scholarly journals Interannual modulation of eddy kinetic energy in the southeast Indian Ocean by Southern Annular Mode

2011 ◽  
Vol 116 (C2) ◽  
Author(s):  
Fan Jia ◽  
Lixin Wu ◽  
Jian Lan ◽  
Bo Qiu
Keyword(s):  
Indian Ocean ◽  
Kinetic Energy ◽  
Southern Annular Mode ◽  
Eddy Kinetic Energy ◽  
Annular Mode

Response of the Southern Ocean to the Southern Annular Mode: Interannual Variability and Multidecadal Trend

2010 ◽  
Vol 40 (7) ◽  
pp. 1659-1668 ◽  
Author(s):  
A. M. Treguier ◽  
J. Le Sommer ◽  
J. M. Molines ◽  
B. de Cuevas
Keyword(s):  
Kinetic Energy ◽  
Southern Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
Meridional Circulation ◽  
Southern Annular Mode ◽  
Eddy Kinetic Energy ◽  
Overturning Circulation ◽  
Annular Mode ◽  
Meridional Overturning

Abstract The authors evaluate the response of the Southern Ocean to the variability and multidecadal trend of the southern annular mode (SAM) from 1972 to 2001 in a global eddy-permitting model of the DRAKKAR project. The transport of the Antarctic Circumpolar Current (ACC) is correlated with the SAM at interannual time scales but exhibits a drift because of the thermodynamic adjustment of the model (the ACC transport decreases because of a low renewal rate of dense waters around Antarctica). The interannual variability of the eddy kinetic energy (EKE) and the ACC transport are uncorrelated, but the EKE decreases like the ACC transport over the three decades, even though meridional eddy fluxes of heat and buoyancy remain stable. The contribution of oceanic eddies to meridional transports is an important issue because a growth of the poleward eddy transport could, in theory, oppose the increase of the mean overturning circulation forced by the SAM. In the authors’ model, the total meridional circulation at 50°S is well correlated with the SAM index (and the Ekman transport) at interannual time scales, and both increase over three decades between 1972 and 2001. However, given the long-term drift, no SAM-linked trend in the eddy contribution to the meridional overturning circulation is detectable. The increase of the meridional overturning is due to the time-mean component and is compensated by an increased buoyancy gain at the surface. The authors emphasize that the meridional circulation does not vary in a simple relationship with the zonal circulation. The model solution points out that the zonal circulation and the eddy kinetic energy are governed by different mechanisms according to the time scale considered (interannual or decadal).

Barotropic and Baroclinic Annular Variability in the Southern Hemisphere

2014 ◽  
Vol 71 (4) ◽  
pp. 1480-1493 ◽  
Author(s):  
David W. J. Thompson ◽  
Jonathan D. Woodworth
Keyword(s):  
Kinetic Energy ◽  
Climate Variability ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Principal Component ◽  
Southern Annular Mode ◽  
Eddy Kinetic Energy ◽  
Propagating Waves ◽  
Vertically Propagating ◽  
High Degree

Abstract The leading patterns of large-scale climate variability in the Southern Hemisphere are examined in the context of extratropical kinetic energy. It is argued that variability in the Southern Hemisphere extratropical flow can be viewed in the context of two distinct and largely independent structures, both of which exhibit a high degree of annularity: 1) a barotropic structure that dominates the variance in the zonal-mean kinetic energy and 2) a baroclinic structure that dominates the variance in the eddy kinetic energy. The former structure corresponds to the southern annular mode (SAM) and has been extensively examined in the literature. The latter structure emerges as the leading principal component time series of eddy kinetic energy and has received seemingly little attention in previous work. The two structures play very different roles in cycling energy through the extratropical troposphere. The SAM is associated primarily with variability in the meridional propagation of wave activity, has a surprisingly weak signature in the eddy fluxes of heat, and can be modeled as Gaussian red noise with an e-folding time scale of approximately 10 days. The baroclinic annular structure is associated primarily with variations in the amplitude of vertically propagating waves, has a very weak signature in the wave fluxes of momentum, and exhibits marked quasi periodicity on time scales of approximately 25–30 days. Implications for large-scale climate variability are discussed.

Baroclinic and Barotropic Annular Variability in the Northern Hemisphere

2015 ◽  
Vol 72 (3) ◽  
pp. 1117-1136 ◽  
Author(s):  
David W. J. Thompson ◽  
Ying Li
Keyword(s):  
Time Series ◽  
Kinetic Energy ◽  
Northern Hemisphere ◽  
Large Scale ◽  
Spectral Power ◽  
Principal Component ◽  
Eddy Kinetic Energy ◽  
Annular Mode ◽  
Teleconnection Patterns ◽  
Mean Kinetic Energy

Abstract Large-scale variability in the Northern Hemisphere (NH) circulation can be viewed in the context of three primary types of structures: 1) teleconnection patterns, 2) a barotropic annular mode, and 3) a baroclinic annular mode. The barotropic annular mode corresponds to the northern annular mode (NAM) and has been examined extensively in previous research. Here the authors examine the spatial structure and time-dependent behavior of the NH baroclinic annular mode (NBAM). The NAM and NBAM have very different signatures in large-scale NH climate variability. The NAM emerges as the leading principal component (PC) time series of the zonal-mean kinetic energy. It dominates the variance in the wave fluxes of momentum, projects weakly onto the eddy kinetic energy and wave fluxes of heat, and can be modeled as Gaussian red noise with a time scale of ~10 days. In contrast, the NBAM emerges as the leading PC time series of the eddy kinetic energy. It is most clearly identified when the planetary-scale waves are filtered from the data, dominates the variance in the synoptic-scale eddy kinetic energy and wave fluxes of heat, and has a relatively weak signature in the zonal-mean kinetic energy and the wave fluxes of momentum. The NBAM is marked by weak but significant enhanced spectral power on time scales of ~20–25 days. The NBAM is remarkably similar to its Southern Hemisphere counterpart despite the pronounced interhemispheric differences in orography and land–sea contrasts.

scholarly journals Seasonal Modulation of Eddy Kinetic Energy and Its Formation Mechanism in the Southeast Indian Ocean

2011 ◽  
Vol 41 (4) ◽  
pp. 657-665 ◽  
Author(s):  
Fan Jia ◽  
Lixin Wu ◽  
Bo Qiu
Keyword(s):  
Indian Ocean ◽  
Kinetic Energy ◽  
Vertical Velocity ◽  
Baroclinic Instability ◽  
Mesoscale Eddy ◽  
Eddy Kinetic Energy ◽  
Velocity Shear ◽  
Austral Spring ◽  
Eddy Activity ◽  
South Indian

Abstract Mesoscale eddy activity in the southeast Indian Ocean (15°–30°S, 60°–110°E) is investigated based on available satellite altimetry observations. The observed sea level anomaly data show that this region is the only eastern basin among the global oceans where strong eddy activity exists. Furthermore, the eddy kinetic energy (EKE) level in this region displays a distinct seasonal cycle with the maximum in austral summer and minimum in austral winter. It is found that this seasonal modulation of EKE is mediated by baroclinic instability associated with the surface-intensified South Indian Countercurrent (SICC) and the underlying South Equatorial Current (SEC) system. In austral spring and summer the enhanced flux forcing of combined meridional Ekman and geostrophic convergence strengthens the upper-ocean meridional temperature gradient, intensifying the SICC front and its vertical velocity shear. Modulation of the vertical velocity shear results in the seasonal changes in the strength of baroclinic instability, leading to the seasonal EKE variations in the southeast Indian Ocean.

scholarly journals Impact of the southern annular mode on extreme changes in indian rainfall during the early 1990s

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Pao-Wei Huang ◽  
Yong-Fu Lin ◽  
Chau-Ron Wu
Keyword(s):  
Indian Ocean ◽  
Southern Oscillation ◽  
Social Systems ◽  
Vertical Motion ◽  
Southern Annular Mode ◽  
Annular Mode ◽  
The Past ◽  
Indian Rainfall ◽  
The Indian Ocean ◽  
Primary Pattern

AbstractThe variability in rainfall amounts in India draws much attention because it strongly influences the country’s ecological and social systems. Indian rainfall is associated with climate factors, including El Niño/Southern Oscillation and the Indian Ocean Dipole. Here we identified the Southern Annular Mode (SAM), the primary pattern of climate variability in the Southern Hemisphere, as the ultimate forcing leading to decadal changes in Indian rainfall. Through statistical analyses using observational data covering the period from 1979 to 2015, we show an increase in the decadal rainfall amount in the early 1990s over the Indian region. Examining atmospheric environmental conditions, we demonstrate that conditions have become more favorable over the past few decades. Specifically, during the positive SAM phase since the early 1990s, changes in the atmospheric fields have evoked anomalous vertical motion over the continent and the Indian Ocean, enhancing the southerly cross-equatorial flow by increased land–sea thermal contrast, thereby increasing decadal rainfall in the region.

Generation and seasonal variability of eddy kinetic energy in the central Indian Ocean

2021 ◽  
Author(s):  
Georgy I. Shapiro ◽  
Jose Maria Gonzalez-Ondina
Keyword(s):  
Indian Ocean ◽  
Kinetic Energy ◽  
Seasonal Variability ◽  
Open Ocean ◽  
Eddy Kinetic Energy ◽  
Horizontal Shear ◽  
Data Set ◽  
Central Indian Ocean ◽  
The Indian Ocean ◽  
Meso Scale

<p>The breakthrough in our knowledge of ocean eddies came with the results of the POLYGON-67 experiment in the central Indian Ocean carried out in January-April 1967 (see Koshlyakov et al, 2016). It was the first direct and unambiguous observation that proved an earlier hypothesis by V. B. Shtockman of the existence of mesoscale eddies in open ocean, not only next to strong jet-stream currents. Now it is well known that the currents in open ocean are almost everywhere dominated by meso-scale eddies also known as synoptic eddies (Robinson, 1983). POLYGON-67 experiment covered a rectangle bounded by 10-15°N and 63-66.5°E. The purpose of this work is to analyse the seasonal variability of meso-scale eddy activity in the area covered by POLYGON-67 using a modern and comprehensive data set produced by an operational data assimilation model over a period from 1998 to 2017.</p><p>The 20-year long eddy resolving reanalysis of velocity fields in the Indian Ocean allows the study of seasonal variability, dynamics and generating mechanisms of eddy kinetic energy (EKE) in the tropical Indian Ocean, including the area covered by the original survey of POLYGON-67. In contrast to some other areas of the World Ocean, the EKE seasonality shows two maxima, the large one in April and the secondary one in October. The main mechanism of EKE generation is the barotropic instability which is evidenced by high correlation between EKE and enstrophy of large-scale currents, representing the strength of horizontal shear. It is found that the main contributor to the EKE variability within POLYGON-67 area is the advection of EKE across the boundaries during January-October, while the local generation has a comparable magnitude during August-December. The direction and strength of surface currents is consistent with the monsoon wind pattern in the area.</p><p>References</p><p>Koshlyakov, M.N., Morozov, E.G., and Neiman, V.G., 2016. Historical findings of the Russian physical oceanographers in the Indian Ocean. Geoscience Letters, 3:19; doi:10.1186/s40562-016-0051-6</p><p>Robinson, A.R. (Ed), 1983. Eddies in Marine Science. Springer, ISBN 978-3-642-69003-7, 612p.</p>

Indian Ocean Subtropical Underwater and the Interannual Variability in its Annual Subduction Rate Associated with the Southern Annular Mode

2022 ◽  
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Mixed Layer Depth ◽  
Potential Temperature ◽  
Southern Annular Mode ◽  
Sea Surface Salinity ◽  
Annular Mode ◽  
South Indian ◽  
Subtropical Underwater ◽  
Subduction Rate

Abstract In this study, the Indian Ocean subtropical underwater (IOSTUW) was investigated as a subsurface salinity maximum using Argo floats (2000–2020) for the first time. It has mean salinity, potential temperature and potential density values of 35.54 ± 0.29 psu, 17.91 ± 1.66 °C, and 25.56 ± 0.35 kg m−3, respectively, and mainly extends between 10°S and 30°S along the isopycnal surface in the subtropical south Indian Ocean. The annual subduction rate of the IOSTUW during the period of 2004-2019 was investigated based on a gridded Argo dataset. The results revealed a mean value of 4.39 Sv (1 Sv=106 m3s−1) with an interannual variability that is closely related to the Southern Annular Mode (SAM). The variation in the annual subduction rate of the IOSTUW is dominated by the lateral induction term, which largely depends on the winter mixed layer depth (MLD) in the sea surface salinity (SSS) maximum region. The anomalies of winter MLD is primarily determined by SAM-related air-sea heat flux and zonal wind anomalies through modulation of the buoyancy. As a result, the annual subduction rate of the IOSTUW generally increased when the SAM index showed negative anomalies and decreased when the SAM index showed positive anomalies. Exceptional cases occurred when the wind anomaly within the SSS maximum region was weak or was dominated by its meridional component.

Impact of the El Niño–Southern Oscillation, Indian Ocean Dipole, and Southern Annular Mode on Daily to Subdaily Rainfall Characteristics in East Australia

2012 ◽  
Vol 140 (5) ◽  
pp. 1665-1682 ◽  
Author(s):  
Alexander Pui ◽  
Ashish Sharma ◽  
Agus Santoso ◽  
Seth Westra
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
El Nino Southern Oscillation ◽  
Rainfall Events ◽  
Annular Mode ◽  
Climate Modes

Abstract The relationship between seasonal aggregate rainfall and large-scale climate modes, particularly the El Niño–Southern Oscillation (ENSO), has been the subject of a significant and ongoing research effort. However, relatively little is known about how the character of individual rainfall events varies as a function of each of these climate modes. This study investigates the change in rainfall occurrence, intensity, and storm interevent time at both daily and subdaily time scales in east Australia, as a function of indices for ENSO, the Indian Ocean dipole (IOD), and the southern annular mode (SAM), with a focus on the cool season months. Long-record datasets have been used to sample a large variety of climate events for better statistical significance. Results using both the daily and subdaily rainfall datasets consistently show that it is the occurrence of rainfall events, rather than the average intensity of rainfall during the events, which is most strongly influenced by each of the climate modes. This is shown to be most likely associated with changes to the time between wet spells. Furthermore, it is found that despite the recent attention in the research literature on other climate modes, ENSO remains the leading driver of rainfall variability over east Australia, particularly farther inland during the winter and spring seasons. These results have important implications for how water resources are managed, as well as how the implications of large-scale climate modes are included in rainfall models to best capture interannual and longer-scale variability.

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