Heat Content Research Articles

Baroclinic Sea Level

AbstractSea level and its horizontal gradient are an expression of oceanic volume, heat content, and currents. Large‐scale currents have historically been viewed as mostly “baroclinic,” and tides as “barotropic,” respectively, in the loose sense of being strongly related to the oceanic density distribution or not. In particular, the evolution of the barotropic velocity is influenced by a horizontal pressure‐gradient force that depends on the gradient of a particular depth‐weighting of the density field as well as on the gradient of the sea‐surface elevation ζ; hence, even the tides must be viewed as a product of the coupled interaction of barotropic and baroclinic fields. The purpose of this note is to give dynamical precision to the distinction between barotropic and baroclinic contributions to ζ and the surface pressure‐gradient force −g∇ζ, and, in the particular case of the tides, demonstrate their combined barotropic‐baroclinic interactions with a realistically forced, high‐resolution simulation of the Pacific Ocean circulation. While the different tidal sea‐level contributions manifest a horizontal scale separation (e.g., more barotropic at larger scales; more baroclinic surface pressure‐gradient force at smaller scales), there are cross‐mode corrections in both at the level of tens of percent. The proposed barotropic‐baroclinic decomposition is generally relevant to the sea‐level expression of oceanic currents.

Impact of temperature and residence time on sewage sludge pyrolysis for combined carbon sequestration and energy production

Environmental challenges related to sewage sludge call for urgent sustainable management of this resource. Sludge pyrolysis might be considered as a sustainable technology and is anticipated to support measures for mitigating climate change through carbon sequestration. The end products of the process have various applications, including the agricultural utilization of biochar, as well as the energy exploitation of bio-oil and syngas. In this research, sewage sludge was pyrolyzed at 500 °C, 600 °C, 750 °C, and 850 °C. At each temperature, pyrolysis was explored at 1hr, 2hrs, and 3hrs residence times. The ratio (H/Corg)at was tapped to imply organic carbon stability and carbon sequestration potential. Optimum operating conditions were achieved at 750 °C and 2hrs residence time. Produced biochar had (H/Corg)at ratio of 0.54, while nutrients’ contents based on dry weight were 3.99%, 3.2%, and 0.6% for total nitrogen (TN), total phosphorus (TP), and total potassium (TK), respectively. Electrical conductivity of biochar was lesser than the feed sludge. Heavy metals in biochar aligned with the recommended values of the International Biochar Initiative. Heat content of condensable and non-condensable volatiles was sufficient to maintain the temperature of the furnace provided that PYREG process is considered. However, additional energy source is demanded for sludge drying.

Ocean Heat Content Increase of the Maritime Continent Since the 1990s

AbstractThe Maritime Continent (MC), a critical region for inter‐basin climate interaction, harbors the world's highest marine biodiversity. Ocean warming in the MC, although with notable impacts on regional climate and marine ecosystems, remains poorly constrained by observations. By applying a volume‐correction algorithm to existing gridded observational data sets, this study provides an estimate for the ocean heat content (OHC) change of the MC. The results suggest a substantial OHC increase of 2.65 ± 0.46 Zettajoules during 1990–2015 (1.08 ± 0.17 W m−2) and limited changes before and after. This increase primarily arose from the enhanced Pacific Walker circulation, which drove a convergence of upper‐layer warm water toward the MC. A potential heat storage “hotspot” with enhanced warming below 500 m emerges within the Sulu Sea, which is supported by analysis of profile data collected in boreal winter but not in other seasons.

Design, fabrication, and performance assessment of a novel biomass gasification-powered all-season climate control unit for perishables

Availability of storage and processing facilities that work off-the-grid is crucial to agrarian economies for meeting sustainable development goals. We report a novel biomass-gasification-powered climate control unit (CCU) with independently controlled temperature and humidity, which enables the system to maintain a wide range of climatic conditions for storage, processing and farming of perishables. The developed all-season CCU has a temperature control subsystem driven by a novel biomass gasification-based hot water generator (heating capacity – 22 kW), which also powers an adsorption refrigerator (cooling capacity – 11 kW). The heat content of the hot flue gas (≈250°C) from the exhaust of gasification-based hot water generator is recovered using flue gas-to-air heat exchanger and utilized to regenerate (3.6 kW) the desiccant wheel thus enabling an off-the-grid humidity control. Auxiliary components such as pumps, blowers, control panels, and valves are operated in an off-the-grid manner using solar photovoltaic panels (≈ 1.5 kWe) backed by storage batteries. An algorithm is devised to demonstrate autonomous and independent control of temperature and relative humidity over a wide range of psychrometric conditions (0–50 °C and 15–90 % RH). We also present the cost analysis and identify the immediate challenges facing the developed system. The waste-to-energy concept of high lignin-based biomass such as forest wood, agricultural residue demonstrated herein lays the foundation for a proper biomass utilization besides empowering farmers with a much-needed technology towards sustainable growth.

Spurious Trends in High Latitude Southern Hemisphere Precipitation Observations

AbstractThe high latitude Southern Hemisphere (SH) is an important region for Earth's climate. Ocean heat content, cryosphere interactions, Antarctic bottom water development and the cloud‐albedo feedbacks need to be understood to form a complete picture of the climate system. However, the high latitude SH is one of the most under‐observed regions due to its remoteness. The advent of satellites and reanalyses have improved our monitoring of this region. Some previous studies observed an increase in precipitation over the SH high latitudes, however we argue that some of the trends in commonly used data sets may be artifacts. We use regression analysis of trends in precipitation and the Southern Annular Mode to contrast these relationships in satellite and reanalysis products, and to evaluate precipitation over the SH. We suggest that sensor changes and the lack of in situ data available for calibration may be responsible for unusual precipitation patterns especially around 65°S.

The North Equatorial Current and rapid intensification of super typhoons

Super Typhoon Mangkhut, which traversed the North Equatorial Current (NEC; 8–17 °N) in the western North Pacific in 2018, was the most intense Category-5 tropical cyclone (TC) with the longest duration in history—3.5 days. Here we show that the combination of two factors—high ocean heat content (OHC) and increased stratification — makes the NEC region the most favored area for a rapid intensification (RI) of super typhoons, instead of the Eddy Rich Zone (17–25 °N), which was considered the most relevant for RI occurrence. The high OHC results from a northward deepening thermocline in geostrophic balance with the westward-flowing NEC. The stratification is derived from precipitation associated with the Inter-Tropical Convergence Zone in the summer peak typhoon season. These factors, which are increasingly significant over the past four decades, impede the TC-induced sea surface cooling, thus enhancing RI of TCs and simultaneously maintaining super typhoons over the NEC region.

Surface Albedo Feedback, Seasonal Heat Storage and Meridional Heat Transport Determine the Seasonality of Recent Warming in Antarctica

AbstractThe reanalysis data suggest that recent surface warming over Antarctica start in 2016. In this study, using reanalysis data and numerical simulations, I attempt to determine the important mechanisms accounting for seasonal surface warming in Antarctica. The results suggested that seasonal surface warming in Antarctica is mainly determined by the surface energy budget over the Antarctic via horizontal heat advection. The surface energy budget anomaly over the Antarctic, which is mainly determined by anomalous solar radiation absorption, anomalous ocean heat content, and anomalous meridional atmospheric heat transport (AHT), is triggered by Antarctic sea‐ice loss and thus determines the observational seasonality of recent warming in Antarctica via surface horizontal heat advection. In austral summer (December–January–February), additional solar radiation absorption induced by sea‐ice loss and additional AHT from lower latitudes increase the energy budget over the Antarctic. Surface warming, more longwave radiation, and additional energy stored in the upper (deeper) ocean for short (long) time periods explain the additional energy sinks. During austral autumn‐winter (March–August), additional seasonal heat storage (SHS; mainly stored in the upper ocean) is released to the atmosphere and warms the surface. Although the AHT anomaly contributes similarly to the solar radiation absorption/SHS anomaly during April–August, the poleward AHT largely decreased in June due to the weaker eddy activity induced by strong warming at Southern Hemisphere midlatitudes, which counteracts the additional SHS release and cools the Antarctic(a).

Man, it's a hot one: Trends and extremes in Florida autumn heat stress

AbstractExtreme heat is the deadliest weather‐related hazard in the United States, and is increasing in frequency, intensity and duration due to climate change. Heat stress is broadly defined as environmental influences on body temperature, and in this study is evaluated using wet bulb globe temperature (WBGT), which incorporates temperature, humidity, wind speed and solar radiation. Heat stress and associated humid heat have increased significantly across many regions of the globe, particularly in the subtropics and Tropics, which exacerbates health and excess mortality risks in those areas. However, heat stress has typically been investigated as a solely summer phenomenon. This study uses WBGT to examine heat stress trends and extremes during climatological autumn from the 1950s to 2022 at eight Florida cities. Results show that average autumn heat stress has increased significantly throughout much of Florida, particularly at coastal locations in the Florida Peninsula. Daytime heat stress increases were larger than their night‐time counterparts in northern Florida, while the opposite was true in central and southern Florida. Extreme (90th percentile) autumn heat stress events also increased in intensity and frequency, particularly in the Florida Peninsula and Florida Keys. Furthermore, locations in the Florida Peninsula and Florida Keys experienced increases of greater than 1.5 extreme autumn heat stress days per decade. Heat stress trends were predominantly largest in urban coastal environments, suggesting links to urbanization as well as statistically significant early autumn warming trends in sea surface temperatures. Overall, results indicated that heat stress in Florida is no longer solely a summer hazard and poses a particular threat to coastal areas in early autumn when ocean heat content is still near its climatological peak.

A Glimpse into the Future: The 2023 Ocean Temperature and Sea Ice Extremes in the Context of Longer-Term Climate Change

Abstract In the year 2023, we have seen extraordinary extrema in high sea surface temperature (SST) in the North Atlantic and in low sea ice extent in the Southern Ocean, outside the 4σ envelope of the 1982–2011 daily time series. Earth’s net global energy imbalance (12 months up to September 2023) amounts to +1.9 W m−2 as part of a remarkably large upward trend, ensuring further heating of the ocean. However, the regional radiation budget over the North Atlantic does not show signs of a suggested significant step increase from less negative aerosol forcing since 2020. While the temperature in the top 100 m of the global ocean has been rising in all basins since about 1980, specifically the Atlantic basin has continued to further heat up since 2016, potentially contributing to the extreme SST. Similarly, salinity in the top 100 m of the ocean has increased in recent years specifically in the Atlantic basin, and in addition in about 2015 a substantial negative trend for sea ice extent in the Southern Ocean began. Analyzing climate and Earth system model simulations of the future, we find that the extreme SST in the North Atlantic and the extreme in Southern Ocean sea ice extent in 2023 lie at the fringe of the expected mean climate change for a global surface-air temperature warming level (GWL) of 1.5°C, and closer to the average at a 3.0°C GWL. Understanding the regional and global drivers of these extremes is indispensable for assessing frequency and impacts of similar events in the coming years.

Definition of springtime easterly wind bursts in the Indian Ocean and their roles in triggering positive IOD events

Using wind reanalysis dataset, we propose a definition for easterly wind bursts (EWBs) occurring in the Indian Ocean and analyze their effects on positive Indian Ocean Dipole (pIOD) events. It was found that there were eight pIOD events during the period from 1980–2020, all of which were accompanied by EWBs occurrence in spring except 2015. The significant impact of EWBs on pIOD events is through the Bjerkness feedback process, strengthening upwelling in the Eastern Indian Ocean (EIO) and triggering a westward zonal current in the equatorial Indian Ocean, both cooling the EIO and in turn strengthening the easterly wind anomalies. Further analysis reveals that the negative upper ocean heat content (OHC) anomalies in EIO, acting as a trigger of Bjerkness feedback process, also plays a critical role in the development of pIOD. Thus, the simultaneous occurrence of EWBs and negative OHC anomalies in spring is an important precursor to pIOD occurrence, although there are possible other triggers.

Flawed Emergency Intervention: Slow Ocean Response to Abrupt Stratospheric Aerosol Injection

AbstractGiven the possibility of irreversible, anthropogenic changes in the climate system, technologies such as solar radiation management (SRM) are sometimes framed as possible emergency interventions. However, little knowledge exists on the efficacy of such deployments. To fill in this gap, we perform Community Earth System Model 2 simulations of an intense warming scenario on which we impose gradual early‐century SRM or rapid late‐century cooling (an emergency intervention), both realized via stratospheric aerosol injection (SAI). While both scenarios cool Earth's surface, ocean responses differ drastically. Rapid cooling fails to release deep ocean heat content or restore an ailing North Atlantic deep convection but partially stabilizes the Atlantic meridional overturning circulation. In contrast, the early intervention effectively mitigates changes in all of these features. Our results suggest that slow ocean timescales impair the efficacy of some SAI emergency interventions.

Optimisation of pH for minimising juice degradation during evaporation

During juice evaporation, sucrose loss can occur due to degradation reactions that are influenced by heat, pH, residence time, and dry substance content. The impacts of heat can be controlled through process and equipment design, and juice pH could be optimised to reduce its effects on degradation reactions. A factory sampling program was conducted with juices collected across an evaporator station comprised of six Robert (rising film) effects in series for a range of juice pH levels and analysed for sucrose loss and overall pH drop from clarified juice to syrup. Measured losses were compared to predictive correlations and showed strong agreement. Using the factory data, two pH control strategies to minimise sucrose degradation and the subsequent impacts on downstream processing were simulated with predictive correlations. The modelling results highlight the potential benefits that can be achieved.

Investigating the effect of coolant on cooling rate of engine oil used in automobile industry using Arduino interfaced temperature sensor

Heat is lost by the system due to temperature difference between the hot object and surroundings. Two models which explain cooling are conduction-convection method and radiation method. During an automobile engine operation, both engine and engine oil get heated up. To overcome the problem of excessive heat generated, coolant is used to cool down the system. In present study, cooling rate of engine oil kept at high temperature was studied in the absence and presence of coolant. In the absence of coolant, engine oil follows the natural law of cooling stated by Newton and follows the exponential decay in temperature. Cooling rate constant was estimated through fitting first order and second order exponential decay with experimental data and found to be 3.35×10−4s−1 and 2.39×10−4s−1 (in first 50 min) respectively. Cooling rate in the presence of coolant was studied which shows rapid decrease in temperature for first few minutes which may be attributed to high heat capacity of coolant which surrounds the hot engine oil. After 50 min of cooling, temperature of both fluids found to decrease exponentially. Thus, the use of coolant was found to absorb the heat content from the engine oil rapidly in comparison to natural environment. Cooling rate constant were estimated through fitting experimental data and found to be 2.44×10−4s−1 and 2.43×10−4s−1 for engine oil and coolant respectively. The percentage change in temperature of oil in first two minutes in the presence of coolant was about 70% which is much higher in comparison to cooling without the use of coolant which was about 16% only. For data acquisition of temperature of engine oil and coolant, MAX6675 module with K-type thermocouple is used which were interfaced with the Arduino board.

Investigating Multidecadal Trends in Ice Cover and Subsurface Temperatures in the Laurentian Great Lakes Using a Coupled Hydrodynamic–Ice Model

Abstract While changing lake surface conditions have received significant research scrutiny, changes in subsurface conditions, including stratification and heat content, remain largely unexplored. In this work, we highlight changes in thermal structure, stratification dynamics, and ice characteristics in the Laurentian Great Lakes (Lakes Superior, Huron, Michigan, Erie, and Ontario) as simulated between 1979 and 2021. Three-dimensional lake hydrodynamics and ice cover were modeled using the Finite Volume Community Ocean Model (FVCOM) coupled with the Los Alamos sea ice model (CICE). Analysis revealed significant increases in surface (0.4°–0.6°C decade−1) and subsurface (0.1°–0.4°C decade−1) temperatures as well as dramatic losses in ice cover (1%–8% decade−1) and ice volume (0–3 km3 decade−1) over the last 40 years. Estimated surface heating rates were strongest during the summer and fall, while subsurface warming was most rapid during the nearly isothermal winter and spring. Intensified (decreased) summer (winter) stratification led to shifts in lake turnover dynamics, with delayed fall turnover dates (2–6 days decade−1) and earlier spring overturn dates (2–9 days decade−1). Modeled surface temperatures (LST), bottom temperatures (LBT), and annual averaged ice cover (AAIC) were used to estimate low-frequency climate signals, which were highly correlated with the Atlantic multidecadal oscillation. Warming trends fit to residual climate signals (LST: 0.1°C decade−1; LBT: 0.03°C decade−1; AAIC: −1% decade−1), calculated by removing low-frequency variability from the raw climate signal, were lower than those fit to associated low-frequency components, suggesting that recent climate change in the Great Lakes may be strongly influenced by natural multidecadal climate variability.

ENSO phase locking, asymmetry and predictability in the INMCM Earth system model

Abstract Advanced numerical climate models are known to exhibit biases in simulating some features of El Niño–Southern Oscillation (ENSO), which is a key mode of interannual climate variability. In this study we analyze how two fundamental features of observed ENSO – asymmetry between hot and cold states and phase-locking to the annual cycle – are reflected in two different versions of the INMCM Earth system model (state-of-the-art Earth system model participating in the Coupled Model Intercomparison Project). We identify the above ENSO features using the conventional empirical orthogonal functions (EOF) analysis, which is applied to both observed and simulated upper ocean heat content (OHC) data in the tropical Pacific. We obtain that the observed tropical Pacific OHC variability is described well by two leading EOF-modes, which roughly reflect the fundamental recharge-discharge mechanism of ENSO. These modes exhibit strong seasonal cycles associated with ENSO phase locking while the revealed nonlinear dependencies between amplitudes of these cycles reflect ENSO asymmetry.We also assess and compare the predictability of observed and simulated ENSO based on linear inverse modelling. We find that the improved INMCM6 model has significant benefits in simulating described features of observed ENSO as compared with the previous INMCM5 model. The improvements of the INMCM6 model providing such benefits are discussed. We argue that proper cloud parameterization scheme is crucial for accurate simulation of ENSO dynamics with numerical climate models.

A new tool for studying seasonality and spatio-temporal structure of ENSO cycles in data and ESM simulations

Abstract In this work, we present a new diagnostic tool for El Niño Southern Oscillation (ENSO) simulations in Earth System Models (ESMs) based on the analysis of upper ocean heat content data. It allows us to identify the seasonally dependent structure of temperature anomalies in the equatorial Pacific Ocean in the form of a dominant spatio-temporal pattern. We demonstrate the results of applying a tool to analysis of real data as well as climate simulations in two versions of the Institute of Numerical Mathematics ESM. We find that the latest version of the model, with improved parameterizations of clouds, large-scale condensation, and aerosols, provides significantly better reproduction of ENSO-related structure of anomalies, as well as the phase locking of ENSO to the annual cycle. We recommend to use the tool for diagnostic analysis of ESMs regarding simulation of climate phenomena with strong seasonality.

Anomalously large latent heat fluxes in low to moderate wind conditions within the eddy-rich zone of the Northwestern Pacific

An air-sea interaction field campaign was conducted in September of 2017 within the warm and cold eddy region of the western Northwest Pacific (WNP) (17.5˚-20.5˚N, 127.5˚E-133.5˚E). Both near-surface oceanic and atmospheric conditions in addition to ocean heat content (OHC) were examined to better understand the mechanisms governing high heat flux magnitudes responsible for rapidly intensifying tropical cyclones. Observations from this experiment indicate that the latent heat flux (LHF) under modest wind conditions reached 400 W m-2 within the vicinity of a warm eddy, with OHC higher than 100 kJ cm-2 of warm eddy region being 2~3 times as large as that of cold eddy region. These high OHC and a resultant high LHF in the warm eddy, comparable to the magnitude of LHF in the North Equatorial Current, may explain the mechanism of why tropical cyclones over a warm eddy in eddy-rich zones often rapidly intensify in the WNP. A month later typhoon Lan rapidly intensified into a super typhoon, while passing over the boundary region of warm and cold eddies during the observation period. Results from this study illustrate that both the wind-normalized LHF and the difference (Qs-Qa) between the specific humidity at air (Qa) and at the sea surface (Qs), closely correlate with OHC patterns, which suggests that the ocean looks likely to control the spatial pattern of LHF. Overall, both the ocean and weather conditions govern the pattern of specific humidity difference between the air-sea interface, with large OHC over the warm eddy controlling higher Qs and the pattern of Qa depending on the pattern of wind direction. Qa as a factor impacting LHF magnitude is strongly linked to wind direction in the experimental area, that is, the drier northwesterly flow and southeasterly moist wind, resulting in the enhanced contrast of specific humidity at cold eddy region.

Adsorption-type aluminium-based direct lithium extraction: The effect of heat, salinity and lithium content

Conventional lithium production through solar evaporation is considered a time-consuming procedure, taking a substantial 12 to 18 months with significant environmental impacts such as aquifer depletion and damaging the basin's complex hydrological system. Direct Lithium Extraction (DLE) has emerged as a promising alternative for lithium extraction from brines, offering reduced environmental impact. Although adsorption-type DLE with aluminium-based adsorbents is the sole commercial technology of DLE, a debate persists concerning its Technology Readiness Level (TRL), which challenges the prevailing notion that adsorption-type DLE undeniably reaches a TRL of 9. Within this narrative, we propose that adsorption is capable of attaining its highest potential TRL in lithium recovery from brines when three critical conditions are met: the presence of a certain level of salinity, a minimum lithium content in the brine, and a heat source to heat up the brine. In this account, an attempt has been made to elucidate the role of these three minimum criteria during adsorption-type DLE.

Processes Driving Subseasonal Variations of Upper Ocean Heat Content in the Equatorial Indian Ocean

AbstractIn the equatorial Indian Ocean, the largest subseasonal temperature variations in the upper ocean are observed below the mixed layer. Subsurface processes can influence mixed layer temperature and consequently air‐sea coupling. However, the physical processes driving temperature variability at these depths are not well quantified. During the boreal winter, the Madden–Julian Oscillation (MJO) partly drives upper ocean heat content (OHC) variations. Therefore, to understand processes driving subseasonal OHC variability in the equatorial Indian Ocean, we use an observationally constrained, physically consistent ocean state estimate from the Estimating the Circulation and Climate of the Ocean (ECCO) Consortium. Using a heat budget analysis, we show that the main driver of subseasonal OHC variability in the ECCO ocean state estimate is horizontal advection. Along the equator, OHC variations are driven by zonal advection while the role of meridional advection becomes more important away from the equator. During the active phase of the MJO, net air‐sea heat fluxes damp OHC variability along the equator, while away from the equator net air‐sea heat fluxes partly drive OHC variability. Equatorial OHC variations are found to be associated with processes driven by Kelvin and Rossby waves consistent with previous studies. By quantifying the physical processes, we highlight the important role of ocean dynamics in contributing to the observed variations of subseasonal OHC in the equatorial Indian Ocean.

On magnitudes of rapid intensification and destruction of tropical cyclones over the North Indian Ocean

AbstractThe study targets long‐term analysis of rapid intensification (RI) magnitudes and destructiveness of tropical cyclones (TCs), as well as factors that are responsible for those magnitudes over the North Indian Ocean (NIO). Out of 131 TCs during 1990–2021, 50 TCs (38%) exhibited RI in their lifetime. Results indicate that the lifetime maximum intensity (LMI) and landfall intensity (LFI), along with the potential destructive index (PDI), are directly proportional (correlation coefficient > 0.8) to the lifetime maximum intensification rate. Most RI TCs (~80%) made landfall with an average LMI, LFI and PDI of 95 knots, 85 knots and 4 × 107 knot3, respectively. And the destructive indices are more than double compared to landfalling non‐RI TCs. Recent years have witnessed an increasing trend in RI magnitude and the frequent occurrence of very RI cases (intensity change ≥50 knots in 24 h). It infers that recent TCs have achieved RI and higher magnitudes in a short duration (~20 h). The higher intensification rates are promoted by lower wind shear as well as strong surface latent and sensible heat fluxes. The higher sea surface temperature by ~0.2°C, oceanic heat content by ~60 × 107 J·m−2, lower tropospheric humidity by ~0.2 g·kg−1 and moist static energy by ~6 × 106 J·m−2 in the recent period (2007–2021) supports higher intensification rates as compared to the earlier period (1990–2006). The deep‐layer wind shear has decreased by 1.0 m·s−1 in recent years, which supports higher RI magnitudes. This study highlights the risk associated with RI magnitudes and the efforts to be made for improved predictions of higher intensification rates.