scholarly journals ON THE CORRESPONDENCE BETWEEN RAINFALL ANOMALY OVER INDIA AND THE EXTRA-TROPICAL CYCLONES OVER SOUTH INDIAN OCEAN

MAUSAM ◽  
2021 ◽  
Vol 57 (2) ◽  
pp. 346-350
Author(s):  
BRIJ BHUSHAN
Keyword(s):  
Indian Ocean ◽  
Tropical Cyclones ◽  
Rainfall Anomaly ◽  
South Indian Ocean ◽  
South Indian

scholarly journals Recent emergence of CAT5 tropical cyclones in the South Indian Ocean

2018 ◽  
Vol 114 (11/12) ◽  
Author(s):  
Jennifer M. Fitchett
Keyword(s):  
Tropical Cyclone ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Satellite Imagery ◽  
Storm Damage ◽  
The South ◽  
South Indian Ocean ◽  
The North ◽  
South Indian ◽  
Recent Emergence

The IBTrACS global best track data set endorsed by the World Meteorological Organization provides a valuable global record of tropical cyclone genesis, track and intensity, and spans 1842 to the present. The record is significantly more robust from the late 1970s onwards, as it is supported by satellite imagery. These records indicate that the first tropical cyclone in the South Indian Ocean to intensify to CAT5 status did so in 1994. This date is significantly later than the first CAT5 storms recorded in the IBTrACS database for the Atlantic Ocean (1924) and the North Pacific (1951) recorded from ship records, and half a decade later than those of the North Indian Ocean (1989) and South Pacific (1988), captured from satellite imagery. Following this late emergence, in the period 1990–2000, eight CAT5 tropical cyclones were recorded for the South Indian Ocean. A further four have been recorded for the period 2010–2015. This recent emergence of tropical cyclones attaining category five intensity in the South Indian Ocean is of significance for the forecasting of tropical cyclone landfall and the anticipation of storm damage for the developing economies that characterise the region. Although an increase in tropical cyclone intensity is frequently projected under global climate change scenarios, the dynamics for the South Indian Ocean have remained poorly understood. Notable are early results indicating an increased frequency and poleward migration of these CAT5 storms, concurrent with a poleward migration in the position of the 26.5 °C, 28 °C and 29 °C sea surface temperature isotherms in the South Indian Ocean. Significance: Category 5 tropical cyclones, the strongest category of storms, have only recently emerged in the South Indian Ocean. Since 1989, their frequency of occurrence has increased. This increase poses a heightened risk of storm damage for the South Indian Ocean Island States and the countries of the southern African subcontinent as a result of the strong winds, heavy rainfall and storm surges associated with these storms, and the large radial extent at category 5 strength.

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.

scholarly journals Structure and origin of the subtropical South Indian Ocean Countercurrent

2006 ◽  
Vol 33 (24) ◽  
Author(s):  
Gerold Siedler ◽  
Mathieu Rouault ◽  
Johann R. E. Lutjeharms
Keyword(s):  
Indian Ocean ◽  
South Indian Ocean ◽  
South Indian

Sea surface temperatures, salinity and pH reconstructions over the last 1,2 Ma in South Indian Ocean using the unique combination of Mg/Ca, d18O and ∆47 in planktonic foraminifera

2021 ◽  
Author(s):  
Marion Peral ◽  
Thibaut Caley ◽  
Bruno Malaizé ◽  
Erin McClymont ◽  
Thomas Extier ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Transfer Function ◽  
Planktonic Foraminifera ◽  
The Other ◽  
Unique Combination ◽  
South Indian Ocean ◽  
Term Evolution ◽  
South Indian ◽  
Clumped Isotope

<p>The Mid-Pleistocene transition (MPT) took place between 1,200 Ma and 800 ka (still debated). During this transition, the Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40 000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical while Earth’s orbital variations remained unchanged. Although orbital variations constitute the first order forcing on glacial-interglacial oscillations of the late Quaternary, they cannot explain alone the shifts in climatic periodicity and amplitude observed during the MPT. In order to explain the MPT, long-term evolution of internal mechanisms and feedbacks have been called upon, in relation with the global cooling trend initiated during the Cenozoic, the expansion of Antarctic and Greenland Ice Sheet and/or the long-term decline in greenhouse gases (particularly CO2). A key point is therefore to accurately reconstruction of oceanic temperatures to decipher the processes driving climate variations.</p><p>In the present work, we studied the marine sediment core MD96-2048 taken from south Indian Ocean (26*10’482’’ S, 34*01’148’’ E) in the region of the Agulhas current. We compared 5 paleothermometers: alkenone, TEX86, foraminiferal- transfer function, Mg/Ca and clumped isotope. Among these approaches, carbonate clumped-isotope thermometry (∆<sub>47</sub>) only depends on crystallization temperature, and the ∆<sub>47</sub> relationship with planktonic foraminifer calcification temperature is well defined. Since Mg/Ca is not only controlled by temperature but is also affected by salinity and pH. The classical d<sup>18</sup>O in planktic is dependent on SST and d<sup>18</sup>Osw, which is regionally correlated with the salinity in the present-day ocean. Assuming that the present-day d<sup>18</sup>O<sub>sw</sub>-salinity relation was the same during the MPT, we are able to separate changes in d<sup>18</sup>O<sub>sw</sub> from temperature effects and reconstruct past salinity. Combining d<sup>18</sup>O, Mg/Ca and ∆<sub>47</sub> on planktonic foraminifera allow in theory to reconstruct SST, SSS and pH.</p><p>Here, we measured d<sup>18</sup>O, Mg/Ca and ∆<sub>47</sub> on the shallow-dwelling planktonic species Globigerinioides ruber ss. at the maximal of glacial and interglacial periods over the last 1.2 Ma. Our set of data makes it possible to estimate the long-term evolution of SST, salinity and pH (and thus have an insight into the atmospheric CO<sub>2</sub> concentration) across the MPT. Frist, strong differences are observed between the 5 derived-SST: the alkenone and TEX86 recorded the higher temperatures than the other SST proxies. Alkenone derived-SST do not show glacial-interglacial variations within the MPT. The Mg/Ca and transfer function derived-SST show a good agreement each other, while the clumped-isotope derived-SST are systematically colder than the other derived-SST. Then, our ∆<sub>47</sub>-SST, salinity and pH results clearly show that amplitude of glacial-interglacial variations was insignificant between 1.2 and 0.8 Ma (within the MPT) and increased after the MPT. Finally, we also discussed the potential to use this unique combination of proxies to reconstruct changes of atmospheric CO<sub>2</sub> concentration.</p>

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.

South Indian Ocean Rossby Waves

2018 ◽  
Vol 56 (5) ◽  
pp. 322-331
Author(s):  
Mark R. Jury
Keyword(s):  
Indian Ocean ◽  
Rossby Waves ◽  
South Indian Ocean ◽  
South Indian
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