Effects of subsurface ocean dynamics on instability waves in the tropical Pacific

Abstract Atmospheric general circulation model experiments are conducted to quantify the contribution of internal oceanic variability in the form of tropical instability waves (TIWs) to interannual wind and rainfall variability in the tropical Pacific. It is found that in the tropical Pacific, along the equator, and near 25°N and 25°S, TIWs force a significant increase in wind and rainfall variability from interseasonal to interannual time scales. Because of the stochastic nature of TIWs, this means that climate models that do not take them into account will underestimate the strength and number of extreme events and may overestimate forecast capability.

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Net heat gain of the tropical Pacific Ocean computed from subsurface ocean data and wind stress data

Deep Sea Research Part A Oceanographic Research Papers ◽

10.1016/0198-0149(87)90119-1 ◽

1987 ◽

Vol 34 (1) ◽

pp. 33-43 ◽

Cited By ~ 5

Author(s):

Thierry Delcroix

Keyword(s):

Pacific Ocean ◽

Wind Stress ◽

Tropical Pacific ◽

Tropical Pacific Ocean ◽

Heat Gain ◽

Subsurface Ocean ◽

The Tropical Pacific

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Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications

Journal of Climate ◽

10.1175/jcli-d-13-00359.1 ◽

2014 ◽

Vol 27 (6) ◽

pp. 2405-2416 ◽

Cited By ~ 30

Author(s):

Elizabeth J. Drenkard ◽

Kristopher B. Karnauskas

Keyword(s):

Heat Budget ◽

Tropical Pacific ◽

Global Climate Models ◽

Ocean Dynamics ◽

Eastern Pacific ◽

Boreal Summer ◽

Trade Winds ◽

Equatorial Undercurrent ◽

The Pacific ◽

The Tropical Pacific

Abstract Several recent studies utilizing global climate models predict that the Pacific Equatorial Undercurrent (EUC) will strengthen over the twenty-first century. Here, historical changes in the tropical Pacific are investigated using the Simple Ocean Data Assimilation (SODA) reanalysis toward understanding the dynamics and mechanisms that may dictate such a change. Although SODA does not assimilate velocity observations, the seasonal-to-interannual variability of the EUC estimated by SODA corresponds well with moored observations over a ~20-yr common period. Long-term trends in SODA indicate that the EUC core velocity has increased by 16% century−1 and as much as 47% century−1 at fixed locations since the mid-1800s. Diagnosis of the zonal momentum budget in the equatorial Pacific reveals two distinct seasonal mechanisms that explain the EUC strengthening. The first is characterized by strengthening of the western Pacific trade winds and hence oceanic zonal pressure gradient during boreal spring. The second entails weakening of eastern Pacific trade winds during boreal summer, which weakens the surface current and reduces EUC deceleration through vertical friction. EUC strengthening has important ecological implications as upwelling affects the thermal and biogeochemical environment. Furthermore, given the potential large-scale influence of EUC strength and depth on the heat budget in the eastern Pacific, the seasonal strengthening of the EUC may help reconcile paradoxical observations of Walker circulation slowdown and zonal SST gradient strengthening. Such a process would represent a new dynamical “thermostat” on CO2-forced warming of the tropical Pacific Ocean, emphasizing the importance of ocean dynamics and seasonality in understanding climate change projections.

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Coupled Ocean–Atmosphere Dynamical Processes in the Tropical Indian and Pacific Oceans and the TBO

Journal of Climate ◽

10.1175/2767.1 ◽

2003 ◽

Vol 16 (13) ◽

pp. 2138-2158 ◽

Cited By ~ 95

Author(s):

Gerald A. Meehl ◽

Julie M. Arblaster ◽

Johannes Loschnigg

Keyword(s):

Indian Ocean ◽

Heat Content ◽

Tropical Pacific ◽

Ocean Dynamics ◽

Upper Ocean ◽

Australian Monsoon ◽

Walker Cell ◽

The Indian Ocean ◽

Equatorial Ocean ◽

The Tropical Pacific

Abstract The transitions (from relatively strong to relatively weak monsoon) in the tropospheric biennial oscillation (TBO) occur in northern spring for the south Asian or Indian monsoon and northern fall for the Australian monsoon involving coupled land–atmosphere–ocean processes over a large area of the Indo-Pacific region. Transitions from March–May (MAM) to June–September (JJAS) tend to set the system for the next year, with a transition to the opposite sign the following year. Previous analyses of observed data and GCM sensitivity experiments have demonstrated that the TBO (with roughly a 2–3-yr period) encompasses most ENSO years (with their well-known biennial tendency). In addition, there are other years, including many Indian Ocean dipole (or zonal mode) events, that contribute to biennial transitions. Results presented here from observations for composites of TBO evolution confirm earlier results that the Indian and Pacific SST forcings are more dominant in the TBO than circulation and meridional temperature gradient anomalies over Asia. A fundamental element of the TBO is the large-scale east–west atmospheric circulation (the Walker circulation) that links anomalous convection and precipitation, winds, and ocean dynamics across the Indian and Pacific sectors. This circulation connects convection over the Asian–Australian monsoon regions both to the central and eastern Pacific (the eastern Walker cell), and to the central and western Indian Ocean (the western Walker cell). Analyses of upper-ocean data confirm previous results and show that ENSO El Niño and La Niña events as well as Indian Ocean SST dipole (or zonal mode) events are often large-amplitude excursions of the TBO in the tropical Pacific and Indian Oceans, respectively, associated with anomalous eastern and western Walker cell circulations, coupled ocean dynamics, and upper-ocean temperature and heat content anomalies. Other years with similar but lower-amplitude signals in the tropical Pacific and Indian Oceans also contribute to the TBO. Observed upper-ocean data for the Indian Ocean show that slowly eastward-propagating equatorial ocean heat content anomalies, westward-propagating ocean Rossby waves south of the equator, and anomalous cross-equatorial ocean heat transports contribute to the heat content anomalies in the Indian Ocean and thus to the ocean memory and consequent SST anomalies, which are an essential part of the TBO.

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Spectral signatures of the tropical Pacific dynamics from model and altimetry: A focus on the meso/submesoscale range

10.5194/os-2018-49 ◽

2018 ◽

Author(s):

Michel Tchilibou ◽

Lionel Gourdeau ◽

Rosemary Morrow ◽

Guillaume Serazin ◽

Bughsin Djath ◽

...

Keyword(s):

Internal Waves ◽

Tropical Pacific ◽

Equatorial Region ◽

Internal Tides ◽

Spectral Energy ◽

Instability Waves ◽

Tropical Instability Waves ◽

Geostrophic Turbulence ◽

The Tropics ◽

The Tropical Pacific

Abstract. The processes that contribute to the flat Sea Surface Height (SSH) wavenumber spectral slopes observed in the tropics by satellite altimetry are examined in the tropical Pacific. The tropical dynamics are first investigated with a 1/12° global model. The equatorial region from 10° N–10° S is dominated by Tropical Instability Waves with a peak of energy at 1000 km wavelength, strong anisotropy, and a cascade of energy from 600 km down to smaller scales. The off-equatorial regions from 10–20° latitude are characterized by a narrower mesoscale range, typical of mid latitudes. In the tropics, the spectral taper window and segment lengths need to be adjusted to include these larger energetic scales. The equatorial and off-equatorial regions of the 1/12° model have surface kinetic energy spectra consistent with quasi-geostrophic turbulence. The balanced component of the dynamics slightly flatten the EKE spectra, but modeled SSH wavenumber spectra maintain a steep slope that does not match the observed altimetric spectra. A second analysis is based on 1/36° high-frequency regional simulations in the western tropical Pacific, with and without explicit tides, where we find a strong signature of internal waves and internal tides that act to increase the smaller-scale SSH spectral energy power and flattening the SSH wavenumber spectra, in agreement with the altimetric spectra. The coherent M2 baroclinic tide is the dominant signal at ~ 140 km wavelength. At short scales, wavenumber SSH spectra are dominated by incoherent internal tides and internal waves which extend up to 200 km in wavelength. These incoherent internal waves impact on space scales observed by today's alongtrack altimetric SSH, and also on the future SWOT 2D swath observations, raising the question of altimetric observability of the shorter mesoscale structures in the tropics.

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U.K. HiGEM: The New U.K. High-Resolution Global Environment Model—Model Description and Basic Evaluation

Journal of Climate ◽

10.1175/2008jcli2508.1 ◽

2009 ◽

Vol 22 (8) ◽

pp. 1861-1896 ◽

Cited By ~ 177

Author(s):

L. C. Shaffrey ◽

I. Stevens ◽

W. A. Norton ◽

M. J. Roberts ◽

P. L. Vidale ◽

...

Keyword(s):

High Resolution ◽

Tropical Pacific ◽

Model Description ◽

Small Scale ◽

Environmental Model ◽

Instability Waves ◽

Tropical Instability Waves ◽

Global Environmental ◽

The Impact ◽

The Tropical Pacific

Abstract This article describes the development and evaluation of the U.K.’s new High-Resolution Global Environmental Model (HiGEM), which is based on the latest climate configuration of the Met Office Unified Model, known as the Hadley Centre Global Environmental Model, version 1 (HadGEM1). In HiGEM, the horizontal resolution has been increased to 0.83° latitude × 1.25° longitude for the atmosphere, and 1/3° × 1/3° globally for the ocean. Multidecadal integrations of HiGEM, and the lower-resolution HadGEM, are used to explore the impact of resolution on the fidelity of climate simulations. Generally, SST errors are reduced in HiGEM. Cold SST errors associated with the path of the North Atlantic drift improve, and warm SST errors are reduced in upwelling stratocumulus regions where the simulation of low-level cloud is better at higher resolution. The ocean model in HiGEM allows ocean eddies to be partially resolved, which dramatically improves the representation of sea surface height variability. In the Southern Ocean, most of the heat transports in HiGEM is achieved by resolved eddy motions, which replaces the parameterized eddy heat transport in the lower-resolution model. HiGEM is also able to more realistically simulate small-scale features in the wind stress curl around islands and oceanic SST fronts, which may have implications for oceanic upwelling and ocean biology. Higher resolution in both the atmosphere and the ocean allows coupling to occur on small spatial scales. In particular, the small-scale interaction recently seen in satellite imagery between the atmosphere and tropical instability waves in the tropical Pacific Ocean is realistically captured in HiGEM. Tropical instability waves play a role in improving the simulation of the mean state of the tropical Pacific, which has important implications for climate variability. In particular, all aspects of the simulation of ENSO (spatial patterns, the time scales at which ENSO occurs, and global teleconnections) are much improved in HiGEM.

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Impact of tropical instability waves-induced SST forcing on the atmosphere in the tropical Pacific, evaluated using CAM5.1

Atmospheric Science Letters ◽

10.1002/asl2.488 ◽

2014 ◽

Vol 15 (3) ◽

pp. 186-194 ◽

Cited By ~ 1

Author(s):

Rong-Hua Zhang ◽

Zhongxian Li ◽

Jieshun Zhu ◽

Xianbiao Kang ◽

Jinzhong Min

Keyword(s):

Tropical Pacific ◽

Instability Waves ◽

Tropical Instability Waves ◽

Sst Forcing ◽

The Tropical Pacific

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Atmosphere-ocean dynamics of persistent cold states of the tropical Pacific Ocean

Journal of Climate ◽

10.1175/jcli-d-20-0694.1 ◽

2021 ◽

pp. 1-44

Author(s):

Richard Seager ◽

Naomi Henderson ◽

Mark Cane ◽

Honghai Zhang ◽

Jennifer Nakamura

Keyword(s):

Heat Flux ◽

Pacific Ocean ◽

Wind Stress ◽

Tropical Pacific ◽

Ocean Dynamics ◽

Dynamical Response ◽

Thermocline Depth ◽

Tropical Pacific Ocean ◽

Flux Divergence ◽

The Tropical Pacific

AbstractPersistent multiyear cold states of the tropical Pacific Ocean drive hydroclimate anomalies worldwide, including persistent droughts in the extratropical Americas. Here, the atmosphere and ocean dynamics and thermodynamics of multiyear cold states of the tropical Pacific Ocean are investigated using European Centre for Medium-Range Weather Forecasts reanalyses and simplified models of the ocean and atmosphere. The cold states are maintained by anomalous ocean heat flux divergence and damped by increased surface heat flux from the atmosphere to ocean. The anomalous ocean heat flux divergence is contributed to by both changes in the ocean circulation and thermal structure. The keys are an anomalously shallow thermocline that enhances cooling by upwelling and anomalous westward equatorial currents that enhance cold advection. The thermocline depth anomalies are shown to be a response to equatorial wind stress anomalies. The wind stress anomalies are shown to be a simple dynamical response to equatorial SST anomalies as mediated by precipitation anomalies. The cold states are fundamentally maintained by atmosphere-ocean coupling in the equatorial Pacific. The physical processes that maintain the cold states are well approximated by linear dynamics for ocean and atmosphere and simple thermodynamics.

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Causal dependences between the coupled ocean-atmosphere dynamics over the Tropical Pacific, the North Pacific and the North Atlantic

10.5194/esd-2018-3 ◽

2018 ◽

Author(s):

Stéphane Vannitsem ◽

Pierre Ekelmans

Keyword(s):

North Atlantic ◽

North Pacific ◽

Thermohaline Circulation ◽

Tropical Pacific ◽

Ocean Dynamics ◽

The North ◽

Ocean Atmosphere ◽

The North Atlantic ◽

The North Pacific ◽

The Tropical Pacific

Abstract. The causal dependences between the dynamics of three different coupled ocean-atmosphere basins, The North Atlantic, the North Pacific and the Tropical Pacific region, NINO3.4, have been explored using data from three reanalyses datasets, namely the ORA-20C, the ORAS4 and the ERA-20C. The approach is based on the Convergent Cross Mapping (CCM) developed by Sugihara et al. (2012) that allows for evaluating the dependences between observables beyond the classical teleconnection patterns based on correlations. The use of CCM on these data mostly reveals that (i) the Tropical Pacific (NINO3.4 region) only influences the dynamics of the North Atlantic region through its annual climatological cycle; (ii) the atmosphere over the North Pacific is dynamically forcing the North Atlantic on a monthly basis; (iii) on longer time scales (interannual), the dynamics of the North Pacific and the North Atlantic are influencing each other through the ocean dynamics, suggesting a connection through the thermohaline circulation. These findings shed a new light on the coupling between these three different important regions of the globe. In particular they call for a deep reassessment of the way teleconnections are interpreted, and for a more rigorous way to evaluate causality and dependences between the different components of the climate system.

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Causal dependences between the coupled ocean–atmosphere dynamics over the tropical Pacific, the North Pacific and the North Atlantic

Earth System Dynamics ◽

10.5194/esd-9-1063-2018 ◽

2018 ◽

Vol 9 (3) ◽

pp. 1063-1083 ◽

Cited By ~ 6

Author(s):

Stéphane Vannitsem ◽

Pierre Ekelmans

Keyword(s):

North Atlantic ◽

North Pacific ◽

Thermohaline Circulation ◽

Tropical Pacific ◽

Ocean Dynamics ◽

The North ◽

Ocean Atmosphere ◽

The North Atlantic ◽

The North Pacific ◽

The Tropical Pacific

Abstract. The causal dependences (in a dynamical sense) between the dynamics of three different coupled ocean–atmosphere basins, the North Atlantic, the North Pacific and the tropical Pacific region (Nino3.4), have been explored using data from three reanalysis datasets, namely ORA-20C, ORAS4 and ERA-20C. The approach is based on convergent cross mapping (CCM) developed by Sugihara et al. (2012) that allows for evaluating the dependences between variables beyond the classical teleconnection patterns based on correlations. The use of CCM on these data mostly reveals that (i) the tropical Pacific (Nino3.4 region) only influences the dynamics of the North Atlantic region through its annual climatological cycle; (ii) the atmosphere over the North Pacific is dynamically forcing the North Atlantic on a monthly basis; (iii) on longer timescales (interannual), the dynamics of the North Pacific and the North Atlantic are influencing each other through the ocean dynamics, suggesting a connection through the thermohaline circulation. These findings shed a new light on the coupling between these three different regions of the globe. In particular, they call for a deep reassessment of the way teleconnections are interpreted and for a more rigorous way to evaluate dynamical dependences between the different components of the climate system.

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