GPS and GRACE inferred uplifts and extracted transient and seasonal signals due to glacial mass change near Upernavik Isstrøm

The continuously operating Global Positioning System (GPS) sites mounted on bedrock around the coast of Greenland provide important geodetic datasets to quantify the solid Earth's response to historical and present-day ice mass variations. The presence of colored noise and changeable seasonal signals makes it difficult to detect transient changes in GPS time series. Here we apply the Multichannel Singular Spectral Analysis to the combination of GPS data and Gravity Recovery and Climate Experiment (GRACE) data so that we can identify and fully utilize the spatial correlations from these two independent datasets. Using the GPS and GRACE data near Upernavik Isstrøm in West Greenland as an example, we demonstrate that this method successfully detects two transient signals in ice mass variations during 2008 and 2014. Our forward modeling of loading displacements due to changes in surface mass balance (SMB) and ice dynamics suggests that the transient change starting in mid-2008 was due to the combined contributions from dynamically-induced mass loss and SMB. The transient change starting in mid-2011 was mainly due to ablation Specifically, the ice melted more in 2012 and less in 2013 with little contribution from anomalies in accumulation.

This dataset includes:
(1) Vertical displacements inferred from GPS and GRACE with atmospheric loading, non-tidal ocean loading, and terrestrial water storage loading removed. Gaps are filled and linear trends are also removed. This data are used for multi-channel singular spectral analysis (M-SSA) in the paper.
(2) Transient and seasonal signals extracted from GPS and GRACE data by M-SSA.
(3) Transient and seasonal signals extracted from surface mass balance data by M-SSA.
(4) Transient signals inferred from glacial dynamics.

持续运行的、安装在格陵兰岛沿岸基岩上的全球定位系统（Global Positioning System，GPS）台站，为量化固态地球对历史及当代冰量变化的响应提供了关键的大地测量数据集。有色噪声与多变的季节性信号的存在，使得GPS时间序列中的瞬态变化难以被精准检测。本文将多通道奇异谱分析（Multichannel Singular Spectral Analysis，下文简称M-SSA）应用于GPS数据与重力恢复与气候实验（Gravity Recovery and Climate Experiment，GRACE）数据的联合分析，从而能够识别并充分利用这两套独立数据集的空间相关性。以格陵兰岛西部乌佩纳维克冰峡湾周边的GPS与GRACE数据为例，我们证明该方法成功检测出2008年与2014年期间冰量变化中的两类瞬态信号。通过对地表质量平衡（Surface Mass Balance，SMB）变化与冰动力学过程导致的荷载位移开展正演模拟，我们发现2008年中期开始的瞬态变化由动力诱导的质量损失与地表质量平衡共同贡献；而2011年中期开始的瞬态变化主要源于消融作用：具体而言，2012年融冰量更高，2013年融冰量更低，且积累异常几乎无贡献。

本数据集包含：
(1) 经去除大气荷载、非潮汐海洋荷载与陆地水储量荷载后，由GPS与GRACE数据反演得到的垂直位移序列。数据间隙已被填补，线性趋势亦已移除，该数据用于本文中的多通道奇异谱分析。
(2) 经M-SSA从GPS与GRACE数据中提取的瞬态与季节性信号。
(3) 经M-SSA从地表质量平衡数据中提取的瞬态与季节性信号。
(4) 由冰川动力学过程反演得到的瞬态信号。