Current Search: Center for Ocean-Atmospheric Prediction Studies (x) » Alford, Matthew H. (x)
Search results
- Title
- Frequency Content Of Sea Surface Height Variability From Internal Gravity Waves To Mesoscale Eddies.
- Creator
-
Savage, Anna C., Arbic, Brian K., Richman, James G., Shriver, Jay F., Alford, Matthew H., Buijsman, Maarten C., Farrar, J. Thomas, Sharma, Hari, Voet, Gunnar, Wallcraft, Alan J....
Show moreSavage, Anna C., Arbic, Brian K., Richman, James G., Shriver, Jay F., Alford, Matthew H., Buijsman, Maarten C., Farrar, J. Thomas, Sharma, Hari, Voet, Gunnar, Wallcraft, Alan J., Zamudio, Luis
Show less - Abstract/Description
-
High horizontal-resolution (1/12: 5 degrees and 1/25 degrees) 41-layer global simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea surface height (SSH) variability. The HYCOM output is separated into steric and nonsteric and into subtidal, diurnal, semidiurnal, and supertidal frequency bands. The model SSH output is compared to two data sets that offer some geographical...
Show moreHigh horizontal-resolution (1/12: 5 degrees and 1/25 degrees) 41-layer global simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea surface height (SSH) variability. The HYCOM output is separated into steric and nonsteric and into subtidal, diurnal, semidiurnal, and supertidal frequency bands. The model SSH output is compared to two data sets that offer some geographical coverage and that also cover a wide range of frequencies-a set of 351 tide gauges that measure full SSH and a set of 14 in situ vertical profilers from which steric SSH can be calculated. Three of the global maps are of interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) two-dimensional swath altimeter mission: (1) maps of the total and (2) nonstationary internal tidal signal (the latter calculated after removing the stationary internal tidal signal via harmonic analysis), with an average variance of 1: 05 and 0: 43 cm(2), respectively, for the semidiurnal band, and (3) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum, with an average variance of 0: 15 cm2. Stationary internal tides (which are predictable), nonstationary internal tides (which will be harder to predict), and nontidal internal gravity waves (which will be very difficult to predict) may all be important sources of high-frequency "noise" that could mask lower frequency phenomena in SSH measurements made by the SWOT mission.
Show less - Date Issued
- 2017-03
- Identifier
- FSU_libsubv1_wos_000400678900047, 10.1002/2016JC012331
- Format
- Citation
- Title
- Geographical Distribution Of Diurnal And Semidiurnal Parametric Subharmonic Instability In A Global Ocean Circulation Model.
- Creator
-
Ansong, Joseph K., Arbic, Brian K., Simmons, Harper L., Alford, Matthew H., Buijsman, Maarten C., Timko, Patrick G., Richman, James G., Shriver, Jay F., Wallcraft, Alan J.
- Abstract/Description
-
The evidence for, baroclinic energetics of, and geographic distribution of parametric subharmonic instability (PSI) arising from both diurnal and semidiurnal tides in a global ocean general circulation model is investigated using 1/12.5 degrees and 1/25 degrees simulations that are forced by both atmospheric analysis fields and the astronomical tidal potential. The paper examines whether PSI occurs in the model, and whether it accounts for a significant fraction of the tidal baroclinic energy...
Show moreThe evidence for, baroclinic energetics of, and geographic distribution of parametric subharmonic instability (PSI) arising from both diurnal and semidiurnal tides in a global ocean general circulation model is investigated using 1/12.5 degrees and 1/25 degrees simulations that are forced by both atmospheric analysis fields and the astronomical tidal potential. The paper examines whether PSI occurs in the model, and whether it accounts for a significant fraction of the tidal baroclinic energy loss. Using energy transfer calculations and bispectral analyses, evidence is found for PSI around the critical latitudes of the tides. The intensity of both diurnal and semidiurnal PSI in the simulations is greatest in the upper ocean, consistent with previous results from idealized simulations, and quickly drops off about 5 degrees from the critical latitudes. The sign of energy transfer depends on location; the transfer is positive (from the tides to subharmonic waves) in some locations and negative in others. The net globally integrated energy transfer is positive in all simulations and is 0.5%-10% of the amount of energy required to close the baroclinic energy budget in the model. The net amount of energy transfer is about an order of magnitude larger in the 1/25 degrees semidiurnal simulation than the 1/12.5 degrees one, implying the dependence of the rate of energy transfer on model resolution.
Show less - Date Issued
- 2018-06-01
- Identifier
- FSU_libsubv1_wos_000437215800012, 10.1175/JPO-D-17-0164.1
- Format
- Citation
- Title
- Semidiurnal Internal Tide Energy Fluxes And Their Variability In A Global Ocean Model And Moored Observations.
- Creator
-
Ansong, Joseph K., Arbic, Brian K., Alford, Matthew H., Buijsman, Maarten C., Shriver, Jay F., Zhao, Zhongxiang, Richman, James G., Simmons, Harper L., Timko, Patrick G.,...
Show moreAnsong, Joseph K., Arbic, Brian K., Alford, Matthew H., Buijsman, Maarten C., Shriver, Jay F., Zhao, Zhongxiang, Richman, James G., Simmons, Harper L., Timko, Patrick G., Wallcraft, Alan J., Zamudio, Luis
Show less - Abstract/Description
-
We examine the temporal means and variability of the semidiurnal internal tide energy fluxes in 1/25 degrees global simulations of the Hybrid Coordinate Ocean Model (HYCOM) and in a global archive of 79 historical moorings. Low-frequency flows, a major cause of internal tide variability, have comparable kinetic energies at the mooring sites in model and observations. The computed root-mean-square (RMS) variability of the energy flux is large in both model and observations and correlates...
Show moreWe examine the temporal means and variability of the semidiurnal internal tide energy fluxes in 1/25 degrees global simulations of the Hybrid Coordinate Ocean Model (HYCOM) and in a global archive of 79 historical moorings. Low-frequency flows, a major cause of internal tide variability, have comparable kinetic energies at the mooring sites in model and observations. The computed root-mean-square (RMS) variability of the energy flux is large in both model and observations and correlates positively with the time-averaged flux magnitude. Outside of strong generation regions, the normalized RMS variability (the RMS variability divided by the mean) is nearly independent of the flux magnitudes in the model, and of order 23% or more in both the model and observations. The spatially averaged flux magnitudes in observations and the simulation agree to within a factor of about 1.4 and 2.4 for vertical mode-1 and mode-2, respectively. The difference in energy flux computed from the full-depth model output versus model output subsampled at mooring instrument depths is small. The global historical archive is supplemented with six high-vertical resolution moorings from the Internal Waves Across the Pacific (IWAP) experiment. The model fluxes agree more closely with the high-resolution IWAP fluxes than with the historical mooring fluxes. The high variability in internal tide energy fluxes implies that internal tide fluxes computed from short observational records should be regarded as realizations of a highly variable field, not as "means" that are indicative of conditions at the measurement sites over all time.
Show less - Date Issued
- 2017-03
- Identifier
- FSU_libsubv1_wos_000400678900015, 10.1002/2016JC012184
- Format
- Citation