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Rainfall Variability over Zimbabwe and its relation to large-scale atmosphere-ocean processes

Title
Rainfall Variability over Zimbabwe and its relation to large-scale atmosphere-ocean processes
Authors
MAMOMBE VIMBAI
Issue Date
2016
Department/Major
대학원 대기과학공학과
Publisher
이화여자대학교 대학원
Degree
Master
Advisors
최용상
Abstract
For Zimbabwe, where rain fed agriculture is the backbone of the economy, the importance of accurate rainfall seasonal forecasts cannot be overemphasized (Makarau and Jury, 1997). In fact, extremes in interseasonal variability of rainfall can significantly complicate human livelihoods. In addition, there have been predictions of increased precipitation variability and hydro-meteorological hazards such as floods, droughts, and erratic rainfall due to global warming (Field et al., 2014; Mushore, 2013a). Thus, detailed understanding of the major contributors to the rainfall variability over Zimbabwe would help in the development of mitigatory measures against the effects of extreme weather events. The aim of this study is to identify significant climate factors that are associated with interseasonal variations in rainfall over Zimbabwe. Observational studies of the possible relationships between rainfall, global SST anomalies and synoptic scale atmospheric features were carried out. The investigation is mainly centered on the large scale circulation acclimatization to SST forcing and the resultant rainfall changes. This is expected to make profound contributions to seasonal rainfall forecasting techniques around the country. Empirical orthogonal function analysis was used to extract homogeneous rainfall regions within the country. Our results suggest that Zimbabwe rainfall is highly variable in time and space, but there are significant correlations between rainfall and large portions of the tropical Indian and Pacific Oceans. The influence of El Niño Southern Oscillation (ENSO) has been found to be significant across the whole country. The Southern Annular Mode (SAM) and Indian Ocean Dipole zonal index (IODZ) related rainfall variation is mostly homogeneous, as depicted by the relationship to the leading mode, but the SAM-related rainfall fluctuation partially induces a north-south contrast of rainfall variability within the country.;고해상도 관측소 강수 자료를 이용하여 짐바브웨 강수의 경년 변동과 대기-해양 상호작용의 관계를 연구하였다. 경험직교함수(EOF; Empirical Orthogonal Functions) 분석을 통하여 강수 구조의 변동성 대부분을 설명할 수 있는 시공간적 모드를 추출하였다. 이 결과에 따르면, 주요 변동성인 첫번째 모드는 강수가 공간적으로 강한 균질성을 보이고 있음을 시사한다. 첫번째 모드와 해수면 온도 변동성과의 상관관계를 살펴본 결과, 엘니뇨-남방진동(ENSO; El Niño-Southern Oscillation)이 짐바브웨 여름철 강수에 유의한 영향을 미치고 있다는 것을 확인하였다. 또한, 짐바브웨 강수와 열대 인도양 및 태평양 해수면 온도 사이에 유의미한 상관관계가 발견된다. 남부환상모드(SAM; Southern Annular Mode)에 의한 강수 변동성은 첫번째와 두번째 모드에서 공히 발현된다. 특히, 첫번째 모드는 짐바브웨 내에서 공간적으로 균질한 강수 변동성을 나타내고, 두번째 모드는 남북 구조의 변동성을 나타낸다. 비록 그 강도는 작지만, 세번째와 네번째 모드는 국지적인 강수 변동 패턴을 설명한다. 이는 더욱 신뢰성있는 고해상도 강수 자료를 통한 분석에 따른 결과로 볼 수 있다. 따라서 이 연구의 결과는 짐바브웨 강수의 계절 예측 성능을 획기적으로 향상시키는 데 기여할 것이다.
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