測高與重力衛星資料應用於重力與水文變化

Abstract

本文的主要研究課題為(1)使用衛星測高(Satellite Altimetry，SA)與熱容(steric)兩種資料計算海水面高度及質量之時變量，並探討海水質量變化對地球質心、扁率及極運動之影響量。(2)使用SA與GRACE (Gravity Recovery and Climate Experiment)重力衛星資料研究監測湖泊水位高度變化之可行性。本文以1992年10月至2007年12月間的SA與steric資料，獲得以下研究結果：(1)海水面高度異常(Sea Leavel Anamaly，SLA)、steric與改正後海水面高度異常(Corrected SLA，CSLA)之全球海水面高度年變率(Global Sea Level Trend，GSLT)結果，分別為2.94±0.18 mm/yr、0.32±0.28 mm/yr及2.47±0.14 mm/yr；(2)在多個海域中CSLA的海水面高度年變率與SLA及steric的結果相反，顯示此些海域受到steric的效應影響極大；(3)由CSLA反演計算的 係數年變率為1.16±0.07×10-10，振幅為5.13×10-10，相位為- 81.2°；(4) 、 與 地球質心偏移量年變率分別為-0.105±0.015 mm/yr、0.011±0.019 mm/yr及-0.234±0.015 mm/yr ；(5) J2年變率為 0.57±0.08×10-11/yr，振幅為1.98×10-11/yr，相位為 -127.21°；(6) 的變化量約為 係數的3倍，即極移運動中x方向變動量大於y方向約3倍。 本文使用SA測算的湖水位、每月的GRACE重力觀測量與美國氣候預測中心(Climate Prediction Center，CPC)水文模式的等效水位高度(Equivalent Water Height，EWH)變化量等資料，推估Baikal與Balkhash湖集水域內，流入這兩個湖泊的水量，分別為 60% 和30%。在相位變化方面， Baikal湖區GRACE結果與SA及CPC模式相差約7個月，此結果差異主要影響因素為湖泊座落位置的氣候環境與人為干擾量。本文中比較Baikal與Balkhash湖各兩個不同時間段的月均溫，其結果均顯示後時間段的月均溫均較前時間高，分別高約0.64 °C與0.7 °C ，其中Baikal湖的年均溫由零度以下，上升至零度以上，此結果將造成原永凍土的解融，增加注入Baikal湖的水量。對照兩湖區年均溫及地球扁率J2係數的變化趨勢，兩者均在1997-1998 El Niño事件發生後變化轉折。

The main research topics of this study are : (1) to determine changes of sea surface heights and oceanic mass using satellite altimetry (SA) and steric heights, and to determine the contributions of such changes to variations of geocenter, J2, and polar motions. (2) to determine lake level changes using SA and Gravity Recovery and Climate Experiment (GRACE) gravimetry data. Using SA and steric heights over October 1992 to December 2007, the following results are obtained : (1) the rates of sea level anomaly (SLA), steric height anomaly and corrected SLA (CSLA) are 2.94 ± 0.18, 0.32 ± 0.28 mm/yr and 2.47 ± 0.14 mm/yr. (2) The trends of CSLA, SLA and steric heights are conflicting over some oceanic areas, suggesting that large uncertainties of the underlying data may exist here. (3) The rate, annual amplitude and phase of , which is the oceanic mass-induced variation of the zero-degree geopotential coefficient, are 1.16 ± 0.07 × 10-10, 5.1 3 × 10-10 and -81.2º. (4) The rates of the geocenter variations in x, y, and z are -0.105 ± 0.015, 0.011 ± 0.019 and -0.234 ± 0.015 mm/yr. (5) The rate and annual amplitude and phase of J2 are 0.57 ± 0.08 × 10-11/yr, 1.98 × 10-11/yr and -127.21∘. (6) The magnitude of is 3 times greater than that of , suggesting that the oceanic mass contributes more to the x component of the polar motion than the y component. Using the variations of lake level from SA and the equivalent water heights (EWH) from the monthly GRACE gravity fields and the Climate Prediction Center (CPC) hydrological model, it is estimated that about 60% and 30% of water in the catchment areas of Lakes Baikal and Balkhash enter these two lakes. The phase of the annual variation of the Baikal lake level from GRACE differ by 7 months from the phases obtained with satellite altimetry and the CPC model. This difference is due to a climate factor and some man-made causes. Monthly temperature data over two time periods around Lakes Baikal and Balkhash show that the mean temperature in the earlier period is larger than that in the later period. On average, temperatures over Baikal and Balkhash increase by 0.64° and 0.7°C. Over these two periods the mean temperature around Baikal changes from sub-zero to above-zero, suggesting that the permafrost here may thaw to increase the amount of water entering Baikal. A common feature in the trends of J2 and the lake levels of Baikal and Balkhash is that the trend before the 1997-1998 El Niño is reversed after this event.