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ENSO Initiation Mechanisms.

Thomas, Erin E.

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ENSO Initiation Mechanisms.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	ENSO Initiation Mechanisms./
作者:	Thomas, Erin E.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2017,
面頁冊數:	198 p.
附註:	Source: Dissertation Abstracts International, Volume: 79-05(E), Section: B.
Contained By:	Dissertation Abstracts International79-05B(E).
標題:	Atmospheric sciences. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10689372
ISBN:	9780355571066

ENSO Initiation Mechanisms.
Thomas, Erin E.

ENSO Initiation Mechanisms. - Ann Arbor : ProQuest Dissertations & Theses, 2017 - 198 p.

Source: Dissertation Abstracts International, Volume: 79-05(E), Section: B.

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2017.

El Nino-Southern Oscillation (ENSO) variability is influenced by numerous oceanic and atmospheric phenomena which complicate our ability to predict and analyze the mechanisms responsible for generating ENSO diversity. This research utilizes statistical and physical modeling to identify both observationally-grounded and physically meaningful mechanisms that influence ENSO development.

ISBN: 9780355571066Subjects--Topical Terms:

3168354
Atmospheric sciences.

ENSO Initiation Mechanisms.
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500 $a Source: Dissertation Abstracts International, Volume: 79-05(E), Section: B.
500 $a Adviser: Daniel Vimont.
502 $a Thesis (Ph.D.)--The University of Wisconsin - Madison, 2017.
520 $a El Nino-Southern Oscillation (ENSO) variability is influenced by numerous oceanic and atmospheric phenomena which complicate our ability to predict and analyze the mechanisms responsible for generating ENSO diversity. This research utilizes statistical and physical modeling to identify both observationally-grounded and physically meaningful mechanisms that influence ENSO development.
520 $a Interactions between the Pacific Meridional Mode (PMM) and ENSO are investigated using the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) and an intermediate coupled model (ICM). The two models are configured so that the CESM simulates the PMM but not ENSO, and the ICM simulates ENSO but not the PMM, allowing for a clean separation between the PMM evolution and the subsequent ENSO response. An ensemble of CESM simulations is run with an imposed surface heat flux associated with the North Pacific Oscillation (NPO) generating a sea surface temperature (SST) and wind response representative of the PMM. The PMM wind is then applied as a forcing to the ICM to simulate the ENSO response. The positive (negative) ensemble-mean PMM wind forcing results in a warm (cold) ENSO event although the responses are not symmetric (warm ENSO events are larger in amplitude than cold ENSO events), and large variability between ensemble members suggests that any individual ENSO event is strongly influenced by natural variability contained within the CESM simulations. Sensitivity experiments show that (i) direct forcing of Kelvin waves by PMM winds dominates the ENSO response, (ii) seasonality of PMM forcing and ENSO growth rates influences the resulting ENSO amplitude, (iii) ocean dynamics within the ICM dominate the ENSO asymmetry, and (iv) the nonlinear relationship between PMM wind anomalies and surface wind stress may enhance the La Nina response to negative PMM variations. Implications for ENSO variability are discussed.
520 $a In a forecasting framework, the predictability of ENSO events depends on the characteristics of both the forecast initial conditions as well as the stochastic forcing that occurs after the forecast is initialized. In this framework, stochastic forcing is capable of improving the predictability of the ENSO event if it excites optimal initial conditions that maximize deterministic ENSO growth. However, it can also be detrimental to the predictability of the event if it excites unpredictable growth or interference after the forecast is initialized. This study describes an empirical framework using Linear Inverse Modeling (LIM) techniques that identifies observationally-grounded spatial and temporal characteristics of the stochastic forcing that contributes to the development of ENSO diversity. The noise forcing patterns show NPO-like patterns are associated with the development of CP conditions and South Pacific Oscillation (SPO)-like conditions as well as positive zonal wind anomalies in the western Pacific are associated with EP development. We apply this framework to several historical ENSO events containing a diverse range of spatial and temporal characteristics to estimate the relative roles of deterministic dynamics versus noise forcing towards ENSO diversity. Overall it is determined ENSO events are impacted by a large variety of phenomena that can influence the event throughout its evolution. Additionally, the role of noise forcing for ENSO development varies greatly for any given event and characterizing the structures within the noise forcing is challenging. However, the methods described in this study provides a single framework for parsing through the myriad processes that contribute to ENSO diversity.
520 $a The LIM framework is used to calculate the noise forcing patterns associated with generating ENSO diversity within NCAR's CESM. The noise forcing structures identified within the model match the observed noise forcing well. The results show an NPO-like pattern during boreal winter (DJF) associated with the CP optimal initial conditions. The SPO-like pattern in the southern Hemisphere and positive zonal wind stress anomalies in the western Pacific also appear in relation to the EP optimal initial conditions although they occur during JJA in the CESM, rather than MAM as seen in observations. These noise forcing structures of interest are then used to force three sets of ensemble experiments using the fully-coupled CESM to determine the physical mechanisms through which they are able to initiate ENSO events. The results support previous findings and show the NPO is capable of initiating ENSO variability through the PMM. Interestingly, neither EP noise forced experiments generate ENSO events. However, the SPO heat flux forcing experiment creates an SST pattern that resembles the EP optimal and the equatorial wind stress experiment generate a thermocline structure that resembles part of the EP optimal.
520 $a These results overwhelming indicate that the noise forcing plays a critical role in the development of ENSO diversity. Unfortunately, noise forcing is highly variable and may or may not be important in the development of any given ENSO event. (Abstract shortened by ProQuest.).
590 $a School code: 0262.
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