Resolving Contrasting Regional Rainfall Responses to El Niño over Tropical Africa

2016 ◽  
Vol 29 (4) ◽  
pp. 1461-1476 ◽  
Author(s):  
Pradipta Parhi ◽  
Alessandra Giannini ◽  
Pierre Gentine ◽  
Upmanu Lall
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
North Atlantic ◽  
El Niño ◽  
Rainy Season ◽  
El Nino ◽  
Sea Surface ◽  
Eastern Africa ◽  
Surface Warming ◽  
Western Sahel

Abstract The evolution of El Niño can be separated into two phases—namely, growth and mature—depending on whether the regional sea surface temperature has adjusted to the tropospheric warming in the remote tropics (tropical regions away from the central and eastern tropical Pacific Ocean). The western Sahel’s main rainy season (July–September) is shown to be affected by the growth phase of El Niño through (i) a lack of neighboring North Atlantic sea surface warming, (ii) an absence of an atmospheric column water vapor anomaly over the North Atlantic and western Sahel, and (iii) higher atmospheric vertical stability over the western Sahel, resulting in the suppression of mean seasonal rainfall as well as number of wet days. In contrast, the short rainy season (October–December) of tropical eastern Africa is impacted by the mature phase of El Niño through (i) neighboring Indian Ocean sea surface warming, (ii) positive column water vapor anomalies over the Indian Ocean and tropical eastern Africa, and (iii) higher atmospheric vertical instability over tropical eastern Africa, leading to an increase in the mean seasonal rainfall as well as in the number of wet days. While the modulation of the frequency of wet days and seasonal mean accumulation is statistically significant, daily rainfall intensity (for days with rainfall > 1 mm day−1), whether mean, median, or extreme, does not show a significant response in either region. Hence, the variability in seasonal mean rainfall that can be attributed to the El Niño–Southern Oscillation phenomenon in both regions is likely due to changes in the frequency of rainfall.

scholarly journals Two Independent Triggers for the Indian Ocean Dipole/Zonal Mode in a Coupled GCM

2005 ◽  
Vol 18 (17) ◽  
pp. 3428-3449 ◽  
Author(s):  
Albert S. Fischer ◽  
Pascal Terray ◽  
Eric Guilyardi ◽  
Silvio Gualdi ◽  
Pascale Delecluse
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Sea Surface ◽  
Dynamical Response ◽  
Thermocline Depth ◽  
Second Phase ◽  
The Indian Ocean

Abstract The question of whether and how tropical Indian Ocean dipole or zonal mode (IOZM) interannual variability is independent of El Niño–Southern Oscillation (ENSO) variability in the Pacific is addressed in a comparison of twin 200-yr runs of a coupled climate model. The first is a reference simulation, and the second has ENSO-scale variability suppressed with a constraint on the tropical Pacific wind stress. The IOZM can exist in the model without ENSO, and the composite evolution of the main anomalies in the Indian Ocean in the two simulations is virtually identical. Its growth depends on a positive feedback between anomalous equatorial easterly winds, upwelling equatorial and coastal Kelvin waves reducing the thermocline depth and sea surface temperature off the coast of Sumatra, and the atmospheric dynamical response to the subsequently reduced convection. Two IOZM triggers in the boreal spring are found. The first is an anomalous Hadley circulation over the eastern tropical Indian Ocean and Maritime Continent, with an early northward penetration of the Southern Hemisphere southeasterly trades. This situation grows out of cooler sea surface temperatures in the southeastern tropical Indian Ocean left behind by a reinforcement of the late austral summer winds. The second trigger is a consequence of a zonal shift in the center of convection associated with a developing El Niño, a Walker cell anomaly. The first trigger is the only one present in the constrained simulation and is similar to the evolution of anomalies in 1994, when the IOZM occurred in the absence of a Pacific El Niño state. The presence of these two triggers—the first independent of ENSO and the second phase locking the IOZM to El Niño—allows an understanding of both the existence of IOZM events when Pacific conditions are neutral and the significant correlation between the IOZM and El Niño.

scholarly journals ANALISIS PENGARUH EL NINO TERHADAP HUJAN DI NTT

2018 ◽  
Vol 3 (2) ◽  
pp. 155-162
Author(s):  
Maria Marselina Kain ◽  
Abdul Wahid ◽  
Apolonaris S. Geru
Keyword(s):  
Water Vapor ◽  
El Niño ◽  
Rainy Season ◽  
El Nino ◽  
Comparative Method ◽  
Comparison And Analysis ◽  
Rain Data

Abstrak Telah dilakukan penelitian tentang pengaruh El Nino Terhadap Hujan di NTT yang terdiri dari 23 Zona Musim dan dianalisis berdasarkan data Curah Hujan tujuh tahun terakhir kejadian El Nino terhadap data Normal selama 30 tahun. Tujuan dari penelitian ini adalah untuk mengetahui pengaruh El Nino terhadap Awal Musim Hujan, Periode Musim Hujan, Panjang Musim Hujan, Curah Hujan Musim Hujan dan Sifat Hujan. Metode yang digunakan dalam penelitian ini adalah metode komparatif atau perbandingan dan Analisis Curah Hujan tahun El Nino  pada tujuh kali kejadian terhadap Normal Hujan selama 30 tahun. Hasil yang diperoleh dari penelitian ini adalah pada tahun terjadi El Nino, sebagian besar ZOM di NTT  dengan Awal Musim Hujan lebih mundur dari Normal, Periode Musim Hujan lebih pendek dari Normal serta Curah Hujan berkurang dari Normal dan Sifat Hujan menjadi di Bawah Normal. Pengaruh kejadian El Nino terhadap Awal Musim Hujan yang lebih mundur dari Normalnya, Periode Musim Hujan yang lebih pendek dari Normalnya dan Sifat Hujan yang di Bawah Normal dari 23 Zona di NTT pada tahun-tahun kejadian El Nino bervariasi dan ZOM yang dipengaruhi kejadian El Nino tidak tetap. Kata kunci : El Nino, Awal Musim Hujan, Periode Musim Hujan, Sifat Hujan. Abstract [Analysis Of The Influence Of El Nino On Rain In NTT] Studies have been conducted about the influence of El Nino on Rain the province which consists of 23 Zones the Season and analyzed based on Rain data for the last seven years the incidence of El Nino against Normal data for 30 years. The purpose  of this studyis to determine the effect of El Nino to the Beginning of the Rainy Season, Long Rainy Season, Precipitation of the Rainy Season and the Nature of the Rain. The method used in this research is the comparative method or comparison and Analysis of precipitation is the year of El Nino on the seven times genesis against the Normal Rain for 30 years. The results obtained from this research is that in the event of El Nino, most of the ZOM in NTT with the Beginning of the Rainy Season is more bacward than Normal, the Period of the Rainy Season is horter than Normal and precipitation is reduced from the Normal and the Nature of Rain to be Below Normal.this is because in the event of El Nino, monsoons coming from the Southest bring the water vapor that a lot of most of the turn toward the coast of Peru. The influence of El Nino to the Beginning of the Rainy Season which is backwards from Normal, the Period of the Rainy Season is shorter than Normal and the Nature of the Rainfall Below Normal from the 23 Zones in the province in the years of El Nino are varied and ZOM that influence the incidence of El Nino is not fixed. Keywords: El Nino, the Beginning of the Rainy Season, the Period of the Rainy Season, the Nature of the Rain

scholarly journals Seasonal Covariability of Dryness or Wetness in China and Global Sea Surface Temperature

2020 ◽  
Vol 33 (2) ◽  
pp. 727-747
Author(s):  
Chunxiang Li ◽  
Chunzai Wang ◽  
Tianbao Zhao
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Sea Surface ◽  
Interdecadal Variability ◽  
Coupled Modes ◽  
Indian Ocean Basin Mode ◽  
Global Sea Surface Temperature

AbstractSeasonal covariability of the dryness/wetness in China and global sea surface temperature (SST) is investigated by using the monthly self-calibrated Palmer drought severity index (PDSI) data and other data from 1950 to 2014. The singular value decomposition (SVD) analysis shows two recurring PDSI–SST coupled modes. The first SVD mode of PDSI is associated with the warm phases of the eastern Pacific–type El Niño–Southern Oscillation (ENSO), the interdecadal Pacific oscillation (IPO) or Pacific decadal oscillation (PDO), the Indian Ocean basin mode (IOBM) in the autumn and winter, and the cold phase of the IOBM in the spring. Meanwhile, the Atlantic multidecadal oscillation (AMO) pattern appears in every season except the autumn. The second SVD mode of PDSI is accompanied by a central Pacific–type El Niño developing from the winter to autumn over the tropical Pacific and a positive phase of IPO or PDO from the winter to summer. Moreover, an AMO pattern is observed in all seasons except the summer, whereas the SST over the tropical Indian Ocean shows negligible variations. The further analyses suggest that AMO remote forcing may be a primary factor influencing interdecadal variability of PDSI in China, and interannual to interdecadal variability of PDSI seems to be closely associated with the ENSO-related events. Meanwhile, the IOBM may be a crucial factor in interannual variability of PDSI during its mature phase in the spring. In general, the SST-related dryness/wetness anomalies can be explained by the associated atmospheric circulation changes.

scholarly journals The Years of El Niño, La Niña, and Interactions with the Tropical Indian Ocean

2007 ◽  
Vol 20 (13) ◽  
pp. 2872-2880 ◽  
Author(s):  
Gary Meyers ◽  
Peter McIntosh ◽  
Lidia Pigot ◽  
Mike Pook
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Sea Surface ◽  
El Nino Southern Oscillation ◽  
La Nina ◽  
The Indian Ocean

Abstract The Indian Ocean zonal dipole is a mode of variability in sea surface temperature that seriously affects the climate of many nations around the Indian Ocean rim, as well as the global climate system. It has been the subject of increasing research, and sometimes of scientific debate concerning its existence/nonexistence and dependence/independence on/from the El Niño–Southern Oscillation, since it was first clearly identified in Nature in 1999. Much of the debate occurred because people did not agree on what years are the El Niño or La Niña years, not to mention the newly defined years of the positive or negative dipole. A method that identifies when the positive or negative extrema of the El Niño–Southern Oscillation and Indian Ocean dipole occur is proposed, and this method is used to classify each year from 1876 to 1999. The method is statistical in nature, but has a strong basis on the oceanic physical mechanisms that control the variability of the near-equatorial Indo-Pacific basin. Early in the study it was found that some years could not be clearly classified due to strong decadal variation; these years also must be recognized, along with the reason for their ambiguity. The sensitivity of the classification of years is tested by calculating composite maps of the Indo-Pacific sea surface temperature anomaly and the probability of below median Australian rainfall for different categories of the El Niño–Indian Ocean relationship.

scholarly journals Cluster Analysis of North Atlantic–European Circulation Types and Links with Tropical Pacific Sea Surface Temperatures

2008 ◽  
Vol 21 (15) ◽  
pp. 3687-3703 ◽  
Author(s):  
D. R. Fereday ◽  
J. R. Knight ◽  
A. A. Scaife ◽  
C. K. Folland ◽  
A. Philipp
Keyword(s):  
Cluster Analysis ◽  
North Atlantic ◽  
El Niño ◽  
Clustering Algorithm ◽  
El Nino ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Optimum Number ◽  
Apparent Lack ◽  
Circulation Types

Abstract Observed atmospheric circulation over the North Atlantic–European (NAE) region is examined using cluster analysis. A clustering algorithm incorporating a “simulated annealing” methodology is employed to improve on solutions found by the conventional k-means technique. Clustering is applied to daily mean sea level pressure (MSLP) fields to derive a set of circulation types for six 2-month seasons. A measure of the quality of this clustering is defined to reflect the average similarity of the fields in a cluster to each other. It is shown that a range of classifications can be produced for which this measure is almost identical but which partition the days quite differently. This lack of a unique set of circulation types suggests that distinct weather regimes in NAE circulation do not exist or are very weak. It is also shown that the stability of the clustering solution to removal of data is not maximized by a suitable choice of the number of clusters. Indeed, there does not appear to be any robust way of choosing an optimum number of circulation types. Despite the apparent lack of preferred circulation types, cluster analysis can usefully be applied to generate a set of patterns that fully characterize the different circulation types appearing in each season. These patterns can then be used to analyze NAE climate variability. Ten clusters per season are chosen to ensure that a range of distinct circulation types that span the variability is produced. Using this classification, the effect of forcing of NAE circulation by tropical Pacific sea surface temperature (SST) anomalies is analyzed. This shows a significant influence of SST in this region on certain circulation types in almost all seasons. A tendency for a negative correlation between El Niño and an anomaly pattern resembling the positive winter North Atlantic Oscillation (NAO) emerges in a number of seasons. A notable exception is November–December, which shows the opposite relationship, with positive NAO-like patterns correlated with El Niño.

scholarly journals A Simple Analytical Model for Understanding the Formation of Sea Surface Temperature Patterns under Global Warming*

2014 ◽  
Vol 27 (22) ◽  
pp. 8413-8421 ◽  
Author(s):  
Lei Zhang ◽  
Tim Li
Keyword(s):  
Global Warming ◽  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Sea Surface ◽  
The Tropics ◽  
The Tropical Pacific

Abstract How sea surface temperature (SST) changes under global warming is critical for future climate projection because SST change affects atmospheric circulation and rainfall. Robust features derived from 17 models of phase 5 of the Coupled Model Intercomparison Project (CMIP5) include a much greater warming in high latitudes than in the tropics, an El Niño–like warming over the tropical Pacific and Atlantic, and a dipole pattern in the Indian Ocean. However, the physical mechanism responsible for formation of such warming patterns remains open. A simple theoretical model is constructed to reveal the cause of the future warming patterns. The result shows that a much greater polar, rather than tropical, warming depends primarily on present-day mean SST and surface latent heat flux fields, and atmospheric longwave radiation feedback associated with cloud change further enhances this warming contrast. In the tropics, an El Niño–like warming over the Pacific and Atlantic arises from a similar process, while cloud feedback resulting from different cloud regimes between east and west ocean basins also plays a role. A dipole warming over the equatorial Indian Ocean is a response to weakened Walker circulation in the tropical Pacific.

scholarly journals A sea surface temperature reconstruction for the southern Indian Ocean trade wind belt from corals in Rodrigues Island (19° S, 63° E)

2016 ◽  
Author(s):  
J. Zinke ◽  
L. Reuning ◽  
M. Pfeiffer ◽  
J. Wassenburg ◽  
E. Hardman ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Sea Surface ◽  
Southern Indian Ocean ◽  
Trade Wind ◽  
The Past ◽  
Indian Ocean Trade

Abstract. The western Indian Ocean has been warming rapidly over the past decades and this has adversely impacted the Asian Monsoon circulation. It is therefore of paramount importance to improve our understanding of links between Indian Ocean Sea Surface Temperature (SST) variability, climate change, and sustainability of reef ecosystems. Here we present two monthly-resolved coral Sr/Ca records (Totor, Cabri) from Rodrigues Island (63° E, 19° S) in the south-central Indian Ocean trade wind belt, and reconstruct SST based on the linear relationship with the Sr/Ca proxy. The records extend to 1781 and 1945, respectively. We assess the reproducibility of the Sr/Ca records, and potential biases in our reconstruction associated with the orientation of corallites. We quantify long-term SST trends and identify interannual relationships with the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). We conclude that careful screening for diagenesis and orientation of corallites is of paramount importance to assess the quality of Sr/Ca-based SST reconstructions. Our proxy records provide a reliable SST reconstruction between 1945 and 2006. We identify strong teleconnections with the ENSO/PDO over the past 60 years, eg. warming of SST during El Niño or positive PDO. We suggest that additional records from Rodrigues Island can provide excellent records of SST variations in the southern Indian Ocean trade wind belt and teleconnections with the ENSO/PDO on longer time scales.

Teleconnected influence of North Atlantic sea surface temperature on the El Niño onset

2010 ◽  
Vol 37 (3-4) ◽  
pp. 663-676 ◽  
Author(s):  
Xin Wang ◽  
Chunzai Wang ◽  
Wen Zhou ◽  
Dongxiao Wang ◽  
Jie Song
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Sea Surface
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