Miller
Arthur J.
Miller
Arthur J.
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ArticleCoupled ocean–atmosphere modeling and predictions(Sears Foundation for Marine Research, 2017-05-01) Miller, Arthur J. ; Collins, Matthew ; Gualdi, Silvio ; Jensen, Tommy G. ; Misra, Vasu ; Pezzi, Luciano Ponzi ; Pierce, David W. ; Putrasahan, Dian ; Seo, Hyodae ; Tseng, Yu-HengKey aspects of the current state of the ability of global and regional climate models to represent dynamical processes and precipitation variations are summarized. Interannual, decadal, and global-warming timescales, wherein the influence of the oceans is relevant and the potential for predictability is highest, are emphasized. Oceanic influences on climate occur throughout the ocean and extend over land to affect many types of climate variations, including monsoons, the El Niño Southern Oscillation, decadal oscillations, and the response to greenhouse gas emissions. The fundamental ideas of coupling between the ocean-atmosphere-land system are explained for these modes in both global and regional contexts. Global coupled climate models are needed to represent and understand the complicated processes involved and allow us to make predictions over land and sea. Regional coupled climate models are needed to enhance our interpretation of the fine-scale response. The mechanisms by which large-scale, low-frequency variations can influence shorter timescale variations and drive regionalscale effects are also discussed. In this light of these processes, the prospects for practical climate predictability are also presented.
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ArticleCoupled impacts of the diurnal cycle of sea surface temperature on the Madden–Julian oscillation(American Meteorological Society, 2014-11-15) Seo, Hyodae ; Subramanian, Aneesh C. ; Miller, Arthur J. ; Cavanaugh, Nicholas R.This study quantifies, from a systematic set of regional ocean–atmosphere coupled model simulations employing various coupling intervals, the effect of subdaily sea surface temperature (SST) variability on the onset and intensity of Madden–Julian oscillation (MJO) convection in the Indian Ocean. The primary effect of diurnal SST variation (dSST) is to raise time-mean SST and latent heat flux (LH) prior to deep convection. Diurnal SST variation also strengthens the diurnal moistening of the troposphere by collocating the diurnal peak in LH with those of SST. Both effects enhance the convection such that the total precipitation amount scales quasi-linearly with preconvection dSST and time-mean SST. A column-integrated moist static energy (MSE) budget analysis confirms the critical role of diurnal SST variability in the buildup of column MSE and the strength of MJO convection via stronger time-mean LH and diurnal moistening. Two complementary atmosphere-only simulations further elucidate the role of SST conditions in the predictive skill of MJO. The atmospheric model forced with the persistent initial SST, lacking enhanced preconvection warming and moistening, produces a weaker and delayed convection than the diurnally coupled run. The atmospheric model with prescribed daily-mean SST from the coupled run, while eliminating the delayed peak, continues to exhibit weaker convection due to the lack of strong moistening on a diurnal basis. The fact that time-evolving SST with a diurnal cycle strongly influences the onset and intensity of MJO convection is consistent with previous studies that identified an improved representation of diurnal SST as a potential source of MJO predictability.
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ArticleEffect of eddy-wind interaction on Ekman pumping and eddy kinetic energy : a regional coupled modeling study for the California Current System(California Cooperative Oceanic Fisheries Investigations, 2015) Seo, Hyodae ; Miller, Arthur J. ; Norris, Joel R.The California Current system (CCS) is characterized by the energetic summertime mesoscale and filamentary eddies with typical anomalies in sea surface temperature (SST) and surface current exceeding 2˚C and 0.5 cms–1, respectively. Recent satellite observations show that both SST and surface current at oceanic mesoscales significantly influence the Ekman pumping velocity, suggestive of a subsequent dynamical feedback effect on the eddy energetics. The extent to which this mesoscale coupling is important for the Ekman pumping and the eddy kinetic energy (EKE) budget in the CCS is the focus of this study.
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ArticleEddy–wind interaction in the California Current System : dynamics and impacts(American Meteorological Society, 2015-11-30) Seo, Hyodae ; Miller, Arthur J. ; Norris, Joel R.The summertime California Current System (CCS) is characterized by energetic mesoscale eddies, whose sea surface temperature (SST) and surface current can significantly modify the wind stress and Ekman pumping. Relative importance of the eddy–wind interactions via SST and surface current in the CCS is examined using a high-resolution (7 km) regional coupled model with a novel coupling approach to isolate the small-scale air–sea coupling by SST and surface current. Results show that when the eddy-induced surface current is allowed to modify the wind stress, the spatially averaged surface eddy kinetic energy (EKE) is reduced by 42%, and this is primarily due to enhanced surface eddy drag and reduced wind energy transfer. In contrast, the eddy-induced SST–wind coupling has no significant impact on the EKE. Furthermore, eddy-induced SST and surface current modify the Ekman pumping via their crosswind SST gradient and surface vorticity gradient, respectively. The resultant magnitudes of the Ekman pumping velocity are comparable, but the implied feedback effects on the eddy statistics are different. The surface current-induced Ekman pumping mainly attenuates the amplitude of cyclonic and anticyclonic eddies, acting to reduce the eddy activity, while the SST-induced Ekman pumping primarily affects the propagation. Time mean–rectified change in SST is determined by the altered offshore temperature advection by the mean and eddy currents, but the magnitude of the mean SST change is greater with the eddy-induced current effect. The demonstrated remarkably strong dynamical response in the CCS system to the eddy-induced current–wind coupling indicates that eddy-induced current should play an important role in the regional coupled ocean–atmosphere system.
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ArticleImpact of extratropical Northeast Pacific SST on U.S. West Coast Precipitation(American Geophysical Union, 2023-02-08) Beaudin, Élise ; Di Lorenzo, Emanuele ; Miller, Arthur J. ; Seo, Hyodae ; Joh, YoungjiThe rainfall over the U.S. West Coast is known to be highly influenced by large‐scale atmospheric circulation and tropical climate teleconnections. However, the role of North Pacific oceanic variability is less understood. Using high‐resolution regional atmospheric model simulations forced by sustained positive and negative phases of the extratropical Pacific Decadal Oscillation sea surface temperature anomalies (SSTa), we diagnose the precipitation changes over the U.S. West Coast during 2010–2020. We find that precipitation anomalies are up to 60% stronger (weaker) for the warm (cold) cases, especially over Northern and Central California during wintertime, and Baja California in the summertime. In both seasons, precipitation is predominantly modulated through changes in the water vapor flux, which are directed toward the coast in wintertime and away from the coast during summertime. These flux anomalies are primarily driven by large‐scale changes in the wind associated with the atmospheric adjustment to the strong ocean SSTa.Plain Language SummaryThis study examines how ocean temperature in the Northeast Pacific affects rainfall in the U.S. West Coast using computer model simulations over the period 2010–2020. Rainfall generally increases when coastal waters are warmer and vice versa. This is especially true in Northern and Central California during wintertime and in Baja California during summertime. The amount of rain is mainly affected by changes in the water vapor that moves toward the coast in the winter and away from the coast in the summer. These changes in water vapor are caused by changes in the wind, which are linked to changes in the surface ocean temperature.Key PointsWarming along the U.S. West Coast can induce wind‐driven vapor fluxes changes leading to enhanced precipitationExtratropical sea surface temperature (SST) forcing can impact large‐scale atmospheric circulationU.S. West Coast precipitation are impacted by extratropical Northeast Pacific SST
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ArticleCoupled ocean-atmosphere forecasting at short and medium time scales(Sears Foundation for Marine Research, 2017-11-01) Pullen, Julie ; Allard, Richard ; Seo, Hyodae ; Miller, Arthur J. ; Chen, Shuyi ; Pezzi, Luciano Ponzi ; Smith, Travis ; Chu, Philip ; Alves, José ; Caldeira, RuiRecent technological advances over the past few decades have enabled the development of fully coupled atmosphere-ocean modeling prediction systems that are used today to support short-term (days to weeks) and medium-term (10–21 days) needs for both the operational and research communities. We overview the coupling framework, including model components and grid resolution considerations, as well as the coupling physics by examining heat fluxes between atmosphere and ocean, momentum transfer, and freshwater fluxes. These modeling systems can be run as fully coupled atmosphere-ocean and atmosphere-ocean-wave configurations. Examples of several modeling systems applied to complex coastal regions including Madeira Island, Adriatic Sea, Coastal California, Gulf of Mexico, Brazil, and the Maritime Continent are presented. In many of these studies, a variety of field campaigns have contributed to a better understanding of the underlying physics associated with the atmosphere-ocean feedbacks. Examples of improvements in predictive skill when run in coupled mode versus standalone are shown. Coupled model challenges such as model initialization, data assimilation, and earth system prediction are discussed.