This paper reviews recent progress toward understanding the dynamics of the middle atmosphere in the framework of the Atmospheric Dynamics Research InfraStructure in Europe (ARISE) initiative. The middle atmosphere, integrating the stratosphere and mesosphere, is a crucial region which influences tropospheric weather and climate. Enhancing the understanding of middle atmosphere dynamics requires improved measurement of the propagation and breaking of planetary and gravity waves originating in the lowest levels of the atmosphere. Inter-comparison studies have shown large discrepancies between observations and models, especially during unresolved disturbances such as sudden stratospheric warmings for which model accuracy is poorer due to a lack of observational constraints. Correctly predicting the variability of the middle atmosphere can lead to improvements in tropospheric weather forecasts on timescales of weeks to season. The ARISE project integrates different station networks providing observations from ground to the lower thermosphere, including the infrasound system developed for the Comprehensive Nuclear-Test-Ban Treaty verification, the Lidar Network for the Detection of Atmospheric Composition Change, complementary meteor radars, wind radiometers, ionospheric sounders and satellites. This paper presents several examples which show how multi-instrument observations can provide a better description of the vertical dynamics structure of the middle atmosphere, especially during large disturbances such as gravity waves activity and stratospheric warming events. The paper then demonstrates the interest of ARISE data in data assimilation for weather forecasting and re-analyzes the determination of dynamics evolution with climate change and the monitoring of atmospheric extreme events which have an atmospheric signature, such as thunderstorms or volcanic eruptions.

Results of systematic analysis of propagation directions and horizontal velocities of gravity waves (GWs) and spread F structures in low-latitude ionosphere (magnetic inclination~27°) in Tucumán region, Argentina, are presented. Measurements were carried out by multipoint continuous Doppler system during 1 year from December 2012 to November 2013. It was found that meridian propagation of GWs dominated and that southward propagation prevailed in the local summer. Oblique spread structures observed in Doppler shift spectrograms and associated with spread F propagated roughly eastward at velocities from 70 to~180 m/s and were observed at night from~September to~March. The velocities were computed for 182 events and the azimuths for 64 events. Continuous Doppler sounding makes it possible to analyze more events compared to optical observations often used for propagation studies since the measurements do not depend on weather.

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[1] A statistical investigation into the horizontal propagation of $8-30 min gravity waves (GWs) in the ionosphere over a 1 year period from June 2010 to May 2011 is presented. The GWs were observed by multipoint continuous Doppler sounding systems installed in the Czech Republic and in the Western Cape, South Africa. Measurements of GW propagation in the ionosphere over South Africa have never been presented before. Simultaneous measurements from nearby ionosondes made it possible to estimate the height of the GW observations and show that the analyzed GWs propagated at altitudes from $150 to $250 km. The analyzed waves were mainly observed after sunrise and around sunset. Our statistical study shows that the analyzed GWs propagated with horizontal velocities from $70 to 250 m/s. The average observed horizontal velocities were $100 m/s in the local summer and 125-150 m/s in the local winter. The waves propagated approximately poleward in the local summer, whereas roughly equatorward propagation was observed in the local winter. Westward propagation was rarely observed in the Czech Republic, and eastward (southeast) propagation was seldom observed in South Africa. A comparison with neutral wind velocities shows that the analyzed GWs propagated approximately against the neutral winds calculated by the HWM07 model. The estimated horizontal wavelengths of the analyzed waves were $100-300 km.

[1] Using a five-point continuous Doppler sounding system operating at 3.59 MHz, developed at the Institute of Atmospheric Physics AS CR (IAP), we investigate propagation directions and velocities of gravity waves (GWs) at altitudes from ∼150 to ∼250 km over the western part of the Czech Republic. The velocities and directions are computed from the time delays between the observations of corresponding GWs at different reflection points that correspond to various sounding paths. We focused on the GWs that produce an S-shaped trace in Doppler shift spectrograms and are observed close to sunrise and sunset. We have selected about 100 of such events. Our results show that the analyzed GWs propagate with typical horizontal velocities from ∼100 to ∼200 m/s. The north-south component of GW velocities depends on the season, it is directed northward in the summer and southward in the winter. At the same time, the north-south component of the neutral winds calculated by the horizontal wind model HWM07 has the opposite sign. Typical observed periods of the analyzed waves range from ∼10 to ∼30 min.