Enhanced Tropical Eastern Indian Ocean Rainfall Breaks down the Tropical Easterly Jet-Indian Rainfall Relationship

2021 ◽  
pp. 1-44
Author(s):  
Sihua Huang ◽  
Bin Wang ◽  
Zhiping Wen ◽  
Zesheng Chen
Keyword(s):  
Indian Ocean ◽  
Rainfall Variability ◽  
Summer Monsoon Rainfall ◽  
Eastern Indian Ocean ◽  
Sst Variability ◽  
Tropical Easterly Jet ◽  
Tight Connection ◽  
Indian Rainfall ◽  
Rainfall Anomalies ◽  
Upper Level

AbstractPrevious studies found a tight connection between the tropical easterly jet (TEJ) and Indian summer monsoon rainfall (ISMR). Here we show that the TEJ-ISMR relationship is nonstationary and breaks down from 1994–2003 (epoch P2), in contrast to the significant positive correlation during the epoch P1 (1979–1993) and P3 (2004–2016). The breakdown of the TEJ-ISMR relationship concurs with the increased rainfall variability over the tropical eastern Indian Ocean (TEIO). The enhanced TEIO rainfall anomalies excite a significant lower-level cyclonic circulation that reduces the ISMR, meanwhile, strengthens the upper-level divergence and excites a pair of upper-level anticyclone to the west of the TEIO as Rossby wave responses, both accelerating the TEJ. Thus, the TEIO rainfall plays a more important role than the ISMR in the TEJ variability during P2, causing the breakdown of the TEJ-ISMR relationship. In contrast, a relatively weak amplitude of the TEIO rainfall during P1 and P3 was unable to change the positive TEJ-ISMR relationship. The changes in the TEIO rainfall variability is mainly attributed to the increased SST variability over the tropical southeastern Indian Ocean, but the cause of it remains elusive.

scholarly journals Opposite Effects of ENSO on the Rainfall over the Northern and Equatorial Great Horn of Africa and Possible Causes

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
K. Abebe Kiflie ◽  
Li Tao
Keyword(s):  
Rainfall Variability ◽  
Summer Rainfall ◽  
Western Indian Ocean ◽  
Annual Rainfall ◽  
Horn Of Africa ◽  
Tropical Africa ◽  
Low Level ◽  
Tropical Easterly Jet ◽  
Rainfall Anomalies ◽  
Upper Level

In this study, we explore the possible mechanism of opposite ENSO effects on summer rainfall in the JJAS region (northern GHA) and autumn rainfall in the OND region (equatorial GHA). The two regions are identified based on the spatial distribution of high seasonal fractions of annual rainfall for the period 1979–2016. The summer rainfall over the JJAS region is negatively correlated with ENSO. It is because the warm Niño3.4 SST triggers zonal wave one pattern in tropics and forces upper-level westerly anomaly and the low-level easterly anomaly over tropical Africa. Thus, the weakened upper-level Tropical Easterly Jet (TEJ) and the low-level westerly over the JJAS region result in deficient rainfall during JJAS over the northern GHA. For the autumn rainfall variability over the equatorial GHA, IOD is a pivotal factor. But, autumn rainfall anomalies are far greater in ENSO and IOD coexisting years than those in IOD alone years. In other words, ENSO has a significant impact on the autumn rainfall over the equatorial GHA by means of IOD. It is because the warming SST, which is fully developed over western Indian Ocean (IO) in autumn of ENSO developing year, causes low-level convergence over the equatorial GHA and enhances upper-level easterly over tropical Africa. Those conditions are favorable for abundant rainfall over the equatorial GHA in autumn.

scholarly journals Influence of Indian Ocean dipole on rainfall variability and extremes over southern Africa

MAUSAM ◽  
2021 ◽  
Vol 71 (4) ◽  
pp. 637-648
Author(s):  
OGWANG B. A. ◽  
ONGOMA V. ◽  
SHILENJE Z. W. ◽  
RAMOTUBEI T. S. ◽  
LETUMA M. ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Africa ◽  
Indian Ocean Dipole ◽  
Rainfall Variability ◽  
Dominant Mode ◽  
Empirical Orthogonal Functions ◽  
Extreme Weather Events ◽  
Orthogonal Functions ◽  
Upper Level ◽  
The Relationship

Extreme weather events; floods and droughts are common in southern Africa (SA) consisting of 8 countries (Botswana, Namibia, South Africa, Lesotho, Swaziland, Mozambique, Zimbabwe, parts of Angola and Zambia). This study examines the linkage between the SA October-December (OND) rainfall, the Indian Ocean Dipole (IOD) and the South Atlantic Oscillation Dipole (SAOD). Empirical Orthogonal Functions (EOF) technique is used to establish the dominant mode of variability of OND rainfall, as correlation analysis is applied to quantify the relationship between the indices; IOD [Dipole Mode Index (DMI)], SAOD Index (SAODI) and OND rainfall variability. Results show that the dominant mode of variability of OND rainfall exhibits a dipole pattern over SA and there exists a significant correlation at 95% confidence level between the area average OND rainfall (rainfall index (RFI)) and DMI, with a correlation coefficient of -0.3. The relationship between the mean SA OND rainfall and the positive phase of IOD varies greatly in space, ranging from one country to another. Further analysis of the dry and wet of SAOND rainfall years reveal that wet years are associated with convergence at  surface level (850 hPa) and divergence at upper level (200 hPa), depicting rising motion in the region, whereas dry years are associated with divergence at low level and convergence at upper level, implying descending motion. The study recommends further research on a reduced spatial scale, for instance at a country level to ascertain the effect of IOD on individual country’s weather. This will help in accurate monitoring of the evolution of IOD events to improve quality of seasonal weather forecasts in the region.

scholarly journals Diagnosing Heat and Vorticity Budgets of Annual Coupled Rossby Waves

2005 ◽  
Vol 35 (7) ◽  
pp. 1173-1189 ◽  
Author(s):  
Warren B. White ◽  
Jeffrey L. Annis
Keyword(s):  
Indian Ocean ◽  
Latent Heat ◽  
Rossby Waves ◽  
Surface Wind ◽  
Phase Speed ◽  
Western Indian Ocean ◽  
Heat Fluxes ◽  
Eastern Indian Ocean ◽  
Wind Stress Curl ◽  
Upper Level

Abstract Annual coupled Rossby waves are generated at the west coast of Australia and propagate westward across the eastern Indian Ocean from 10° to 30°S in covarying sea level height (SLH), sea surface temperature (SST), and meridional surface wind (MSW) residuals, generally traveling slower than uncoupled Rossby waves while increasing amplitude. The waves decouple in the western Indian Ocean as SST and SLH residuals become decorrelated, with wave amplitudes decreasing and westward phase speeds increasing. Here, the ocean and atmosphere thermal and vorticity budgets of the coupled Rossby waves in the eastern Indian Ocean along 20°S are diagnosed. In the upper ocean, these diagnostics find the residual SST tendency driven by the residual meridional geostrophic advection of mean temperature with warm SST residuals dissipated by upward latent heat flux to the atmosphere. In the troposphere, these upward latent heat fluxes drive mid-to-upper-level residual diabatic heating via excess condensation, balanced there by upward residual vertical thermal advection. The resulting upward residual vertical velocity drives residual upper-level divergence and lower-level convergence, the latter balanced in the troposphere vorticity budget by the residual meridional advection of planetary vorticity. This yields poleward MSW residuals collocated with warm SST residuals, as observed. The SLH tendency is modified by a positive feedback from wind stress curl residuals, the latter acting to increase the amplitude and decrease the westward phase speed of the wave. These diagnostics allow a more exact analytical model for coupled Rossby waves to be constructed, yielding wave characteristics as observed.

scholarly journals Does the El Niño-Southern Oscillation Impact on the Indian Summer Monsoon 1-Dimensional? Quantifying the Role of Antecedent Southwestern Indian Ocean Capacitance on the Variability of Summer Monsoon Rainfall over Homogeneous Regions of India

2022 ◽  
Author(s):  
Venugopal Thandlam ◽  
Hasibur Rahaman ◽  
Anna Rutgersson ◽  
Erik Sahlee ◽  
Ravichandran Muthulagu ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Summer Monsoon Rainfall ◽  
Homogeneous Regions ◽  
The Impact ◽  
Southwestern Indian Ocean

Abstract Recent rapid changes in the global climate and warming temperatures increase the demand for local and regional weather forecasting and analysis to improve the accuracy of seasonal forecasting of extreme events such as droughts and floods. On the other hand, the role of ocean variability is at a focal point in improving the forecasting at different time scales. Here we study the effect of Indian Ocean mean sea level anomaly (MSLA) and sea surface temperature anomalies (SSTA) on Indian summer monsoon rainfall during 1993-2019. While SSTA and MSLA have been increasing in the southwestern Indian Ocean (SWIO), these parameters' large-scale variability and pre-monsoon winds could impact the inter-annual Indian monsoon rainfall variability over homogeneous regions. Similarly, antecedent heat capacitance over SWIO on an inter-annual time scale has been the key to the extreme monsoon rainfall variability from an oceanic perspective. Though both SSTA and MSLA over SWIO have been influenced by El Niño-southern oscillation (ENSO), the impact of SWIO variability was low on rainfall variability over several homogeneous regions. However, rainfall over northeast (NE) and North India (NI) has been moulded by ENSO, thus changing the annual rainfall magnitude. Nevertheless, the impact of ENSO on monsoon rainfall through SWIO variability during the antecedent months is moderate. Thus, the ENSO influence on the atmosphere could be dominating the ocean part in modulating the inter-annual variability of the summer monsoon. Analysis shows that the cooler (warmer) anomaly over the western Indian Ocean affects rainfall variability adversely (favourably) due to the reversal of the wind pattern during the pre-monsoon period.

scholarly journals Differential Influences of Teleconnections from the Indian and Pacific Oceans on Rainfall Variability in Southeast Asia

Atmosphere ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 886
Author(s):  
Abdul Azim Amirudin ◽  
Ester Salimun ◽  
Fredolin Tangang ◽  
Liew Juneng ◽  
Muhamad Zuhairi
Keyword(s):  
Indian Ocean ◽  
Southeast Asia ◽  
El Niño ◽  
El Nino ◽  
Rainfall Variability ◽  
June July August ◽  
Rainfall Patterns ◽  
Negative Impacts ◽  
The Individual ◽  
June July

This study investigates the individual and combined impacts of El Niño and the positive Indian Ocean Dipole (IOD) on the Southeast Asia (SEA) rainfall variability. Using composite and partial correlation techniques, it is shown that both inter-annual events have individually distinct impacts on the SEA rainfall anomaly distribution. The results showed that the impacts of the co-occurrence of El Niño and IOD events are significant compared to the individual effects of pure El Niño or pure IOD. During June-July-August and September-October-November, the individual impacts of the pure El Niño and IOD events are similar but less significant. Both events caused negative impacts over the southern part of SEA during June-July-August (JJA) and propagated northeastward/eastward during September-October-November (SON). Thus, there are significant negative impacts over the southern part of SEA during the co-occurrence of both events. The differential impacts on the anomalous rainfall patterns are due to the changes in the sea surface temperature (SST) surrounding the region. Additionally, the differences are also related to the anomalous regional atmospheric circulations that interact with the regional SST. The anomalous Walker circulation that connects the Indian Ocean and tropical Pacific Ocean also plays a significant role in determining the regional anomalous rainfall patterns.

scholarly journals Impact of the Strong Downwelling (Upwelling) on Small Pelagic Fish Production during the 2016 (2019) Negative (Positive) Indian Ocean Dipole Events in the Eastern Indian Ocean off Java

Climate ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 29
Author(s):  
Jonson Lumban-Gaol ◽  
Eko Siswanto ◽  
Kedarnath Mahapatra ◽  
Nyoman Metta Nyanakumara Natih ◽  
I Wayan Nurjaya ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Pelagic Fish ◽  
Eastern Indian Ocean ◽  
Fish Production ◽  
Small Pelagic Fish ◽  
Field Surveys ◽  
Chl A ◽  
Positive Indian Ocean Dipole ◽  
The Impact

Although researchers have investigated the impact of Indian Ocean Dipole (IOD) phases on human lives, only a few have examined such impacts on fisheries. In this study, we analyzed the influence of negative (positive) IOD phases on chlorophyll a (Chl-a) concentrations as an indicator of phytoplankton biomass and small pelagic fish production in the eastern Indian Ocean (EIO) off Java. We also conducted field surveys in the EIO off Palabuhanratu Bay at the peak (October) and the end (December) of the 2019 positive IOD phase. Our findings show that the Chl-a concentration had a strong and robust association with the 2016 (2019) negative (positive) IOD phases. The negative (positive) anomalous Chl-a concentration in the EIO off Java associated with the negative (positive) IOD phase induced strong downwelling (upwelling), leading to the preponderant decrease (increase) in small pelagic fish production in the EIO off Java.

scholarly journals Two-year consecutive concurrences of positive Indian Ocean Dipole and Central Pacific El Niño preconditioned the 2019/2020 Australian “black summer” bushfires

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Guojian Wang ◽  
Wenju Cai
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Greenhouse Warming ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Positive Indian Ocean Dipole ◽  
The Future ◽  
Rainfall Anomalies

Abstract The 2019/20 Australian black summer bushfires were particularly severe in many respects, including its early commencement, large spatial coverage, and large number of burning days, preceded by record dry and hot anomalies. Determining whether greenhouse warming has played a role is an important issue. Here, we examine known modes of tropical climate variability that contribute to droughts in Australia to provide a gauge. We find that a two-year consecutive concurrence of the 2018 and 2019 positive Indian Ocean Dipole and the 2018 and 2019 Central Pacific El Niño, with the former affecting Southeast Australia, and the latter influencing eastern and northeastern Australia, may explain many characteristics of the fires. Such consecutive events occurred only once in the observations since 1911. Using two generations of state-of-the-art climate models under historical and a business-as-usual emission scenario, we show that the frequency of such consecutive concurrences increases slightly, but rainfall anomalies during such events are stronger in the future climate, and there are drying trends across Australia. The impact of the stronger rainfall anomalies during such events under drying trends is likely to be exacerbated by greenhouse warming-induced rise in temperatures, making such events in the future even more extreme.

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