| 1. |
- Belova, A., et al.
(författare)
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Five-day planetary waves in the middle atmosphere from Odin satellite data and ground-based instruments in Northern Hemisphere summer 2003, 2004, 2005 and 2007
- 2008
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 26:11, s. 3557-3570
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Tidskriftsartikel (refereegranskat)abstract
- A number of studies have shown that 5-day planetary waves modulate noctilucent clouds and the closely related Polar Mesosphere Summer Echoes (PMSE) at the summer mesopause. Summer stratospheric winds should inhibit wave propagation through the stratosphere and, although some numerical models (Geisler and Dickinson, 1976) do show a possibility for upward wave propagation, it has also been suggested that the upward propagation may in practice be confined to the winter hemisphere with horizontal propagation of the wave from the winter to the summer hemisphere at mesosphere heights causing the effects observed at the summer mesopause. It has further been proposed (Garcia et al., 2005) that 5-day planetary waves observed in the summer mesosphere could be excited in-situ by baroclinic instability in the upper mesosphere. In this study, we first extract and analyze 5-day planetary wave characteristics on a global scale in the middle atmosphere (up to 54 km in temperature, and up to 68 km in ozone concentration) using measurements by the Odin satellite for selected days during northern hemisphere summer from 2003, 2004, 2005 and 2007. Second, we show that 5-day temperature fluctuations consistent with westward-traveling 5-day waves are present at the summer mesopause, using local ground-based meteor-radar observations. Finally we examine whether any of three possible sources of the detected temperature fluctuations at the summer mesopause can be excluded: upward propagation from the stratosphere in the summer-hemisphere, horizontal propagation from the winter-hemisphere or in-situ excitation as a result of the baroclinic instability. We find that in one case, far from solstice, the baroclinic instability is unlikely to be involved. In one further case, close to solstice, upward propagation in the same hemisphere seems to be ruled out. In all other cases, all or any of the three proposed mechanisms are consistent with the observations.
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| 2. |
- Belova, A., et al.
(författare)
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Planetary waves in ozone and temperature in the Northern Hemisphere winters of 2002/2003 and early 2005
- 2009
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Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 27:3, s. 1189-1206
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Tidskriftsartikel (refereegranskat)abstract
- Temperature and ozone data from the submillimetre radiometer (SMR) installed aboard the Odin satellite have been examined to study the relationship between temperature and ozone concentration in the lower and upper stratosphere in winter time. The retrieved ozone and temperature profiles have been considered between the range of 24-46 km during the Northern Hemisphere (NH) winter of December 2002 to March 2003 and January to March 2005. A comparison between the ozone mixing ratio and temperature fields has been made for the zonal means, wavenumber one variations and 5-day planetary waves. The amplitude values in temperature variations are similar to 5 K in the wavenumber one and 0.5-1 K in the 5-day wave. In ozone mixing ratio, the amplitudes reach similar to 0.5 ppmv in the wavenumber one and 0.05-0.1 ppmv in the 5-day wave. Several stratospheric warming events were observed during the NH winters of 2002/2003 and early 2005. Along with these warming events, amplification of the amplitude has been detected in wavenumber one (up to 30 K in temperature and 1.25 ppmv in ozone) and partly in the 5-day perturbation ( up to 2 K in temperature and 0.2 ppmv in ozone). In general, the results show the expected in-phase behavior between the temperature and ozone fields in the lower stratosphere due to dynamic effects, and an out-of-phase pattern in the upper stratosphere, which is expected as a result of photochemical effects. However, these relationships are not valid for zonal means and wavenumber one components when the wave amplitudes are changing dramatically during the strongest stratospheric warming event (at the end of December 2002/beginning of January 2003). Also, for several shorter intervals, the 5-day perturbations in ozone and temperature are not well-correlated at lower heights, particularly when conditions change rapidly. Odin's basic observation schedule provides stratosphere mode data every third day and to validate the reliability of the 5-day waves extracted from the Odin measurements, additional independent data have been analysed in this study: temperature assimilation data by the European Centre for Medium-range Weather Forecasts (ECMWF) for the NH winter of 2002/2003, and satellite measurements of temperature and ozone by the Microwave Limb Sounder (MLS) on board the Aura satellite for the NH winter in early 2005. Good agreement between the temperature fields from Odin and ECMWF data is found at middle latitude where, in general, the 5-day perturbations from the two data sets coincide in both phase and amplitude throughout the examined interval. Analysis of the wavenumber one and the 5-day wave perturbations in temperature and ozone fields from Odin and from Aura demonstrates that, for the largest part of the examined period, quite similar characteristics are found in the spatial and temporal domain, with slightly larger amplitude values seen by Aura. Hence, the comparison between the Odin data, sampled each third day, and daily data from Aura and the ECMWF shows that the Odin data are sufficiently reliable to estimate the properties of the 5-day oscillations, at least for the locations and time intervals with strong wave activity.
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| 3. |
- Kirkwood, Stella, et al.
(författare)
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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
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 33:5, s. 561-572
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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.
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| 4. |
- Kirkwood, Sheila, et al.
(författare)
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Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres : The importance of nitric oxide
- 2013
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 31:2, s. 333-347
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic I K indices) is examined. Calibrated PMSE reflectivities for the period May 2006-February 2012 are used from two 52.0/54.5 MHz radars located in Arctic Sweden (68 N, geomagnetic latitude 65 ) and at two different sites in Queen Maud Land, Antarctica (73/72 S, geomagnetic latitudes 62/63 ). In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours) at almost all local times. At the NH (auroral zone) site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral) sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic particle precipitation, the delayed response can largely be explained by changes in nitric oxide concentrations. Observations of nitric oxide concentration at PMSE heights by the Odin satellite support this hypothesis. Sensitivity to geomagnetic disturbances, including nitric oxide produced during these disturbances, can explain previously reported differences between sites in the auroral zone and those at higher or lower magnetic latitudes. The several-day lifetime of nitric oxide can also explain earlier reported discrepancies between high correlations for average conditions (year-by-year PMSE reflectivities and indices) and low correlations for minute-to-day timescales
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