Sources of Eddy Energy Simulated by a Model of the Northeast Pacific Ocean

Abstract

This paper examines the energy sources for eddy variability in the Gulf of Alaska using a numerical model and a novel form of data assimilation referred to as spectral nudging. Spectral nudging is distinguished from conventional nudging by its ability to operate only on specified frequency and wavenumber bands; in the present case, only the subannual variability is nudged, and only on spatial scales of 100 km or more. By using this approach, the broad-brush aspects of the model's mean state are constrained to remain near the mean climatological conditions, while the simulated eddy field is determined by the model dynamics. Simulations of the North Pacific Ocean with a 0.25°horizontal resolution and spectral nudging have been previously shown to produce eddy fields that are significantly more energetic and more realistic than those produced by prognostic (i.e., not nudged) simulations. The analysis of the spectrally nudged model results undertaken here reveals the tendency of the circulation to be both baroclinically and barotropically unstable in different regions and to differing degrees. Along the north coast of the Gulf of Alaska, the simulation suggests that barotropic instability is more important overall as an energy source for eddies than is baroclinic instability. Along the east coast of the Gulf of Alaska, the simulation suggests that both baroclinic and barotropic instabilities are important. Although the overall energy transfer is from the mean state to the eddy field, there are regions of the model, particularly along the north coast of the Gulf of Alaska, where the transfer of energy is from the eddy field to the mean flow.

Research on the interannual variability of the great whirl and the related mechanisms

“…The former, however, can not be estimated here due to lack of data. The latter is calculated by the following formula (Meng et al, 2006;Shore et al, 2008) , e bt th z p gk…”

Rossby Waves and the Variability of the North Pacific Current during 2002–03

“…We use the Parallel Ocean Program (POP) [the model also used by Stacey et al (2006) and Shore et al (2008)] to simulate the circulation in the North Pacific Ocean between 1970 and 2006. (The simulation was started in 1960, but the first 10 yr of the simulation were considered to be spinup time.)…”

“…The basic model setup for the North Pacific simulation discussed in this paper is the same as that used by Stacey et al (2006) and Shore et al (2008). However, although they used the monthly climatological National Centers for Environmental Prediction (NCEP) forcing (i.e., the forcing repeated itself on an annual cycle), we have used the mean NCEP observations/reanalyses of monthly wind stress, surface heat flux, pressure, and freshwater flux.…”

Simulation of Mixed Layer Depth in the Northeast Pacific Utilizing Spectral Nudging

“…Midway between each layer and below the w point is a potential temperature, salinity, and pressure (u, S, p) point; midway between each layer and offset is a horizontal velocity point. Stacey et al (2006) and Shore et al (2008) …”

“…The model setup for the North Pacific simulation discussed in this paper is the same as that used by Stacey et al (2006) and Shore et al (2008), with three major exceptions: 1) they used climatological forcing, whereas this study has used the mean monthly NCEP observations/reanalyses; 2) the model used here is nudged to the Levitus monthly climatology only, without melding additional climatology obtained from the Institute of Ocean Sciences (IOS); and 3) the model used here has 28 vertical levels (Table 1). The model domain is shown in Fig.…”