博士 / 國立中央大學 / 地球物理研究所 / 99 / As recent global climate fast shifting, the impact of sea-level change to human socioeconomics is almost equivalent to the disaster which is stricken by severe weather accompanying with global warming. The variability of global sea-level change is characterized by small magnitude in short time span but large scale distribution from the last century. Even though the secular trend and seasonal strength are merely a few mm to cm, the quantity is an immense amount of hydrological redistribution which happens near Earth surface. By means of enriched post processes and longer time series of global time-variable gravity measurements, this study is dedicated to analyzing contemporary sea-level variation from global to regional scale in an integrative view. Using space geodetic satellites data, the secular trend, seasonal and non-seasonal terms are examined and intercompared to various geophysical signals, e.g. ocean bottom pressure
from a global ocean model, temperature profiles (mixed layer depth) from Argo floats, etc.
Sea-level variation (SLV) is dominated by steric (SLVsteric) and water mass discharge from land (SLVmass). Multi-oceanic altimeters reveal the global SLV rises at a rate of +3.2mm/yr (1993−2010); SLVmass, GRACE, is about +0.81mm/yr; SLVsteric, Argo, is about +0.25mm/yr (2004−2010). For the seasonal variations, the periodic time series peak of both SLVmass and SLVtotal are located around September to October, but SLVmass shows out of phase around March when the initial time set on January 1st which has been fully documented in recent studies. A significant and prevailing correlation to interannual ENSO events exists in global nonseasonal SLV including SLVsteric & SLVmass from conventional EOF analysis. Unfortunately, SLVmass from GRACE is highly contaminated by north-south stripes in low latitude regions, hence the SLVmass shows blurred results. In addition to two dominate contributors to SLV, anthropogenic contribution to GSL also suggest that the impoundments of reservoirs on land may reduce global sea-level change as large as −0.55mm/yr since 1950-2008. The equivalent −3 cm sea-level height has been stored on land. The latter not only disagree the global SLV
budget but enlarges the discrepancy within the contributions from two natural causes we have known.
This study therefore selects Tropical Pacific and Indian Ocean as the major study region. Extracting SLVmass accompanied with ENSO is to quantify the portions of non-steric induced SLV from GRACE, and collaborates with updated post processing techniques, e.g. de-correlations, various smoothing filters, etc., to retrieve time-variable gravity over oceans. Owing to a suite of empirical orthogonal functions (EOF) the ENSO-like interannual expansion coefficients are extracted in Tropical Pacific. However, the SLVmass from GRACE is less characterized as seesaw oscillating patterns due to large error in low latitude. For tropical regions, the hydrological effects from land is enormously larger than oceanic response, thus the leakage reduction is applied to eliminate coastal leakages. Unfortunately, either little ENSO signals in Tropical Pacific or strong error in low latitude, the compensated outputs remain obscure. Moreover, the eigen vectors, EOF patterns, shows filter-depend reactions when the empirical parameterized filters are chosen. On the other hand, after comparisons between oceanic altimeter data and in-situ Argo measurements, the SLVmass shows see-saw oscillation despite of an order less than SLVsteric which is correlated to ENSO events.
As a sequence of extraction and comparison with relative ENSO signals, Complex EOF (CEOF), Canonical Correlation Analysis (CCA), Multivariate Signular Spectral Analysis (MSSA), Wavele, etc. time series analyses are employed. CEOF can fully reveal spatio-temporal propagating signals with magnitude and phase shifts. ENSO is a non-stationary wave in Tropical Pacific, and the pairs of strength and phase terms could be another ENSO index; CCA is dedicated to maximizing the correlation based on empirical orthogonal functions which adequately reveal the SLVmass patterns as breathing over oceans but oscillating against to SLVmass around Indonesia; MSSA shows multivariates of singular decomposition within empirical window length is selected where the index matches SOI, Nino3.4 well; wavelet provides time-frequency distribution which suggests a quasi-biennial component prevailing in various geophysical responses in oceans and indirect connection to QBO.
| Identifer | oai:union.ndltd.org:TW/099NCU05134017 |
| Date | January 2011 |
| Creators | Yun-Hao Wu, 伍允豪 |
| Contributors | Benjamin F. Chao, 趙丰 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 139 |
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