Vertical Temperature Gradient Research Articles

Linear dynamics of a thick liquid layer subjected to an oblique temperature gradient

The present study aims to demonstrate the application of the oblique temperature gradient (OTG) to manipulate the buoyancy instabilities and resulting mixing. To accomplish this, we consider a model consisting of a liquid layer supported by a perfectly conducting bottom wall from below and the upper surface is exposed to ambient inert gas in a shallow container. The stability analysis employs the pseudospectral method and perturbation energy budget approach. The imposed OTG consists of a negative vertical temperature gradient (VTG), which leads to unstable density stratification, and a negative horizontal temperature gradient (HTG) component responsible for the Hadley circulation, which can be utilised to control instabilities. Without the HTG, a Rayleigh–Bénard mode of instability exists due to the imposed VTG termed as a VTG mode. The imposed HTG induces a linear VTG term and a quintic polynomial VTG term in the bottom wall-normal coordinate $y$ . The induced linear VTG term reinforces the imposed VTG, while the induced quintic polynomial VTG term opposes the imposed VTG. For the vanishing Biot number ( $Bi$ ), the induced quintic VTG term stabilises the VTG mode for the Prandtl number, $Pr=7$ . However, for $Pr=0.01$ , the Reynolds stresses associated with the Hadley circulation destabilise the VTG mode. For non-zero $Bi$ , new streamwise and spanwise instability modes arise for $Pr=7$ due to the induced linear VTG term. Physical arguments show that the unstable density stratification near the gas–liquid interface caused by the synergistic effect of the imposed VTG and the induced linear VTG term lead to the existence of the predicted new modes. The present study thus shows that the strength of the HTG can be utilised to control the instability modes and critical parameters, thereby demonstrating the utility of the OTG in manipulating the buoyancy instabilities.

Influence of Prandtl number on the chaos transition for pure natural and Rayleigh–Bénard convections inside a rectangular cavity

A peculiar flow instability known as multiple chaos transitions was recently reported for the free convection in an enclosure where the direction of the temperature gradient changes continuously; it has been explained to be attributed to the competition for dominance between pure natural and Rayleigh–Bérnard convections. In this study, the chaos transition of free convection is investigated when a horizontal or vertical temperature gradient forms in a rectangular cavity. Analyses are conducted under a laminar flow regime, with Prandtl numbers ranging from 0.01 to 50 and Rayleigh numbers up to 109. In the horizontal temperature gradient, the chaos-transition Rayleigh number increases monotonically with the Prandtl number. However, under vertical temperature gradient conditions, it reaches the maximum value at approximately Pr = 0.5. Contrary to the general knowledge that higher-Prandtl number fluids effectively stabilize natural convection, a free convection in a vertical temperature gradient initiates a new flow instability when the Prandtl number is over 1.0, where momentum and thermal diffusions balance each other. The oscillation pattern, 2D phase trajectory, power spectral density, and Poincaré point of equivalent thermal conductivity are used to assess the free-convection flow instability.

Synchronizing the Western Gotland Basin (Baltic Sea) and Lake Kälksjön (central Sweden) sediment records using common cosmogenic radionuclide production variations

Multi-archive studies of climate events and archive-specific response times require synchronous time scales. Aligning common variations in the cosmogenic radionuclide production rate via curve fitting methods provides a tool for the continuous synchronization of natural environmental archives down to decadal precision. Based on this approach, we synchronize 10Be records from Western Gotland Basin (WGB, Baltic Sea) and Lake Kälksjön (KKJ, central Sweden) sediments to the 14C production time series from the IntCal20 calibration curve during the Mid-Holocene period ~6400 to 5200 a BP. Before the synchronization, we assess and reduce non-production variability in the 10Be records by using 10Be/9Be ratios and removing common variability with the TOC record from KKJ sediments based on regression analysis. The synchronizations to the IntCal20 14C production time scale suggest decadal to multi-decadal refinements of the WGB and KKJ chronologies. These refinements reduce the previously centennial chronological uncertainties of both archives to about ± 20 (WGB) and ±40 (KKJ) years. Combining proxy time series from the synchronized archives enables us to interpret a period of ventilation in the deep central Baltic Sea basins from ~6250 to 6000 a BP as possibly caused by inter-annual cooling reducing vertical water temperature gradients allowing deep water formation during exceptionally cold winters.

Early frost detection in wheat using machine learning from vertical temperature distributions

Frost damage significantly reduces global wheat production. Temperature development in wheat crops is a complex and dynamic process. During frost events, a vertical temperature gradient develops from soil to canopy due to the heat loss from the soil and canopy boundary. Understanding these temperature gradients is essential for improving frost management strategies in wheat crops. We hypothesise that the relationship between the temperatures of the canopy, plant and ground can be an early indicator of frost. We collected infrared thermal (IRT) images from field-grown wheat crops and extracted the temperatures from the canopy, plant and ground layers. We analysed these temperatures and applied four machine learning (ML) models to detect coldness scales leading to frost nights with different degrees of severity. We implemented a gated recurrent unit, convolutional neural network, random forest and support vector machines to evaluate the classification. Our study shows that in these three layers, temperatures have a relationship that can be used to determine frost early. The patterns of these three temperatures on a frost night differ from a cold no-frost winter night. On a no-frost night we observed that the canopy is the coldest, plant is warm, and the soil is warmest, and these three temperatures did not converge. On the other hand, on a frost night, before the frost event, the canopy and plant temperatures converged as the cold air penetrated through the canopy. These patterns in temperature distribution were translated into an ML problem to detect frost early. We classified coldness scales based on the temperatures conducive to frost formation of a certain severity degree. Our results show that the ML models can determine the coldness scales automatically with 93%–98% accuracy across the four models. The study presents a strong foundation for the development of early frost detection systems.

A Satellite Analysis: Comparing Two Medicanes

Morphological features of the Mediterranean Sea basin have recently been precursors to a significant increase in the formation of extreme events, in relation to climate change effects. It happens very frequently that rotating air masses and the formation of mesoscale vortices can evolve into events with characteristics similar to large-scale tropical cyclones. Generally, they are less intense, with smaller size and duration; thus, they are called Medicanes, a short name for Mediterranean hurricanes, or tropical-like cyclones (TLCs). In this paper, we propose a new perspective for the study and analysis of cyclonic events, starting with data and images acquired from satellites and focusing on the diagnostics of the evolution of atmospheric parameters for these events. More precisely, satellite remote sensing techniques are employed to elaborate on different high spatial-resolution satellite images of the events at a given sensing time. Two case studies are examined, taking into account their development into Medicane stages: Ianos, which intensified in the Ionian Sea and reached the coast of Greece between 14 and 21 September 2020, and Apollo, which impacted Mediterranean latitudes with a long tracking from 24 October to 2 November 2021. For these events, 20 images were acquired from two different satellite sensors, onboard two low-Earth orbit (LEO) platforms, by deeply exploiting their thermal infrared (TIR) spectral channels. A useful extraction of significant physical information was carried out from every image, highlighting several atmospheric quantities, including temperature and altitude layers from the top of the cloud, vertical temperature gradient, atmospheric pressure field, and deep convection cloud. The diagnostics of the two events were investigated through the spatial scale capabilities of the instruments and the spatiotemporal evolution of the cyclones, including the comparison between satellite data and recording data from the BOLAM forecasting model. In addition, 384 images were extracted from the geostationary (GEO) satellite platform for the investigation of the events’ one-day structure intensification, by implementing time as the third dimension.

Temperature Distribution Characteristics and Action Pattern of Concrete Box Girder under Low-Temperature and Cold Wave Conditions

In regions with severe cold and high latitudes, concrete structures are susceptible to cracking and displacement due to uneven temperature stress, which directly impacts their normal utilization. Therefore, to investigate the temperature distribution characteristics of concrete box girders under the combined influence of low temperatures and cold waves, a temperature test was conducted on a model of concrete box girders in Xinjiang Province, China. Based on the measured data, the distribution pattern of the most unfavorable negative temperature differential observed in high-latitude regions was determined. Long-term numerical simulation and extreme value analysis were performed using historical meteorological data, revealing that the vertical negative temperature gradient in the concrete box girder structures follows a composite exponential distribution. The temperature differential at the top complies with Chinese code requirements, while at the bottom, it aligns more closely with British standard BS5400. Statistical analysis of historical meteorological data predicts that the 50-year temperature differential will result in a drop amplitude of 26.42 °C, which is 1.44 times higher than measured values obtained from experiments. The proposed negative temperature gradient pattern for concrete box girders presented in this study can encompass general design codes and provide guidance for designing concrete bridges in severe cold areas.

Optimizing the Return Vent Height for Improved Performance in Stratified Air Distribution Systems

One of the factors that strongly impacts the efficacy of stratified air distribution (STRAD) systems is the return vent height (H), for which different studies have yielded different suggested values. This theoretical research uses a displacement ventilation (DV) system as an example to examine how the H affects the efficacy of STRAD systems through analysis of the trade-offs between the cost of the vertical temperature gradient and the benefits of energy reduction. The key results are as follows: (a) The energy savings due to a lower H are smaller than the cost of the vertical temperature gradient for all STRAD systems. (b) With a supply temperature (Ts) set at 18 °C, elevated return vent positions can result in excessively cooled areas, while extremely low vent positions create a temperature gradient exceeding 3 °C between the head and ankles. (c) The TOPSIS methodology reveals that the optimal H value lies in the range of 1.5–2.3 m when Ts is 18 °C. (d) When adjusting the Ts value to achieve thermal neutrality, 2.3 m is identified as the optimal H value, demonstrating superior performance over the 1.5 m to 2.3 m range at 18 °C Ts. These findings highlight the benefit of a higher H for STRAD systems and the significance of configuring ventilation systems for thermal neutrality.

Generation mechanisms of SST anomalies associated with the canonical El Niño focusing on vertical mixing

Abstract The mean vertical advection of anomalous vertical temperature gradient is considered as the dominant generation mechanism of positive sea surface temperature (SST) anomalies associated with the canonical El Niño. However, most past studies had a residual term in their heat budget analysis and/or did not quantify the role of vertical mixing even though active vertical turbulent mixing in the upper ocean is observed in the eastern equatorial Pacific. To quantitatively assess the importance of vertical mixing, a mixed layer heat budget analysis is performed using a hindcast simulation forced by daily mean atmospheric reanalysis data. It is found that when the mixed layer depth is defined as the depth at which potential density increases by 0.125 kg m−3 from the sea surface, the development of positive SST anomalies is predominantly governed by reductions in the cooling by vertical mixing, and their magnitude is much larger than those by vertical advection. The anomalous warming by vertical mixing may be partly explained by an anomalous deepening of the thermocline that leads to a decrease in the vertical temperature gradient, giving rise to suppression of the climatological cooling by vertical mixing. Also, an anomalously thick mixed layer reduces sensitivity to cooling by the mean vertical mixing and contributes to the anomalous SST warming. On the other hand, the dominant negative feedbacks are attributed to both anomalous surface heat loss and anomalous deepening of the mixed layer that weakens warming by the mean surface heat flux.

On the deformation of CRTS-Ⅲ ballastless track during the casting process of self-compacting concrete: Numerical simulations and random forest-based prediction models

CRTS (China railway track system)-Ⅲ slab track is a main structural type of ballastless track in Chinse high-speed railway (HSR), which requires precise positioning of prefabricated concrete track slabs. However, the cast-in-place process of the self-compacting concrete (SCC) filling layer induces a large deformation as the flowing SCC generates an up-lift force on the bottom of the track slab. Currently, the deformation mechanism and influencing factors of the track slab during the SCC casting process have not been thoroughly studied. In this work, a fluid-solid interaction finite element model (FEM) is created to calculate the upward deformation of the CRTS-Ⅲ track slab caused by the flowing SCC. The main influencing factors, including the SCC’s casting height and speed, SCC’s viscosity, constraint stiffness of the limiting beams, and vertical temperature gradient, have been systematically analyzed and discussed. The relationship between the influencing factors and the track slab’s deformation is obtained. Furthermore, machine learning prediction models using random forest algorithms are developed to evaluate the deformation and up-lift force. A dataset comprising 603 calculation cases obtained from FEM simulations is used to train the prediction models. The random forest-based models developed in this study give an accurate estimation of the deformation and up-lift force based on the SCC properties and construction parameters. In addition, the feature importance of each influencing factor is obtained and studied. The findings of this study can provide guidance for the control of the deformation in CRTS-Ⅲ track slab during the SCC construction process.

Experimental and numerical study of the three-dimensional temperature field in the arch ribs of the reinforced concrete ribbed arch bridge during construction

The unique structural design of an arch ring featuring varying inclination angles for individual segments causes variations in the longitudinal distribution of the temperature field d along the arch axis. This study aims to enhance the understanding of temperature fields in reinforced concrete (RC) arch bridges with diverse arch ring structural configurations during their construction phases. A comprehensive investigation into the three-dimensional distribution pattern of solar-induced temperature fields within arch ribs during the construction of RC ribbed arch bridges was conducted. A field test specifically measuring the temperature distribution across arch rib cross-sections was conducted on-site, involving an RC arch bridge constructed using the cable-stayed cantilever cast in situ method. Analyzing the monitored on-site temperature data revealed the distribution characteristics of temperature fields at the arch foot cross-section under solar radiation. By comparing these findings with international standards, a vertical temperature gradient fitting model for arch rib cross-sections under solar radiation was formulated. Drawing upon meteorological records and solar radiation principles, an adaptive numerical simulation finite element model was developed to depict the temperature field within an arch rib section. This model was rigorously verified. Subsequently, a comprehensive analysis of the three-dimensional temperature field of the arch rib under solar radiation was performed. Additionally, a three-dimensional temperature gradient fitting model was proposed, accounting for the longitudinal inclination of the bridge.

Change in sound signal propagation at the place of formation of the diffusive convection (DC) structure; in the west of the Strait of Hormuz

Double diffusion (DD) structures, in two types of diffusive convection (DC) and salt-fingering (SF), occur due to vertical temperature and salinity gradients with different diffusion coefficients. Areas such as the Strait of Hormuz, which has a thermohaline exchange between the Persian Gulf and the Sea of Oman, are suitable places for the formation of DD structures. Based on the results, the formation of DC structure is significant compared to other processes in the west of the Strait of Hormuz in December. Fluctuations in temperature and the growth of DC structure cause mixing and changing the depth of the boundary layer of temperature and salinity in the water. So that in the presence of the DC structure, the decrease in the value of the sound speed (1552 m/s) extends to a depth of 40 m, but the sound speed increases to 1555 m/s at the place where the warm water rises. The results show that the sound transmission loss increases by 5-15 dB in the place of strong DC structure. When the sound frequency increases, the transmission loss caused by the DC structure decreases. But for rays with a small propagation angle, a significant expansion is created in the propagation steps and wavelength of the rays, which increases up to 2 times with the increase in the depth of the sound source.

The radiative and dynamical impact of clouds in the atmosphere of the hot Jupiter WASP-43 b

Context. Hot Jupiters are tidally locked gaseous exoplanets that exhibit large day-night temperature contrasts. Their cooler nightsides are thought to host clouds, as has been suggested by numerous observations. However, the exact nature of these clouds, their spatial distribution, and their impact on atmospheric dynamics, thermal structure, and spectra is still unclear. Aims. We investigate the atmosphere of WASP-43 b, a short period hot Jupiter recently observed with James Webb Space Telescope (JWST), to understand the radiative and dynamical impact of clouds on the atmospheric circulation and thermal structure. We aim to understand the impact of different kinds of condensates potentially forming in WASP-43 b, with various sizes and atmospheric metallicities. Methods. We used a 3D global climate model (GCM) with a new temperature-dependent cloud model that includes radiative feedbacks coupled with hydrodynamical integrations to study the atmospheric properties of WASP-43 b. We produced observables from our GCM simulations and compared them to spectral phase curves from various observations to derive constraints on the atmospheric properties. Results. We show that clouds have a net warming effect, meaning that the greenhouse effect caused by clouds is stronger than the albedo cooling effect. We show that the radiative effect of clouds has various impacts on the dynamical and thermal structure of WASP-43 b. Depending on the type of condensates and their sizes, the radiative-dynamical feedback will modify the horizontal and vertical temperature gradient and reduce the wind speed. For super-solar metallicity atmospheres, fewer clouds form in the atmosphere, leading to a weaker feedback. Comparisons with spectral phase curves observed with HST, Spitzer, and JWST indicate that WASP-43 b's nightside is cloudy and rule out sub-micron Mg2SiO4 cloud particles as the main opacity source. Distinguishing between cloudy solarand cloudy super-solar-metallicity atmospheres is not straightforward, and further observations of both reflected light and thermal emission are needed.

Identification of Convective Boundary Layer Depth over the Great Lakes Region Using Aircraft Observations: A Comparison of Various Methods

Abstract This study evaluates the methods of identifying the height zi of the top of the convective boundary layer (CBL) during winter (December and January) over the Great Lakes and nearby land areas using observations taken by the University of Wyoming King Air research aircraft during the Lake-Induced Convection Experiment (1997/98) and Ontario Winter Lake-effect Systems (2013/14) field campaigns. Since CBLs facilitate vertical mixing near the surface, the most direct measurement of zi is that above which the vertical velocity turbulent fluctuations are weak or absent. Thus, we use zi from the turbulence method as the “reference value” to which zi from other methods, based on bulk Richardson number (Rib), liquid water content, and vertical gradients of potential temperature, relative humidity, and water vapor mixing ratio, are compared. The potential temperature gradient method using a threshold value of 0.015 K m−1 for soundings over land and 0.011 K m−1 for soundings over lake provided the estimates of zi that are most consistent with the turbulence method. The Rib threshold-based method, commonly used in numerical simulation studies, underestimated zi. Analyzing the methods’ performance on the averaging window zavg we recommend using zavg = 20 or 50 m for zi estimations for lake-effect boundary layers. The present dataset consists of both cloudy and cloud-free boundary layers, some having decoupled boundary layers above the inversion top. Because cases of decoupled boundary layers appear to be formed by nearby synoptic storms, we recommend use of the more general term, elevated mixed layers. Significance Statement The depth zi of the convective atmospheric boundary layer (CBL) strongly influences precipitation rates during lake-effect snowstorms (LES). However, various zi approximation methods produce significantly different results. This study utilizes extensive concurrently collected observations by project aircraft during two LES field studies [Lake-Induced Convection Experiment (Lake-ICE) and OWLeS] to assess how zi from common estimation methods compare with “reference” zi derived from turbulent fluctuations, a direct measure of CBL mixing. For soundings taken both over land and lake; with cloudy or cloud-free conditions, potential temperature gradient (PTG) methods provided the best agreement with the reference zi. A method commonly employed in numerical simulations performed relatively poorly. Interestingly, the PTG method worked equally well for “coupled” and elevated decoupled CBLs, commonly associated with nearby cyclones.

Increases in the Local Eddy Energetics of the Extratropical Atmosphere over the Last Four Decades

Abstract Changes in the vertical and meridional temperature gradients of the atmosphere drive competing influences on storm track activity. We apply local eddy energetics to the ERA5, JRA55, MERRA2, and NCEP2 reanalyses during 1980–2020 to determine the locations, magnitudes, and trends of the energy transfer mechanisms for synoptic-scale eddies. Eddy kinetic energy (EKE) increases more rapidly in the Southern Hemisphere at all altitudes and seasons, with larger increases during austral winter and spring. In the Northern Hemisphere, increases occur within the Atlantic and Pacific storm tracks at pressures below 300 hPa but only during boreal winter and spring and confined within a narrow zonal band; EKE decreases during boreal summer and fall. Most EKE changes correspond with trends in baroclinic energy conversion upstream of storm tracks and appear to align with increases in the growth rate of the most unstable baroclinic mode. Barotropic energy conversion of EKE to the mean flow becomes locally more intense downstream of the storm tracks. Conversion of EKE to long-period eddies plays a minor role averaged over a hemisphere but can be important locally. The primary strengthening pathway for removal of EKE is a combination of surface friction and viscous dissipation. The increased baroclinic conversion in the Southern Hemisphere appears related to upper-level tropical temperature increases. In the Northern Hemisphere, baroclinic conversion is enabled by a combination of increased vertical heat fluxes and a region of temperature increases within 30°–60°N.

Evaluation of WRF-Chem-simulated meteorology and aerosols over northern India during the severe pollution episode of 2016

Abstract. We use a state-of-the-art regional chemistry transport model (WRF-Chem v4.2.1) to simulate particulate air pollution over northern India during September–November 2016. This period includes a severe air pollution episode marked by exceedingly high levels of hourly PM2.5 (particulate matter having an aerodynamic diameter ≤ 2.5 µm) during 30 October to 7 November, particularly over the wider Indo-Gangetic Plain (IGP). We provide a comprehensive evaluation of simulated seasonal meteorology (nudged by ERA5 reanalysis products) and aerosol chemistry (PM2.5 and its black carbon (BC) component) using a range of ground-based, satellite and reanalysis products, with a focus on the November 2016 haze episode. We find the daily and diurnal features in simulated surface temperature show the best agreement followed by relative humidity, with the largest discrepancies being an overestimate of night-time wind speeds (up to 1.5 m s−1) confirmed by both ground and radiosonde observations. Upper-air meteorology comparisons with radiosonde observations show excellent model skill in reproducing the vertical temperature gradient (r>0.9). We evaluate modelled PM2.5 at 20 observation sites across the IGP including eight in Delhi and compare simulated aerosol optical depth (AOD) with data from four AERONET sites. We also compare our model aerosol results with MERRA-2 reanalysis aerosol fields and MODIS satellite AOD. We find that the model captures many features of the observed aerosol distributions but tends to overestimate PM2.5 during September (by a factor of 2) due to too much dust, and underestimate peak PM2.5 during the severe episode. Delhi experiences some of the highest daily mean PM2.5 concentrations within the study region, with dominant components nitrate (∼25 %), dust (∼25 %), secondary organic aerosols (∼20 %) and ammonium (∼10 %). Modelled PM2.5 and BC spatially correlate well with MERRA-2 products across the whole domain. High AOD at 550nm across the IGP is also well predicted by the model relative to MODIS satellite (r≥0.8) and ground-based AERONET observations (r≥0.7), except during September. Overall, the model realistically captures the seasonal and spatial variations of meteorology and ambient pollution over northern India. However, the observed underestimations in pollutant concentrations likely come from a combination of underestimated emissions, too much night-time dispersion, and some missing or poorly represented aerosol chemistry processes. Nevertheless, we find the model is sufficiently accurate to be a useful tool for exploring the sources and processes that control PM2.5 levels during severe pollution episodes.

Temperature distribution in CrMnNi steel-Mg-PSZ functionally graded material during FAST/SPS

Within the scope of this study, the macroscopic temperature distribution in the steady-state temperature condition during Field Assisted Sintering Technique/Spark Plasma Sintering (FAST/SPS) in functionally graded materials (FGM) was investigated. The sample material exhibited a diameter of 50 mm and a thickness of 9 mm. The FGM samples were composed of steel X2CrMnNi 16-7-6 and Mg-PSZ ceramic (MgO partly stabilized ZrO2). By varying the sintering tool setup, a specific modification of the macroscopic temperature distribution within the sample material and the sintering tool was achieved. The aim of the modifications was to optimize the temperature gradients in order to allow for the simultaneous compaction of all FGM layers under ideal circumstances. This involves achieving enhanced ceramic densification without inducing steel melting. Finite element method (FEM) simulations were carried out to get information about the temperature distribution within the sample material and the sintering tool. Furthermore, for this propose, thermocouple temperature measurements were conducted at various measurement points on pre-sintered FGM within the specific sintering tool setup. Additionally, all findings regarding the temperature distribution within the sample material and the sintering tool were compared with results concerning the temperature distribution from the microstructural and mechanical characterization of the center and edge regions of the FGM samples. The FGM samples exhibited a significant increase in temperature from the center to the edge in the radial direction depending on the used sintering tool setup. While the FGM samples showed only minor vertical temperature gradients in the center, the highest vertical temperature gradients were determined at the edge of the FGM sample using an asymmetric sintering tool setup.

Flowing Bottomhole Pressure during Gas Lift in Unconventional Oil Wells

Summary We present artificial neural network (ANN) models for predicting the flowing bottomhole pressure (FBHP) of unconventional oil wells under gas lift operations. Well parameters, fluid properties, production/injection data, and bottomhole gauge pressures from 16 shale oil wells in Permian Basin, Texas, USA, are analyzed to determine key parameters affecting FBHP during the gas lift operation. For the reservoir fluid properties, several pressure-volume-temperature (PVT) models, such as Benedict-Webb-Rubin (BWR); Lee, Gonzalez, and Eakin; and Standing, among others, are examined against experimentally tuned fluid properties (i.e., viscosity, formation volume factor, and solution gas-oil ratio) to identify representative fluid (PVT) models for oil and gas properties. Pipe flow models (i.e., Hagedorn and Brown; Gray, Begs and Brill; and Petalas and Aziz) are also examined by comparing calculated FBHP against the bottomhole gauge pressures to identify a representative pipe flow model. Training and test data sets are then generated using the representative PVT and pipe flow models to develop a physics-based ANN model. The physics-based ANN model inputs are hydrocarbon fluid properties, liquid flow rate (qL), gas-liquid ratio (GLR), water-oil ratio (WOR), well true vertical depth (TVD), wellhead pressure (Pwh), wellhead temperature (Twh), and temperature gradient (dT/dh). A data-based ANN model is also developed based on only TVD, Pwh, qL, GLR, and WOR. Both physics- and data-based ANN models are trained through hyperparameter optimization using genetic algorithm and K-fold validation and then tested against the gauge FBHP. The results reveal that both models perform well with the FBHP prediction from field data with a normalized mean absolute error (NMAE) of around 10%. However, a comparison between results from the physics- and data-based ANN models shows that the accuracy of the physics-based model is higher at the later phase of the gas lift operation when the steady-state pipe flow is well established. On the contrary, the data-based model performs better for the early phase of gas lift operation when transient flow behavior is dominant. Developed ANN models and workflows can be applied to optimize gas lift operations under different fluid and well conditions.

Origins of Underestimated Indian Ocean Dipole Skewness in CMIP5/6 Models

Abstract The Indian Ocean dipole (IOD) is the dominant mode of interannual variability in the tropical Indian Ocean (TIO), characterized by warming (cooling) in western TIO and cooling (warming) in eastern TIO during its positive (negative) phase. Observed IOD events exhibit distinct amplitude asymmetry in relation to negative nonlinear dynamic heating. Nearly all models in phase 5 of the Coupled Model Intercomparison Project (CMIP) simulate a less-skewed IOD than observed, but 6 out of 20 CMIP6 models can reproduce realistic high skewness. Analysis of less-skewed models indicates that the positive IOD-like biases in the mean state, which can be traced back to their weaker simulations of the preceding Indian summer monsoon, reduce the convective response to positive sea surface temperature anomalies in the western TIO, resulting in a weaker zonal wind response and weaker nonlinear zonal advection during positive IOD events. Besides, ocean stratification in the eastern TIO influences the IOD skewness: stronger stratification leads to larger mixed-layer temperature response to thermocline changes, contributing to larger anomalous vertical temperature gradient, larger nonlinear vertical advection, and thus stronger positive IOD skewness. Our findings underscore the importance of reducing Indian summer monsoon biases and eastern TIO stratification biases, for properly representing the IOD in Earth system models.

Analysis of Radon Near-Surface Measurements, Using Co-Located Ozone Data, Radio-Sounding Vertical Profiles, Sensible Heat Flux and Back-Trajectory Calculation

Simultaneous and co-located observations of near-surface Radon-222, ozone and meteorological parameters in a central Italy observation site operated by the University of L’Aquila (Italy), are used to study the physical drivers of the radon abundance during night-time hours. The knowledge of the potential temperature vertical gradient in the surface layer of nocturnal thermal inversion is made possible using co-located radio-sounding vertical profiles of pressure and temperature, thus making possible to indirectly infer the local surface flux of atmospheric radon (16 ± 6 mBq m−2 s−1). The dynamical removal due to turbulent convective motions is found to be the dominant controlling process, determining large differences in the near-surface radon abundance between stable and unstable conditions of the nocturnal Planetary Boundary Layer (PBL). Usual unstable PBL conditions during daytime hours induce an effective dynamical vertical dilution of surface radon, which rapidly reaches a quasi-steady-state abundance during mid-day and afternoon hours, with very low concentration values (5.1 ± 2.0 Bq m−3). Using back-trajectory reanalyses, estimates of local radon fluxes and vertical mixing efficiencies inside the PBL along the air mass latitudinal-longitudinal path and finally the irreversible radon loss due to radioactive decay, we have explored the fraction of daytime radon attributable to long-range advection in the continental near-mountain measurement site of L’Aquila (44 ± 18%).

The Influence of Freshwater Input on the Evolution of the 1995 Benguela Niño

AbstractBenguela Niño events are characterized by strong warm sea surface temperature (SST) anomalies off the Angolan and Namibian coasts. In 1995, the strongest event in the satellite era took place, impacting fish availability in both Angolan and Namibian waters. In this study, we use direct observations, satellite data, and reanalysis products to investigate the impact that the up‐until‐now unnoticed mechanism of freshwater input from Congo River discharge (CRD) and precipitation had on the evolution of the 1995 Benguela Niño. In the onset phase of the event, anomalous rainfall in November/December 1994 at around 6°S, combined with a high CRD, generated a low salinity plume. The plume was advected into the Angola‐Namibia region in the following February/March 1995 by an anomalously strong poleward surface current generated by the relaxation of the southerly winds and shifts in the coastal wind stress curl. The presence of this low surface salinity anomaly of about −2 psu increased ocean stability by generating barrier layers, thereby reducing the turbulent heat loss, since turbulent mixing acted on a weak vertical temperature gradient. A mixed layer heat budget analysis demonstrates that southward advection of Angolan waters drove the warming at the onset, while reduced mixing played the main role at the event's peak. We conclude that a freshwater input contributed to the SST increase in this exceptionally strong event and suggest that this input can influence the SST variability in Angola‐Namibia waters through a combination of high CRD, precipitation, and the presence of a strong poleward surface current.