ABSTRACT High resolution radiosoundings of wind and temperature are analyzed in view of un- derst... more ABSTRACT High resolution radiosoundings of wind and temperature are analyzed in view of un- derstanding the spatial distribution and characteristics of inertia-gravity waves in the vicinity of strongly anisotropic large-scale features such as jets or fronts. In order to detect possible systematic trends in the organization of the wave fields, data from different situations are considered: soundings from Antarctic stations which sample the border of the polar vortex, and data from the FASTEX campaign which describe developing surface and upper-level fronts and their associated jets. Wave packets are identified and isolated using wavelet transforms, and characteristics of the waves are then obtained using the Stokes parameter method. Wave characteritics and propagation directions are analysed as functions of the distance and orientation relative to the jet or front. Simple theoretical models are considered to interpret these observations, and the relevance of certain two-dimensional models is discussed.
Starting from the description of ideal 2-D hydrodynamics in the framework of the Lie algebra of a... more Starting from the description of ideal 2-D hydrodynamics in the framework of the Lie algebra of area-preserving diffeomorphisms sdiff two observations are made: 1st — this construction may be generalized by means of the central extension of the latter algebra, giving equations equivalent to variants of the vorticity equation on the β-plane; 2nd — a regular way to obtain finite-mode analogs of 2-D hydrodynamical equations preserving the essential algebraic features of these latter exists due to the relation between sdiff and su(N), N— ≻ ∞, algebras recently pointed out in literature.
Anticyclonically-trapped plumes were first discovered following the 2020 Australian fires. Since ... more Anticyclonically-trapped plumes were first discovered following the 2020 Australian fires. Since then, they have been reported after several extreme wildfires and volcanic eruptions, including the 2017 Canadian wildfires, the 2019 Raikoke and the 2022 Hunga Tonga-Hunga Ha’apai eruptions. They appear as coherent plumes of aerosols and combustion/volcanic compounds confined within mesoscale anticyclones (100s to 1000 km diameter), which for several months resist dispersion and dilution by the large-scale flow. Due to their unusual composition, large radiative forcing is prevailing inside the plumes, generating significant diabatic responses in terms of vertical motions and potential vorticity.In this presentation, we propose a conceptual model of the anticyclonic plumes. We will explore ramifications through idealized numerical simulations and theoretical investigations. Particular focus will be put on the condition of their formation and the dynamics of their maintenance and diabatic motions in the stratosphere.
Advances in mathematical fluid mechanics, Dec 29, 2020
Atmospheric dynamics in the equatorial region significantly differs from that in higher latitudes... more Atmospheric dynamics in the equatorial region significantly differs from that in higher latitudes due to the simple fact that the rotation axis of the Earth lies in the tangent plane to the equator. As is well known starting from the pioneering paper by Matsuno [11], see also [4], the dynamics is dominated by equatorial waves. These waves are specific, due to orthogonality of the gravity acceleration and rotation axis, and are well-identified in meteorological in situ and satellite observations, e.g., [18]. It is important that equatorial waves are well-captured already in the simplest rotating shallow water (RSW) model of the atmosphere that was used in the classical works of Matsuno and Gill. The exposition below will be based on this model, with an important addition of the effects of moist convection, which are primordial in the tropical atmosphere. After having recalled the construction of the RSW model and its moist-convective generalization, the mcRSW model [1], we will analyze the linear wave spectrum, with an accent on its long-wave part, the most important for weather and climate, and then analyze the nonlinear effects in the equatorial wave dynamics, which lead to formation of specific coherent structures.
ABSTRACT Electron temperatures at the source of the solar wind are now obtained routinely and con... more ABSTRACT Electron temperatures at the source of the solar wind are now obtained routinely and continuously from measurements of charge states of solar wind ions with modern so- lar wind composition spectrometers over a wide range of solar wind speeds. While the general anti-correlation between solar wind speed and electron temperature was previously noted, the physical processes responsible for this anti-correlation were not well understood and there was no general agreement on the mechanisms that would produce this relationship. We present here a detailed analysis of solar wind measure- ments made with the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses over nearly an entire solar cycle and the full latitude range of Ulysses. We show that the electron temperature (T) derived from the oxygen-7/oxygen-6 density ratios is not only well anti-correlated with solar wind speed (V) in general but also that a plot of V vs. 1/T gives a characteristic and reproducible curve. We find that the solar wind equation derived by Fisk [2002], based on a simple model in which the plasma of both the fast and slow wind is released from magnetic loops that are opened by reconnec- tion with open field lines, is an excellent fit to the SWICS V vs. 1/T data. Fitting these SWICS data to the Fisk equation we infer poorly known solar parameters, such as the electron density and magnetic field at the base of the loops, and show the solar cycle and latitude dependence of these parameters.
Direct numerical simulation of the geostrophic adjustment of a thin layer of homogeneous fluid de... more Direct numerical simulation of the geostrophic adjustment of a thin layer of homogeneous fluid described by the rotating shallow water equations (RSW) is carried out focusing on the finite time singularity formation. High-resolution finite volume shock-capturing procedures are applied to both the reduced one dimensional shallow water model (1d-RSW) and the full two dimensional equations (2d-RSW). In the 1d-RSW, the
The fundamental process of geostrophic adjustment is treated by the method of multi-scale asympto... more The fundamental process of geostrophic adjustment is treated by the method of multi-scale asymptotic expansions in Rossby number and fast-time averaging (which is explained), first in the barotropic one-layer case, and then in the baroclinic two-layer case. Together with the standard quasi-geostrophic regime of parameters, the frontal (or semi-) geostrophic regime is considered. Dynamical separation of slow and fast motions is demonstrated in both regimes. The former obey quasi-geostrophic or frontal-geostrophic equations, thus providing formal justification of the heuristic derivation of Chapter 5. Fast motions are inertia-gravity waves in quasi-geostrophic case, and inertial oscillations in the frontal-geostrophic case. Geostrophic adjustment is also considered in the presence of coastal, topographic, and equatorial wave-guides, and, again, separation of fast and slow motions is demonstrated, the latter now including long Kelvin waves in the first case, long topographic waves in the second case, and long Kelvin and Rossby waves in the third case.
ABSTRACT High resolution radiosoundings of wind and temperature are analyzed in view of un- derst... more ABSTRACT High resolution radiosoundings of wind and temperature are analyzed in view of un- derstanding the spatial distribution and characteristics of inertia-gravity waves in the vicinity of strongly anisotropic large-scale features such as jets or fronts. In order to detect possible systematic trends in the organization of the wave fields, data from different situations are considered: soundings from Antarctic stations which sample the border of the polar vortex, and data from the FASTEX campaign which describe developing surface and upper-level fronts and their associated jets. Wave packets are identified and isolated using wavelet transforms, and characteristics of the waves are then obtained using the Stokes parameter method. Wave characteritics and propagation directions are analysed as functions of the distance and orientation relative to the jet or front. Simple theoretical models are considered to interpret these observations, and the relevance of certain two-dimensional models is discussed.
Starting from the description of ideal 2-D hydrodynamics in the framework of the Lie algebra of a... more Starting from the description of ideal 2-D hydrodynamics in the framework of the Lie algebra of area-preserving diffeomorphisms sdiff two observations are made: 1st — this construction may be generalized by means of the central extension of the latter algebra, giving equations equivalent to variants of the vorticity equation on the β-plane; 2nd — a regular way to obtain finite-mode analogs of 2-D hydrodynamical equations preserving the essential algebraic features of these latter exists due to the relation between sdiff and su(N), N— ≻ ∞, algebras recently pointed out in literature.
Anticyclonically-trapped plumes were first discovered following the 2020 Australian fires. Since ... more Anticyclonically-trapped plumes were first discovered following the 2020 Australian fires. Since then, they have been reported after several extreme wildfires and volcanic eruptions, including the 2017 Canadian wildfires, the 2019 Raikoke and the 2022 Hunga Tonga-Hunga Ha’apai eruptions. They appear as coherent plumes of aerosols and combustion/volcanic compounds confined within mesoscale anticyclones (100s to 1000 km diameter), which for several months resist dispersion and dilution by the large-scale flow. Due to their unusual composition, large radiative forcing is prevailing inside the plumes, generating significant diabatic responses in terms of vertical motions and potential vorticity.In this presentation, we propose a conceptual model of the anticyclonic plumes. We will explore ramifications through idealized numerical simulations and theoretical investigations. Particular focus will be put on the condition of their formation and the dynamics of their maintenance and diabatic motions in the stratosphere.
Advances in mathematical fluid mechanics, Dec 29, 2020
Atmospheric dynamics in the equatorial region significantly differs from that in higher latitudes... more Atmospheric dynamics in the equatorial region significantly differs from that in higher latitudes due to the simple fact that the rotation axis of the Earth lies in the tangent plane to the equator. As is well known starting from the pioneering paper by Matsuno [11], see also [4], the dynamics is dominated by equatorial waves. These waves are specific, due to orthogonality of the gravity acceleration and rotation axis, and are well-identified in meteorological in situ and satellite observations, e.g., [18]. It is important that equatorial waves are well-captured already in the simplest rotating shallow water (RSW) model of the atmosphere that was used in the classical works of Matsuno and Gill. The exposition below will be based on this model, with an important addition of the effects of moist convection, which are primordial in the tropical atmosphere. After having recalled the construction of the RSW model and its moist-convective generalization, the mcRSW model [1], we will analyze the linear wave spectrum, with an accent on its long-wave part, the most important for weather and climate, and then analyze the nonlinear effects in the equatorial wave dynamics, which lead to formation of specific coherent structures.
ABSTRACT Electron temperatures at the source of the solar wind are now obtained routinely and con... more ABSTRACT Electron temperatures at the source of the solar wind are now obtained routinely and continuously from measurements of charge states of solar wind ions with modern so- lar wind composition spectrometers over a wide range of solar wind speeds. While the general anti-correlation between solar wind speed and electron temperature was previously noted, the physical processes responsible for this anti-correlation were not well understood and there was no general agreement on the mechanisms that would produce this relationship. We present here a detailed analysis of solar wind measure- ments made with the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses over nearly an entire solar cycle and the full latitude range of Ulysses. We show that the electron temperature (T) derived from the oxygen-7/oxygen-6 density ratios is not only well anti-correlated with solar wind speed (V) in general but also that a plot of V vs. 1/T gives a characteristic and reproducible curve. We find that the solar wind equation derived by Fisk [2002], based on a simple model in which the plasma of both the fast and slow wind is released from magnetic loops that are opened by reconnec- tion with open field lines, is an excellent fit to the SWICS V vs. 1/T data. Fitting these SWICS data to the Fisk equation we infer poorly known solar parameters, such as the electron density and magnetic field at the base of the loops, and show the solar cycle and latitude dependence of these parameters.
Direct numerical simulation of the geostrophic adjustment of a thin layer of homogeneous fluid de... more Direct numerical simulation of the geostrophic adjustment of a thin layer of homogeneous fluid described by the rotating shallow water equations (RSW) is carried out focusing on the finite time singularity formation. High-resolution finite volume shock-capturing procedures are applied to both the reduced one dimensional shallow water model (1d-RSW) and the full two dimensional equations (2d-RSW). In the 1d-RSW, the
The fundamental process of geostrophic adjustment is treated by the method of multi-scale asympto... more The fundamental process of geostrophic adjustment is treated by the method of multi-scale asymptotic expansions in Rossby number and fast-time averaging (which is explained), first in the barotropic one-layer case, and then in the baroclinic two-layer case. Together with the standard quasi-geostrophic regime of parameters, the frontal (or semi-) geostrophic regime is considered. Dynamical separation of slow and fast motions is demonstrated in both regimes. The former obey quasi-geostrophic or frontal-geostrophic equations, thus providing formal justification of the heuristic derivation of Chapter 5. Fast motions are inertia-gravity waves in quasi-geostrophic case, and inertial oscillations in the frontal-geostrophic case. Geostrophic adjustment is also considered in the presence of coastal, topographic, and equatorial wave-guides, and, again, separation of fast and slow motions is demonstrated, the latter now including long Kelvin waves in the first case, long topographic waves in the second case, and long Kelvin and Rossby waves in the third case.
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Papers by Vladimir Zeitlin