Vertical Velocity Variance Research Articles

Monin–Obukhov Similarity and Local-Free-Convection Scaling in the Atmospheric Boundary Layer Using Matched Asymptotic Expansions

The Monin–Obukhov similarity theory (MOST) is the foundation for understanding the atmospheric surface layer. It hypothesizes that nondimensional surface-layer statistics are functions of [Formula: see text] only, where z and L are the distance from the ground and the Obukhov length, respectively. In particular, it predicts that in the convective surface layer, local free convection (LFC) occurs at heights [Formula: see text] and [Formula: see text], where [Formula: see text] is the inversion height. However, as a hypothesis, MOST is based on phenomenology. In this work we derive MOST and the LFC scaling from the equations for the velocity and potential temperature variances using the method of matched asymptotic expansions. Our analysis shows that the dominance of the buoyancy and shear production in the outer ([Formula: see text]) and inner ([Formula: see text]) layers, respectively, results in a nonuniformly valid solution and a singular perturbation problem and that [Formula: see text] is the thickness of the inner layer. The inner solutions are found to be functions of [Formula: see text] only, providing a proof of MOST for the vertical velocity and potential temperature variances. Matching between the inner and outer solutions results in the LFC scaling. We then obtain the corrections to the LFC scaling near the edges of the LFC region ([Formula: see text] and [Formula: see text]). The nondimensional coefficients in the expansions are determined using measurements. The resulting composite expansions provide unified expressions for the variance profiles in the convective atmospheric surface layer and show very good agreement with the data. This work provides strong analytical support for MOST.

Flow Separation and Vortex Dynamics in Waves Propagating over A Submerged Quartercircular Breakwater

The interactions of cnoidal waves with a submerged quartercircular breakwater are investigated by a Reynolds-Averaged Navier–Stokes (RANS) flow solver with a Volume of Fluid (VOF) surface capturing scheme (RANS-VOF) model. The vertical variation of the instantaneous velocity indicates that flow separation occurs at the boundary layer near the breakwater. The temporal evolution of the velocity and vorticity fields demonstrates vortex generation and shedding around the submerged quartercircular breakwater due to the flow separation. An empirical relationship between the vortex intensity and a few hydrodynamic parameters is proposed based on parametric analysis. In addition, the instantaneous and time-averaged vorticity fields reveal a pair of vortices of opposite signs at the breakwater which are expected to have significant effect on sediment entrainment, suspension, and transportation, therefore, scour on the leeside of the breakwater.

The Effect of Aerosol Radiative Heating on Turbulence Statistics and Spectra in the Atmospheric Convective Boundary Layer: A Large-Eddy Simulation Study

Turbulence statistics and spectra in a radiatively heated convective boundary layer (CBL) under aerosol pollution conditions are less investigated than their counterparts in the clear CBL. In this study, a large-eddy simulation (LES) coupled with an aerosol radiative transfer model is employed to determine the impact of aerosol radiative heating on CBL turbulence statistics. One-dimensional velocity spectra and velocity–temperature cospectra are invoked to characterize the turbulence flow in the CBL with varying aerosol pollution conditions. The results show that aerosol heating makes the profiles of turbulent heat flux curvilinear, while the total (turbulent plus radiative) heat flux profile retains the linear relationship with height throughout the CBL. The horizontal and vertical velocity variances are reduced significantly throughout the radiatively heated CBL with increased aerosol optical depth (AOD). The potential temperature variance is also reduced, especially in the entrainment zone and near the surface. The velocity spectral density tends to be smaller overall, and the peak of the velocity spectra is shifted toward larger wavenumbers as AOD increases. This shift reveals that the energy-containing turbulent eddies become smaller, which is also supported by visual inspection of the vertical velocity pattern over horizontal planes. The modified CBL turbulence scales for velocity and temperature are found to be applicable for normalizing the corresponding profiles, indicating that a correction factor for aerosol radiative heating is needed for capturing the general features of the CBL structure in the presence of aerosol radiative heating.

Influence of Relative Humidity, Mixed-Layer Height, and Mesoscale Vertical-Velocity Variations on Column and Surface Aerosol Characteristics Over an Urban Region

Investigations into the influence of variations in relative humidity, mixed-layer height, and mesoscale vertical velocity on column and surface aerosol characteristics over urban regions are quite rare. Here we report on a comprehensive investigation that was conducted over Ahmedabad, an urban location in western India, during December 2006. In this campaign columnar and surface aerosol characteristics were measured and compared to relative humidity, mixed-layer height, and mesoscale vertical velocity to examine their influence on urban aerosol characteristics. The 500-nm aerosol optical depth was found to be approximately 0.8 between 24 and 26 December while on a cleaner day such as 7 and 18 December the aerosol optical depth was 0.1. Aerosol optical depths based on Moderate Resolution Imaging Spectroradiometer (MODIS) level-2 and level-3 data, and on in situ Sun photometer measurements, show good agreement. The scattering coefficient ( $$\beta _{\mathrm{sca}}$$ ) and absorption coefficient ( $$\beta _{\mathrm{abs}}$$ ) increased by a factor of 5–10 on 26 December compared to 7 December (a normal day). This latter date was characterized by a clear atmosphere, a lower mixed-layer height ( $$\approx $$ 1650 m), positive vertical velocity and higher aerosol scale height (>3 km), while 26 December was marked with hazy and smoky conditions, a larger mixed-layer height ( $$\approx $$ 2500 m), negative vertical velocity and smaller aerosol scale height ( $$\approx $$ 1 km). These atmospheric conditions lead to lower and higher values of surface and columnar aerosol concentrations on 7 and 26 December respectively. A measure of spectral aerosol absorption, $$\alpha '_{\mathrm{abs}}$$ > 2, indicating the dominance of carbonaceous aerosols from biomass/biofuel emissions (open biomass burning), is rather surprising as fossil-fuel emissions that produce strongly light absorbing carbonaceous particles usually dominate urban regions. The single-scattering albedo on both days is 0.56 and 0.67 respectively, while monthly mean hemispheric backscatter fraction b and asymmetry parameter g values are 0.16 and 0.53 respectively. Higher b and lower g values on 7 December, and lower b and higher g values on 26 December, provide the relative scale of variation in the amount of sub-micron aerosols that dominate on a normal/clear day vis-a-vis a smoky/perturbed day. Lower single-scattering albedo indicates the dominance of absorbing aerosols above Ahmedabad, and higher b and lower g values suggest the abundance of fine mode particles in aerosol size distribution. The in-depth results serve as representative inputs to modelling the column and surface characteristics, and the resultant radiative forcing of urban aerosols influenced by variations in relative humidity, mixed-layer height, and mesoscale vertical velocity.

Study of Moisture Budget of Meteorological Droughts over Indian Region

The study mainly focuses on heat and moisture budget components and its variations during meteorological drought conditions over India for the period 1951-2013. IITM sub-divisional summer monsoon standardized rainfall anomaly is considered to identify the meteorological drought where the standardized summer monsoon rainfall anomaly is less than one. From the analysis, there are thirteen meteorological droughts are identified, and the rainfall decreased on spatial and temporal scales with significant changes in the frequency, duration and total amount of rainfall. Mainly, anticyclonic circulation is observed along 60⁰-70⁰E with weak westerlies at lower levels. At the upper level, the intensity of easterly jet stream is decreased and shifted southward during drought years.Anomalous variations in relative humidity and vertical velocity induce the maximum reduction in the moisture amount (15%) at lower and upper levels leads to weakening of the strength of local Hadley circulation. Next, the heat budget components are decreased over Bay of Bengal and coastal regions with a magnitude of 40 to 200 W/m2 in drought years. It is observed that more moisture is transported to the equatorial region producing below average rainfall over the Indian subcontinent during weak monsoon periods. Hence, this study will help to identify the quantitative and qualitative estimation of drought conditions for long-range prediction of rainfall forecasting.

Laboratory study of the effect of vertically varying vegetation density on waves, currents and wave-current interactions

Under the influence of vegetation, waves, currents, turbulence as well as sediment processes are all changed, which significantly affect aquatic environment. Vegetation appears spatially heterogeneous in terms of vegetation density in most natural wetlands. However, how vertical heterogeneity of vegetation canopy affects turbulence under waves and currents is still not well understood. In this paper, the effects of different vegetation densities (i.e. sparse, dense and vertically-varying density) on vegetation-induced wave attenuation, mean flow adjustment as well as turbulence are studied through laboratory experiments. For regular waves, higher vegetation density results in smaller wave transmission coefficients and local wave heights. The difference between the effects of vertically uniform and varying vegetation density on wave height decay is significant for deep water waves and insignificant for intermediate water waves. The vertically varying vegetation density slightly changes the wave-averaged velocity distribution, producing reverse flows within the canopy. Turbulence intensity decreases more significantly with increasing water depth in the case with vertically varying vegetation density. For unidirectional flow, the vertically varying vegetation density increases the vertical gradient of mean streamwise velocity compared with the emergent uniform vegetation. The time series of u oscillates relatively stronger near bottom, and causes higher TKE, which is different with that in oscillatory flow. Compared with the submerged uniform vegetation, the vertical variation of mean velocity affected by vegetation with vertically varying density is smaller in both pure current and wave-current flow. Affected by dense submerged vegetation, the mean velocity of combined wave-current flow is significantly lower than that of pure current, while it is reduced near the bottom and increased in the upper layer comparing with that of pure current under the influence of sparse submerged vegetation. TKE values in wave-current flow is promoted in the upper layer with coexisting waves in the case of submerged uniform vegetation, while it is barely affected near the bed. In the case with vertically varying vegetation density, TKE values in the wave-current flow are slightly decreased than that in the pure current condition, especially near the bottom.

A TKE‐Based Framework for Studying Disturbed Atmospheric Surface Layer Flows and Application to Vertical Velocity Variance Over Canopies

AbstractWe propose an approach to study disturbed surface layer flows based on a simplified form of the turbulent kinetic energy (TKE) budget equation (the reduced TKE budget), which can be represented by a two‐dimensional phase space. The phase space provides a way to quantify relative contributions of shear and buoyancy production/destruction of TKE, as well as the local imbalance between local production and dissipation. In this framework, Monin‐Obukhov Similarity Theory represents one possible approach to reduce the dimensionality of the phase space. We apply this framework to study the vertical velocity variance in the canonical surface layer and in the canopy roughness sublayer above the Amazon forest. Results reveal interesting insight into the behavior of the vertical velocity variance over forests, linking its magnitude to the imbalance between local production and dissipation of TKE.

Observed Boundary Layer Controls on Shallow Cumulus at the ARM Southern Great Plains Site

Abstract The boundary layer controls on shallow cumulus (ShCu) convection are examined using a suite of remote and in situ sensors at ARM Southern Great Plains (SGP). A key instrument in the study is a Doppler lidar that measures vertical velocity in the CBL and along cloud base. Using a sample of 138 ShCu days, the composite structure of the ShCu CBL is examined, revealing increased vertical velocity (VV) variance during periods of medium cloud cover and higher VV skewness on ShCu days than on clear-sky days. The subcloud circulations of 1791 individual cumuli are also examined. From these data, we show that cloud-base updrafts, normalized by convective velocity, vary as a function of updraft width normalized by CBL depth. It is also found that 63% of clouds have positive cloud-base mass flux and are linked to coherent updrafts extending over the depth of the CBL. In contrast, negative mass flux clouds lack coherent subcloud updrafts. Both sets of clouds possess narrow downdrafts extending from the cloud edges into the subcloud layer. These downdrafts are also present adjacent to cloud-free updrafts, suggesting they are mechanical in origin. The cloud-base updraft data are subsequently combined with observations of convective inhibition to form dimensionless “cloud inhibition” (CI) parameters. Updraft fraction and liquid water path are shown to vary inversely with CI, a finding consistent with CIN-based closures used in convective parameterizations. However, we also demonstrate a limited link between CBL vertical velocity variance and cloud-base updrafts, suggesting that additional factors, including updraft width, are necessary predictors for cloud-base updrafts.

Patterns of Vertical Velocity Induced by Eddy Distortion in an Ocean Model

AbstractVertical motions within eddies play an important role in the exchange of properties and energy between the upper ocean and the ocean interior. Here we analyze alternating upward and downward cells in anticyclonic eddies in the East Australian Current region using a global eddy‐resolving model. The cells explain over 50% of the variance of vertical velocity within these eddies. We show that the upward and downward cells relate to eddy distortion, defined as the change in eddy shape over time. In anticyclonic eddies in the Southern Hemisphere, an inward distortion is associated with upward motion and an outward distortion is associated with downward motion. We discuss two mechanisms that link eddy distortion to vertical velocity. One mechanism relates to changes in stratification and relative vorticity in the eddy interior. The other mechanism relates to divergence of the horizontal flow in different quadrants of the eddy. We show that mesoscale changes in sea level anomaly can be used to infer the vertical motion within eddies.

Simulation of the Lunar Regolith and Lunar-Penetrating Radar Data Processing

Lunar-penetrating radar (LPR) was conducted by the “Yutu” rover of China's Chang-E 3 lunar mission to study the shallow subsurface of the Moon. Both regolith modeling and numerical simulation can provide a reliable reference for data processing of the Moon. In this study, a 3-D lunar regolith model that considered some key factors including terrain, rocks, randomness of medium, and permittivity change with depth is built. Based on LPR numerical simulation, v(z) f-k migration, with high accuracy for vertical velocity variations, is carried out. Compared with Stolt f-k migration, which is limited to constant velocity, v(z) f-k migration performs better. We have designed a workflow for LPR data of Chang-E 3 mission, such as v(z) f-k migration, filters, and gain. Finally, according to the LPR real data result, we estimate the thickness of the regolith, the location and physical parameters of several rocks, and randomness of medium. Besides, the present study provides a good reference for further understanding of lunar near-surface geological information.

Vertical Profiles of Wave-Coherent Momentum Flux and Velocity Variances in the Marine Atmospheric Boundary Layer

AbstractThe wave-coherent momentum flux and velocity variances are investigated using a theoretical model and open-ocean measurements. The spectrum-integrated wave-coherent (SIWC) momentum flux and velocity variances decay roughly exponentially with height. The exponential decay coefficients of the SIWC momentum flux and velocity variances decrease with increasing peak wavenumber. The phases of the wave-coherent horizontal (vertical) velocity fluctuations are approximately 180° (90°) under waves with wind-wave angle |α1| < 90°. In general, the ratio of the SIWC momentum flux to the total momentum flux under swell conditions is higher than that under wind-wave conditions at the same height. At a height of 9.9 m, the SIWC vertical (horizontal) velocity variances can exceed 30% (10%) of the total vertical (horizontal) velocity variances at high wave ages. The impact of SIWC momentum flux on wind profiles is determined mainly by the surface SIWC momentum flux ratio, the decay coefficient of the SIWC momentum flux, and the sea surface roughness length, with the first two factors being dominant. The results of this study suggest a methodology for parameterizing the SIWC momentum flux and the total momentum flux over the ocean. These results are important for simulating the marine atmospheric boundary layer and should be used in model development.

Gravity Wave Dynamics in a Mesospheric Inversion Layer: 2. Instabilities, Turbulence, Fluxes, and Mixing

AbstractA companion paper by Fritts, Laughman, et al. (2017) employed an anelastic numerical model to explore the dynamics of gravity waves (GWs) encountering a mesospheric inversion layer (MIL) having a moderate static stability enhancement and a layer of weaker static stability above. That study revealed that MIL responses, including GW transmission, reflection, and instabilities, are sensitive functions of GW parameters. This paper expands on two of the Fritts, Laughman, et al. (2017) simulations to examine GW instability dynamics and turbulence in the MIL; forcing of the mean wind and stability environments by GW, instability, and turbulence fluxes; and associated heat and momentum transports. These direct numerical simulations resolve turbulence inertial‐range scales and yield the following results: GW breaking and turbulence in the MIL occur below where they would otherwise, due to enhancements of GW amplitudes and shears in the MIL. 2‐D GW and instability heat and momentum fluxes are ~20–30 times larger than 3‐D instability and turbulence fluxes. Mean fields are driven largely by 2‐D GW and instability dynamics rather than 3‐D instabilities and turbulence. 2‐D and 3‐D heat fluxes in regions of strong turbulence yield small departures from initial T(z) and N2(z) profiles, hence do not yield nearly adiabatic “mixed” layers. Our MIL results are consistent with the relation between the turbulent vertical velocity variance and energy dissipation rate proposed by Weinstock (1981) for the limited intervals evaluated.

Sediment Suspension by Straining‐Induced Convection at the Head of Salinity Intrusion

AbstractThe tidal straining can generate convective motions and exert a periodic modification of turbulence and sediment transport in estuarine and coastal bottom boundary layers. However, the evidence and physics of convection and sediment suspension induced by tidal straining have not been straightforward. To examine these questions, mooring and transect surveys have been conducted in September 2015 in the region of the Yangtze River plume influence. Field observations and scaling analyses indicate an occurrence of convective motions at the head of saline wedge. Theoretical analyses of stratification evolution in the saline wedge show that unstable stratification and resultant convection are induced by tidal straining. Vertical turbulent velocity and eddy viscosity at the head of saline wedge are both larger than their neutral counterparts in the main body, largely enhancing sediment suspension at the head of saline wedge. Moreover, sediment suspension in both neutral and convection‐affected flows is supported by the variance of vertical turbulent velocity, rather than the shearing stress. Finally, the stability correction functions in the Monin‐Obukhov similarity theory can be simply derived from the local turbulent kinetic energy balance to successfully describe the effects of tidal straining on turbulent length scale, eddy viscosity, and sediment diffusivity in the convection‐affected flow. These recognitions may provide novel understanding of estuarine turbidity maxima, and the dynamical structure and processes for coastal hypoxia.

Crust and upper mantle velocity structure beneath the Ordos Block and its tectonic significance

The Ordos Block in the western North China Craton (NCC) occupies an important position in the tectonic evolution and deep earthquake environment research in China continent. In previous seismic tomography studies, the sparse distribution of seismic stations resulted in a relatively low lateral resolution of 3D structure of crust and upper mantle in the Ordos Block. In this paper, a dense broadband seismograph network was established, including the permanent seismic stations of the regional networks and the temporary seismic stations funded by the ″Destruction of the North China Craton″ project and the North China Scientific Seismic Array. Based on the waveform data recorded by 338 seismic stations in the Ordos Block and surrounding regions, we used FMTOMO traveltime tomography method to determine the high-resolution P-wave velocity structures of the crust and upper mantle down to 400 km depth, and analyzed the relationship between deep structure and a range of geodynamic issues, such as the volcanic and strong earthquake activities and the destruction of the NCC. The tectonic implications of the lateral and the vertical variations of P-wave velocity in the crust and upper mantle structures are described as follow. The transverse variation and vertical difference of velocity structure of crust and uppermost mantle indicate significant correlations between deep tectonics and surface geological setting. The thick lithosphere with positive velocity anomaly beneath the Ordos block suggests that the Ordos block did not suffer extensive destruction. The velocity anomaly distribution of the Taihang orogenic belt in the central NCC is characterized by discontinuous strip anomalies, which is significantly different from that of the North China Plain and Ordos block. The low-velocity anomalies deeper than 400 km might be related to the lithosphere destruction in the eastern NCC. A low-velocity columnar anomaly down to 400 km depth beneath the Datong volcanic groups indicates that the magmatism of the Datong volcanic group might originate from the mantle transitional zone, due to the upwelling and expulsion of basaltic magma caused by the subduction of the Pacific plate. The low-velocity zone in approximately EW direction in the upper mantle between the Ordos Block and the Sichuan basin suggests the possible existence of a narrow outflow channel of the asthenosphere. In summary, the low-velocity anomaly down to the upper mantle in the Ordos Block and surrounding regions indicates that the north-eastward compressive stress of the Tibetan Plateau and the westward subduction of the Pacific plate may induce the migration and upwelling of mantle materials, causing the overall uplift of the Ordos Block and the formation of extensional fault belt in surrounding regions. The vertical upwelling and lateral movement of the deep materials provide the stress conditions for the preparation and occurrence of strong earthquakes resulting in frequent occurrence of strong earthquakes in the regions around the Ordos Block.

Characterization of Convective Plumes Associated With Oceanic Deep Convection in the Northwestern Mediterranean From High‐Resolution In Situ Data Collected by Gliders

AbstractNumerous gliders have been deployed in the Gulf of Lions (northwestern Mediterranean Sea) and in particular during episodes of open‐ocean deep convection in the winter 2012–2013. The data collected represents an unprecedented density of in situ observations providing a first in situ statistical and 3‐D characterization of the important mixing agents of the deep convection phenomenon, the so‐called plumes. A methodology based on a glider‐static flight model was applied to infer the oceanic vertical velocity signal from the glider navigation data. We demonstrate that during the active phase of mixing, the gliders underwent significant oceanic vertical velocities up to 18 cm s−1. Focusing on the data collected by two gliders during the 2012–2013 winter, 120 small‐scale convective downward plumes were detected with a mean radius of 350 m and separated by about 2 km. We estimate that the plumes cover 27% of the convection area. Gliders detected downward velocities with a magnitude larger than that of the upward ones (−6 versus +2 cm s−1 on average). Along‐track recordings of temperature and salinity as well as biogeochemical properties (dissolved oxygen, fluorescence, and turbidity) allow a statistical characterization of the water masses' properties in the plumes' core with respect to the “background”: the average downward signal is of colder (−1.8 × 10−3 °C), slightly saltier (+4.9 × 10−4 psu) and thus denser waters (+7.5 × 10−4 kg m−3). The plunging waters are also on average more fluorescent (+2.3 × 10−2 μg L−1). The plumes are associated with a vertical diffusion coefficient of 7.0 m2 s−1 and their vertical velocity variance scales with the ratio of the buoyancy loss over the Coriolis parameter to the power 0.86.

Year-Long Vertical Velocity Statistics Derived from Doppler Lidar Data for the Continental Convective Boundary Layer

AbstractOne year of coherent Doppler lidar data collected at the U.S. Department of Energy’s Atmospheric Radiation Measurement site in Oklahoma was analyzed to provide profiles of vertical velocity variance, skewness, and kurtosis for cases of cloud-free convective boundary layers. The variance was normalized by the Deardorff convective velocity scale, which was successful when the boundary layer depth was stationary but failed in situations in which the layer was changing rapidly. In this study, the data are sorted according to time of day, season, wind direction, surface shear stress, degree of instability, and wind shear across the boundary layer top. The normalized variance was found to have its peak value near a normalized height of 0.25. The magnitude of the variance changes with season, shear stress, degree of instability, and wind shear across the boundary layer top. The skewness was largest in the top half of the boundary layer (with the exception of wintertime conditions). The skewness was also found to be a function of the season, shear stress, and wind shear across the boundary layer top. Like skewness, the vertical profile of kurtosis followed a consistent pattern, with peak values near the boundary layer top. The normalized altitude of the peak values of kurtosis was found to be higher when there was a large amount of wind shear at the boundary layer top.

Post-midnight equatorial irregularity distributions and vertical drift velocity variations during solstices

Longitudinal distributions of post-midnight equatorial ionospheric irregularity occurrences observed by ROCSAT-1 (1st satellite of the Republic of China) during moderate to high solar activity years in two solstices are studied with respect to the vertical drift velocity and density variations. The post-midnight irregularity distributions are found to be similar to the well-documented pre-midnight ones, but are different from some published distributions taken during solar minimum years. Even though the post-midnight ionosphere is sinking in general, longitudes of frequent positive vertical drift and high density seems to coincide with the longitudes of high irregularity occurrences. Large scatters found in the vertical drift velocity and density around the dip equator in different ROCSAT-1 orbits indicate the existence of large and frequent variations in the vertical drift velocity and density that seem to be able to provide sufficient perturbations for the Rayleigh-Taylor (RT) instability to cause the irregularity occurrences. The need of seeding agents such as gravity waves from atmospheric convective clouds to initiate the Rayleigh-Taylor instability may not be necessary.

Diurnal variation of natural convective wall flows and the resulting air change rate in a homogeneous urban canopy layer

The natural convective wall flows along an exterior wall of a 16-story high-rise building were measured in Guangzhou city, China. The Rayleigh number reached as high as 1014. The correlation between the vertical velocity along the wall and the temperature difference between the wall surface and ambient air was analyzed. The diurnal variation of the mean vertical velocity calculated according to a two-layer structure theory agreed well with the measured values. In this theory, the boundary layer along a high wall is characterized as a two-layer structure: the inner viscous layer is dominated by viscous force and buoyancy force/shear stress and has laminar flow, while the outer turbulent layer is dominated by buoyancy force, inertia and Reynolds stress. The velocity profile of the vertical component normal to the wall across the outer turbulent layer can be represented by a Gaussian profile. The air change rate due to natural convection for a homogeneous urban area, presenting a diurnal variation, was also estimated. As the mean building height h increases, the mean air change rate due to natural convection along the building walls increases slightly in the form of h1/30. The marginal benefit to the air change rate caused by natural convection decreases as the building height increases.

3-D crustal velocity structure of western Turkey: Constraints from full-waveform tomography

The Sea of Marmara and western Turkey are characterized by intense seismicity and crustal deformation due to transition tectonics between the North Anatolian Fault Zone (NAFZ) and the extensional Aegean. Seismic imaging of the crust and uppermost mantle in W-NW Turkey is crucial to obtain a better understanding of its seismotectonics and geodynamics. So far, the Sea of Marmara and surroundings were considered in various active and passive seismic experiments providing significant information on crustal properties. Here, we further investigate the 3-D seismic velocity structure in this rapidly deforming region using non-linear full-waveform tomography based on the adjoint method. Our model is constrained by complete waveforms of 62 regional earthquakes (epicentral distance<10°) with magnitudes Mw≥3.7, which occurred between 2007 and 2015. Validation tests show that our final 3-D Earth model is able to explain seismic waveforms from earthquakes not used in the inversion at periods from 8-100s to within the data uncertainties. Furthermore, quantitative resolution analyses yield 15 to 35km horizontal resolution lengths in the shallow and deep crust beneath well-covered areas of W-NW Turkey. Our full-waveform tomography results indicate the presence of strong lateral and vertical velocity variations (2.55≤VS≤4.0km/s) down to depths of ∼35km. The seismic velocity distribution is characteristic of highly deformed and distributed crustal features along major fault zones (e.g. NAFZ and its branches), historic and recent regional volcanism (e.g. Kula volcanic province), and metamorphic core complex developments (e.g. Menderes and Kazdağ massifs). Radial anisotropy is very strong (around 20%) throughout the crust, further attesting to strong deformation and heterogeneity. Generally, our 3-D model is overall consistent with the active tectonics of western Turkey.

Vertical turbulent exchange in the Black Sea pycnocline and its relation to water dynamics

Estimates of vertical turbulent diffusion coefficient (K t ) in the Black Sea pycnohalocline have been obtained from data of simultaneous observations of seawater temperature, salinity, density, and horizontal current velocity, obtained in the northeastern part of the Black Sea during 2013–2014 with a moored Aqualog profiler. A Munk and Andersson (1948) type parameterization, adapted for the Black Sea environment, is proposed for calculating K t . Strong short-period (several days) variability of turbulent exchange is revealed, induced by vertical shear variations of the current velocity.