In this paper we employ Thermosphere Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry temperature measurements from 20 to 120 km and between ...about ±72° latitude to investigate several aspects of the quasi‐two‐day wave (QTDW) during the 2002–2011 decade, including interannual variability of its seasonal‐latitudinal structure, its penetration into the lower thermosphere, and various wave‐wave interactions. We focus on two components of the QTDW: the westward‐propagating component with zonal wave number s=3 (TDW3), and the eastward‐propagating component with s=−2 (TDE2). TDW3(TDE2) has maximum amplitudes during 2003, 2004, and 2011(2006 and 2011) and both waves have their lowest amplitudes during the deep solar minimum years of 2008–2009. TDW3 and to some degree TDE2 penetrate with significant amplitudes up to 120 km altitude, well into the region where neutral winds generate electric fields through the dynamo mechanism. A new “longitude subdivision method (LSM)” is presented that enhances temporal resolution of TDW3 and enables the determination of 9.6 h and 16 h waves that result from nonlinear interaction between TDW3 and/or TDE2 and diurnal migrating (DW1) and semidiurnal migrating (SW2) tides. Evidence is presented for westward‐propagating 9.6 h and 16 h waves with s=5 and s=4, respectively, and a zonally symmetric (s=0) 9.6 h wave. The s=5(s=0) wave only occurs as a result of nonlinear interaction between SW2 and TDW3(TDE2), whereas the s=4 wave can result from interaction of TDW3 with DW1 or of TDE2 with SW2. We payed special attention to possible aliasing between different waves.
Key Points
The QTDW exhibits significant interannual variability
The QTDW extends into the dynamo region with significant amplitudes
QTDW‐tide interactions produce 9.6h and 16h secondary waves
In this paper, we globally characterize the solar terdiurnal tide in the 80–110 km region of Earth's atmosphere through analysis of 10 years of temperature measurements made by the Sounding of the ...Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics spacecraft. The Sun‐synchronous (“migrating”) component (TW3), which is longitude‐independent and achieves maximum amplitudes of order of 5 K (10 K) at 90 km (110 km), not too different than the 7–15 K amplitudes that are typical of the migrating diurnal and semidiurnal tides in this region. Significant longitude variability (∼ 20–25%) in terdiurnal temperature amplitudes also exists, which is decomposed into zonal wave number components. The largest of these (TE1, TW4, and TW5) reveal distinct seasonal‐latitudinal and height versus latitude patterns and interannual consistency. In addition, it is demonstrated that these particular components vary in ways that suggest that they originate from nonlinear interactions between diurnal and semidiurnal tides, specifically between DE3 and SW2 for TE1, between DW2 and SW2 for TW4, and between DW1 and SW4 for TW5. We also demonstrate that the terdiurnal tides derived here are not influenced to any significant degree by aliasing due to the presence of other waves.
Key Points
Climatology and inter‐annual variability of terdiurnal tides
Interaction sources of terdiurnal tides
Longitude variability of terdiurnal tides
In this paper we demonstrate how the interplay between surface‐generated tidal components and those excited by longitudinally varying solar absorption due to dust can explain the seasonal asymmetry ...of nonmigrating tides as seen in middle‐atmosphere Mars Climate Sounder's observations. This seasonal asymmetry, which is consistent in all 3 years of available observations, is not readily explained by the current theory of nonmigrating tides on Mars. Sources traditionally include the changes in the Martian topography and the nonuniformity of the surface thermal properties. We show that the seasonal asymmetry can be explained by the destructive interference from an asymmetric tidal component forced by the wave number patterns in dust opacity in the northern low latitudes.
Key Points
There is a visible and strong asymmetry in Martian nonmigrating tides
The strongest zonal variability in dust is always located between the 0N and 30N
Dust's zonal variability controls the asymmetry in nonmigrating tides
In this paper we demonstrate how observations from Sun‐synchronous and quasi‐Sun‐synchronous satellites can be analyzed to reveal the signatures of nonlinear interactions between tides and planetary ...waves in Earth's mesosphere and lower thermosphere. This is done by ordering data in longitude space, and demonstrating how peaks in the spectra of such data series can be identified with specific waves or combinations of waves. We use as an example the quasi‐two‐day wave (QTDW) oscillations in temperature observed by the Microwave Limb Sounder (MLS) instrument on the Aura satellite and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the TIMED satellite. We show that the QTDW not only produces secondary waves due to nonlinear interactions with the migrating (Sun‐synchronous) diurnal and semidiurnal tides, but that secondary waves are also produced by nonmigrating tide‐QTDW interactions. Moreover, these latter secondary waves are of similar amplitude to the resident tides and the QTDW, and serve an important role in defining longitude structures due to the presence of these waves.
Key Points
Demonstrates how PW‐tide interactions can be identified in satellite data
Demonstrates the importance of the secondary waves on the longitudinal structure
Explains the longitude variability of the 2‐day wave response of the ionosphere
In a recent paper, a method called morphological component analysis (MCA) has been proposed to separate the texture from the natural part in images. MCA relies on an iterative thresholding algorithm, ...using a threshold which decreases linearly towards zero along the iterations. This paper shows how the MCA convergence can be drastically improved using the mutual incoherence of the dictionaries associated to the different components. This modified MCA algorithm is then compared to basis pursuit, and experiments show that MCA and BP solutions are similar in terms of sparsity, as measured by the lscr 1 norm, but MCA is much faster and gives us the possibility of handling large scale data sets.
Over the last few years, the development of multichannel sensors motivated interest in methods for the coherent processing of multivariate data. Some specific issues have already been addressed as ...testified by the wide literature on the so-called blind source separation (BSS) problem. In this context, as clearly emphasized by previous work, it is fundamental that the sources to be retrieved present some quantitatively measurable diversity. Recently, sparsity and morphological diversity have emerged as a novel and effective source of diversity for BSS. Here, we give some new and essential insights into the use of sparsity in source separation, and we outline the essential role of morphological diversity as being a source of diversity or contrast between the sources. This paper introduces a new BSS method coined generalized morphological component analysis (GMCA) that takes advantages of both morphological diversity and sparsity, using recent sparse overcomplete or redundant signal representations. GMCA is a fast and efficient BSS method. We present arguments and a discussion supporting the convergence of the GMCA algorithm. Numerical results in multivariate image and signal processing are given illustrating the good performance of GMCA and its robustness to noise.
Atmospheric densities derived from measured acceleration of several Mars orbiters reveal large amplitude Sun‐synchronous longitudinal density variations at altitudes of about 100–160 km. These ...variations are associated with vertically‐propagating nonmigrating solar thermal tides that are excited near Mars' surface and propagate into the thermosphere. Excitation of these waves is associated with the zonally asymmetric component of the near‐surface heating distribution and is commonly attributed to topographic modulation of solar heating. However, there are other possible contributors to the excitation of nonmigrating tides, including zonal variations in surface properties and wave‐wave nonlinear interactions, whose relative contributions remain unexplored. In this study we use a general circulation model in combination with the Mars Global Surveyor accelerometer measurements to isolate the different waves responsible for the observed density structures. While it is evident that topography accounts for most of the waves' amplitudes, the surface thermal inertia and albedo are found to have a nonnegligible contribution to the eastward‐propagating diurnal tide with zonal wave number s = −1 and the standing s = 0 diurnal tide. Previous studies have reported the dominance of wave numbers 2 and 3 in the resulting Sun‐synchronous aerobraking density maps. We show that wave number 1 has a comparable amplitude and is mostly the result of mapping the diurnal standing wave into a near Sun‐synchronous orbit. While most of the nonmigrating tides at thermospheric altitudes are generated by an interaction between the migrating solar radiation and the dominant topography harmonics, we also find that wave‐wave interaction is necessary to explain some of the observed density features.
This study presents a new interpretation of Mars aerobraking density observations in terms of planetary wave‐tide interactions. Mars Global Surveyor and Mars Reconnaissance Orbiter provide invaluable ...information about tidal activity in the lower thermosphere of Mars through the longitude structure that they reveal in near‐Sun‐synchronous frame of reference. However, this same perspective does not permit one to uncover the origins of day‐to‐day variability of these structures. Herein, by employing a new arrangement of the data and understanding the relationship between spectral features in longitude space versus UT space, we are able to attribute a significant amount of density variability in the aerobraking region to the effect of tidal modulation by planetary waves in the 5–20 day period range.
The 500 MJ superconducting toroidal field magnet of TORE SUPRA-WEST has been providing a 4 T magnetic field on the tokamak plasma axis since 1988. The magnet is bath-cooled with superfluid helium at ...1.8 K, and operates in steady state each experimental day. During those years, the magnet internal structure has not been modified, but several interfaces and auxiliary systems required for its operation have been upgraded. This paper aims at giving an overview of the Tore Supra-WEST toroidal field magnet system. Main issues and upgrades are described while providing the community a valuable long-life operation feedback and return on experience. We will go through the normal operation sequences and the incidental events, trying to point out key components failures and recovery actions undertaken. We will also develop the main subsystems evolutions such as the quench protection system, the data acquisition and the control systems. We will outline the major risks and mitigation schemes followed as well as the strategies adopted to ensure adequate maintenance, to preserve skills and knowledge continuity over such a long and eventful operating time-frame.
The WEST platform aims at testing ITER like W divertor targets in an integrated tokamak environment. To operate long plasma discharges, IR thermography is required to monitor the main plasma facing ...components by means of real time surface temperature measurements, while providing essential data for various physics studies.
To monitor the new divertor targets, the WEST IR thermography protection system has been deeply renewed, to match the new tokamak configuration. It consists of 7 endoscopes located in upper ports viewing the whole lower divertor and the 5 heating devices. Electronic devices and computers allow data storage of ≈3 Gb/s IR images and real time video frames processing at 50 Hz rate, to ensure the protection of the main plasma facing components during plasma discharges by a feedback control of the power injected by the heating systems.
Each endoscope provides 2 views covering 2 divertor sectors of 30° (toroidally) and 1 view of a heating antenna. Each optical line is composed of a tight entrance window followed by a head objective which forms an image transported through the endoscope by a series of 4 optical relays and mirrors, up to a camera objective. Finally, 12 IR cameras specially developed for WEST environment capture the thermographic data, at the wavelength of 3.9 μm, with a 640 × 512 pixels frame size.
The paper describes the design constraints and diagnostic technologies: optics, mechanics, electronics, hard & software, cameras. Tvhe laboratory characterization procedures (Modulation Transfer Function, slit response, calibration), and the measurement performance results are given (spatial resolution, temperature threshold). Finally, first results obtained during experimental campaigns in WEST are presented.
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