scholarly journals Role of moist energy advection in formulating anomalous Walker Circulation associated with El Niño

2007 ◽  
Vol 112 (D24) ◽  
Author(s):  
Yoo-Geun Ham ◽  
Jong-Seong Kug ◽  
In-Sik Kang
Keyword(s):  
El Niño ◽  
El Nino ◽  
Walker Circulation

scholarly journals Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration

2012 ◽  
Vol 25 (9) ◽  
pp. 3321-3335 ◽  
Author(s):  
Masamichi Ohba ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Enso Asymmetry ◽  
Sst Anomalies

Warm and cold phases of El Niño–Southern Oscillation (ENSO) exhibit a significant asymmetry in their transition/duration such that El Niño tends to shift rapidly to La Niña after the mature phase, whereas La Niña tends to persist for up to 2 yr. The possible role of sea surface temperature (SST) anomalies in the Indian Ocean (IO) in this ENSO asymmetry is investigated using a coupled general circulation model (CGCM). Decoupled-IO experiments are conducted to assess asymmetric IO feedbacks to the ongoing ENSO evolution in the Pacific. Identical-twin forecast experiments show that a coupling of the IO extends the skillful prediction of the ENSO warm phase by about one year, which was about 8 months in the absence of the IO coupling, in which a significant drop of the prediction skill around the boreal spring (known as the spring prediction barrier) is found. The effect of IO coupling on the predictability of the Pacific SST is significantly weaker in the decay phase of La Niña. Warm IO SST anomalies associated with El Niño enhance surface easterlies over the equatorial western Pacific and hence facilitate the El Niño decay. However, this mechanism cannot be applied to cold IO SST anomalies during La Niña. The result of these CGCM experiments estimates that approximately one-half of the ENSO asymmetry arises from the phase-dependent nature of the Indo-Pacific interbasin coupling.

The essential role of early-spring westerly wind burst in generating the centennial extreme 1997/98 El Niño

2021 ◽  
pp. 1-38
Author(s):  
Tao Lian ◽  
Dake Chen
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Coupled Model ◽  
Early Spring ◽  
Strong Nonlinearity ◽  
Westerly Wind ◽  
Enso Dynamics

AbstractWhile both intrinsic low-frequency atmosphere–ocean interaction and multiplicative burst-like event affect the development of the El Niño–Southern Oscillation (ENSO), the strong nonlinearity in ENSO dynamics has prevented us from separating their relative contributions. Here we propose an online filtering scheme to estimate the role of the westerly wind bursts (WWBs), a type of aperiodic burst-like atmospheric perturbation over the western-central tropical Pacific, in the genesis of the centennial extreme 1997/98 El Niño using the CESM coupled model. This scheme highlights the deterministic part of ENSO dynamics during model integration, and clearly demonstrates that the strong and long-lasting WWB in March 1997 was essential for generating the 1997/98 El Niño. Without this WWB, the intrinsic low-frequency coupling would have only produced a weak warm event in late 1997 similar to the 2014/15 El Niño.

scholarly journals Indo-Pacific Variability on Seasonal to Multidecadal Time Scales. Part II: Multiscale Atmosphere–Ocean Linkages

2018 ◽  
Vol 31 (2) ◽  
pp. 693-725 ◽  
Author(s):  
Dimitrios Giannakis ◽  
Joanna Slawinska
Keyword(s):  
Time Scales ◽  
El Niño ◽  
El Nino ◽  
Walker Circulation ◽  
La Niña ◽  
Central Pacific ◽  
Australian Monsoon ◽  
La Nina ◽  
Combination Modes ◽  
Sst Anomalies

The coupled atmosphere–ocean variability of the Indo-Pacific domain on seasonal to multidecadal time scales is investigated in CCSM4 and in observations through nonlinear Laplacian spectral analysis (NLSA). It is found that ENSO modes and combination modes of ENSO with the annual cycle exhibit a seasonally synchronized southward shift of equatorial surface zonal winds and thermocline adjustment consistent with terminating El Niño and La Niña events. The surface winds associated with these modes also generate teleconnections between the Pacific and Indian Oceans, leading to SST anomalies characteristic of the Indian Ocean dipole. The family of NLSA ENSO modes is used to study El Niño–La Niña asymmetries, and it is found that a group of secondary ENSO modes with more rapidly decorrelating temporal patterns contributes significantly to positively skewed SST and zonal wind statistics. Besides ENSO, fundamental and combination modes representing the tropospheric biennial oscillation (TBO) are found to be consistent with mechanisms for seasonally synchronized biennial variability of the Asian–Australian monsoon and Walker circulation. On longer time scales, a multidecadal pattern referred to as the west Pacific multidecadal mode (WPMM) is established to significantly modulate ENSO and TBO activity, with periods of negative SST anomalies in the western tropical Pacific favoring stronger ENSO and TBO variability. This behavior is attributed to the fact that cold WPMM phases feature anomalous decadal westerlies in the tropical central Pacific, as well as an anomalously flat zonal thermocline profile in the equatorial Pacific. Moreover, the WPMM is found to correlate significantly with decadal precipitation over Australia.

scholarly journals Influence of the 2015–2016 El Niño on the record-breaking mangrove dieback along northern Australia coast

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
S. Abhik ◽  
Pandora Hope ◽  
Harry H. Hendon ◽  
Lindsay B. Hutley ◽  
Stephanie Johnson ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Multiple Linear Regression Model ◽  
Frequency Component ◽  
Enso Cycle ◽  
Northern Australia ◽  
Climate Conditions

AbstractThis study investigates the underlying climate processes behind the largest recorded mangrove dieback event along the Gulf of Carpentaria coast in northern Australia in late 2015. Using satellite-derived fractional canopy cover (FCC), variation of the mangrove canopies during recent decades are studied, including a severe dieback during 2015–2016. The relationship between mangrove FCC and climate conditions is examined with a focus on the possible role of the 2015–2016 El Niño in altering favorable conditions sustaining the mangroves. The mangrove FCC is shown to be coherent with the low-frequency component of sea level height (SLH) variation related to the El Niño Southern Oscillation (ENSO) cycle in the equatorial Pacific. The SLH drop associated with the 2015–2016 El Niño is identified to be the crucial factor leading to the dieback event. A stronger SLH drop occurred during austral autumn and winter, when the SLH anomalies were about 12% stronger than the previous very strong El Niño events. The persistent SLH drop occurred in the dry season of the year when SLH was seasonally at its lowest, so potentially exposed the mangroves to unprecedented hostile conditions. The influence of other key climate factors is also discussed, and a multiple linear regression model is developed to understand the combined role of the important climate variables on the mangrove FCC variation.

scholarly journals Water vapor anomaly over the tropical western Pacific in El Niño winters from radiosonde and satellite observations

2021 ◽  
Author(s):  
Minkang Du ◽  
Kaiming Huang ◽  
Shaodong Zhang ◽  
Chunming Huang ◽  
Yun Gong ◽  
...  
Keyword(s):  
Water Vapor ◽  
El Niño ◽  
El Nino ◽  
Walker Circulation ◽  
Western Pacific ◽  
Monsoon Circulation ◽  
Circulation Anomaly ◽  
Tropical Western Pacific ◽  
Ep El Niño ◽  
The Walker Circulation

Abstract. Using radiosonde observations at five stations in the tropical western Pacific and reanalysis data for 15 years from 2005 to 2019, we report an extremely negative anomaly in atmospheric water vapor during the super El Niño winter of 2015/16, and compare the anomaly with that in the other three El Niño winters. Strong specific humidity anomaly is concentrated below 8 km of the troposphere with a peak at 2.5–3.5 km, and column integrated water vapor mass anomaly over the five radiosonde sites has a large negative correlation coefficient of −0.63 with oceanic Niño3.4 index, but with a lag of about 2–3 months. In general, the tropical circulation anomaly in the El Niño winter is characterized by divergence (convergence) in the lower troposphere over the tropical western (eastern) Pacific, thus the water vapor decreases over the tropical western Pacific as upward motion is suppressed. The variability of the Hadley circulation is quite small and has little influence on the observed water vapor anomaly. The anomaly of the Walker circulation makes a considerable contribution to the total anomaly in all the four El Niño winters, especially in the 2006/07 and 2015/16 eastern-Pacific (EP) El Niño events. The monsoon circulation shows a remarkable change from one to the other event, and its anomaly is large in the 2009/10 and 2018/19 central-Pacific (CP) El Niño winters and small in the two EP El Niño winters. The observed water vapor anomaly is caused mainly by the Walker circulation anomaly in the supper EP event of 2015/16 but by the monsoon circulation anomaly in the strong CP event of 2009/10. Owing to the anomalous decrease in upward transport of water vapor during the El Niño winter, less cloud amount and more outgoing longwave radiation over the five stations are clearly presented in satellite observation.

scholarly journals On the role of trend and variability in the hydroxyl radical (OH) in the global methane budget

2020 ◽  
Vol 20 (21) ◽  
pp. 13011-13022
Author(s):  
Yuanhong Zhao ◽  
Marielle Saunois ◽  
Philippe Bousquet ◽  
Xin Lin ◽  
Antoine Berchet ◽  
...  
Keyword(s):  
Hydroxyl Radical ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Interannual Variations ◽  
Atmospheric Methane ◽  
Tropical Regions ◽  
Ch4 Emissions ◽  
Methane Budget

Abstract. Decadal trends and interannual variations in the hydroxyl radical (OH), while poorly constrained at present, are critical for understanding the observed evolution of atmospheric methane (CH4). Through analyzing the OH fields simulated by the model ensemble of the Chemistry–Climate Model Initiative (CCMI), we find (1) the negative OH anomalies during the El Niño years mainly corresponding to the enhanced carbon monoxide (CO) emissions from biomass burning and (2) a positive OH trend during 1980–2010 dominated by the elevated primary production and the reduced loss of OH due to decreasing CO after 2000. Both two-box model inversions and variational 4D inversions suggest that ignoring the negative anomaly of OH during the El Niño years leads to a large overestimation of the increase in global CH4 emissions by up to 10 ± 3 Tg yr−1 to match the observed CH4 increase over these years. Not accounting for the increasing OH trends given by the CCMI models leads to an underestimation of the CH4 emission increase by 23 ± 9 Tg yr−1 from 1986 to 2010. The variational-inversion-estimated CH4 emissions show that the tropical regions contribute most to the uncertainties related to OH. This study highlights the significant impact of climate and chemical feedbacks related to OH on the top-down estimates of the global CH4 budget.

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