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The Madden‐Julian oscillation (MJO) prominently influences weather systems in the tropical Indian Ocean region. Although understanding of the MJO has improved over the last decade, insufficient simulation of the MJO still considerably degrades forecasting skill of atmospheric models. In this study we investigate the interaction of gravity waves (GWs) from convection with the background atmosphere during MJO cycles between 1979 and 2010. For this, we utilize a parameterization of convective GW (CGW) forcing and propagation to evaluate the entire life cycle of GWs from their convective excitation to their dissipation in the tropical upper stratosphere region. CGW forcing at source level was calculated using the Song and Chun (2005, https://doi.org/10.1175/JAS-3363.1) parameterization. We performed simulations for all respective MJO phases and MJO cycles during a period of 32 years using Climate Forecast System Reanalysis data for the full spectrum of CGWs. Our results show a clear connection between 850 hPa winds and zonal momentum flux during all MJO phases. This prominent momentum flux feature changes with the progress of each MJO cycle. Zonal means of eastward directed momentum flux also show this correlation. Furthermore, we estimated the spectral characteristics of launched GWs and found significant GW momentum flux for horizontal wavelengths as short as 80 km at launch altitude. Eastward GW drag (GWD) consistently shows a maximum at altitudes below 40 km and prominent westward GWD at altitudes higher than 40 km. Additionally, we investigated the impact of the phase of the quasi‐biennial oscillation (QBO) on our findings with GWD found stronger during the QBO easterly phase compared to the QBO westerly phase. MJO affects forcing of convective gravity waves in the tropicsSource of convective gravity waves propagates eastward in the Indian Ocean and western Pacific regionConvective gravity wave forcing was found to be stronger during easterly QBO phase

A major sudden stratospheric warming event occurred on January 24, 2009 and showed a unique and pronounced planetary wave 2 amplitude with a subsequent split in the polar vortex. While research about the role of planetary waves during sudden stratospheric warming events exists, the contribution of gravity waves (GWs) is still uncertain. We therefore investigated the role of stratospheric GWs in the Northern Hemisphere during the 2009 winter season. We use observational data from NASA's Atmospheric Infrared Sounder (AIRS) satellite instrument for our analysis. Variances in the 4.3 µm brightness temperature perturbations are analyzed together with Level 3 temperature retrievals to investigate the connection between GWs and the warming event. Our planetary wave analysis shows zonal wavenumber 1 amplitudes during December 2008 and early January 2009. However, zonal wavenumber 2 is more dominant between mid‐January and January 24, 2009. We also found a decrease in Northern hemisphere GW activity a few days before the maximum warming and the wind reversal occur at 30 hPa altitude. Furthermore, prominent GW activity was found at Labrador Peninsula and southern Greenland, both are locations of elevated GW activity (hotspots), until mid‐January 2009. We discuss the potential of these orographic GWs to amplify planetary waves during the onset of the sudden stratospheric warming (SSW) event. Atmospheric Infrared Sounder (AIRS) satellite observations analyzed for gravity waves during the 2009 major sudden stratospheric warming (SSW) eventReduced gravity wave activity was found during the SSW eventProminent gravity wave activity was found at orographic hotspots prior the SSW event Atmospheric Infrared Sounder (AIRS) satellite observations analyzed for gravity waves during the 2009 major sudden stratospheric warming (SSW) event Reduced gravity wave activity was found during the SSW event Prominent gravity wave activity was found at orographic hotspots prior the SSW event

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. Coupled model of convective gravity wave forcing and three-dimensional propagation was developedDifferent scales of convective GW show remarkable difference in spectra and momentum flux distributionsFound very good agreement with satellite observations specifically in the tropics