Convection-generated gravity waves (CGWs) transport momentum and energy, and this momentum is a dominant driver of global features of Earth’s atmosphere’s general circulation (e.g. the quasi-biennial oscillation, the pole-to-pole mesospheric circulation). As CGWs are not generally resolved by global weather and climate models, their effects on the circulation need to be parameterized. However, quality observations of GWs are spatiotemporally sparse, limiting understanding and preventing constraints on parameterizations. Convection-permitting or -resolving simulations do generate CGWs, but validation is not possible as these simulations cannot reproduce the forcing convection at correct times, locations, and intensities. Here, realistic convective diabatic heating, learned from full-physics convection-permitting Weather Research and Forecasting (WRF) simulations, is predicted from weather radar observations using neural networks and a previously developed look-up table. These heating rates are then used to force an idealized GW-resolving dynamical model. Simulated CGWs forced in this way did closely resemble those observed by the Atmospheric InfraRed Sounder in the upper stratosphere. CGW drag in these validated simulations extends 100s of kilometers away from the convective sources, highlighting errors in current gravity wave drag parameterizations due to the use of the ubiquitous single-column approximation. Such validatable simulations have significant potential to be used to further basic understanding of CGWs, improve their parameterizations physically, and provide more restrictive constraints on tuning \textit{with confidence}.

A document by Emily J Lear. Click on the document to view its contents.

During winter, the latitude belt at 60S is one of the most intense hotspots of stratospheric gravity wave (GW) activity. However, producing accurate representations of GW dynamics in this region in numerical models has proved exceptionally challenging. One reason for this is that questions remain regarding the relative contributions of different orographic and non-orographic sources of GWs here. We use 3-D satellite GW observations from the Atmospheric InfraRed Sounder (AIRS) from winter 2012 in combination with the Gravity-wave Regional Or Global Ray Tracer (GROGRAT) to backwards ray trace GWs to their sources. We trace over 14.2 million rays, which allows us to investigate GW propagation and to produce systematic estimates of the relative contribution of orographic and non-orographic sources to the total observed stratospheric GW momentum flux in this region. We find that in winter 56% of momentum flux (MF) traces back to the ocean and 44% to land, despite land representing less than a quarter of the region’s area. This demonstrates that, while orographic sources contribute much more momentum flux per unit area, the large spatial extent of non-orographic sources leads to a higher overall contribution. The small islands of Kerguelen and South Georgia specifically contribute up to 1.6% and 0.7% of average monthly stratospheric MF, and the intermittency of these sources suggests that their short-timescale contribution is even higher. These results provide the important insights needed to significantly advance our knowledge of the atmospheric momentum budget in the Southern polar region.

The January 2022 Hunga Tonga–Hunga Haʻapai eruption was one of the most explosive volcanic events of the modern era, producing a vertical plume which peaked > 50km above the Earth. The initial explosion and subsequent plume triggered atmospheric waves which propagated around the world multiple times. A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves5,6 propagating at phase speeds of 318.2+/-6 ms-1 at surface level and between 308+/-5 to 319+/-4 ms-1 in the stratosphere, and gravity waves propagating at 238+/-3 to 269+/-3 ms-1 in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source. Latent heat release from the plume remained the most significant individual gravity wave source worldwide for >12 hours, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.

We conducted simulations with a 4-km resolution for Hurricane Joaquin in 2015 using the Weather Research and Forecast (WRF) model. The model data are used to study stratospheric gravity waves (GWs) generated by the hurricane and how they correlate with hurricane intensity. The simulation results show spiral GWs propagating upward and anticlockwise away from the hurricane center. GWs with vertical wavelengths up to 14 km are generated. We find that GW activity is more frequent and intense during hurricane intensification than during weakening, particularly for the most intense GW activity. There are significant correlations between the change of stratospheric GW intensity and hurricane intensity. Therefore, the emergence of intensive stratospheric GW activity may be considered a useful proxy for identifying hurricane intensification.

Aeolus is the first Doppler wind lidar in space. It provides unique high-resolution measurements of horizontal wind in the sparsely-observed upper-troposphere/lower-stratosphere (UTLS), with global coverage. In this study, Aeolus’ ability to resolve atmospheric gravity waves (GWs) is demonstrated. The accurate representation of these small-scale waves is vital to properly simulate dynamics in global weather and climate models. In a case study over the Andes, Aeolus GW measurements show coherent phase structure from the surface to the lower stratosphere, with wind perturbations >10 m/s, a vertical wavelength ~8 km and an along-track horizontal wavelength ~900 km. Good agreement is found between Aeolus and colocated satellite, ground-based lidar and reanalysis data sets for this example. Our results show that data from satellites of this type can provide unique information on GW sources and propagation in the UTLS, filling a key knowledge gap that underlies known major deficiencies in weather and climate modelling.

We conduct a mesoscale simulation with a 4-km resolution for Hurricane Joaquin in 2015 using the Weather Research and Forecast (WRF) model. The model data are used to study stratospheric gravity waves (GWs) generated by the hurricane and how they correlate with hurricane intensity. The simulation results show spiral GWs propagating upward and anticlockwise away from the hurricane center. GWs with vertical wavelengths up to 14 km are generated. We find that GW activity is more frequent during hurricane intensification than during weakening, particularly for the most intense GW activity. There is a significant time offset between the appearance of intense stratospheric GWs and hurricane intensification. Therefore, the emergence of intensive stratospheric GW activity may be considered a useful proxy for identifying hurricane intensification.

A mountain wave with a significant brightness temperature amplitude and ~500 km horizontal wavelength was observedover the Southern Andes on 24–25 July 2017 in AIRS/Aqua satellite data. In the MERRA-2 reanalysis data, a mesoscale vortex-like pattern appeared to the west of the Andes at 2 km, and the wind flowed over the Andes. VIIRS/Suomi-NPP did not detect the mountain waves; however, it observed concentric ring-like waves in the nightglow emissions at ~87 km with ~100 km wavelengths on the same night over and leeward of the Southern Andes. A ray tracing analysis showed that the mountain waves propagated to the east of the Andes, where concentric ring-like waves appeared while mountain waves broke. Therefore, the concentric ring-like waves were likely secondary gravity waves generated by momentum deposition that accompanied mountain wave breaking. These results provide the first direct evidence for secondary gravity waves generated by momentum deposition.