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Interannual variability of precipitation over the Maritime Continent
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| Title: | Interannual variability of precipitation over the Maritime Continent |
| Other Titles: | 海洋大陸における降水の経年変動 |
| Authors: | Alsepan, Givo1 Browse this author |
| Authors(alt): | アルセパン, ギヴォ1 |
| Issue Date: | 24-Sep-2021 |
| Publisher: | Hokkaido University |
| Abstract: | Understanding the relationship between El Niño and the interannual climate variability over the Maritime Continent (MC) region has important socio-economic implications. Given that El Niño has tremendous impacts, studying how it affects the precipitation would create better awareness and preparedness for the potential effects when El Niño is predicted. This thesis describes a comprehensive understanding of the role of El Niño to precipitation variability by analyzing a high-resolution gauge-based precipitation dataset as well as the role of local and remote sea surface temperature (SST) anomalies during the El Niño events to the precipitation through numerical experiments.
Regional-scale precipitation responses over Indonesia, a region occupying almost 70% of the MC, to major climate modes in the tropical Indo–Pacific Oceans, namely, canonical El Niño, El Niño Modoki, and the Indian Ocean Dipole (IOD), and how the responses are related to large-scale moisture convergences are investigated. The precipitation responses, analyzed using a high-spatial-resolution (0.5° × 0.5°) terrestrial precipitation dataset for the period 1960–2007, exhibit differences between the dry (July–September) and wet (November–April) seasons. Canonical El Niño strongly reduces precipitation in central to eastern Indonesia from the dry season to the early wet season and northern Indonesia in the wet season. El Niño Modoki also reduces precipitation in central to eastern Indonesia during the dry season, but conversely increases precipitation in western Indonesia in the wet season. Moisture flux analysis indicates that corresponding to the dry (wet) season precipitation reduction due to the canonical El Niño and El Niño Modoki anomalous divergence occurs around the southern (northern) edge of the convergence zone when one of the two edges is located near the equator (10°S–15°N) associated with their seasonal migration. This largely explains the seasonality and regionality of precipitation responses to canonical El Niño and El Niño Modoki. IOD reduces precipitation in southwestern Indonesia in the dry season, associated with anomalous moisture flux divergence. The seasonality of precipitation response to IOD is likely to be controlled by the seasonality of local sea surface temperature anomalies in the eastern pole of the IOD.
The contribution of remote and local SST forcing during El Niño in shaping the interannual variations of large-scale precipitation over the MC during July-October (JASO) and January-April (JFMA) seasons is investigated by using an atmospheric general circulation model (AGCM). Two idealized AGCM experiments are designed to isolate the effect of anomalous SST forcing from the tropical central-eastern Pacific (CEP) and tropical western Pacific (WP). In the first (second) experiment, the climatological SST field is specified in the tropical CEP (WP), while observed SST is specified elsewhere. Our numerical experiments indicate that, in the JASO season, the precipitation reduction over the southern hemisphere (SH) side of MC is likely explained as a direct influence of El Niño. In response to El Niño-related positive SST anomalies over the tropical CEP, twin Rossby wave cyclonic anomalies are generated to the tropical WP. The southern branch of the twin cyclonic anomalies advects dry air into the SH side of MC, which then suppresses convection and precipitation there. In the JFMA season, the reduced precipitation over the northern hemisphere (NH) side of MC is likely induced by the in-situ ocean surface cooling. The local cooling forcing promotes the generation of the Philippine Sea anticyclonic anomalies in the NH region. The eastern flank of the anomalous anticyclone transfers dry air into the NH side of MC and then reduces local precipitation. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第14644号 |
| Degree Level: | 博士 |
| Degree Discipline: | 理学 |
| Examination Committee Members: | (主査) 教授 見延 庄士郎, 教授 稲津 將, 准教授 佐々木 克徳, 特任准教授 佐藤 陽祐, 副主任研究員 土井 威志 （国立研究開発法人海洋研究開発機構，気候変動予測情報創生グループ） |
| Degree Affiliation: | 理学院（自然史科学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/87090 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 理学院(Graduate School of Science)
学位論文 (Theses) > 博士 （理学）
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