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Ocean Dipole (ocean + dipole)
Kinds of Ocean Dipole Selected AbstractsInfluences of the Indian Ocean dipole on the Asian summer monsoon in the following yearINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2008Yuan Yuan Abstract By exploring the spatiotemporal features of the Indian Ocean Dipole (IOD) both on the sea surface and in the subsurface ocean, the present article reveals that the subsurface dipole mode, with larger amplitude than the surface one, is likely to prolong the dipole signal for a long time. Using the wind and geopotential height data from NCEP/NCAR, this article further investigates IOD impacts on the Asian summer monsoon activities in the following year. A normal (late) South China Sea summer monsoon onset is associated with the previous positive (negative) IOD. In the summer after an IOD year, a positive (negative) IOD tends to induce a stronger (weaker) 100-hPa South Asian High, with a more (less) eastward-extending high ridge, and also an enhanced (a weakened) 500-hPa western Pacific subtropical high, with a westward-advancing (an eastward-retreating) high ridge. Influenced by the anomalous 850-hPa Asian monsoon circulations and the longitudinal position of the 500-hPa subtropical high ridge, summer rainfall in China also exhibits different patterns corresponding to different phases of the IOD in the previous year. Copyright © 2008 Royal Meteorological Society [source] Basin-wide warming of the Indian Ocean during El Niño and Indian Ocean dipole yearsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2007J. S. Chowdary Abstract Basin-wide wintertime surface warming is observed in the Indian Ocean during El Niño years. The basin-wide warming is found to be stronger when El Niño and Indian Ocean Dipole (IOD) co-occur. The mechanisms responsible for the basin-wide warming are different for the years with El Niño only (El Niño without IOD) and for the co-occurrence (both El Niño and IOD) years. Strong westward propagation of downwelling Rossby waves is observed in the southern Indian Ocean during the IOD years. Such strong propagation is not seen in the case of the El Niño-only years. This indicates that the ocean dynamics play an important role in winter warming of the western Indian Ocean during the IOD years. The weak easterly wind anomalies in the El Niño-only years show no measurable impact on the Wyrtki Jets, but weakening or reversal of these jets is seen in the IOD years. This strongly suggests that the variability related to surface circulation is due to the local IOD forcing rather than El Niño induced wind anomaly. For the El Niño-only composites, surface heat fluxes (mainly latent heat flux and short wave radiation) play an important role in maintaining the basin-wide surface warming in the Indian Ocean. In the IOD-only composites (when there is no El Niño in the Pacific), such basin-wide warming is not seen because of the absence of ENSO (El Niño and Southern Oscillation) induced subsidence over the eastern Indian Ocean. For the years in which both El Niño in the Pacific and dipole in the Indian Ocean co-occur, warming in the western Indian Ocean is due to the ocean dynamics and that in the eastern Indian Ocean is due to the anomalous latent heat flux and solar radiation. Copyright © 2007 Royal Meteorological Society [source] Individual and combined influence of El Niño,Southern Oscillation and Indian Ocean Dipole on the Tropospheric Biennial OscillationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 647 2010Prasanth A. Pillai Abstract Tropospheric biennial oscillation (TBO) is the tendency of a strong monsoon to be followed by a weaker one and vice versa. It involves both oceanic and atmospheric processes in the tropical Indian and Pacific Ocean regions. The present study analyses the effect of dynamical processes of the Indian and Pacific Oceans like the Indian Ocean Dipole (IOD) and El Niño,Southern Oscillation (ENSO) on the TBO. The 200 hPa velocity potential, 850 hPa zonal wind and sea-surface temperature datasets obtained from NCEP/NCAR reanalysis for the period 1950,2006 are used for the study of the TBO. The IOD and TBO have both in-phase (positive/negative IOD with positive/negative TBO) and out-of-phase (positive/negative IOD with negative/positive TBO) relationships. On the other hand, La Niña is associated with the positive phase of TBO and El Niño with the negative phase. In the presence of El Niño (La Niña), positive (negative) IOD is associated with negative (positive) TBO and in the absence of ENSO, positive (negative) IOD is associated with positive (negative) phase of TBO. When ENSO is associated with TBO, it tends to dominate the biennial transition irrespective of IOD. In-phase Indian to Australian monsoon transition of TBO is controlled by ENSO. IOD,TBO association is strong and significant in the absence of ENSO only. The biennial reversal is confined to the Indian Ocean in the TBO cycle associated with IOD only. Thus IOD can be considered as the local forcing for the biennial monsoon cycle, and ENSO the remote effect. Copyright © 2010 Royal Meteorological Society [source] Changes in northern Tanzania coral reefs during a period of increased fisheries management and climatic disturbanceAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2009Tim R. McClanahan Abstract 1.Surveys of coral reefs in northern Tanzania were conducted in 2004/5 with the aim of comparing them over an,8-year period during a time of increased efforts at fisheries management and the 1998 El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) coral mortality event that caused 45% mortality in northern Tanzania and much of the Indian Ocean. 2.Changes associated with both management, its absence, and the ENSO were found but changes were generally small and ecological measures indicated stability or improvements over this period, particularly when compared with reports from much of the northern Indian Ocean. 3.Fisheries management in two areas increased the biomass of fish and benthic communities. A small fisheries closure (0.3,km2) displayed little change in the coral community but ecological conditions declined as measured by sea urchins and fish abundances. This change may be associated with its small size because similar changes were not measured in the large closure (28,km2). 4.The few sites without any increased management were still degraded and one site had experienced a population explosion of a pest sea urchin, Echinometra mathaei. 5.The lack of significant changes across this disturbance indicates that these reefs are moderately resilient to climate change and, therefore, a high priority for future conservation actions. Copyright © 2009 John Wiley & Sons, Ltd. [source] The impact of the positive Indian Ocean dipole on Zimbabwe droughtsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2008D. Manatsa Abstract A comparative study of the impact of the anomalous positive Indian Ocean SST gradient, referred to as the Indian Ocean Dipole/Zonal Mode (IODZM), and El Niño-Southern Oscillation (ENSO) on Zimbabwe seasonal rainfall variability for the period 1940,1999, is documented. Composite techniques together with simple and partial correlation analyses are employed to segregate the unique association related to IODZM/ENSO with respect to the Zimbabwe seasonal rainfall. The analysis reveals that the IODZM impact on the country's summer rainfall is overwhelming as compared to that of ENSO when the two are in competition. The IODZM influence remains high (significant above 99% confidence level), even after the influence of ENSO has been removed, while that of ENSO collapses to insignificance (even at 90% confidence level) when the IODZM contribution is eliminated. The relationship between ENSO and Zimbabwe seasonal rainfall seems to be sustained through El Niño occurring in the presence of positive IODZM events. However, when the co-occurring positive IODZM and El Niño events are removed from the analysis, it is apparently clear that ENSO has little to do with the country's rainfall variability. On the other hand, positive IODZM is mostly associated with the rainfall deficits, whether or not it co-occurs with El Niño. However, the co-occurrence of the two events does not necessarily suggest that El Niño influences droughts through the positive IODZM events. The El Niño event components during co-occurrence seem to be unrelated (at least linearly) to the droughts, while the positive IODZM events display a relatively strong relationship that is significant above the 95% confidence level. It thus becomes important to extend the study of this nature to cover the whole of southern Africa, so that the extent of the impact of the phenomena can be realized over the whole region. Copyright © 2008 Royal Meteorological Society [source] Influences of the Indian Ocean dipole on the Asian summer monsoon in the following yearINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2008Yuan Yuan Abstract By exploring the spatiotemporal features of the Indian Ocean Dipole (IOD) both on the sea surface and in the subsurface ocean, the present article reveals that the subsurface dipole mode, with larger amplitude than the surface one, is likely to prolong the dipole signal for a long time. Using the wind and geopotential height data from NCEP/NCAR, this article further investigates IOD impacts on the Asian summer monsoon activities in the following year. A normal (late) South China Sea summer monsoon onset is associated with the previous positive (negative) IOD. In the summer after an IOD year, a positive (negative) IOD tends to induce a stronger (weaker) 100-hPa South Asian High, with a more (less) eastward-extending high ridge, and also an enhanced (a weakened) 500-hPa western Pacific subtropical high, with a westward-advancing (an eastward-retreating) high ridge. Influenced by the anomalous 850-hPa Asian monsoon circulations and the longitudinal position of the 500-hPa subtropical high ridge, summer rainfall in China also exhibits different patterns corresponding to different phases of the IOD in the previous year. Copyright © 2008 Royal Meteorological Society [source] The Indian Ocean dipole , the unsung driver of climatic variability in East AfricaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2007Rob Marchant Abstract A growing body of evidence suggests that an independent ocean circulation system in the Indian Ocean, the Indian Ocean dipole (IOD), is partly responsible for driving climate variability of the surrounding landmasses. The IOD had traditionally been viewed as an artefact of the El Niño,Southern Oscillation (ENSO) system although increasingly the evidence is amassing that it is separate and distinct phenomenon. We review the causes of the IOD, how it develops within the Indian Ocean, the relationships with ENSO, and the consequences for East African climate dynamics and associated impacts on ecosystems, in particular along the Eastern Arc Mountains of Kenya and Tanzania. We evaluate current research initiatives focussed on characterizing and constraining the IOD and examine how effective these will be in determining climate change impacts on East African ecosystems and how such predictive capacity can be used in developing policy. Résumé Un nombre croissant de preuves suggère qu'un système indépendant de circulation des eaux de l'océan Indien, le Dipôle de l'océan Indien (IOD), est partiellement responsable de la variabilité du climat des terres environnantes. L'IOD est habituellement considéré comme un artéfact de l'Oscillation Méridionale El Niño (ENSO) bien que les preuves s'accumulent pour montrer que c'est un phénomène séparé et distinct. Nous revoyons les causes de l'IOD, comment il se développe au sein de l'océan Indien, ses liens avec l'ENSO et ses conséquences pour la dynamique du climat de l'Afrique de l'Est, ainsi que son impact sur les écosystèmes, particulièrement sur la chaîne des montagnes orientales au Kenya et en Tanzanie. Nous évaluons les initiatives de recherches actuelles qui visent à caractériser et à circonscrire l'impact de l'IOD et nous examinons dans quelle mesure elles seront efficaces pour déterminer les impacts du changement climatique sur les écosystèmes est-africains et comment on pourra se servir d'un tel moyen de prévision pour mettre au point des politiques. [source] | |||||||||||||