Fan, Yalin, Shian-Jiann Lin, Stephen M Griffies, and Mark A Hemer, May 2014: Simulated Global Swell and Wind Sea Climate and Their responses to Anthropogenic Climate Change at the End of the 21st Century. Journal of Climate, 27(10), DOI:10.1175/JCLI-D-13-00198.1.
Fan, Yalin, and Stephen M Griffies, June 2014: Impacts of parameterized Langmuir turbulence and non-breaking wave mixing in global climate simulations. Journal of Climate, 27(12), DOI:10.1175/JCLI-D-13-00583.1. Abstract
We assess the impacts of parameterized upper ocean wave mixing on global climate simulations through modification to the K-profile ocean boundary layer parameterization (KPP; Large et al 1994) in a coupled atmosphere-ocean-wave global climate model. We consider three parameterizations and focus on impacts to high latitude ocean mixed layer depths and related ocean diagnostics. The McWilliams and Sullivan (2000) parameterization (MS2000) adds a Langmuir turbulence enhancement to the non-local component of KPP. We find 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 Smyth et al (2002) 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 (2002) scheme improves the simulated winter Mixed Layer Depth in our simulations, 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/submesoscale eddies, are found to be key elements for improving mixed layer simulations. Secondary impacts include strengthening the Atlantic Meridional Overturning Circulation and reducing the Antarctic Circumpolar Current. The Qiao et al (2004) non-breaking wave parameterization is the third scheme we assess. 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.
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.
Hemer, Mark A., Yalin Fan, N Mori, A Semedo, and X L Wang, May 2013: Projected changes in wave climate from a multi-model ensemble. Nature Climate Change, 3(5), DOI:10.1038/nclimate1791. Abstract
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 sea-level rise. 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 (HS) 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 HS 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 (TM) over 30.2% of the global ocean and associated rotation of the annual mean wave direction (θM). 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 study describes a 29-year (1981 to 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 ERA-40 reanalysis 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 our model simulations. The model fields show strong response to the NAO in the North Atlantic and the 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.
Fan, Yalin, Isaac Ginis, and Tetsu Hara, October 2010: Momentum flux budget across the air–sea interface under uniform and tropical cyclone winds. Journal of Physical Oceanography, 40(10), DOI:10.1175/2010JPO4299.1. Abstract
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 WAVEWATCH
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.