Futoshi Takahashi's research while affiliated with Kyushu University and other places
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Publications (105)
Short-period magnetic enhancements were detected by the MAP-LMAG magnetometer onboard Kaguya orbiting the moon in solar wind at an altitude of 100 km. The duration was typically 10 seconds, which corresponds to 0.5 degrees in latitude along the Kaguya orbit and a scale size of 15 km. The magnitude of the magnetic field was enhanced up to 1.5 to 3.6...
Wave–particle interactions are fundamental processes in space plasma, and some plasma waves, including electrostatic solitary waves (ESWs), are recognised as broadband noises (BBNs) in the electric field spectral data. Spacecraft observations in recent decades have detected BBNs around the Moon, but the generation mechanism of the BBNs is not fully...
The solar wind particles reflected by the lunar magnetic field are the major energy source of electromagnetic wave activities, such as the 100 s magnetohydrodynamic waves and the 1 Hz whistler‐mode waves generated by protons and the non‐monochromatic whistler‐mode waves generated by mirror‐reflected electrons. Kaguya found a new type of whistler‐mo...
The Moon drives observable perturbations in the upstream solar wind in a similar manner to the terrestrial foreshock. Recent observations suggested that lunar dayside electrostatic waves can arise from two different driving mechanisms, both involving reflected particles from lunar crustal magnetic fields. However, their association with the global...
A structure of polarization of magnetic field variation in the frequency range from 0.01 to 0.3 Hz was found by Kaguya in the lunar wake. In a dawnward‐directed magnetic field, the polarization was left‐handed in the southern hemisphere and right‐handed in the northern hemisphere of the lunar wake. The sense of rotation was consistent with vortices...
The fluxgate magnetometer MGF on board the Mio spacecraft of the BepiColombo mission is introduced with its science targets, instrument design, calibration report, and scientific expectations. The MGF instrument consists of two tri-axial fluxgate magnetometers. Both sensors are mounted on a 4.8-m long mast to measure the magnetic field around Mercu...
We have submitted a secular variation (SV) candidate model for the thirteenth generation of International Geomag- netic Reference Field model (IGRF-13) using a data assimilation scheme and a magnetohydrodynamic (MHD) dynamo simulation code. This is the first contribution to the IGRF community from research groups in Japan. A geomagnetic field model...
Carbon is a volatile element that has a considerable influence on the formation and evolution of planetary bodies, although it was previously believed to be depleted in the Moon. We present observations by the lunar orbiter KAGUYA of carbon ions emitted from the Moon. These emissions were distributed over almost the total lunar surface, but amounts...
Manuscript accepted for publication in the IGRF-13 Special Issue in Earth, Planets and Space.
The Moon interacts with the incident solar wind plasma in various ways, and most of these interactions are accompanied by variations of the interplanetary magnetic field (IMF) around the Moon. Here we first report decreases of the IMF strength observed at 100 km altitude on the lunar dayside and over the polar region, comparing upstream solar wind...
The Earth's ocean tide has affected the Moon's orbital evolution. Recent studies suggest that the ocean would cover almost the entire surface of the early Earth, possibly with larger seawater volume than the present day. It is also suggested that the tidal energy in the present deep ocean is mostly dissipated by internal gravity waves comprising th...
The discovery of Mercury’s unusually axisymmetric, anomalously axially offset dipolar magnetic field reveals a new regime of planetary magnetic fields. The cause of the offset dipole remains to be resolved, although some exotic models have been proposed. Deciphering why Mercury has such an anomalous field is crucial not only for understanding the i...
Narrowband electromagnetic ion cyclotron waves first discovered by the Apollo 15 and 16 Lunar Surface Magnetometers were surveyed in the magnetic field data obtained by the Kaguya satellite at an altitude of ∼ 100 km above the Moon in the tail lobe and plasmasheet boundary layer of the Earth's magnetosphere. The frequencies of the waves were typica...
There forms a tenuous region called the wake behind the Moon in the solar wind, and plasma entry/refilling into the wake is a fundamental problem of the lunar plasma science. High-energy ions and electrons in the foreshock of the Earth’s magnetosphere were detected at the lunar surface in the Apollo era, but their effects on the lunar night-side en...
Numerical simulations of the geodynamo have successfully represented many observable characteristics of the geomagnetic field, yielding insight into the fundamental processes that generate magnetic fields in the Earth's core. Because of limited spatial resolution, however, the diffusivities in numerical dynamo models are much larger than those in t...
Magnetic fluctuations in the extremely low-frequency (ELF) range from 0.1 to 10 Hz were found by the Lunar Magnetometer (LMAG) of the magnetic field and plasma experiment (MAP) on board the spacecraft Kaguya in the deepest wake behind the moon, where the magnetic field is usually quiet. The fluctuations were compressional and non-monochromatic, sho...
Harmonic spectral features of electromagnetic waves in the frequencies of several Hz around the Moon have been identified by Kaguya. The waves have steepened waveforms peculiarly in the compressional component. The fundamental waves have almost the same properties as narrowband whistler-mode waves with the frequencies near 1 Hz, which have been obs...
We have provided preliminary global maps of three components of the lunar magnetic anomaly on the surface applying the surface vector mapping (SVM) method. The data used in the present study consist of about 5 million observations of the lunar magnetic field at 10–45 km altitudes by Kaguya and Lunar Prospector. The lunar magnetic anomalies were map...
Plasma signature around crustal magnetic fields is one of the most important topics of the lunar plasma sciences. Although recent spacecraft measurements are revealing solar–wind interaction with the lunar crustal fields on the dayside, plasma signatures around crustal fields on the night side have not been fully studied yet. Here we show evidence...
In the Earth's magnetotail, Japanese Moon orbiter Kaguya repeatedly encountered the plasmoid or plasma sheet. The encounters were characterized by the low energy ion signatures including lobe cold ions, cold ion acceleration in the plasma sheet-lobe boundaries, and hot plasma sheet ions or fast flowing ions associated with plasmoids. Different from...
I quantitatively test a method of toroidal field imaging at the core-mantle boundary (CMB) using a synthetic magnetic field and core surface flow data from a 3-D self-consistent numerical dynamo model with a thin electrically conducting layer overlying the CMB, like the D ″ layer. With complete knowledge of the core flow, the imaged toroidal field...
The near-Moon space environment is characterised by formation of a plasma cavity region on the night side along the solar wind flow, which is called the lunar wake. Because the Moon obstructs the solar wind flow on the dayside, the wake region is much more tenuous than the ambient (unperturbed) solar wind region. Before the SELENE (Kaguya) measurem...
Palaeomagnetic measurements suggest that an active core dynamo operated on the Moon from 4.2 to 3.56 billion years ago(1-3). Since the Apollo era, many magnetic anomalies have been observed on the Moon. The magnetization of the lunar crust in some of these regions could preserve the signature of an early dipolar magnetic field generated by a core d...
We investigate Kaguya observation of ion acceleration around a lunar crustal magnetic anomaly located in the South Pole-Aitken basin at an altitude of 100 km. The accelerated ions in the 230 eV to 1.5 keV energy range were identified by a characteristic dispersion signature in the energy-time spectrogram that appeared repeatedly upon Kaguya's appro...
Narrowband whistler-mode waves with frequencies near 1 Hz have been observed near the Moon. We reveal that the narrowband spectra, the frequency concentration near 1 Hz, and the relations between the wave vector, magnetic field vector, and sunward directions can be explained by a condition in which the group velocity vector is almost cancelled by t...
We present latitude and longitude distributions of Na+ and K+ fluxes from the Moon derived from Kaguya low-energy ion data. Although the latitude distribution agrees with previous ground-based telescope observations, dawn-dusk asymmetry has been determined in the longitude distribution. Our model of the lunar surface abundance and yield of Na and K...
We have developed a new method for regional mapping of the lunar magnetic anomalies as the vector field at the surface using the satellite observation, that is the surface vector mapping (SVM). The SVM is based on the inverse boundary value problem with a spherical boundary surface. There are two main procedures for reducing effects of bias and noi...
Our recent observations around the Moon revealed that so-called type-II (T2) entry of the solar wind protons into the near-Moon wake occurs when the IMF is dominated by the non-radial components (i.e. BY and/or BZ). Under this condition a part of the solar wind protons scattered/reflected at the lunar dayside surface subsequently enters the central...
The origins of the lunar crustal magnetic fields remain unclear although dozens of magnetic field measurements have been conducted on and above the lunar surface. A major obstacle to resolving this problem is the extreme difficulty of determining a surface distribution of small-scale magnetization. We present a new technique to map small-scale magn...
We have attempted to constrain the lunar core size from electrical conductivity sounding by using magnetic field data from the Kaguya (KG) and Lunar Prospector (LP) satellites. As suggested by previous studies, the signature of induction in the core can sometimes be detected by the satellites as an internal dipole field when the Moon enters from th...
The convection in the Earth’s outer core is driven by thermal and compositional buoyancy. Here we examine the effects of the co-existence of these two buoyancy sources on the core dynamics and morphology of the geomagnetic field using numerical dynamo models with double diffusive convection at the thermal Prandtl number, PrTPrT = 0.1 and compositio...
We study an interaction between the solar wind and crustal magnetic fields on the lunar surface using SELENE (Kaguya) data. It has been known that magnetic enhancements are at times detected near the limb external to the lunar wake, which is thus called lunar external magnetic enhancement (LEME), as a result of direct interaction between the solar...
Broadband whistler-mode waves in the frequency range from 0.1 to 10 Hz are detected near the Moon by the Lunar Magnetometer (LMAG) on board Kaguya. The generation process and statistical properties of the waves have not been understood yet. We analyze the distributions of their occurrence and reveal that most of the waves are generated by the solar...
Although ions and electrons are usually expected to have gyrotropic
(symmetric relative to the magnetic field line) velocity distribution
functions (VDFs) in the plasma rest frame, they can form non-gyrotropic
VDFs related to shocks, boundaries, or waves. Actually, non-gyrotropic
ions have been widely observed associated with the Earth's bow shock,...
We present an improved solution method for modeling thermally driven convection and dynamo in a rotating spherical shell. In this method, we introduce a high-order three-point combined compact difference scheme (CCDS) on non-uniform grid points in radius, while spherical harmonic expansion is conventionally performed in the angular direction. The g...
Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell are investigated using a numerical dynamo model with an Ekman number of . A strong dipolar solution with a magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small vis...
Large amplitude, monochromatic ultra low frequency (ULF) waves were detected by MAP/LMAG magnetometer onboard Kaguya during the period from 1 January 2008 to 30 November 2008 on its orbit 100 km above the lunar surface. The dominant frequency was 8.3 × 10−3 – 1.0 × 10−2 Hz, corresponding to the periods of 120 s – 100 s. The amplitude was as large a...
We study an interaction between the solar wind (SW) and the magnetic
anomalies on the lunar surface using SELENE (Kaguya) data. It has been
known that magnetic enhancements are at times detected near the limb
external to the lunar wake, which is thus called lunar external magnetic
enhancement (LEME), as a result of direct interaction between the SW...
At ∼25 km altitude over magnetic anomalies on the Moon, the deceleration of the solar wind ions, acceleration of the solar wind electrons parallel to the magnetic field, and heating of the ions reflected by magnetic anomalies were simultaneously observed by MAP-PACE on Kaguya. Deceleration of the solar wind ions was observed for two major solar win...
The electrical conductivity structure of the moon can be determined by
electromagnetic responses. From the simultaneous Apollo 12 and Explorer
35 magnetometer observations, the electrical conductivity structure of
the lunar interior has been estimated (e.g. Sonett et al. 1972,
Wiskerchen and Sonett 1977, Hood et al.1982). However, it so far
contain...
We study interaction between the solar wind (SW) flow and lunar magnetic
anomalies using SELENE (Kaguya) data. Our recent study showed that
incident SW protons are decelerated at low altitude (say, ˜25 km)
above strong magnetic anomalies, and that SW protons are less or not
affected by the magnetic anomalies at higher altitude (˜100 km).
Here we re...
The study on the lunar magnetic anomalies gives key information about
the evolution of the lunar interior, in particular, a possible dynamo of
the early Moon. There are two main problems of the origin of the lunar
magnetic anomalies, the ambient field and the magnetization acquisition
process. Based on the Apollo and Lunar Prospector observations,...
The near-Moon space environment is characterized by formation of a plasma cavity region on the night side along the solar wind (SW) flow, which is called the lunar wake. Because the Moon obstructs the SW plasma flow, the wake region is much more tenuous than the ambient SW region. The plasma environment of the lunar wake has been considered as foll...
The Moon has no global intrinsic magnetic field and thick atmosphere. These properties of the Moon significantly affect the
interaction between the solar wind and the Moon. Recent in-situ measurements of low energy ions around the Moon by Kaguya
(SELENE) have revealed dynamic aspect of the lunar plasma environment. Besides the solar wind, there exi...
Observations are presented of monochromatic whistler waves near the Moon
detected by the Lunar Magnetometer (LMAG) on board Kaguya. The waves were
observed as narrowband magnetic fluctuations with frequencies close to 1 Hz,
and were mostly left-hand polarized in the spacecraft frame. We performed a
statistical analysis of the waves to identify the...
Because the solar wind (SW) flow is usually super-sonic, a fast-mode bow shock (BS) is formed in front of the Earth's magnetosphere, and the Moon crosses the BS at both dusk and dawn flanks. On the other hand, behind of the Moon along the SW flow forms a tenuous region called lunar wake, where the flow can be sub-Alfvénic (and thus sub-sonic) becau...
Non-monochromatic fluctuations of the magnetic field over the frequency range of 0.03–10 Hz were detected by Kaguya at an altitude of 100 km above the lunar surface. The fluctuations were almost always observed on the solar side of the moon, irrespective of the local lunar crustal field. They were also detected just nightside of the terminator (SZA...
Along its orbital motion around the Earth, the Moon crosses the bow shock (BS) at the dusk and dawn flanks. Meanwhile, behind of the Moon along the solar wind (SW) flow forms a tenuous region called lunar wake, because the SW plasma is obstructed by the Moon. Here we report, with simultaneous observations by Chang'E-1 and SELENE, that the Earth's B...
We have reported the correlation between the high albedo marking (HAM) on the moon surface and the strength of horizontal component (Bh) of the near surface lunar magnetic field, at 2009 AGU Fall meeting, using the Lunar Prospector magnetometer data (LP-MAG). The correlation is further examined using the lowest altitude data at the latest orbits of...
Mapping of the lunar magnetic anomaly gives a crucial constraint on the crustal magnetization structure of the Moon. High spatial resolution of the magnetic anomaly map requires low altitude mapping. We have developed a new method for mapping three components of the lunar magnetic anomaly field on the lunar surface using magnetic field observations...
We present observations of electrostatic solitary waves (ESWs) near the Moon by SELENE (KAGUYA) in the solar wind and in the lunar wake. SELENE is a lunar orbiter with an altitude of 100 km and measured wave electric field, background magnetic field, and fluxes of ions and electrons, etc. ESWs are categorized into three types depending on different...
Analysis of the data obtained by SELENE (Kaguya) revealed a partial loss in the electron velocity distribution function due to the “gyro-loss effect”, namely gyrating electrons being absorbed by the lunar surface. The Moon enters the Earth's magnetosphere for a few days around full moon, where plasma conditions are significantly different from thos...
The magnetic field around the Moon has been successfully observed at a nominal altitude of ∼100 km by the lunar magnetometer (LMAG) on the SELENE (Kaguya) spacecraft in a polar orbit since October 29, 2007. The LMAG mission has three main objectives: (1) mapping the magnetic anomaly of the Moon, (2) measuring the electromagnetic and plasma environm...
We study effect of the solar wind (SW) proton entry deep into the
near-Moon wake that was recently discovered by the SELENE mission.
Because previous lunar-wake models are based on electron dominance, no
effect of SW proton entry has been taken into account. We show that the
type-II entry of SW protons forms proton-governed region (PGR) to
drastica...
To achieve the scientific objectives related to the lunar magnetic field measurements in a polar orbit at an altitude of 100km,
strict electromagnetic compatibility (EMC) requirements were applied to all components and subsystems of the SELENE (Kaguya)
spacecraft. The magnetic cleanliness program was defined as one of the EMC control procedures, an...
MAP-PACE (MAgnetic field and Plasma experiment—Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed
its ∼1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum
Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2...
Recent lunar observations have renewed the understanding of the interaction between the solar wind and the moon. In the classical view, the non-conducting surface of the moon was thought to absorb all the incident solar wind particles, creating the lunar wake downstream of the moon, since the moon does not have the global magnetic field like the Ea...
A theoretical model suggests a short-lived lunar dynamo driven by a mantle overturn forming crustal thickness dichotomy, while the lunar paleomagnetic data and crustal magnetic fields suggest both of presence and absence of a global magnetic field of the Moon ˜4 billion years (Gyr) ago. Here we carry out numerical simulations of a possible lunar dy...
The correlation between high albedo markings (HAM) on the surface of the moon and strong magnetic anomalies has been claimed since the early time of the lunar magnetic field study (Hood and Schubert, 1980). Hood et al. (1989) mapped the smoothed magnetic field over the Reiner Gamma region using Lunar Prospector magnetometer (LP-MAG) data, and showe...
The magnetometer on board Kaguya (Kaguya-LMAG) has been almost continuously observed the magnetic field at about 100km altitude since October 29, 2007. The magnetic field observations are beautiful because of the very low solar activity, the crustal field is well observed at 100km altitude from the record in the lunar wake and the tail-lobe environ...
We study solar wind (SW) intrusion into the near-Moon wake using plasma data obtained by the SELENE (KAGUYA) spacecraft. It has been known that SW protons flowing around the Moon access the central region of the distant lunar wake, while SW intrusion deep into the near-Moon wake has never been expected. Here we report two mechanisms (which we call...
The magnetic field around the Moon has been successfully observed at
nominal and lower altitudes by the lunar magnetometer (LMAG) on the
SELENE (KAGUYA) spacecraft in a polar orbit from October 29, 2007 to
June 10, 2009. Since the solar activity has been very low during the
observation, relatively weak anomalies can be observed even at a nominal
al...
In contrast to many ground-based optical observations of the thin lunar alkali exosphere, in situ observations of the exospheric ions by satellite-borne plasma instruments have been quite rare. MAP-PACE-IMA onboard Japanese lunar orbiter SELENE (KAGUYA) succeeded in detecting Moon originating ions at 100 km altitude. Here we make the first report o...
The high-sensitivity fluxgate Lunar MAGnetometer (LMAG) is mounted on SELENE (KAGUYA) to investigate the near-surface electromagnetic environment and the evolution of the Moon through magnetic field observation. To avoid possible electromagnetic interferences, a triaxial fluxgate sensor (MGF-S) is installed at the far end of a 12-m-long mast. It is...
Paleointensity of the Cretaceous normal superchron (CNS) has been studied using the middle Cretaceous Iritono granite of the Abukuma massif in northeast Japan. Our previous study [Wakabayashi, K., Tsunakawa, H., Mochizuki, N., Yamamoto, Y., Takigami, Y., 2006. Paleomagnetism of the middle Cretaceous Iritono granite in the Abukuma region, northeast...
We study solar wind (SW) entry deep into the near-Moon wake using SELENE (KAGUYA) data. It has been known that SW protons flowing around the Moon access the central region of the distant lunar wake, while their intrusion deep into the near-Moon wake has never been expected. We show that SW protons sneak into the deepest lunar wake (anti-subsolar re...
1] We study solar wind (SW) intrusion into the near-Moon wake using SELENE (KAGUYA) data. It has been known that SW protons are gradually accelerated toward the wake center along magnetic field in the distant lunar wake, while SW intrusion into the near-Moon wake has never been measured. We show that the SW protons come into the lunar wake at $100...
The Moon has no global intrinsic magnetic field and only has a very thin atmosphere. Ion measurements made from lunar orbit provide us with information regarding interactions between the solar wind and planetary surface, the surface composition through secondary ion mass spectrometry and the source and loss mechanisms of planetary tenuous atmospher...
The Moon maintain thin atmospheres. The lunar atmosphere is called
surface-bounded exosphere because it is thin enough to be regarded as an
exosphere and it bounds on the solid surface differently from the
terrestrial atmosphere-bounded exosphere. Although there have been only
limited ion measurements by lunar orbiters, ground-based optical
observa...
Erratm of a 2001 article DOI of the Original article: 10.1016/S0031-9201(01)00275-8
The Japanese Lunar Mission "Kaguya" carried out its first magnetic field and plasma measurements in the Earth's magnetotail on 22 December 2007. Fortuitously, three well-defined multiple onset substoms took place. Kaguya was located in the premidnight magnetotail at radial distances of 56 RE and observed plasmoids and/or traveling compression...
Magnetic field And Plasma experiment - Plasma energy Angle and Composition Experiment (MAP-PACE) on KAGUYA (SELENE) completed its ˜1.5-year observation of the low energy charged particles around the Moon. SELENE was successfully launched on 14 September 2007 by H2A launch vehicle from Tanegashima Space Center in Japan. SELENE was inserted into a ci...
1] Interaction between the solar wind and objects in the solar system varies largely according to the settings, such as the existence of a global intrinsic magnetic field and/or thick atmosphere. The Moon's case is characterized by the absence of both of them. Low energy ion measurements on the lunar orbit is realized more than 30 years after the A...
The magnetic field around the Moon has been successfully observed at a nominal altitude of 100 km by the lunar magnetometer (MAP-LMAG) on the SELENE (KAGUYA) spacecraft in a polar orbit since October 29, 2007. Here we report the initial global mapping of the lunar magnetic anomaly based on the observations during November 2007 to June 2008. Since t...
The moon spends more than 80 percent of its life staying in the solar wind (SW), where a quasi-vacuum region called the lunar wake is formed on the night side. The SW electrons with higher energy can come to the lunar night-side surface, while it has been thought that the SW ions are unlikely to approach the low altitude region on the night side be...
In the 2007 AGU fall meeting, we reported an objective scheme for estimating the spatial (3-d) distribution of the lunar crustal magnetic field from the satellite magnetometer data, and applied it to the Reiner Gamma magnetic anomaly on the nearside of the moon. Here, we provide the global vector map of the lunar crustal magnetic field using this s...
Low energy charged particles around the Moon were observed by Moon
orbiting satellites and plasma instrumentation placed on the lunar
surface in 1960s and 1970s. Though there were some satellites that
explored the Moon afterwards, most of them were dedicated to the global
mapping of the lunar surface. There has been almost no new information
about...
We have undertaken a numerical study of convection-driven MHD dynamos in a rapidly rotating spherical shell with the Ekman number, E, down to 2×10−6 and the magnetic Prandtl number, Pm, down to 0.2. We focus on the characteristic scales of the flow and the magnetic field. Smaller-scale convection vortices responsible for generating the magnetic fie...
We have conducted a study of numerical dynamos in a rapidly rotating spherical shell with prescribed non-uniform heat-flux patterns at the outer boundary to examine effects of thermal structure at the core–mantle boundary (CMB) on the geodynamo, especially on the magnetic field strength. Large heat-flux heterogeneity with equatorial symmetry enhanc...
Ground calibration experiments of the SELENE high sensitivity fluxgate Lunar Magnetometer (LMAG) have been performed in order to determine the alignment, sensitivity, and offset of the sensors (MGF-S). It is checked out that the sensors are orthogonal to each other within 0.4 degrees, and the linearity of the ambient magnetic field and the output f...
Mariner 10 measurements proved the existence of a large-scale internal magnetic field on Mercury. The observed field amplitude,
however, is too weak to be compatible with typical convective planetary dynamos. The Lorentz force based on an extrapolation
of Mariner 10 data to the dynamo region is 10−4 times smaller than the Coriolis force. This is at...
Mariner 10 measurements proved the existence of a large-scale internal
magnetic field on Mercury. The observed field amplitude, however, is too
weak to be compatible with typical convective planetary dynamos. The
Lorentz force based on an extrapolation of Mariner 10 data to the dynamo
region is 10-4 times smaller than the Coriolis force. This is
at...
Earth's core surface flow models have been estimated from geomagnetic
field models to understand a realistic geodynamo mechanism, to
investigate the thermal structure at the core surface, and to constrain
the effect of core-mantle boundary (CMB) on the fluid flow. In most of
core surface flow models, magnetic lines of force are considered to move
a...
Magnetic polarity transitions in a Takahashi-Matsushima-Honkura dynamo model are analyzed. Distinctive differences in behavior of the axisymmetric poloidal magnetic field are found among a polarity reversal and excursions, including short polarity events. At the beginning of magnetic polarity transitions, the magnetic field with the reversed polari...
Dynamo action possibly working in the fluid core of Mercury is examined using numerical models in a thin spherical shell. Dipolar (DP) dynamos are obtained in the regime of columnar flows outside the tangent cylinder (TC), whereas non-dipolar (NDP) dynamos dominated by the multipole components are found in the regime of flows both inside and outsid...
It is of importance to estimate fluid motion in the Earth's outer core to understand a realistic geodynamo mechanism. When the advective time scale is much shorter than the magnetic diffusion time scale, the diffusion term in the induction equation can be neglected for such a short time scale (Roberts and Scott, 1965). Then magnetic lines of force...
It is generally believed that the geomagnetic field is generated by convective motion of an electrically conducting fluid in the Earth's outer core, known as the geodynamo. However, it is still unclear whether numerical models represent the dynamics in the Earth's core, properly, since nondimensional parameters in the present numerical models of th...
High-resolution, low-viscosity geodynamo simulations have been carried out on the Earth Simulator, one of the fastest supercomputers, in a dynamic regime similar to that of Earth's core, that is, in a quasi-Taylor state. Our dynamo models exhibit features of the geodynamo not only in spatial and temporal characteristics but also in dynamics. Polari...
We investigate convection-driven dynamos in a rotating spherical shell with the Rayleigh number Ra up to about 53 times the critical value Rac, emphasizing Rayleigh number dependence of the thermal convection and the magnetic field generated by dynamo action. The Rayleigh numbers used in calculations are chosen so as to be in a range which allows u...
A number of dynamo simulations were performed during 2005 based on a Spectral Transform Method (STM). In one series of geodynamo simulations, the Ekman (Ek) and the Rayleigh (Ra) number dependences of the dynamo action were examined in detail. The change of the pattern of the fluid motion was observed as a function of Ra at Ek = 4 · 10-5.. The dyna...
We have carried out 3D numerical simulations of MHD dynamo in a rotating spherical shell to investigate behavior of the convection structure and the generated magnetic field. Here, we focus on Rayleigh number (Ra) dependence of numerical dynamos to make extrapolation to the geodynamo regime, and thus, performed parameter survey varying Ra up to abo...
We have been performing numerical simulations of MHD dynamos. In this paper, we present the results of our parameter survey for this problem. We consider a spherical shell rotating about its rotation axis (z-axis) and it is filled with electrically conducting Boussinesq fluid. The solid inner core has the same electrical conductivity as that of the...
In order to investigate the resistivity structure beneath the northern and the southern branches of the western part of the
North Anatolian Fault Zone (NAFZ), which has been known as a seismic gap area, we started wideband magnetotelluric (MT) measurements
on 27 July 1999, along a north-south profile crossing the northern branch near İzmit and the...
Citations
... Unlike the Earth, the Moon does not have an intrinsic global magnetosphere; rather, smaller crustal magnetic fields dot the lunar surface. Previous studies have revealed a dynamic interaction between the lunar environment and the incident solar wind plasma near these crustal magnetic field regions (Halekas et al., 2008;Harada et al., 2021;Lue et al., 2011;Saito et al., 2008Saito et al., , 2010Saito et al., , 2012. For example, incident solar wind ions and electrons are either reflected above the surface or impact the regolith, depending on the magnetization of the lunar crust. ...
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... In addition we use magnetic field data obtained by the MMO-MGF instrument (Baumjohann et al., 2020) down-sampled to 4 s time resolution and temperature and voltage data recorded by several platform house keeping sensors mounted on MMO, MPO, MTM, and the solar arrays-usually down-sampled to 1 min resolution. We should note that all instruments have been designed for operation after separation of the BepiColombo stack and not for operation in cruise phase. ...
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... 首次探讨了数据同化在地磁学中的应用，并利用一维磁场和速度场的简化动力学方程 结合变分数据同化方法进行了概念性分析， 并倡议将数据同化引入地磁学研究 [44] 。 同期， Sun 等人 [45] 利用一维非线性磁流体动力学方程结合顺序最优插值同化方法进行了相关的理论验 证。 此外， Liu 等人 [46] 成功地采用最优插值方案将地磁观测数据同化到地球动力学模型中。 这些简化或一维的模拟实验为后续的 GDA 研究打下了基础。 最优插值法 [47] ， 标准 KF [48][49][50] ，SV 同化(secular variation assimilation，长期变化同化) [51] 等同化方法开始在地核动力学的 观测约束上开始被应用。自 Kuang 等人 [52] 提出了首个地磁数据同化框架以来，随后 GDA 的 误差统计和模型开发工作逐渐展开 [49,[53][54][55][56][57][58][59][60] 。Kuang 等人 [61] 进一步尝试使用数据同化预测地 磁场的长期变化，促使多种地磁预测的 GDA 系统被开发 [62][63][64][65] 。可以看出，近十几年来，数 据同化在地磁学的各个领域都取得了显著的进步。尽管由于其较短的发展历程，在模型和观 测偏差校正、预测协方差矩阵的收敛性以及非线性数据同化算法等方面仍存在挑战，但这并 不会阻碍 GDA 的快速发展。预计 GDA 将在地球内部研究中得到更广泛的应用。 ...
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... As a consequence, the flux of pickup ions originating from a region with the crustal magnetic anomaly may be lower than that originating from a region without the anomaly. For example, Yokota et al. (2020) showed a negative correlation of crustal magnetic field intensities with pickup carbon ion (C + ) fluxes detected by the Kaguya spacecraft at an altitude of about 100 km. ...
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... We speculate that, since, the Moon lacks a significant atmosphere and an intrinsic magnetic field, solar wind particles can be absorbed or backscattered to space when they collide with the solid Moon surface. Those particles scattered back into space by the solid Moon can interact with the upstream solar wind, changing the fore-Moon interplanetary magnetic field structure by the diamagnetic current system (e.g., Nishino et al., 2020). Fortunately, the Moon was located at a different side (duskside) from Wind (dawnside) during the event. ...
... The emphasis is on long-term physical solutions for the planetary spin axis, the satellite's orbital inclination, and (here) explicit obliquity and precession solutions. In a number of related, but somewhat distinct studies, the emphasis has shifted toward a detailed model framework for the Earth-Moon's tidal evolution (Framework II hereafter), particularly the history of ocean tidal dissipation (e.g., Webb, 1982;Hansen, 1982;Kagan & Maslova, 1994;Motoyama et al., 2020;Daher et al., 2021;Tyler, 2021;Farhat et al., 2022). The advance in modeling past ocean tidal evolution provided by these studies is clearly desirable. ...
Reference: Milanković Forcing in Deep Time
... Thin-shell dynamo models with a large solid inner core (of radius greater than about 0.8 core radii, or about 1,600 km) can explain the observed field strength (Heimpel et al., 2005;Stanley et al., 2005). Alternatively, a "deep dynamo" beneath a stably stratified layer would generate a magnetic field similar in morphology and strength to that of Mercury (Christensen, 2006;Takahashi et al., 2019) and would imply an inner core of less than a 1,000 km radius. As discussed, such a stably stratified layer can be the consequence of the core cooling history with a subadiabatic temperature gradient near the core-mantle boundary and a convecting deeper core (Knibbe & Van Hoolst, 2021;Knibbe & van Westrenen, 2018). ...
... EMWs have been observed extensively in many plasma environments, such as the magnetosphere (Russell & Blancocano 2007;Meredith et al. 2014;Sugiyama et al. 2015;Lee & Lee 2016), the magnetotail (Nakagawa et al. 2018), the Earth's magnetosheath (Denton et al. 1994(Denton et al. , 1998Song et al. 1994), and the solar wind (Jian et al. 2009(Jian et al. , 2010(Jian et al. , 2014Aggarwal et al. 2016;Gary et al. 2016;Wicks et al. 2016;Zhao et al. 2017a). In the solar wind, interplanetary magnetic clouds (IMCs) are the most important subset of CMEs erupted from the Sun and have a large-scale magnetic flux rope structure. ...
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... The typical energy of the reflected ions ranges from several keV to MeV (which is included in the red curve in Fig. 14). When the Moon is located in the foreshock, these high-energy ions backstreaming from the bow shock can directly access the lunar surface (Benson et al. 1975;Nishino et al. 2017). The high-energy ion bombardment on the lunar surface may facilitate sputtering of volatile species there. ...
... Experimental difficulties related to the radial direction of gravity make the advances in spherical shell convection almost entirely dependent on massively parallel numerical simulations. A comparative study among the existing solvers to address these issues has been reported by Matsui et al. (2016). Existing solvers primarily use spherical harmonic decomposition of the flow variables in the azimuthal and latitudinal directions, while the Chebyshev collocation method (Wicht 2002;Featherstone & Hindman 2016;Simitev & Busse 2005;Glatzmaier 1984;Sasaki et al. 2011) or finitedifference schemes (Willis et al. 2007;Hollerbach 2000;Jiang & Kuang 2008;Takahashi 2012;Matsui et al. 2014;Marti 2012;Schaeffer et al. 2017;Dormy et al. 1998), are used in the radial direction. ...
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