@article{234ebb52d48140dd80070f2b0e5b6567,
title = "Evaluating Proxy Influence in Assimilated Paleoclimate Reconstructions—Testing the Exchangeability of Two Ensembles of Spatial Processes",
abstract = "Abstract–Climate field reconstructions (CFRs) attempt to estimate spatiotemporal fields of climate variables in the past using climate proxies such as tree rings, ice cores, and corals. Data assimilation (DA) methods are a recent and promising new means of deriving CFRs that optimally fuse climate proxies with climate model output. Despite the growing application of DA-based CFRs, little is understood about how much the assimilated proxies change the statistical properties of the climate model data. To address this question, we propose a robust and computationally efficient method, based on functional data depth, to evaluate differences in the distributions of two spatiotemporal processes. We apply our test to study global and regional proxy influence in DA-based CFRs by comparing the background and analysis states, which are treated as two samples of spatiotemporal fields. We find that the analysis states are significantly altered from the climate-model-based background states due to the assimilation of proxies. Moreover, the difference between the analysis and background states increases with the number of proxies, even in regions far beyond proxy collection sites. Our approach allows us to characterize the added value of proxies, indicating where and when the analysis states are distinct from the background states. Supplementary materials for this article are available online.",
keywords = "Climate field reconstructions, Data assimilation, Functional depth, Spatial fields",
author = "Trevor Harris and Bo Li and Steiger, {Nathan J.} and Smerdon, {Jason E.} and Naveen Narisetty and Tucker, {J. Derek}",
note = "This research was supported in part by the National Science Foundation through awards OISE-1743738, AGS-1602581, AGS-1602920, AGS-1805490, NSF-AGS-1602845, and NSF-DMS-1830312. Dr. Narisetty was also partially supported by NSF Award DMS-1811768. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy\u2019s National Nuclear Security Administration under contract DE-NA0003525. Lamont contribution no. 8428. Fig. 3 distance between the permutation distribution and the Kolmogorov distribution under 12 different ranges, r, and smoothness, \u03BD, settings. Fig. 10 p -values of KD over time by region. Gray points indicate p -values over 0.05 after the Benjamini\u2013Yekutieli FDR adjustment. Except for in the early years, most regions have statistically significant differences between their background and analysis ensembles across the reconstruction. The Arctic Ocean and Antarctica fail to reject in many more cases due to their relatively small size and lack of proxies. This research was supported in part by the National Science Foundation through awards OISE-1743738, AGS-1602581, AGS-1602920, AGS-1805490, NSF-AGS-1602845, and NSF-DMS-1830312. Dr. Narisetty was also partially supported by NSF Award DMS-1811768. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy\u2019s National Nuclear Security Administration under contract DE-NA0003525. Lamont contribution no. 8428.",
year = "2021",
doi = "10.1080/01621459.2020.1799810",
language = "English (US)",
volume = "116",
pages = "1100--1113",
journal = "Journal of the American Statistical Association",
issn = "0162-1459",
publisher = "Taylor and Francis Ltd.",
number = "535",
}