The 8-h tide in the mesosphere and lower thermosphere over Collm (51.3° N; 13.0° E), 2004–2011

The horizontal winds in the mesosphere and lower thermosphere (MLT) at heights of about 80–100 km have been measured continuously since summer 2004 using an all-sky 36.2 MHz VHF meteor radar at Collm, Germany (51.3° N, 13° E). A climatology of the 8-h solar tide has been constructed from these data. The amplitude shows a seasonal behaviour with maximum values during the equinoxes, and it is generally increasing with altitude. The largest amplitudes are measured in autumn, partly reaching values up to 15 m s⁻¹. The phase, defined as the time of maximum eastward or northward wind, respectively, has earlier values in winter and later ones in summer. Except for summer, the phase difference between the zonal and meridional components is close to +2 h, indicating circular polarization of the tidal components. The vertical wavelengths are short in summer (~20 km) but significantly longer during the rest of the year. The terdiurnal tide is generally assumed to originate from either a terdiurnal component of solar heating or nonlinear interaction between the diurnal and semidiurnal tide. Analysing monthly means reveals positive correlation during the spring maximum, but negative correlation in autumn

Global distribution of the migrating terdiurnal tide seen in sporadic E occurrence frequencies obtained from GPS radio occultations

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 (ES) 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 ES. 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° 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

Model results of OH airglow considering four different wavelength regions to derive night-time atomic oxygen and atomic hydrogen in the mesopause region

Based on the zero-dimensional box model Module Efficiently Calculating the Chemistry of the Atmosphere/Chemistry As A Box model Application (CAABA/MECCA-3.72f), an OH airglow model was developed to derive night-time number densities of atomic oxygen ([O(3P)]) and atomic hydrogen ([H]) in the mesopause region ( ∼ 75–100&thinsp;km). The profiles of [O(3P)] and [H] were calculated from OH airglow emissions measured at 2.0&thinsp;µm by the Sounding of the Atmosphere using Broadband Emission Radiography (SABER) instrument on board NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. The two target species were used to initialize the OH airglow model, which was empirically adjusted to fit four different OH airglow emissions observed by the satellite/instrument configuration TIMED/SABER at 2.0&thinsp;µm and at 1.6&thinsp;µm as well as measurements by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument on board the Environmental Satellite (ENVISAT) of the transitions OH(6-2) and OH(3-1). Comparisons between the best-fit model obtained here and the satellite measurements suggest that deactivation of vibrationally excited OH(ν) via OH(ν ≥ 7)+O2 might favour relaxation to OH(ν′ ≤ 5)+O2 by multi-quantum quenching. It is further indicated that the deactivation pathway to OH(ν′ = ν − 5)+O2 dominates. The results also provide general support of the recently proposed mechanism OH(ν)+O(3P) → OH(0 ≤ ν′ ≤ ν − 5)+O(1D) but suggest slower rates of OH(ν = 8,7,6,5)+O(3P), partly disagreeing with laboratory experiments. Additionally, deactivation to OH(ν′ = ν − 5)+O(1D) might be preferred. The profiles of [O(3P)] and [H] derived here are plausible between 80 and 95&thinsp;km but should be regarded as an upper limit. The values of [O(3P)] obtained in this study agree with the corresponding TIMED/SABER values between 80 and 85&thinsp;km but are larger from 85 to 95&thinsp;km due to different relaxation assumptions of OH(ν)+O(3P). The [H] profile found here is generally larger than TIMED/SABER [H] by about 50&thinsp;% from 80 to 95&thinsp;km, which is primarily attributed to our faster OH(ν = 8)+O2 rate.</p

Energetic particle induced intra-seasonal variability of ozone inside the Antarctic polar vortex observed in satellite data

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 O3 volume mixing ratio (vmr) inside the Antarctic polar vortex due to solar and geomagnetic activity. In this study, we individually analysed the relative O3 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 O3 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 O3 signal associated to the geomagnetic activity (Ap index) around 1 April, on average reaching amplitudes between -5 and -10% of the respective O3 background. The O3 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 O3 vmr pattern simulated with a three-dimensional chemistry-transport model, which includes particle impact ionisation

Energetic particle induced inter-annual variability of ozone inside the Antarctic polar vortex observed in satellite data

Measurements from 2002-2011 by three independent satellite instruments, namely MIPAS, SABER, and SMR on board the ENVISAT, TIMED, and Odin satellites are used to investigate the inter-annual variability of stratospheric and mesospheric O3 volume mixing ratio (vmr) inside the Antarctic polar vortex due to solar and geomagnetic activity. In this study, we individually analysed the relative O3 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 O3 is based on 26 day running means from 1 April-1 November at altitudes from 20-70 km. During solar quiet time from 2005-2010, the composite of all three instruments reveals an apparent negative O3 feedback associated to the geomagnetic activity (Ap index) around 1 April, on average reaching amplitudes between -5 and -10% of the respective O3 background. The O3 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 O3 vmr pattern simulated with a three-dimensional chemistry-transport model, which includes particle impact ionisation

Energetic particle induced intra-seasonal variability of ozone inside the Antarctic polar vortex observed in satellite data

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 O3 volume mixing ratio (vmr) inside the Antarctic polar vortex due to solar and geomagnetic activity. In this study, we individually analysed the relative O3 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 O3 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 O3 signal associated to the geomagnetic activity (Ap index) around 1 April, on average reaching amplitudes between -5 and -10% of the respective O3 background. The O3 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 O3 vmr pattern simulated with a three-dimensional chemistry-transport model, which includes particle impact ionisation