The statistical probability of deep flow structures that fit Jupiter's asymmetric gravity

2020 ◽  
Author(s):  
Keren Duer ◽  
Eli Galanti ◽  
Yohai Kaspi
Keyword(s):  
Zonal Wind ◽  
Gravity Data ◽  
Flow Structures ◽  
Statistical Probability ◽  
Zonal Jets ◽  
Flow Profiles ◽  
Gravity Measurements ◽  
Meridional Profile ◽  
Wind Profiles ◽  
Level Profile

<div id="magicparlabel-56675" class="abstract"> <div class="abstract_item">Juno's measurements of Jupiter's North-South asymmetric gravity field allowed estimating the depth of the zonal jets trough the relation between the measured density anomaly and the flow field. While the deep zonal jets structure has many degrees of freedom, the gravity measurements are manifested only by four gravity harmonics, which implies that the problem is ill-posed. Hence, any suggested solution for Jupiter's deep jets that fit the gravity measurements is non-unique. Here, we perform a thorough statistical analysis of the deep flow structures' range that is bounded by physical considerations. We begin by examining the vertical range of the deep flow, where the meridional structure of the zonal wind is identical to the measured cloud-level profile. Then, we relax the constraint on the meridional profile and allow reasonable variations from the cloud-level profile along with the varying vertical decay. Finally, we examine random meridional profiles that are independent of Jupiter's measured cloud-level profile and explore the possibility that the interior wind structure, which influences the gravity measurements, is entirely different from the cloud-level flow. A sample population of vertical decay structures is used to compare the statistical likelihood of the various cases. We find that only a relatively narrow envelope of vertical solutions can fit the gravity data. Deep flow profiles constructed from perturbations to the cloud-level winds allow a more extensive range of solutions, yet when the patterns differ substantially from the cloud-level observed wind profile, the ability to match the gravity data reduces significantly. Moreover, only 1% of the tested random zonal wind profiles yield any solution that fits the gravity data. Overall, we find that while interior wind profiles that diverge considerably from those at the cloud-level are possible, they are statistically unlikely. In addition to the gravity measurements, Juno's microwave radiometer (MWR) measurements might reveal information about the wind's structure below the cloud level. Inspired by the MWR's nadir brightness temperature estimations, which are dominated by ammonia abundance, we show that depth-dependent flow profiles are still compatible with the gravity measurements if the variation at depth from the measured cloud-level meridional profile is not too substantial.</div> </div>

The Range of Jupiter's Flow Structures that Fit the Juno Asymmetric Gravity Measurements

2021 ◽  
Author(s):  
Keren Duer ◽  
Eli Galanti ◽  
Yohai Kaspi
Keyword(s):  
Gravity Data ◽  
Microwave Radiometer ◽  
Jet Streams ◽  
Zonal Jets ◽  
Flow Profiles ◽  
Gravity Measurements ◽  
Interior Flow ◽  
Dependent Flow ◽  
Meridional Profile ◽  
Wind Profiles

<p>The asymmetric gravity field measured by the Juno spacecraft has allowed the estimation of the depth of Jupiter's zonal jets, showing that the winds extend approximately 3,000 km beneath the cloud level. This estimate was based on an analysis using a combination of all measured odd gravity harmonics, <em>J</em><sub>3</sub>, <em>J</em><sub>5</sub>, <em>J</em><sub>7</sub>, and <em>J</em><sub>9</sub>, but the wind profile's dependence on each of them separately has yet to be investigated. Furthermore, these calculations assumed the meridional profile of the cloud‐level wind extends to depth. However, it is possible that the interior jet profile varies somewhat from that of the cloud level. Here we analyze in detail the possible meridional and vertical structure of Jupiter's deep jet streams that can match the gravity measurements. We find that each odd gravity harmonic constrains the flow at a different depth, with <em>J</em><sub>3</sub> the most dominant at depths below 3,000 km, <em>J</em><sub>5</sub> the most restrictive overall, whereas <em>J</em><sub>9</sub> does not add any constraint on the flow if the other odd harmonics are considered. Interior flow profiles constructed from perturbations to the cloud‐level winds allow a more extensive range of vertical wind profiles, yet when the meridional profiles differ substantially from the cloud level, the ability to match the gravity data significantly diminishes. Overall, we find that while interior wind profiles that do not resemble the cloud level are possible, they are statistically unlikely. Finally, inspired by the Juno microwave radiometer measurements, assuming the brightness temperature is dominated by the ammonia abundance, we find that depth‐dependent flow profiles are still compatible with the gravity measurements.</p>

The range of flow structures fitting Jupiter's asymmetric gravity field

2020 ◽  
Author(s):  
Keren Duer ◽  
Eli Galanti ◽  
Yohai Kaspi
Keyword(s):  
Brightness Temperature ◽  
Temperature Profile ◽  
Gravity Field ◽  
Zonal Wind ◽  
Gravity Data ◽  
Flow Profile ◽  
Jet Streams ◽  
Uncertainty Range ◽  
Meridional Profile ◽  
Wind Profiles

<div>Jupiter's North-South asymmetric gravity field, measured by the Juno spacecraft, allowed estimating the depth of the zonal jets trough the relation between the measured density anomaly and the flow. This analysis was based on a combination of all four measured odd gravity harmonics, so the direct effect of each of them on the flow profile has not been investigated. Moreover, past calculations assumed that the cloud-level zonal wind maintains its meridional structure with depth; However, the Juno microwave radiometer measurements imply that a vertically dependent meridional profile might be more suitable, due to the reasonable relation between the Nadir brightness temperature profile and the zonal wind. In this study, we analyze in detail the possible range of structures of Jupiter’s deep jet-streams, fitting each of the Juno's measured asymmetric gravity harmonics. Specifically, we examine the possible vertical structure of Jupiter’s deep jet streams, different meridional structures of the cloud-level zonal wind and depth-dependent meridional profile compatible with the Nadir temperature tendency. We find that each odd gravity harmonic constrains the flow at a different depth, with J3 being the most dominant at depths below 3000 km, where the electrical conductivity becomes significant. J5 is the most restrictive harmonic overall, and J9 does not constrain the flow at all if the other odd harmonics are within the measurement range. Deep flow profiles constructed from perturbations to the cloud-level winds allow a more extensive range of solutions, yet when the patterns differ substantially from the cloud-level observed wind profile, the ability to match the gravity data reduces significantly. Random zonal wind profiles, unconnected to the cloud-level profile allow almost no solutions for the gravity data, and only 1% of the tested wind profiles yield any solution. Overall, we find that while interior wind profiles that diverge considerably from those at the cloud-level are possible, they are statistically unlikely. Finally, we find that meridional smoothing of the wind with depth, according to the Juno MWR brightness temperature profile, still allows fitting the measured gravity signal within the uncertainty range.</div>

scholarly journals Forty-three years of absolute gravity observations of the Fennoscandian postglacial rebound in Finland

2021 ◽  
Vol 95 (2) ◽  
Author(s):  
Mirjam Bilker-Koivula ◽  
Jaakko Mäkinen ◽  
Hannu Ruotsalainen ◽  
Jyri Näränen ◽  
Timo Saari
Keyword(s):  
Gravity Data ◽  
Gravity Change ◽  
Global Navigation Satellite Systems ◽  
Absolute Gravity ◽  
Data Sets ◽  
Postglacial Rebound ◽  
Land Uplift ◽  
Satellite Systems ◽  
Gravity Measurements ◽  
Global Navigation Satellite

AbstractPostglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.

Estimating saturation and density changes caused by CO2 injection at Sleipner — Using time-lapse seismic amplitude-variation-with-offset and time-lapse gravity

2017 ◽  
Vol 5 (2) ◽  
pp. T243-T257 ◽  
Author(s):  
Martin Landrø ◽  
Mark Zumberge
Keyword(s):  
Gravity Data ◽  
Time Lapse ◽  
Co2 Injection ◽  
Injection Point ◽  
Amplitude Variation With Offset ◽  
Seismic Method ◽  
Seismic Amplitude ◽  
Gravity Measurements ◽  
Measured Time ◽  
Best Fit

We have developed a calibrated, simple time-lapse seismic method for estimating saturation changes from the [Formula: see text]-storage project at Sleipner offshore Norway. This seismic method works well to map changes when [Formula: see text] is migrating laterally away from the injection point. However, it is challenging to detect changes occurring below [Formula: see text] layers that have already been charged by some [Formula: see text]. Not only is this partly caused by the seismic shadow effects, but also by the fact that the velocity sensitivity for [Formula: see text] change in saturation from 0.3 to 1.0 is significantly less than saturation changes from zero to 0.3. To circumvent the seismic shadow zone problem, we combine the time-lapse seismic method with time-lapse gravity measurements. This is done by a simple forward modeling of gravity changes based on the seismically derived saturation changes, letting these saturation changes be scaled by an arbitrary constant and then by minimizing the least-squares error to obtain the best fit between the scaled saturation changes and the measured time-lapse gravity data. In this way, we are able to exploit the complementary properties of time-lapse seismic and gravity data.

scholarly journals Research Article. A new gravity laboratory in Ny-Ålesund, Svalbard

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
K. Breili ◽  
R. Hougen ◽  
D. I. Lysaker ◽  
O. C. D. Omang ◽  
B. Tangen
Keyword(s):  
Noise Level ◽  
Gravity Data ◽  
Ocean Tide ◽  
Gravity Gradients ◽  
Svalbard Archipelago ◽  
Ocean Tide Loading ◽  
Lower Elevation ◽  
Gravity Measurements ◽  
Space Geodetic Techniques ◽  
Under Construction

AbstractThe Norwegian Mapping Authority (NMA) has recently established a new gravity laboratory in Ny-Ålesund at Svalbard, Norway. The laboratory consists of three independent pillars and is part of the geodetic core station that is presently under construction at Brandal, approximately 1.5 km north of NMA’s old station. In anticipation of future use of the new gravity laboratory, we present benchmark gravity values, gravity gradients, and final coordinates of all new pillars. Test measurements indicate a higher noise level at Brandal compared to the old station. The increased noise level is attributed to higher sensitivity to wind.We have also investigated possible consequences of moving to Brandal when it comes to the gravitational signal of present-day ice mass changes and ocean tide loading. Plausible models representing ice mass changes at the Svalbard archipelago indicate that the gravitational signal at Brandal may differ from that at the old site with a size detectable with modern gravimeters. Users of gravity data from Ny-Ålesund should, therefore, be cautious if future observations from the new observatory are used to extend the existing gravity record. Due to its lower elevation, Brandal is significantly less sensitive to gravitational ocean tide loading. In the future, Brandal will be the prime site for gravimetry in Ny-Ålesund. This ensures gravity measurements collocated with space geodetic techniques like VLBI, SLR, and GNSS.

scholarly journals Comparison of the deep atmospheric dynamics of Jupiter and Saturn in light of the Juno and Cassini gravity measurements

2020 ◽  
Author(s):  
Yohai Kaspi ◽  
Eli Galanti ◽  
Adam Showman ◽  
David Stevenson ◽  
Tristan Guillot ◽  
...  
Keyword(s):  
Planetary Science ◽  
Gravity Inversion ◽  
Zonal Flows ◽  
Zonal Jets ◽  
Cassini Mission ◽  
Gravity Measurements ◽  
Order Of Magnitude ◽  
The Magnetic Field ◽  
Intrinsic Characteristic

<p>The nature and structure of the observed east-west flows on Jupiter and Saturn has been a long-standing mystery in planetary science. This mystery has been recently unraveled by the accurate gravity measurements provided by the Juno mission to Jupiter and the Grand Finale of the Cassini mission to Saturn. These two experiments, which coincidentally happened around the same time, allowed the determination of the overall vertical and meridional profiles of the zonal flows on both planets. In this talk, we discuss what has been learned about the zonal jets on the gas giants in light of the new data from these two experiments. The gravity measurements not only allow the depth of the jets to be constrained, yielding the inference that the jets extend to roughly 3000 and 9000 km below the observed clouds on Jupiter and Saturn, respectively, but also provide insights into the mechanisms controlling these zonal flows. Specifically, for both planets this depth corresponds to the depth where electrical conductivity is within an order of magnitude of 1 S/m, implying that the magnetic field likely plays a key role in damping the zonal flows. An intrinsic characteristic of any gravity inversion, as discussed here, is that the solutions might not be unique. We analyze the robustness of the solutions and present several independent lines of evidence supporting the inference that the jets reach these depths.</p>

scholarly journals Accuracy Analysis of Gravity Field Changes from Grace RL06 and RL05 Data Compared to in Situ Gravimetric Measurements in the Context of Choosing Optimal Filtering Type

2020 ◽  
Vol 55 (3) ◽  
pp. 100-117
Author(s):  
Viktor Szabó ◽  
Dorota Marjańska
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Gravity Data ◽  
The Other ◽  
Subsurface Water ◽  
Satellite Gravity ◽  
Absolute Gravimetry ◽  
The Earth ◽  
Gravity Measurements ◽  
Gravity Recovery

AbstractGlobal satellite gravity measurements provide unique information regarding gravity field distribution and its variability on the Earth. The main cause of gravity changes is the mass transportation within the Earth, appearing as, e.g. dynamic fluctuations in hydrology, glaciology, oceanology, meteorology and the lithosphere. This phenomenon has become more comprehensible thanks to the dedicated gravimetric missions such as Gravity Recovery and Climate Experiment (GRACE), Challenging Minisatellite Payload (CHAMP) and Gravity Field and Steady-State Ocean Circulation Explorer (GOCE). From among these missions, GRACE seems to be the most dominating source of gravity data, sharing a unique set of observations from over 15 years. The results of this experiment are often of interest to geodesists and geophysicists due to its high compatibility with the other methods of gravity measurements, especially absolute gravimetry. Direct validation of gravity field solutions is crucial as it can provide conclusions concerning forecasts of subsurface water changes. The aim of this work is to present the issue of selection of filtration parameters for monthly gravity field solutions in RL06 and RL05 releases and then to compare them to a time series of absolute gravimetric data conducted in quasi-monthly measurements in Astro-Geodetic Observatory in Józefosław (Poland). The other purpose of this study is to estimate the accuracy of GRACE temporal solutions in comparison with absolute terrestrial gravimetry data and making an attempt to indicate the significance of differences between solutions using various types of filtration (DDK, Gaussian) from selected research centres.

scholarly journals Improvement of density models of geological structures by fusion of gravity data and cosmic muon radiographies

2015 ◽  
Vol 5 (1) ◽  
pp. 83-116 ◽  
Author(s):  
K. Jourde ◽  
D. Gibert ◽  
J. Marteau
Keyword(s):  
Gravity Data ◽  
Field Measurements ◽  
Small Scale ◽  
Density Structure ◽  
Spatial Filters ◽  
Muon Tomography ◽  
Mathematical Expressions ◽  
Integration Formulas ◽  
Muon Radiography ◽  
Gravity Measurements

Abstract. This paper examines how the resolution of small-scale geological density models is improved through the fusion of information provided by gravity measurements and density muon radiographies. Muon radiography aims at determining the density of geological bodies by measuring their screening effect on the natural flux of cosmic muons. Muon radiography essentially works like medical X-ray scan and integrates density information along elongated narrow conical volumes. Gravity measurements are linked to density by a 3-D integration encompassing the whole studied domain. We establish the mathematical expressions of these integration formulas – called acquisition kernels – and derive the resolving kernels that are spatial filters relating the true unknown density structure to the density distribution actually recovered from the available data. The resolving kernels approach allows to quantitatively describe the improvement of the resolution of the density models achieved by merging gravity data and muon radiographies. The method developed in this paper may be used to optimally design the geometry of the field measurements to perform in order to obtain a given spatial resolution pattern of the density model to construct. The resolving kernels derived in the joined muon/gravimetry case indicate that gravity data are almost useless to constrain the density structure in regions sampled by more than two muon tomography acquisitions. Interestingly the resolution in deeper regions not sampled by muon tomography is significantly improved by joining the two techniques. The method is illustrated with examples for La Soufrière of Guadeloupe volcano.

Airborne gravity measurements over mountainous areas by using a LaCoste & Romberg air‐sea gravity meter

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 807-816 ◽  
Author(s):  
Jérôme Verdun ◽  
Roger Bayer ◽  
Emile E. Klingelé ◽  
Marc Cocard ◽  
Alain Geiger ◽  
...  
Keyword(s):  
Data Reduction ◽  
Classical Method ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Mountainous Area ◽  
Vertical Acceleration ◽  
Mountainous Areas ◽  
Free Air ◽  
Gravity Measurements ◽  
Free Air Anomaly

This paper introduces a new approach to airborne gravity data reduction well‐suited for surveys flown at high altitude with respect to gravity sources (mountainous areas). Classical technique is reviewed and illustrated in taking advantage of airborne gravity measurements performed over the western French Alps by using a LaCoste & Romberg air‐sea gravity meter. The part of nongravitational vertical accelerations correlated with gravity meter measurements are investigated with the help of coherence spectra. Beam velocity has proved to be strikingly correlated with vertical acceleration of the aircraft. This finding is theoretically argued by solving the equation of the gravimetric system (gravity meter and stabilized platform). The transfer function of the system is derived, and a new formulation of airborne gravity data reduction, which takes care of the sensitive response of spring tension to observable gravity field wavelengths, is given. The resulting gravity signal exhibits a residual noise caused by electronic devices and short‐wavelength Eötvös effects. The use of dedicated exponential filters gives us a way to eliminate these high‐frequency effects. Examples of the resulting free‐air anomaly at 5100‐m altitude along one particular profile are given and compared with free‐air anomaly deduced from the classical method for processing airborne gravity data, and with upward‐continued ground gravity data. The well‐known trade‐off between accuracy and resolution is discussed in the context of a mountainous area.

scholarly journals Grid preparation for magnetic and gravity data using fractal fields

2012 ◽  
Vol 19 (2) ◽  
pp. 291-296 ◽  
Author(s):  
M. Pilkington ◽  
P. Keating
Keyword(s):  
Potential Field ◽  
Fourier Transforms ◽  
Gravity Data ◽  
Fractal Model ◽  
Data Sets ◽  
Spectral Character ◽  
Aeromagnetic Survey ◽  
Fractal Method ◽  
Gravity Measurements ◽  
Interpretive Method

Abstract. Most interpretive methods for potential field (magnetic and gravity) measurements require data in a gridded format. Many are also based on using fast Fourier transforms to improve their computational efficiency. As such, grids need to be full (no undefined values), rectangular and periodic. Since potential field surveys do not usually provide data sets in this form, grids must first be prepared to satisfy these three requirements before any interpretive method can be used. Here, we use a method for grid preparation based on a fractal model for predicting field values where necessary. Using fractal field values ensures that the statistical and spectral character of the measured data is preserved, and that unwanted discontinuities at survey boundaries are minimized. The fractal method compares well with standard extrapolation methods using gridding and maximum entropy filtering. The procedure is demonstrated on a portion of a recently flown aeromagnetic survey over a volcanic terrane in southern British Columbia, Canada.

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