Accurate estimate of ocean surface currents is both a challenging issue and a growing end‐users requirement. In this paper ocean currents are calculated at two levels (surface and 15 m depth) as the ...sum of the geostrophic and Ekman components. First, a new, global, 14° Mean Dynamic Topography, called the CNES‐CLS13 MDT, has been calculated and is now available for use by the oceanographic community. By exploiting information from surface drifters and Argo floats, the new MDT resolves spatial scales beyond the resolution permitted by the recent Gravity and Ocean Circulation Experiment (GOCE) geoid models (125 km). Associated mean geostrophic speeds in strong currents are increased by 200% on average compared to GOCE‐based mean currents. In addition, for the first time, a two‐level, monthly, empirical Ekman model that samples a spiral‐like behavior is estimated. We show that combining both pieces of information leads to improved ocean currents compared to other existing observed products.
Key Points
New global Mean Dynamic Topography from GOCE, altimetry, and in situ dataNew two‐level Ekman model from the joint analysis of Argo floats and SVP driftersNew ocean currents by combining geostrophy and Ekman at surface and 15m depth
We examined the first‐ever laser ranging interferometer (LRI) measurements of inter‐satellite tracking acquired by Gravity Recovery and Climate Experiment (GRACE) Follow‐On satellites. Through direct ...along‐orbit analysis of instantaneous inter‐satellite measurements, we demonstrate the higher sensitivity of LRI (than K‐band microwave ranging KBR) to anomalies associated with the Earth static gravity field at high spatial resolutions of 100–200 km. We found that LRI captures gravitational signals as small as 0.1 nm/s2 at 490 km altitude, improved by 1 order of magnitude from KBR. This allows LRI to uniquely detect un‐/mis‐modeled short‐wavelength gravitational perturbations. We employed all LRI data in 2019 to validate various state‐of‐the‐art global static gravity field models and show that LRI measurements, even over 1 month, can distinguish subtle differences among the models computed from ~15 years of GRACE KBR and ~4 years of Gravity Field and Steady‐State Ocean Circulation Explorer (GOCE) gradiometry data. Ultra‐precise LRI measurements will be yet another critical data set for future gravity field model development.
Key Points
We examined the first‐ever measurements of inter‐satellite laser ranging interferometer (LRI) from GRACE Follow‐On satellites
LRI measures static gravity perturbations as small as 100 km by more than 1 order of magnitude better than microwave‐based measurements
Laser data are accurate enough to detect subtle errors in global gravity field models from ~15 years of GRACE and ~4 years of GOCE data
Texto original: Yannis Stavrakakis, “Symbolic Authority, Fantasmatic Enjoyment and the Spirits of Capitalism: Genealogies of Mutual Engagement”, en Lacan and Organization, eds. Carl Cederström y ...Casper Hoedemaekers (Londres: MayFlyBooks, 2010), 59-100. Traducción a cargo de Liliana Betancourt. Candidata a Magister en Psicoanálisis y Cultura, Universidad Nacional de Colombia.
Reprocessed Gravity Field and Steady‐State Ocean Circulation Explorer (GOCE) gravity gradient data were combined with data from Laser Geodynamics Satellite (LAGEOS) 1/2 and Gravity Recovery and ...Climate Experiment (GRACE) to generate a satellite‐only gravity field model to degree 260 using the direct approach, named DIR‐R4. When compared to Earth Gravitational Model 2008 (EGM2008), it is more accurate at low to medium resolution thanks to GOCE and GRACE data. When compared to earlier releases of ESA GOCE models, it is more accurate at high degrees owing to the larger amount of data ingested. It is also slightly more accurate than ESA's fourth release of the time‐wise model (TIM‐R4), as demonstrated by GPS/leveling, orbit determination tests, and an oceanographic evaluation. According to the formal, probably too optimistic by a factor of 2–2.5, cumulated geoid (1.3 cm) and gravity anomaly (0.4 mGal) errors at 100 km resolution, the GOCE mission objectives have been reached.
Key Points
Satellite‐only gravity field model
LAGEOS, GRACE and GOCE data
Geostrophic ocean circulation
After more than 4.5 years in orbit, the Gravity field and steady‐state Ocean Circulation Explorer (GOCE) mission ended with the reentry of the satellite on 11 November 2013. This publication serves ...as a reference for the fifth gravity field model based on the time‐wise approach (EGM_TIM_RL05), a global model only determined from GOCE observations. Due to its independence of any other gravity data, a consistent and homogeneous set of spherical harmonic coefficients up to degree and order 280 (corresponding to spatial resolution of 71.5 km on ground) is provided including a full covariance matrix characterizing the uncertainties of the model. The associated covariance matrix realistically describes the model quality. It is the first model which is purely based on GOCE including all observations collected during the entire mission. The achieved mean global accuracy is 2.4 cm in terms of geoid heights and 0.7 mGal for gravity anomalies at a spatial resolution of 100 km.
Key Points
A new Earth's gravity field model from the entire GOCE mission is presentedGOCE data are converted to a user‐friendly product with quality descriptionThe processing and use of GOCE‐only data allow the usage in many applications
The International Centre for Global Earth Models (ICGEM, http://icgem.gfz-potsdam.de/, last access: 6 May 2019) hosted at the GFZ German Research Centre for Geosciences (GFZ) is one of the five ...services coordinated by the International Gravity Field Service (IGFS) of the International Association of Geodesy (IAG). The goal of the ICGEM service is to provide the scientific community with a state-of-the-art archive of static and temporal global gravity field models of the Earth, and develop and operate interactive calculation and visualization services of gravity field functionals on user-defined grids or at a list of particular points via its website. ICGEM offers the largest collection of global gravity field models, including those from the 1960s to the 1990s, as well as the most recent ones, which have been developed using data from dedicated satellite gravity missions, CHAMP, GRACE, GOCE, advanced processing methodologies, and additional data sources such as satellite altimetry and terrestrial gravity. The global gravity field models have been collected from different institutions at international level and after a validation process made publicly available in a standardized format with DOI numbers assigned through GFZ Data Services. The development and maintenance of such a unique platform is crucial for the scientific community in geodesy, geophysics, oceanography, and climate research. In this article, we present the development history and future plans of ICGEM and its current products and essential services. We present the ICGEM's data by means of Earth's static, temporal, and topographic gravity field models as well as the gravity field models of other celestial bodies together with examples produced by the ICGEM's calculation and 3-D visualization services and give an insight into how the ICGEM service can additionally contribute to the needs of research and society.
We use multi‐year observations of cross‐track winds (u) from the CHAllenging Minisatellite Payload (CHAMP) and the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) to calculate ...third‐order structure functions in the thermosphere as a function of horizontal separation (s). They are computed using the mean (〈δu3〉) and the median 〈δu3〉med $\left({\langle \delta {u}^{3}\rangle }_{\text{med}}\right)$ and implemented over non‐polar satellite paths in both hemispheres. On height averages, 〈δu3〉 is shown to scale with s2 for s ≃ 80–1,000 km, in agreement with equivalent estimates in the lower atmosphere from aircraft observations. Conversely, 〈δu3〉med ${\langle \delta {u}^{3}\rangle }_{\text{med}}$ follows an s3 power law for almost the whole s range, consistent with the two‐dimensional turbulence scaling law for a direct enstrophy cascade. These scaling laws appear independent of winds in distinct atmospheric regions. Furthermore, the functions are predominantly positive, indicating a preferential cyclonic motion for the wind.
Plain Language Summary
The dynamics of upper atmosphere winds differ significantly from those at lower altitudes, with larger magnitudes and increased sensitivity to solar events. Satellites, especially those in polar orbits, offer an effective means of studying these winds, particularly their East‐West component. To mitigate the chaotic nature of individual measurements influenced by various physical processes, it is common to compute wind averages. A particular way of doing this is by calculating the so‐called third‐order structure functions (SFs), a statistical quantity that provides information on the underlying turbulence processes. The third‐order SFs of satellites' zonal wind observations present two main characteristics. First, they are consistently positive, predicting a preferential cyclonic rotational motion. This is, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Second, and more importantly, the functions display the same type of dependence on the horizontal distance as third‐order SFs of winds in the lower atmosphere. This suggests that similar underlying large‐scale turbulence mechanisms may be at play.
Key Points
Third‐order structure functions of zonal winds in the thermosphere at mid‐ and low‐ to mid‐latitudes are calculated
Meso‐ and Synoptic‐scale structures share a preferential cyclonic motion in the thermosphere
Measured scaling laws of third‐order structure functions seem to be independent of the atmospheric region
The satellite‐only gravity field model GOCO01S is a combination solution based on 61 days of GOCE gravity gradient data, and 7 years of GRACE GPS and K‐band range rate data, resolved up to ...degree/order 224 of a harmonic series expansion. The combination was performed consistently by addition of full normal equations and stochastic modeling of GOCE and GRACE observations. The model has been validated against external global gravity models and regional GPS/leveling observations. While low to medium degrees are mainly determined by GRACE, significant contributions by the new measurement type of GOCE gradients can already be observed at degree 100. Beyond degree 150, GOCE becomes the dominant contributor. Correspondingly, with GOCO01S a global gravity field model with high performance for the complete spectral range up to degree/order 224 is now available. This new gravity model will be beneficial for many applications in geophysics, oceanography, and geodesy.
PDF
