Several decades after E. Dewan predicted that the shallowing of the atmospheric energy spectrum in mesoscale is produced by the inertia–gravity (IG) waves, global analyses have reached the resolution at which the IG waves across many scales are resolved. The authors discuss the spatial filtering method based on the Hough harmonics that provides the temperature and wind perturbations associated with the IG waves in global analysis data. The method is applied to the ECMWF interim reanalysis and the operational 2014–16 analysis fields. The derived spectrum of IG wave energy is divided into three regimes: a part associated with the large-scale unbalanced circulations that has a slope close to −1 for zonal wavenumbers 1 ≤ k ≤ 6, a synoptic-scale range between 3000 and around 500 km (7 ≤ k ≲ 35) that is characterized by a nearly −5/3 slope, and a mesoscale range below 500 km where the slope of the IG energy spectrum in the 2015/16 analyses is steeper. In contrast, the energy spectrum of the Rossby waves has a −3 slope for all zonal wavenumbers k > 6. Presented results suggest that energy associated with the IG modes exceeds the level of energy associated with the Rossby waves around zonal wavenumber 35. The exact wavenumber depends on the season and considered atmospheric depth and it is suggested as a cutoff scale for studies of gravity waves.

Abstract. An exceptionally deep upper-air sounding launched from Kiruna airport (67.82∘ N, 20.33∘ E) on 30 January 2016 stimulated the current investigation of internal gravity waves excited during a minor sudden stratospheric warming (SSW) in the Arctic winter 2015/16. The analysis of the radiosonde profile revealed large kinetic and potential energies in the upper stratosphere without any simultaneous enhancement of upper tropospheric and lower stratospheric values. Upward-propagating inertia-gravity waves in the upper stratosphere and downward-propagating modes in the lower stratosphere indicated a region of gravity wave generation in the stratosphere. Two-dimensional wavelet analysis was applied to vertical time series of temperature fluctuations in order to determine the vertical propagation direction of the stratospheric gravity waves in 1-hourly high-resolution meteorological analyses and short-term forecasts. The separation of upward- and downward-propagating waves provided further evidence for a stratospheric source of gravity waves. The scale-dependent decomposition of the flow into a balanced component and inertia-gravity waves showed that coherent wave packets preferentially occurred at the inner edge of the Arctic polar vortex where a sub-vortex formed during the minor SSW.

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General awareness and overall interest regarding hailstorms and hail properties in Europe have increased significantly in the last several decades and have resulted in numerous local, national, and even Europe-wide studies on hail and hail properties. To contribute to this field, we determined the hail climatology in the northeastern (NE) Adriatic region and analyzed its spatial and temporal patterns and performed an objectively derived weather type analysis of ERA5 daily mean data and instability indices. We studied the NE Adriatic region due to its focus on agricultural activities and on quality wine production. Our results are based on approximately 60 years of high spatial resolution measurements collected from 27 stations across complex terrain. The results show (i) high levels of spatial variability, (ii) significant annual variations, and (iii) hail throughout the whole year that (iv) intensifies in summer months. Furthermore, redistribution of hail among seasons (in particular, from summer to spring) was detected. Most significant changes were visible in the June-October period, with a negative trend of −0.06 hail days/year, and the period from November to March exhibited a positive trend of 0.13 hail cases/year. We found that deep cyclonic systems in front of and above our domain were most responsible for hail generation, often supported by southwesterly winds. Additionally, the vast majority of observed hail events occurred in unstable and sheared environments.

The Madden–Julian Oscillation (MJO) is the dominant form of intraseasonal variability in the Tropics. The MJO is a complex convectively coupled phenomenon, which is still poorly represented in the current generation of climate models, and our understanding of its essential dynamics and its influence on the midlatitude circulation is still incomplete. Here, we use a normal‐mode decomposition method to decompose the MJO systematically into Kelvin, inertio‐gravity (IG), and Rossby‐wave components in the ERA‐Interim reanalysis data for the period 1980–2015 to provide a climatology of the eight MJO phases for the Kelvin, IG, and Rossby‐wave components. Our analysis shows that the Rossby modes provide a larger contribution to the magnitude of the MJO in terms of geopotential height and winds than the Kelvin wave and IG modes. Moreover, the kinetic energy associated with the Rossby modes of the MJO accounts for about 93% of the kinetic energy. Our decomposition also shows that the Kelvin wave is the dominant mode in the unbalanced wave part, which is flanked by Rossby waves on both sides of the Equator, consistent with previous studies. The extratropical response to the MJO also consists of both IG and Rossby‐wave components in the Northern Hemisphere (NH). The midlatitude MJO response is also linked to well‐known teleconnection patterns like the North Atlantic Oscillation and the Pacific–North American pattern. The transient NH atmospheric response is fast, of the order of 5–7 days. While the extratropical response is dominated by Rossby waves, IG waves also show a prominent response in the NH.