Analysis of the Equatorial Lower Stratosphere Quasi-Biennial Oscillation (QBO) Using ECMWF-Interim Reanalysis Data Set

The ERA-Interim data set from Europe Center for Medium Range Weather Forecasting (ECMWF) was used to quantitatively analyze the characteristic of equatorial quasi-biennial oscillation (QBO). Analysis of spatial and temporal of the data showed that the zonally symmetric easterly and westerly phase of QBO regimes alternate with period of ~27.7 months. Based on Equivalent QBO Amplitude (EQA) method, the maximum amplitudes in zonal mean zonal wind (u), temperature (T), vertical shear (du/dz) and quadratic vertical shear (d2u/dz2) are ~28.3 m/s, ~3.4 K, ~4.8 m/s/km, and ~1.0 m/s/km2 respectively. The amplitudes decay exponentially with a Gaussian distribution in latitude. The twofold-structure of QBO descends downward at rate of ~1 km/month. The temperature anomaly can be used to analyze the characteristic of QBO which satisfies the thermal wind balance relation in the lower- stratosphere due to very small contribution of the mean meridional and vertical motion. Moreover, the concentration of the total column ozone (TCO) in the tropics is significantly influenced by QBO. During the westerly phase of QBO, the TCO is relatively increased in the lower-stratosphere, but decreased during the opposite phase

海洋大陸における降水の経年変動

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

Relations between Interannual Variability of Regional-Scale Indonesian Precipitation and Large-Scale Climate Modes during 1960-2007

Regional-scale precipitation responses over Indonesia to major climate modes in the tropical Indo-Pacific Oceans, namely canonical El Nino, El Nino 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 degrees x 0.5 degrees) terrestrial precipitation dataset for the period 1960-2007, exhibit differences between the dry (July-September) and wet (November-April) seasons. Canonical El Nino 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 Nino 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 Nino and El Nino 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 degrees S-15 degrees N) associated with their seasonal migration. This largely explains the seasonality and regionality of precipitation responses to canonical El Nino and El Nino 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

Kuantifikasi Osilasi Kuasi Dua Tahunan Stratosfer (QBO) Menggunakan Data Ecmwfinterim Reanalysis

Hlm.153-16