The researchers turned their attention to a well-documented event from the Deep Propagating Gravity Wave Experiment, or DEEPWAVE, a field campaign conducted over New Zealand in 2014. On 12 July of that year, a research aircraft flown by the German Aerospace Center traced a rectangular path across the South Island, sampling the atmosphere at two stacked levels: one near 7.9 kilometers altitude and another near 10.9 kilometers, close to the tropopause. The meteorological setup was favorable for wave generation, with moderate northwesterly winds of roughly 10 to 15 meters per second at 5 kilometers altitude blowing perpendicular to the Southern Alps, and about 20 meters per second near the tropopause, with little change in wind direction with height. Those stacked flight legs provided rare, high-frequency in situ measurements of waves and turbulence signatures near the tropopause, exactly the kind of ground truth that model developers crave.

The simulation tool at the heart of the study is the ICON model, the ICOsahedral Nonhydrostatic modeling framework developed jointly by the German Weather Service and the Max Planck Institute for Meteorology. ICON uses an icosahedral-triangular grid built from geodesic Delaunay triangulation, a height-based vertical coordinate and C-grid staggering of its variables. Jagan and Schmidli ran ICON in numerical weather prediction mode at horizontal grid spacings of approximately 2 kilometers, 1 kilometer and 500 meters, all with 137 vertical levels and a model top at 30 kilometers. They then varied the maximum vertical grid spacing in the upper troposphere and lower stratosphere, the critical region spanning roughly 6 to 25 kilometers altitude, among 400, 200 and 100 meters. To anchor the finest end of the comparison, they added an online-nested large-eddy simulation that zoomed down to a remarkable 130 meters over the southern flight segment, using four nested domains stepping from 1 kilometer down to the 130-meter innermost nest.

The turbulence question was addressed by pitting two schemes against each other. The first is the operational turbulent kinetic energy scheme, which predicts a single TKE value and augments the classical shear-driven turbulence budget with empirical extra source terms, one for large-scale horizontal shear and one for breaking subgrid-scale mountains, both originally designed to support aviation turbulence products such as the eddy dissipation rate. The second is the newly developed two-energy scheme, which carries two prognostic turbulence energies, dynamically adjusts its mixing length, avoids prescribed minimum diffusion coefficients and employs an assumed probability density function method for buoyancy production, all intended to better handle the anisotropic, strongly stratified turbulence found aloft rather than the boundary-layer conditions for which most closures were originally tuned.

The reference simulation, run at 1 kilometer resolution with the two-energy scheme, painted a vivid picture of the event. Alternating bands of ascent and descent stretched downstream of the main ridge from the mid-troposphere into the lower stratosphere, strongest in the troposphere and weakening with height. A powerful wave with vertical velocities exceeding 3 meters per second rose above the Mount Cook region, New Zealand’s highest summit, while a weaker wave formed above the Two Thumb Range farther southeast. The simulated wave field proved quasi-stationary across the three-hour flight window, which made the comparison with the aircraft data meaningful. Against the observations, the model agreed reasonably well on the lower flight leg but underestimated wave amplitude on the upper leg, and the large-eddy simulation better captured the wavelength and phase of the waves even though the coarser NWP runs better reproduced their amplitude.

Resolution emerged as a decisive factor. At 2 kilometers, the simulated waves took on an artificially hydrostatic character, their horizontal wavelengths stretching as the model lost the ability to represent shorter scales. At 500 meters the waves became more non-hydrostatic and vertically aligned, and the number of resolved waves multiplied as shorter wavelengths entered the picture, an effect even more pronounced at 130 meters in the large-eddy simulation, where clear examples of trapped lee waves appeared in the stable layer below about 5 kilometers. Vertical resolution mattered just as much: simulations with 400-meter vertical spacing showed clear differences from the reference, particularly in the stratosphere, while 200-meter and 100-meter runs were nearly identical, indicating that near-convergence of the primary wave requires vertical grid spacing of 200 meters or finer in the upper troposphere and lower stratosphere.

The most striking finding concerned the turbulence schemes themselves. Both produced essentially the same resolved wave structures, yet the parameterized turbulent kinetic energy differed enormously between them. The operational TKE scheme generated substantially higher TKE throughout the wave field, with turbulence patches sprinkled across the troposphere and even reaching into the lower stratosphere, whereas the two-energy scheme sensibly confined turbulence to the atmospheric boundary layer and the strongest low-level wave regions. By systematically switching off the empirical source terms, the researchers traced the excess to the horizontal-shear term. This term is a two-dimensional Smagorinsky-type closure that assumes grid-scale deformation feeds an irreversible cascade into unresolved turbulence, but in the simulated mountain-wave case much of the deformation came from large, coherent, largely reversible gravity waves. Unable to tell the difference, the closure converted wave-related deformation into spurious TKE, which is why the excess energy appeared spatially correlated with the wave field rather than with genuinely turbulent regions.

Further confirmation came from bulk diagnostics averaged over a subdomain of the Southern Alps. Area-averaged vertical velocity variance at 500 meters matched the large-eddy simulation closely in the lower troposphere, while the 1 and 2 kilometer runs systematically underestimated it in the trapped-lee-wave layer. Above that layer, the 1 and 0.5 kilometer runs agreed well, signaling near-convergence for the dominant wave. Notably, the momentum flux profiles at 1 kilometer were nearly identical regardless of turbulence scheme, and the spurious horizontal-shear TKE left no corresponding signature in the wave drag, a decoupling the authors interpret as further evidence that the extra turbulence was artificial. The low-level gravity-wave momentum flux, a key target quantity for gravity-wave drag parameterizations, kept increasing as resolution improved from 1 kilometer to 500 meters, meaning the bulk momentum budget had not yet converged even at these very fine grids. Intriguingly, the comparison also showed that the large-eddy simulation is not automatically the more realistic reference: at 130 meters it resolved the shortest waves’ wavelength and phase but damped their amplitude, likely over-dissipating near-grid-scale wave energy, and it underestimated the vertical velocity fluctuations observed in the upper troposphere.

The practical implications reach well beyond academic curiosity. Turbulence in the upper troposphere and lower stratosphere is intermittent and localized, shaping stratosphere-troposphere exchange of greenhouse gases and pollutants and posing real hazards on long-haul routes that cross major mountain ranges. The study’s guidance is concrete: reliable simulation of small-scale mountain waves and turbulence at kilometer-scale resolution demands horizontal grid spacings of 1 kilometer or finer and vertical spacings of 200 meters or finer in the UTLS, while trapped lee waves and downstream wave structure remain stubbornly resolution-sensitive even then. Equally important, operational centers running kilometer-scale models over mountainous terrain should reconsider the empirical horizontal-shear and subgrid-orography terms of their TKE closures, which can inflate turbulence where none exists, or adopt alternatives like the two-energy scheme, which behaves stably in strongly stratified conditions without exhibiting the artifact. The authors caution that they do not claim the new scheme is more accurate everywhere, and genuine sub-kilometer turbulence downstream of the secondary ridge remained under-resolved in every configuration, including the large-eddy run. Future work will extend the analysis to additional DEEPWAVE cases and seek to couple the two-energy scheme with gravity-wave parameterizations, bridging the gap between explicitly resolved and parameterized wave-turbulence interactions in global and climate models, a step that could ultimately make turbulence forecasts that pilots and passengers depend on considerably more trustworthy.

Subject of Research: Simulation of mountain waves and turbulence in the upper troposphere and lower stratosphere using the ICON model at varying resolutions and turbulence schemes

Article Title: Impact of model resolution and turbulence scheme on the representation of mountain waves and turbulence

Article References: Impact of model resolution and turbulence scheme on the representation of mountain waves and turbulence. (n.d.). https://doi.org/10.5194/acp-26-13721-2026

Image Credits: AI Generated

DOI: 10.5194/acp-26-13721-2026

Keywords: mountain waves, gravity waves, turbulence, ICON model, DEEPWAVE, large-eddy simulation, turbulent kinetic energy, model resolution, upper troposphere, lower stratosphere, aviation safety, numerical weather prediction

A new study published in the journal Weather and Climate Dynamics by Ninghui Li of Tsinghua University and colleagues now offers a sharper lens on this problem. The team analyzed twenty-one years of warm-season data, from 2000 to 2020, drawn from three of the most modern atmospheric reanalysis products available: the European Centre for Medium-Range Weather Forecasts’ ERA5, NASA’s MERRA-2, and the Japan Meteorological Agency’s JRA-3Q. By combining a sophisticated vortex-tracking algorithm with a purpose-built diagnostic based on potential vorticity tendencies, they have produced one of the most detailed mechanistic accounts to date of how the anticyclone is born, moves, strengthens, and decays.

The first headline finding concerns structure. For years, scientists debated whether the anticyclone was fundamentally bimodal, alternating between centers over the Iranian Plateau and the Tibetan Plateau, or whether it simply drifted between them. The new analysis, performed on the 370 Kelvin isentropic surface using the Montgomery stream function, a dynamically consistent measure of flow on surfaces of constant potential temperature, confirms that the system is robustly trimodal. Three preferred centers emerge: one near 50 degrees east over the Iranian Plateau, one near 90 degrees east over the Tibetan Plateau, and a third over the Western Pacific near 135 to 150 degrees east, corresponding to the well-known Bonin High. All three reanalysis products agree on this threefold structure, and the agreement is particularly strong between JRA-3Q and ERA5.

The tracking algorithm itself is elegant in its simplicity. The researchers first locate the zero-zonal-wind ridgeline, the line separating easterly tropical flow from westerly subtropical flow, and then search for local maxima in the Montgomery stream function along that line. Each candidate center must pass strict filters: the relative vorticity at the center and its neighbors must be anticyclonic, the winds poleward must be westerly while those equatorward must be easterly, and the ridgeline must be long enough to exclude small-scale noise. Vortices that persist for more than eighteen hours and move less than ten degrees between successive six-hour snapshots are classified as persistent; the rest are transient. Persistent vortices accounted for more than 65 percent of all identified centers in ERA5 and JRA-3Q, underscoring how stable these features can be.

The seasonal choreography of the three modes is striking. Tibetan Plateau centers dominate in May, Iranian Plateau centers take over from mid-June to mid-July, and the balance shifts back toward the Tibetan Plateau as the Bonin High emerges in August and September, coinciding with the maturation of the Western North Pacific monsoon. The latitude of the vortices also migrates, drifting northward to about 40 degrees north between mid-July and mid-August before retreating southward. Many features show evidence of westward propagation, though eastward motion appears early and late in the season, and time-longitude diagrams reveal tails of low potential vorticity stretching in both directions, the telltale signature of eddy shedding, in which subsidiary anticyclones break away from the main circulation.

The heart of the study, however, lies in its diagnostic innovation. Potential vorticity, a quantity that combines rotation and stratification, is conserved in adiabatic, frictionless flow, making it a powerful tracer of atmospheric motion. But instantaneous potential vorticity fields cannot distinguish between a vortex that is moving and one that is intensifying in place. To resolve this ambiguity, the team developed a decomposition of the potential vorticity tendency, separating dynamical contributions from horizontal advection of potential vorticity by the winds from thermodynamic contributions arising from diabatic heating, both latent heating from condensation in convective clouds and radiative heating from sunlight and infrared exchange.

The results reveal a characteristic tripole pattern in the potential vorticity tendency around each anticyclonic vortex. An advective dipole, with positive tendencies to the west of the center and negative tendencies to the east, governs the eastward translation of the vortex: positive tendencies erode the low-potential-vorticity anomaly on the western flank while negative tendencies reinforce it on the eastern flank, nudging the entire core eastward. Superimposed on this dipole is a central monopole, driven mainly by diabatic heating and its vertical gradient, which modulates the vortex’s intensity without displacing it. A negative central tendency strengthens the anticyclone; a positive one weakens it. This separation of propagation from intensification is precisely what earlier diagnostics could not achieve.

The heating story is nuanced. Deep convective latent heating, concentrated below and to the east of the vortex centers, generates negative potential vorticity tendencies that intensify the anticyclone, particularly for the Tibetan Plateau mode, where heating along the southern slopes of the Himalayas is strongest. Radiative heating, by contrast, generally acts to spin the anticyclone down: because radiative heating increases with height through the upper troposphere and lower stratosphere, its vertical divergence produces positive potential vorticity tendencies that erode the low-potential-vorticity core. Latent heating partially offsets this radiative damping near the vortex centers. Meanwhile, the composite analysis shows that diabatic heating exerts a southward pull on the vortices, tugging them back toward the convective core of the monsoon and inhibiting their escape from it.

When it comes to propagation, the winds rule. Mean zonal advection by the subtropical westerly jet pushes all three vortex modes eastward relative to the surface, but meridional advection, the dominant term in Rossby wave propagation, pushes them westward relative to the background flow, and the two effects largely offset each other in the net. The balance of terms differs across the reanalysis products, with MERRA-2 showing stronger radiative damping and weaker advective tendencies than ERA5 or JRA-3Q, differences the authors attribute in part to how each system represents anvil cloud radiative effects and prognostic cloud ice. These inter-product discrepancies are a sobering reminder that mechanistic attribution in the upper troposphere and lower stratosphere still carries real uncertainty.

The implications extend well beyond academic bookkeeping. Because the anticyclone controls the leakage of Asian monsoon pollution and moisture into the global stratosphere, a reliable framework for separating its propagation from its intensification could improve predictions of stratospheric composition and, ultimately, of monsoon-related climate variability itself. The authors suggest that their potential vorticity tendency diagnostic could help clarify the differences between westward- and eastward-shedding eddies, processes first linked to baroclinic instability more than two decades ago but never fully quantified. Future work, they note, will need objective criteria for identifying eddy shedding events and a fuller accounting of data assimilation effects and parameterized momentum sources. For now, the study establishes a unified theoretical framework for one of the atmosphere’s most important summer circulations, showing that winds set the anticyclone’s course while heating sets its strength, a division of labor now made visible for the first time.

Subject of Research: Dynamics and potential vorticity tendency diagnostics of the Asian Summer Monsoon Anticyclone in the upper troposphere and lower stratosphere

Article Title: Dynamics of the Asian Summer Monsoon Anticyclone: insights from potential vorticity tendency diagnostics

Article References: Li, N., Wright, J. S., Rupp, P., Ming, A., Zhang, S., & Gao, J. (2026). Dynamics of the Asian Summer Monsoon Anticyclone: insights from potential vorticity tendency diagnostics. Weather and Climate Dynamics, 7(3), 1853-1874. https://doi.org/10.5194/wcd-7-1853-2026

Image Credits: AI Generated

DOI: 10.5194/wcd-7-1853-2026

Keywords: Asian Summer Monsoon Anticyclone, potential vorticity, upper troposphere, lower stratosphere, diabatic heating, vortex tracking, reanalysis, Bonin High, Tibetan Plateau, eddy shedding, monsoon circulation, atmospheric dynamics

The stakes of this question are considerable. Dust particles that reach the upper troposphere can serve as ice nuclei, seeding the formation of cirrus clouds that modulate how much sunlight Earth reflects and how much infrared radiation it traps. Because cirrus clouds exert a complex influence on the planet’s radiation budget, the abundance and composition of particles available to nucleate ice crystals matter for climate projections. Dust in the upper troposphere is also positioned for long-range travel: once entrained in the strong westerly jet streams that circle the globe at mid-latitudes, particles can be carried across entire continents before gravitational settling, precipitation, or mixing removes them from the airstream. Understanding how dust gets to those altitudes in the first place is therefore a prerequisite for modeling both its climatic effects and its intercontinental journeys.

Observational evidence at these heights has been fragmentary. Ground-based and satellite lidar instruments can detect dust layers aloft by their optical signatures, and aircraft campaigns and balloon-borne sensors have sampled particles directly in the upper troposphere on occasion. Simulations have traced plausible transport pathways connecting source deserts to remote sampling sites. What has remained scarce, however, is in situ evidence capturing how dust is distributed layer by layer as it rises through the troposphere and crosses the tropopause, the transition zone that separates the troposphere, where most weather occurs, from the stably stratified stratosphere above. That observational gap has left a key stage of the dust journey poorly documented, forcing modelers to rely on indirect constraints when validating how their schemes lift and loft mineral particles.

The new measurements come from a location unusually well suited to the task. The launch site is Golmud, a city sitting at roughly 2,800 meters above sea level in the Qaidam Basin on the northern flank of the Qinghai-Tibet Plateau. While Golmud is not among the highest points of the plateau, a balloon released from there already begins several kilometers closer to the tropopause than one launched from a lowland site. That head start shortens the ascent, reduces the time and battery resources consumed before the instrument package reaches the critical layers, and improves the odds of capturing clean, high-resolution data on how particles behave near the troposphere-stratosphere boundary. In effect, the plateau’s elevation converts a routine sounding into a targeted probe of one of the atmosphere’s most consequential interfaces.

The observations were carried out as part of the Sounding Water Vapour, Ozone, and Particle campaign, known by the acronym SWOP, organized by the Institute of Atmospheric Physics. Corresponding author Jianchun Bian led the campaign, working with co-authors including atmospheric scientist Dan Li, senior engineer Zhixuan Bai, and other specialists. Since 2009, the team has used instrumented balloons to measure the composition of the atmosphere over the Qinghai-Tibet Plateau, building one of the longer continuous records of vertical profiles in this topographically complex region. The plateau itself plays an outsized role in Asian meteorology: its massive elevated terrain redirects winds, pumps air upward through deep convection and orographic lifting, and influences the very circulation systems that can carry aerosols to extreme altitudes.

This was not the team’s first encounter with high-altitude dust. In March 2021, a SWOP balloon sounding over Golmud documented dust in the upper troposphere and lower stratosphere, with trajectory analysis tracing the particles near the tropopause back to a dust storm over the Middle East and northeastern Africa. That earlier detection demonstrated the potential of the technique but left open the question of whether such events could be observed again under more favorable circumstances. The 2023 campaign provided exactly that opportunity, because a dust event was directly affecting Golmud at the time of the observations, allowing the researchers to design their soundings around a known transport episode rather than stumbling upon one after the fact.

The experimental design was elegantly simple. The team conducted two balloon soundings: the first before the dust arrived, establishing a reference profile of the particle population over Golmud, and a second during the event, with an instrumented balloon rising through the atmosphere carrying a compact particle counter. When the researchers compared the two vertical profiles, the difference was unmistakable. Larger particles associated with dust were more abundant throughout the troposphere during the event, and critically, the enhancement extended above the tropopause itself. A balloon sounding, as Bian explained, provides a vertical snapshot of the atmosphere, giving researchers a direct, layer-by-layer view of its particles; combined with satellite observations and atmospheric simulations, that snapshot can help reveal how dust travels from distant deserts into the lower stratosphere.

Having established that the particles were present, the team turned to the question of origin. By combining the balloon records with satellite observations and atmospheric transport simulations, the researchers traced the air masses carrying the dust back to their source regions, and the answer revealed a layered transport story. Dust at lower altitudes came mainly from the nearby Taklamakan Desert, the vast sand sea of northwestern China that lies within relatively short reach of the Qaidam Basin. The dust found above the tropopause, by contrast, was traced to the much more distant Thar Desert, on the Indian subcontinent, in an air-mass journey of roughly thirty hours to reach Golmud. The evidence suggests that a trough and jet streams helped lift dust over the Thar Desert, southwesterly winds then carried it toward Golmud, and the high terrain of the Tibetan Plateau provided the final lift that pushed the particles even higher.

That sequence illustrates why the Tibetan Plateau occupies a special place in aerosol transport science. The plateau’s bulk acts as an elevated heating surface and a physical barrier, and air approaching it from the south and west is forced to rise, in some cases carrying embedded aerosol layers across altitude thresholds they could not otherwise attain. For dust originating in the Thar Desert, the plateau appears to function as the last step of an elevator, converting a long-range transport episode into a stratosphere-adjacent injection. The distinction between the local Taklamakan contribution at lower levels and the remote Thar contribution above the tropopause also underscores that different source regions populate different vertical layers, a nuance that coarse models may struggle to reproduce without targeted observational validation.

The measurements arrive at a moment when the scientific community is working to constrain how much mineral dust enters the lower stratosphere and what that influx means for climate. The new dataset provides valuable observational benchmarks for evaluating dust-transport models, offering vertical structure information that satellites alone cannot supply, and it highlights the value of sustained, long-term balloon observations over the Qinghai-Tibet Plateau. As the SWOP record continues to grow, each dust episode captured by these soundings adds a data point to a sparsely sampled but climatically important corner of the atmosphere, where the fate of desert dust, and its influence on ice clouds and the energy balance of the planet, is ultimately decided.

Subject of Research: Balloon-borne in situ measurements of desert dust transport to the tropopause layer over the northern Qinghai-Tibet Plateau

Article Title: A balloon offers a fresh eye on desert dust’s journey to the tropopause

Article References: A balloon offers a fresh eye on desert dust’s journey to the tropopause. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: desert dust, tropopause, Qinghai-Tibet Plateau, balloon sounding, aerosol transport, ice nuclei, cirrus clouds, Taklamakan Desert, Thar Desert, SWOP campaign, upper troposphere, lower stratosphere