Seasonal features in the response of the mesopause temperature and emission intensities to solar activity variations

The seasonal dependences of the response of the hydroxyl ((6–2) band) and molecular oxygen O₂(b ¹Σ _g ⁺ ) ((0–1) band) emission intensities, temperature, and density indicator in the region of the hydroxyl emission maximum (87 km) to solar activity have been obtained based on the spectral observations of the mesopause emissions at Zvenigorod observatory during 2000–2007. The ratio of the OH (7–3) and (9–4) band intensities, characterizing the behavior of the vibrational temperature, has been used as an indicator of density. It has been established that the response of the studied mesopause characteristics to solar activity is positive in all seasons. In winter the response is maximal in the intensities and temperature and is minimal in the density indicator. The main mechanisms by which solar activity affects the mesopause characteristics have been considered. The behavior of the internal gravity waves with periods of 0.33–7 h depending on solar activity has been studied. It has been noted that these waves become more active at a minimum of the 11-year solar cycle.     

The Magmatic–Hydrothermal Transition and Origin of Brine in the Oceanic Core Complex of the Mid-Atlantic Ridge at 13° N

New data on local mineral associations and the microheterogeneity of minerals and fluid inclusions in gabbro were obtained for the gabbro–peridotite oceanic core complex with a long-lived detachment fault controlling the hydrothermal activity. It is assumed that the hydrothermal hydrogen-bearing fluid with a NaCl content of >30 wt % is formed in the seawater/harzburgite (~1/5) reaction of serpentinization. The brine residual after serpentinization interacted with gabbro at the final stages of crystallization of an intrusion and assimilated some components (K, REEs, and Ba) from the residual melt. The interaction was resulted in metamorphic transformations of gabbro at decreasing temperature below 500°C. The reaction of the decomposition of magmatic titanomagnetite with the transition of iron reduced to Fe²⁺ into newly formed chlorinebearing amphibole at 540–450°C and logf(O₂) from–20 to–24 is shown.

     

Aklimaite, Ca4[Si2O5(OH)2](OH)4 · 5H2O, a new natural hydrosilicate from Mount Lakargi, the Northern Caucasus, Russia

A new mineral aklimaite, Ca₄[Si₂O₅(OH)₂](OH)₄ · 5H₂O, has been found near Mount Lakargi, Upper Chegem caldera, Kabardino-Balkaria, the Northern Caucasus, Russia, in the skarnified limestone xenolith in ignimbrite. This hydrothermal mineral occurs in a cavity of altered larnite skarn and is associated with larnite, calcium humite-group members, hydrogarnets, bultfonteinite, afwillite, and ettringite. Aklimaite forms transparent, colorless (or occasionally with pinkish tint) columnar or lath-shaped crystals up 3 × 0.1 × 0.01 mm in size, flattened on {001} and elongated along {010}; they are combined in spherulites. The luster is vitreous; the cleavage parallel to the {001} is perfect. D _calc = 2.274 g/cm³. The Mohs’ hardness is 3–4. Aklimaite is optically biaxial, negative, 2V _meas > 70°, 2V _calc = 78°, α = 1.548(2), β = 1.551(3), γ = 1.553(2). The IR and Raman spectra are given. The chemical composition (wt %, electron microprobe) is as follows: 0.06 Na₂O, 0.02 K₂O, 45.39 CaO, 0.01 MnO, 0.02 FeO, 24.23 SiO₂, 0.04 SO₃, 3.22 F, 27.40 H₂O_(calc.), ?1.36 -O=F₂; the total is 99.03. The empirical formula calculated on the basis of 2Si apfu with O + OH + F = 16 is as follows: (Ca_4.02Na_0.01)_Σ4.03[Si_2.00O_5.07(OH)_1.93][(OH)_3.16F_0.84] _Σ4.00 · 5H₂O. The mineral is monoclinic, space group C2/m, a = 16.907(5), b = 3.6528(8), c = 13.068(4) Å, β = 117.25(4)·, V= 717.5(4) ų, Z = 2. Aklimaite is representative of the new structural type, the sorosilicate with disilicate groups [Si₂O₅(OH)₂]. The strongest reflections in the X-ray powder patterns [d, Å (hkl)] are: 11.64(100)(001), 2.948(32)(310, 203), 3.073(20) ( $\bar 404$ , $\bar 311$ ), 2.320(12)(005, 510), 2.901 (11)(004), 8.30(10) $\left( {\bar 201} \right)$ . The type specimen is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

The behavior of emissions and temperature of the mesopause during stratospheric warmings according to observations at midlatitudes

Regularities in variations in the intensity of hydroxyl radiation (the (6–2) λ834.4-nm band) and the Atmospheric system of molecular oxygen (the A(0–1) λ864.5-nm band) of the mesopause, hydroxyl temperature, and its night variability during sudden winter warmings of the stratosphere have been obtained based on long-term observations in Zvenigorod.     

Recent massive sulfide deposits of the Semenov ore district, Mid-Atlantic Ridge, 13°31′ N: Associated rocks of the oceanic core complex and their hydrothermal alteration

The oceanic core complexes and large-offset detachment faults characteristic of the slow-spreading Mid-Atlantic Ridge are crucial for the structural control of large hydrothermal systems, including those forming sub-seafloor polymetallic sulfide mineralization. The structural-geological, petrographic, and mineralogical data are considered for the oceanic core complex enclosing the Semenov-1, -2, -3, -4, and -5 inactive hydrothermal sulfide fields recently discovered on the Mid-Oceanic Ridge at 13°31?? N. The oceanic core complex is composed of serpentinized and talc-replaced peridotites and sporadic gabbroic rocks, however, all hydrothermal fields reveal compositional indications of basaltic substrate. The volcanic structures superposed on the oceanic core complex are marked by outcrops of pillow lavas with fresh quenched glass. Dolerites regarded as volcanic conduits seem to represent separate dike swarms. The superposed volcanic structures develop largely along the near-latitudinal high-angle tectonic zone controlling the Semenov-1, -2, -5, and -3 hydrothermal sulfide fields. The manifestations of hydrothermal metasomatic alteration are diverse. The widespread talcose rocks with pyrrhotite-pyrite mineralization after serpentinite, as well as finding of talc-chlorite metabasalt are interpreted as products of hydrothermal activity in the permeable zone of detachment fault. Chloritization and brecciation of basalts with superposed quartz or opal, barite, and pyrite or chalcopyrite mineralization directly related to the sub-seafloor sulfide deposition. The native copper mineralization in almost unaltered basalts at the Semenov-4 field is suggested to precipitate from ore-forming fluids before they reach the level of sub-seafloor sulfide deposition. Amphibolites with plagiogranite veinlets are interpreted as tectonic fragments of the highest-temperature portions of hydrothermal systems, where partial melting of basic rocks in the presence of aqueous fluid with formation of plagiogranitic melt is possible. Silicic rocks (plagiogranite, tonalite and diorite) revealed in the tectonic zone controlling the Semenov-1, -2, -5, and -3 hydrothermal sulfide fields are related to both plutonic and subvolcanic bodies and considered to be products of partial melting of basic rocks at deep levels of the hydrothermal systems. The hydrothermal fields differ in their structural position. The giant Semenov-4 field is located at the area where the hanging-wall basalt wedges out and the detachment fault zone reaches the oceanic floor. The range of relatively small Semenov-1, -2, -3, and 5 fields develops on the oceanic core complex massif, being localized in the superposed volcanic structures within the near-latitudinal steeply dipping tectonic zone. The structural control of the hydrothermal fields at 13°31?? N is also interpreted in different ways. For the Semenov-4 field, the ascending fluid flow can be related to the permeable detachment fault zone. The root zone of the hydrothermal system with a magmatic heater could have been localized at a significant distance beneath the axial spreading zone. For the other four relatively small fields, it is suggested that the ascending fluid flows and roots of the hydrothermal systems are controlled by the volcanic structures superposed on the oceanic ore complex within the steeply dipping tectonic zone.     

Temperature variations in the mesopause region according to the hydroxyl-emission observations at midlatitudes

The seasonal temperature variations in the mesopause region and the inter-day and nighttime temperature variability, the measure of which is standard deviations, have been studied based on the hydroxyl emission spectral observations at the Zvenigorod station of the Obukhov Institute of Atmospheric Physics in 2000–2011 and Institute of Solar Terrestrial Physics geophysical station (Tory) in 2008–2011. The long-term variations in all temperature variability parameters have been analyzed.     

Tidal corrections to gravity measurements

Methods taking into account the effect of tidal forces on gravity measurements are considered. Corrections for the effect of tidal forces can exceed 250 μGal. Only the structure of the Earth and positions of tide-generating celestial bodies are necessary for taking into account earth tides, while cotidal charts are additionally required for the correct incorporation of the effect of ocean tides. The effect can reach a few tens of μGal near shorelines. The modern accuracy of gravity measurements being 1–2 μGal, the ocean tide effect, together with other less significant factors, should be considered for the correct interpretation of gravity data.     

A case study of the evolution of a Kelvin–Helmholtz wave and turbulence in noctilucent clouds

Bright and extensive noctilucent clouds (NLC) were observed in Århus (Denmark) on 3/4 July of 2008 with an automatic digital camera taking images every minute. This event was unique in the sense that bright NLC were seen at high elevation angles (more than 30°) that allowed observing the evolution of a Kelvin–Helmholtz (KH) wave, resulted in well-developed turbulence. In particular, coherent vortex structures of a horseshoe-shaped form were observed for the first time in noctilucent clouds. The turbulent diffusion coefficient and turbulent energy dissipation rate around the mesopause are estimated in the range 162–667 m²/s and 300–1235 mW/kg, respectively, representing a case of strong neutral air turbulence in noctilucent clouds. Turbulent structures were observed to be in the vicinity of breaking small-scale gravity waves that seems to be responsible for a high level of turbulence.At the same time, it has been demonstrated that it is of importance to take into account non-turbulent process such as the gravity wave motion that is always present in NLC layers. Unless non-turbulent process is taken into account, this certainly leads to overestimating of the value of the turbulent diffusion coefficient. More accurate characteristics of turbulence in NLC can be obtained by analyzing a sequence of high-resolution images with a high frame-rate high-resolution digital camera.     

Lunar semimonthly signal in cloudiness: Lunar-phase or lunar-declination effect?

The cloud amount summer nighttime data obtained from the 1994 to 2007 NASA satellite infrared and visible range measurements taken within the framework of the International Satellite Cloud Climatology Project (ISCCP) were analyzed, and the contribution by lunar signal to the cloud amount was extracted. Although the fact of lunar influence on cloudiness is known, this investigation has made it possible to separate the lunar-phase and lunar-declination effects on cloudiness. The relative cloud amount tends to grow with a change in lunar phase from a quadrature to the New Moon or Full Moon and with an increase in lunar declination by absolute value. Both the effects are statistically significant, the lunar-declination effect is a little stronger. The obtained results do not seem to contradict the theory of lunar tides.     

P_{CO_2 } -T-Evolution and origin of zoning in melilite during the regressive stage of contact metamorphism in carbonate-bearing rocks

The article describes the thermal metamorphism of siliceous carbonate rocks near the dolerite intrusive body in Eastern Siberia. The mineral associations at the immediate contact with dolerite are the following: wollastonite+rankinite, rankinite+spurrite (+melilite?), spurrite+melilite+merwinite+calcite and merwinite+monticellite+melilite+calcite. The melilite in these associations is usually unzoned; its composition being essentially gehlenitic. During the regressive stage of contact metamorphism new akermanite-rich melilite and calcite were formed by replacement of merwinite and earlier gehlenitic melilite through participation of CO₂. The newly forming melilite grains have sharp compositional zoning. The origin of zoning was connected with the fall of temperature and decrease of the mole fraction of CO₂ in the fluid equilibrated with the minerals.