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El Nino Diversity, Intraseasonal Win...

Hu, Shineng.

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El Nino Diversity, Intraseasonal Wind Bursts, and Decadal Climate Change.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	El Nino Diversity, Intraseasonal Wind Bursts, and Decadal Climate Change./
Author:	Hu, Shineng.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
Description:	162 p.
Notes:	Source: Dissertations Abstracts International, Volume: 80-09, Section: B.
Contained By:	Dissertations Abstracts International80-09B.
Subject:	Physical oceanography. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13841668
ISBN:	9780438907317

El Nino Diversity, Intraseasonal Wind Bursts, and Decadal Climate Change.
Hu, Shineng.

El Nino Diversity, Intraseasonal Wind Bursts, and Decadal Climate Change. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 162 p.

Source: Dissertations Abstracts International, Volume: 80-09, Section: B.

Thesis (Ph.D.)--Yale University, 2018.

This item must not be added to any third party search indexes.

This thesis examines tropical ocean-atmosphere interactions on a range of timescales, from intraseasonal to decadal, linking intraseasonal wind bursts, El Nino, and global climate change. The El Nino-Southern Oscillation (ENSO) dominates interannual climate variability, while each El Nino event exhibits unique spatiotemporal patterns. The interplay of westerly and easterly wind bursts (WWBs and EWBs), as a major component of stochastic atmospheric forcings, is shown to significantly contribute to the diversity of El Nino events. ENSO cycle affects interannual-to-decadal global mean temperature variation, and is in turn affected by climate change. The recent El Nino development in 2014-2016 presents a perfect illustration on how these key elements of the climate system interact with each other on these different timescales. As the first step. I examine the impacts of WWBs on the diversity of El Nino events by superimposing an observed WWB (from March of 1997) to a coupled global climate model. The impacts of this WWB are found to be state dependent. The same WWB can either induce a strong Eastern Pacific El Nino or a moderate Central Pacific El Nino, and the system response depends on the ocean initial state and subsequent ocean-atmosphere interactions. Ocean energetics is computed to better understand the system response. The diversity of El Nino events is closely reflected by the available potential energy (APE) in the tropical Pacific basin, and it is modulated by wind power controlled by surface wind activity and ocean currents. Application of ocean energetics as a potential prediction tool is also presented. Next. I investigate El Nino development in 2014-2016 using high-resolution satellite observations and ensemble numerical simulations. Strong WWBs were observed in the early months of both 2014 and 2015, favorable for El Nino development, but only in 2015 the system eventually developed into an extreme El Nino. It is shown that. during 2014, the onset of El Nino was interrupted mid-year by an exceptionally strong EWB, but the failed 2014 event created favorable conditions for El Nino development during 2015. Analogue coupled simulations wherein we superimpose the observed sequences of WWBs and EWBs support these conclusions. These findings, together with the results of the first project described above, stress the critical role of the interplay between WWBs and EWBs in shaping El Nino development and diversity, and thus imposing inherent limits on El Nino predictability. Further, I explore potential causes for the recent changes in the tropical mean state and El Nino. I identify an observed multidecadal strengthening of cross-equatorial winds in the eastern Pacific that has been overlooked before. This strengthening of meridional winds, forced most likely from outside the Pacific, is a robust feature of in-situ, satellite, and reanalysis wind data. I conduct coupled climate simulations by superimposing the observed multidecadal cross-equatorial wind anomalies; and successfully reproduce the key features of the recent changes in the tropical Pacific. In particular, tropical mean state experiences a La Nina-like change, ENSO amplitude weakens by about 20%, the center of SST anomalies shifts westward, and the ITCZ crosses the equator less frequently. Finally, I examine the effect of the extreme El Nino of 2015 on global mean surface temperature (GA/1ST). It is shown that ENSO effectively modulates GMST on interannual-to-decadal timescales by tightly controlling heat release into the tropical atmosphere (r = 0.9). Accordingly, a physically-based simple model is constructed to describe changes in GMST due to greenhouse gas emissions, ENSO forcing, and volcanic eruptions. This model closely reproduces GMST variations since the 1880s, including the global warming hiatus of 1998 - 2013 and the subsequent rapid temperature rise. The model results confirm that the global warming hiatus resulted primarily from weak El Nino activity, and ended with El Nino conditions in 2014-2016 combined with the ongoing background warming trend.

ISBN: 9780438907317Subjects--Topical Terms:

3168433
Physical oceanography.

El Nino Diversity, Intraseasonal Wind Bursts, and Decadal Climate Change.
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520 $a This thesis examines tropical ocean-atmosphere interactions on a range of timescales, from intraseasonal to decadal, linking intraseasonal wind bursts, El Nino, and global climate change. The El Nino-Southern Oscillation (ENSO) dominates interannual climate variability, while each El Nino event exhibits unique spatiotemporal patterns. The interplay of westerly and easterly wind bursts (WWBs and EWBs), as a major component of stochastic atmospheric forcings, is shown to significantly contribute to the diversity of El Nino events. ENSO cycle affects interannual-to-decadal global mean temperature variation, and is in turn affected by climate change. The recent El Nino development in 2014-2016 presents a perfect illustration on how these key elements of the climate system interact with each other on these different timescales. As the first step. I examine the impacts of WWBs on the diversity of El Nino events by superimposing an observed WWB (from March of 1997) to a coupled global climate model. The impacts of this WWB are found to be state dependent. The same WWB can either induce a strong Eastern Pacific El Nino or a moderate Central Pacific El Nino, and the system response depends on the ocean initial state and subsequent ocean-atmosphere interactions. Ocean energetics is computed to better understand the system response. The diversity of El Nino events is closely reflected by the available potential energy (APE) in the tropical Pacific basin, and it is modulated by wind power controlled by surface wind activity and ocean currents. Application of ocean energetics as a potential prediction tool is also presented. Next. I investigate El Nino development in 2014-2016 using high-resolution satellite observations and ensemble numerical simulations. Strong WWBs were observed in the early months of both 2014 and 2015, favorable for El Nino development, but only in 2015 the system eventually developed into an extreme El Nino. It is shown that. during 2014, the onset of El Nino was interrupted mid-year by an exceptionally strong EWB, but the failed 2014 event created favorable conditions for El Nino development during 2015. Analogue coupled simulations wherein we superimpose the observed sequences of WWBs and EWBs support these conclusions. These findings, together with the results of the first project described above, stress the critical role of the interplay between WWBs and EWBs in shaping El Nino development and diversity, and thus imposing inherent limits on El Nino predictability. Further, I explore potential causes for the recent changes in the tropical mean state and El Nino. I identify an observed multidecadal strengthening of cross-equatorial winds in the eastern Pacific that has been overlooked before. This strengthening of meridional winds, forced most likely from outside the Pacific, is a robust feature of in-situ, satellite, and reanalysis wind data. I conduct coupled climate simulations by superimposing the observed multidecadal cross-equatorial wind anomalies; and successfully reproduce the key features of the recent changes in the tropical Pacific. In particular, tropical mean state experiences a La Nina-like change, ENSO amplitude weakens by about 20%, the center of SST anomalies shifts westward, and the ITCZ crosses the equator less frequently. Finally, I examine the effect of the extreme El Nino of 2015 on global mean surface temperature (GA/1ST). It is shown that ENSO effectively modulates GMST on interannual-to-decadal timescales by tightly controlling heat release into the tropical atmosphere (r = 0.9). Accordingly, a physically-based simple model is constructed to describe changes in GMST due to greenhouse gas emissions, ENSO forcing, and volcanic eruptions. This model closely reproduces GMST variations since the 1880s, including the global warming hiatus of 1998 - 2013 and the subsequent rapid temperature rise. The model results confirm that the global warming hiatus resulted primarily from weak El Nino activity, and ended with El Nino conditions in 2014-2016 combined with the ongoing background warming trend.
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