheme assessed here. It adds a wave orbital velocity to the Reynolds stress calculation and provides the strongest summer mixed layer deepening in the Southern Ocean among the three experiments, but with weak impacts during winter.
Journal of Climate, 2012
ABSTRACT This study describes a 29-yr (1981-2009) global ocean surface gravity wave simulation ge... more ABSTRACT This study describes a 29-yr (1981-2009) global ocean surface gravity wave simulation generated by a coupled atmosphere wave model using NOAA/GFDL's High-Resolution Atmosphere Model (HiRAM) and the WAVEWATCH III surface wave model developed and used operationally at NOAA/NCEP. Extensive evaluation of monthly mean significant wave height (SWH) against in situ buoys, satellite altimeter measurements, and the 40-yr ECMWF Re-Analysis (ERA-40) show very good agreements in terms of magnitude, spatial distribution, and scatter. The comparisons with satellite altimeter measurements indicate that the SWH low bias in ERA-40 reanalysis has been improved in these model simulations. The model fields show a strong response to the North Atlantic Oscillation (NAO) in the North Atlantic and the Southern Oscillation index (SOI) in the Pacific Ocean that are well connected with the atmospheric responses. For the NAO in winter, the strongest subpolar wave responses are found near the northern Europe coast and the coast of Labrador rather than in the central-northern Atlantic where the wind response is strongest. Similarly, for the SOI in the Pacific Ocean, the wave responses are strongest in the northern Bering Sea and the Antarctic coast.
Journal of Climate, 2014
The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface grav... more The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface gravity wave climatology produced using a coupled atmosphere-wave model. The swell energy fraction analysis shows that swell dominates most of the World Ocean basins for all four seasons, and the Southern Ocean swells dominate swell in the global ocean. The swells are loosely correlated with the surface wind in the midlatitude storm region in both hemispheres, while their energy distribution and propagation direction do not show any relation with local winds and vary significantly with season because of nonlinear interactions. The same coupled system is then used to investigate the projected future change in wind-sea and swell climate through a timeslice simulation. Forcing of the coupled model was obtained by perturbing the model sea surface temperatures and sea ice with anomalies generated by representative Working Group on Coupled Modelling (WGCM) phase 3 of the Coupled Model Intercomparison Project (CMIP3) coupled models that use the IPCC Fourth Assessment Report (AR4) A1B scenario late in the twenty-first century. Robust responses found in the wind seas are associated with modified climate indices. A dipole pattern in the North Atlantic during the boreal winter is associated with more frequent occurrence of the positive North Atlantic Oscillation (NAO) phases under global warming, and the wind-sea energy increase in the Southern Ocean is associated with the continuous shift of the southern annular mode (SAM) toward its positive phase. Swell responses are less robust because of nonlinearity. The only consistent response in swells is the strong energy increase in the western Pacific and Indian Ocean sector of the Southern Ocean during the austral winter and autumn.