# 格陵兰冰盖质量变化的特征与机制初探Analysis on the Characteristics of Greenland Ice Sheet Mass Change and a Preliminary Study on Mechanism

Abstract: Greenland ice sheet (GrIS) is an important regulator of global climate. The melting water of the ice sheet not only increases the global sea level, but also weakens the deep convection in the North Atlantic Subpolar Region, thus slowing down the meridional reversal circulation of the Atlantic Ocean, which will affect the global thermohaline circulation and change the global heat distribution. Based on GRACE gravity satellite data, MAR regional model data, DMI weather station data and ERA global reanalysis data, the temporal and spatial characteristics of GrIS mass change during GRACE observation period are analyzed. The main factors that control GrIS mass change are studied by means of mass balance and surface energy balance method, and the dynamic mechanism of GrIS mass change is preliminarily discussed. The results show that the accelerated mass loss of GrIS in 2003-2012 has decelerated since 2013, and the main slowdown area is in the southeast of GrIS. The GrIS mitigation events started in 2013 were due to increased cloud cover, enhanced albedo, reduced net shortwave radiation and subsequent summer melting, which may be related to the sea level pressure of the summer North Atlantic Oscillation changes.

1. 引言

GrIS巨大的蓄积率和显著的径流以及融水生成，使其成为一个高度动态变化的地方。GrIS的快速变化可能会影响全球海平面上升，并可能改变AMOC和全球气候 [1] [2] 。GrIS是正在发生的气候变化的一个指标，整个冰盖对气候的影响已经被许多研究所证明。1990s使用机载高度计测量的GrIS显示其边缘地区冰盖变薄，在中部区域有轻微的增厚 [3] 。随后的测量结果显示，沿海地区冰盖变薄加剧，并集中在被冰川出口占据的狭窄山谷中 [4] 。高度计数据研究显示 [5] [6] ，从1992年到2003/4年，2000米以上的GrIS内部出现了显著的(2~5 cm/yr)增长，这可能是由大气湿度和降水量的增加和(或)风暴路径的移动所致 [7] 。Velicogna等人 [8] 利用22个月的GRACE重力场首次从太空测量估算整个GrIS的质量变化。Ramillien等人 [9] 于2006年使用GRACE数据(利用新的大地水准面)计算了(2002年7月~2005年3月)这一时间段的GrIS质量变化及其对海平面上升的贡献。由于GRACE卫星数据的采样时间跨度非常短，尚无法区分年际振荡与气候变化相关的长期趋势。Velicogna等人 [10] 使用了一段较长的连续时间(2002~2009年)的GRACE数据分析格陵兰的冰盖质量变化。但是，这些开创性的分析估计之间存在许多差异和不确定性，对于影响格陵兰的冰盖质量变化的物理机制的探讨也比较少。

Hanna等人 [11] 将1990年代以来冰盖变薄融化及径流增加与夏季温度显著增加归因于全球气候变暖。如果GrIS全部融化，全球海平面将上升约7.4 m，另外研究也表明GrIS容易受到人类行为导致的气候变暖的影响 [12] 。自上世纪90年代初以来，随着大气变暖，GrIS地表径流增加，格陵兰表面融化过程约占整个GIS总质量损失的一半 [13] ，在表面温度长期升高的情况下，这一比例甚至更大 [14] 。然而，由于针对GrIS整体研究的数据跨度较短，尚未有研究提供一个更有说服力的多年代际视角，来研究冰盖如何应对长期气候变化，尤其是自20世纪70年代以来明显的全球变暖现象。

2. 数据资料与研究方法

2.1. 数据资料

2.2. 研究方法

3. 格陵兰冰盖质量变化特征

3.1. 格陵兰冰盖质量的时空变化

Figure 1. The time series of GrIS mass change observed by GRACE satellite since 2003. The grey points represent the data of missing months filled with linear interpolation method

Figure 2. (a) The linear trend of GrIS melting observed by GRACE satellite in 2003-2012 and (b) the spatial pattern in 2013-2016, respectively. Except for the light grey dotted area in (b), all other spatial lattice points have passed 95% confidence test for linear trend estimation

3.2. 格陵兰冰盖质量收支

MAR模式数据中的SMB及其变量的冬季(DJF)季节变化如图5所示。冬季SMB主要受降雪控制，除了振幅在1997年以后减小，并无其他变化趋势。融化降雨和径流都接近于零。

Figure 3. The anomaly time series of melt, runoff, snowfall, rainfall and SMB in MAR model data from 1979 to 2017

Figure 4. The anomaly time series of summer melt, runoff, snowfall, rainfall and SMB in MAR model data from 1979 to 2017

Figure 5. The anomaly time series of winter melt, runoff, snowfall, rainfall and SMB in MAR model data from 1979 to 2017

3.3. 格陵兰冰盖表面能量平衡

Figure 6. Variation of melting water (blue line) and melting water volume (red line) calculated by net heat flux from 1979 to 2017 based on MAR model data

Figure 7. Time series of surface net heat flux, short wave radiation, long wave radiation, sensible heat flux and latent heat flux in Greenland from 1979 to 2016

GrIS表现出的质量损失是由于冬季净增加质量(结冰量)小于夏季净减少质量(融化量)形成的，而导致质量减少的速度减缓的可能原因有两个，分别是夏季融化量减少和冬季结冰量增加。

Figure 8. Time series of ice sheet melting in Greenland in summer (a) and winter (b) based on net heat flux and its components (net short wave radiation, net long wave radiation, sensible heat flux and latent heat flux) and MAR model melt production

3.4. 格陵兰冰盖表面能量平衡的控制因素

Figure 9. Trends of GrIS cloud cover (blue line) and albedo (red line) in summer

4. 格陵兰冰盖质量变化动力机制的初步研究

Figure 10. Summer time series and mean values of near-surface temperature in Greenland; changes in summer melting of GrIS (black line)

Figure 11. Empirical mode decomposition (EMD) components (IMF) of GrT in summer of 1910-2016

Figure 12. The spatial pattern of IMF components of GrT in summer that projected to sea level pressure field (SLP) and sea surface temperature field (SST) from 1982 to 2016, respectively

5. 结语

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