Advective Conditions Research Articles

Two Regimes of Turbulent Fluxes Above a Frozen Small Lake Surrounded by Forest

We present experimental results of turbulent heat exchange between a small frozen lake surrounded by forest and the atmospheric boundary layer. Heat fluxes are measured at three levels using the eddy-covariance method and estimated by Monin–Obukhov similarity theory (MOST). In addition, we estimate the heat flux due to non-local turbulent transport of heat by coherent structures originating at the forest/lake transition, given the measured skewness of \( w^{\prime } \) and \( \overline{{w^{\prime } w^{\prime } T^{\prime } }} \), using a bimodal bottom-up–top-down model or the mass-flux models appropriate to the convective boundary layer. Two heat-flux-formation regimes in the surface layer are clearly distinguished. When the flow is from the vast forest, wind shear at the tree height leads to increased turbulent kinetic energy above the centre of the lake. Under conditions of simultaneous horizontal advection of warm air in the boundary layer above the canopy, a downward turbulent diffusion of negative heat flux leads to increased negative sensible heat flux in the surface layer, accompanied by an increasing third moment \( \overline{{w^{\prime } w^{\prime } T^{\prime } }} \). Since MOST does not account for this mechanism, MOST-based fluxes poorly correspond to the eddy-covariance data in this case. At the same time the contribution of coherent structures increases. In contrast, when the flow is from the gap connecting the lake with the wide clearing, the effects of landscape inhomogeneity significantly reduce. In this case the turbulent transport of the heat flux from the upper part of the boundary layer vanishes, \( \overline{{w^{\prime } w^{\prime } T^{\prime } }} \) is negligible, and the heat flux is now primarily determined by the wind speed and temperature differences between the surface and near-surface atmosphere. This is a surface-flow regime for which MOST has been developed, and MOST-based fluxes correlate well with eddy-covariance data.

Synoptyczne uwarunkowania napływu mas powietrza polarnego nad Lubelszczyznę

<p>Celem opracowania jest charakterystyka częstości i uwarunkowań synoptycznych napływu mas powietrza polarnego nad obszar Lubelszczyzny. Ich występowanie w ujęciu regionalnym określono dla godziny 12 UTC na podstawie dolnych map synoptycznych PIHM/IMGW-PIB z okresu 1951–2010. Częstość napływu mas powietrza polarnego (morskiego „świeżego” – PPm, morskiego starego – PPms, morskiego ciepłego – PPmc i kontynentalnego – PPk) w ciągu roku wynosiła 82,5%. Spośród wyróżnionych typów mas powietrza najczęściej notowano powietrze polarne morskie stare (PPms), z częstością przekraczającą 37% (maksimum w lecie, minimum wiosną). W latach 1951–2010 zaznaczyły się istotne zmiany w częstości napływu nad Lubelszczyznę mas PPk (spadek średnio o 11 dni na 10 lat), PPm (spadek 7 dni na 10 lat) i PPmc (wzrost o blisko 11 dni na 10 lat). We wszystkich porach roku masy PPms najczęściej napływały nad Lubelszczyznę z zachodu, PPmc z południowego zachodu i zachodu, PPm z zachodu i północo-zachodu, a PPk ze wschodu i południowego wschodu.</p>

COMPARISONS OF DYE PLUME MIGRATION AT THE NEAR-WALL REGION OF TWO DIFFERENT FLAT BEDS ROUGHENED WITH 7 MM AND 10 MM SYNTHETIC PLEXIGLAS BEADS

The detection of moving particles and the ability of processing the captured images using high-speed cameras can be an effective means of monitoring the sliding, and rolling movement of bed-load sediment along river beds. In this study, two different types of synthetic Plexiglas Beads of size 7mm and 10mm with porosity 0.7125 and 0.8522 respectively were used for the evaluation of the velocity profiles in a flume bath. Potassium permanganate (KMnO4) crystal of molecular weight 158.03 and density 1450 kg/m3 was used as a passive dye-tracer. The cavity region of the flat plate was attached to the oscillatory mechanism in the flume bath where plume activities were monitored. When there is oscillatory flow, the crest of roughness elements induce elevation zones to force (advection) the flow upwards and pull it down at the trough phases as the tracer plume scales over the obstacles, establishing low and high pressure zones in the flow. The enhanced particles in the process mix and dissolve or decay faster with increasing oscillatory frequency, resulting into inter-particle collisions which initiate the conditions of advection and shear dispersion. This phenomenon could be a combination or coupling of the processes of gradient fluctuations enhanced through dispersion due to pressure in the macroscopic pore-fluid field caused by the oscillatory motion. The lightening as the dye-particles cascade in the porous medium is associated with mixing-gain due to the enhanced oscillatory motion. It was observed that the depth of the tracer-blob entrapment is inversely proportional to the friction velocity.

An inclusive view of Saharan dust advections to Italy and the Central Mediterranean

We address observations of physical and chemical properties of Saharan dust advections (SDA) as observed in the Central Mediterranean basin, within the framework of the LIFE+10, DIAPASON project (www.diapason-life.eu). DIAPASON aimed at the definition of best practices and tools to detect and evaluate the contribution of Saharan dust to ground particulate matter (PM) loads. Polarization-sensitive, automated lidar-ceilometers (PLC) are one of the tools prototyped and used in the Rome area to reach this goal. The results presented in this study focus on: 1) the effectiveness of various observational tools at detecting and characterizing atmospheric dust plumes, and 2) processes and properties of Saharan dust advections reaching the central Mediterranean region. In this respect, the combination of numerical model forecasts and time-resolved (at least hourly) PLC or chemical observations was found to constitute an efficient way to predict and confirm the presence of Saharan dust. In the period 2011–2014, Saharan dust advections were observed to reach over Rome on about 32% of the days. In some 70% of these days the dust reached the ground in dry conditions, while 30% of advection days involved wet deposition. Dry (wet) deposition was found to maximize (minimize) in summer. The northern Sahara between Algeria and Tunisia (Grand Erg Oriental), was confirmed as the most frequent region of origin of the dust mobilized towards central Italy. Secondary source regions include northern Morocco and Libya. On a statistical basis, Saharan advections to Rome were preceded by increasing atmospheric pressure and stability. These conditions were found to favor the accumulation of aerosols related to local emission sources before the SDA reached the ground. Meteorology (precipitation and turbulence in primis) resulted to be an important modulator of PM concentrations during SDAs. Magnitude and timing of these factors should be well considered to correctly evaluate the dust share in PM loads or the related health effects. Saharan advections observed during DIAPASON affected particle concentrations down to diameters of about 0.6–1 μm, with number concentrations peaking at the 2.5 μm diameter range. These advections were associated with a significant increase in Si-rich particles containing a non-negligible fraction of water. Rainfall was observed to preferentially remove dust particles larger than 2 μm, causing a significant depletion in the Ca-rich fraction with respect to the Si-rich one. The increase in PLC depolarization ratios above 5%, as well as the hourly PIXE records of the Si/Ca ratio increasing above 1 were found to represent good markers for the actual presence of Saharan dust particulate matter, when Saharan advection conditions are occurring.

Simulation of Buffered Advection Diffusion of Calcium in a Hepatocyte Cell

The calcium signaling is the basic and vital component of cell communication in almost all types of human and animal cells. All the vital functions of parenchymal cell of liver known as hepatocyte cell are regulated by this calcium signaling. The calcium concentration at specific levels are responsible for each of the various functions of the cell. The deeper understanding of the mechanisms and the factors affecting the calcium dynamics in a hepatocyte cell is vital for various clinical applications related to diseases of the liver. In this paper, mathematical model is proposed to study intracellular calcium dynamics in hepatocyte cell by incorporating the processes like diffusion, advection, buffering etc. The reaction advection diffusion equation has been employed for a two dimensional unsteady state case, to form an initial and boundary value problem. The initial and boundary conditions are formulated based on the physical conditions of cell. Finite volume method and Crank Nicolson scheme have been employed along spatial and temporal dimension respectively to obtain numerical solution. The impact of endogenous and exogenous buffers, advection and diffusion on calcium dynamics in hepatocyte cell has been studied with the help of numerical results. The rise and fall in spatio-temporal calcium concentration in hepatocyte cell in response to specific conditions of advection, diffusion and buffer concentrations is observed. These variations in spatio-temporal calcium concentrations are regulated in narrow range due to fine coordination among these processes of cell under normal environmental and physiological conditions. The proposed model gives better understanding of interrelationship and interdependence of these physical processes for fine coordination among them to maintain structure and functions of cell.

The effect of weather patterns on winter small city urban heat islands

The urban heat island (UHI) phenomenon has been gaining intensity because of population growth, continuous urbanization and inappropriate urban planning and design. Geospatial models can importantly contribute to solving the negative impacts left behind by these developments in the urban environment. Here, the influence of different weather patterns (anticyclonic, cyclonic and advective), occurring as a consequence of regional synoptic conditions, on UHI intensity and morphology was studied. The previously published geographically weighted regression UHI model was used in order to predict the behaviour of the urban–rural temperature anomaly in different weather patterns in a small city named Ljutomer (8 km2 of built‐up area occupied by 3,500 inhabitants) located in the northeast part of Slovenia. As expected, UHI intensity was significantly higher in the anticyclonic weather pattern compared to cyclonic and advective conditions. The urban–rural temperature contrast was at least recognizable under a turbulent windy atmosphere. Surprisingly, Ljutomer's UHI can be most accurately modelled in the cyclonic weather pattern, followed by advective and anticyclonic conditions, and statistically significant cold‐spots can be better predicted, with selected predictor variables, than hot‐spots.

Heat storage and its effect on the surface energy balance closure under advective conditions

High quality estimates of evapotranspiration (ET) are needed for water-limited agriculture where irrigation is necessary to efficiently grow crops. Eddy covariance (EC) systems are observational tools used to measure water and heat fluxes, but a tendency to underestimate fluxes causes a lack of surface energy balance closure. Surface energy budgets are useful for verifying ET estimates, especially in advective conditions that affect energy partitioning. Here, we explored the effect of heat storage and advective conditions on surface energy balance closure for the 2014 and 2015 growing seasons in Bushland, Texas. Storage components were estimated near the center of an irrigated sorghum field using an array of soil and surface layer measurements. A comparison of EC estimated turbulent fluxes and available energy consisting of net radiation, soil heat flux, and storage was used to identify advective conditions and assess surface energy balance closure. Our results indicated daytime mean heat storage of approximately 40 W m−2 with a diurnal pattern featuring a midday peak that exceeded the evening minimum in magnitude, mostly reflective of soil heat storage but also affected by air, water, and biomass heat storage during the morning hours and photosynthesis storage during midday hours. Daytime advective conditions were associated with higher heat storage frequently under stable atmospheric conditions. The surface energy balance was more closed in 2014 than 2015; the 2014 energy balance exhibited a hysteretic pattern with a surplus of turbulent energy in the afternoon, whereas systematic underestimation was common in 2015. This finding is related to a larger proportion of data in 2014 being advective, characterized by a lower Bowen ratio and greater ET, particularly during the late afternoon. Regardless of advection classification, heat storage was demonstrated to be important for daytime energy balance in this irrigated cropland.

One-step approach for estimating maize actual water use: Part I. Modeling a variable surface resistance

In a global scenario of climate change, water scarcity and population growth, it is imperative to optimize crop water management. One way is by calibrating a physically based crop evapotranspiration (ET) model, in the so-called one-step approach; as opposed to the two-step approach that uses reference evapotranspiration and crop coefficients. The Penman–Monteith (Symposium of the society for experimental biology, the state and movement of water in living organisms, Academic Press, Inc., New York; Monteith, Symposium of the society for experimental biology, the state and movement of water in living organisms, Academic Press, Inc., New York, 1965) ET model uses a bulk surface resistance (rs) term. This variable describes the resistance (stomatal, leaf, and canopy) to crop water transpiration and water evaporation from the soil surface. If the crop is not transpiring at a potential rate the rs resistance depends on the water status of the soil and vegetation. The stomatal resistance is influenced by climate and by water availability. However, this influence is different from crop to crop. The resistance increases when the crop is stressed and when the soil water availability limits ET. In this study, surface resistance was parameterized for grain maize considering a number of plant and environmental variables for water stressed and non-stressed conditions. The independent explanatory variables that facilitated a good calibration of rs, on a half-hourly basis, were: net radiation, photosynthetic active radiation, aerodynamic resistance, crop height, and leaf area index. The application of the obtained “rs” model (based on the variables mentioned above) resulted in maize ET (mm 30-min−1) estimation error of less than 1 ± 10% when evaluated with eddy covariance based ET data. This result is evidence that it is possible to calculate maize ET with a small associated error at very small time scales, for water deprived and advective conditions, using the one-step ET approach.

Synoptyczne uwarunkowania napływu mas powietrza arktycznego i zwrotnikowego nad Lubelszczyznę

<p>Celem opracowania jest charakterystyka częstości i uwarunkowań synoptycznych napływu mas powietrza arktycznego i zwrotnikowego nad obszar Lubelszczyzny. Ich występowanie w ujęciu regionalnym określono dla godziny 12 UTC na podstawie dolnych map synoptycznych PIHM/IMGW z okresu 1951-2010. Do oceny uwarunkowań synoptycznych napływu analizowanych mas powietrza wykorzystano kalendarz typów cyrkulacji dla Lubelszczyzny. Częstość napływu mas powietrza arktycznego w ciągu roku wynosiła 13,4%. Największy udział tych mas występuje wiosną, z maksimum w kwietniu (20,4%), najmniejszy zaś latem (w lipcu i sierpniu poniżej 5%). Rzadziej notuje się napływ powietrza zwrotnikowego (4,1% wszystkich dni w roku). Najczęściej nad Lubelszczyzną występuje ono w lecie (z maksimum w lipcu – 9,2%), natomiast najrzadziej w zimie (< 1%). W latach 1951-2010 zaznaczyły się istotne zmiany w częstości napływu nad Lubelszczyznę mas arktycznych (wzrost średnio o 8 dni na 10 lat) i zwrotnikowych (wzrost o blisko 3 dni na 10 lat). Udział mas arktycznych zwiększył się w zimie, jesieni i na wiosnę, mas zwrotnikowych zaś w lecie. We wszystkich porach roku największe prawdopodobieństwo występowania powietrza arktycznego notowano podczas typów cyrkulacji ze składową północną i północno-wschodnią, najmniejsze zaś w typach warunkujących adwekcję powietrza z południa i południo-zachodu. W przypadku powietrza zwrotnikowego największe prawdopodobieństwo jego wystąpienia notuje się podczas napływu powietrza z kierunków E-SE-S-SW. Niezależnie od pory roku, podczas występowania powietrza arktycznego i zwrotnikowego wykazano występowanie wyraźnych anomalii, zarówno temperatury powietrza na powierzchni izobarycznej 850 hPa, jak i średniej grubości warstwy powietrza między powierzchnią izobaryczną 850 i 1000 hPa.</p>

Impact of local diffusion on macroscopic dispersion in three-dimensional porous media

While macroscopic longitudinal and transverse dispersion in three-dimensional porous media has been simulated previously mostly under purely advective conditions, the impact of diffusion on macroscopic dispersion in 3D remains an open question. Furthermore, both in 2D and 3D, recurring difficulties have been encountered due to computer limitation or analytical approximation. In this work, we use the Lagrangian velocity covariance function and the temporal derivative of second-order moments to study the influence of diffusion on dispersion in highly heterogeneous 2D and 3D porous media. The first approach characterizes the correlation between the values of Eulerian velocity components sampled by particles undergoing diffusion at two times. The second approach allows the estimation of dispersion coefficients and the analysis of their behaviours as functions of diffusion. These two approaches allowed us to reach new results. The influence of diffusion on dispersion seems to be globally similar between highly heterogeneous 2D and 3D porous media. Diffusion induces a decrease in the dispersion in the direction parallel to the flow direction and an increase in the dispersion in the direction perpendicular to the flow direction. However, the amplification of these two effects with the permeability variance is clearly different between 2D and 3D. For the direction parallel to the flow direction, the amplification is more important in 3D than in 2D. It is reversed in the direction perpendicular to the flow direction.

An Analytical Model of Fickian and Non-Fickian Dispersion in Evolving-Scale Log-Conductivity Distributions

The characteristics of solute transport within log-conductivity fields represented by power-law semi-variograms are investigated by an analytical Lagrangian approach that accounts for the automatic frequency cut-off induced by the initial contaminant plume size. The transport process anomaly is critically controlled by the magnitude of the Péclet number. Interestingly enough, unlike the case of fast-decaying correlation functions (i.e., exponential or Gaussian), the presence of intensive transverse diffusion acts as an antagonist mechanism in the process of Fickian regime achievement. On the other hand, for markedly advective conditions and finite initial plume size, even the ergodic longitudinal dispersion coefficient turns out to be asymptotically constant, and the corresponding expected concentration distribution can therefore be obtained by conventional mathematical methods.

Ocean Acidification Changes Abiotic Processes but Not Biotic Processes in Coral Reef Sediments

In coral reefs, sediments play a crucial role in element cycling by contributing to primary production and the remineralization of organic matter. We studied how future ocean acidification (OA) will affect biotic and abiotic processes in sediments from two coral reefs of the Great Barrier Reef, Australia. This was investigated in the laboratory under conditions where water-sediment exchange was dominated by molecular diffusion (Magnetic Island) or by porewater advection (Davies Reef). OA conditions (+ΔpCO2: 170–900 µatm, -ΔpH: 0.1–0.4) did not affect photosynthesis, aerobic and anaerobic organic matter remineralization and growth of microphytobenthos. However, microsensor measurements showed that OA conditions reduced the porewater pH. Under diffusive conditions these changes were limited to the upper sediment layers. In contrast, advective conditions caused a deeper penetration of low pH water into the sediment resulting in an earlier pH buffering by dissolution of calcium carbonate (CaCO3). This increased the dissolution of Davis Reef sediments turning them from net precipitating (-0.8 g CaCO3 m-2 d-1) under ambient to net dissolving (1 g CaCO3 m-2 d-1) under OA conditions. Comparisons with in-situ studies on other reef sediments show that our dissolution rates are reasonable estimates for field settings. We estimate that enhanced dissolution due to OA will only have a minor effect on net ecosystem calcification of the Davies Reef flat (< 4%). However, it could decrease recent sediment accumulation rates in the lagoon by up to 31% (by 0.2–0.4 mm year-1), reducing valuable reef space. Furthermore, our results indicate that high-magnesium calcite is predominantly dissolving in the studied sediments and a drastic reduction in this mineral can be expected on Davis Reef lagoon in the near future, leaving sediments of an altered mineral composition. This study demonstrates that biotic sediment processes will likely not directly be affected by OA. Ensuing indirect effects of OA-induced sediment dissolution on biotic processes are discussed.

Assessment of the Energy Balance Closure under Advective Conditions and Its Impact Using Remote Sensing Data

AbstractA unique and intensive flux observation matrix was established during May to September of 2012 in an oasis–desert area located in the middle reaches of the Heihe River basin, China. The flux observation matrix included 22 eddy covariance systems belonging to the first thematic experiment of the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) project. The energy balance closure ratio (EBR) was assessed and possible mechanisms were investigated using remote sensing data. The results showed that 1) the EBR was in the range of 0.78–1.04 at all sites with an average EBR of 0.92, and 2) the calculated daily EBR exhibited better performance than the 30-min averages. 3) The heat storage cannot be ignored during the crop growing season. An improvement of approximately 6% in the total closure was found after considering the heat storage terms (canopy and photosynthesis storage) in the energy budget at the maize surface, and the canopy and photosynthesis showed approximately equal contributions of 3% for each storage term. The results also showed that 4) the land heterogeneous surface had a significant effect on the EBR. The EBR decreased with land surface heterogeneity increasing (taking the standard deviation of the surface temperature in the eddy covariance system source area as an index). The EBR also decreased when irrigation occurred and increased after irrigation was completed. The advection or secondary circulation broke the closed system of the energy balance given the phenomenon of EBR increasing when the advection or secondary circulation occurred.

Evapotranspiration and energy balance measurements over a soybean field in the semiarid sowthwestern region of Buenos Aires province (Argentina)

Two field experiments were carried out in a semiarid region of Argentina over a soybean (<i>Glycine max</i> L. Merrill) field. The sites of study were San Adolfo (39˚ 23’ S, 62˚ 22’ W, 22 m.a.s.l.) and Nueva Roma (38˚ 29’ S, 62˚ 39’ W, 70 m.a.s.l.). Soybeans were planted on Jan 4 (San Adolfo) and Nov 27 (Nueva Roma) in 0.75 m wide rows and at 400000 pl/ha during two consecutive growing seasons. Energy balance and evapotranspiration (ET) were estimated during the reproductive stages from full bloom (R2) to full maturity (R8). In Nueva Roma ET or latent heat flux (LE) was estimated using the Bowen ratio-energy balance (BREB) (LEβ) and the Priestley-Taylor equation (LE_PT) with α_PT =1.26, 48 h after irrigationor rain. Both methods could be used to predict ET since the ratio LEβ/LE_PT ranged between 0.83 and 0.95. The observed Bowen ratio values were almost 0 during and after rain and increased to approximately 0.45 several days after rain. In San Adolfo LE was estimating using the Priestley-Taylor equation. For both sites the regression analysis for comparison available energy (Rn-G) and LE using BREB or LE_PT indicated that, approximately 90% of the available energy was consumed by LE without detecting significative advective conditions.

Investigating the sealing capacity of a seal system in rock salt (DOPAS project)

Abstract This paper describes research and development work on plugging and sealing repositories, an issue of fundamental importance for the rock salt option which represents one of the three European repository options, besides the clay rock and the crystalline rock options. The programme aims at providing experimental data needed for the theoretical analysis of the long-term sealing capacity of concrete-based sealing materials. In order to demonstrate hydro-mechanical material stability under representative load scenarios, a comprehensive laboratory testing programme is carried out. This comprises investigation of the sealing capacity of the combined seal system and impact of the so-called excavation-damaged zones (EDZ) as well as investigation of the hydro-chemical long-term stability of the seal in contact with different brines under diffusive and advective conditions. This paper presents experimental approaches and preliminary results from laboratory investigations on salt concrete and combined systems as obtained to date.

Applications of a thermal-based two-source energy balance model using Priestley-Taylor approach for surface temperature partitioning under advective conditions

In this study ground measured soil and vegetation component temperatures and composite temperature from a high spatial resolution thermal camera and a network of thermal-IR sensors collected in an irrigated maize field and in an irrigated cotton field are used to assess and refine the component temperature partitioning approach in the Two-Source Energy Balance (TSEB) model. A refinement to TSEB using a non-iterative approach based on the application of the Priestley-Taylor formulation for surface temperature partitioning and estimating soil evaporation from soil moisture observations under advective conditions (TSEB-A) was developed. This modified TSEB formulation improved the agreement between observed and modeled soil and vegetation temperatures. In addition, the TSEB-A model output of evapotranspiration (ET) and the components evaporation (E), transpiration (T) when compared to ground observations using the stable isotopic method and eddy covariance (EC) technique from the HiWATER experiment and with microlysimeters and a large monolithic weighing lysimeter from the BEAREX08 experiment showed good agreement. Difference between the modeled and measured ET measurements were less than 10% and 20% on a daytime basis for HiWATER and BEAREX08 data sets, respectively. The TSEB-A model was found to accurately reproduce the temporal dynamics of E, T and ET over a full growing season under the advective conditions existing for these irrigated crops located in arid/semi-arid climates. With satellite data this TSEB-A modeling framework could potentially be used as a tool for improving water use efficiency and conservation practices in water limited regions. However, TSEB-A requires soil moisture information which is not currently available routinely from satellite at the field scale.

The solubility of nickel and its migration through the cementitious backfill of a geological disposal facility for nuclear waste

This work describes the solubility of nickel under the alkaline conditions anticipated in the near field of a cementitious repository for intermediate level nuclear waste. The measured solubility of Ni in 95%-saturated Ca(OH)2 solution is similar to values obtained in water equilibrated with a bespoke cementitious backfill material, on the order of 5×10−7M. Solubility in 0.02M NaOH is one order of magnitude lower. For all solutions, the solubility limiting phase is Ni(OH)2; powder X-ray diffraction and scanning transmission electron microscopy indicate that differences in crystallinity are the likely cause of the lower solubility observed in NaOH. The presence of cellulose degradation products causes an increase in the solubility of Ni by approximately one order of magnitude. The organic compounds significantly increase the rate of Ni transport under advective conditions and show measurable diffusive transport through intact monoliths of the cementitious backfill material.

Simplified heat transfer analysis method for large-scale boreholes ground heat exchangers

A simplified heat transfer method to analyze the thermal performance of large-scale boreholes ground heat exchangers (GHE) has been proposed considering the geometric symmetry of borehole layout. Taking the ground heat exchanger with matrix layout of vertical boreholes as the example, the ground temperature distribution is analyzed under the conditions of no groundwater advection by the proposed simplified method. Based on the simulation results, a representative boreholes matrix can be proposed to replace the original large-scale ground heat exchanger for heat transfer analysis. Meanwhile, the results show that the representative boreholes matrix can be determined by the thermal influence radius of a single borehole by assuming all the boreholes have the same thermal loads and also in the same geological conditions, geometry parameters and operating conditions. It is indicated that the thermal influence radius of a single borehole can be obtained according to the allowed error range of the ground temperature responses, which can correspondingly determine the number of the representative boreholes matrix.

Tomography-based characterization of ice-air interface dynamics of temperature gradient snow metamorphism under advective conditions

Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. A functional understanding of this process is essential for many disciplines, from modeling the effects of snow on regional and global climate to assessing avalanche formation. Time-lapse X-ray microtomography was applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Experiments specifically analyzed sublimation and deposition of water vapor on the ice structure. In addition, an analysis of the ice-air interface dynamics was carried out using a macroscopic equivalent model of heat and water vapor transport through a snow layer. The results indicate that sublimation of the ice matrix dominated for flow rates < 10−6 m3 s−1 while during increased mass flow rates the water vapor deposition supplied by the advective flow counteracted sublimation. A flow rate dependence of water vapor deposition at the ice interface was observed, asymptotically approaching an average estimated maximum deposition rate on the whole sample of 1.05 · 10−4 kg m−3 s−1. The growth of microsized whisker-like crystals on larger ice crystals was detected on microscope photographs, leading to an increase of the specific surface area and thus suggest a change of the physical and optical properties of the snow. The estimated values of the curvature effect of the ice crystals and the interface kinetic coefficient are in good agreement with previously published values.

SEBAL-A: A Remote Sensing ET Algorithm that Accounts for Advection with Limited Data. Part I: Development and Validation

The Surface Energy Balance Algorithm for Land (SEBAL) is one of the remote sensing (RS) models that are increasingly being used to determine evapotranspiration (ET). SEBAL is a widely used model, mainly due to the fact that it requires minimum weather data, and also no prior knowledge of surface characteristics is needed. However, it has been observed that it underestimates ET under advective conditions due to its disregard of advection as another source of energy available for evaporation. A modified SEBAL model was therefore developed in this study. An advection component, which is absent in the original SEBAL, was introduced such that the energy available for evapotranspiration was a sum of net radiation and advected heat energy. The improved SEBAL model was termed SEBAL-Advection or SEBAL-A. An important aspect of the improved model is the estimation of advected energy using minimal weather data. While other RS models would require hourly weather data to be able to account for advection (e.g., METRIC), SEBAL-A only requires daily averages of limited weather data, making it appropriate even in areas where weather data at short time steps may not be available. In this study, firstly, the original SEBAL model was evaluated under advective and non-advective conditions near Rocky Ford in southeastern Colorado, a semi-arid area where afternoon advection is common occurrence. The SEBAL model was found to incur large errors when there was advection (which was indicated by higher wind speed and warm and dry air). SEBAL-A was then developed and validated in the same area under standard surface conditions, which were described as healthy alfalfa with height of 40–60 cm, without water-stress. ET values estimated using the original and modified SEBAL were compared to large weighing lysimeter-measured ET values. When the SEBAL ET was compared to SEBAL-A ET values, the latter showed improved performance, with the ET Mean Bias Error (MBE) reduced from −17.1% for original SEBAL to 2.2% for SEBAL-A and the Root Mean Square Error (RMSE) reduced from 25.1% to 10.9%, respectively. It was therefore concluded that the developed SEBAL-A model was capable of accounting for advection and therefore suitable for arid and semi-arid regions where advection is common.