On the Origins of the Oceanic Ultraviolet Catastrophe

We provide a first-principles analysis of the energy fluxes in the oceanic internal wavefield. The resulting formula is remarkably similar to the renowned phenomenological formula for the turbulent dissipation rate in the ocean which is known as the Finescale Parameterization. The prediction is based on the wave turbulence theory of internal gravity waves and on a new methodology devised for the computation of the associated energy fluxes. In the standard spectral representation of the wave energy density, in the two-dimensional vertical wavenumber – frequency (m – w) domain, the energy fluxes associated with the steady state are found to be directed downscale in both coordinates, closely matching the Finescale-Parameterization formula in functional form and in magnitude. These energy transfers are composed of a ‘local’ and a ‘scale-separated’ contributions; while the former is quantified numerically, the latter is dominated by the Induced Diffusion process and is amenable to analytical treatment. Contrary to previous results indicating an inverse energy cascade from high frequency to low, at odds with observations, our analysis of all non-zero coefficients of the diffusion tensor predicts a direct energy cascade. Moreover, by the same analysis fundamental spectra that had been deemed ‘no-flux’ solutions are reinstated to the status of ‘constant-downscale-flux’ solutions. This is consequential for an understanding of energy fluxes, sources and sinks that fits in the observational paradigm of the Finescale Parameterization, solving at once two long-standing paradoxes that had earned the name of ‘Oceanic Ultraviolet Catastrophe’.

The stability of internal gravity waves in a bounded atmospheric shear layer in the presence of moisture

The stability characteristics of internal gravity waves, generated by an isothermal bounded tangent velocity profile in the presence of a saturated finite layer, are studied. The moist layer with constant thickness the structure of the ness is introduced at different levels in respect to the point of inflection and the variations of moisture content and distance from the origin are examined. The characteristics of the unstable waves are obtained by solving numerically the linearized versions or the full equations of motion, in the inviscid and Boussinesq limit, through the technique of Lalas and Elnaudi (1976). It is shown that the presence of the moist layer can significantly affect the stability characteristics of the waves. Increases in the moisture and distance of the layer from the Inflection point are found to amplify or decay the wave response, because the saturated layer behaves as a solid boundary to the flow. The presence of such effective layer is shown to stabilize short wavelengths and destabilize. Finally, an application of the model's results to the real atmosphere is discussed.

QG-DL-Ekman: Dynamics of a diabatic layer in the quasi-geostrophic framework

Quasi-geostrophic (QG) theory describes the dynamics of synoptic scale flows in the troposphere that are balanced with respect to both acoustic and internal gravity waves. Within this framework, effects of (turbulent) friction near the ground are usually represented by Ekman Layer theory. The troposphere covers roughly the lowest ten kilometers of the atmosphere while Ekman layer heights are typically just a few hundred meters. However, this two-layer asymptotic theory does not explicitly account for substantial changes of the potential temperature stratification due to diabatic heating associated with cloud formation or with radiative and turbulent heat fluxes which can be significant in about the lowest three kilometers and in the middle latitudes. To address this deficiency, this paper extends the classical QG–Ekman layer model by introducing an intermediate dynamically and thermodynamically active layer, called the “diabatic layer” (DL) from here on. The flow in this layer is also in acoustic, hydrostatic, and geostrophic balance but, in contrast to QG flow, variations of potential temperature are not restricted to small deviations from a stable and time independent background stratification. Instead, within the DL diabatic processes are allowed to affect the leading-order stratification. As a consequence, this layer modifies the pressure field at the top of the Ekman layer, and with it the intensity of Ekman pumping seen by the quasi-geostrophic bulk flow. The result is the proposed extended quasi-geostrophic three-layer QG-DL-Ekman model for mid-latitude dynamics.

In situ measurement of wave attractor induced forces

An underwater force sensor for internal waves is presented. Using this sensor, we measure forces at a location near the surface of a fluid. The sensor performs a point measurement with a high temporal resolution. We perform measurements in a density-stratified fluid contained in a trapezoidal basin. By shaking this basin longitudinally, internal gravity waves are generated. Controlling the frequency with which the basin oscillates, these waves propagate toward a wave attractor whose shape varies from complicated to rectangular. We measure the force exerted by these waves on a plate that is partially submerged into the fluid. We observe the formation and decay of wave attractors. When a surface reflection of a wave attractor is near our sensor we measure (relatively) strong forces. We confirm our findings with simulations. We observe an asymmetry in the direction of the force. This asymmetry leads to a net force and could imply the driving of a mean flow. Graphical Abstract

Estimated influence of stratospheric activity on the ionosphere according to measurements with ISTP SB RAS tools

We present the results of a comprehensive study of the manifestation of wave activity with periods of internal gravity waves (IGW) in various regions of the atmosphere: in the stratosphere, upper mesosphere, and in the F2-region of the ionosphere. The study is based on radiophysical and spectrometric measurements made with tools of the Institute of Solar-Terrestrial Physics (ISTP) SB RAS and the Era-Interim reanalysis data. The correlation coefficient with time shift between ionospheric and stratospheric activity for the annual interval varies in the range from 0.45 to 0.54, and for the 27-day interval it reaches the levels 0.4–0.8 in seventy percent of the cases. Thirty percent of correlation coefficients less than 0.4 can be explained by the influence of neutral wind, geomagnetic activity, and non-stratospheric IGW sources. Comparison between stratospheric activity and variations in characteristics of traveling ionospheric disturbances (TID) has shown that a ~15 day shift in stratospheric activity results in a fairly high correlation between stratospheric activity and disturbance of IGW characteristics (~0.6). The delay of about 15 days can be attributed to the delay in the temperature variations at heights of the lower thermosphere relative to the temperature variations at the altitude pressure level of 1 hPa. Comparative analysis of variations in mesospheric and ionospheric activity has revealed time intervals when their behavior is consistent.

Estimated influence of stratospheric activity on the ionosphere according to measurements with ISTP SB RAS tools

We present the results of a comprehensive study of the manifestation of wave activity with periods of internal gravity waves (IGW) in various regions of the atmosphere: in the stratosphere, upper mesosphere, and in the F2-region of the ionosphere. The study is based on radiophysical and spectrometric measurements made with tools of the Institute of Solar-Terrestrial Physics (ISTP) SB RAS and the Era-Interim reanalysis data. The correlation coefficient with time shift between ionospheric and stratospheric activity for the annual interval varies in the range from 0.45 to 0.54, and for the 27-day interval it reaches the levels 0.4–0.8 in seventy percent of the cases. Thirty percent of correlation coefficients less than 0.4 can be explained by the influence of neutral wind, geomagnetic activity, and non-stratospheric IGW sources. Comparison between stratospheric activity and variations in characteristics of traveling ionospheric disturbances (TID) has shown that a ~15 day shift in stratospheric activity results in a fairly high correlation between stratospheric activity and disturbance of IGW characteristics (~0.6). The delay of about 15 days can be attributed to the delay in the temperature variations at heights of the lower thermosphere relative to the temperature variations at the altitude pressure level of 1 hPa. Comparative analysis of variations in mesospheric and ionospheric activity has revealed time intervals when their behavior is consistent.

Towards a transient gravity wave parametrization in atmospheric models

<p>Subgrid-scale internal gravity waves (IGWs) are important distributors of energy in a stratified atmosphere. While they are mostly excited at lower altitudes their effects are most important between the upper troposphere to the mesopause (~85km). During propagation–both in the vertical and the horizontal–nonlinear IGWs can exert a wave drag on the mean winds, interact with the mean potential temperature, and mix atmospheric tracers such as aerosols or greenhouse gases.</p> <p>In state-of-the art weather prediction models IGWs are typically parametrized using the single-column and the steady-state assumptions. These parametrizations take into account dissipative effects of IGWs but neglect their horizontal propagation and all of their transient interaction mechanisms such as direct wave-mean-flow interactions. However, the latter have been shown to contribute to IGW dynamics in various idealized studies.</p> <p>Here we present advances of the use of the transient Multi Scale Gravity Wave Model (MS-GWaM) in the upper atmosphere model UA-ICON. Based on Lagrangian ray-tracing the parametrization includes various non-orographic wave sources, transient propagation in both the horizontal and vertical directions, direct wave-mean-flow interactions and wave breaking. The resulting setup satisfactorily reproduces the observed mean-wind and potential temperature climatology and already shows promising insights into the details of the role of IGWs in the atmosphere.</p>

Parameterized orographic gravity wave drag in CMIP6 models, distribution, variability, trends and intermodel spread

<p>Internal gravity waves (GWs) are a naturally occurring and intermittent phenomenon in the atmosphere. GWs can propagate horizontally and vertically and are important for atmospheric dynamics, influencing the atmospheric thermal and dynamical structure. Research on GWs is connected with some of the most challenging issues of Earth climate and atmospheric science. Consideration of GW-related processes is necessary for a proper description and modelling of the middle and upper atmosphere. However, as GWs exist on scales from a few to thousands of kilometers, they cannot be fully resolved by general circulation models (GCMs) and hence have to be parameterized. Although recently satellite and reanalysis datasets with improved resolution and novel analysis methods together with high-resolution atmospheric models have been tightening the constraints for GW parameterizations in GCMs, the parameterized GW effects still bear a significant margin of uncertainty.</p> <p>To quantify this uncertainty, we analyze the three-dimensional distribution and interannual variability of orographic gravity wave drag (OGWD) in chemistry-climate model simulations. For this, we use a set of AMIP simulations produced within the CMIP6 activity. In particular, we focus on the intermodel spread in the vertical and horizontal OGWD distribution. The different models generaly agree on the areas of the OGWD hotspots. However, in all these regions we find considerable intermodel differences in OGWD magnitude as well as in the altitude of the strongest GW dissipation. In this presentation, we show our findings and discuss possible explanations for the intermodel differences, like different parametrization schemes and choices of tunable parameters.</p>

Analysis of interaction between parameterized orographic gravity wave drag and resolved dynamics in CMAM.

<div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics herein. In current generation chemistry-climate models (CCMs), GWs are usually smaller than the model resolution and the majority of their spectrum therefore must be parameterized. From observations, we know that GWs are intermittent and asymmetrically distributed around the globe, which holds to some extent also for the parameterized GW drag (GWD) (in particular for orographic GWD (oGWD)). The GW parameterizations in CCMs are usually tuned to mitigate biases in the zonal mean climatology of particular quantities, but the complex interaction of parameterized GWs with the large- scale circulation and resolved waves in the models remains to date poorly understood.</p> <p>This presentation will combine observational evidence, idealized modeling and dynamical analysis of a CCM output to study both the short-term and long-term model response to the oGWD. Our results demonstrate that the oGW-resolved dynamics interaction is a complex two-way process, with the most prominent oGWD impact being the alteration of propagation of planetary-scale Rossby waves on a time-scale of a few days. The conclusions give a novel perspective on the importance of oGWD for the stratospheric polar vortex and atmospheric transport studies outlining potential foci of future research.</p> </div> </div> </div>