利用GRACE重力卫星求解南极洲冰川质量变化的精度研究

Accuracy investigations of GRACE-borne ice mass variations in Antarctica

GRACE重力卫星可用于观测南极洲冰川的质量变化。由GRACE重力卫星提供的月解重力场能有效探测质量的年变化及长期变化(周期和非周期性)。通过GRACE观测的质量变化时间序列,计算得到南极洲质量的长期变化及周期性年变化。计算结果受多种误差影响,其中GRACE模型误差的影响较小,而研究时段及其跨度的影响较为显著,以不同宽度的时间窗口进行平移,得到无穷时间序列下该误差的参考值为±14.89mm/a。南极地区的气压修正误差可达±10mm/a,GIA修正误差与其量级相同。由此我们认为,目前对于南极洲冰川质量变化的一些认识仍需商榷。南极洲西部地区冰川加速消融,Dronning Maud Land和Enderby Land等地区的质量持续累积;其他地区的质量变化情况仍需进一步研究。

Glacial ice mass baIance of Antarctica can be observed by the GRACE satellites. The gravity model with monthly resolution enables efficient detection of annual, long periodic and secular variations. The present study delivers an estimation of the long-periodic and secular variations by determining the linear trend of the observed surface mass anomaly series. The estimation is contaminated by plenty of errors. Among them GRACE model errors are the less hurting. It was found that the trend estimate is highly influenced by the timing and the time interval of observations. Based on the RMS values of trend estimations by windowing 10 a long data with 2 a, 3 a, 4 a and 5 a time spans, an error of 4-14. 89 mm/a has been determined for imaginary, infinite long time series. Errors due to atmospheric correction in Antarctica may reach ± 10 mm/a, GIA correction error can be in the same order. Based on this, we think that the present knowledge of Antarctic ice mass balance is arguable. Regionally, at several parts of the Antarctics mass variations are in an uncertain state, and thus neither the melting, nor the mass accumulation is found to be relevant. Exceptions are West Antarctica, where the melting occurs with notably increased rate, and Dronning Maud Land and Enderby Land where the mass accumulation is found to be stable.