利用GRACE測高資料和海洋溫度及鹽度資料研究海洋質量變化

• Main Author: 郭重言
• Other Authors: 測量系
• Language: Chinese; English
• Published: 2008
• Subjects: Antarctic; Southern Ocean; Antarc*; Sea ice
• Online Access: http://ir.lib.ncku.edu.tw/handle/987654321/132592; http://ir.lib.ncku.edu.tw/bitstream/987654321/132592/1/index.html

年度編號:970141 南極洋藉由南極洲冰原和附近海冰融化和積累之複雜交互作用連結世界其他海洋，然而除了近年來近極地衛星所觀測的資料外，此處觀測資料相當貧乏。本研究利用三種獨立資料分別計算季節性之南極洋質量變化：(1) GRACE重力衛星所測之海底壓力（ocean bottom pressure, OBP)資料；(2) 改正steric sea level後之測高資料；(3) ECCO model之OBP資料。測高衛星觀測海水面高和利用海溫資料計算之steric sea level間的差值含有因地球彈性負載所造成的地殼垂直位移，因此我們提供一公式來計算，並證明此改正量在區域性研究中不可忽略。本文利用此三種資料分別計算全球海洋質量變化，並相互比較，結果顯示三種結果相當吻合，相關係數可達0.81，而差異量之RMS為3~5公厘，然而計算之南極洋質量變化相對較不吻合，RMS為12~17公厘。不精確之地心變化資料和J2資料會降低利用GRACE求得之海洋質量變化精度，另外精度不足之steric sea level也會影響比較結果。最後本研究指出GRACE和測高衛星可提供計算南極洋質量變化之約制。 The Southern Ocean is a major link between the world oceans via complicated processes associated with the melting and accumulation of the vast Antarctic ice sheets and the surrounding sea ice. The Southern Ocean sea level is poorly observed except from recent near-polar orbiting space geodetic satellites. In this study, the Southern Ocean mass variations at the seasonal scale are compared using three independent data sets: (1) the Gravity Recovery And Climate Recovery Experiment (GRACE) observed ocean bottom pressure (OBP), (2) steric-corrected satellite altimetry (ENVISAT) and, (3) the Estimating the Circulation and Climate of the Ocean (ECCO) model OBP data. Height difference between sea level derived from altimetry and steric sea level contains the vertical displacement of the Earth surface due to elastic loading. Here we provide a formulation of this loading term which has not been considered before in other studies, and demonstrate that it is not negligible especially for regional studies. In this study, we first conduct a global comparison using steric-corrected JASON-1 altimetry with GRACE, to validate our technique and to compare with recent studies. The global ocean mass variation comparison shows excellent agreement with high correlation (~0.81) and with discrepancies at 3–5 mm RMS. However, the discrepancies in the Southern Ocean are much larger at 12–17 mm RMS. It is found that the mis-modeling of geocenter variations and the 2nd degree zonal harmonic (J2) degrade the accuracy of GRACE derived mass variations, and the choice of ocean temperature data sets and neglecting the loading correction on altimetry affect the OBP comparisons between GRACE and altimetry. This study indicates that the satellite observations (GRACE and ENVISAT) are capable of providing an improved constraint of oceanic mass variations in the Southern Ocean.