A deep upper-air sounding 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. In combination with high-resolution meteorological analyses we identified an elevated source of gravity wave excitation.

The equatorial Kelvin wave (KW) is the most studied wave feature of the tropical atmosphere, yet not well quantified. Our study simultaneously analyses wind and temperature fields of KWs from ECMWF analyses without any prior data filtering. We provide the KW energy spectrum and its seasonal variability for three KW frequency ranges. We developed a webpage to show the spatial structure of KWs propagating in time through the ECMWF data, http://modes.fmf.uni-lj.si, updated on a daily basis.

The article presents MODES, a new software for the analysis of properties of balanced and inertio-gravity circulations across many scales in (re)analyses, weather forecasts and climate models. The software and real-time results based on ECMWF model can be found at http://meteo.fmf.uni-lj.si/MODES. Evaluation of models' ability to reproduce the unbalanced tropical circulation is expected to provide new insights on model performance that is helpful to diagnose deficiencies and define improvements.

The paper deals with the comparison of the common periodization methods used to obtain spectral fields of limited-area models for numerical weather prediction. The focus is on the impact the methods have on the spectra of the fields. The results show that detrending and DCT have little impact on the spectra, as does the Boyd method for extension zone. For the ALADIN and HIRLAM methods, the impact depends on the width of the extension zone - the wider the zone, the larger impact on the spectra.