Browsing by Author "Lambert, F."

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    Global-Krigger: A Global Kriging Interpolation Toolbox With Paleoclimatology Examples
    (2023) Cosentino, N. J.; Opazo, N. E.; Lambert, F.; Osses, A.; van 't Wout, E.
    Many applications in Earth sciences require spatial prediction, that is, obtaining a continuous scalar field from a set of discrete scalar data points on the Earth's surface. Such applications include model data comparisons and derivation of continuous scalar fields as input for Earth system models. The advantage of kriging as an interpolation method is that it provides predictions with confidence intervals for data sets of irregularly distributed points in space. However, the theory of kriging for non-Euclidean domains such as oblate spheroids (e.g., the Earth's surface) is poorly developed, and existing kriging algorithms for global interpolation oftentimes cannot guarantee the validity of their predictions. Here, we present Global-Krigger, a new kriging interpolation algorithm adapted for local to global applications that (a) incorporates a numerical check to guarantee that the necessary conditions for the kriging system of linear equations are met, and (b) derives a combined uncertainty field due both to spatial variations in data density and measurement error. The robustness of the method is demonstrated by cross-validating predictions against reanalysis fields of traditional climatological scalar variables. We also show an example application in paleoclimatology for Holocene mineral dust deposition fluxes. The toolbox includes a user-friendly graphical user interface that guides users through a range of choices during data pre-interpolation analysis, kriging, and post-processing.Plain Language Summary Many climatic variables such as temperature and precipitation are measured by monitoring stations on the Earth's surface at irregularly distributed locations. Similarly, paleoclimatic proxy variables are available at specific locations where paleoclimatic archives such as marine sediment cores have been retrieved. Such data sets can be used to guide Earth system simulations, but this works best when they are available as a regular grid. Kriging is an interpolation method that produces regular grids from irregularly distributed measurements. However, while kriging theory is well-developed for measurements on a plane surface, its application on curved surfaces is problematic. To improve this, we have developed Global-Krigger, a user-friendly kriging interpolation toolbox for the surface of the Earth. It incorporates new tests to check the validity of kriging results on curved surfaces. The toolbox also provides a quantification of the interpolation uncertainty, taking into account both the uncertainty of the measurements and the spatial distribution of the measurement sites. We show that our algorithm gives robust results by applying it to a sub-sample of known modern climatology fields, and also provides a paleoclimatic application for Holocene mineral dust deposition fluxes. Finally, we develop a graphical user interface to guide users in the process of kriging.
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    Permafrost evolution in a mountain catchment near Santiago de Chile
    (2021) Ruiz Pereira, S.; Marquardt, C.; Beriain, E.; Lambert, F.
    The Chilean Central Andes near Santiago are a semi-arid region with substantial frozen water reserves in their high altitude cryosphere. Millions of people depend on the Andean cryosphere for freshwater supply. Over the last sixty years, global warming has altered the mountains' water balance, as the temperature rose, precipitation decreased, and deglacierization exposed hundreds of square kilometers. The distribution of solid water stored in soil permafrost and the potential effects of climate change on it are unknown.
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    Present-Day Patagonian Dust Emissions: Combining Surface Visibility, Mass Flux, and Reanalysis Data
    (AMER GEOPHYSICAL UNION, 2021) Cosentino, N. J.; Gaiero, D. M.; Lambert, F.
    The magnitude of the climatic forcing associated with mineral dust aerosols remains uncertain due in part to a lack of observations on dust sources. While modeling and satellite studies provide spatially extensive constraints, they must be supported by surface-validating dust monitoring. Southern South America is the main dust source to the southern oceans (>45 degrees S), a region of low biological productivity potentially susceptible to increased micronutrient fertilization through dust deposition, as well as one of the main dust sources to Antarctica, implying long-range transport of dust from Patagonia and potentially affecting snow cover albedo. We present multiyear time series of dust-related visibility reduction (DRVR) and dust mass flux in Patagonia. We find that local DRVR is partly controlled by long-term (i.e., months) water deficit, while same-day conditions play a smaller role, reflective of water retention properties of fine-grained dust-emitting soils in low-moisture conditions. This is supported independently by reanalysis data showing that large-scale dust outbreaks are usually associated with anomalously high long-term water deficit. By combining visibility data, surface dust sampling, and particle dispersion modeling, we derive regional dust emission rates. Our results suggest that the inclusion of long-term soil hydrologic balance parameterizations under low-moisture conditions may improve the performance of dust emission schemes in Earth system models.