The low background values at nighttime of the mesospheric hydroxyl (OH) radical make it easier to single out the atmospheric response to the external solar forcing in Polar Regions. Because of the short lifetime of HOx, it is possible to follow the trails of Solar Energetic Particle (SEP) events in the terrestrial atmosphere, as shown by Storini and Damiani (2008). The sensitivity of this indicator makes discernible not only extreme particle events with a flux peak of several thousand pfu [1 pfu = 1 particle/(cm2 s sr)] at energies >10 MeV, but also those with lower flux up to about 300 pfu. Using data from the Microwave Limb Sounder (MLS) on board the EOS AURA satellite, we examined the correlation of OH abundance vs. solar proton flux for almost all the identified SEP events spanning from November 2004 to December 2006 (later on no more SEP events occurred during Solar Cycle no. 23). The channels at energies greater than 5 MeV and 10 MeV showed the best correlation values (r ∼ 0.90–0.95) at altitudes around 65–75 km whereas, as expected, the most energetic channels were most highly correlated at lower altitudes. Therefore, it is reasonably possible to estimate the solar proton flux from values of mesospheric OH (and viceversa) and it could be useful in studying periods with gaps in the records of solar particles. 相似文献
A new and original stereo imaging method is introduced to measure the altitude of the OH nightglow layer and provide a 3D perspective map of the altitude of the layer centroid. Near-IR photographs of the OH layer are taken at two sites separated by a 645 km distance. Each photograph is processed in order to provide a satellite view of the layer. When superposed, the two views present a common diamond-shaped area. Pairs of matched points that correspond to a physical emissive point in the common area are identified in calculating a normalized cross-correlation coefficient (NCC). This method is suitable for obtaining 3D representations in the case of low-contrast objects. An observational campaign was conducted in July 2006 in Peru. The images were taken simultaneously at Cerro Cosmos (12°09′08.2″ S, 75°33′49.3″ W, altitude 4630 m) close to Huancayo and Cerro Verde Tellolo (16°33′17.6″ S, 71°39′59.4″ W, altitude 2272 m) close to Arequipa. 3D maps of the layer surface were retrieved and compared with pseudo-relief intensity maps of the same region. The mean altitude of the emission barycenter is located at 86.3 km on July 26. Comparable relief wavy features appear in the 3D and intensity maps. It is shown that the vertical amplitude of the wave system varies as exp (Δz/2H) within the altitude range Δz = 83.5–88.0 km, H being the scale height. The oscillatory kinetic energy at the altitude of the OH layer is comprised between 3 × 10−4 and 5.4 × 10−4 J/m3, which is 2–3 times smaller than the values derived from partial radio wave at 52°N latitude. 相似文献
The SCIAMACHY instrument on board Envisat is able to measure nearly all vibrational transitions of mesospheric hydroxyl – from the ultraviolet to the near infrared spectral region.
In this paper, we analyze SCIAMACHY limb emission data in the 1000–1750 nm spectral region by means of a new vibrational non-LTE model of OH. Several hydroxyl hotbands are identified. Vibrational non-LTE model calculations applying different collisional relaxation models are able to reproduce the measured spectra. Best agreement between model calculations and measured spectra is obtained, if a combination of multiquantum and step ladder single-quantum relaxation model is applied. Emissions from the OH(v = 9) vibrational state are used to derive chemical heating rates from the SCIAMACHY spectra. Instantaneous heating rates are in the order of 10 K/day. 相似文献
Based on an advanced numerical model for excited hydroxyl (OH*) we simulate the effects of gravity waves (GWs) on the OH*-layer in the upper mesosphere. The OH* model takes into account (1) production by the reaction of atomic hydrogen (H) with ozone (O3), (2) deactivation by atomic oxygen (O), molecular oxygen (O2), and molecular nitrogen (N2), (3) spontaneous emission, and (4) loss due to chemical reaction with O. This OH* model is part of a chemistry-transport model (CTM) which is driven by the high-resolution dynamics from the KMCM (Kühlungsborn Mechanistic general Circulation Model) which simulates mid-frequency GWs and their effects on the mean flow in the MLT explicitly. We find that the maximum number density and the height of the OH*-layer peak are strongly determined by the distribution of atomic oxygen and by the temperature. As a results, there are two ways how GWs influence the OH*-layer: (1) through the instantaneous modulation by O and T on short time scales (a few hours), and (2) through vertical mixing of O (days to weeks). The instantaneous variations of the OH*-layer peak altitude due to GWs amount to 5–10 km. Such variations would introduce significant biases in the GW parameters derived from airglow when assuming a constant pressure level of the emission height. Performing a sensitivity experiment we find that on average, the vertical mixing by GWs moves the OH*-layer down by ~2 to 7 km and increases its number density by more than 50%. This effect is strongest at middle and high latitudes during winter where secondary GWs generated in the stratopause region account for large GW amplitudes. 相似文献
In the frame of the European H2020 project ARISE, a short wave infrared (SWIR) InGaAs camera has been operated at the Haute-Provence Observatory, during a night that corresponds to the peak of Geminid meteor shower to investigate infrasound associated with meteor arrivals. This camera allows continuous observations during clear-sky nighttime of the OH airglow layer centered at 87 km. These observations were collocated with Rayleigh lidar measurements providing vertical temperature profiles from the lower stratosphere to the altitude of the OH layer around the mesopause. Spectral analysis of OH images did not allow to detect infrasound associated with meteor trails, however it reveals a peak corresponding to infrasound signals in the frequency band of those produced by ocean swell. Infrasound wave activity observed from ground-based microbarometers as well as the OH camera, appear to be modified with the presence of a temperature inversion described by Rayleigh lidar. Indeed, there is a difference in energy related to infrasonic activity between the first part of the night during the temperature inversion and after the inversion. 相似文献