ALBERT

Description: We thank Dahlen & Nolet for the comments (DN05) on our paper (HH05). There are many points of agreement, as we think is clear from HH05, but we respectfully continue to differ in opinion on some fundamental aspects of the finite frequency sensitivity kernels known as 'banana doughnut' kernels—hereinafter BDKs, as per the original nomenclature of Dahlen et al.—and their benefit to global tomography. In contrast to DN05's summary statement, HH05's main concern about BDKs is not the effect of uncertainty in the earthquake source signature or origin time. HH05 argue that (i) the evaluation of sensitivity kernels in simple media has limitations for the interpretation of broad-band signals by means of (linearized) finite frequency tomography; (ii) finite frequency kernels are (indeed) oscillatory, but in general heterogeneity their structure will be complex and different from BD features; (iii) the resolved length scales of model variations are induced by the spectral scales present in the data, which makes the notion of 'hole' irrelevant; and (iv) with the need for 'damping' (regularization) and without a basis that matches properly the multi-scale aspects of finite frequency sensitivity, ray theory or finite frequency theory inversions are likely to yield results that are practically the same.

Description: The following authors were omitted from the original version of this Data Descriptor: Markus Reichstein and Nicolas Vuichard. Both contributed to the code development and N. Vuichard contributed to the processing of the ERA-Interim data downscaling. Furthermore, the contribution of the co-author Frank Tiedemann was re-evaluated relative to the colleague Corinna Rebmann, both working at the same sites, and based on this re-evaluation a substitution in the co-author list is implemented (with Rebmann replacing Tiedemann). Finally, two affiliations were listed incorrectly and are corrected here (entries 190 and 193). The author list and affiliations have been amended to address these omissions in both the HTML and PDF versions. © 2021, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.

Description: On November 5–8, 2019, the “Mars Extant Life: What's Next?” conference was convened in Carlsbad, New Mexico. The conference gathered a community of actively publishing experts in disciplines related to habitability and astrobiology. Primary conclusions are as follows: A significant subset of conference attendees concluded that there is a realistic possibility that Mars hosts indigenous microbial life. A powerful theme that permeated the conference is that the key to the search for martian extant life lies in identifying and exploring refugia (“oases”), where conditions are either permanently or episodically significantly more hospitable than average. Based on our existing knowledge of Mars, conference participants highlighted four potential martian refugium (not listed in priority order): Caves, Deep Subsurface, Ices, and Salts. The conference group did not attempt to reach a consensus prioritization of these candidate environments, but instead felt that a defensible prioritization would require a future competitive process. Within the context of these candidate environments, we identified a variety of geological search strategies that could narrow the search space. Additionally, we summarized a number of measurement techniques that could be used to detect evidence of extant life (if present). Again, it was not within the scope of the conference to prioritize these measurement techniques—that is best left for the competitive process. We specifically note that the number and sensitivity of detection methods that could be implemented if samples were returned to Earth greatly exceed the methodologies that could be used at Mars. Finally, important lessons to guide extant life search processes can be derived both from experiments carried out in terrestrial laboratories and analog field sites and from theoretical modeling.

Description: The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

Description: The ESA Data User Element (DUE) Permafrost (2009-2012) created an Earth Observation service for permafrost-related applications with extensive involvement from the permafrost research community. The DUE Permafrost consortium produced time series on regional and circum-arctic scales of‘Land Surface Temperature’(LST), ‘Surface Soil Moisture’ (SSM), ‘Frozen/Thawed Surface Status’ (Freeze/Thaw), and static products of ‘Terrain’, ‘Land Cover’ (LC), and ‘Surface Waters’. Most of the DUE Permafrost services are based on operationally available remote sensing products. However, permafrost landscapes are a challenge for qualitative and quantitative remote sensing. The land surface is highly heterogeneous characterized by patterned ground, disturbances, abundant small water bodies, and sharp moisture gradients. Only few error estimates or standard evaluation methods exist for remote sensing products from high-latitude terrestrial landscapes. An additional significant challenge in the evaluation of remote sensing products in high-latitude permafrost landscapes is the very sparse availability of ground data. Ground-based evaluation of the operationally available remote sensing products is needed. International programs, such as the Global Terrestrial Network for Permafrost (GTN-P) initiated by the International Permafrost Association (IPA) as well as national programs such as the scientific preparation programs for two national satellite missions (hyperspectral EnMAP satellite mission, Tandem-L radar satellite mission (Helmholtz Alliance Remote Sensing and Earth System Dynamics HGF-EDA) provide ground data and evaluation experiments. We will show examples of: • Evaluation experiments of remote sensing products of ‘Land surface temperature’ (LST) and ‘Frozen/ Thawed Surface Status’ (Freeze/Thaw) using GTN-P data (ESA DUE Permafrost). • Evaluation experiments of optical and microwave remote sensing products using the method of ‘homogeneous measurement fields’ (HGF-EDA, PAGE21, EnMAP). • field-based spectral and BRDF measurements of vegetation at different scales collected in Alaska, Yamal (Western Siberia) and the Lena Delta (Arctic Siberia) (EnMAP).

Description: Ground radars can be used to study plasma convection, satellite magnetometers can be used to study field-aligned currents, and ground magnetometers can be used to study the electrojet – but combining these measurements to a coherent picture of the full ionospheric electrodynamics is not trivial. We present a method to accomplish this using the ionospheric Ohm’s law in combination with spherical elementary current systems. The technique, called Local mapping of polar ionospheric electrodynamics (Lompe) is implemented in Python, and is open-source, well documented, and includes several examples. The Lompe technique can be applied on grids with arbitrary extent and resolution, chosen by the user depending on the available data. We present examples of how the technique can be used to produce physics-based interpolation of ground magnetic field disturbances to regions with no magnetometers.

Description: Seasonal snow cover extent is an essential climate variable that is, in principle, easy to measure with optical remote sensing because of the high contrast in albedo between snow and snow-free ground. In practice, however, the amount of information is severely limited by cloud cover globally and seasonal darkness at high latitudes. The European Space Agency snow cci project has now generated long-term global, daily snow cover products from AVHRR (1982-2018 at 5 km resolution) and MODIS (2000-2020 at 1 km resolution). To investigate the information content of these products and the level of uncertainty in gap filling with data assimilation for Arctic tundra snow, we take advantage of newly available in situ 1991-2022 meteorological time series for Trail Valley Creek, Northwest Territories, Canada. As a contribution to the ESM-SnowMIP project, we evaluate the ability of snow cover observations with and without gap filling to discriminate between climate model simulations submitted for CMIP6.

Description: The boundaries of the auroral oval describe the extent of auroral ionospheric activity. We can find these boundaries with a number of datasets by looking at different aspects of auroral activity. The poleward boundary is often considered to be the boundary between open and closed magnetic field lines. Knowing this boundary allows us to quantify the amount of open flux in the polar cap. It is most commonly measured with optical measurements or in-situ measurements of precipitating particles in Low Earth Orbit. In this study we consider how the auroral electrojets can be used as a proxy for the auroral oval boundaries. We derive the electrojet boundaries using east-west sheet current profiles along the 105◦ magnetic meridian, estimated using ground magnetometers. Additionally, we include electrojet boundaries derived from the magnetometers onboard the Swarm satellites, particle precipitation boundaries found by measurements from the DMSP satellites and FUV auroral images from the IMAGE satellite to compare and contrast the datasets. We find clear similarities between the two electrojet datasets but find the Swarm based equatorward boundaries to reach too low latitudes and the poleward boundaries to be unstable during low geomagnetic activity. We find the statistical averages of particle precipitation boundaries and auroral image boundaries to be in good agreement. The relationship between equatorial boundary of the electrojet and auroral boundaries is shown to have an MLT dependence, where the precipitation and image boundaries appear poleward of the electrojet boundaries in the dusk sector but equatorward in the dawn sector.