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6 results on '"Han-Ching Chen"'

1. Fundamental Behavior of ENSO Phase Locking

Author

Han-Ching Chen and Fei-Fei Jin

Subjects
Physics, Atmospheric Science, El Niño Southern Oscillation, 010504 meteorology & atmospheric sciences, Oscillation, Climatology, 010502 geochemistry & geophysics, 01 natural sciences, Physics::Atmospheric and Oceanic Physics, Phase locking, Physics::Geophysics, 0105 earth and related environmental sciences
Abstract

El Niño–Southern Oscillation (ENSO) events tend to peak at the end of the calendar year, a phenomenon called ENSO phase locking. This phase locking is a fundamental ENSO property that is determined by its basic dynamics. The conceptual ENSO recharge oscillator (RO) model is adopted to examine the ENSO phase-locking behavior in terms of its peak time, strength of phase locking, and asymmetry between El Niño and La Niña events. The RO model reproduces the main phase-locking characteristics found in observations, and the results show that the phase locking of ENSO is mainly dominated by the seasonal modulation of ENSO growth/decay rate. In addition, the linear/nonlinear mechanism of ENSO phase preference/phase locking is investigated using RO model. The difference between the nonlinear phase-locking mechanism and linear phase-preference mechanism is largely smoothed out in the presence of noise forcing. Further, the impact on ENSO phase locking from annual cycle modulation of the growth/decay rate, stochastic forcing, nonlinearity, and linear frequency are examined in the RO model. The preferred month of ENSO peak time depends critically on the phase and strength of the seasonal modulation of the ENSO growth/decay rate. Furthermore, the strength of phase locking is mainly controlled by the linear growth/decay rate, the amplitude of seasonal modulation of growth/decay rate, the amplitude of noise, the SST-dependent factor of multiplicative noise, and the linear frequency. The asymmetry of the sharpness of ENSO phase locking is induced by the asymmetric effect of state-dependent noise forcing in El Niño and La Niña events.

Published
2020

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

Author

Han-Ching Chen, Bohua Huang, Chung-Hsiung Sui, and Yu-Heng Tseng

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Event (relativity), Phase (waves), Low frequency, 010502 geochemistry & geophysics, 01 natural sciences, Ocean dynamics, symbols.namesake, El Niño Southern Oscillation, Climatology, symbols, Thermocline, Kelvin wave, Geology, 0105 earth and related environmental sciences
Abstract

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.

Published
2018

3. Enhancing the ENSO Predictability beyond the Spring Barrier

Author

Ruiqiang Ding, Zeng-Zhen Hu, Yu-Heng Tseng, and Han-Ching Chen

Subjects
Tropical pacific, Multidisciplinary, 010504 meteorology & atmospheric sciences, lcsh:R, Forecast skill, lcsh:Medicine, 010502 geochemistry & geophysics, 01 natural sciences, Article, Atmosphere, El Niño Southern Oscillation, Ocean sciences, 13. Climate action, Climatology, Extratropical cyclone, Environmental science, Atmospheric science, Climate change, lcsh:Q, 14. Life underwater, Predictability, lcsh:Science, 0105 earth and related environmental sciences
Abstract

El Niño-Southern Oscillation (ENSO) is the dominant interseasonal–interannual variability in the tropical Pacific and substantial efforts have been dedicated to predicting its occurrence and variability because of its extensive global impacts. However, ENSO predictability has been reduced in the 21st century, and the impact of extratropical atmosphere on the tropics has intensified during the past 2 decades, making the ENSO more complicated and harder to predict. Here, by combining tropical preconditions/ocean–atmosphere interaction with extratropical precursors, we provide a novel approach to noticeably increase the ENSO prediction skill beyond the spring predictability barrier. The success of increasing the prediction skill results mainly from the longer lead-time of the extratropical–tropical ocean-to-atmosphere interaction process, especially for the first 2 decades of the 21st century.

Published
2019

4. The Role of Reversed Equatorial Zonal Transport in Terminating an ENSO Event

Author

Zeng-Zhen Hu, Han-Ching Chen, Bohua Huang, and Chung-Hsiung Sui

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Advection, Ocean current, Equator, Zonal and meridional, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, Physics::Geophysics, Ocean dynamics, El Niño Southern Oscillation, Climatology, Physics::Space Physics, Thermocline, Physics::Atmospheric and Oceanic Physics, Geology, 0105 earth and related environmental sciences
Abstract

This study shows the sudden basinwide reversal of anomalous equatorial zonal transport above the thermocline at the peaking phase of ENSO triggers rapid termination of ENSO events. The anomalous equatorial zonal transport is controlled by the concavity of anomalous thermocline meridional structure across the equator. During the developing phase of ENSO, opposite zonal transport anomalies form in the western-central and central-eastern equatorial Pacific, respectively. Both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western-central equatorial ocean. At this stage, the anomalous zonal transport in the east enhances ENSO growth through zonal SST advection. In the mature phase of ENSO, off-equatorial thermocline depth anomalies become more dominant in the eastern Pacific because of the reflection of equatorial signals at the eastern boundary. As a result, the meridional concavity of the thermocline anomalies is reversed in the east. This change reverses zonal transport rapidly in the central-to-eastern equatorial Pacific, joining with the existing reversed zonal transport anomalies farther to the west, and forms a basinwide transport reversal throughout the equatorial Pacific. This basinwide transport reversal weakens the ENSO SST anomalies by reversed advection. More importantly, the reversed zonal transport reduces the existing zonal tilting of the equatorial thermocline and weakens its feedback to wind anomalies effectively. This basinwide reversal is built in at the peak phase of ENSO as an oceanic control on the evolution of both El Niño and La Niña events. The reversed zonal transport anomaly after the mature phase weakens El Niño in the eastern Pacific more efficiently than it weakens La Niña.

Published
2016

5. An ENSO prediction approach based on ocean conditions and ocean–atmosphere coupling

Author

Han-Ching Chen, Ruiqiang Ding, Yu-Heng Tseng, and Zeng-Zhen Hu

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Anomaly (natural sciences), Multivariate ENSO index, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, La Niña, Sea surface temperature, symbols.namesake, Climatology, Extratropical cyclone, symbols, Environmental science, Hindcast, Thermocline, Kelvin wave, 0105 earth and related environmental sciences
Abstract

A simple statistical model for the El Nino–Southern Oscillation (ENSO) prediction is derived based on the evolution of the ocean heat condition and the oceanic Kelvin wave propagation associated with westerly wind events (WWEs) and easterly wind surges (EWSs) in the tropical Pacific. The multivariate linear regression model solely relies on the pentad thermocline depth anomaly evolution in 25 days along with the zonal surface wind modulation. It successfully hindcasts all ENSOs except for the 2000/01 La Nina, using the pentad (or monthly) mean tropical atmosphere ocean array data since 1994 with an averaged skill (measured by anomaly correlation) of 0.62 (or 0.67) with a 6-month lead. The exception is mainly due to the long-lasting cold sea surface temperature anomalies in the subtropics resulting from the strong 1998/99 La Nina, even though the tropical warm water volume (WWV) had rebounded and turned phases after 2000. We also note that the hindcast skill is comparable using pentad or monthly mean NCEP global ocean data assimilation system data for the same time period. The hindcast skill of the proposed statistical model is better than that based on the WWV index in terms of the monthly correlation, normalized RMSEs and ENSO occurrences, which suggest that including the evolution of the subsurface ocean temperature anomaly and the WWEs/EWSs in the central tropical Pacific can enhance the ability to predict ENSO. The hindcast skill is also comparable to the predictions using other dynamical and statistical models, indicating that these processes are the keys to ENSO development. The dynamics behind the statistical model are consistent with the physical processes of ENSO development as follows: the tropical WWV resulting from the interannually-varying meridional subtropical cell transport provides a sufficient heat source. When the seasonal phase lock of ocean–atmosphere coupling triggers the positive (negative) zonal wind anomaly in boreal summer and fall, an El Nino (a La Nina) will develop as evidenced by the Kelvin wave propagation. The triggering dynamic may be suppressed or enhanced by the influence of extratropical Pacific sea surface temperature.

Published
2016

6. El Niño–Southern Oscillation complexity

Author

Ken Takahashi, Matthieu Lengaigne, Guomin Wang, Tim Li, Antonietta Capotondi, Tobias Bayr, Michael J. McPhaden, Axel Timmermann, WonMoo Kim, Wenju Cai, Malte F. Stuecker, Sunyong Kim, Ruihuang Xie, Harun Rashid, Fei-Fei Jin, Alexander Todd, Jong-Seong Kug, Boris Dewitte, Sang-Wook Yeh, Yoo-Geun Ham, Kim M. Cobb, Elke Zeller, Agus Santoso, Scott B. Power, Dietmar Dommenget, Daehyun Kang, Michiya Hayashi, Soon Il An, Kyung-Sook Yun, Pamela R. Grothe, Guojian Wang, June-Yi Lee, Karl Stein, Jing-Jia Luo, Shayne McGregor, Eric Guilyardi, Yoshimitsu Chikamoto, Xuebin Zhang, Sarah Ineson, Andrew T. Wittenberg, Woo Hyun Yang, Han Ching Chen, Jin-Ho Yoon, Yann Planton, Hong Li Ren, Institute of Basic Science (IBS), Pusan National University, Department of Atmospheric Sciences, Yonsei University, Pohang University of Science and Technology (POSTECH), School of Ocean and Earth Science and Technology (SOEST), University of Hawai‘i [Mānoa] (UHM), Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Qingdao National Laboratory for Marine Science and Technology, NOAA Earth System Research Laboratory (ESRL), National Oceanic and Atmospheric Administration (NOAA), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado [Boulder]-National Oceanic and Atmospheric Administration (NOAA), School of Earth and Atmospheric Sciences [Atlanta], Georgia Institute of Technology [Atlanta], Océan et variabilité du climat (VARCLIM), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU), NOAA Pacific Marine Environmental Laboratory [Seattle] (PMEL), Department of Atmospheric Sciences [Seattle], University of Washington [Seattle], NOAA Geophysical Fluid Dynamics Laboratory (GFDL), Helmholtz Centre for Ocean Research [Kiel] (GEOMAR), National Taiwan University [Taiwan] (NTU), Department of Plants, Soils and Climate, Utah State University (USU), Centro de Estudios Avanzados en Zonas Aridas (CEAZA), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), School of Earth, Atmosphere and Environment, Monash University, Monash University [Clayton], NCAS-Climate [Reading], Department of Meteorology [Reading], University of Reading (UOR)-University of Reading (UOR), Met Office Hadley Centre for Climate Change (MOHC), United Kingdom Met Office [Exeter], Centre for Australian Weather and Climate Research (CAWCR), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), ARC Centre of Excellence for Climate System Science, University of New South Wales [Sydney] (UNSW)-Australian Research Council [Canberra] (ARC), Instituto Geofísico del Perú (IGP), Exeter Climate Systems, College of Engineering, Mathematics and Physical Science, University of Exeter, Exeter, United Kingdom, Korean Ocean Research and Development Institute (KORDI), Gwangju Institute of Science and Technology (GIST), CSIRO, Oceans and Atmosphere, Hobart, TAS, Australia, Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), School of Earth, Atmosphere and Environment, Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), and University of Exeter

Subjects
El Nino-Southern Oscillation, Tropical Climate, Multidisciplinary, 010504 meteorology & atmospheric sciences, Climate Change, Equator, Climate change, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], 15. Life on land, 010502 geochemistry & geophysics, 01 natural sciences, Earth system science, Sea surface temperature, La Niña, El Niño, 13. Climate action, Climatology, Tropical climate, Water Movements, Environmental science, Terrestrial ecosystem, 14. Life underwater, 0105 earth and related environmental sciences
Abstract

El Niño events are characterized by surface warming of the tropical Pacific Ocean and weakening of equatorial trade winds that occur every few years. Such conditions are accompanied by changes in atmospheric and oceanic circulation, affecting global climate, marine and terrestrial ecosystems, fisheries and human activities. The alternation of warm El Niño and cold La Niña conditions, referred to as the El Niño–Southern Oscillation (ENSO), represents the strongest year-to-year fluctuation of the global climate system. Here we provide a synopsis of our current understanding of the spatio-temporal complexity of this important climate mode and its influence on the Earth system.

Published
2018

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