After New Horizons, a new Pluto Climate Model for new challenges

The generation of acoustic-gravity waves by meteorological heat sources in the troposphere and the propagation of these waves to the heights of the upper atmosphere are studied theoretically. Equations that describe separately the generation and propagation of acoustic and gravity waves by a local heat source are derived. The heat source of the waves is divided into partial sources of gravity and acoustic waves (AWs). The power of these partial sources is estimated and it is shown that the power of the sources differs by about a factor of two, regardless of the shape, size, and frequency of the heat source. It is shown that in the case of heat sources of the waves, the generation of gravity waves cannot occur without the corresponding generation of AWs: these waves are generated only in pairs. The splitting of the problem of waves from a heat source into problems of waves from gravity and acoustic sources is illustrated by the direct modeling of these waves. The application of the obtained results to the problem of parametrization of acoustic-gravity waves in general circulation and climate models is discussed.

Elevated stratopauses formed at ~80–90 km altitude during the recovery phase of stratospheric sudden warmings in February 2006 and 2009. These likely occurred in response to changes in the downward circulation due to gravity waves (GWs) and/or planetary waves in the mesosphere and the lower thermosphere (MLT). However, the physical mechanisms are not fully understood, due in part to the lack of global GW observations in the MLT. This study presents global‐scale GW observations in the MLT during elevated stratopause events using Thermosphere, Ionosphere, Mesosphere Energetics Dynamics (TIMED)‐Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature observation, which provide a better insight into the formation of an elevated stratopause. During the downward movement of elevated stratopause events in 2006 and 2009, GWs were suppressed below ~60 km and enhanced above ~60 km at high latitudes compared to non‐elevated stratopause years (2005 and 2007). Global SABER GW observations indicate that the regions of GW enhancement propagate from low‐mid latitudes to high latitudes in association with the equatorward shift of the polar night jet during elevated stratopause events. Ray‐tracing simulations show enhancements of the poleward propagation of GWs during elevated stratopause events as well as continuous propagation of non‐orographic GWs within high latitudes. Therefore, our results suggest that meridional propagation of GWs from lower to higher latitudes, which is typically not included in global‐scale models, plays an important role in determining GW variations and thus the downward movement of an elevated stratopause, in addition to non‐orographic GWs originating at high latitudes.

Abstract. Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly affected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not adequately implemented in many circulation models. The daylight-capable Rayleigh–Mie–Raman (RMR) lidar at Kühlungsborn (54∘ N, 12∘ E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement, which shows a large variability of gravity waves and tides on timescales of days. Using a one-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement period a strong 24 h wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4–8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement period and therefore a strong GW activity. The analysis indicates a further change in wave–wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GWs in general circulation models.

The parabolic equation (PE) method is a useful approach for solving range-dependent ocean acoustics problems. The PE method can also be used to model the propagation of internal gravity waves in the ocean. One of the possible applications of a range-dependent gravity wave model to ocean acoustics would be to generate a model-based noise spectrum that could be used as an alternative or complement to the empirical spectrum of Garrett and Munk [J. Geophys. Res. 80, 291–297 (1975)]. This could be done using the approach of Kuperman and Ingenito for modeling surface-generated acoustic noise [J. Acoust. Soc. Am. 67, 1988–1996 (1980)] for an appropriate distribution of gravity wave sources. The mathematical details of a PE for gravity waves will be discussed. Examples will be presented to illustrate the propagation of gravity waves in range-dependent environments. [Work supported by ONR.]

Observation of the gravity waves from GPS/MET radio occultation data

Convective generation and vertical propagation of fast gravity waves on Mars: One- and two-dimensional modeling

Our case study investigates coincidental occurrence of intense tropospheric convection and upper atmospheric variability, focusing on gravity wave (GW) generation in the tropospheric height and its possible effects on the ionospheric layers E, sporadic E (Es), and F2. Our analysis presents: several extreme convective storm events that occurred over Central Europe under tropical air mass conditions, not directly linked to the passage of a cold front. Two primary classifications of convective systems are considered: (1) rapidly propagating supercells characterized by strong, rotating updrafts; and (2) long-lived linear mesoscale convective systems (MSCs) connected to derecho. The latter are distinguished by their broad horizontal extent, long lifetimes of several hours and storm trajectories exceeding 400 km. Based on satellites data, meteorological radar data, and ionospheric radar and Doppler sounding techniques, we investigate ability of such types of severe weather events acting as an effective sources of gravity waves capable of propagating into the middle and eventually reaching the upper atmosphere. We focus on effects of GW within the stratosphere and ionosphere in E, Es, and F2 regions. Results contribute and enlarge our investigation of connection between the intense activity of the lower atmosphere and the dynamics of the upper atmosphere in mid-latitudes.Our previous studies identified simultaneous (a few hour delay) effects in the ionospheric parametrs from the lower ionosphere up to peak of F2 layer. Our study indicates differences in the ionospheric response according to the GW source. In particular, we focus on sporadic E characteristics, its occurrence and blanketing ability. Es layer formation in midlatitude, during low geomagnetic conditions and stable solar forcing, is dependent on neutral atmosphere motion, hence is influenced by GW propagation or depositing their momentum. Sporadic E layers in well pronounced summer phenomenon, while the tropospheric convective events appeared to intensify according to recent climatic studies.This research was supported by the Johannes Amos Comenius Programme (P JAC), project No. CZ.02.01.01/00/22_008/0004605, Natural and anthropogenic georisks, by the GA ČR GA25-14158L, and also by the ESA project HORIZON 2020, PITHIA-NRF 101007599.

<p>Effects of realistic propagation of gravity waves (GWs) on distribution of GW pseudomomentum fluxes are explored using a global ray-tracing model for the 2009 sudden stratospheric warming (SSW) event. Four-dimensional (4D; <span><em>x</em></span>–<span><em>z</em></span> and <span><em>t</em></span>) and two-dimensional (2D; <span><em>z</em></span> and <span><em>t</em></span>) results are compared for various parameterized pseudomomentum fluxes. In ray-tracing equations, refraction due to horizontal wind shear and curvature effects are found important and comparable to one another in magnitude. In the 4D, westward pseudomomentum fluxes are enhanced in the upper troposphere and northern stratosphere due to refraction and curvature effects around fluctuating jet flows. In the northern polar upper mesosphere and lower thermosphere, eastward pseudomomentum fluxes are increased in the 4D. GWs are found to propagate more to the upper atmosphere in the 4D, since horizontal propagation and change in wave numbers due to refraction and curvature effects can make it more possible that GWs elude critical level filtering and saturation in the lower atmosphere. GW focusing effects occur around jet cores, and ray-tube effects appear where the polar stratospheric jets vary substantially in space and time. Enhancement of the structure of zonal wavenumber 2 in pseudomomentum fluxes in the middle stratosphere begins from the early stage of the SSW evolution. An increase in pseudomomentum fluxes in the upper atmosphere is present even after the onset in the 4D. Significantly enhanced pseudomomentum fluxes, when the polar vortex is disturbed, are related to GWs with small intrinsic group velocity (wave capture), and they would change nonlocally nearby large-scale vortex structures without substantially changing local mean flows.</p>

Atmospheric gravity wave (AGW) is a typical phenomenon in the upper atmosphere. At mid/low latitudes, climatological sources such as unstable barometric activity in the troposphere play an important role to generate AGWs in the thermosphere. While these sources are also important at high latitudes, energy input from the magnetosphere has additional large contributions to AGW generation. This paper reviews previous studies of AGWs associated with auroral activity at high latitudes. Theoretical studies have indicated that Joule/particle heating and the Lorentz force are major processes for generating AGWs in the thermosphere. Many observations show that AGWs can propagate horizontally for thousands of km from the source region. The paper summarizes equations regarding AGW generation by Joule/particle heating and the Lorentz force, and discusses the relative importance of these two processes.

A dispersion relation governing the propagation of hydromagnetic gravity waves in a rotating, non-isentropic medium is derived. It is found that a convectively stable medium remains stable and that the effect of a constant entropy gradient is most pronounced in a direction normal to the gravity field. The effect of a small coriolis force is to reduce the phase speed of the Alfven mode. The speed of the entropy mode is, however, increased due to the presence of rotation. The variation of the phase speed, as a function of the angle between the wave vector and the gravity field, is shown in a polar diagram.

Modelled effect of changes in the CO 2 concentration on the middle and upper atmosphere: Sensitivity to gravity wave parameterization

Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena such as tectonic events or explosions or as contributors to atmosphere dynamics. To get a better understanding of the physics behind these dynamic processes, both acoustic and gravity waves propagation should be modelled in a 3-D attenuating and windy atmosphere extending from the ground to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale, we introduce a finite difference in the time domain (FDTD) approach that relies on the linearized compressible Navier–Stokes equations with a background flow (wind). One significant benefit of such a method is its versatility because it handles both acoustic and gravity waves in the same simulation, which enables one to observe interactions between them. Simulations can be performed for 2-D or 3-D realistic cases such as tsunamis in a full MSISE-00 atmosphere or gravity-wave generation by atmospheric explosions. We validate the computations by comparing them to analytical solutions based on dispersion relations in specific benchmark cases: an atmospheric explosion, and a ground displacement forcing.

Background: UV occultations measured by Voyager 2 during its flyby of Uranus in 1986 detected a warm stratosphere and extremely hot thermosphere [1, 2], far in excess of solar irradiance [3, 4] or internal heating [5]. These measurements imply that Uranus has the coldest lower stratosphere and yet the hottest thermosphere of any Solar System planet [6] (see Figure 1, dashed line). Uranus has the weakest internal heat of any of the giant planets [5]. The fundamental lack of understanding about the energy balance of Uranus is an example of the “giant planet energy crisis” [7].Furthermore, the Voyager 2 UV occultation measurements and models were in stark tension with Earth-based stellar occultations observed between 1977 and 1996. In [8] and [9], we present the results of reprocessing 26 archival occultations using modern techniques. While stratospheric tensions have decreased, thermospheric tensions remain, calling into question the Voyager 2 findings. In [9], we present a new 1-D atmospheric model that successfully reproduces these results. Aims: We present a new representative temperature-pressure profile for the atmosphere of Uranus from reprocessed stellar occultation observations and 1-D atmospheric modeling [8, 9]. We discuss the energy inputs to the thermosphere, circulation necessary to explain the new profiles, and the significant, potential magnetosphere-ionosphere-thermosphere interactions at Uranus. We describe critical measurements from a likely Uranus Orbiter and Probe (UOP) mission as well as from Earth beforehand that would enable the study of the energy inputs to Uranus. Prior Results & Conclusions: We reprocessed 26 archival Uranus stellar occultations, which produced temperature-pressure profiles inconsistent with Voyager 2 UVS profiles [8, 9]. A 1-D atmospheric model comprised of radiative-convective and conduction models was developed for Uranus based on these reprocessed profiles. The model reproduces the profiles and suggests a heat sink exists in the lower thermosphere. Figure 1 shows the new reference temperature-pressure profile for Uranus in comparison to the Voyager 2 profile and profiles for other planets.We conclude that the mesopause of Uranus is likely significantly higher in altitude (~10-4 mbar) than suggested from Voyager 2 profiles (~1 mbar), consistent with the mesopause levels of the other giant planets [9, 10]. We find that the stratosphere of Uranus likely contains a nearly isothermal region, again, consistent with those of the other giant planets [9, 10]. Last, we find that the required thermospheric energy flux is tens of times the solar EUV flux, underscoring the energy crisis and motivating detailed study of energy sources in the Uranian system. Ongoing Work: Measurements of Jupiter and Saturn have identified an energy crisis similar to that of Uranus. The emerging solution involves gravity waves activity that facilitates heating of the thermospheres by inducing Rayleigh drag in the polar regions. This breaks down the Coriolis force and enables meridional transport of strong auroral [11, 12] heating. While it is likely that Uranus has significant gravity wave activity [13, 14], it is possible that the auroral inputs to Uranus occur around the entire planet and are not limited to the poles [15, 16]. Much work is underway to better understand the shape and behavior of the magnetosphere of Uranus. Gravity waves may also provide the dynamical transport needed to create the heat sink observed in our new 1-D model.Therefore, additional observations of the prevalence and properties of gravity waves are critical to extending recent modeling work from Jupiter and Saturn to Uranus. While UOP may make many such observations in the 2050s, we outline Earth-based observations that can be made prior. Upcoming Stellar Occultations: In [17], we predicted Uranus and Neptune occultations 2025 – 2035 that could be observed from the ground and/or from low-Earth orbit. Additional predictions can be found in [18]. The most promising Uranus events occur in 2025, 2031, and 2032. We will describe how we intend to observe the 2025 occultation from ground-based and airborne assets, as well as other upcoming observing campaigns. We will present simulated results for temperature profiles of Uranus as well as gravity wave detections. The Shadow Chaser: In [17], we outlined the case for a low-Earth orbit small satellite to observe stellar occultations to better constrain the temperature and density profiles of the upper atmosphere of Uranus and to detect gravity waves. This mission concept, called the Shadow Chaser, is being explored at NASA Langley Research Center. By observing above the atmosphere, the Shadow Chaser could observe during the day and would not be impacted by scintillation, greatly increasing signal-to-noise. We will present simulations showing the Uranus profiles that would result from the Shadow Chaser observing the 2031 Uranus event, during which Uranus will occult a 4th magnitude K-band star. 

We present the occurrence of waves patterns on the southern polar region of Mars as traced by the O2 dayglow emission at λ = 1.27 μm during late winter/early spring of MY 28. The observations were carried out by the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) imaging spectrometer on board Mars Express (MEX). Waves are found preferentially at high incidence angles and latitudes between 55° and 75°S. The dayglow intensity fluctuations are of the order of ±3% at incidence angle <88.5° and they can be explained by the propagation of gravity waves in the Martian atmosphere. Mesoscale meteorological modeling predicts gravity wave activity in the same range of latitude as the observed O2(a1Δg) wave patterns with temperature oscillations consistent with existing measurements. Moreover, gravity waves simulated through mesoscale modeling can induce dayglow fluctuations of the same order‐of‐magnitude as observed in the OMEGA maps. This study confirms that airglow imagery is a powerful method to detect and study the bi‐dimensional propagation of gravity waves, as foreseen in previous studies coupling photochemical and dynamical models.

A high-resolution nonlinear numerical model is used to simulate propagation of internal gravity waves (IGWs) from the troposphere to the upper atmosphere. This simulation takes into account background wind profiles containing critical levels at which the horizontal wind velocity becomes equal to the horizontal phase speed of IGW. According to traditional linear theories of atmospheric waves, near critical levels the vertical wavelength approaches zero, which should lead to a strong dissipation of IGWs propagating from the troposphere and may significantly decrease their ampli-tudes in the upper atmosphere. The wave sources in the model are defined as vertical velocity perturbations propagating along the Earth surface. The mean horizontal wind in the atmosphere is approximated by the Gaussian profile with a maximum at an altitude of 50 km. We analyze the spectra of wave fields near criti-cal levels and at a distance from them. It has been found that the instability of waves near critical levels intensifies the energy transition from primary IGWs propagating from surface sources to secondary wave modes. This causes an increase in spectral peaks at wavelengths shorter than the horizontal length of primary IGW. Therefore, above critical levels, spectral modes with shorter horizontal wavelengths begin to prevail with increasing altitude, and the amplitudes of these secondary waves at the same altitudes can exceed the amplitudes of analogous primary IGW propagating in the absence of critical levels in the middle atmosphere.