Robertson Franklin R, Bosilovich Michael G, Roberts Jason B
NASA / Marshall Space Flight Center, Earth Science Office MSFC, AL 35812.
GSFC Global Modeling and Assimilation Office Greenbelt, MD 20771.
J Clim. 2016 Dec 1;29(23):8625-8646. doi: 10.1175/JCLI-D-16-0379.1. Epub 2016 Nov 15.
Vertically-integrated atmospheric moisture transport from ocean to land, VMFC, is a dynamic component of the global climate system but remains problematic in atmospheric reanalyses with current estimates having significant multi-decadal global trends differing even in sign. Regional VMFC trends over continents are especially uncertain. Continual evolution of the global observing system, particularly step-wise improvements in satellite observations, has introduced discrete changes in the ability of data assimilation to correct systematic model biases, manifesting as non-physical variability. Land Surface Models (LSMs) forced with observed precipitation, P, and near-surface meteorology and radiation provide estimates of evapotranspiration, ET. Since variability of atmospheric moisture storage is small on interannual and longer time scales, VMFC = P-ET is a good approximation and LSMs can provide an alternative estimate. However, heterogeneous density of rain gauge coverage, especially the sparse coverage over tropical continents, remains a serious concern. Rotated Principal Component Analysis (RPCA) with pre-filtering of VMFC to isolate the artificial variability is used to investigate artifacts in five reanalysis systems. This procedure, though ad hoc, enables useful VMFC corrections over global land. P-ET estimates from seven different LSMs are evaluated and subsequently used to confirm the efficacy of the RPCA-based adjustments. Global VMFC trends over the period 1979-2012 ranging from 0.07 to -0.03 mmd decade are reduced by the adjustments to 0.016 mmd decade, much closer to the LSM P-ET estimate (0.007 mmd decade). Neither is significant at the 90 percent level. ENSO-related modulation of VMFC and P-ET remains the largest global interannual signal with mean LSM and adjusted reanalysis time series correlating at 0.86.
从海洋到陆地的垂直整合大气水分输送（VMFC）是全球气候系统的一个动态组成部分，但在大气再分析中仍存在问题，目前的估计显示存在显著的年代际全球趋势，甚至在趋势的正负号上都存在差异。各大洲的区域VMFC趋势尤其不确定。全球观测系统的不断发展，特别是卫星观测的逐步改进，在数据同化纠正系统模型偏差的能力方面引入了离散变化，表现为非物理变率。用观测到的降水量（P）、近地表气象和辐射强迫陆地表面模型（LSMs）来估算蒸散量（ET）。由于大气水分储存的变率在年际和更长时间尺度上较小，VMFC = P - ET是一个很好的近似，LSMs可以提供一个替代估计。然而，雨量计覆盖的不均匀密度，特别是热带大陆上的稀疏覆盖，仍然是一个严重问题。采用旋转主成分分析（RPCA）对VMFC进行预滤波以分离人为变率，用于研究五个再分析系统中的人为因素。这个过程虽然是临时的，但能在全球陆地上进行有用的VMFC校正。对来自七个不同LSMs的P - ET估计进行了评估，并随后用于确认基于RPCA调整的有效性。1979 - 2012年期间全球VMFC趋势范围从0.07到 -0.03毫米/十年，经调整后降至0.016毫米/十年，更接近LSM的P - ET估计值（0.007毫米/十年）。两者在90%的置信水平下均不显著。与ENSO相关的VMFC和P - ET调制仍然是最大的全球年际信号，平均LSM和调整后的再分析时间序列的相关性为0.86。
