| 1. |
- Bender, Stefan, et al.
(författare)
-
Comparison of nitric oxide measurements in the mesosphere and lower thermosphere from ACE-FTS, MIPAS, SCIAMACHY, and SMR
- 2015
-
Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 8:10, s. 4171-4195
-
Tidskriftsartikel (refereegranskat)abstract
- We compare the nitric oxide measurements in the mesosphere and lower thermosphere (60 to 150 km) from four instruments: the Atmospheric Chemistry Experiment–Fourier Transform Spectrometer (ACE-FTS), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY), and the Sub-Millimetre Radiometer (SMR). We use the daily zonal mean data in that altitude range for the years 2004–2010 (ACE-FTS), 2005–2012 (MIPAS), 2008–2012 (SCIAMACHY), and 2003–2012 (SMR).We first compare the data qualitatively with respect to the morphology, focussing on the major features, and then compare the time series directly and quantitatively. In three geographical regions, we compare the vertical density profiles on coincident measurement days. Since none of the instruments delivers continuous daily measurements in this altitude region, we carried out a multi-linear regression analysis. This regression analysis considers annual and semi-annual variability in the form of harmonic terms and inter-annual variability by responding linearly to the solar Lyman-α radiation index and the geomagnetic Kp index. This analysis helps to find similarities and differences in the individual data sets with respect to the inter-annual variations caused by geomagnetic and solar variability.
|
|
| 2. |
- Fytterer, Tilo, et al.
(författare)
-
Energetic particle induced intra-seasonal variability of ozone inside the Antarctic polar vortex observed in satellite data
- 2015
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 15:6, s. 3327-3338
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements from 2002 to 2011 by three inde-pendent satellite instruments, namely MIPAS, SABER, andSMR on board the ENVISAT, TIMED, and Odin satellitesare used to investigate the intra-seasonal variability of strato-spheric and mesospheric O3 volume mixing ratio (vmr) in-side the Antarctic polar vortex due to solar and geomagneticactivity. In this study, we individually analysed the relativeO3 vmr variations between maximum and minimum condi-tions of a number of solar and geomagnetic indices (F10.7cm solar radio flux, Ap index, ≥2 MeV electron flux). Theindices are 26-day averages centred at 1 April, 1 May, and1 June while O3 is based on 26-day running means from1 April to 1 November at altitudes from 20 to 70 km. Dur-ing solar quiet time from 2005 to 2010, the composite ofall three instruments reveals an apparent negative O3 sig-nal associated to the geomagnetic activity (Ap index) around1 April, on average reaching amplitudes between −5 and−10 % of the respective O3 background. The O3 responseexceeds the significance level of 95 % and propagates down-wards throughout the polar winter from the stratopause downto ∼ 25 km. These observed results are in good qualitativeagreement with the O3 vmr pattern simulated with a three-dimensional chemistry-transport model, which includes par-ticle impact ionisation.
|
|
| 3. |
- Kirkwood, Stella, et al.
(författare)
-
Ionization and NO production in the polar mesosphere during high-speed solar wind streams: model validation and comparison with NO enhancements observed by Odin-SMR
- 2015
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 33:5, s. 561-572
-
Tidskriftsartikel (refereegranskat)abstract
- Precipitation of high-energy electrons (EEP) intothe polar middle atmosphere is a potential source of signif-icant production of odd nitrogen, which may play a role instratospheric ozone destruction and in perturbing large-scaleatmospheric circulation patterns. High-speed streams of so-lar wind (HSS) are a major source of energization and pre-cipitation of electrons from the Earth’s radiation belts, butit remains to be determined whether these electrons makea significant contribution to the odd-nitrogen budget in themiddle atmosphere when compared to production by solarprotons or by lower-energy (auroral) electrons at higher al-titudes, with subsequent downward transport. Satellite ob-servations of EEP are available, but their accuracy is notwell established. Studies of the ionization of the atmospherein response to EEP, in terms of cosmic-noise absorption(CNA), have indicated an unexplained seasonal variation inHSS-related effects and have suggested possible order-of-magnitude underestimates of the EEP fluxes by the satelliteobservations in some circumstances. Here we use a model ofionization by EEP coupled with an ion chemistry model toshow that published average EEP fluxes, during HSS events,from satellite measurements (Meredith et al., 2011), are fullyconsistent with the published average CNA response (Ka-vanagh et al., 2012). The seasonal variation of CNA responsecan be explained by ion chemistry with no need for any sea-sonal variation in EEP. Average EEP fluxes are used to esti-mate production rate profiles of nitric oxide between 60 and100 km heights over Antarctica for a series of unusually wellseparated HSS events in austral winter 2010. These are com-pared to observations of changes in nitric oxide during theevents, made by the sub-millimetre microwave radiometer onthe Odin spacecraft. The observations show strong increasesof nitric oxide amounts between 75 and 90 km heights, at alllatitudes poleward of 60 ◦ S, about 10 days after the arrival ofthe HSS. These are of the same order of magnitude but gen-erally larger than would be expected from direct productionby HSS-associated EEP, indicating that downward transportlikely contributes in addition to direct production.
|
|
