Variability of Intraseasonal Kelvin Waves in the Equatorial Pacific Ocean

2008 ◽  
Vol 38 (5) ◽  
pp. 921-944 ◽  
Author(s):  
Toshiaki Shinoda ◽  
Paul E. Roundy ◽  
George N. Kiladis
Keyword(s):  
Wind Stress ◽  
General Circulation ◽  
Phase Speed ◽  
Circulation Model ◽  
Kelvin Waves ◽  
Upper Ocean ◽  
Equatorial Pacific Ocean ◽  
Model Experiments ◽  
Stress Changes ◽  
Background State

Abstract Previous observational work has demonstrated that the phase speed of oceanic equatorial Kelvin waves forced by the Madden–Julian oscillation (MJO) appears to vary substantially. Processes that are responsible for systematic changes in the phase speed of these waves are examined using an ocean general circulation model. The model was integrated for 26 yr with daily wind stress derived from the NCEP–NCAR reanalysis. The model is able to reproduce observed systematic changes of Kelvin wave phase speed reasonably well, providing a tool for the analysis of their dynamics. The relative importance of the upper ocean background state and atmospheric forcing for phase speed changes is determined based on a series of model experiments with various surface forcings. Systematic changes in phase speed are evident in all model experiments that have different slowly varying basic states, showing that variations of the upper ocean background state are not the primary cause of the changes. The model experiments that include and exclude intraseasonal components of wind stress in the eastern Pacific demonstrate that wind stress changes to the east of the date line can significantly alter the speed of Kelvin waves initially generated over the western Pacific, which often results in a phase propagation faster than the free wave speed. These faster waves contribute to the systematic changes of phase speed evident in observations. Similar results are also obtained using a linear stratified model, eliminating nonlinearity as a possible cause of the phase speed changes.

Seasonal Variation of the Indonesian Throughflow in Makassar Strait

2012 ◽  
Vol 42 (7) ◽  
pp. 1099-1123 ◽  
Author(s):  
Toshiaki Shinoda ◽  
Weiqing Han ◽  
E. Joseph Metzger ◽  
Harley E. Hurlburt
Keyword(s):  
Seasonal Variation ◽  
Indian Ocean ◽  
Wind Stress ◽  
General Circulation ◽  
Ocean Currents ◽  
Upper Ocean ◽  
Indonesian Throughflow ◽  
Subsequent Recovery ◽  
Model Experiments ◽  
The Pacific

Abstract The seasonal variation of Indonesian Throughflow (ITF) transport is investigated using ocean general circulation model experiments with the Hybrid Coordinate Ocean Model (HYCOM). Twenty-eight years (1981–2008) of ⅓° Indo-Pacific basin HYCOM simulations and three years (2004–06) from a global HYCOM simulation are analyzed. Both models are able to simulate the seasonal variation of upper-ocean currents and the total transport through Makassar Strait measured by International Nusantara Stratification and Transport (INSTANT) moorings reasonably well. The annual cycle of upper-ocean currents is then calculated from the Indo-Pacific HYCOM simulation. The reduction of southward currents at Makassar Strait during April–May and October–November is evident, consistent with the INSTANT observations. Analysis of the upper-ocean currents suggests that the reduction in ITF transport during April–May and October–November results from the wind variation in the tropical Indian Ocean through the generation of a Wyrtki jet and the propagation of coastal Kelvin waves, while the subsequent recovery during January–March originates from upper-ocean variability associated with annual Rossby waves in the Pacific that are enhanced by western Pacific winds. These processes are also found in the global HYCOM simulation during the period of the INSTANT observations. The model experiments forced with annual-mean climatological wind stress in the Pacific and 3-day mean wind stress in the Indian Ocean show the reduction of southward currents at Makassar Strait during October–November but no subsequent recovery during January–March, confirming the relative importance of wind variations in the Pacific and Indian Oceans for the ITF transport in each season.

scholarly journals Buffering Effect and Its Related Ocean Dynamics in the Indonesian Throughflow Region*

2008 ◽  
Vol 38 (2) ◽  
pp. 503-516 ◽  
Author(s):  
Tangdong Qu ◽  
Yan Du ◽  
Julian P. McCreary ◽  
Gary Meyers ◽  
Toshio Yamagata
Keyword(s):  
General Circulation ◽  
Thermal Structure ◽  
Circulation Model ◽  
Equatorial Indian Ocean ◽  
Kelvin Waves ◽  
Ocean Dynamics ◽  
Upper Ocean ◽  
Energy Propagation ◽  
Buffering Effect ◽  
Indonesian Seas

Abstract Analysis of results from a high-resolution general circulation model confirms the existence of a “buffering” effect in the Indo-Australian Basin in which the upper ocean receives an excess of water from February to June and releases it during the rest of the year. A similar, but significantly weaker, phenomenon exists in the Indonesian seas. The buffering mostly results from geostrophic convergence, with the directly wind-driven Ekman divergence playing a role only within the Indonesian seas. Upward phase propagation, or equivalently, downward energy propagation, is revealed, indicating the prominent influence of remotely forced Kelvin waves originating in the equatorial Indian Ocean. The model demonstrates that these Kelvin waves penetrate as far eastward as the Ombai Strait along the southern Indonesian coastal waveguide, and that they have a notable influence on the upper-ocean convergence/divergence in the Indo-Australian Basin. Some of the semiannual signal turns northward through the Lombok and Ombai Straits to impact the circulation and thermal structure within the Indonesian seas.

scholarly journals A Wake due to the Maldives in the Eastward Wyrtki Jet

2015 ◽  
Vol 45 (7) ◽  
pp. 1858-1876 ◽  
Author(s):  
Motoki Nagura ◽  
Yukio Masumoto
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Zonal Flow ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Wind Forcing ◽  
Equatorial Pacific Ocean ◽  
Layer Model ◽  
Model Experiments ◽  
Budget Analysis

AbstractA wake due to islands in background zonal flow has been observed in the equatorial Pacific Ocean. This study detects and examines a wake due to the Maldives in the eastward Wyrtki jet in the Indian Ocean. Observations by acoustic Doppler current profilers deployed east of the Maldives show semiannual variability in cross-equatorial currents, which cannot be explained by annual monsoonal wind forcing. Output from a high-resolution ocean general circulation model (OGCM) shows that the semiannual current variability is a part of a stationary wavelike pattern of meridional currents, which appears east of the Maldives concurrently with the eastward Wyrtki jet. Idealized numerical experiments are conducted using a 1.5-layer model, in which an equatorial jet driven by wind forcing or steady inflow impinges islands that are similar to the Maldives in shape. The results show the meandering of the equatorial eastward jet east of the model islands, and the resulting cross-equatorial currents have a similar pattern compared to those in the OGCM simulation. The momentum budget analysis obtained from the OGCM simulation and the layer model experiments shows a significant contribution of momentum advection to the generation of the wake. Also, the layer model experiments exhibit that the wake is essentially stationary; its zonal wavelength becomes larger when the eastward jet is stronger, and the wake is absent when the equatorial jet is westward. The similarity of the wake in the equatorial jet to stationary damped Rossby waves in the quasigeostrophic barotropic ocean model is discussed.

scholarly journals Influence of the sudden stratospheric warming on quasi-2-day waves

2016 ◽  
Vol 16 (8) ◽  
pp. 4885-4896 ◽  
Author(s):  
Sheng-Yang Gu ◽  
Han-Li Liu ◽  
Xiankang Dou ◽  
Tao Li
Keyword(s):  
General Circulation ◽  
Phase Speed ◽  
Circulation Model ◽  
Meridional Wind ◽  
Equatorial Region ◽  
Wave Number ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Middle Latitudes ◽  
Zonal Wave Number

Abstract. The influence of the sudden stratospheric warming (SSW) on a quasi-2-day wave (QTDW) with westward zonal wave number 3 (W3) is investigated using the Thermosphere–Ionosphere–Mesosphere Electrodynamics General Circulation Model (TIME-GCM). The summer easterly jet below 90 km is strengthened during an SSW, which results in a larger refractive index and thus more favorable conditions for the propagation of W3. In the winter hemisphere, the Eliassen–Palm (EP) flux diagnostics indicate that the strong instabilities at middle and high latitudes in the mesopause region are important for the amplification of W3, which is weakened during SSW periods due to the deceleration or even reversal of the winter westerly winds. Nonlinear interactions between the W3 and the wave number 1 stationary planetary wave produce QTDW with westward zonal wave number 2 (W2). The meridional wind perturbations of the W2 peak in the equatorial region, while the zonal wind and temperature components maximize at middle latitudes. The EP flux diagnostics indicate that the W2 is capable of propagating upward in both winter and summer hemispheres, whereas the propagation of W3 is mostly confined to the summer hemisphere. This characteristic is likely due to the fact that the phase speed of W2 is larger, and therefore its waveguide has a broader latitudinal extension. The larger phase speed also makes W2 less vulnerable to dissipation and critical layer filtering by the background wind when propagating upward.

scholarly journals Argon as a Tracer of Cross-Isopycnal Mixing in the Thermocline

2006 ◽  
Vol 36 (11) ◽  
pp. 2090-2105 ◽  
Author(s):  
Cara C. Henning ◽  
David Archer ◽  
Inez Fung
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Vertical Mixing ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Global Ocean ◽  
Equatorial Pacific Ocean ◽  
Subsurface Waters ◽  
Different Temperatures ◽  
Ocean Gyre

Abstract Noble gases such as argon are unaffected by chemical reactions in the ocean interior, but a number of physical mechanisms can lead to measurable sea level atmospheric disequilibrium in subsurface waters of the ocean. One such mechanism is the mixing of waters of different temperatures, which can lead to supersaturation in the ocean interior. The authors simulate the supersaturation mixing signature in the thermocline in a global ocean general circulation model, Parallel Ocean Program model, version 1.4 (POP 1.4). In contrast to existing mixing diagnostics such as dye tracers or microstructure measurements, which yield the local, recent rate of diabatic mixing, argon disequilibrium traces an integrated lifetime history of subsurface mixing. A theoretical model of the subtropical Atlantic Ocean gyre is built, based on the competing time scales of horizontal and vertical mixing, that agrees well with the full general circulation model argon supersaturation gradient in the thermocline. These results suggest that gyre-scale argon data from the real ocean could be similarly interpreted. The variation of the argon supersaturation with diffusivity in the equatorial Pacific Ocean is also investigated.

scholarly journals Variability of the Stratospheric Quasi-Biennial Oscillation and Its Wave Forcing Simulated in the Beijing Climate Center Atmospheric General Circulation Model

2019 ◽  
Vol 77 (1) ◽  
pp. 149-165 ◽  
Author(s):  
Yixiong Lu ◽  
Tongwen Wu ◽  
Weihua Jie ◽  
Adam A. Scaife ◽  
Martin B. Andrews ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
General Circulation Models ◽  
Kelvin Waves ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Atmospheric General Circulation ◽  
Biennial Oscillation

Abstract It is well known that the stratospheric quasi-biennial oscillation (QBO) is forced by equatorial waves with different horizontal/vertical scales, including Kelvin waves, mixed Rossby–gravity (MRG) waves, inertial gravity waves (GWs), and mesoscale GWs, but the relative contribution of each wave is currently not very clear. Proper representation of these waves is critical to the simulation of the QBO in general circulation models (GCMs). In this study, the vertical resolution in the Beijing Climate Center Atmospheric General Circulation Model (BCC-AGCM) is increased to better represent large-scale waves, and a mesoscale GW parameterization scheme, which is coupled to the convective sources, is implemented to provide unresolved wave forcing of the QBO. Results show that BCC-AGCM can spontaneously generate the QBO with realistic periods, amplitudes, and asymmetric features between westerly and easterly phases. There are significant spatiotemporal variations of parameterized convective GWs, largely contributing to a great degree of variability in the simulated QBO. In the eastward wind shear of the QBO at 20 hPa, forcing provided by resolved waves is 0.1–0.2 m s−1 day−1 and forcing provided by parameterized GWs is ~0.15 m s−1 day−1. On the other hand, westward forcings by resolved waves and parameterized GWs are ~0.1 and 0.4–0.5 m s−1 day−1, respectively. It is inferred that the eastward forcing of the QBO is provided by both Kelvin waves and mesoscale convective GWs, whereas the westward forcing is largely provided by mesoscale GWs. MRG waves barely contribute to the formation of the QBO in the model.

scholarly journals Past monsoons : A review of proxy data and modelling

MAUSAM ◽  
2021 ◽  
Vol 52 (1) ◽  
pp. 275-284
Author(s):  
D. Jagadheesha ◽  
R. Ramesh
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Northern Africa ◽  
Surface Boundary ◽  
Equatorial Pacific Ocean ◽  
Middle Holocene ◽  
Modelling Studies ◽  
Monsoon Strength ◽  
Early And Middle Holocene

Recent modelling studies have given insight into the role of internal feedback processes among components of the climate system on the evolution of monsoon strength since the Last Glacial Maximum (21,000 years ago). Here we present an overview of these modelling studies related to the summer monsoon over India and northern Africa. These studies indicate that the seasonal insolation changes alone do not explain the observed extent of hydrological changes during the early and middle Holocene over northern Africa. To simulate the extent of observed changes during this period incorporation of vegetation as an active component in climate models appears to be necessary. Over the Indian region, model results show that precipitation-soil moisture feedbacks play an important role in determining the response of the monsoon to changes in insolation and glacial-age surface boundary conditions. Indian monsoon strength from  proxy records during the early and middle. Holocene have also been used in conjunction with coupled ocean atmosphere general circulation model experiments to refute the suggestion that semi-permanent warm surface conditions prevailed over equatorial Pacific ocean from 11 to 5ka.

scholarly journals On the presence of equatorial waves in the lower stratosphere of a general circulation model

2013 ◽  
Vol 13 (8) ◽  
pp. 22607-22637 ◽  
Author(s):  
P. Maury ◽  
F. Lott
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Lower Stratosphere ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Kelvin Waves ◽  
Flux Analysis ◽  
Equatorial Waves ◽  
Quasi Biennial Oscillation ◽  
The Waves

Abstract. To challenge the hypothesis that equatorial waves in the lower stratosphere are essentially forced by convection, we use the LMDz atmospheric model extended to the stratosphere and compare two versions having very different convection schemes but no quasi biennial oscillation (QBO). The two versions have realistic time mean precipitation climatologies but very different precipitation variabilities. Despite these differences, the equatorial stratospheric Kelvin waves at 50 hPa are almost identical in the two versions and quite realistic. The Rossby-gravity waves are also very close but significantly weaker than in observations. We demonstrate that this bias on the Rossby-gravity waves is essentially due to a dynamical filtering occurring because the model zonal wind is systematically westward: during a westward phase of the QBO, the Rossby-gravity waves in ERA-Interim compare well with those in the model. These results suggest that in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering and the waves are produced by other sources than equatorial convection. For the Kelvin waves, this last point is illustrated by an Eliassen and Palm flux analysis, showing that in the model they come more from the subtropics and mid-latitude regions whereas in the ERA-Interim reanalysis the sources are more equatorial. We also show that non-equatorial sources are significant in reanalysis data, and we consider the case of the Rossby-gravity waves. We identify situations in the reanalysis where here are large Rossby-gravity waves in the middle stratosphere, and for dates when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a "stratospheric reloading".

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