Impact of gravity waves on ice-cloud microphysics in a global NWP model using online coupling

One of the sources of uncertainties in climate models and numerical weather prediction (NWP) models is cirrus clouds. They are highly sensitive to subgrid-scale dynamics, such as gravity waves (GWs) and turbulence, making them challenging to model in detail within coarse-resolution settings.  Additionally, their net radiative effect remains poorly understood, highlighting the importance of accurately representing their microphysical properties as one of the main areas of focus for research and model refinement.The current work focuses on a coupled approach to GW–ice microphysics interactions and its application in the global NWP model ICON. The ice scheme, developed by Dolaptchiev et al. (J. Atmos. Sci., 2023), describes GW-induced homogeneous nucleation of ice crystals and proposes a prototype parameterization used in this study. The representation of a local GW field is diagnosed using the Multi-Scale Gravity Wave Model (MS-GWaM) parameterization. MS-GWaM parameterization supports multiple GW source types, and allows for 3D GW propagation, enhancing its physical realism. The full coupling of GW forcing, along with feedback from the new scheme into the overall microphysics and radiation schemes, has been implemented in a test regime in ICON model.To validate the approach and assess the impact of GWs, several global ICON simulations were conducted. The results show a significant influence of GWs on ice number density, indicating higher concentrations of ice crystals in tropical regions. These findings highlight the potential of the coupled approach to improve predictions of cloud microphysics and their radiative impacts. Further investigations will explore the role of different GW sources and account for the superposition of GWs, offering deeper insights into the broader effects of GW representation on global atmospheric processes.

ABstractGravity waves generated by the Vestfjella Mountains (in western Droning Maud Land, Antarctica, southwest of the Finnish/Swedish Aboa/Wasa station) have been observed with the Moveable atmospheric radar for Antarctica (MARA) during the SWEDish Antarctic Research Programme (SWEDARP) in December 2007/January 2008. These radar observations are compared with a 2-month Weather Research Forecast (WRF) model experiment operated at 2 km horizontal resolution. A control simulation without orography is also operated in order to separate unambiguously the contribution of the mountain waves on the simulated atmospheric flow. This contribution is then quantified with a kinetic energy budget analysis computed in the two simulations. The results of this study confirm that mountain waves reaching lower-stratospheric heights break through convective overturning and generate inertia gravity waves with a smaller vertical wavelength, in association with a brief depletion of kinetic energy through frictional dissipation and negative vertical advection. The kinetic energy budget also shows that gravity waves have a strong influence on the other terms of the budget, i.e. horizontal advection and horizontal work of pressure forces, so evaluating the influence of gravity waves on the mean-flow with the vertical advection term alone is not sufficient, at least in this case. We finally obtain that gravity waves generated by the Vestfjella Mountains reaching lower stratospheric heights generally deplete (create) kinetic energy in the lower troposphere (upper troposphere–lower stratosphere), in contradiction with the usual decelerating effect attributed to gravity waves on the zonal circulation in the upper troposphere–lower stratosphere.

We present trace gas and aerosol measurements obtained by the airborne infrared imaging limb sounder GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) that has been operated onboard HALO (High Altitude and Long Range Research Aircraft) during the PHILEAS campaign (Probing High Latitude Export of air from the Asian Summer Monsoon ; August-September 2023). We measured outflow from the Asian Monsoon above the North Pacific, and the Mediterranean, as well as pollution plumes from biomass burning events in North America. In this contribution, we present retrieval results of ammonia (NH3), solid ammonium nitrate and other pollution trace gases (e.g. PAN) as two-dimensional distributions with high vertical resolution, derived from GLORIA observations in the UTLS (Upper Troposphere Lower Stratosphere).Our GLORIA observations reveal considerable abundances of solid ammonium nitrate, which is connected to the Asian Monsoon, in the lower stratosphere outside the Asian Monsoon Anticyclone. Measurements from a previous airborne campaign within the Asian Monsoon (StratoClim 2017) showed large enhancements of NH3 (precursor of ammonium nitrate), and solid ammonium nitrate in the Asian Monsoon upper troposphere.Further, GLORIA measured UTLS air masses heavily influenced by biomass burning during PHILEAS. Due to the ability of GLORIA to measure pollution trace gases with different atmospheric life times, we are able to estimate the age of individual plumes, based on their chemical composition. As an example, we show measurements from a PHILEAS flight, influenced by aged and fresh pollution.In a first analysis, we compare our measurements with atmospheric models to examine air mass origins. In particular, we use artificial tracers calculated by the ICON-ART (ICOsahedral Nonhydrostatic - Aerosol and Reactive Trace gases), one of the models that was also used in forecast configuration for flight planning.

Future space-based gravity wave experiments such as the Big Bang Observatory (BBO), with their excellent projected, one sigma angular resolution, will measure the luminosity distance to a large number of gravity wave (GW) sources to high precision, and the redshift of the single galaxies in the narrow solid angles towards the sources will provide the redshifts of the gravity wave sources. One sigma BBO beams contain the actual source only in 68 per cent cases; the beams that do not contain the source may contain a spurious single galaxy, leading to misidentification. To increase the probability of the source falling within the beam, larger beams have to be considered, decreasing the chances of finding single galaxies in the beams. Saini, Sethi and Sahni (2010) argued, largely analytically, that identifying even a small number of GW source galaxies furnishes a rough distance-redshift relation, which could be used to further resolve sources that have multiple objects in the angular beam. In this work we further develop this idea by introducing a self-calibrating iterative scheme which works in conjunction with Monte-Carlo simulations to determine the luminosity distance to GW sources with progressively greater accuracy. This iterative scheme allows one to determine the equation of state of dark energy to within an accuracy of a few percent for a gravity wave experiment possessing a beam width an order of magnitude larger than BBO (and therefore having a far poorer angular resolution). This is achieved with no prior information about the nature of dark energy from other data sets such as SN Ia, BAO, CMB etc.

Warm conveyor belts (WBCs) are large-scale ascending airstreams found in extratopical cyclones. They constitute a major source of upper tropospheric/lower stratospheric (UTLS) water vapor—a potent greenhouse gas—and hydrometeors, which can form cirrus clouds. Therefore, WCBs play an important role for Earth’s radiative budget. Additionally, WCBs transport large amounts of heat across latitudes and can influence large scale upper tropospheric circulation after their dissipation, underscoring their significance for Earth’s weather and climate.Recent studies using high-resolution, convection-permitting simulations have shown that convection is a prominent feature of WCBs, with convective air parcels transporting significantly more hydrometeors into the UTLS than their slower-ascending counterparts. Furthermore, the cloud and precipitation development in convective air parcels is dominated by different processes than in slower ascending air. However, the global numerical weather prediction and climate models commonly used to assess the climatological and future impacts of WCBs operate at coarse grid resolutions (15–50 km) that are not convection-permitting, relying instead on convection parametrization schemes. The widely used Tiedtke-Bechtold convection parameterization scheme is designed to simulate heat, moisture, and momentum transport in convective systems but includes only basic representations of cloud microphysics. This raises the question of whether low-resolution simulations fail to accurately represent the transport of hydrometeors into the UTLS by WCBs when compared to high-resolution, convection-permitting simulations.To address this, we analyze two simulations of the same WCB—one convection-permitting and one using convection parameterization—with a specific focus on vapor and hydrometeor transport. Our results show that the WCB in the high-resolution simulation transports substantially larger amounts of hydrometeors into the UTLS, while UTLS vapor conditions remain comparable between the two simulations. Microphysics processes also shift from liquid-dominated to frozen-dominated depending on the grid-scale.

Abstract. We previously considered various aspects of gravity wave penetration and effects at mesospheric and thermospheric altitudes, including propagation, viscous effects on wave structure, characteristics, and damping, local body forcing, responses to solar cycle temperature variations, and filtering by mean winds. Several of these efforts focused on gravity waves arising from deep convection or in situ body forcing accompanying wave dissipation. Here we generalize these results to a broad range of gravity wave phase speeds, spatial scales, and intrinsic frequencies in order to address all of the major gravity wave sources in the lower atmosphere potentially impacting the thermosphere. We show how penetration altitudes depend on gravity wave phase speed, horizontal and vertical wavelengths, and observed frequencies for a range of thermospheric temperatures spanning realistic solar conditions and winds spanning reasonable mean and tidal amplitudes. Our results emphasize that independent of gravity wave source, thermospheric temperature, and filtering conditions, those gravity waves that penetrate to the highest altitudes have increasing vertical wavelengths and decreasing intrinsic frequencies with increasing altitude. The spatial scales at the highest altitudes at which gravity wave perturbations are observed are inevitably horizontal wavelengths of ~150 to 1000 km and vertical wavelengths of ~150 to 500 km or more, with the larger horizontal scales only becoming important for the stronger Doppler-shifting conditions. Observed and intrinsic periods are typically ~10 to 60 min and ~10 to 30 min, respectively, with the intrinsic periods shorter at the highest altitudes because of preferential penetration of GWs that are up-shifted in frequency by thermospheric winds.

Geostationary Operational Environmental Satellite-14 (GOES-14) 1-km visible satellite data with 1-min frequency revealed horizontally propagating internal gravity waves emanating from tropopause-penetrating deep convection on 3–4 June 2015 during the Plains Elevated Convection at Night (PECAN) field experiment. These waves had horizontal wavelengths of ~6–8 km and approximate ground-relative phase speeds of 35 m s−1. PECAN radiosonde data are used to document the environment supporting the horizontally propagating gravity waves within the 200-km-long downstream thunderstorm anvil. Comparisons among soundings within the anvil core, at the downstream anvil edge, and outside of the anvil, together with supporting high-resolution numerical simulations, establish the importance of the storm-induced upper-tropospheric/lower-stratospheric (UTLS) outflow in providing conditions allowing vertical trapping of internal gravity waves over large horizontal distances within the mesoscale anvil. Turbulence was reported by commercial aviation in proximity to the gravity waves near the downstream anvil edge. The simulations suggest that the strongest turbulence was consistent with a mesoscale destabilization of the outer portion of the downstream anvil at elevations immediately below the outflow jet, where differential temperature advection owing to the strong associated vertical shear reduces static stability. The simulated gravity waves are trapped at this elevation and extend for several kilometers below. Local minima of moist gradient Richardson number occur immediately above the simulated warm gravity wave temperature perturbations at anvil base, suggesting a possible role these waves could play in establishing precise locations for the onset of turbulence.

Atmospheric gravity waves contribute significantly to the driving of the global atmospheric circulation. Because of their small spatial scales, their effect on the circulation is usually parameterized in general circulation models. These parameterizations, however, are strongly simplified. One important effect that is often neglected is the fact that gravity wave sources, and thus the global distribution of gravity waves, are both very intermittent. Therefore, time series of global observations of gravity waves are needed to study the distribution, seasonal variation, and strength of this effect. For gravity wave absolute momentum fluxes and potential energies observed by the limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), we investigate the global distribution of gravity wave intermittency by deriving probability density functions (PDFs) in different regions, as well as global distributions of Gini coefficients. In the stratosphere, we find that intermittency is strongest in mountain wave regions, followed by the polar night jets, and regions of deep convection in the summertime subtropics. Intermittency is weakest in the tropics. A better comparability of intermittency in different years and regions is achieved by normalizing single observations by their monthly median distributions. Our results are qualitatively in agreement with previous findings from satellite observations, and quantitatively in good agreement with previous findings from superpressure balloons and high resolution models. Generally, momentum fluxes exhibit stronger intermittency than potential energies, and lognormal distributions are often a reasonable approximation of the PDFs. In the tropics, we find that, for monthly averages, intermittency increases with altitude, which might be a consequence of variations in the atmospheric background, and thus varying gravity wave propagation conditions. Different from this, in regions of stronger intermittency, particularly in mountain wave regions, we find that intermittency decreases with altitude, which is likely related to the dissipation of large-amplitude gravity waves during their upward propagation.

To understand the main orographic and non‐orographic sources of gravity waves (GWs) over South America during an Experiment (Rapp et al., 2021, https://doi.org/10.1175/BAMS-D-20-0034.1), we propose the application of a rotational spectral analysis based on methods originally developed for oceanographic studies. This approach is deployed in a complex scenario of large‐amplitude GWs by applying it to reanalysis data. We divide the atmospheric region of interest into two height intervals. The simulations are compared with lidar measurements during one of the flights. From the degree of polarization and the total energy of the GWs, the contribution of the upward and downward wave packets is described as a function of their vertical wavenumbers. At low levels, a larger downward energy flux is observed in a few significant harmonics, suggesting inertial GWs radiated at polar night jet levels, and below, near to a cold front. In contrast, the upward GW energy flux, per unit area, is larger than the downward flux, as expected over mountainous areas. The main sub‐regions of upward GW energy flux are located above Patagonia, the Antarctic Peninsula and only some oceanic sectors. Above the sea, there are alternating sub‐regions dominated by linearly polarized GWs and sectors of downward GWs. At the upper levels, the total available GW energy per unit mass is higher than at the lower levels. Regions with different degrees of polarization are distributed in elongated bands. A satisfactory comparison is made with an analysis based on the phase difference between temperature and vertical wind disturbances.

Abstract. Six medium-scale gravity waves (GWs) with horizontal wavelengths of λH=60–160 km were detected on four nights by Taylor et al. (2009) in the OH airglow layer near Brasilia, at 15° S, 47° W, during the Spread F Experiment (SpreadFEx) in Brazil in 2005. We reverse and forward ray trace these GWs to the tropopause and into the thermosphere using a ray trace model which includes thermospheric dissipation. We identify the convective plumes, convective clusters, and convective regions which may have generated these GWs. We find that deep convection is the highly likely source of four of these GWs. We pinpoint the specific deep convective plumes which likely excited two of these GWs on the nights of 30 September and 1 October. On these nights, the source location/time uncertainties were small and deep convection was sporadic near the modeled source locations. We locate the regions containing deep convective plumes and clusters which likely excited the other two GWs. The last 2 GWs were probably also excited from deep convection; however, they must have been ducted ~500–700 km if so. Two of the GWs were likely downwards-propagating initially (after which they reflected upwards from the Earth's surface), while one of the GWs was likely upwards-propagating initially from the convective plume/cluster. We also estimate the amplitudes and vertical scales of these waves at the tropopause, and compare their scales with those from a simple, linear convection model. Finally, we calculate each GW's dissipation altitude, location, and amplitude. We find that the dissipation altitude depends sensitively on the winds at and above the OH layer. We also find that several of these GWs may have penetrated to high enough altitudes to potentially seed equatorial spread F (ESF) if located somewhat farther from the magnetic equator.

This study leverages the Field Experiment on Sub‐mesoscale Spatio‐Temporal Variability in Lindenberg (FESSTVaL), including comprehensive observations of the surface, atmospheric boundary layer (ABL), and clouds, to compare the performance of a numerical weather prediction (NWP) model at sub‐km resolutions with traditional large‐eddy simulations (LES). This comparison is both relevant and timely: as the typical grid spacings of both techniques are converging, so should their results if the LES is assumed to be a good virtual laboratory for the ABL and if NWP is resolving the turbulence well. The representative of NWP is the Icosahedral Nonhydrostatic (ICON) model run at horizontal resolutions ranging from 2.5 km to 78 m. The LES model MicroHH is run at resolutions from 75 m to 38 m. ICON is set up in a limited area with realistic boundary conditions and heterogeneous land surface, whereas the setup of MicroHH is doubly periodic above a homogeneous surface and flat terrain. We focus our comparison at a horizontal grid resolution of about 78 m, where the two models overlap. ICON can represent the ABL processes with high fidelity. It approaches the performance of the MicroHH‐LES in representing surface turbulent and radiation fluxes due to better‐resolved ABL dynamics, clouds, and land‐surface properties at sub‐km resolutions. The modeled turbulence shows good agreement with observations, highlighting the equal importance of resolved and subgrid turbulent mixing at sub‐km resolutions. Our modeling setup also reproduces deep convective cold pools, although with only a qualitatively realistic onset and development. In addition to the FESSTVaL observations used here, extensive datasets are available for follow‐up studies focusing on specific processes. The complete set of ICON simulations covers the intensive observation period between June 5 and July 5, 2021, and can be used in process studies as well as providing a benchmark for model development.

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.

The extratropical transition layer of (ExTL) has been recognized about 20 years ago as part of the upper troposphere / lower stratosphere (UTLS) of the extratropics, which shows the chemical characteristics of both, the stratosphere and the troposphere. Its composition is to a large extent dominated by rapid transient small scale dynamical processes, driven by mid-latitude synoptics. The dynamical processes may include frontal uplift and shear at the tropopause , convection and gravity wave breaking, all in sum leading to turbulence and mixing. As a result gradients of tracer, moisture, and aerosol are highly perturbed on small scales and cross tropopause exchange may occur.Here we report on a novel measurement approach during June 2024 with a double platform airborne approach targeting small scale variability in the UTLS. This allowed for simultaneous measurements of ozone, humidity and aerosol size distribution on two platforms, which provide information on the vertical gradients of these quantities. The gradients of ozone and aerosol number concentration show a surprisingly high variability in the UTLS and at the tropopause highlighting the importance of small scale processes for the composition of the tropopause region. The measurements were complemented by surface-based and balloon-borne observations at one surface site and comprehensive forecasts including forward trajectories based on ICON forecast data as well as ECMWF forecast data. We will present highlights from the mission including convective overshoots deep into the LMS at high latitudes, probing of convective outflow and mixing at the tropopause, as well as cirrus occurrence in the stratosphere. The mission was a central part of the collaborative research center TPChange (The tropopause region in a changing atmosphere).

Infrasonic waves propagate at long ranges through atmospheric ducts resulting from the stratification of atmospheric properties. In order to study the infrasonic wave propagation, we resort to atmospheric specification combining Numerical Weather Prediction and climatological models. However, these models do not describe small‐scale variability such as perturbations associated to the presence of internal gravity waves. These waves play an important role in the atmospheric dynamic by transferring momentum to the mean flow at critical levels and at wave‐breaking altitudes. In this study we intend to describe the interaction of infrasonic waves with internal gravity waves in order to understand the extended wave trains observed in broadband infrasound signals. We use a numerical model for the propagation of internal waves to generate realistic perturbations of the background atmospheric states. By using a linear full‐wave model of infrasound propagation, our goal is to ultimately relate infrasound characteristics to internal waves properties. We apply those numerical models to different atmospheric mean states including gravity wave perturbations and compare the simulations to infrasound signals recorded from rocket motor fuel elimination events at the Utah Test and Training Range (UTTR). Our results, based on an intensive simulation of infrasound waveforms, show that combining atmospheric background with gravity wave propagation model is relevant to explain, to first order, the behavior of the infrasound field at the distance of the first stratospheric arc. In particular we obtain a better match between pulse duration and peak‐to‐peak amplitude along the stratospheric arc. Such study supports the use of gravity wave simulation in conjunction with infrasound modeling in order to improve gravity wave parameterization in Numerical Weather Forecasting.

Ice clouds have a significant impact on the thermodynamic structure of their environment due to diabatic effects such as latent heat release in phase transitions. On the other hand, the ice clouds themselves are crucially affected by the local dynamics e.g. due to atmospheric gravity waves generated by frontal systems or the flow over a mountain. The interaction of the relevant dynamical processes and ice cloud microphysics on different length and time scales is not yet well understood. We investigate the influence of atmospheric gravity waves on ice cloud microphysics using a Lagrangian approach.The ice cloud properties are modelled by an ODE system where the variables are number and mass concentration as well as the supersaturation of water vapour over ice, while the vertical updraft is externally driving the system. The dynamical effects due to gravity waves are described by a Taylor-Goldstein type equation, which is then used to calculate trajectories of air parcels. We investigate the ice cloud microphysical properties along such trajectories. In this framework, we are able to run many simulations and thus study the setting for several different initial and environmental conditions.While the ice cloud system can be regarded as a non-linear oscillator for constant vertical motion, more complex behaviour emerges in the case of the non-constant updraft along trajectories. Due to the non-linearity of the ice cloud model and the overall complexity of the equations of the coupled systems, the feasibility of analytical calculations is limited and the investigation of the coupled system is largely based on numerical approaches.