Gravity Wave Mixing and Effective Diffusivity for Minor Chemical Constituents in the Mesosphere/Lower Thermosphere

Grygalashvyly, M.; Becker, Erich; Sonnemann, G. R.

doi:10.1007/s11214-011-9857-x

Cited by 39 publications

(52 citation statements)

References 94 publications

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“…Changes in the (zonal) wind patterns result in changes in the OH * distribution. Also, changes in gravity wave activity impact the distribution of chemical minor constituents by wave mixing transport only in the mesopause region (Grygalashvyly et al, , 2012. The photochemical rate constants depend on temperature.…”

Section: Discussionmentioning

confidence: 99%

“…The temperature has a strong annual variation at high latitudes but a less strong day-to-day variability which is larger at the equator. The variability in atomic oxygen triggered by vertical wind and gravity waves mixing transport has the strongest influence (Grygalashvyly et al, , 2012. The temperature has a minimum in summer, whereas atomic oxygen possesses a broad maximum over winter between autumn and spring with a certain semiannual component.…”

Section: Correlations and Intra-annual Variabilitymentioning

confidence: 99%

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Hydroxyl layer: trend of number density and intra-annual variability

et al. 2015

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Abstract. The layer of vibrationally excited hydroxyl (OH * ) near the mesopause in Earth's atmosphere is widely used to derive the temperature at this height and to observe dynamical processes such as gravity waves. The concentration of OH * is controlled by the product of atomic hydrogen, with ozone creating a layer of enhanced concentration in the mesopause region. However, the basic influences on the OH * layer are atomic oxygen and temperature. The long-term monitoring of this layer provides information on a changing atmosphere. It is important to know which proportion of a trend results from anthropogenic impacts on the atmosphere and which proportion reflects natural variations. In a previous paper (Grygalashvyly et al., 2014), the trend of the height of the layer and the trend in temperature were investigated particularly in midlatitudes on the basis of our coupled dynamic and chemical transport model LIMA (Leibniz Institute Middle Atmosphere). In this paper we consider the trend for the number density between the years 1961 and 2009 and analyze the reason of the trends on a global scale. Further, we consider intra-annual variations. Temperature and wind have the strongest impacts on the trend. Surprisingly, the increase in greenhouse gases (GHGs) has no clear influence on the chemistry of OH * . The main reason for this lies in the fact that, in the production term of OH * , if atomic hydrogen increases due to increasing humidity of the middle atmosphere by methane oxidation, ozone decreases. The maximum of the OH * layer is found in the mesopause region and is very variable. The mesopause region is a very intricate domain marked by changeable dynamics and strong gradients of all chemically active minor constituents determining the OH * chemistry. The OH * concentration responds, in part, very sensitively to small changes in these parameters.The cause for this behavior is given by nonlinear reactions of the photochemical system being a nonlinear enforced chemical oscillator driven by the diurnal-periodic solar insolation. At the height of the OH * layer the system operates in the vicinity of chemical resonance. The solar cycle is mirrored in the data, but the long-term behavior due to the trend in the Lyman-α radiation is very small. The number density shows distinct hemispheric differences. The calculated OH * values show sometimes a step around a certain year. We introduce a method to find out the date of this step and discuss a possible reason for such behavior.

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Section: Discussionmentioning

confidence: 99%

Section: Correlations and Intra-annual Variabilitymentioning

confidence: 99%

Hydroxyl layer: trend of number density and intra-annual variability

et al. 2015

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“…This was surprising since the mean atmospheric motion is upwards in the upper mesosphere at high latitudes during summer, so rather high values for the vertical diffusion coefficient were needed to counteract the upward mean circulation. However, the summer mesopause region is characterised by large-amplitude gravity waves and high levels of turbulence due to windshears and wave breaking (Lübken, 1997), and more recent estimates of effective diffusion coefficients (Grygalashvyly et al, 2012) suggest even higher values than those found necessary by Siskind et al (1997).…”

Section: Discussionmentioning

confidence: 97%

Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres: the importance of nitric oxide

et al. 2013

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The relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic <I>K</I> 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 <I>K</I> indices) and low correlations for minute-to-day timescales

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“…The alternative point of view is that the semi-annual variation of OH * at low latitudes is related to seasonal variability of GWs and changes in turbulent diffusion due to GW dissipation (Garcia and Solomon, 1985). In view of new knowledge on GW mixing (Grygalashvyly et al, 2011(Grygalashvyly et al, , 2012, it can be stated that the semi-annual variation of OH * is related to down-gradient fluxes of atomic oxygen by GW mixing. All three potentially responsible processes are connected to the downward flux of atomic oxygen, which, according to Eqs.…”

Section: Discussionmentioning

confidence: 99%