scholarly journals Characteristics of the Near-Surface Currents in the Indian Ocean as Deduced from Satellite-Tracked Surface Drifters. Part I: Pseudo-Eulerian Statistics

2015 ◽  
Vol 45 (2) ◽  
pp. 441-458 ◽  
Author(s):  
Shiqiu Peng ◽  
Yu-Kun Qian ◽  
Rick Lumpkin ◽  
Yan Du ◽  
Dongxiao Wang ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Kinetic Energy ◽  
Eastern Coast ◽  
Western Boundary ◽  
Surface Currents ◽  
Mean Velocity ◽  
Near Surface ◽  
The Indian Ocean ◽  
Central Eastern ◽  
Surface Drifters

AbstractUsing the 1985–2013 record of near-surface currents from satellite-tracked drifters, the pseudo-Eulerian statistics of the near-surface circulation in the Indian Ocean (IO) are analyzed. It is found that the distributions of the current velocities and mean kinetic energy (MKE) in the IO are extremely inhomogeneous in space and nonstationary in time. The most energetic regions with climatologic mean velocity over 50 cm s−1 and MKE over 500 cm2 s−2 are found off the eastern coast of Somalia (with maxima of over 100 cm s−1 and 1500 cm2 s−2) and the equatorial IO, associated with the strong, annually reversing Somalia Current and the twice-a-year eastward equatorial jets. High eddy kinetic energy (EKE) is found in regions of the equatorial IO, western boundary currents, and Agulhas Return Current, with a maximum of over 3000 cm2 s−2 off the eastern coast of Somalia. The lowest EKE (<500 cm2 s−2) occurs in the south subtropical gyre between 30° and 40°S and the central-eastern Arabian Sea. Annual and semiannual variability is a significant fraction of the total EKE off the eastern coast of Somalia and in the central-eastern equatorial IO. In general, both the MKE and EKE estimated in the present study are qualitatively in agreement with, but quantitatively larger than, estimates from previous studies. These pseudo-Eulerian MKE and EKE fields, based on the most extensive drifter dataset to date, are the most precise in situ estimates to date and can be used to validate satellite and numerical results.

Structure and Seasonal Variation of the Indian Ocean Tropical Gyre Based on Surface Drifters

2021 ◽  
Author(s):  
Wei Wu ◽  
Yan Du ◽  
Yu-Kun Qian ◽  
Xuhua Cheng ◽  
Tianyu Wang ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Indian Ocean ◽  
Water Mass ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
Western Boundary ◽  
Boundary Current ◽  
Boreal Spring ◽  
The Indian Ocean ◽  
Surface Drifters

&lt;p&gt;Using the Gauss&amp;#8211;Markov decomposition method, this study investigates the mean structure and seasonal variation of the tropical gyre in the Indian Ocean based on the observations of surface drifters. In the climatological mean, the clockwise tropical gyre consists of the equatorial Wyrtki Jets (WJs), the South Equatorial Current (SEC), and the eastern and western boundary currents. This gyre system redistributes the water mass over the entire tropical Indian Ocean basin. Its variations are associated with the monsoon transitions, featuring a typical clockwise pattern in the boreal spring and fall seasons. The relative importance of the geostrophic and Ekman components of the surface currents as well as the role of eddy activity were further examined. It was found that the geostrophic component dominates the overall features of the tropical gyre, including the SEC meandering, the broad eastern boundary current, and the axes of the WJs in boreal spring and fall, whereas the Ekman component strengthens the intensity of the WJs and SEC. Eddies are active over the southeastern tropical Indian Ocean and transport a warm and fresh water mass westward, with direct impact on the southern branch of the tropical gyre. In particular, the trajectories of drifters reveal that during strong Indian Ocean Dipole or El Ni&amp;#241;o-Southern Oscillation events, long-lived eddies were able to reach the southwestern Indian Ocean with a moving speed close to that of the first baroclinic Rossby waves.&lt;/p&gt;

Characteristics of the Near-Surface Currents in the Indian Ocean as Deduced from Satellite-Tracked Surface Drifters. Part II: Lagrangian Statistics

2015 ◽  
Vol 45 (2) ◽  
pp. 459-477 ◽  
Author(s):  
Shiqiu Peng ◽  
Yu-Kun Qian ◽  
Rick Lumpkin ◽  
Ping Li ◽  
Dongxiao Wang ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Time Scale ◽  
Eastern Coast ◽  
Length Scale ◽  
Time Lags ◽  
Horizontal Shear ◽  
Mean Flow ◽  
Near Surface ◽  
Lagrangian Statistics ◽  
The Indian Ocean

AbstractLagrangian statistics of the surface circulation in the Indian Ocean (IO) are investigated using drifter observations during 1985–2013. The methodology isolates the influence of low-frequency variations and horizontal shear of mean flow. The estimated Lagrangian statistics are spatially inhomogeneous and anisotropic over the IO basin, with values of ~6–85 × 107 cm2 s−1 for diffusivity, ~2–7 days for integral time scale, and ~33–223 km for length scale. Large diffusivities (>20 × 107 cm2 s−1) occur in the central-eastern equatorial IO and the eastern African coast. Small diffusivities (~6–8 × 107 cm2 s−1) appear in the subtropical gyre of the southern IO and the southeastern Arabian Sea. The equatorial IO has the largest zonal diffusivity (~85 × 107 cm2 s−1), corresponding to the largest time scale (~7 days) and length scale (~223 km), while the eastern coast of Somalia has the largest meridional diffusivity (~31 × 107 cm2 s−1). The minor component of the Lagrangian length scale is approximately equal to the first baroclinic Rossby radius (R1) at midlatitudes (R1 ~ 30–50 km), while the major component equals R1 in the equatorial region (R1 > 80 km). The periods of the energetic eddy-containing bands in the IO in Lagrangian spectra range from several days to a couple of months, where anticyclones dominate. A significant result is that the drifter-derived diffusivities asymptote to constant values in relatively short time lags (~10 days) for some subregions of the IO if they are correctly calculated. This is an important contribution to the ongoing debate regarding drifter-based diffusivity estimates with relatively short Lagrangian velocity time series versus tracer-based estimates.

scholarly journals Analysis of Drought-Sensitive Areas and Evolution Patterns through Statistical Simulations of the Indian Ocean Dipole Mode

Water ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 1302 ◽  
Author(s):  
Qing-Gang Gao ◽  
Vonevilay Sombutmounvong ◽  
Lihua Xiong ◽  
Joo-Heon Lee ◽  
Jong-Suk Kim
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Diagnostic Techniques ◽  
Eastern Coast ◽  
Indochina Peninsula ◽  
Indian Ocean Dipole Mode ◽  
Sensitive Areas ◽  
The Indian Ocean ◽  
Long Term Trend

In this study, we investigated extreme droughts in the Indochina peninsula and their relationship with the Indian Ocean Dipole (IOD) mode. Areas most vulnerable to drought were analyzed via statistical simulations of the IOD based on historical observations. Results of the long-term trend analysis indicate that areas with increasing spring (March–May) rainfall are mainly distributed along the eastern coast (Vietnam) and the northwestern portions of the Indochina Peninsula (ICP), while Central and Northern Laos and Northern Cambodia have witnessed a reduction in spring rainfall over the past few decades. This trend is similar to that of extreme drought. During positive IOD years, the frequency of extreme droughts was reduced throughout Vietnam and in the southwestern parts of China, while increased drought was observed in Cambodia, Central Laos, and along the coastline adjacent to the Myanmar Sea. Results for negative IOD years were similar to changes observed for positive IOD years; however, the eastern and northern parts of the ICP experienced reduced droughts. In addition, the results of the statistical simulations proposed in this study successfully simulate drought-sensitive areas and evolution patterns of various IOD changes. The results of this study can help improve diagnostic techniques for extreme droughts in the ICP.

Mauritius

2020 ◽  
Author(s):  
Marius Schneider ◽  
Vanessa Ferguson
Keyword(s):  
Indian Ocean ◽  
Eastern Coast ◽  
Official Language ◽  
The South ◽  
South Eastern ◽  
The Indian Ocean ◽  
The Republic ◽  
Local Languages

Situated off the south-eastern coast of Africa in the Indian Ocean, the Republic of Mauritius is an island nation of 2,040 square kilometres (km) with a population of 1.26 million. English is generally accepted as the official language as it is used by the administration and the courts. French is also widely spoken among the population, and most inhabitants are bilingual. Local languages include Créole and Bhojpuri. The working week on the island is from Monday to Friday and the Mauritian rupee (MUR) is the currency used.

scholarly journals Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean

2013 ◽  
Vol 10 (10) ◽  
pp. 6677-6698 ◽  
Author(s):  
J. C. Currie ◽  
M. Lengaigne ◽  
J. Vialard ◽  
D. M. Kaplan ◽  
O. Aumont ◽  
...  
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Near Surface ◽  
Climate Modes ◽  
The Indian Ocean

Abstract. The Indian Ocean Dipole (IOD) and the El Niño/Southern Oscillation (ENSO) are independent climate modes, which frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled biophysical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997/1998 ENSO and IOD event. Results suggest that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. A negative influence of IOD on chlorophyll concentrations is shown in a region around the southern tip of India in fall. IOD also depresses depth-integrated chlorophyll in the 5–10° S thermocline ridge region, yet the signal is negligible in surface chlorophyll. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Yet unlike most other regions examined, the combined explanatory power of IOD and ENSO in predicting depth-integrated chlorophyll anomalies is relatively low in this region, suggestive that other drivers are important there. We show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. Our results suggest that ENSO and IOD cause significant and predictable regional re-organisation of chlorophyll via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon budgets.

Seasonal variations in the Indian Ocean along 110°E. I. Hydrological structure of the upper 500 m

1969 ◽  
Vol 20 (1) ◽  
pp. 1 ◽  
Author(s):  
DJ Rochford
Keyword(s):  
Indian Ocean ◽  
Surface Waters ◽  
Water Masses ◽  
Surface Currents ◽  
Temperature Changes ◽  
East Indian ◽  
Hydrological Structure ◽  
The Indian Ocean ◽  
The Tropics ◽  
East Indian Ocean

Tropical and subtropical water masses at surface and subsurface depths were separated by their salinity, temperature, oxygen, and nutrient characteristics. The annual mean depths and latitudinal extent of these water masses were determined. Annual changes in the upper 50 m were generally so small relative to those found in other oceans that advection and mixing must have been less important in their genesis than local climatic changes. There was a barely significant seasonal rhythm in surface phosphate and nitrate, with peak occurrences of each some 6 months apart. At each latitude the permanent thermal discontinuity centred around a particular isotherm varied little in intensity during the year, but rose and fell in accordance with surface currents. The thermocline south of c. 18�S. varied little in depth but greatly in intensity during the summer. The depth of the mixed layer was much less in summer and at all times shallower in the tropics. The depth of this layer was governed more by the accumulation of surface waters by zonal currents and eddies, than by wind stress or convective overturn. Therefore there was little difference from south to north, or month to month, in average nutrient values of this mixed column. The movement of the various surface waters, deduced from salinity and temperature changes during the year, usually agrees with geostrophic currents across 110�E, and ships' observations of surface currents in the south-east Indian Ocean.

scholarly journals Water Mass Export from Drake Passage to the Atlantic, Indian, and Pacific Oceans: A Lagrangian Model Analysis

2005 ◽  
Vol 35 (7) ◽  
pp. 1206-1222 ◽  
Author(s):  
Yann Friocourt ◽  
Sybren Drijfhout ◽  
Bruno Blanke ◽  
Sabrina Speich
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Drake Passage ◽  
General Circulation Models ◽  
Lagrangian Model ◽  
Global Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The Indian Ocean

Abstract The northward export of intermediate water from Drake Passage is investigated in two global ocean general circulation models (GCMs) by means of quantitative particle tracing diagnostics. This study shows that a total of about 23 Sv (Sv ≡ 106 m3 s−1) is exported from Drake Passage to the equator. The Atlantic and Pacific Oceans are the main catchment basins with 7 and 15 Sv, respectively. Only 1–2 Sv of the water exported to the Atlantic equator follow the direct cold route from Drake Passage without entering the Indian Ocean. The remainder loops first into the Indian Ocean subtropical gyre and flows eventually into the Atlantic Ocean by Agulhas leakage. The authors assess the robustness of a theory that relates the export from Drake Passage to the equator to the wind stress over the Southern Ocean. Our GCM results are in reasonable agreement with the theory that predicts the total export. However, the theory cannot be applied to individual basins because of interocean exchanges through the “supergyre” mechanism and other nonlinear processes such as the Agulhas rings. The export of water from Drake Passage starts mainly as an Ekman flow just northward of the latitude band of the Antarctic Circumpolar Current south of South America. Waters quickly subduct and are transferred to the ocean interior as they travel equatorward. They flow along the eastern boundaries in the Sverdrup interior and cross the southern basins northwestward to reach the equator within the western boundary current systems.

scholarly journals On the Indonesian throughflow in the OCCAM 1/4 degree ocean model

2007 ◽  
Vol 4 (2) ◽  
pp. 325-370 ◽  
Author(s):  
U. W. Humphries ◽  
D. J. Webb
Keyword(s):  
Indian Ocean ◽  
Ocean Model ◽  
Global Ocean ◽  
Indonesian Throughflow ◽  
Island Rule ◽  
Near Surface ◽  
The North ◽  
The Pacific ◽  
The Indian Ocean ◽  
Pass Through

Abstract. The Indonesian Throughflow is analysed in two runs of the OCCAM 1/4 degree global ocean model, one using monthly climatological winds and one using ECMWF analysed six-hourly winds for the period 1993 to 1998. The long-term model throughflow agrees with observations and the value predicted by Godfrey's Island Rule. The Island Rule has some skill in predicting the annual signal each year but is poor at predicting year to year and shorter term variations in the total flow especially in El Nino years. The spectra of transports in individual passages show significant differences between those connecting the region to the Pacific Ocean and those connecting with the Indian Ocean. This implies that different sets of waves are involved in the two regions. Vertical profiles of transport are in reasonable agreement with observations but the model overestimates the near surface transport through the Lombok Strait and the dense overflow from the Pacific through the Lifamatola Strait into the deep Banda Sea. In both cases the crude representation of the passages by the model appears responsible. In the north the model shows, as expected, that the largest transport is via the Makassar Strait. However this is less than expected and instead there is significant flow via the Halmahera Sea. If Godfrey's Island Rule is correct and the throughflow is forced by the northward flow between Australia and South America, then the Halmahers Sea route should be important. It is the most southerly route around New Guinea to the Indian Ocean and there is no apparent reason why the flow should go further north in order to pass through the Makassar Strait. The model result thus raises the question of why in reality the Makassar Strait route appears to dominate the throughflow.

scholarly journals Atmospheric pollutant outflow from southern Asia: a review

2010 ◽  
Vol 10 (22) ◽  
pp. 11017-11096 ◽  
Author(s):  
M. G. Lawrence ◽  
J. Lelieveld
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Hydrological Cycle ◽  
Scale Effects ◽  
Long Distance ◽  
Atmospheric Pollutant ◽  
Near Surface ◽  
Air Masses ◽  
Southern Asia ◽  
The Indian Ocean

Abstract. Southern Asia, extending from Pakistan and Afghanistan to Indonesia and Papua New Guinea, is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern Asian atmospheric pollutant outflow and its large scale effects. An outlook is provided as a guideline for future research, pointing out particularly critical issues such as: resolving discrepancies between top down and bottom up emissions estimates; assessing the processing and aging of the pollutant outflow; developing a better understanding of the observed elevated pollutant layers and their relationship to local sea breeze and large scale monsoon circulations; and determining the impacts of the pollutant outflow on the Asian monsoon meteorology and the regional hydrological cycle, in particular the mountain cryospheric reservoirs and the fresh water supply, which in turn directly impact the lives of over a billion inhabitants of southern Asia.

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