Outflow Temperature Research Articles

Laboratory investigation on the influence of factors on the outflow temperature from stratified reservoir regulated by temperature control curtain.

A temperature control curtain can effectively mitigate the negative effect of outflow temperature on the river eco-environment downstream. To investigate the response of outflow temperature to influence factors (i.e., installation position of temperature control curtain, submerged depth, temperature distribution, and outflow discharge), experiments were conducted in a nonlinearly stratified fluid. The important degree of influence factors was determined by entropy weight method. The results indicated that the effect extent of influence factors on the outflow temperature was temperature distribution, submerged depth, outflow discharge, and installation position in turn. The installation position had little effect on the outflow temperature. Increasing the outflow discharge could withdraw more warm water near the surface and increase the outflow temperature. The outflow temperature also rose with decreasing submerged depth, and more warm water above the temperature control curtain level tended to be extracted when the submerged depth was enough. Although the outflow temperature increased, its variation amplitude depended on the temperature gradient of temperature distribution and was not affected by the structural form of selective withdrawal. From the point of operation management, the minimum submerged depth was determined using sensitivity analysis to obtain maximum improvement of outflow temperature.

Multi-objective optimal operation of a large deep reservoir during storage period considering the outflow-temperature demand based on NSGA-II

Thermal stratification occurs in deep reservoirs and causes an outflow temperature that is significantly different from the inflow temperature, which is harmful to the ecology of downstream reaches. Optimal operation of reservoirs using the multi-objective evolutionary algorithm (MOEA), which focuses on power generation, flood control, agricultural irrigation, navigation, etc., has been performed. However, the outflow temperature has not been considered. Focusing on this deficiency, we considered Sanbanxi Reservoir as a case study and used the non-dominated sorting genetic algorithm II (NSGA-II) by combining it with the calibrated 1-D General Lake Model. The trade-off relationships among three objectives, namely, total power generation (TPG), root-mean-square deviation between the inflow and outflow temperatures (RMSDtem) and weighted aggregate eco-index (EI) based on indicators of hydrologic alteration (IHAs) parameters, were estimated as Pareto frontiers during the storage period from March 15 to July 15. The results demonstrated the following. 1) Through reservoir re-operation, RMSDtem could be reduced by 1.60 °C from 5.99 to 4.39 °C at the expense of reducing TPG from 7.43 × 108 to 6.56 × 108 kW·h (–11.8%) during a normal year. 2)The optimized operating schemes were extracted as Pareto frontiers, and the slope of the outflow discharge curve (SODC) could be a useful parameter for determining the operating scheme in practice. A large SODC yielded high TPG, a small SODC resulted in low RMSDtem, and a medium SODC yielded minimum EI. The medium SODCs ranged from –0.1 to 0.4 m3/(s·d), –0.4 to 0.6 m3/(s·d), and –0.6 to 1.2 m3/(s·d) for dry, normal, and wet years, respectively. 3) As the yearly inflow increased, the absolute value of the SODC for the best individuals for a single objective became larger. The range of TPG and RMSDtem in the Pareto frontier expanded, and that of EI remained basically unchanged. The results of the Sanbanxi Reservoir can be applied to other reservoirs to support reservoir re-operation, especially for the deep reservoirs in southwest China that suffer from outflow-temperature problems.

A Fast Simulation Approach to the Thermal Recovery Characteristics of Deep Borehole Heat Exchanger after Heat Extraction

Necessary intermittence after heat extraction for a deep borehole heat exchanger (DBHE) is beneficial for sustainable operation. This paper centers on the fast simulation for thermal recovery characteristics of DBHE under intermittent condition. First of all, in view of the existing temperature gradient and multi-layer heterogeneity of rock underground that could never be ignored for DBHE, we extend the classical finite line source model based on heat source theory and superposition principle to account for the vertical heat flux distribution varying along depth and heterogeneous thermal conductivities in the multi-layer rock zone. Moreover, a fast simulation approach for heat transfer analysis inside the borehole coupled with the extended finite line source model is put forward to depict the transient thermal response and dynamic thermal recovery of rock outside borehole. To the authors’ knowledge, no such algorithm for deep BHE has yet been suggested in the previous literature. This approach has proven to be reliable and efficient enough for DBHE simulation under the intermittent condition. Simulation results show that at least 65 days of intermittence for the model in study should be spared after the heating season to achieve sustainable heat extraction in the next cyclic operation. Compared to the detailed solution based on full discretization numerical schemes, the relative error for borehole bottom temperature was 0.79%. In addition, comparison of the simulation results for thermal performance during the heating season in a three-year cyclic operation with 205 days intermittence shows that both the outflow temperature and heat extraction rate in the subsequent cycle after intermittence are in good agreement with the full 3D numerical solution in the reference (with a relative error of 6.36% for the outflow temperature and 9.3% for the heat extraction rate). Regarding the calculation speed, around a 13 times acceleration can be achieved. Finally, it is also promising to be applicable for thermal recovery simulation after heat extraction of vertical closed loop borehole heat exchangers at arbitrary length from shallow to deep.

Conjugate heat transfer model for feedback control and state estimation in a volumetric solar receiver

Open volumetric solar receivers (VSRs) are a promising technology for concentrated solar power plants due to their capability to provide heat using ambient air as the working fluid operating at temperatures over 700°C. Nevertheless, VSRs are challenged by the unsteadiness and high intensity of the radiation flux, which may cause unreliable or unsafe outflow temperatures, and may compromise the lifetime of the porous ceramic absorbers due to extreme thermal loads, thermal shock or thermal fatigue. We propose a data assimilation framework to address these matters using blower actuation, measurements from sensors located in the outflow stream of air, and a model for the conjugate heat transfer in an open VSR. We formulate said model and compare it against full three-dimensional CFD simulations to show that it captures the relevant dynamics while reducing the computational cost enough to allow for online calculations. A linear quadratic Gaussian (LQG) controller is used with the model to perform simultaneous state estimation and feedback control in three simulated scenarios. Our framework proves capable of stabilizing outflow air temperatures during the passing of a cloud, estimating the radiation flux hitting the absorber during daily operation, monitoring temperature cycling in the solid matrix, and avoiding extreme temperature gradients during start-up procedures. Artificial noise and disturbances are added to the system for all scenarios and the LQG controller proves to be robust, rejecting disturbances and attenuating noise, as well as compensating for model uncertainty.

Modelling Multi-layer Hydronic Radiators

This report simulates Purmo type C22 and C33 radiators with both standard calculation and heat transfer method with help of Matlab/Simulink. Simulation results are presented to describe the radiators’ thermal performances with different simulation strategies. The deviations between two different calculation methods are identified and the heat transfer radiator model can be improved with more investigations regarding thermal dynamics and controlling strategy. Under simulation scenarios of simple room model with a PID controller, type C33 has shorter response time and faster stabilization of room temperature; and it has lower outflow temperature, which implies higher energy efficiency.

Geothermal sources and utilization practice in six countries along the southern part of the Pannonian basin

Data on thermal water sources with outflow temperature of 30 °C and above were analyzed from the N-ern parts of Bosnia and Herzegovina, Serbia and Croatia, S-ern parts of Hungary, W-ern parts of Romania, and NE-ern parts of Slovenia, altogether from an area of 99,347 km2. The overview identified 771 geothermal sources; only 7 were thermal springs. The average well depth is about 1.2 km. About 13% of wells are younger than 10 years, additional 17% below 30 years; while 26% are older than 50 years. Average thermal water outflow temperature is 54 °C being the highest, 170 °C, in Croatia. Most thermal water is produced from basin fill sediments—Lower and Upper Pannonian (Mio-Pliocene) loose sandstones which are tapped by 86% of wells. The rest appertains to basement rocks—fissured, fractured and karstified Paleozoic, Mesozoic and Middle Miocene metamorphic, carbonate and siliciclastic rocks. In total, 72% sources hold water rights, 6% mining rights, 2% geothermal rights and 1% has no rights. The permits allow much higher water abstraction as currently listed. Usage for bathing and balneology encompasses 24% of all active sources (155), some of these also with heating (23). 104 objects (16%) are used for heating, also district heating (13) and individual space heating (3). An additional 10% (70) are used in agriculture, mainly greenhouse heating. There are 41 reinjection wells (5%). It is primarily in Hungary that drinking water (17%), industrial usage (5%) and monitoring wells (2%) are also common.

Considerations of Regional Coherences for the Development of Renewable Energy Technologies Used in South Part of Transdanubian Region of Hungary

Abstract The existing effective domestic regional development framework requires analyses for increasingly wider areas (micro, meso and even macro regions) before operational – short-term – local developments to be prepared and implemented. Such comprehensive complex studies or larger-term programmes may demonstrate the profitability of the given project and can complement it with combined utilization technologies; in the case of Himesháza several locally known renewable energy sources could facilitate geothermal heat, later electricity supply, e.g. local biomass (biogas-based) recovery technology (organic waste of the local pig farm) and, for example, the construction of a low-power “dwarf” hydroelectric power plant chain based on rich watercourses of the region (the “southern dwarves” in Hungary) and the connection of existing solar utility facilities to a modern “smart grid” system in the longer term. Himesháza, located in southern Hungary in Baranya county, is developing; it has a detailed feasibility study of a thermal energy supply network and an energy supply development plan. Based on the geothermal characteristics of Baranya county it would be reasonable to encourage the development of smaller-scale, decentralized heating systems for dynamic settlements. Several settlements in close proximity to Himesháza have already explored thermal wells. Power generation with a small scale, closed-loop system can be used in the project region for thermal water with an outflow temperature of 90 °C. The heating system may also be able to fulfill the needs of recreational, vacation-based or complex thermal spa facilities formerly planned in the region. Moreover, the system could also be capable of utilizing a larger spectrum of renewable energy through its combination with photovoltaic technology. Due to the country's favorable agricultural characteristics, Hungary's biomass potential is higher than the European average. The utilization of organic waste from agricultural and farming sectors is highly recommended in Baranya county; biogas production seems to be the most suitable in the region of Himesháza too, broadening the utilization of renewable resources. The realization of the current project could contribute to shifting the energy resource sector in a more modern, environmentally conscious direction. The background for shorter-term plans and investment (carried out within the framework of operational programs) necessary for the optimal operation and maintenance of longer-term (25–50 years) energy development strategies is created by the analysis (at multiple scales) of complex regional characteristics and future potential, and the selection of optimal sites.

Influence of Track Changes on the Poleward Shift of LMI Location of Western North Pacific Tropical Cyclones

AbstractThe annual mean latitude at which tropical cyclones (TCs) reach their lifetime maximum intensity (LMI) over the western North Pacific Ocean basin has shifted northward since the early 1980s, and it is suggested that the shift is due to the northward migration of the mean TC formation location. In this study, the TC intensity is simulated with an intensity model to assess the historical records of TC intensity. During the period 1980–2015, the simulated poleward trend in the mean latitude of LMI is 0.44° (10 yr)−1, which agrees well with the one [0.48° (10 yr)−1] derived from the Joint Typhoon Warning Center (JTWC) dataset. This suggests that the observed poleward trend in the mean latitude of LMI is physically consistent with changes in the large-scale ocean–atmosphere environment and TC track. This study also demonstrates that the temporal change in the environmental parameters (sea surface temperature, outflow temperature, vertical wind shear, and ocean mixed layer depth) has little influence on the observed shift of the mean LMI latitude. The poleward migration of the mean LMI latitude is mainly due to the TC track shift, which results primarily from the change in the large-scale steering flow.

Possible influences of a La Niña event on a continuous tropical cyclone landfall event in east China

Four tropical cyclones (TCs) formed over the western North Pacific (WNP) basin and continuously made landfall on the coastal areas of the eastern China mainland during July–August in 2018 and caused significant damage to the coastwise areas. Such a continuous TC landfall event affecting adjacent regions within a short period has never happened in previous decades, and the landfall event was attributed to anomalous environments over the WNP. During July–August in 2018, the dynamic and thermodynamic conditions were favorable for increased TC genesis, which is a prerequisite for the continuous TC landfall. However, the low sea surface temperature and high outflow temperature prohibited further intensification of the four landfall TCs. More importantly, the northwestward shift of the subtropical high and stronger monsoonal circulation resulted in anomalous easterlies that steered the four TCs toward the coastline of East China. Further investigation indicates that an earlier La Nina event that occurred from late autumn in 2017 to early spring in 2018 may have played a key role during the period. The robust monsoon circulation and enhanced precipitation over the low-latitudinal regions of the WNP basin were induced by the earlier La Nina event and provided advantageous conditions for TC genesis and movement, thus leading to the continuous TC landfall event. Significant negative correlations are found between the summer monsoon activity and earlier El Nino Southern Oscillation (ENSO) events. After an earlier La Nina event, more TCs are expected to form during the following summer such as in the scenario in 2018 due to the vigorous monsoonal circulation, which provides favorable large-scale environments. In addition, the abnormal Hadley circulation, which may be associated with the earlier La Nina event, shifted the subtropical high northward and resulted in the anomalous easterlies that steered the TCs toward East China.

Machine learning-based modeling and controller tuning of a heat pump

In this paper, we consider the problem of controller tuning for an operating unit in a building energy system. The illustrative example used here is a real heat pump located in the NEST building at Empa, Dubendorf, Zurich, with its outflow temperature controlled by a PI-controller. The plant is in use and accordingly, intervening in its normal operation is not allowed. Moreover, the model of plant is not available or it can be changed due to aging or possible modification. Accordingly, it is desired to utilize a tuning method which is model-free, operates online, does not intervene with the normal operation of the plant and use only the available historical measurement data. Additionally, it is required to guarantee the safety of the plant during the tuning procedure. In this regard, we formulate the controller tuning problem as a black-box optimization and adopt a safe Bayesian optimization approach for controller parameters tuning. In order to assess numerically the performances of the scheme, first we model the plant as a nonlinear ARX model in form of a feedforward neural network. Subsequently, we train the neural network using the available historical measurement data. Finally, the obtained model is used as an oracle in the controller tuning procedure in order to numerically verify the effectivity of the proposed approach.

A Multilayer Reservoir Thermal Stratification Module for Earth System Models

AbstractThermal stratification in reservoirs is a critical process that regulates downstream riverine energy and biogeochemical cycling. Current stratification models either simplify vertical energy process, reservoir geometry or neglecting the effects of reservoir operation. Here we present a new multilayer reservoir stratification model that can be applied for reservoir and stream temperature simulation at regional or global scale. With a multilayer vertical discretization, we introduce a newly developed storage‐area‐depth dataset to improve parameterization of advection processes in and out of the reservoir. The new model better represents vertical temperature gradient and subsequently temperature of water released to downstream. The stratification model is applied to 1,400 reservoirs over the contiguous United States and validated against observed surface, profile, and outflow temperature data over 130 reservoirs subjected to various levels of regulation. The Nash‐Sutcliffe values are higher than 0.5 for about 77% of the validated reservoirs using surface temperature while the average values of root mean square error and bias are 3.6 °C and −1.1 °C, respectively. Using the new reservoir storage‐area‐depth dataset improves the simulation of surface temperature at over 69% of the validated reservoirs compared to using simplified reservoir geometry. The reservoir stratification model contributes to improving predictive understanding of anthropogenic impact on terrestrial hydrological, ecological, and biogeochemical cycles.

Hydrogeochemistry and geothermometry of the carbonate-evaporite aquifers controlled by deep-seated faults using major ions and environmental isotopes

Carbonate aquifers probably constitute the most important thermal water resources in non-volcanic areas, and are characteristic of great energy potential and easier production as the most ideal targets for development in the future. The thermal waters in the aquifers within Southeast Chongqing (SEC) of China occur in an extensive region with an area of 198,000 km2, which are mainly hosted in the Cambrian and Ordovician carbonate-evaporite rocks. The thermal waters are mainly in pristine conditions and their genesis has not yet been fully understood. The occurrence of thermal waters in SEC is closely related to the presence of deep-seated faults which constitute pathways for the hydrothermal circulation. In this study, an investigation of water major ions and environmental isotopes from 14 hot springs and three drilled wells was carried out to examine their hydrogeochemical evolution and to estimate reservoir temperature. The thermal waters have outflow temperatures from 19 to 54.2 °C. They are divided into two hydrochemical groups with the Yushan Fault as a boundary: Group A, located to the west of the fault, are characterized by facies of chloride sodium waters with higher TDS; Group B, to the east of the fault, are more complicated sulfate-bicarbonate-chloride alkaline-earth waters with lower TDS. The hydrochemical processes such as dissolution of carbonate, gypsum and/or anhydrite, and halite, the common ion effect, and dedolomitization are evident based on the major ions and δ34SSO4 and δ18OSO4. The δ18O and δD compositions of the thermal waters suggest a meteoric recharge in a relatively wetter and colder climatic condition. The silica geothermometers show that the average reservoir temperatures are 63 ± 18 °C for Group A, and 82 ± 15 °C for Group B. The corresponding average reservoir depths are estimated to be 2.5 ± 0.7 km for Group A, and 3.2 ± 0.7 km for Group B. The corrected 14C ages of the thermal waters average at 14.8 ka BP, corresponding to the late Pleistocene. A conceptual circulation model is proposed for the thermal waters. Driven by gravity of topographic gradients, the percolating groundwater circulates at a specific depth, reaching a higher temperature and interacting with the host carbonate with imbedded evaporitic minerals (gypsum and/or anhydrite, and additional halite for Group A) to be saline deep-seated thermal fluids. The fluids rise along faults and emerge at the surface as thermal springs. The slow renewability rate of the thermal aquifers highlights the importance of assessing the resource before groundwater exploitation and extraction.

Management and Limnology Interact to Drive Water Temperature Patterns in a Middle Rockies River‐Reservoir System

AbstractThis study seeks to improve understanding of temperature patterns in reservoir outflows. We examined water temperatures in an irrigation storage reservoir, Island Park Reservoir, and its outflow, Henry’s Fork of the Snake River in eastern Idaho. Our objectives were to (1) quantify the extent to which daily temperature ranges in the reservoir outflow deviated from other reaches of the Henry’s Fork, and (2) test whether the reservoir’s net volume change during the summer — expressed as the volume of water remaining in the reservoir on September 1 — predicted mean summer temperature in the outflow. Two years of temperature data showed dampened diel temperature cycles in the reservoir outflow. Model selection with 17 years of climatic, hydrologic, and reservoir management variables found mean summer temperature in the outflow was best predicted by September 1 reservoir volume and average summer air temperature. Two years of weekly reservoir thermal profiles indicated large changes in reservoir volume eliminated cool hypolimnetic water and encouraged mixing, allowing warm epilimnetic water to be discharged into the outflow. Increases in future drought frequency and severity and increases in summer air temperatures could increase the frequency of occurrence of high mean summertime water temperatures in the outflow. Our study provides important information for local managers by quantifying influences on outflow temperatures and the downstream river ecosystem.

PIV experimental investigation of the outflow temperature from nonlinearly stratified reservoir regulated by floating intake

Floating intake is an effective facility of selective withdrawal to regulate the outflow temperature from thermally stratified reservoirs. The outflow temperature was the result of the interaction among temperature field, flow field and artificial regulation.To characterize them, three influencing factors (i.e., temperature distribution, outflow rate and submerged depth) were chosen. Experiments were conducted to investigate the response of outflow temperature to influencing factors in a nonlinearly stratified fluid with the particle image velocimetry (PIV) technique. Results showed that the withdrawal layer was formed near the level of floating intake inhibited by the density gradient, and its thickness was proportional to stratification intensity. The withdrawal layer ascended with the decrease in submerged depth, and the thickness also changed due to the variation in density gradient. Although the outflow temperature increased, the variation amplitude depended on the temperature gradient between the two submerged depths. However, enlarging the outflow rate within a certain range had relatively small influence on the withdrawal layer thickness and the outflow temperature. Considering the experimental results, a formula was developed for predicting the outflow temperature based on dimensional analysis and energy conservation.

Effects of temperature-control curtain on algae biomass and dissolved oxygen in a large stratified reservoir: Sanbanxi Reservoir case study

A temperature-control curtain (TCC) is a new technique of selective withdrawal for controlling the outflow temperature of a reservoir. A TCC can significantly affect the reservoir hydrodynamic and thermal structure, but its effects on water quality and ecology remain unknown. In this study, we developed and calibrated a hydro-thermal-water quality model to numerically analyze how a TCC located 1 km from a dam affected algal biomass and water quality in a reservoir. According to our results, when a TCC was used, the mean annual chlorophyll a (Chl-a) concentrations in the reservoir decreased. Chl-a concentrations remained constant during the heating period until normal water levels were reached, and increased during the cooling period and decreased until year-end drawdown levels were reached. The dissolved oxygen (DO) concentrations decreased and the anoxic proportions increased throughout the year. The yearly mean Chl-a and DO concentrations in the reservoir declined continuously as the water-retaining proportion (Pr) of the TCC increased from 0 to 87.5%, while the anoxic proportion (DO < 2 mg/L) first increased and then decreased, peaking at a Pr of 62.5%. The change patterns of the anoxic proportion were consistent with those of thermal stability, demonstrating the applicability of thermal stability in predicting reservoir hypoxia. Moreover, the environmental impact of TCCs will increase under global warming, and TCCs can mitigate the increased algal biomass and further decrease DO in warmer climate conditions. Under a medium-high climate scenario, Representative Concentration Pathway 6.0, and a TCC having 75% Pr, the yearly mean Chl-a, DO concentrations, and anoxic proportions of Sanbanxi Reservoir are predicted to reach 10.7 μg/L, 4.2 mg/L, and 39.6%, respectively, by 2046–2065. Thus, changes in the water environment and ecology (particularly the likely deterioration of water quality because of selective withdrawal under global warming) should be considered as a component of water management practices.

Numerical investigation on the performance, sustainability, and efficiency of the deep borehole heat exchanger system for building heating

In densely inhabited urban areas, deep borehole heat exchangers (DBHE) have been proposed to be integrated with the heat pump in order to utilize geothermal energy for building heating purposes. In this work, a comprehensive numerical model was constructed with the OpenGeoSys (OGS) software applying the dual-continuum approach. The model was verified against analytical solution, as well as by comparing with the integrated heat flux distribution. A series of modeling scenarios were designed and simulated in this study to perform the DBHE system analysis and to investigate the influence of pipe materials, grout thermal conductivity, geothermal gradient, soil thermal conductivity, and groundwater flow. It was found that the soil thermal conductivity is the most important parameter for the DBHE system performance. Both thermally enhanced grout and the thermally insulated inner pipe will elevate the outflow temperature of the DBHE. With an elevated geothermal gradient of 0.04 °C m−1, the short-term sustainable specific heat extraction rate imposed on the DBHE can be increased to 150–200 W m−1. The quantification of maximum heat extraction rate was conducted based on the modeling of 30-year-long operation scenarios. With a standard geothermal gradient of 0.03 °C m−1, the extraction rate has to be kept below 125 W m−1 in the long-term operation. To reflect the electricity consumption by circulating pump, the coefficient of system performance (CSP) was proposed in this work to better quantify the system efficiency. With the typical pipe structure and flow rate specified in this study, it is found that the lower limit of the DBHE system is at a CSP value of 3.7. The extended numerical model presented in this study can be applied to the design and optimization of DBHE-coupled ground source heat pump systems.

Factors Affecting the Variability of Maximum Potential Intensity (MPI) of Tropical Cyclones Over the North Atlantic

AbstractContributions of atmospheric factors to the variability of the calculated theoretical maximum potential intensity (MPI) of tropical cyclones (TCs) over the North Atlantic are explored using the 6‐hourly atmospheric reanalysis and TC best track data from 1980 to 2015. The results show that for a given sea surface temperature (SST), the calculated theoretical MPI between the medians of top 10% and bottom 10% samples can vary by as large as 10–15 m/s, which accounts for 20–25% of the median of the MPI. It is shown that the drier (moister) and colder (warmer) environment favors higher (lower) MPI, and the TC‐MPI is more sensitive to atmospheric temperature at lower SSTs but more sensitive to atmospheric humidity at higher SSTs. Results from sensitivity experiments show that the tropospheric temperature and humidity profiles and the outflow layer temperature are all responsible for the MPI variability, but their relative importance vary with SST. The atmospheric humidity accounts for 12–13 (7–11) m/s at SSTs over (below) 28 °C, the tropospheric temperature accounts for about 7–12 (5–6) m/s at SSTs below (above) 28 °C, and the outflow temperature accounts for 7–8 m/s almost independent of SST. These results strongly suggest that the modulation of MPI by synoptic variability needs to be considered when MPI is calculated and used as a predictor/parameter in operational TC intensity prediction schemes, especially for strong TCs. Some other implications of the results are also discussed.

Seasonal Cycles of Along-Track Tropical Cyclone Maximum Intensity

Abstract This study investigates relationships between observed tropical cyclone (TC) maximum intensities and potential intensity (PI) over the seasonal cycle. To directly compare observed and potential intensities, one must account for month-to-month variability in TC tracks and frequencies. Historical TC best track data and reanalysis PI calculations are combined to develop an along-track record of observed maximum and potential intensities for each storm in the satellite-era (1980–2015) across four ocean basins. Overall, observed maximum intensity seasonal cycles agree well with those of along-track PI. An extreme value theory application shows that at least 25 storms must be observed in a given month to have high confidence that the most intense wind speeds of historical TCs follow along-track PI seasonality. In the North Atlantic and Southern Hemisphere regions, there are too few observed storms outside their traditional TC seasons, limiting PI applicability across the seasonal cycle. Small intraseasonal along-track PI variabilities in these regions are driven by TC thermodynamic disequilibrium and sea surface temperatures. Thermodynamic disequilibrium drives seasonal cycles of eastern North Pacific along-track PI and observed maximum intensity, which minimize in August and maximize in June and October. Western North Pacific along-track PI and observed maximum intensity seasonal cycles are relatively flat, and have a local minimum in August because of reduced thermodynamic efficiency, which is linked to anomalously warm near-tropopause outflow temperatures. Powerful (&amp;gt;65 m s−1) western Pacific TCs historically occur in every month except January, due to a combination of tropopause region and SST seasonal influences.

Non-relativistic and relativistic magnetic reconnection with the effects of optically thin synchrotron cooling

Abstract We performed special relativistic resistive magnetohydrodynamic simulations of Petscheck-type magnetic reconnection including an optically thin synchrotron cooling. The magnetization parameter, σ0, which is the ratio of Poynting flux to mass flux in the upstream plasma, is taken to be 0.01 and 3. For the non-relativistic plasma (σ0 = 0.01), the radiative cooling subtracts thermal energy mainly in the upstream plasma and a plasma is strongly compressed at the slow shock. The cooling in the post-shock region and plasmoid also reduces the thermal energy and it forms a narrower outflow. The reconnection rate slightly increases as a result of the radiative cooling, since the plasma beta in the inflow region becomes small. The effect of decreasing thermal energy in the outflow region is more prominent for the relativistic plasma (σ0 = 3). In this case, the outflow temperature increases and the plasma internal energy becomes comparable to the plasma rest mass energy. The subtraction of this thermal energy by radiative cooling leads to a decrease in plasma inertia and the outflows are more accelerated than without radiative cooling. The reconnection rate is also enhanced by its Lorentz contraction effect. For both non-relativistic and relativistic simulations, it is concluded that the reconnection rate is determined by the plasma beta in the inflow region.

Enhancing heat production by managing heat and water flow in confined geothermal aquifers

Doublet-well systems are widely used to exploit geothermal energy and maintain aquifer pressure. Well placement is a primary optimization target to enhance the geothermal energy production. However, there is a lack of general principles to locate the wells considering both regional groundwater flow and density-driven flow. This study investigated the optimized well placement against the natural status of fluid and heat transport in the confined geothermal aquifer. The natural status of fluid and heat transport is revisited and categorized into four types: forced convection, free convection, mixed convection and conduction. In forced convection system the low-temperature water injection well located down-gradient to the extraction well can reduce the low-temperature breakthrough. In conduction system, the extraction well located in the deeper zone of a confined aquifer can yield high outflow temperature. In free-convection system the low-temperature water injecting in the deeper zone in the aquifer and the extraction section in the shallower zone are preferred, as the injected low-temperature water can move downward, and after heated, is extracted from the production well. These results can help determine the relative positions of extraction and injection sections in the confined geothermal aquifer according to the initial fluid and heat patterns.