Vertical Diffusion Coefficient Research Articles

A self-consistent model for dust settling and the vertical shear instability in protoplanetary disks

Abstract The spatial distribution of dust particles in protoplanetary disks affects dust evolution and planetesimal formation processes. The vertical shear instability (VSI) is one of the candidate hydrodynamic mechanisms that can generate turbulence in the outer disk region and affect dust diffusion. Turbulence driven by the VSI has a predominant vertical motion that can prevent dust settling. On the other hand, the dust distribution controls the spatial distribution of the gas cooling rate, thereby affecting the strength of VSI-driven turbulence. Here, we present a semi-analytic model that determines the vertical dust distribution and the strength of VSI-driven turbulence in a self-consistent manner. The model uses an empirical formula for the vertical diffusion coefficient in VSI-driven turbulence obtained from our recent hydrodynamical simulations. The formula returns the vertical diffusion coefficient as a function of the vertical profile of the cooling rate, which is determined by the vertical dust distribution. We use this model to search for an equilibrium vertical dust profile where settling balances with turbulent diffusion for a given maximum grain size. We find that if the grains are sufficiently small, there exists a stable equilibrium dust distribution where VSI-driven turbulence is sustained at a level of αz ∼ 10−3, where αz is the dimensionless vertical diffusion coefficient. However, as the maximum grain size increases, the equilibrium solution vanishes because the VSI can no longer stop the settling of the grains. This runaway settling may explain highly settled dust rings found in the outer part of some protoplanetary disks.

Investigating the impact of coupling HARMONIE-WINS50 (cy43) meteorology to LOTOS-EUROS (v2.2.002) on a simulation of NO2 concentrations over the Netherlands

Abstract. Meteorological fields calculated by numerical weather prediction (NWP) models drive offline chemical transport models (CTMs) to solve the transport, chemical reactions, and atmospheric interaction over the geographical domain of interest. HARMONIE (HIRLAM ALADIN Research on Mesoscale Operational NWP in Euromed) is a state-of-the-art non-hydrostatic NWP community model used at several European weather agencies to forecast weather at the local and/or regional scale. In this work, the HARMONIE WINS50 (cycle 43 cy43) reanalysis dataset at a resolution of 0.025° × 0.025° covering an area surrounding the North Sea for the years 2019–2021 was coupled offline to the LOTOS-EUROS (LOng-Term Ozone Simulation-EURopean Operational Smog model, v2.2.002) CTM. The impact of using either meteorological fields from HARMONIE or from ECMWF on LOTOS-EUROS simulations of NO2 has been evaluated against ground-level observations and TROPOMI tropospheric NO2 vertical columns. Furthermore, the difference between crucial meteorological input parameters such as the boundary layer height and the vertical diffusion coefficient between the hydrostatic ECMWF and non-hydrostatic HARMONIE data has been studied, and the vertical profiles of temperature, humidity, and wind are evaluated against meteorological observations at Cabauw in The Netherlands. The results of these first evaluations of the LOTOS-EUROS model performance in both configurations are used to investigate current uncertainties in air quality forecasting in relation to driving meteorological parameters and to assess the potential for improvements in forecasting pollution episodes at high resolutions based on the HARMONIE NWP model.

Day/Night Differences in Molecular Oxygen in the Martian Upper Atmosphere

AbstractWe use the extensive stellar occultation data set of the Imaging Ultraviolet Spectrograph aboard the Mars Atmosphere and Volatile EvolutioN spacecraft to determine the first quantification of vertical variation in O2 mole fraction separately for day and night in the ∼90–130 km altitude range. The upper atmospheric O2 variation is expected to be due to the interplay between diffusion and advection because of its long photochemical lifetime. It is therefore a useful tracer of the state of atmospheric mixing and circulation. The altitude‐averaged mixing ratio is measured to be 2.69(±0.03) × 10−3 for the nightside and 2.05(±0.03) × 10−3 for the dayside. The average O2 mole fraction for day and night are nearly identical below 105 km, consistent with the value of 1.61 × 10−3 derived from the Mars Curiosity Rover/Sample Analysis at Mars near‐surface measurements. At higher altitudes, dominated by molecular diffusive separation, the measured O2 mole fraction demonstrates a vertical gradient with a local time dependence. The nightside mole fraction is a factor of 1.37 ± 0.04 larger than the dayside value at ∼125 km. This nightside enhancement is explained in terms of the relative role of solar‐driven rapid horizontal winds at high altitudes and slower vertical diffusion, resulting in a nightside (dayside) downward (upward) diffusive flux. Using the 1‐D diffusion model, the measured profiles correspond to a vertical eddy diffusion coefficient K = 3.5(±1.5) × 106 cm2/s. The Mars Climate Database predicts comparable but lower day‐night differences in oxygen mole fraction due to an overestimated K = 7.0(±1.0) × 106 cm2/s, which affects atmospheric mixing as well as the rate of atmospheric escape to space.

A holistic model for microplastic dispersion in a free-surface wetland flow

The holistic model for microplastic dispersion is essential to conserving natural wetlands and enhancing the sewage treatment efficiency of constructed wetlands. A holistic mode is presented to analyze the microplastic transport caused by a continuous point-source discharge of substances into a wetland with an exposed water surface. The microplastic cloud's total quantity and centroid movement over each streamline are rigorously derived using the method of separation of variables and integral transform, and its longitudinal dispersion, skewness, and kurtosis are numerically analyzed using the finite difference method. Three dimensionless groups for the microplastic movement in wetland are presented. The relative importance of autonomous movement to the vertical diffusion coefficient can noticeably influence the mass center velocity and the longitudinal spread of the microplastic cloud, and its augments can enhance the amplitude of skewness and kurtosis in the initial transport stage. For the transient stage of transport during which microplastic cloud develops, the pulsating term of emission intensity shows little effect on skewness and kurtosis. The oscillation of skewness and kurtosis show less obvious for the long term evolution of microplastic cloud when the time scale across the water depth by diffusion is much larger than the oscillatory period.

Parameter estimation for ocean background vertical diffusivity coefficients in the Community Earth System Model (v1.2.1) and its impact on El Niño–Southern Oscillation forecasts

Abstract. This study investigates parameter estimation (PE) to enhance climate forecasts of a coupled general circulation model by adjusting the background vertical diffusivity coefficients in its ocean component. These parameters were initially identified through sensitivity experiments and subsequently estimated by assimilating the sea surface temperature and temperature–salinity profiles. This study expands the coupled data assimilation system of the Community Earth System Model (CESM) and the ensemble adjustment Kalman filter (EAKF) to enable parameter estimation. PE experiments were performed to establish balanced initial states and adjusted parameters for forecasting the El Niño–Southern Oscillation (ENSO). Comparing the model states between the PE experiment and a state estimation (SE) experiment revealed that PE can significantly reduce the uncertainty of these parameters and improve the quality of analysis. The forecasts obtained from PE and SE experiments further validate that PE has the potential to improve the forecast skill for ENSO.

Impact of different approaches to computing rotating stellar models. I. The case of solar metallicity

The physics of stellar rotation plays a crucial role in the evolution of stars, in their final fates, and for the properties of compact remnants. Diverse approaches have been adopted to incorporate the effects of rotation in stellar evolution models. This study seeks to explore the consequences that these various prescriptions for rotation have for the essential outputs of massive star models. We computed a grid of 15 and 60 M$_ odot $ stellar evolution models with the Geneva Stellar Evolution Code that accounted for both hydrodynamical and magnetic instabilities induced by rotation. In the 15 and 60 M$_ odot $ models, the choice of the vertical and horizontal diffusion coefficients for the nonmagnetic models strongly impacts the evolution of the chemical structure, but has a weak impact on the angular momentum transport and the rotational velocity of the core. In the 15 M$_ odot $ models, the choice of the diffusion coefficient impacts the convective core size during the core H-burning phase, regardless of whether the model begins core He-burning as a blue or red supergiant and regardless of the core mass at the end of He-burning. In the 60 M$_ odot $ models, the evolution is dominated by mass loss and is less strongly affected by the choice of the diffusion coefficient. In the magnetic models, magnetic instability dominates the angular momentum transport, and these models are found to be less strongly mixed than their rotating nonmagnetic counterparts. Stellar models with the same initial mass, chemical composition, and rotation may exhibit diverse characteristics depending on the physics applied. By conducting thorough comparisons with observational features, we can ascertain which method(s) produce the most accurate results in different cases.

Investigation of hydrothermal activity in the South West Indian ridge region using Ra isotopes and 227Ac as tracers

Hydrothermal vents have been shown to be important vectors for various chemical elements into the ocean. However, both the intensity of the chemical fluxes associated with these systems and the fate of the chemical elements along the plume are still largely overlooked. At two stations located above the South West Indian Ridge (SWIR), we investigate the distributions of the Ra quartet (223Ra, 224Ra, 226Ra and 228Ra) and 227Ac that have been used as tracers of hydrothermal activity. While the vertical distributions of 226Ra, 228Ra and 227Ac do not show a clear enrichment at depth, unusual signatures of excess 223Ra and 224Ra near the seafloor are attributed to the presence of a hydrothermal activity. The discrepancy observed between the different isotopes is attributed to different chemical reactivity when seawater circulates within the crust and/or to different regeneration rates within the fluid. A 1D diffusion model applied to the vertical profiles of short-lived Ra isotopes provided an estimation of the vertical eddy diffusivity coefficients (KZ) between 38 cm2 s−1 and 149 cm2 s−1. These high values suggest strong mixing likely favored by the complex bathymetry in the region. By combining these KZ with the vertical gradient of dissolved Fe (dFe), we estimate a vertical flux of dFe that ranges from 139 to 1173 nmol m−2 d-1. These results confirm that low-expansion-rate ridges could be significant sources of dFe to the deep ocean.

Analysis of the calibration and validation of hydrodynamic simulations with TELEMAC-3D model of the Patos Lagoon

This work presents the analysis of the calibration and validation of the computational model for two configurations of the Jetties of the Rio Grande Barra for hydrodynamic studies of the Patos Lagoon and the continental shelf of southern Brazil. The model used was TELEMAC-3D, which solves the three-dimensional Navier-Stokes equations, considering the hydrostatic hypothesis, to describe the dynamics of free surface geophysical fluids. We developed two finite element triangular meshes, with about 75.000 elements and seven sigma levels. The numerical domain reaches depths up to 2.427 m, with fluvial and oceanic liquid boundaries. The horizontal turbulence model adopted was Smagorinsky and the vertical model of mixing length. Current velocity data obtained from December 2005 were used for calibration, varying the coefficient of wind friction, horizontal and vertical velocity diffusion, and the salinity tracer. The coefficient of wind influence was the factor that most influenced the model results. The calculated Relative Mean Absolute Error was 0.383 dn. for surface and 0.167 dn. for depth, rated good and excellent, respectively. For validation, we evaluated the model performance on reproducing the salinity behavior, related to the depth of the environment, in January 2017. The calculated Root Mean Square Error was 7.37 dn. and the Relative Mean Absolute Error was 0.228 dn., rating the model performance as good. These variances between metrics is uniformly acceptable for real models. Salt transport is a complex phenomenon and depends on both advective and diffusive transport. Thus, it is possible to conclude that he proposed computational model is able to reproduce a complex phenomenon reliably.

Comprehensive evaluation of typical planetary boundary layer (PBL) parameterization schemes in China – Part 1: Understanding expressiveness of schemes for different regions from the mechanism perspective

Abstract. The optimal choice of the planetary boundary layer (PBL) parameterization scheme is of particular interest and urgency to a wide range of scholars, especially for many works involving models. At present, there have been many works to evaluate the PBL schemes. However, little research has been conducted into a more comprehensive and systematic assessment of the performance capability of schemes in key regions of China, especially when it comes to the differences in the mechanisms of the schemes themselves, primarily because there is scarcely sufficient observational data, computer resources, and storage support to complete the work. In this companion paper (i.e., Part 1), four typical schemes (i.e., YSU, ACM2, BL, and MYJ) are selected to systematically analyze and evaluate near-surface meteorological parameters, PBL vertical structure, PBL height (PBLH), and turbulent diffusion coefficient (TDC) in five key regions of China (i.e., North China Plain, NCP; Yangtze River Delta, YRD; Sichuan Basin, SB; Pearl River Delta, PRD and Northwest Semi-arid region, NS) in different seasons (i.e., January, April, July, and October). The differences in the simulated 2 m temperatures between the nonlocal closure schemes are mainly affected by the downward shortwave radiation, but to compare the nonlocal closure schemes with the local closure schemes, the effect of sensible heat flux needs to be further considered. The 10 m wind speed is under the influence of factors like the momentum transfer coefficient and the integrated similarity functions at night. The wind speeds are more significantly overestimated in the plains and basin, while less overestimated or even underestimated in the mountains, as a result of the effect on topographic smoothing in the model. Moreover, the overestimation of small wind speeds at night is attributable to the inapplicability of the Monin–Obukhov similarity theory (MOST) at night. The model captures the vertical structure of temperature well, while the wind speed is outstandingly overestimated below 1000 m, largely because of the TDC. The difference between the MOST and the mixing length theory, PBLH, and Prandtl number is cited as the reason for the difference between the TDC of the YSU and ACM2 schemes. The TDCs of the BL and MYJ schemes are affected by the mixing length scale, which of BL is calculated on the basis of the effect of buoyancy, while MYJ calculates it with the consideration of the effect of the total turbulent kinetic energy. The PBLH of the BL scheme is better than the other schemes because of the better simulation results of temperature. In general, to select the optimal scheme, it is necessary to offer different options for different regions with different focuses (heat or momentum). The first focus is on the temperature field. The BL scheme is recommended for January in the NCP region, especially for Beijing, and the MYJ scheme is better for the other 3 months. The ACM2 scheme would be a good match for the YRD region, where the simulation differences between the four schemes are small. The topography of the SB region is more complex, but for most of the areas in the basin, the MYJ scheme is proposed, and if more stations outside the basin are involved, the BL scheme is recommended. The MYJ scheme is applied to the PRD region in January and April, and the BL scheme in July and October. The MYJ scheme is counseled for the NS region. The second focus is the wind field. The YSU scheme is recommended if the main concern is the near-surface layer, and the BL scheme is suggested if focusing on the variation in the vertical direction. The final evaluation of the parameterization scheme and uncertainties will lay the foundation for the improvement of the modules and forecasting of the GRAPES_CUACE regional model developed independently in China.

Determination of the eddy diffusion in the Venusian clouds from VeRa sulfuric acid observations

Context. The vertical eddy diffusion coefficient (Kzz) characterizing the efficiency of vertical atmospheric mixing is essential for 1D planetary atmospheric modeling, but poorly constrained in the Venusian clouds, where our ability to observe tracer gases is limited. The Venusian clouds are mainly composed of H2SO4, which has significant mass cycles in this region. A critical process herein is that the H2SO4 vapor abundance in the middle and lower clouds of Venus is regulated by both condensation and eddy diffusion processes. Aims. This study is devoted to proposing a novel approach to estimating the Venusian cloud Kzz, examining the variability of the cloud Kzz in both equatorial and polar regions, and evaluating the derived Kzz through the implementation of a 1D photochemical model. Methods. The H2SO4 vapor data used in this study were obtained from observations conducted by Venus Express. A novel approach that relies on the premise that both eddy diffusion and condensation regulate the abundance of H2SO4 vapor was then applied to estimate the Venusian cloud Kzz. The global mean Kzz and its latitudinal variation were discussed. A 1D photochemistry-diffusion model was applied to evaluate the estimations. Results. Our calculations indicate that the global mean Kzz reaches 5 × 108 cm2 s−1 in the lower clouds, which is an order of magnitude larger than several observation-based estimations and model results. It rapidly decreases as the altitude increases above 54 km. Equatorial Kzz is three times as large as polar Kzz at 48 km, while polar Kzz reaches its peak below 46.5 km, where equatorial Kzz rapidly decreases as the altitude decreases. Conclusions. We provide an estimate of the Venusian cloud Kzz based on H2SO4 vapor observations. Significant latitudinal variations exist in the Venusian cloud Kzz.

Development of a Marine Radioactivity Expert System based on the Extended Marine Food Web: Experiments with Initial Bottom Contamination

An extended version of an expert system was developed as an effort to provide technical support to decision makers for the initial prompt assessment of environmental impacts of marine radioactivity, considering both pelagic and benthic marine food webs. The preliminary version of this system was firstly developed to determine the transfer of radionuclides through a pelagic marine food web (Kim et al, 2020). This system's approach was similar to the Cornell Mixing Zone Expert System (CORMIX) developed by Jirka (1995), as it used idealized settings for the physical/hydrodynamic coastal conditions. Existing or extended systems were executed by taking into account different kinds of radioactivity sources. The initial contamination of bottom sediment is considered in the present study, while the direct discharge to the coastal ocean from the nuclear power plant was considered in the early study. Assuming initial contamination, sensitivity experiments of temporal <sup>137</sup>Cs variations without/with horizontal advection and diffusion (EXP-WOHAD and EXP-WHAD, respectively) were conducted. In EXP-WOHAD, a total of six test cases were constructed, considering a range of vertical diffusion coefficients and sediment fluxes at the water-sea bed interface. The EXP-WHAD experiments were classified into two categories with six cases each, considering the horizontal diffusion and advection processes. The EXP-WOHAD results show that the vertical diffusion processes in the bottom sediment result in the exponential decay of the <sup>137</sup>Cs concentrations in the top sediment layer through upward and downward diffusive fluxes, producing pulse-like time variations in <sup>137</sup>Cs in the water column and the middle sediment layer. These sediment fluxes affect the peak height and its occurrence time in the water column and the middle sediment layer. From EXP-WHAD, it has been confirmed that part of <sup>137</sup>Cs diffused into the water column experiences horizontal dispersion and thereafter deposition to the bottom sediment. It is noted that due to the limited diffusion to the water column, the <sup>137</sup>Cs concentrations in benthic organisms are larger than those in pelagic organisms.

The Infrared Colors of 51 Eridani b: Micrometeoroid Dust or Chemical Disequilibrium?

We reanalyze the near-infrared spectra of the young extrasolar giant planet 51 Eridani b, which was originally presented in Macintosh et al. and Rajan et al. using modern atmospheric models, including a self-consistent treatment of disequilibrium chemistry due to turbulent vertical mixing. In addition, we investigate the possibility that significant opacity from micrometeors or other impactors in the planet’s atmosphere may be responsible for shaping the observed spectral energy distribution (SED). We find that disequilibrium chemistry is useful for describing the mid-infrared colors of the planet’s spectra, especially in regard to photometric data at the M band around 4.5 μm, which is the result of superequilibrium abundances of carbon monoxide, while the micrometeors are unlikely to play a pivotal role in shaping the SED. The best-fitting, micrometeoroid dust–free, disequilibrium chemistry, patchy cloud model has the following parameters: effective temperature T eff = 681 K with clouds (or without clouds, i.e., the grid temperature T grid = 900 K), surface gravity g = 1000 m s−2, sedimentation efficiency f sed = 10, vertical eddy diffusion coefficient K zz = 103 cm2 s−1, cloud hole fraction f hole = 0.2, and planet radius R planet = 1.0 R Jup.

Solute cloud evolution in channels with suspended vegetation of different configurations

Suspended vegetation's ability to handle solute accumulation in natural waters through their roots has sparked significant interest and research in using them to improve water quality. This research semi-analytically investigates the unsteady solute cloud evolution in channels with suspended vegetation after the point source release on the water surface, by solving the solute transport model with spatially variable flow field coefficients. Results show that regardless of gap ratio (the ratio of the height of the gap region to the water depth) and vegetation density, the solute cloud evolution in the preasymptotic stage (the dimensionless time ⟨Dz*⟩t*/h*2<1, where ⟨Dz*⟩ is the depth-averaged vertical turbulent diffusion coefficient. t* is the time, and h* is water depth.) can be featured by: the cloud centroid shifts upstream; the longitudinal dispersion coefficient increases; the solute cloud is positively skewed; and the solute accumulates in the vegetation layer on the upstream side and the bottom boundary layer on the downstream side. At around ⟨Dz*⟩t*/h*2∼1, the cloud centroid position and the longitudinal dispersion coefficient approach their asymptotic values, and the solute cloud is basically considered to follow the normal distribution longitudinally. In terms of the influences of configurations on the solute cloud during the whole dispersion process, the cloud centroid moves faster and reaches a farther asymptotic location due to a more serious blockage effect for a smaller gap ratio or larger vegetation density. In addition, a small gap ratio enhances the skewness and kurtosis of the cloud, while the vegetation density has little effect on them. Benefiting from the combined action of the violent velocity shear and the strong shear-scale diffusion which dominates the vertical mixing, the smallest gap ratio or highest vegetation density promotes the vertical mixing and yields the largest asymptotic longitudinal dispersion coefficient. Consequently, the vertical concentration distribution is the most uniform and the longitudinal concentration distribution is the flattest in these two cases.

Prediction of atmospheric air pollution near a coal stack in adverse weather conditions

Coal piles on the territory of enterprises are long-term sources of dust pollution of atmospheric air. Forecasting the level of dust pollution of the air for such objects is carried out, as a rule, for convection conditions. But during inversion, very high concentrations of dust can occur on industrial sites. The task of assessing the level of dust pollution of atmospheric air at an industrial site during dust emission in conditions of inversion from a coal stack is considered. A three-dimensional equation of convective-diffusion dispersion of contamination in atmospheric air, compatible with the approach of Prof. Berliand M. on determining the value of the vertical diffusion coefficient in the surface layer of the atmosphere for the case of inversion, to model dispersion of dust from a coal stack under inversion conditions is used. Numerical integration of the modeling equation of convective-diffusion transport of contamination is carried out on the basis of the splitting method compatible with the use of a locally one-dimensional finite-difference scheme. The results of a computational experiment to determine dust pollution zones at the Prydniprovsk thermal power station are presented.

CALCULATION OF ATMOSPHERIC AIR POLLUTION IN CASE OF CHEMICALLY DANGEROUS SUBSTANCE SPILL

Problem statement. The task of forecasting for chemical pollution areas at the industrial site during atmospheric inversion and chemically hazardous substance evaporation from the spill zone is considered. The purpose of the work is to develop a method for calculating the intensity and shape of pollution areas in the atmosphere that are formed under inversion conditions. Methodology. The three-dimensional impurity transport equation is used to calculate the atmospheric spread of chemically hazardous substances under inversion conditions, together with the M. Berland’s approach, to determine the vertical diffusion coefficient for this adverse meteorological condition. Numerical integration of the impurity transfer equation is realised using two finite-difference schemes. Both schemes are based on the splitting method. Results. An effective calculating method of atmospheric pollution areas formed during the evaporation of a chemically hazardous substance from the spill zone is proposed. A computer code to allow quick determination of these atmospheric pollution zones under inversion conditions is developed. The results of the computational experiment are presented. Scientific novelty. A method is developed to assess the size and intensity of chemical pollution zones formed in the atmosphere during inversion and evaporation of the substance from the spill area. Practical value. Based on the developed method, a code for a computational experiment to assess atmospheric pollution zones at industrial sites during emergency spills of chemically hazardous substances is generated.

Probing the Extent of Vertical Mixing in Brown Dwarf Atmospheres with Disequilibrium Chemistry

Evidence of disequilibrium chemistry due to vertical mixing in the atmospheres of many T- and Y-dwarfs has been inferred due to enhanced mixing ratios of CO and reduced NH3. Atmospheric models of planets and brown dwarfs typically parameterize this vertical mixing phenomenon with the vertical eddy diffusion coefficient, K zz . While K zz can perhaps be approximated in the convective regions in the atmosphere with mixing length theory, in radiative regions, the strength of vertical mixing is uncertain by many orders of magnitude. With a new grid of self-consistent 1D model atmospheres from T eff of 400–1000 K, computed with a new radiative-convective equilibrium python code PICASO 3.0, we aim to assess how molecular abundances and corresponding spectra can be used as a probe of depth-dependent K zz . At a given surface gravity, we find nonmonotonic behavior in the CO abundance as a function of T eff, as chemical abundances are sometimes quenched in either of two potential atmospheric convective zones, or quenched in either of two possible radiative zones. The temperature structure and chemical quenching behavior also change with gravity. We compare our models with available near-infrared and M-band spectroscopy of several T- and Y-dwarfs and assess their atmospheric vertical mixing profiles. We also compare to color–magnitude diagrams and make predictions for James Webb Space Telescope spectra. This work yields new constraints, and points the way to significant future gains, in determining K zz , a fundamental atmospheric parameter in substellar atmospheres, with significant implications for chemistry and cloud modeling.

Vertical circulation due to deep-water renewal and phytoplankton blooms in the tropical fjord of Ambon Bay, eastern Indonesia

This study provides the first observational evidence on the role of deep-water renewal in triggering phytoplankton blooms in a rare shallow-silled tropical fjord (Ambon Bay). Seasonal variation in the tidal-induced deep-water intrusions into inner Ambon Bay (IAB, the fjord basin) upwardly displaces water from the IAB deep layer towards the surface. The budget method was employed to quantify vertical mixing in the deep layer of IAB (below sill depth) post-intrusions (stagnant periods). Within a spring-neap sequence (~ 2 weeks), deep-water intrusion pulses in IAB were observed to be more frequent in the easterly monsoon (July, eight pulses) than the transitional season (October, three pulses). These intrusion pulses uplifted the resident deep waters of IAB with rates of 2.4 - 4.0 m/day in the easterly monsoon and 1.5 - 1.8 m/day in the transitional season. Depth-averaged vertical diffusion coefficient (Kv) in the deep layer of IAB slightly varied between easterly monsoon (3.3 × 10-4 m2/s) and transitional season (3.7 × 10-4 m2/s). The parameterization of the vertical mixing-stratification relationship (Kv ∝ [N2]-β) in the IAB deep layer was found to be larger in easterly monsoon (β = 1.104) than in transitional season (β = 0.694). Chlorophyll-a concentration in the water column of IAB increased during uplifting events with phytoplankton bloom conditions (> 5 mg/m3) found only in the easterly monsoon. The described uplift mechanism as a driver of phytoplankton blooms should be included in future analyses of water quality for IAB.

A Clear View of a Cloudy Brown Dwarf Companion from High-resolution Spectroscopy

Direct imaging studies have mainly used low-resolution spectroscopy (R ∼ 20–100) to study the atmospheres of giant exoplanets and brown dwarf companions, but the presence of clouds has often led to degeneracies in the retrieved atmospheric abundances (e.g., carbon-to-oxygen ratio, metallicity). This precludes clear insights into the formation mechanisms of these companions. The Keck Planet Imager and Characterizer (KPIC) uses adaptive optics and single-mode fibers to transport light into NIRSPEC (R ∼ 35,000 in the K band), and aims to address these challenges with high-resolution spectroscopy. Using an atmospheric retrieval framework based on petitRADTRANS, we analyze the KPIC high-resolution spectrum (2.29–2.49 μm) and the archival low-resolution spectrum (1–2.2 μm) of the benchmark brown dwarf HD 4747 B (m = 67.2 ± 1.8 M Jup, a = 10.0 ± 0.2 au, T eff ≈ 1400 K). We find that our measured C/O and metallicity for the companion from the KPIC high-resolution spectrum agree with those of its host star within 1σ–2σ. The retrieved parameters from the K-band high-resolution spectrum are also independent of our choice of cloud model. In contrast, the retrieved parameters from the low-resolution spectrum are highly sensitive to our chosen cloud model. Finally, we detect CO, H2O, and CH4 (volume-mixing ratio of log(CH4) = −4.82 ± 0.23) in this L/T transition companion with the KPIC data. The relative molecular abundances allow us to constrain the degree of chemical disequilibrium in the atmosphere of HD 4747 B, and infer a vertical diffusion coefficient that is at the upper limit predicted from mixing length theory.

VERTICAL MIXING NEAR THE SEA SURFACE OBSERVED BY SHORT-LIVED NATURAL RADIONUCLIDES ( 214PB AND 214BI).

I performed continuous gamma-ray measurements in seawater to observe the temporal variation of radon progenies ( 214Pb and 214Bi) derived from atmospheric precipitation. Underwater gamma-ray measurements using two NaI(Tl) detectors at different installation depths (1 and 4m) were recorded from July to November 2011 at the marine observation buoy. An increase in the concentration of 214Pb+214Bi in seawater was observed due to precipitation when the wind velocity was<2ms-1. However, this increase was only detected at 1m depth and a downward spread of 214Pb+214Bi was not observed. In contrast, at a wind velocity of>8ms-1, the 214Pb+214Bi concentration ratio at 4m/1m was almost constant (0.6-0.7) for most of the measurement irrespective of precipitation intensity. Assuming one-dimensional diffusion in the water column, the apparent vertical diffusion coefficient estimated from the temporal variation of 214Pb+214Bi concentrations at 4m/1m varied from<10 to 500cm2s-1 depending on the wind velocity.

Wavetrisk-2.1: an adaptive dynamical core for ocean modelling

Abstract. This paper introduces wavetrisk-2.1 (i.e. wavetrisk-ocean), an incompressible version of the atmosphere model wavetrisk-1.x with free surface. This new model is built on the same wavelet-based dynamically adaptive core as wavetrisk, which itself uses dynamico's mimetic vector-invariant multilayer rotating shallow water formulation. Both codes use a Lagrangian vertical coordinate with conservative remapping. The ocean variant solves the incompressible multilayer shallow water equations with inhomogeneous density layers. Time integration uses barotropic–baroclinic mode splitting via an semi-implicit free surface formulation, which is about 34–44 times faster than an unsplit explicit time-stepping. The barotropic and baroclinic estimates of the free surface are reconciled at each time step using layer dilation. No slip boundary conditions at coastlines are approximated using volume penalization. The vertical eddy viscosity and diffusivity coefficients are computed from a closure model based on turbulent kinetic energy (TKE). Results are presented for a standard set of ocean model test cases adapted to the sphere (seamount, upwelling and baroclinic turbulence). An innovative feature of wavetrisk-ocean is that it could be coupled easily to the wavetrisk atmosphere model, thus providing a first building block toward an integrated Earth system model using a consistent modelling framework with dynamic mesh adaptivity and mimetic properties.