scholarly journals Combined Role of High- and Low-Frequency Processes of Equatorial Zonal Transport in Terminating an ENSO Event

2018 ◽  
Vol 31 (14) ◽  
pp. 5461-5483 ◽  
Author(s):  
Han-Ching Chen ◽  
Chung-Hsiung Sui ◽  
Yu-Heng Tseng ◽  
Bohua Huang
Keyword(s):  
El Niño ◽  
High Frequency ◽  
Rossby Waves ◽  
El Nino ◽  
Low Frequency ◽  
Kelvin Waves ◽  
La Niña ◽  
La Nina ◽  
Eastern Boundary ◽  
Peak Phase

This study investigates the sudden reversal of anomalous zonal equatorial transport above thermocline at the peak phase of ENSO. The oceanic processes associated with zonal transport are separated into low-frequency ENSO cycle and high-frequency oceanic wave processes. Both processes can generate a reversal of equatorial zonal current at the ENSO peak phase, which is a trigger for the rapid termination of ENSO events. For the low-frequency process, zonal transport exhibits slower and basinwide evolution. During the developing phase of El Niño (La Niña), eastward (westward) transport prevails in the central-eastern Pacific, which enhances ENSO. At the peak of ENSO, a basinwide reversal of the zonal transport resulting from the recharge–discharge process occurs and weakens the existing SST anomalies. High-frequency zonal transport presents clear eastward propagation related to Kelvin wave propagation at the equator, reflection at the eastern boundary, and the westward propagating Rossby waves. The major westerly wind bursts (easterly wind surges) occur in late boreal summer and fall with coincident downwelling (upwelling) Kelvin waves for El Niño (La Niña) events. After the peak of El Niño (La Niña), Kelvin waves reach the eastern boundary in boreal winter and reflect as off-equatorial Rossby waves; then, the zonal transport switches from eastward (westward) to westward (eastward). The high-frequency zonal transport can be represented by equatorial wave dynamics captured by the first three EOFs based on the high-pass-filtered equatorial thermocline. The transport anomaly during the decaying phase is dominated by the low-frequency process in El Niño. However, the transport anomaly is caused by both low- and high-frequency processes during La Niña.

scholarly journals The Nature of the Stochastic Wind Forcing of ENSO

2018 ◽  
Vol 31 (19) ◽  
pp. 8081-8099 ◽  
Author(s):  
Antonietta Capotondi ◽  
Prashant D. Sardeshmukh ◽  
Lucrezia Ricciardulli
Keyword(s):  
El Niño ◽  
High Frequency ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Kelvin Waves ◽  
Wind Forcing ◽  
Alternative View ◽  
Low Frequencies ◽  
Wind Events

El Niño–Southern Oscillation (ENSO) is commonly viewed as a low-frequency tropical mode of coupled atmosphere–ocean variability energized by stochastic wind forcing. Despite many studies, however, the nature of this broadband stochastic forcing and the relative roles of its high- and low-frequency components in ENSO development remain unclear. In one view, the high-frequency forcing associated with the subseasonal Madden–Julian oscillation (MJO) and westerly wind events (WWEs) excites oceanic Kelvin waves leading to ENSO. An alternative view emphasizes the role of the low-frequency stochastic wind components in directly forcing the low-frequency ENSO modes. These apparently distinct roles of the wind forcing are clarified here using a recently released high-resolution wind dataset for 1990–2015. A spectral analysis shows that although the high-frequency winds do excite high-frequency Kelvin waves, they are much weaker than their interannual counterparts and are a minor contributor to ENSO development. The analysis also suggests that WWEs should be viewed more as short-correlation events with a flat spectrum at low frequencies that can efficiently excite ENSO modes than as strictly high-frequency events that would be highly inefficient in this regard. Interestingly, the low-frequency power of the rapid wind forcing is found to be higher during El Niño than La Niña events, suggesting a role also for state-dependent (i.e., multiplicative) noise forcing in ENSO dynamics.

scholarly journals Seasonal and Interannual Variabilities of the Central Indian Ocean Mode

2017 ◽  
Vol 30 (16) ◽  
pp. 6505-6520 ◽  
Author(s):  
Lei Zhou ◽  
Raghu Murtugudde ◽  
Dake Chen ◽  
Youmin Tang
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Wind Shear ◽  
El Nino ◽  
Low Frequency ◽  
La Niña ◽  
Barotropic Instability ◽  
Zonal Winds ◽  
Central Indian Ocean ◽  
La Nina

The central Indian Ocean (CIO) mode, an intrinsic coupled mode, plays an important role in the intraseasonal variabilities over the Indian monsoon region. Besides the intraseasonal variabilities, the CIO mode also has pronounced seasonal and interannual variabilities. The CIO mode is active during boreal summer but suppressed during boreal winter. The seasonality is mainly attributable to the barotropic instability, which is caused by the large meridional shear of zonal winds. By decomposing the temporal tendency of the meridional gradient of zonal winds, it is found that the zonal wind shear mainly follows the variation of the horizontal eddy flux, which indicates the importance of the multiscale interaction in tropical dynamics. The interannual variability of the CIO mode also depends on the energy transfer associated with the barotropic instability. The influences of El Niño or La Niña and Indian Ocean dipole–zonal mode (IODZM) on the CIO mode are analyzed. El Niño and La Niña have moderate impacts on the CIO mode. El Niño weakens the CIO mode and La Niña strengthens it via the changes in the low-level zonal wind shear. IODZM does not significantly change the amplitude of the CIO mode but can shift its latitudinal position by modifying the meridional shear of the zonal winds. The low-frequency variabilities of the CIO mode at seasonal and interannual time scales unveil the impacts of the background circulations at the intraseasonal variabilities during the Indian summer monsoon in a multiscale framework. While the low-frequency variabilities of this mode will clearly have an implication for monsoon variability and prediction, further studies are needed to quantify the impacts.

scholarly journals ENSO Impact on Kelvin Waves and Associated Tropical Convection

2013 ◽  
Vol 70 (11) ◽  
pp. 3513-3532 ◽  
Author(s):  
Gui-Ying Yang ◽  
Brian Hoskins
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tropical Convection ◽  
Kelvin Waves ◽  
La Niña ◽  
Eastern Pacific ◽  
Substantial Impact ◽  
La Nina ◽  
Central Eastern ◽  
The Impact

Abstract The impact of El Niño–Southern Oscillation (ENSO) on atmospheric Kelvin waves and associated tropical convection is investigated using the ECMWF Re-Analysis, NOAA outgoing longwave radiation (OLR), and the analysis technique introduced in a previous study. It is found that the phase of ENSO has a substantial impact on Kelvin waves and associated convection over the equatorial central-eastern Pacific. El Niño (La Niña) events enhance (suppress) variability of the upper-tropospheric Kelvin wave and the associated convection there, in both extended boreal winter and summer. The mechanism of the impact is through changes in the ENSO-related thermal conditions and the ambient flow. In El Niño years, because of SST increase in the equatorial central-eastern Pacific, variability of eastward-moving convection, which is mainly associated with Kelvin waves, intensifies in the region. In addition, owing to the weakening of the equatorial eastern Pacific westerly duct in the upper troposphere in El Niño years, Kelvin waves amplify there. In La Niña years, the opposite occurs. However, the stronger westerly duct in La Niña winters allows more NH extratropical Rossby wave activity to propagate equatorward and force Kelvin waves around 200 hPa, partially offsetting the in situ weakening effect of the stronger westerlies on the waves. In general, in El Niño years Kelvin waves are more convectively and vertically coupled and propagate more upward into the lower stratosphere over the central-eastern Pacific. The ENSO impact in other regions is not clear, although in winter over the eastern Indian and western Pacific Oceans Kelvin waves and their associated convection are slightly weaker in El Niño than in La Niña years.

scholarly journals Interannual Sea Level Variations in the South Pacific from 5° to 28°S

2007 ◽  
Vol 37 (12) ◽  
pp. 2882-2894 ◽  
Author(s):  
Jianke Li ◽  
Allan J. Clarke
Keyword(s):  
Sea Level ◽  
Rossby Wave ◽  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
La Niña ◽  
Shelf Edge ◽  
Sea Level Variability ◽  
Sea Level Anomalies ◽  
La Nina

Abstract Ocean Topography Experiment (TOPEX)/Poseidon/Jason-1 satellite altimeter observations for the 11-yr period from January 1993 to December 2003 show that in the South Pacific Ocean most of the interannual sea level variability in the region 5°–28°S is west of 160°W. This interannual variability is largest from about 5° to 15°S and from 155°E to 160°W, reaching a root-mean-square value of over 11 cm. Calculations show that this interannual sea level signal can be described by first and second baroclinic vertical mode Rossby waves forced by the curl of the interannual Ekman transport. This curl, which tends to be positive during El Niño and negative during La Niña, generates positive (negative) sea level anomalies during El Niño (La Niña) that increase westward in amplitude in accordance with Rossby wave dynamics. The sea level anomalies are not exactly in phase with the curl forcing because Sverdrup balance does not hold—vortex stretching also contributes to the response. East of 160°W is a large “quiet” region of low interannual sea level variability, especially south of about 15°S. This is surprising because there is no flow into the coast, so the interannual sea level amplitude of equatorial origin should be constant along the coast, resulting in a source of westward-propagating Rossby waves of considerable amplitude. The large low-variability region results because coastal sea level amplitude falls between 5° and 15°S, so the Rossby wave source south of 15°S is weak. During El Niño the sea level is higher than normal at the coast, so the southward fall in anomalous sea level implies, by geostrophy, that there is an anomalous onshore flow. This flow feeds an anomalous southward El Niño current of up to 20 cm s−1 above the 30–50-km-wide shelf edge. During La Niña the sea level is lower than normal at the coast and the flows reverse: a narrow anomalously northward shelf-edge flow feeding a broad offshore flow between 5° and 15°S. South of 16°S the coastal flow is much weaker.

scholarly journals Discussion on the Application of Statistical Analysis Method in Geography Education Research —— Taking Drought and Snow Disaster in Xilingol League as an Example

2021 ◽  
Vol 4 (2) ◽  
pp. 28
Author(s):  
Jingbo Cao
Keyword(s):  
Statistical Analysis ◽  
El Niño ◽  
High Frequency ◽  
El Nino ◽  
Geography Education ◽  
La Niña ◽  
Analysis Method ◽  
La Nina ◽  
Statistical Analysis Method ◽  
Temporal And Spatial

Based on the statistical analysis method, this paper studies the temporal and spatial correlation between drought and snow Based on the statistical analysis method, this paper studies the temporal and spatial correlation between drought and snow disasters and El Nino/La Nina events in various counties of Xilingol League. According to the research results, it is found that the number of disasters in Xilingol League in El Nino/La Nina year accounts for 54% of the total number of disasters in Xilingol League. El Nino has more disasters than La Nina. In El Nino/La Nina years, the frequency of snow disasters in Xilingol League is higher than that of drought disasters. The areas with high frequency of El Nino disasters are East Ujimqin Banner, West Ujimqin Banner and Abaga Banner. The areas with high frequency of disasters in La Nina are Sonid Zuoqi, Erenhot, Xilinhot and Xianghuang Banner. Using statistical analysis method can accurately and effectively study whether there is obvious correlation between drought and snow disasters and El Nino/La Nina events in Xilingol League, and enrich the methods and contents in geography education and research, which is of great significance for monitoring and preventing drought and snow disasters in Xilingol League.

scholarly journals The 10–20 d Low-Frequency Oscillation Characteristics of Summer Precipitation in Eastern China in the Decaying Year of CP ENSO

Atmosphere ◽  
2019 ◽  
Vol 10 (10) ◽  
pp. 616
Author(s):  
Cong Cai ◽  
Lijuan Wang ◽  
Junyu Wang ◽  
Zhiqiang Wang
Keyword(s):  
El Niño ◽  
El Nino ◽  
Eastern China ◽  
Low Frequency ◽  
Summer Precipitation ◽  
La Niña ◽  
Low Frequency Oscillation ◽  
Cp El Niño ◽  
La Nina ◽  
Oscillation Characteristics

Using National Centers for Atmospheric Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and observational data, the low-frequency oscillation characteristics of precipitation in eastern China during the decaying summer of central Pacific El Niño–Southern Oscillation (CP ENSO) and the corresponding low-frequency atmospheric oscillation characteristic were investigated. The results showed that summer precipitation in eastern China during the decaying year of CP El Niño (La Niña) was more (less) than the climatological mean and that 10–20 d was its dominant period. Low-frequency oscillations at different tropospheric levels had different effects on low-frequency precipitation. In the upper troposphere, Eastern China was dominated by low-frequency divergence and positive (negative) anomaly of low-frequency height during the decaying year of CP El Niño (La Niña), and there was strong (weak) northwest–southeast wave-active flux transport. In the middle troposphere, the range and intensity of the subtropical western Pacific High (SWPH) of CP El Niño was larger and stronger than that of CP La Niña, which may be related to the low-frequency height fields. Meanwhile, the correspnding low-frequency wind field, water vapor circulation systems and moisture transport channels in the lower troposphere, along with the low-frequency vertical movement were significantly different, causing the low-frequency precipitation of CP El Niño to be stronger than CP La Niña.

ANALISIS DAERAH RAWAN KEKERINGAN LAHAN JAGUNG BERDASARKAN IKLIM OLDEMAN DAN KETERSEDIAN AIR TANAH DI NUSA TENGGARA TIMUR SAAT PERIODE EL NINO DAN LA NINA

2019 ◽  
Vol 3 ◽  
pp. 1219
Author(s):  
Oki Adrianto ◽  
Sudirman Sudirman ◽  
Suwandi Suwandi
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
La Nina

Perekonomian Provinsi Nusa Tenggara Timur secara sektoral masih didominasi sektor pertanian.Tanaman jagung menjadi salah satu produksi tanaman pangan terbesar berdasarkan data dari Dinas Pertanian dan Perkebunan Provinsi Nusa Tenggara Timur tahun 2015. Peningkatan produksi pertanian dapat dilakukan melalui berbagai strategi adaptasi dan upaya penanganan bencana, salah satu upaya tersebut adalah dengan penyediaan informasi iklim terkait penentuan daerah-daerah rawan kekeringan. Tujuan dari penelitian ini adalah untuk mengetahui sebaran wilayah rawan kekeringan lahan jagung bulanan di Provinsi Nusa Tenggara Timur saat kondisi El Nino dan La Nina dengan periodeisasi bulanan januari hingga desember. Data yang digunakan dalam penelitian ini adalah data curah hujan rata rata bulanan di 19 pos hujan di Provinsi Nusa Tenggara Timur dan suhu udara rata-rata bulanan dihitung menggunakan pendekatan teori Brack dengan titik referensi Stasiun Klimatologi Lasiana Kupang. Periode dari masing-masing data yang digunakan adalah dari tahun 1991 dan 1997 digunakan sebagai tahun El Nino dan tahun 1999 dan 2010 digunakan sebagai tahun La Nina. Metode yang digunakan untuk menentukan tingkat rawan kekeringan dengan menggunakan pembobotan berdasarkan penjumlahan bobot tipe iklim Oldeman dan bobot ketersediaan air tanah. Hasil penelitian menunjukkan sebaran daerah kekeringan di Provinsi Nusa Tenggara Timurpada tahun el nino lebih luas dibandingkan tahun la nina.

A Influência dos fenômenos El Niño e La Niña sobre a dinâmica climática da região Amazônica

2018 ◽  
Vol 1 ◽  
pp. e2018014
Author(s):  
Samya de Freitas MOREIRA ◽  
Cleiciane Silva da CONCEIÇÃO ◽  
Milla Cristina Santos da CRUZ ◽  
Antônio PEREIRA JÚNIOR
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
La Nina
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