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In order to investigate the driving of the QBO a high-resolution, convection-permitting run of the ICON model with 5km grid spacing was performed. Neither convection nor gravity waves (GWs) were parametrized. Here we analyze the resolved GWs in the model data by applying a small-volume sinusoidal fit method (S3D). By using a cascade of cube sizes, horizontal wavelengths of 150km - 2000km are addressed. This acts as a compromise between spectral resolution and spatial location. Phase speed spectra and gravity wave momentum flux (GWMF) can be reconstructed for individual regions and single snap-shots. Via the comparison of phases from wave fits of temperature and winds, the vertical propagation direction of individual waves can be separated and ray-tracing can be initialized accordingly. Using the results of this analysis we study the effect of the critical level GW filtering by comparing the vertical variation of phase speed spectra by means of blocking diagrams. Despite the generally good agreement, GWs with unexpected phase speeds at given altitudes due to critical level filtering are present. Multiple potential reasons are identified. Ray-tracing studies are carried out to investigate the potential influence of these various processes and quantify deviations from simple propagation and filtering assumptions used in GW parametrizations. The origin of these GWs is investigated and the regional variation of the blocking due to wind filtering is studied in more detail. Further, a ray-tracing is initialized using the results to improve the understanding of the role of horizontal GW propagation when compared to GW parametrization., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Absolute values of gravity wave momentum flux (GWMF) deduced from satellite measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument and the High Resolution Dynamics Limb Sounder (HIRDLS) are correlated with sea surface temperature (SST) with the aim of identifying those oceanic regions for which convection is a major source of gravity waves (GWs). Our study identifies those latitude bands where high correlation coefficients indicate convective excitation with confidence. This is based on a global ray-tracing simulation, which is used to delineate the source and wind-filtering effects. Convective GWs are identified at the eastern coasts of the continents and over the warm water regions formed by the warm ocean currents, in particular the Gulf Stream and the Kuroshio. Potential contributions of tropical cyclones to the excitation of the GWs are discussed. Convective excitation can be identified well into the mid-mesosphere. In propagating upward, the centers of GWMF formed by convection shift poleward. Some indications of the main forcing regions are even shown for the upper mesosphere/lower thermosphere (MLT).

In order to reduce uncertainties in modeling the stratospheric circulation, global observations of gravity wave momentum flux (GWMF) vectors are required for comparison with distributions of resolved and parametrized GWMF in global models. For the first time, we derive GWMF vectors globally from data of a nadir-viewing satellite instrument: we apply a 3D method to an Atmospheric Infrared Sounder (AIRS) temperature dataset that was optimized for gravity wave (GW) analysis. For January 2009, the resulting distributions of GW amplitudes and of net GWMF highlight the importance of GWs in the polar vortex and the summertime subtropics. Net GWMF is preferentially directed opposite to the background wind, and, interestingly, it is dominated by large amplitude GWs of relatively long horizontal wavelength. For convective GW sources, these large horizontal scales are in contradiction with traditional thoughts. However, the observational filter effect needs to be kept in mind when interpreting the results.

Gravity waves (GWs) from convection have horizontal wavelengths typically shorter than 100 km. Resolving these waves in state-of-the-art atmospheric models still remains challenging. Also, their time-dependent excitation process cannot be represented by a common GW drag parametrization with static launch distribution. Thus, the aim of this paper is to investigate the excitation and three-dimensional propagation of GWs forced by deep convection in the troposphere and estimate their influence on the middle atmosphere. For that purpose, the GW ray tracer Gravity-wave Regional Or Global Ray Tracer (GROGRAT) has been coupled to the Yonsei convective GW source model. The remaining free model parameters have been constrained by measurements. This work led to a coupled convective GW model representing convective GWs forced from small cells of deep convection up to large-scale convective clusters. In order to compare our simulation results with observed global distributions of momentum flux, limitations of satellite instruments were taken into account: The observational filter of a limb-viewing satellite instrument restricts measurements of GWs to waves with horizontal wavelengths longer than 100 km. Convective GWs, however, often have shorter wavelengths. This effect is taken into account when comparing simulated and observable GW spectra. We find good overall agreement between simulated and observed GW global distributions, if superimposed with a nonorographic background spectrum for higher-latitude coverage. Our findings indicate that parts of the convective GW spectrum can indeed be observed by limb-sounding satellites.

A new data set of atomic oxygen abundance in the upper mesosphere and lower thermosphere is presented. The data are derived from the nighttime atomic oxygen green line limb emission measurements of the SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) instrument on the European Environmental Satellite. The temporal coverage is October 2002 until April 2012, and the latitudinal extent is 50°S to 80°N at 10 P.M. local time. This data set is compared to other satellite data sets, in particular to recently published data of SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) and the Mass Spectrometer and Incoherent Scatter model. SCIAMACHY atomic oxygen peak abundances are typically 3–6×1011 mol/cm3 at the atomic oxygen maximum region, depending on latitude and season. These values are similar to previous values based on chemiluminescence measurements of the atomic oxygen three-body recombination reaction but at least 30% lower than atomic oxygen abundances obtained from SABER.

The spectral distribution in terms of horizontal and vertical wavenumber is deduced for gravity wave (GW) momentum flux observations from space for the first time. The paper focuses on High Resolution Dynamics Limb Sounder (HIRDLS) observations in the subtropics and compares spectra over particularly strong deep convective forcing with a background inferred from regions of less momentum flux. The deep convective spectra are strongly enhanced at high horizontal wavenumbers over a wide range of vertical wavenumbers and phase speeds. The observations indicate that GWs generated by deep convection are an important contribution on top of the background spectrum due to other GW sources (at least about 20-30% on zonal average is from convective GWs). The implications for global modeling are discussed. Citation: Ern, M., and P. Preusse (2012), Gravity wave momentum flux spectra observed from satellite in the summertime subtropics: Implications for global modeling, Geophys. Res. Lett., 39, L15810, doi:10.1029/2012GL052659.

The quasi-biennial oscillation (QBO) of the zonal mean zonal wind is a dynamical phenomenon of the tropical middle atmosphere. Influences of the QBO can even be found at mid and high latitudes. It is widely accepted that the phase descent of alternating tropical easterlies and westerlies is driven by atmospheric waves of both global scale (equatorial wave modes like Kelvin, equatorial Rossby, Rossby-gravity, or inertia-gravity waves), as well as mesoscale gravity waves. However, the relative distribution of the different types of waves to the forcing of the QBO winds is highly uncertain. This is the case because until recently there were no high resolution long-term global measurements in the stratosphere. In our study we estimate Kelvin wave momentum flux and the contribution of zonal wind forcing by Kelvin waves based on space-time spectra determined from both Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements as well as temperatures from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. Peak values of total Kelvin wave zonal wind forcing found are about 0.2 m/s/day. There is good agreement between SABER and ECMWF results. Altitude-time cross sections are shown and the results are compared to the total wave forcing required to balance the background atmosphere. Sometimes Kelvin wave forcing is sufficient to explain almost the whole total wave forcing required for the momentum balance during the transition from QBO easterly to westerly winds. This is especially the case during the periods of strong westerly wind shear when the zonal wind is between -20 and 10 m/s at the equator in the altitude range 20 to 35 km. During other parts of the phases of strong westerly wind shear, however, the contribution of Kelvin waves can be comparably low and the missing wave forcing, which is often attributed to mesoscale gravity waves or intermediate scale waves, can be the by far dominant contribution of the QBO forcing. It is also found that seasonal variations of Kelvin wave accelerations could play an important role for the maintenance of the QBO westerly wind jets in the lower stratosphere.