Abstract
The release 06 (RL06) of the Gravity Recovery and Climate Experiment (GRACE) Atmosphere and Ocean De-Aliasing Level-1B (AOD1B) product has been prepared for use as a time-variable background ...model in global gravity research. Available since the year 1976 with a temporal resolution of 3 hr, the product is provided in Stokes coefficients up to degree and order 180. RL06 separates tidal and non-tidal signals, and has an improved long-term consistency due to the introduction of a time-invariant reference orography in continental regions. Variance reduction tests performed with globally distributed in situ ocean bottom pressure recordings and sea-surface height anomalies from Jason-2 over a range of different frequency bands indicate a generally improved performance of RL06 compared to its predecessor. Orbit tests for two altimetry satellites remain inconclusive, but GRACE K-band residuals are reduced by 0.031 nm s−2 in a global average, and by more than 0.5 nm s−2 at numerous places along the Siberian shelf when applying the latest AOD1B release. We therefore recommend AOD1B RL06 for any upcoming satellite gravimetry reprocessing effort.
Short-term forecasts of atmospheric, oceanic, and hydrological effective angular momentum functions (EAM) of Earth rotation excitation are combined with least-squares extrapolation and autoregressive ...modeling to routinely predict polar motion (PM) and
Δ
UT1
for up to 90 days into the future. Based on hindcast experiments covering the years 2016 and 2017, a best performing parametrization was elaborated. At forecast horizons of 10 days, remaining prediction errors are 3.02 and 5.39 mas for PM and
Δ
UT1
, respectively, corresponding to improvements of 34.5 and 44.7% when compared to predictions reported routinely in Bulletin A of the International Earth Rotation and Reference Systems Service. At forecast horizons of 60 days, prediction errors are 12.52 and 107.96 mas for PM and
Δ
UT1
, corresponding to improvements of 34.5 and 8.2% over Bulletin A. The 90-day-long EAM forecasts leading to those improved EOP predictions are routinely published on a daily basis at isdc.gfz-potsdam.de/esmdata/eam.
High‐resolution load‐induced crustal deformations calculated from numerical models are tested for their ability to predict hydrologically‐induced station height variability, as they are known to be ...large enough to affect epoch‐wise parameters obtained from the analysis of global geodetic networks. Loading contributions due to terrestrial water storage as given by global hydrological models are calculated on a 0.5° global regular grid with daily temporal resolution. Apart from the dominant seasonal variations, the hydrological loading signal discloses also rapid changes exceeding 1 mm in several regions that can be associated with major precipitation events and river floods. Locally strong loading signals with exceptionally high amplitudes, in many cases even with nonseasonal nature, occur along the major river channels. Only high‐resolution loading calculations considering also the water mass anomalies stored in the model river flow can resolve the correct amplitudes in the surrounded area up to 100 km distance. The comparison of the modeled hydrological surface deformation with GPS station time series shows that high‐resolution hydrological loading estimates based on global‐scale models are able to explain a considerable fraction (up to 54%) of the observed vertical station movements caused by continental water storage variations.
Key Points
Calculation of daily crustal deformations from LSDM, OMCT, and ECMWF
Consideration of surface water contributions and its high spatial gradients
Validation of predicted vertical motions against GPS station time‐series
SUMMARY
Global mass redistribution between the Earth subsystems oceans, atmosphere and continental hydrosphere causes a predominantly seasonal signal in Earth rotation excitation that superimposes ...the effects of each individual Earth subsystem. Especially for annual length-of-day variations a consistent consideration of the global mass balance among atmosphere, ocean and continental water is necessary to compare the simulated effective angular momentum functions for Earth rotation from geophysical models with geodetic observations. In addition to atmospheric, oceanic and hydrological contributions, we estimate the contributions due to the global mass balance effect using the new ESMGFZ SLAM product as well as estimates of the barystatic ocean bottom pressure anomalies from the GRACE Level 3 GravIS products. For the annual cycle the global mass balance effect overcompensates the contributions to length-of-day variations from terrestrial hydrology. Moreover, most of the atmospheric surface pressure contribution is also compensated. The global mass balance effect has to be calculated for each combination of geophysical Earth system models individually. Considering the global mass balance, model based mass induced excitation on seasonal length-of-day variations coincide well with estimates from satellite gravimetry. Moreover, the mass terms can be determined accurate enough to attribute the remaining gap in the length-of-day excitation budget between models and observation clearly to an underestimation of atmospheric wind speeds in the global European weather forecast model. Magnifying its wind speeds by +7 per cent the sum of all ESMGFZ angular momentum functions can almost perfectly explain the total length-of-day excitation.
Display omitted
•Local Green's functions to estimate hydrological loading displacements.•Consideration of heterogeneities in Earth's crust.•Scatter plots show dependency between loading response and ...local crustal structure.•Crustal stratification influences near-field displacements.•Impact of crustal structure is relevant for hydrological loading displacements.
The influence of the elastic Earth properties on seasonal or shorter periodic surface deformations due to atmospheric surface pressure and terrestrial water storage variations is usually modeled by applying a local half-space model or an one dimensional spherical Earth model like PREM from which a unique set of elastic load Love numbers, or alternatively, elastic Green's functions are derived. The first model is valid only if load and observer almost coincide, the second model considers only the response of an average Earth structure. However, for surface loads with horizontal scales less than 2500km2, as for instance, for strong localized hydrological signals associated with heavy precipitation events and river floods, the Earth elastic response becomes very sensitive to inhomogeneities in the Earth crustal structure.
We derive a set of local Green's functions defined globally on a 1°×1° grid for the 3-layer crustal structure TEA12. Local Green's functions show standard deviations of ±12% in the vertical and ±21% in the horizontal directions for distances in the range from 0.1° to 0.5°. By means of Green's function scatter plots, we analyze the dependence of the load response to various crustal rocks and layer thicknesses. The application of local Green's functions instead of a mean global Green's function introduces a variability of 0.5–1.0mm into the hydrological loading displacements, both in vertical and in horizontal directions. Maximum changes due to the local crustal structures are from −25% to +26% in the vertical and −91% to +55% in the horizontal displacements. In addition, the horizontal displacement can change its direction significantly. The lateral deviations in surface deformation due to local crustal elastic properties are found to be much larger than the differences between various commonly used one-dimensional Earth models.
Fusarium culmorum (Fc) and F. graminearum (Fg) belong to the predominant causal agents of fusarium crown and root rot (FCR) in wheat. While many studies have been done to investigate crown rot, ...including stem base infection, root colonization and mycotoxin production associated with root rot is not well understood. In this study the impact of mycotoxins on the colonization of wheat roots and stem bases was analysed by using Fc and Fg isolates that varied in both quantity and types of trichothecenes they produce. Seedling inoculations in growth chambers with a high deoxynivalenol (DON)‐ and 3‐acetyldeoxynivalenol (3ADON)‐producing isolate led to more severe symptoms and 20‐times greater colonization of the stem base, as measured by Fc DNA accumulation, than isolates that produced less DON/3ADON. In contrast to stem base colonization, in vitro inoculations of roots with a Tri5 deletion mutant deficient in Fg trichothecene production led to three‐times higher colonization than the wildtype. Furthermore, an Fc isolate that produced low levels of zearalenone resulted in twice the level of colonization of a high DON/3ADON‐producing isolate included in the study. When root inoculation with a low DON/3ADON‐producing Fc isolate was supplemented with exogenous DON, DON production decreased by more than half per unit weight of Fc DNA, and root colonization doubled compared to the untreated control. Therefore, in contrast to its potential role as an aggressiveness factor in stem base infection, trichothecene production by Fc and Fg is detrimental to the early stages of wheat root colonization in FCR.
Utilization of quantitative trait loci (QTL) identified in bi-parental mapping populations has had limited success for improving complex quantitative traits with low to moderate heritability. ...Association mapping in contemporary breeding germplasm may lead to more effective marker strategies for crop improvement. To test this approach, we conducted association mapping of two complex traits with moderate heritability; Fusarium head blight (FHB) severity and the grain concentration of mycotoxin associated with disease, deoxynivalenol (DON). To map FHB resistance in barley, 768 breeding lines were evaluated in 2006 and 2007 in four locations. All lines were genotyped with 1,536 SNP markers and QTL were mapped using a mixed model that accounts for relatedness among lines. Average linkage disequilibrium within the breeding germplasm extended beyond 4 cM. Four QTL were identified for FHB severity and eight QTL were identified for the DON concentration in two independent sets of breeding lines. The QTL effects were small, explaining 1-3% of the phenotypic variation, as might be expected for complex polygenic traits. We show that using breeding germplasm to map QTL can complement bi-parental mapping studies by providing independent validation, mapping QTL with more precision, resolving questions of linkage and pleiotropy, and identifying genetic markers that can be applied immediately in crop improvement.
Earth angular momentum forecasts are naturally accompanied by forecast errors that typically grow with increasing forecast length. In contrast to this behavior, we have detected large quasi‐periodic ...deviations between atmospheric angular momentum wind term forecasts and their subsequently available analysis. The respective errors are not random and have some hard to define yet clearly visible characteristics which may help to separate them from the true forecast information. These kinds of problems, which should be automated but involve some adaptation and decision‐making in the process, are most suitable for machine learning methods. Consequently, we propose and apply a neural network to the task of removing the detected artificial forecast errors. We found that a cascading forward neural network model performed best in this problem. A total error reduction with respect to the unaltered forecasts amounts to about 30% integrated over a 6‐days forecast period. Integrated over the initial 3‐days forecast period, in which the largest artificial errors are present, the improvements amount to about 50%. After the application of the neural network, the remaining error distribution shows the expected growth with forecast length. However, a 24‐hourly modulation and an initial baseline error of 2 × 10−8 became evident that were hidden before under the larger forecast error.
Plain Language Summary
Variations in Earth rotation can be described by changes in Earth angular momentum. Angular momentum functions are calculated from mass redistributions, for example, given by atmospheric models. Typically, atmospheric model forecasts are naturally accompanied by forecast errors that grow with increasing forecast length. In contrast to this behavior, atmospheric angular momentum wind term forecasts show large quasi‐periodic deviations when compared to their subsequently available model analysis data. The detected errors are not random and have some hard to define yet clearly visible characteristics. A postprocessing step using machine learning methods was established to remove the detected artificial forecast errors. A cascading forward neural network approach was able to reduce the forecast error by about 50% for the first forecast days and about 30% for a 6‐day forecast horizon. Moreover, the remaining error distribution shows the expected growth with forecast length. This postprocessing step improves atmospheric angular momentum forecasts without touching the numerical weather prediction model itself. Improved angular momentum forecasts should help to further decrease Earth rotation predictions errors.
Key Points
Motion terms of atmospheric angular momentum forecasts contain systematic errors
Machine learning is used to learn and reduce these errors
Remaining stochastic errors show modulations with a 24‐hr period
Effective angular momentum functions from atmosphere, oceans, and terrestrial water storage are obtained from European Centre for Medium‐Range Weather Forecasts atmospheric data and corresponding ...simulations with the Ocean Model for Circulation and Tides and the Land Surface and Discharge Model (LSDM). Mass exchanges among the subsystems are realized by means of freshwater fluxes, causing the total ocean mass to vary predominantly annually. Variations in total ocean mass affect the oceanic excitations of the annual wobble by almost 1 milliarc second (mas) for both prograde and retrograde components, whereas the motion term contributions of terrestrial water flow derived from LSDM are found to be 3 orders of magnitude smaller. Since differences to geodetic excitations are not substantially reduced and regional decompositions demonstrate the large spatial variability of contributions to seasonal polar motion excitation that compensate each other when integrated globally, it is concluded that the closure of the seasonal excitation budget is still inhibited by remaining model errors in all subsystems.
PDF
