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Seasonality and Regionality of ENSO Teleconnections and Impacts on North America
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Seasonality and Regionality of ENSO Teleconnections and Impacts on North America. |
| 개인저자 | Jong, Bor-Ting. |
| 단체저자명 | Columbia University. Earth and Environmental Sciences. |
| 발행사항 | [S.l.]: Columbia University., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 141 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-05B. Dissertation Abstract International |
| ISBN | 9781088344606 |
| 학위논문주기 | Thesis (Ph.D.)--Columbia University, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-05, Section: B.
Advisor: Ting, Mingfang. |
| 이용제한사항 | This item must not be sold to any third party vendors. |
| 요약 | The El Nino - Southern Oscillation (ENSO) has far-reaching impacts across the globe and provides the most reliable source of seasonal to interannual climate prediction over North America. Though numerous studies have discussed the impacts of ENSO teleconnections on North America during boreal winter, it is becoming more and more apparent that the regional impacts of ENSO teleconnections are highly sensitive to the seasonal evolution of ENSO events. Also, the significant impacts of ENSO are not limited to the boreal winter seasons. To address these knowledge gaps, this thesis examines the seasonal dependence of ENSO teleconnections and impacts on North American surface climate, focusing on two examples. Chapter 1 examines the relationship between El Nino - California winter precipitation. Results show that the probability of the anomalous statewide-wetness increases as El Nino intensity increases. Also, the influences of El Nino on California winter precipitation are statistically significant in late winter (Feb-Apr), but not in early winter even though that is when El Nino usually reaches its peak intensity. Chapter 2 further investigates why the strong 2015/16 El Nino failed to bring above normal winter precipitation to California, focusing on the role of westward shifted equatorial Pacific sea surface temperature anomalies (SSTAs) based on two reasons: the maximum equatorial Pacific SSTAs was located westward during the 2015/16 winter compared to those during the 1982/83 and 1997/98 winters, both of which brought extremely wet late winters to California. Also, the North American Multi-Model Ensemble (NMME) forecasts overestimated the eastern tropical Pacific SSTAs and California precipitation in the 2015/16 late winter, compared to observations. The Atmospheric General Circulation Model (AGCM) experiments suggested that the SST forecast error in NMME contributed partially to the wet bias in California precipitation forecast in the 2015/16 late winter. However, the atmospheric internal variability could have also played a large role in the dry California winter during the event. ENSO also exerts significant impacts on agricultural production over the Midwest during boreal summer. Chapter 3 examines the physical processes of the ENSO summer teleconnection, focusing on the summer when a La Nina is either transitioning from an earlier El Nino winter or persisting from an existing La Nina winter. The results demonstrate that the impacts are most significant during the summer when El Nino is transitioning to La Nina compared to that when La Nina is persisting, even though both can loosely be defined as developing La Nina summer. During the transitioning summer, both the decaying El Nino and the developing La Nina induce suppressed deep convection over the tropical Pacific and thereby the corresponding Rossby wave propagations toward North America, resulting in a statistically significant anomalous anticyclone over northeastern North America and, therefore, a robust warming signal over the Midwest. These features are unique to the developing La Nina transitioning from El Nino, but not the persistent La Nina. In Chapter 4, we further evaluate the performance of NCAR CAM5 forced with historical SSTA in terms of the La Nina summer teleconnections. Though the model ensemble mean well reproduces the features in the preceding El Nino/La Nina winters, the model ensemble mean has very limited skill in simulating the tropical convection and extratropical teleconnections during both the transitioning and persisting summers. The weak responses in the model ensemble mean are attributed to large variability in both the tropical precipitation, especially over the western Pacific, and atmospheric circulation during summer season.This thesis synthesizes the physical processes and assessments of climate models in different seasons to establish the sensitivity of regional climate to the seasonal dependence of ENSO teleconnections. We demonstrate that the strongest impacts of ENSO on North American regional climate might not be necessarily simultaneous with maximum tropical Pacific SST anomalies. We also emphasize the importance of the multi-year ENSO evolutions when addressing the seasonal impacts on North American summertime climate. The findings in this thesis could benefit the improvement of seasonal hydroclimate forecasting skills in the future. |
| 일반주제명 | Atmospheric sciences. |
| 언어 | 영어 |
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