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

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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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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An Empirical Model for Surface Wind Stress Response to SST Forcing Induced by Tropical Instability Waves (TIWs) in the Eastern Equatorial Pacific

Monthly Weather Review ◽

10.1175/2008mwr2712.1 ◽

2009 ◽

Vol 137 (6) ◽

pp. 2021-2046 ◽

Cited By ~ 15

Author(s):

Rong-Hua Zhang ◽

Antonio J. Busalacchi

Keyword(s):

Wind Stress ◽

Empirical Model ◽

Stress Responses ◽

Large Scale ◽

Climate Models ◽

Surface Wind ◽

Microwave Remote Sensing ◽

Instability Waves ◽

Tropical Instability Waves ◽

Sst Forcing

Abstract High-resolution space-based observations reveal significant two-way air–sea interactions associated with tropical instability waves (TIWs); their roles in budgets of heat, salt, momentum, and biogeochemical fields in the tropical oceans have been recently demonstrated. However, dynamical model-based simulations of the atmospheric response to TIW-induced sea surface temperature (SSTTIW) perturbations remain a great challenge because of the limitation in spatial resolution and realistic representations of the related processes in the atmospheric planetary boundary layer (PBL) and their interactions with the overlying free troposphere. Using microwave remote sensing data, an empirical model is derived to depict wind stress perturbations induced by TIW-related SST forcing in the eastern tropical Pacific Ocean. Wind data are based on space–time blending of Quick Scatterometer (QuikSCAT) Direction Interval Retrieval with Thresholded Nudging (DIRTH) satellite observations and NCEP analysis fields; SST data are from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). These daily data are first subject to a spatial filter of 12° moving average in the zonal direction to extract TIW-related wind stress (τTIW) and SSTTIW perturbations. A combined singular value decomposition (SVD) analysis is then applied to these zonal high-pass-filtered τTIW and SSTTIW fields. It is demonstrated that the SVD-based analysis technique can effectively extract TIW-induced covariability patterns in the atmosphere and ocean, acting as a filter by passing wind signals that are directly related with the SSTTIW forcing over the TIW active regions. As a result, the empirical model can well represent TIW-induced wind stress responses as revealed directly from satellite measurements (e.g., the structure and phase), but the amplitude can be underestimated significantly. Validation and sensitivity experiments are performed to illustrate the robustness of the empirical τTIW model. Further applications are discussed for taking into account the TIW-induced wind responses and feedback effects that are missing in large-scale climate models and atmospheric reanalysis data, as well as for uncoupled ocean and coupled mesoscale and large-scale air–sea modeling studies.

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Eddies and Tropical Instability Waves in the eastern tropical Pacific: A review

Progress In Oceanography ◽

10.1016/j.pocean.2006.03.010 ◽

2006 ◽

Vol 69 (2-4) ◽

pp. 218-238 ◽

Cited By ~ 116

Author(s):

Cynthia S. Willett ◽

Robert R. Leben ◽

Miguel F. Lavín

Keyword(s):

Tropical Pacific ◽

Eastern Tropical Pacific ◽

Instability Waves ◽

Tropical Instability Waves

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

Journal of Geophysical Research Atmospheres ◽

10.1029/98jc01684 ◽

1998 ◽

Vol 103 (C9) ◽

pp. 18649-18663 ◽

Cited By ~ 5

Author(s):

Sean P. Lawrence ◽

Myles R. Allen ◽

David L. T. Anderson ◽

David T. Llewellyn-Jones

Keyword(s):

Tropical Pacific ◽

Ocean Dynamics ◽

Instability Waves ◽

Subsurface Ocean ◽

The Tropical Pacific

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

Ocean Science ◽

10.5194/os-14-1283-2018 ◽

2018 ◽

Vol 14 (5) ◽

pp. 1283-1301 ◽

Cited By ~ 6

Author(s):

Michel Tchilibou ◽

Lionel Gourdeau ◽

Rosemary Morrow ◽

Guillaume Serazin ◽

Bughsin Djath ◽

...

Keyword(s):

Internal Waves ◽

Tropical Pacific ◽

Equatorial Region ◽

Internal Tides ◽

Spectral Energy ◽

Tropical Instability Waves ◽

Geostrophic Turbulence ◽

Ocean Topography ◽

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 to 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 to 20∘ latitude are characterized by a narrower mesoscale range, typical of midlatitudes. 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 flattens 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 flatten 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 space scales observed by today's along-track altimetric SSH, and also on the future Surface Water Ocean Topography (SWOT) mission 2-D swath observations, raising the question of altimetric observability of the shorter mesoscale structures in the tropics.

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Temperature Advection by Tropical Instability Waves

Journal of Physical Oceanography ◽

10.1175/jpo2870.1 ◽

2006 ◽

Vol 36 (4) ◽

pp. 592-605 ◽

Cited By ~ 83

Author(s):

Markus Jochum ◽

Raghu Murtugudde

Keyword(s):

Mixed Layer ◽

Heat Budget ◽

Basic Mechanism ◽

Tropical Pacific Ocean ◽

Instability Waves ◽

Tropical Instability Waves ◽

Temperature Advection ◽

Mixed Layer Heat Budget ◽

Oscillatory Temperature ◽

The Tropical Pacific

Abstract A numerical model of the tropical Pacific Ocean is used to investigate the processes that cause the horizontal temperature advection of tropical instability waves (TIWs). It is found that their temperature advection cannot be explained by the processes on which the mixing length paradigm is based. Horizontal mixing of temperature across the equatorial SST front does happen, but it is small relative to the “oscillatory” temperature advection of TIWs. The basic mechanism is that TIWs move water back and forth across a patch of large vertical entrainment. Outside this patch, the atmosphere heats the water and this heat is then transferred into the thermocline inside the patch. These patches of strong localized entrainment are due to equatorial Ekman divergence and due to thinning of the mixed layer in the TIW cyclones. The latter process is responsible for the zonal temperature advection, which is as large as the meridional temperature advection but has not yet been observed. Thus, in the previous observational literature the TIW contribution to the mixed layer heat budget may have been underestimated significantly.

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On the Role of SST Forcing in the 2011 and 2012 Extreme U.S. Heat and Drought: A Study in Contrasts

Journal of Hydrometeorology ◽

10.1175/jhm-d-13-069.1 ◽

2014 ◽

Vol 15 (3) ◽

pp. 1255-1273 ◽

Cited By ~ 37

Author(s):

Hailan Wang ◽

Siegfried Schubert ◽

Randal Koster ◽

Yoo-Geun Ham ◽

Max Suarez

Keyword(s):

United States ◽

General Circulation ◽

Rapid Development ◽

The United States ◽

Tropical Pacific ◽

Extreme Heat ◽

The Pacific ◽

Sst Forcing ◽

The Tropical Pacific

Abstract This study compares the extreme heat and drought that developed over the United States in 2011 and 2012 with a focus on the role of sea surface temperature (SST) forcing. Experiments with the NASA Goddard Earth Observing System, version 5 (GEOS-5), atmospheric general circulation model show that the winter/spring response over the United States to the Pacific SST is remarkably similar for the two years despite substantial differences in the tropical Pacific SST. As such, the pronounced winter and early spring temperature differences between the two years (warmth confined to the south in 2011 and covering much of the continent in 2012) primarily reflect differences in the contributions from the Atlantic and Indian Oceans, with both acting to cool the east and upper Midwest during 2011, while during 2012 the Indian Ocean reinforced the Pacific-driven, continental-wide warming and the Atlantic played a less important role. During late spring and summer of 2011, the tropical Pacific SST forced a continued warming and drying over the southern United States, though considerably weaker than observed. Nevertheless, the observed 2011 anomalies fall well within the model’s intraensemble spread. In contrast, the observed rapid development of intense heat and drying over the central United States during June and July 2012 falls on the margins of the model’s intraensemble spread, with the response to the SST giving little indication that 2012 would produce record-breaking precipitation deficits and heat. A diagnosis of the 2012 observed circulation anomalies shows that the most extreme heat and drought was tied to the development of a stationary Rossby wave and an associated anomalous upper-tropospheric high maintained by weather transients.

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Effect of tropical instability waves on the eastern tropical Pacific basin: damping of TIWs in a high-resolution ocean circulation model

10.5194/egusphere-egu21-7802 ◽

2021 ◽

Author(s):

Lisa Maillard ◽

Julien Boucharel ◽

Lionel Renault

Keyword(s):

High Resolution ◽

Ocean Circulation ◽

Heat Budget ◽

Tropical Pacific ◽

Eastern Tropical Pacific ◽

Instability Waves ◽

Tropical Instability Waves ◽

Equatorial Wave ◽

Modelling Studies ◽

The Impact

<p>Tropical instability waves (TIWs) are oceanic cusp-like features propagating westward along the northern front of the tropical pacific cold tongue. Observational and modelling studies suggest that TIWs may have a large impact on the eastern tropical Pacific background state from seasonal to interannual time-scales, through heat advection and mixing. However, observations are coarse or limited to surface data, and modelling studies are often based on the comparison of low- vs. high-resolution simulations. In this study, we perform a set of regional high-resolution ocean simulations (CROCO 1/12&#176;) in which we strongly damp (NUDG-RUN) or not (CTRL-RUN) TIWs propagation, by nudging the mixed layer meridional current velocities in the TIWs active region toward their climatological values. We first show that this approach do not alter the model internal physics, in particular related to the equatorial wave dynamics. The impact of TIWs on the oceanic mean state (zonal current and heat budget) is then assessed by comparing CTRL-RUN to NUDG-RUN. This approach allows quantifying for the first time the rectified effect of TIWs without degrading the model horizontal resolution, and may lead to a better understanding of ENSO asymmetry and the development of accurate TIWs parameterizations in Earth system models.</p>

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