Carbon dioxide glaciers on Mars: Products of recent low obliquity epochs (?)

Three localized sets of small arcuate ridges associated with slopes in the northern polar area of Mars (∼70°N latitude) are morphologically similar to sets of drop moraines left by episodes of advance and retreat of cold-based glaciers. Comparison with other glacial features on Mars shows that these features differ in important aspects from those associated with water–ice flow. Instead, we interpret these features to be due to perennial accumulation and flow of solid carbon dioxide during recent periods of very low spin-axis obliquity.     

Global geological map of Venus

The surface area of Venus (∼460×10⁶ km²) is ∼90% of that of the Earth. Using Magellan radar image and altimetry data, supplemented by Venera-15/16 radar images, we compiled a global geologic map of Venus at a scale of 1:10 M. We outline the history of geological mapping of the Earth and planets to illustrate the importance of utilizing the dual stratigraphic classification approach to geological mapping. Using this established approach, we identify 13 distinctive units on the surface of Venus and a series of structures and related features. We present the history and evolution of the definition and characterization of these units, explore and assess alternate methods and approaches that have been suggested, and trace the sequence of mapping from small areas to regional and global scales. We outline the specific defining nature and characteristics of these units, map their distribution, and assess their stratigraphic relationships. On the basis of these data, we then compare local and regional stratigraphic columns and compile a global stratigraphic column, defining rock-stratigraphic units, time-stratigraphic units, and geological time units. We use superposed craters, stratigraphic relationships and impact crater parabola degradation to assess the geologic time represented by the global stratigraphic column. Using the characteristics of these units, we interpret the geological processes that were responsible for their formation. On the basis of unit superposition and stratigraphic relationships, we interpret the sequence of events and processes recorded in the global stratigraphic column. The earliest part of the history of Venus (Pre-Fortunian) predates the observed surface geological features and units, although remnants may exist in the form of deformed rocks and minerals. We find that the observable geological history of Venus can be subdivided into three distinctive phases. The earlier phase (Fortunian Period, its lower stratigraphic boundary cannot be determined with the available data sets) involved intense deformation and building of regions of thicker crust (tessera). This was followed by the Guineverian Period. Distributed deformed plains, mountain belts, and regional interconnected groove belts characterize the first part and the vast majority of coronae began to form during this time. The second part of the Guineverian Period involved global emplacement of vast and mildly deformed plains of volcanic origin. A period of global wrinkle ridge formation largely followed the emplacement of these plains. The third phase (Atlian Period) involved the formation of prominent rift zones and fields of lava flows unmodified by wrinkle ridges that are often associated with large shield volcanoes and, in places, with earlier-formed coronae. Atlian volcanism may continue to the present. About 70% of the exposed surface of Venus was resurfaced during the Guineverian Period and only about 16% during the Atlian Period. Estimates of model absolute ages suggest that the Atlian Period was about twice as long as the Guineverian and, thus, characterized by significantly reduced rates of volcanism and tectonism. The three major phases of activity documented in the global stratigraphy and geological map, and their interpreted temporal relations, provide a basis for assessing the geodynamical processes operating earlier in Venus history that led to the preserved record.     

Dynamic Model of Mesoscale Eddies

Oceanic mesoscale eddies which are analogs of well known synoptic eddies (cyclones and anticyclones), are studied on the basis of the turbulence model originated by Dubovikov (Dubovikov, M.S., "Dynamical model of turbulent eddies", Int. J. Mod. Phys. B7, 4631-4645 (1993).) and further developed by Canuto and Dubovikov (Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: I. General formalism", Phys. Fluids 8, 571-586 (1996a) (CD96a); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: II. Sheardriven flows", Phys. Fluids 8, 587-598 (1996b) (CD96b); Canuto, V.M., Dubovikov, M.S., Cheng, Y. and Dienstfrey, A., "A dynamical model for turbulence: III. Numerical results", Phys. Fluids 8, 599-613 (1996c)(CD96c); Canuto, V.M., Dubovikov, M.S. and Dienstfrey, A., "A dynamical model for turbulence: IV. Buoyancy-driven flows", Phys. Fluids 9, 2118-2131 (1997a) (CD97a); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: V. The effect of rotation", Phys. Fluids 9, 2132-2140 (1997b) (CD97b); Canuto, V.M., Dubovikov, M.S. and Wielaard, D.J., "A dynamical model for turbulence: VI. Two dimensional turbulence", Phys. Fluids 9, 2141-2147 (1997c) (CD97c); Canuto, V.M. and Dubovikov, M.S., "Physical regimes and dimensional structure of rotating turbulence", Phys. Rev. Lett. 78, 666-669 (1997d) (CD97d); Canuto, V.M., Dubovikov, M.S. and Dienstfrey, A., "Turbulent convection in a spectral model", Phys. Rev. Lett. 78, 662-665 (1997e) (CD97e); Canuto, V.M. and Dubovikov, M.S., "A new approach to turbulence", Int. J. Mod. Phys. 12, 3121-3152 (1997f) (CD97f); Canuto, V.M. and Dubovikov, M.S., "Two scaling regimes for rotating Raleigh-Benard convection", Phys. Rev. Letters 78, 281-284, (1998) (CD98); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: VII. The five invariants for shear driven flows", Phys. Fluids 11, 659-664 (1999a) (CD99a); Canuto, V.M., Dubovikov, M.S. and Yu, G., "A dynamical model for turbulence: VIII. IR and UV Reynolds stress spectra for shear driven flows", Phys. Fluids 11, 656-677 (1999b) (CD99b); Canuto, V.M., Dubovikov, M.S. and Yu, G., "A dynamical model for turbulence: IX. The Reynolds stress for shear driven flows", Phys. Fluids 11, 678-694 (1999c) (CD99c).). The CD model derives from general principles and does not resort to any free parameters. Yet, it successfully describes a wide variety of quite different turbulent flows. In the present work we apply CD model to the compressible ocean. The model yields mesoscale eddies generated by the baroclinic instability. The latter, in turn, arises from the nonhorizontal orientation of the surfaces of the constant potential density (isopycnals). The obtained dynamic equations for eddy fields reduce to a vertical eigen value problem, an eigen value real part yielding an eddy radius, while an imaginary part - an eddy drift velocity. The size of the eddy is about 3r_d (where r_d is the Rossby deformation radius). The eddy dynamics has the following distinctive features: (1) the large scale potential energy feeds the eddy potential energy (EPE) at scales ～ r_d , (2) from r_d EPE cascades to the smaller scales down to ～ l ₁ determined from the condition that the spectral Rossby number Ro(q) ≡ qU'(q)f^?1 becomes ～ 1 (q is two-dimensional wave number within an isopycnal surface), (3) at scales ～ l ₁ EPE transforms into eddy kinetic energy (EKE) which cascades backwards to the larger scales up to ～ r_d , where it transforms back into EPE, thereby closing the energy flux circulation in a wavenumber space, (4) dissipation of the eddy energy (EE) occurs at scales ～ l ₁ since at those scales the fluctuating component of the vertical shear is maximal and equals to the Brunt-Vaisala frequency. The latter equality is the well known condition for generating the vertical turbulence which dissipates EE. The model enables to determine all turbulence characteristics, including the horizontal (isopycnal) diffusivity κ _h in terms of the large scale mean fields. From the typical values of the latter follow estimates for the parameters of an eddy which agree well with the observational and simulational data: k_h ～ 10³m²s^?1, EKE K ～ 10³m²s^?1, r_d ～ 3 × 10⁴m, l_I ～ 10. In what concerns the bolus velocity, it contains additional terms (as compared to the model of Gent and McWilliams (Gent, P.R. and McWilliams, J.C., "Isopycnal mixing in ocean circulation models", J. Phys. Oceanogr. 20, 150-155 (1990)) which result from the eddy fields advection by a mean velocity ū. Since the latter varies with depth, it is inevitable to differ from the eddy drift velocity that produces a shearing force eroding the eddy coherent structures and, therefore, contributing negatively to EE production. This is in contrast with the positive contribution from the GM term (which is due to the baroclinic instability). In those regions where the disruptive action is stronger, there is no eddy generation.     

Imaging heterogeneity of the crust adjacent to the Dead Sea fault using ambient seismic noise tomography

For the purpose of studying the Earth’s crust by means of tomography, we investigated cross-correlation functions emerging from long-term observations of propagating ambient seismic noise at pairs of broadband stations in Israel and Jordan. The data was provided by the eight permanent broadband stations of the Israel Seismic Network evenly distributed over Israel and the 30 stations of the DESERT2000 experiment distributed across the Arava Fault (South of the Dead Sea basin). To eliminate the influence of earthquakes and explosions, we have applied the methodology of Bensen et al. (Geophys J Int 169:1239–1260, 2007), including bandpass filtering and amplitude normalization in time and frequency domain. The cross-correlation functions estimated from continuous recordings of a few months were used to extract Rayleigh waves group velocity dispersion curves using automatic version of the frequency–time analysis procedure. Subsequently, these curves have been converted into the Rayleigh wave group velocity maps in the period range 5–20 s and S waves velocity maps in the depth range 5–15 km. In these maps, four velocity anomalies are prominent. Two of them are outlined by the previous reflection-refraction profiles and body wave tomography studies, i.e. a low velocity anomaly corresponds to the area of the extremely deep (down to 14 km) sedimentary infill in the Southern Dead Sea Basin and a high velocity anomaly in the Southern Jordan corresponds to the area of the Precambrian crystalline rocks of the Nubian Shield on the flanks of the Red Sea. The two other anomalies have not been reported before - the high velocity zone close to the Beersheba city and the low velocity anomaly in the region of Samaria-Carmel mountains - Southern Galilee. They have relatively low resolution and hence need further investigations for approving and contouring. The highest contrast between the average Rayleigh wave group velocity (2.7 km/s) and the anomalies is 10–13 %, comparable, however, to the level of noise in the data. The results have been verified by modeling the revealed anomalies which showed that all the four zones mentioned above could be detected by the tomography study.     

Polarimetric Study of the Fine Aerosol Fraction in Beijing

Measurements of aerosol optical characteris- tics were carried out with a Photoelectric Aerosol Nephelometer （PhAN） in Beijing and at Xinglong Obser- vatory, which is located 150 km northeast of Beijing. Aerosol size distributions were retrieved by means of the inverse problem solution. Mean volume size distributions of the fine aerosol fraction were unimodal with the maximum radius in the range 0.11-0.15 pm. Accumula- tion of aerosol matter in the air basin of Beijing takes place mainly due to the growth of particle size, but not their number. A simple optical method to detect aerosol nonsphericity is proposed.     

Optical layouts of the WSO-UV spectrographs

Electron acoustic blow up solitary waves and periodic waves are studied in a classical unmagnetized plasma containing cold electron fluid, kappa distributed hot electrons and stationary ions. We obtain Korteweg-de Vries (KdV) equation for electron acoustic waves (EAWs) using the reductive perturbation technique (RPT). Applying bifurcation theory of planar dynamical systems to the obtained KdV equation, we prove the existence of electron acoustic blowup solitary and periodic wave solutions. Depending on different physical parameters, two types of exact explicit solutions of the mentioned waves are derived. Our model may be applied to explain blow up solitary and periodic wave features that may occur in the planetary magnetosphere and the plasma sheet boundary layer.     

1900 Draconid Trail Activity in 2011 and the Prospects for 2014

The article provides an explanation of stronger than expected by the Author Draconids 2011 activity basing on the assumption of unusually high density of 1900 trail of the comet 21P Giacobini-Zinner. Also, a revised prediction for Draconids 2014 is presented, which should also be caused by 1900 trail. For this prediction a “vertical trails” approach is used. This approach is described in the article.     

High‐latitude cold‐based glacial deposits on Mars: Multiple superposed drop moraines in a crater interior at 70°N latitude

Abstract— An impact crater 26.8 km in diameter, located in the northern lowlands (70.32°N, 266.45°E) at the base of the flanking slopes of the shield volcano Alba Patera, is characterized by highly unusual deposits on its southeastern floor and interior walls and on its southeastern rim. These include multiple generations of distinctive arcuate ridges about 115–240 m in width and lobate deposits extending down the crater wall and across the crater floor, forming a broad, claw‐like, ridged deposit around the central peak. Unusual deposits on the eastern and southeastern crater rim include frost, dunes, and a single distal arcuate ridge. Based on their morphology and geometric relationships, and terrestrial analogs from the Mars‐like Antarctic Dry Valleys, the floor ridges are interpreted to represent drop moraines, remnants of the previous accumulation of snow and ice, and formation of cold‐based glaciers on the crater rim. The configuration and superposition of the ridges indicate that the accumulated snow and ice formed glaciers that flowed down into the crater and across the crater floor, stabilized, covering an area of about 150 km² produced multiple individual drop moraines due to fluctuation in the position of the stable glacier front. Superposition of a thin mantle and textures attributed to a recent ice‐age period (?0.5–2 Myr ago) suggest that the glacial deposits date to at least 4–10 Myr before the present. At least five phases of advance and retreat are indicated by the stratigraphic relationships, and these may be related to obliquity excursions. These deposits are in contrast to other ice‐related modification and degradation processes typical of craters in the northern lowlands, and may be related to the distinctive position of this crater in the past atmospheric circulation pattern, leading to sufficient preferential local accumulation of snow and ice to cause glacial flow.