scholarly journals Mechanisms of Mixed-Layer Salinity Seasonal Variability in the Indian Ocean

2018 ◽  
Vol 123 (1) ◽  
pp. 466-496 ◽  
Author(s):  
Julia Köhler ◽  
Nuno Serra ◽  
Frank O. Bryan ◽  
Benjamin K. Johnson ◽  
Detlef Stammer
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Seasonal Variability ◽  
The Indian Ocean

Variability of Mixed-Layer Heights over the Indian Ocean and Central Arabian Sea during INDOEX, IFP-99

2003 ◽  
Vol 107 (3) ◽  
pp. 683-695 ◽  
Author(s):  
D. Bala Subrahamanyam ◽  
Radhika Ramachandran ◽  
K. Sen Gupta ◽  
Tuhin K. Mandal
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Arabian Sea ◽  
The Indian Ocean

scholarly journals Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian Sea and the Indian Ocean during pre-INDOEX and INDOEX-FFP campaigns

2004 ◽  
Vol 22 (8) ◽  
pp. 2679-2691 ◽  
Author(s):  
M. V. Ramana ◽  
P. Krishnan ◽  
S. Muraleedharan Nair ◽  
P. K. Kunhikrishnan
Keyword(s):  
Boundary Layer ◽  
Indian Ocean ◽  
Atmospheric Boundary Layer ◽  
Mixed Layer ◽  
Arabian Sea ◽  
Trade Wind ◽  
Back Trajectory ◽  
Spatial And Temporal Variability ◽  
Air Mass ◽  
The Indian Ocean

Abstract. Spatial and temporal variability of the Marine Atmospheric Boundary Layer (MABL) height for the Indian Ocean Experiment (INDOEX) study period are examined using the data collected through Cross-chained LORAN (Long-Range Aid to Navigation) Atmospheric Sounding System (CLASS) launchings during the Northern Hemispheric winter monsoon period. This paper reports the results of the analyses of the data collected during the pre-INDOEX (1997) and the INDOEX-First Field Phase (FFP; 1998) in the latitude range 14°N to 20°S over the Arabian Sea and the Indian Ocean. Mixed layer heights are derived from thermodynamic profiles and they indicated the variability of heights ranging from 400m to 1100m during daytime depending upon the location. Mixed layer heights over the Indian Ocean are slightly higher during the INDOEX-FFP than the pre-INDOEX due to anomalous conditions prevailing during the INDOEX-FFP. The trade wind inversion height varied from 2.3km to 4.5km during the pre-INDOEX and from 0.4km to 2.5km during the INDOEX-FFP. Elevated plumes of polluted air (lofted aerosol plumes) above the marine boundary layer are observed from thermodynamic profiles of the lower troposphere during the INDOEX-FFP. These elevated plumes are examined using 5-day back trajectory analysis and show that one group of air mass travelled a long way from Saudi Arabia and Iran/Iraq through India before reaching the location of measurement, while the other air mass originates from India and the Bay of Bengal.

scholarly journals Asymmetry of the Indian Ocean Dipole. Part I: Observational Analysis

2008 ◽  
Vol 21 (18) ◽  
pp. 4834-4848 ◽  
Author(s):  
Chi-Cherng Hong ◽  
Tim Li ◽  
LinHo ◽  
Jong-Seong Kug
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Indian Ocean Dipole ◽  
Heat Budget ◽  
Mature Phase ◽  
Budget Analysis ◽  
Nonlinear Advection ◽  
Negative Skewness ◽  
The Indian Ocean ◽  
The Asymmetry

The physical mechanism for the amplitude asymmetry of SST anomalies (SSTA) between the positive and negative phases of the Indian Ocean dipole (IOD) is investigated, using Simple Ocean Data Assimilation (SODA) and NCAR–NCEP data. It is found that a strong negative skewness appears in the IOD east pole (IODE) in the mature phase [September–November (SON)], while the skewness in the IOD west pole is insignificant. Thus, the IOD asymmetry is primarily caused by the negative skewness in IODE. A mixed-layer heat budget analysis indicates that the following two air–sea feedback processes are responsible for the negative skewness. The first is attributed to the asymmetry of the wind stress–ocean advection–SST feedback. During the IOD developing stage [June–September (JJAS)], the ocean linear advection tends to enhance the mixed-layer temperature tendency, while nonlinear advection tends to cool the ocean in both the positive and negative events, thus contributing to the negative skewness in IODE. The second process is attributed to the asymmetry of the SST–cloud–radiation (SCR) feedback. For a positive IODE, the negative SCR feedback continues with the increase of warm SSTA. For a negative IODE, the same negative SCR feedback works when the amplitude of SSTA is small. After reaching a critical value, the cold SSTA may completely suppress the mean convection and lead to cloud free conditions; a further drop of the cold SSTA does not lead to additional thermal damping so that the cold SSTA may grow faster. A wind–evaporation–SST feedback may further amplify the asymmetry induced by the aforementioned nonlinear advection and SCR feedback processes.

Drivers of oceanic exchange through the Indonesian Throughflow since the late 1800s – a synthesis of coral δ18O and high-resolution ocean models

2020 ◽  
Author(s):  
Sujata Murty ◽  
Caroline Ummenhofer ◽  
Markus Scheinert ◽  
Erik Behrens ◽  
Arne Biastoch ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Heat Content ◽  
Phase Changes ◽  
Boreal Winter ◽  
Indonesian Throughflow ◽  
Layer Depth ◽  
Ocean Variability ◽  
The Indian Ocean

<p>The Indonesian Throughflow (ITF) serves as an important oceanic teleconnection for Indo-Pacific climate, altering heat and buoyancy transport from the Pacific to the Indian Ocean. Equatorial Pacific wind forcing transmitted through the ITF impacts interannual to interdecadal Indian Ocean thermocline depth and heat content, with implications for preconditioning Indian Ocean Dipole events. Yet the modulation of Indian Ocean thermal properties at seasonal timescales is still poorly understood. Here we synthesize coral δ<sup>18</sup>O records, instrumental indices (El Niño Southern Oscillation (ENSO), Asian Monsoon), and simulated ocean variability (sea surface salinity (SSS) and temperature (SST), heat content, mixed layer depth) from state-of-the-art NEMO ocean model hindcasts to explore drivers of seasonal to multi-decadal variability. All coral sites are located within main ITF pathways and are influenced by monsoon-driven, buoyant South China Sea (SCS) surface waters during boreal winter that obstruct surface ITF flow and reduce heat transport to the Indian Ocean. Makassar and Lombok Strait coral δ<sup>18</sup>O co-varies with simulated SSS, subsurface heat content anomalies (50-350m) and mixed layer depth at the coral sites and in the eastern Indian Ocean. At decadal timescales, simulated boreal winter ocean variability at the coral sites additionally indicates a potential intensification of the SCS buoyancy plug from the mid- to late-20<sup>th</sup> century. Notably, the variability in these coral and model responses reveals sensitivity to phase changes in the Interdecadal Pacific Oscillation and the East Asian Winter Monsoon. These results collectively suggest that the paleoproxy records are capturing important features of regional hydrography and Indo-Pacific exchange, including responses to regional monsoon variability. Such proxy-model comparison is critical for understanding the drivers of variability related to changes in ITF oceanic teleconnections over the 19<sup>th</sup> and 20<sup>th</sup> centuries.</p>

A numerical investigation of dynamics, thermodynamics and mixed-layer processes in the Indian Ocean

1993 ◽  
Vol 31 (3) ◽  
pp. 181-244 ◽  
Author(s):  
Julian P. McCreary ◽  
Pijush K. Kundu ◽  
Robert L. Molinari
Keyword(s):  
Indian Ocean ◽  
Numerical Investigation ◽  
Mixed Layer ◽  
The Indian Ocean

Genesis of Indian Ocean Mixed Layer Temperature Anomalies: A Heat Budget Analysis

2010 ◽  
Vol 23 (20) ◽  
pp. 5375-5403 ◽  
Author(s):  
Agus Santoso ◽  
Alexander Sen Gupta ◽  
Matthew H. England
Keyword(s):  
Indian Ocean ◽  
Time Scales ◽  
Mixed Layer ◽  
Heat Budget ◽  
Heat Fluxes ◽  
Temperature Anomalies ◽  
Mixed Layer Temperature ◽  
The Indian Ocean ◽  
The Tropics

Abstract The genesis of mixed layer temperature anomalies across the Indian Ocean are analyzed in terms of the underlying heat budget components. Observational data, for which a seasonal budget can be computed, and a climate model output, which provides improved spatial and temporal coverage for longer time scales, are examined. The seasonal climatology of the model heat budget is broadly consistent with the observational reconstruction, thus providing certain confidence in extending the model analysis to interannual time scales. To identify the dominant heat budget components, covariance analysis is applied based on the heat budget equation. In addition, the role of the heat budget terms on the generation and decay of temperature anomalies is revealed via a novel temperature variance budget approach. The seasonal evolution of the mixed layer temperature is found to be largely controlled by air–sea heat fluxes, except in the tropics where advection and entrainment are important. A distinct shift in the importance and role of certain heat budget components is shown to be apparent in moving from seasonal to interannual time scales. On these longer time scales, advection gains importance in generating and sustaining anomalies over extensive regions, including the trade wind and midlatitude wind regimes. On the other hand, air–sea heat fluxes tend to drive the evolution of thermal anomalies over subtropical regions including off northwestern Australia. In the tropics, however, they limit the growth of anomalies. Entrainment plays a role in the generation and maintenance of interannual anomalies over localized regions, particularly off Sumatra and over the Seychelles–Chagos Thermocline Ridge. It is further shown that the spatial distribution of the role and importance of these terms is related to oceanographic features of the Indian Ocean. Mixed layer depth effects and the influence of model biases are discussed.

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>

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