Analysis of diurnal to seasonal variability of Integrated Water Vapour in the South Indian Ocean basin using ground‐based GNSS and fifth‐generation ECMWF reanalysis (ERA5) data

2020 ◽  
Author(s):  
Edouard Lees ◽  
Olivier Bousquet ◽  
Denis Roy ◽  
Jimmy Leclair de Bellevue
Keyword(s):  
Indian Ocean ◽  
Water Vapour ◽  
Seasonal Variability ◽  
Ocean Basin ◽  
The South ◽  
South Indian Ocean ◽  
Fifth Generation ◽  
South Indian ◽  
Integrated Water Vapour ◽  
Ecmwf Reanalysis

scholarly journals Feature-Based Jet Variability in the Upper Troposphere

2020 ◽  
Vol 33 (16) ◽  
pp. 6849-6871 ◽  
Author(s):  
Clemens Spensberger ◽  
Thomas Spengler
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Storm Track ◽  
Ocean Basin ◽  
The South ◽  
South Indian Ocean ◽  
Upper Troposphere ◽  
South Indian ◽  
Jet Variability

AbstractJets in the upper troposphere constitute a cornerstone of both synoptic meteorology and climate dynamics, providing a direct link between weather and midlatitude climate variability. Conventionally, jet variability is often inferred indirectly through the variability of geopotential or sea level pressure. As recent findings pointed to physical discrepancies of this interpretation for the Southern Hemisphere, this study presents a global overview of jet variability based on automated jet detections in the upper troposphere. Consistent with previous studies, most ocean basins are dominated by variability patterns comprising either a latitudinal shift of the jet or a so-called pulsing, a broadening/narrowing of the jet distribution without a change in the mean position. Whereas previous studies generally associate a mode of storm track variability with either shifting or pulsing, jet-based variability patterns frequently represent a transition from shifting to pulsing, or vice versa, across the respective ocean basin. In the Northern Hemisphere, jet variability is consistent with geopotential variability, confirming earlier analyses. In the Southern Hemisphere, however, the variability of geopotential and jets often indicates different modes of variability. Notable exceptions are the consistent dominant modes of jet and geopotential variability in the South Pacific and, to a lesser extent, the south Indian Ocean during winter, as well as the dominant modes in the South Atlantic and south Indian Ocean during summer. Finally, tropical variability is shown to modulate the jet distribution in the Northern Hemisphere, which is in line with previous results. The response in the Southern Hemispheric, however, is shown to be markedly different.

scholarly journals Inertially Induced Connections between Subgyres in the South Indian Ocean

2009 ◽  
Vol 39 (2) ◽  
pp. 465-471 ◽  
Author(s):  
V. Palastanga ◽  
H. A. Dijkstra ◽  
W. P. M. de Ruijter
Keyword(s):  
Indian Ocean ◽  
Ocean Basin ◽  
Subtropical Gyre ◽  
Nonlinear Regime ◽  
Water Model ◽  
The South ◽  
South Indian Ocean ◽  
Southern Boundary ◽  
South Indian ◽  
Highly Nonlinear

Abstract A barotropic shallow-water model and continuation techniques are used to investigate steady solutions in an idealized South Indian Ocean basin containing Madagascar. The aim is to study the role of inertia in a possible connection between two subgyres in the South Indian Ocean. By increasing inertial effects in the model, two different circulation regimes are found. In the weakly nonlinear regime, the subtropical gyre presents a recirculation cell in the southwestern basin, with two boundary currents flowing westward from the southern and northern tips of Madagascar toward Africa. In the highly nonlinear regime, the inertial recirculation of the subtropical gyre is found to the east of Madagascar, while the East Madagascar Current overshoots the island’s southern boundary and connects through a southwestward jet with the current off South Africa.

scholarly journals Variability in the Mozambique Channel Trough and Impacts on Southeast African Rainfall

2020 ◽  
Vol 33 (2) ◽  
pp. 749-765 ◽  
Author(s):  
Rondrotiana Barimalala ◽  
Ross C. Blamey ◽  
Fabien Desbiolles ◽  
Chris J. C. Reason
Keyword(s):  
Indian Ocean ◽  
Austral Summer ◽  
Western Indian Ocean ◽  
Strong Relationship ◽  
Ocean Basin ◽  
Moist Convection ◽  
South Indian Ocean ◽  
Mozambique Channel ◽  
Mascarene High ◽  
South Indian

AbstractThe Mozambique Channel trough (MCT) is a cyclonic region prominent in austral summer in the central and southern Mozambique Channel. It first becomes evident in December with a peak in strength in February when the Mozambique Channel is warmest and the Mascarene high (MH) is located farthest southeast in the Indian Ocean basin. The strength and the timing of the mean MCT are linked to that of the cross-equatorial northeasterly monsoon in the tropical western Indian Ocean, which curves as northwesterlies toward northern Madagascar. The interannual variability in the MCT is associated with moist convection over the Mozambique Channel and is modulated by the location of the warm sea surface temperatures in the south Indian Ocean. Variability of the MCT shows a strong relationship with the equatorial westerlies north of Madagascar and the latitudinal extension of the MH. Summers with strong MCT activity are characterized by a prominent cyclonic circulation over the Mozambique Channel, extending to the midlatitudes. These are favorable for the development of tropical–extratropical cloud bands over the southwestern Indian Ocean and trigger an increase in rainfall over the ocean but a decrease over the southern African mainland. Most years with a weak MCT are associated with strong positive south Indian Ocean subtropical dipole events, during which the subcontinent tends to receive more rainfall whereas Madagascar and northern Mozambique are anomalously dry.

Impacts of ocean currents on the South Indian Ocean extratropical storm track through the relative wind effect

2021 ◽  
pp. 1-61
Author(s):  
Hyodae Seo ◽  
Hajoon Song ◽  
Larry W. O’Neill ◽  
Matthew R. Mazloff ◽  
Bruce D. Cornuelle
Keyword(s):  
Indian Ocean ◽  
Ocean Circulation ◽  
Storm Track ◽  
Ocean Current ◽  
Wind Effect ◽  
Turbulent Heat ◽  
The South ◽  
South Indian Ocean ◽  
South Indian ◽  
Relative Wind

AbstractThis study examines the role of the relative wind (RW) effect (wind relative to ocean current) in the regional ocean circulation and extratropical storm track in the South Indian Ocean. Comparison of two high-resolution regional coupled model simulations with/without the RW effect reveals that the most conspicuous ocean circulation response is the significant weakening of the overly energetic anticyclonic standing eddy off Port Elizabeth, South Africa, a biased feature ascribed to upstream retroflection of the Agulhas Current (AC). This opens a pathway through which the AC transports the warm and salty water mass from the subtropics, yielding marked increases in sea surface temperature (SST), upward turbulent heat flux (THF), and meridional SST gradient in the Agulhas retroflection region. These thermodynamic and dynamic changes are accompanied by the robust strengthening of the local low-tropospheric baroclinicity and the baroclinic wave activity in the atmosphere. Examination of the composite lifecycle of synoptic-scale storms subjected to the high THF events indicates a robust strengthening of the extratropical storms far downstream. Energetics calculations for the atmosphere suggest that the baroclinic energy conversion from the basic flow is the chief source of increased eddy available potential energy, which is subsequently converted to eddy kinetic energy, providing for the growth of transient baroclinic waves. Overall, the results suggest that the mechanical and thermal air-sea interactions are inherently and inextricably linked together to substantially influence the extratropical storm tracks in the South Indian Ocean.

Eastward Shift of Interannual Climate Variability in the South Indian Ocean since 1950

2021 ◽  
pp. 1-46
Author(s):  
Lei Zhang ◽  
Weiqing Han ◽  
Kristopher B. Karnauskas ◽  
Yuanlong Li ◽  
Tomoki Tozuka
Keyword(s):  
Indian Ocean ◽  
Climate Variability ◽  
Decadal Variability ◽  
Dominant Role ◽  
Tropical Pacific ◽  
The South ◽  
South Indian Ocean ◽  
Climate Modes ◽  
South Indian ◽  
Interannual Climate Variability

AbstractThe subtropical Indian Ocean Dipole (SIOD) and Ningaloo Niño are the two dominant modes of interannual climate variability in the subtropical South Indian Ocean. Observations show that the SIOD has been weakening in the recent decades, while Ningaloo Niño has been strengthening. In this study, we investigate the causes for such changes by analyzing climate model experiments using the NCAR Community Earth System Model version 1 (CESM1). Ensemble-mean results from CESM1 large-ensemble (CESM1-LE) suggest that the external forcing causes negligible changes in the amplitudes of the SIOD and Ningaloo Niño, suggesting a dominant role of internal climate variability. Meanwhile, results from CESM1 pacemaker experiments reveal that the observed changes in the two climate modes cannot be attributed to the effect of sea surface temperature anomalies (SSTA) in either the tropical Pacific or tropical Indian Oceans. By further comparing different ensemble members from the CESM1-LE, we find that a Warm Pool Dipole mode of decadal variability, with opposite SSTA in the southeast Indian Ocean and the western-central tropical Pacific Ocean plays an important role in driving the observed changes in the SIOD and Ningaloo Niño. These changes in the two climate modes have considerable impacts on precipitation and sea level variabilities in the South Indian Ocean region.

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