Global Positioning System radio occultation measurements by FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere and Climate satellites were used to analyse the characteristics of the 8-h oscillation in sporadic E (E S) layers. Six-year averages based on the 3-monthly mean zonal means from December 2006 to November 2012 were constructed for the amplitude of the terdiurnal oscillation in the occurrence frequency of E S. A global distribution from 60°S to 60°N is given, revealing two peaks above 100 km during solstice with one maximum at low and midlatitudes (approximately 10°to 40°) in each hemisphere. During equinox, the global distribution is marked by two dominant peaks centred at midlatitudes, while an additional weak maximum is located at very low southern latitudes. The seasonal characteristics around 110 km reveal large values during equinox at low and midlatitudes (<40°N), while further peaks occur in April at >40°S and in July near 30°S. The pattern around 90 km is dominated by a broad peak between 20°and 30°S from March to September. Comparisons with the terdiurnal oscillation in the neutral atmosphere derived from zonal wind and vertical zonal wind shear simulated with a circulation model of the middle atmosphere, as well as with satellite observations of the terdiurnal tide in temperature, fit quite well for the results above 100 km, but do not show agreement for lower altitudes.

Abstract.Measurements from 2002 to 2011 by three independent satellite instruments, namely MIPAS, SABER, and SMR on board the ENVISAT, TIMED, and Odin satellites are used to investigate the intra-seasonal variability of stratospheric and mesospheric O 3 volume mixing ratio (vmr) inside the Antarctic polar vortex due to solar and geomagnetic activity. In this study, we individually analysed the relative O 3 vmr variations between maximum and minimum conditions of a number of solar and geomagnetic indices (F10.7 cm solar radio flux, Ap index, ≥2 MeV electron flux). The indices are 26-day averages centred at 1 April, 1 May, and 1 June while O 3 is based on 26-day running means from 1 April to 1 November at altitudes from 20 to 70 km. During solar quiet time from 2005 to 2010, the composite of all three instruments reveals an apparent negative O 3 signal associated to the geomagnetic activity (Ap index) around 1 April, on average reaching amplitudes between −5 and −10 % of the respective O 3 background. The O 3 response exceeds the significance level of 95 % and propagates downwards throughout the polar winter from the stratopause down to ∼ 25 km. These observed results are in good qualitative agreement with the O 3 vmr pattern simulated with a threedimensional chemistry-transport model, which includes particle impact ionisation.

Observations performed by the Earth Observing System Microwave Limb Sounder instrument on board the Aura satellite from 2004 to 2009 (2004 to 2014) were used to investigate the 27 day solar rotational cycle in mesospheric OH (O 3 ) and the physical connection to geomagnetic activity. Data analysis was focused on nighttime measurements at geomagnetic latitudes connected to the outer radiation belts (55°N/S–75°N/S). The applied superposed epoch analysis reveals a distinct 27 day solar rotational signal in OH and O 3 during winter in both hemispheres at altitudes >70 km. The OH response is positive and in‐phase with the respective geomagnetic activity signal, lasting for 1–2 days. In contrast, the O 3 feedback is negative, delayed by 1 day, and is present up to 4 days afterward. Largest OH (O 3 ) peaks are found at ~75 km, exceeding the 95% significance level and the measurement noise of <2% (<0.5%), while reaching variations of +14% (−7%) with respect to their corresponding background. OH at 75 km is observed to respond to particle precipitation only after a certain threshold of geomagnetic activity is exceeded, depending on the respective OH background. The relation between OH and O 3 at 75 km in both hemispheres is found to be nonlinear. In particular, OH has a strong impact on O 3 for relatively weak geomagnetic disturbances and accompanying small absolute OH variations (<0.04 ppb). In contrast, catalytic O 3 depletion is seen to slow down for stronger geomagnetic variations and OH anomalies (0.04–0.13 ppb), revealing small variations around −0.11 ppm.

Abstract. Global Positioning System radio occultation measurements by the FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere and Climate satellites were used to analyse the behaviour of the signature of the terdiurnal tide in sporadic E (E S ) layers at midlatitudes (43-63 • N). According to theory, the occurrence of E S is expected when the vertical zonal wind shear, which is mainly owing to solar tides, is negative. 4 yr means, based on 3-monthly running mean zonal means from December 2006-November 2010, were constructed for the terdiurnal oscillation in the occurrence frequency of E S . Comparison of the results with VHF meteor radar observations of the terdiurnal tide and the 8 h oscillation in the vertical zonal wind shear at Collm, Germany (51.3 • N, 13 • E) shows a clear correspondence between the 8 h in E S and in wind shear signature.

The 3‐D global chemistry and transport model (3dCTM) was used to investigate NO, OH, and O3 from January 2002 to May 2010 between 60 km and 133 km. Their daytime and nighttime mean zonal means (55°–75° geomagnetic latitude) were analyzed with respect to short‐term variations associated with particle precipitation. The corresponding ionization rates were derived from the 3‐D atmospheric ionization module Osnabrück (AIMOS), which is based on particle flux measurements. The trace gas variations with respect to their background were investigated by using a superposed epoch analysis. The 27 day signature associated with particle precipitation is found in NO, while it is only indicated in OH and O3 during winter. A varying solar spectrum associated with the 11 year solar cycle causes modifications of this signal up to 10%, while the main patterns are conserved. Published observations show a clear 27 day signal, qualitatively agreeing with the model results at altitudes >70 km except for O3 in Northern Hemisphere winter. Further differences occur with respect to the magnitude of the trace gas variations, primarily attributed to the different trace gas background and dynamical variations of the background atmosphere. Absolute OH variations are overestimated by the 3dCTM during winter, while the opposite is true for O3. These differences might originate from an unknown offset in AIMOS, incorrect chemical reaction rates, a different background of H2O and O3, and the model dynamics. However, their nonlinear relationship and their altitude of largest response are qualitatively captured in Southern Hemisphere winter.