Publications

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2018
Yi, DLL, Gan BL, Wu LX, Miller AJ.  2018.  The North Pacific Gyre Oscillation and Mechanisms of Its Decadal Variability in CMIP5 Models. Journal of Climate. 31:2487-2509.   10.1175/jcli-d-17-0344.1   AbstractWebsite

Based on the Simple Ocean Data Assimilation (SODA) product and 37 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) database, the North Pacific Gyre Oscillation (NPGO) and its decadal generation mechanisms are evaluated by studying the second leading modes of North Pacific sea surface height (SSH) and sea level pressure (SLP) as well as their dynamical connections. It is found that 17 out of 37 models can well simulate the spatial pattern and decadal time scales (10-30 yr) of the NPGO mode, which resembles the observation-based SODA results. Dynamical connections between the oceanic mode (NPGO) and the atmospheric mode [North Pacific Oscillation (NPO)] are strongly evident in both SODA and the 17 models. In particular, about 30%-40% of the variance of the NPGO variability, which generally exhibits a preferred time scale, can be explained by the NPO variability, which has no preferred time scale in most models. Two mechanisms of the decadal NPGO variability that had been proposed by previous studies are evaluated in SODA and the 17 models: 1) stochastic atmospheric forcing and oceanic spatial resonance and 2) low-frequency atmospheric teleconnections excited by the equatorial Pacific. Evaluation reveals that these two mechanisms are valid in SODA and two models (CNRM-CM5 and CNRM-CM5.2), whereas two models (CMCC-CM and CMCC-CMS) prefer the first mechanism and another two models (CMCC-CESM and IPSL-CM5B-LR) prefer the second mechanism. The other 11 models have no evident relations with the proposed two mechanisms, suggesting the need for a fundamental understanding of the decadal NPGO variability in the future.

2017
Stukel, MR, Aluwihare LI, Barbeau KA, Chekalyuk AM, Goericke R, Miller AJ, Ohman MD, Ruacho A, Song H, Stephens BM, Landry MR.  2017.  Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction. Proceedings of the National Academy of Sciences of the United States of America. 114:1252-1257.   10.1073/pnas.1609435114   AbstractWebsite

Enhanced vertical carbon transport (gravitational sinking and subduction) at mesoscale ocean fronts may explain the demonstrated imbalance of new production and sinking particle export in coastal upwelling ecosystems. Based on flux assessments from U-238:Th-234 disequilibrium and sediment traps, we found 2 to 3 times higher rates of gravitational particle export near a deep-water front (305 mg C.m(-2).d(-1)) compared with adjacent water or to mean (nonfrontal) regional conditions. Elevated particle flux at the front wasmechanistically linked to Fe-stressed diatoms and high-mesozooplankton fecal pellet production. Using a data assimilative regional ocean model fit to measured conditions, we estimate that an additional similar to 225 mg C.m(-2).d(-1) was exported as subduction of particle-rich water at the front, highlighting a transport mechanism that is not captured by sediment traps and is poorly quantified by most models and in situ measurements. Mesoscale fronts may be responsible for over a quarter of total organic carbon sequestration in the California Current and other coastal upwelling ecosystems.

2007
Seo, H, Miller AJ, Roads JO.  2007.  The Scripps Coupled Ocean-Atmosphere Regional (SCOAR) Model, with applications in the eastern Pacific sector. Journal of Climate. 20:381-402.   10.1175/jcli4016.1   AbstractWebsite

A regional coupled ocean-atmosphere model is introduced. It is designed to admit the air-sea feedbacks arising in the presence of an oceanic mesoscale eddy field. It consists of the Regional Ocean Modeling System (ROMS) and the Regional Spectral Model (RSM). Large-scale forcing is provided by NCEP/DOE reanalysis fields, which have physics consistent with the RSM. Coupling allows the sea surface temperature (SST) to influence the stability of the atmospheric boundary layer and, hence, the surface wind stress and heat flux fields. The system is denominated the Scripps Coupled Ocean-Atmosphere Regional (SCOAR) Model. The model is tested in three scenarios in the eastern Pacific Ocean sector: tropical instability waves of the eastern tropical Pacific, mesoscale eddies and fronts of the California Current System, and gap winds of the Central American coast. Recent observational evidence suggests air-sea interactions involving the oceanic mesoscale in these three regions. Evolving SST fronts are shown to drive an unambiguous response of the atmospheric boundary layer in the coupled model. This results in significant model anomalies of wind stress curl, wind stress divergence, surface heat flux, and precipitation that resemble the observations and substantiate the importance of ocean-atmosphere feedbacks involving the oceanic mesoscale.

2003
McGowan, JA, Bograd SJ, Lynn RJ, Miller AJ.  2003.  The biological response to the 1977 regime shift in the California Current. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 50:2567-2582.   10.1016/s0967-0645(03)00135-8   AbstractWebsite

Among the least understood interactions between physics and biology in the oceans are those that take place on the decadal scale. But this temporal scale is important because some of the greatest ecological events take place on this time scale. More than 50 years of measurement in the California Current System have revealed significant ecosystem changes, including a large, decadal decline in zooplankton biomass, along with a rise in upper-ocean temperature. The temperature change was a relatively abrupt shift around 1976-77, concurrent with other basin-wide changes associated with an intensification of the Aleutian Low-pressure system. This intensification generates temperature anomalies in the ocean by altering the patterns of net surface-heat fluxes, turbulent mixing, and horizontal transport. Changes in the mean abundance of zooplankton in the southern California Current have been attributed to variations in the strength of coastal upwelling, variations in the horizontal transport of nutrient-rich water from the north, or increased stratification due to warming, all of which could be affected by fluctuations in the Aleutian Low. Here we show that a deepening of the thermocline accompanied the warming and increased the stratification of the water column, leading to a decrease in the supply of plant nutrients to the upper layers. This is the most likely mechanism for the observed plankton decline, and subsequent ecosystem changes. A global change in upper-ocean heat content, accompanied by an increase in stratification and mixed-layer deepening relative to the critical depth for net production, could lead to a widespread decline in plankton abundance. (C) 2003 Elsevier Ltd. All rights reserved.