Characteristics of Gravity Waves over an Antarctic Ice Sheet during an Austral Summer

Cava, Daniela; Giostra, U.; Katul, Gabriel G.

doi:10.3390/atmos6091271

Cited by 21 publications

(18 citation statements)

References 46 publications

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“…In the SBL, waves are ubiquitous, however they are rarely linear waves: they occur in local packets and consist of only a few cycles with changing amplitude and period. These non-stationary wavelike disturbances, often called "dirty" waves, frequently degrade and lead to the generation of intermittent turbulence influencing turbulent transport of momentum, mass and energy in the SBL (Durden et al, 2013;Mahrt, 2014;Cava et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Influence of submeso motions on scalar oscillations and surface energy balance

Stefanello

Cava

Giostra

et al. 2020

Quart J Royal Meteoro Soc

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The presence of wave‐like structures in the planetary boundary layer and their influence on the scalar fluxes and on the surface energy balance were investigated analyzing one year of continuous measurements collected in southern Brazil. Submeso oscillating patterns in the wind velocity components, temperature and scalar (CO2, H2O) concentrations were isolated using their auto‐correlation functions. The analysis showed that low wind speeds are necessary to trigger wavy motions. During night‐time, in the presence of large vertical temperature gradients, horizontal meandering and internal gravity waves are dominant features of the stable boundary layer. Furthermore, a significant number of meandering cases were identified also during daytime in neutral conditions associated with low values of net radiation. One case‐study showed how, during daytime, the wave‐like patterns may be triggered by variations in the net radiation. Spectral analysis on the whole dataset showed that oscillations in the wind velocity and temperature field are frequently associated with CO2 and H2O wavy patterns with similar time‐scales. These non‐turbulent oscillations produce unpredictable large‐scale contributions to vertical fluxes of temperature and scalar concentrations. The energy budget analysis showed how the choice of a proper averaging time filters out these contributions and improves the energy budget closure, as well as the estimation of the net ecosystem exchange. The results confirm the influence of submeso motions in scalar dispersion, flux patterns and surface energy balance during low wind speed conditions and stable stratification.

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Section: Introductionmentioning

confidence: 99%

Influence of submeso motions on scalar oscillations and surface energy balance

Stefanello

Cava

Giostra

et al. 2020

Quart J Royal Meteoro Soc

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“…Similarly, the influence of gravity waves over turbulent eddies has been studied over Antarctica (see , e.g. [15]), and intense gradients are identified as well in that region of the globe [16]. In fact, strong vertical winds, as well as vertically sheared horizontal winds, can be viewed as common features of stably stratified turbulence [17], in the presence or not of rotation.…”

Section: Introductionmentioning

confidence: 99%

Coupling Large Eddies and Waves in Turbulence: Case Study of Magnetic Helicity at the Ion Inertial Scale

2020

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In turbulence, for neutral or conducting fluids, a large ratio of scales is excited because of the possible occurrence of inverse cascades to large, global scales together with direct cascades to small, dissipative scales, as observed in the atmosphere and oceans, or in the solar environment. In this context, using direct numerical simulations with forcing, we analyze scale dynamics in the presence of magnetic fields with a generalized Ohm's law including a Hall current. The ion inertial length H serves as the control parameter at fixed Reynolds number. Both the magnetic and generalized helicity -invariants in the ideal case -grow linearly with time, as expected from classical arguments. The cross-correlation between the velocity and magnetic field grows as well, more so in relative terms for a stronger Hall current. We find that the helical growth rates vary exponentially with H , provided the ion inertial scale resides within the inverse cascade range. These exponential variations are recovered phenomenologically using simple scaling arguments. They are directly linked to the wavenumber power-law dependence of generalized and magnetic helicity, ∼ k −2 , in their inverse ranges. This illustrates and confirms the important role of the interplay between large and small scales in the dynamics of turbulent flows. arXiv:2001.11625v1 [physics.flu-dyn] 31 Jan 2020 and large scales play an essential role in estimating the efficiency of mixing in such flows [28][29][30], and it is found to vary linearly with the control parameter, namely the Froude number [31,32]. B. The case of space plasmasSimilar phenomena are observed as well for turbulent flows in the presence of magnetic fields. Such fields, together with charged particles, are abundant in the cosmos. At large scales, the magnetohydrodynamic (MHD) approximation, in which the displacement current is neglected in Maxwell's equations, is adequate, and observations of the Solar Wind, dating back to the Voyager spacecraft, confirmed the physical description of a medium governed by the interactions of turbulent, nonlinear eddies and Alfvén waves (see, e.g., for recent reviews, [33-36] and references therein). Turbulence is also found to play a central role in shaping these media [37][38][39].However, as the direct turbulent cascade of energy approaches smaller scales, plasma effects and dispersive waves come into effect, appearing for example through a generalized Ohm's law whose expression depends on the degree of ionization of the medium, which itself can differ greatly from the solar wind to the interstellar gas. Current spacecraft technologies allow for the resolution of much smaller temporal and spatial scales than what was available previously, and one can now reach the ion inertial length, H , and perhaps the electron inertial length (see for definitions the next section, and e.g. [40]). Other types of waves, kinetic Alfvén waves or whistler waves for example, come into play between the ion and electron scales, and the distribution of energy among modes is altered...

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“…Usually, these are referred to as dirty waves (Mahrt, 2014). In the SBL and vSBL, the separation between the smallest waves and turbulent scales can become ambiguous (Mahrt, 2011; Nappo et al , 2014), leading to a possible overestimation of the turbulence energy (Cava et al , 2015). A broad review of wave–turbulence interactions in the SBL is given by Sun et al (2015b).…”

Section: Introductionmentioning

confidence: 99%

Observations of submeso motions and intermittent turbulent mixing across a low level jet with a 132‐m tower

Mortarini

Cava

Giostra

et al. 2017

Quart J Royal Meteoro Soc

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The coexistence of wave‐like submeso motions and anisotropic intermittent turbulence in a night‐time stable boundary layer is investigated. Submeso motions of different characteristics and amplitudes interact with each other. These interactions may lead to intermittent turbulence production which alters the turbulent structure of the stable boundary layer. On the other hand, the production and transfer of turbulence affect the delicate balance of submeso motions. In this work, sonic anemometer data collected at 11 levels in southeastern Brazil have been used to study a case of a nocturnal boundary layer at a coastal site. The absence of forcing at the synoptic scale allows the development of a breeze circulation on which a low‐level jet of moderate intensity (4 m s−1) and low height (about 50 m) takes place. The jet evolution is coupled with dirty waves, while its full development is associated with gravity waves driven by a strong vertical temperature gradient. The layer centred at the low‐level jet nose is characterized by horizontal meandering and very weak turbulence intensity. The air far below and above the low‐level jet maximum experiences bursts of significant increase of the turbulence intensity, showing a three‐layer structure. The oscillations of the horizontal wind components exhibit the same frequency as the temperature oscillations, suggesting that the presence of an adequate temperature horizontal gradient is one of the fundamental drivers of the meandering phenomenon. The considered night has been studied by means of the Eulerian auto‐correlation functions for the detection of the meandering hours and their oscillation time‐scales, and by means of the continuous Morlet wavelet function for the detection of the gravity waves and the characterization of their spatial time‐scales and temporal evolution.

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Characteristics of Gravity Waves over an Antarctic Ice Sheet during an Austral Summer

Cited by 21 publications

References 46 publications

Influence of submeso motions on scalar oscillations and surface energy balance

Influence of submeso motions on scalar oscillations and surface energy balance

Coupling Large Eddies and Waves in Turbulence: Case Study of Magnetic Helicity at the Ion Inertial Scale

Observations of submeso motions and intermittent turbulent mixing across a low level jet with a 132‐m tower

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