scholarly journals Seasonal and regional signatures of ENSO in upper tropospheric jet characteristics from reanalyses

2021 ◽  
pp. 1
Author(s):  
Gloria L Manney ◽  
Michaela I Hegglin ◽  
Zachary D Lawrence
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Eastern Pacific ◽  
Eastern Hemisphere ◽  
Subtropical Jet ◽  
Jet Variability ◽  
Relationship Of ◽  
Jet Characteristics

AbstractThe relationship of upper tropospheric jet variability to El Niño / Southern Oscillation (ENSO) in reanalysis datasets is analyzed for 1979–2018, revealing robust regional and seasonal variability. Tropical jets associated with monsoons and the Walker circulation are weaker and the zonal mean subtropical jet shifts equatorward in both hemispheres during El Niño, consistent with previous findings. Regional and seasonal variations are analyzed separately for subtropical and polar jets. The subtropical jet shifts poleward during El Niño over the NH eastern Pacific in DJF, and in some SH regions in MAMand SON. Subtropical jet altitudes increase during El Niño, with significant changes in the zonal mean in the NH and during summer/fall in the SH. Though zonal mean polar jet correlations with ENSO are rarely significant, robust regional/seasonal changes occur: The SH polar jet shifts equatorward during El Niño over Asia and the western Pacific in DJF, and poleward over the eastern Pacific in JJA and SON. Polar jets are weaker (stronger) during El Niño in the western (eastern) hemisphere, especially in the SH; conversely, subtropical jets are stronger (weaker) in the western (eastern) hemisphere during El Niño in winter and spring; these opposing changes, along with an anticorrelation between subtropical and polar jet windspeed, reinforce subtropical/polar jet strength differences during El Niño, and suggest ENSO-related covariability of the jets. ENSO-related jet latitude, altitude, and windspeed changes can reach 4(3)°, 0.6(0.3) km, and 6(3) ms−1, respectively, for the subtropical (polar) jets.

scholarly journals Interannual and Interdecadal Variability of Thailand Summer Monsoon Season

2005 ◽  
Vol 18 (11) ◽  
pp. 1697-1708 ◽  
Author(s):  
Nkrintra Singhrattna ◽  
Balaji Rajagopalan ◽  
K. Krishna Kumar ◽  
Martyn Clark
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
Large Scale ◽  
Monsoon Rainfall ◽  
El Nino ◽  
Southern Oscillation ◽  
Negative Relationship ◽  
Walker Circulation ◽  
Planning And Management ◽  
The Walker Circulation

Abstract Summer monsoon rains are a critical factor in Thailand’s water resources and agricultural planning and management. In fact, they have a significant impact on the country’s economic health. Consequently, understanding the variability of the summer monsoon rains over Thailand is important for instituting effective mitigating strategies against extreme rainfall fluctuations. To this end, the authors systematically investigated the relationships between summer monsoon precipitation from the central and northern regions of Thailand and large-scale climate features. It was found that Pacific sea surface temperatures (SSTs), in particular, El Niño–Southern Oscillation (ENSO), have a negative relationship with the summer monsoon rainfall over Thailand in recent decades. However, the relationship between summer rainfall and ENSO was weak prior to 1980. It is hypothesized that the ENSO teleconnection depends on the SST configuration in the tropical Pacific Ocean, that is, an eastern Pacific–based El Niño pattern, such as is the case in most of the post-1980 El Niño events, tends to place the descending limb of the Walker circulation over the Thailand–Indonesian region, thereby significantly reducing convection and consequently, rainfall over Thailand. It is believed that this recent shift in the Walker circulation is instrumental for the nonstationarity in ENSO–monsoon relationships in Thailand. El Niños of 1997 and 2002 corroborate this hypothesis. This has implications for monsoon rainfall forecasting and, consequently, for resources planning and management.

scholarly journals Atmospheric torques and Earth's rotation: what drove the millisecond-level length-of-day response to the 2015–2016 El Niño?

2017 ◽  
Vol 8 (4) ◽  
pp. 1009-1017 ◽  
Author(s):  
Sébastien B. Lambert ◽  
Steven L. Marcus ◽  
Olivier de Viron
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Winter Season ◽  
Eastern Pacific ◽  
Earth’S Rotation ◽  
Length Of Day ◽  
Central Pacific ◽  
Earth's Rotation ◽  
Enso Events

Abstract. El Niño–Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east–west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982–1983 event produced a lengthening of the day of about 0.9 ms, while a major ENSO event during the 2015–2016 winter season produced an LOD excursion reaching 0.81 ms in January 2016. By evaluating the anomaly in mountain and friction torques, we found that (i) as a mixed eastern–central Pacific event, the 2015–2016 mountain torque was smaller than for the 1982–1983 and 1997–1998 events, which were pure eastern Pacific events, and (ii) the smaller mountain torque was compensated for by positive friction torques arising from an enhanced Hadley-type circulation in the eastern Pacific, leading to similar AAM–LOD signatures for all three extreme ENSO events. The 2015–2016 event thus contradicts the existing paradigm that mountain torques cause the Earth rotation response for extreme El Niño events.

scholarly journals Relationships between Extratropical Sea Level Pressure Variations and the Central Pacific and Eastern Pacific Types of ENSO

2011 ◽  
Vol 24 (3) ◽  
pp. 708-720 ◽  
Author(s):  
Jin-Yi Yu ◽  
Seon Tae Kim
Keyword(s):  
Sea Level ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Nodal Point ◽  
Eastern Pacific ◽  
Central Pacific ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Sst Anomalies

Abstract This study examines the linkages between leading patterns of interannual sea level pressure (SLP) variability over the extratropical Pacific (20°–60°N) and the eastern Pacific (EP) and central Pacific (CP) types of El Niño–Southern Oscillation (ENSO). The first empirical orthogonal function (EOF) mode of the extratropical SLP anomalies represents variations of the Aleutian low, and the second EOF mode represents the North Pacific Oscillation (NPO) and is characterized by a meridional SLP anomaly dipole with a nodal point near 50°N. It is shown that a fraction of the first SLP mode can be excited by both the EP and CP types of ENSO. The SLP response to the EP type is stronger and more immediate. The tropical–extratropical teleconnection appears to act more slowly for the CP ENSO. During the decay phase of EP events, the associated extratropical SLP anomalies shift from the first SLP mode to the second SLP mode. As the second SLP mode grows, subtropical SST anomalies are induced beneath via surface heat flux anomalies. The SST anomalies persist after the peak in strength of the second SLP mode, likely because of the seasonal footprinting mechanism, and lead to the development of the CP type of ENSO. This study shows that the CP ENSO is an extratropically excited mode of tropical Pacific variability and also suggests that the decay of an EP type of ENSO can lead to the onset of a CP type of ENSO with the aid of the NPO. This extratropical linking mechanism appears to be at work during the 1972, 1982, and 1997 strong El Niño events, which were all EP events and were all followed by strong CP La Niña events after the NPO was excited in the extratropics. This study concludes that extratropical SLP variations play an important role in exciting the CP type of ENSO and in linking the transitions from the EP to CP events.

scholarly journals Convective Control of ENSO Simulated in MIROC

2011 ◽  
Vol 24 (2) ◽  
pp. 543-562 ◽  
Author(s):  
Masahiro Watanabe ◽  
Minoru Chikira ◽  
Yukiko Imada ◽  
Masahide Kimoto
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
High Sensitivity ◽  
Eastern Pacific ◽  
Entrainment Rate ◽  
Cold Tongue ◽  
Nonlinear Feedback ◽  
Bjerknes Feedback ◽  
The Mean

Abstract The high sensitivity of the El Niño–Southern Oscillation (ENSO) to cumulus convection is examined by means of a series of climate simulations using an updated version of the Model for Interdisciplinary Research on Climate (MIROC), called MIROC5. Given that the preindustrial control run using MIROC5 shows a realistic ENSO, the integration is repeated with four different values of the parameter, λ, which affects the efficiency of the entrainment rate in cumuli. The ENSO amplitude is found to be proportional to λ−1 and to vary from 0.6 to 1.6 K. A comparison of four experiments reveals the mechanisms for which the cumulus convections control behavior of ENSO in MIROC as follows. Efficient entrainment due to a large λ increases congestus clouds over the intertropical convergence zone (ITCZ) and reduces the vertical temperature gradient over the eastern Pacific, resulting in a wetter ITCZ and drier cold tongue via accelerated meridional circulation. The dry cold tongue then shifts the atmospheric responses to El Niño/La Niña westward, thereby reducing the effective Bjerknes feedback. The first half of these processes is identifiable in a companion set of atmosphere model experiments, but the difference in mean precipitation contrast is quite small. On one hand, the mean meridional precipitation contrast over the eastern Pacific is a relevant indicator of the ENSO amplitude in MIROC. On the other hand, the nonlinear feedback from ENSO affects the mean state, the latter therefore not regarded as a fundamental cause for different ENSO amplitudes.

El Niño controls Holocene rabbit and hare populations in Baja California

2015 ◽  
Vol 84 (1) ◽  
pp. 46-56 ◽  
Author(s):  
Isaac A. Hart ◽  
Jack M. Broughton ◽  
Ruth Gruhn
Keyword(s):  
El Niño ◽  
Late Holocene ◽  
Baja California ◽  
El Nino ◽  
Southern Oscillation ◽  
Modern Human ◽  
Taxonomic Composition ◽  
Eastern Pacific ◽  
Long Term Effects ◽  
Animal Populations

The El Niño/Southern Oscillation (ENSO) is a major source of climatic variation worldwide, with significant impacts on modern human and animal populations. However, few detailed records exist on the long-term effects of ENSO on prehistoric vertebrate populations. Here we examine how lagomorph (rabbit and hare) deposition rate, population age structure and taxonomic composition from Abrigo de los Escorpiones, a well-dated, trans-Holocene vertebrate fauna from northern Baja California, Mexico, vary as a function of the frequency of wet El Niño events and eastern Pacific sea-surface temperatures (SSTs) derived from eastern Pacific geological records. Faunal indices vary significantly in response to El Niño-based precipitation and SST, with substantial moisture-driven variability in the middle and late Holocene. The late Holocene moisture pulse is coincident with previously documented changes in the population dynamics of other vertebrates, including humans. As the frequency and intensity of ENSO is anticipated to vary in the future, these results have important implications for change in future vertebrate populations.

scholarly journals ANALISIS KEJADIAN EL NINO TAHUN 2015 DAN PENGARUHNYA TERHADAP PENINGKATAN TITIK API DI WILAYAH SUMATERA DAN KALIMANTAN

2016 ◽  
Vol 17 (1) ◽  
pp. 11 ◽  
Author(s):  
Ardila Yananto ◽  
Saraswati Dewi
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
Southern Oscillation Index ◽  
Rainfall Intensity ◽  
El Nino ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Temporal And Spatial

IntisariKejadian El Nino yang berdampak pada sebagian besar wilayah Indonesia akan selalu berasosiasi dengan kekeringan akibat dari berkurangnya intensitas curah hujan. Lebih jauh akibat dari kekeringan tersebut telah menimbulkan meningkatnya titik api secara signifikan dibandingkan dengan tahun-tahun sebelumnya khususnya di wilayah Sumatera dan Kalimantan, dimana hal tersebut telah mengakibatkan terjadinya bencana asap pada tahun 2015. Tujuan utama penulisan karya tulis ini adalah untuk menganalisis kejadian El Nino pada tahun 2015 dan pengaruhnya terhadap peningkatan titik api di wilayah Sumatera dan Kalimantan baik dalam skala temporal maupun spasial. Dari hasil penelitian ini dapat diketahui bahwa berdasarkan parameter NINO 3.4 SST Indeks dan Southern Oscillation Index (SOI) pada tahun 2015 telah terjadi fenomana El Nino pada level kuat yang ditandai dengan adanya pelemahan sirkulasi walker sehingga pusat tekanan rendah perpindah dari Samudera Pasifik bagian Barat ke Samudera Pasifik bagian Timur, dimana hal ini telah menyebabkan adanya penurunan intensitas curah hujan (anomali negatif) disebagian besar wilayah Indonesia terutama pada bulan Juli hingga Oktober 2015 dan oleh karena itulah pada bulan Juli hingga Oktober 2015 tersebut terjadi peningkatan jumlah titik api yang sangat tajam di wilayah Indonesia dimana persebaran titik api tersebut sebagian besar terkonsentrasi di Provinsi Sumatera Selatan dan Kalimantan Tengah. AbstractEl Nino that impact most areas of Indonesia will always be associated in drought due to reduced rainfall intensity. Drought, in further, has resulted in increasing titik apis significantly compared to previous years, especially in the Sumatra and Kalimantan, that was creating smog disaster in 2015. The main objective of this research was to analyze the occurrence of El Nino in 2015 and its influence on increase of titik api in Sumatera and Kalimantan both in temporal and spatial scale. From this research it is known that based on the NINO 3.4 SST index and the Southern Oscillation Index (SOI) it is known there was a strong El Niño event occurred in 2015 showed there was a weakening Walker circulation so that the low pressure center moved from Western part of the Pacific Ocean to the Eastern Pacific Ocean, where this has led to a decrease rainfall intensity (negative anomaly) in most parts of Indonesia, especially from July to October 2015 and because of that from July to October 2015 there was very hight increasing number of titik apis in Indonesia where the spread of titik api the mostly concentrated in the province of South Sumatera and Central Kalimantan. 

scholarly journals Synchronized spatial shifts of Hadley and Walker circulations

2020 ◽  
Author(s):  
Kyung-Sook Yun ◽  
Axel Timmermann ◽  
Malte F. Stuecker
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Warm Pool ◽  
Central Pacific ◽  
Spatial Shift ◽  
Southern Central ◽  
Spatio Temporal

Abstract. The El Niño-Southern Oscillation (ENSO) influences the most extensive tropospheric circulation cells on our planet, known as Hadley and Walker circulations. Previous studies have largely focused on the effect of ENSO on the strength of these cells. However, what has remained uncertain is whether interannual sea surface temperature anomalies can also cause synchronized spatial shifts of these circulations. Here, by examining the spatio-temporal relationship between Hadley and Walker cells in observations and climate model experiments, we demonstrate that the seasonally evolving warm pool SST anomalies in the decay phase of an El Niño event generate a meridionally asymmetric Walker circulation response, which couples the zonal and meridional atmospheric overturning circulations. This process, which can be characterized as a phase-synchronized spatial shift in Walker and Hadley cells, is accompanied by cross-equatorial northwesterly low-level flow that diverges from an area of anomalous drying in the western North Pacific and converges towards a region with anomalous moistening in the southern central Pacific. Our results show that the SST-induced concurrent spatial shifts of the two circulations are climatically relevant as they can further amplify extratropical precipitation variability on interannual timescales.

scholarly journals On the Relationship between ENSO, Stratospheric Sudden Warmings, and Blocking

2014 ◽  
Vol 27 (12) ◽  
pp. 4704-4720 ◽  
Author(s):  
David Barriopedro ◽  
Natalia Calvo
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Eastern Pacific ◽  
Strong Preference ◽  
Planetary Scale ◽  
Stratospheric Sudden Warmings ◽  
Enso Modulation ◽  
The Relationship

Abstract This paper examines the influence of El Niño–Southern Oscillation (ENSO) on different aspects of major stratospheric sudden warmings (SSWs), focusing on the precursor role of blocking events. The results reveal an ENSO modulation of the blocking precursors of SSWs. European and Atlantic blocks tend to precede SSWs during El Niño (EN), whereas eastern Pacific and Siberian blocks are the preferred precursors of SSWs during La Niña (LN) winters. This ENSO preference for different blocking precursors seems to occur through an ENSO effect on regional blocking persistence, which in turn favors the occurrence of SSWs. The regional blocking precursors of SSWs during each ENSO phase also have different impacts on the upward propagation of planetary-scale wavenumbers 1 and 2; hence, they determine ENSO differences in the wavenumber signatures of SSWs. SSWs occurring during EN are preceded by amplification of wavenumber 1, whereas LN SSWs are predominantly associated to wavenumber-2 amplification. However, there is not a strong preference for splitting or displacement SSWs during any ENSO phase. This is mainly because during EN, splitting SSWs do not show a wavenumber-2 pattern.

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