A heat source is applied to different surface locations in a fully coupled climate model to study the cross‐equatorial energy transport and tropical precipitation responses. Remarkably different ...tropical precipitation responses are seen, varying from a large shift toward, to a small shift away from, the heated hemisphere. These differences are dominated by changes in top‐of‐atmosphere radiation, with some contribution from changes in ocean cross‐equatorial heat flux. The atmospheric fraction of the total cross‐equatorial heat flux is consistently larger for Northern Hemisphere (NH) heating relative to Southern Hemisphere heating. This results in a larger tropical rainfall shift in response to NH heating. Positive shortwave radiative feedbacks, associated with a burn‐off of low clouds in the North Pacific, also amplify the tropical rainfall response to NH heating. The Pacific Ocean dominates the ocean response to Southern Hemisphere heating, while the Atlantic Ocean dominates the ocean response to NH heating.
Plain Language Summary
When there is a change in the energy balance between the Northern and Southern Hemispheres, for example, because of aerosol emissions (or clean‐up), then heat transport across the equator must shift to maintain energy balance. If that cross‐equatorial heat transport is produced by changes in the atmospheric circulation (instead of ocean circulation), then tropical precipitation shifts toward the more heated hemisphere. We perturb a fully coupled atmosphere‐ocean climate model with localized heating at the ocean surface in different hemispheres, latitudes, and ocean basins, and study the circulation and tropical precipitation responses. The largest response is from heating in the extratropical North Pacific; this is largely because of strong positive cloud feedbacks in this region and partially because changes in ocean heat transport contribute relatively little to the required change in cross‐equatorial heat transport. In this climate model we find that tropical precipitation is more sensitive to Northern Hemisphere heating than Southern Hemisphere heating and more sensitive to heating in the North Pacific than the North Atlantic. This will have implications for the tropical precipitation response to aerosol clean‐up, and perhaps to cloud feedbacks in different regions in response to global warming.
Key Points
Heating in different basins/hemispheres in a fully coupled GCM gives remarkably different circulation, TOA radiation, and ITCZ responses
The ITCZ is more sensitive to Northern Hemispheric (particularly North Pacific) heating than Southern Hemispheric heating
Strong Northern Hemisphere positive feedbacks can result in a northward ITCZ shift in response to local heating in the Southern Hemisphere
Physics basis for the first ITER tungsten divertor Pitts, R.A.; Bonnin, X.; Escourbiac, F. ...
Nuclear materials and energy,
August 2019, 2019-08-00, 2019-08-01, Letnik:
20, Številka:
C
Journal Article
Recenzirano
Odprti dostop
•Reviews the fundamental physics aspects of the first ITER W divertor and defines the required operational lifetime within the Staged Approach.•Uses the ITER divertor SOLPS simulation database to ...establish the target peak heat flux and neutral pressure burning plasma operating domain.•Assesses consequences of narrow SOL heat flux channels, fluid drifts, component shaping and 3D magnetic fields for ELM control.•Uses W recrystallization to define an operational budget and shows that heat fluxes ∼50% higher than previously assumed may be acceptable.•Shows that Ne and N should be equally good as seed impurities and suggests that very strong ELM mitigation will be required at high performance.•Provides a list of key outstanding R&D areas to consolidate the divertor physics basis in the period up to ITER operation.
On the eve of component procurement, this paper discusses the present physics basis for the first ITER tungsten (W) divertor, beginning with a reminder of the key elements defining the overall design, and outlining relevant aspects of the Research Plan accompanying the new “staged approach” to ITER nuclear operations which fixes the overall divertor lifetime constraint. The principal focus is on the main design driver, steady state power fluxes in the DT phases, obtained from simulations using the 2-D SOLPS-4.3 and SOLPS-ITER plasma boundary codes, assuming the use of the low Z seeding impurities nitrogen (N) and neon (Ne). A new perspective on the simulation database is adopted, concentrating purely on the divertor physics aspects rather than on the core-edge integration, which has been studied extensively in the course of the divertor design evolution and is published elsewhere. Emphasis is placed on factors which may increase the peak steady state loads: divertor target shaping for component misalignment protection, the influence of fluid drifts, and the consequences of narrow scrape-off layer heat flux channels. All tend to push the divertor into an operating space at higher sub-divertor neutral pressure in order to remain at power flux densities acceptable for the target material. However, a revised criterion for the maximum tolerable loads based on avoidance of W recrystallization, sets an upper limit potentially ∼50% higher than the previously accepted value of ∼10 MW m−2, a consequence both of the choice of material and the finalized component design. Although the simulation database is currently restricted to the 2-D toroidally symmetric situation, considerable progress is now also being made using the EMC3-Eirene 3-D code suite for the assessment of power loading in the presence of magnetic perturbations for ELM control. Some new results for low input power corresponding to the early H-mode operation phases are reported, showing that even if realistic plasma screening is taken into account, significant asymmetric divertor heat fluxes may arise far from the unperturbed strike point. The issue of tolerable limits for transient heat pulses is an open and key question. A new scaling for ELM power deposition has shown that whilst there may be more latitude for operation at higher current without ELM control, the ultimate limit is likely to be set more by material fatigue under large numbers of sub-threshold melting events.
This study investigated the impacts of extensive and semi-intensive green roofs on both building insulation and surface urban heat island effect under winter conditions. To this aim we compared ...measurements of surface and building envelope temperatures as well as conductive heat fluxes reaching the external building envelope with those measured on a conventional bituminous roof under identical climatic conditions. The main effect of green roofs was to decrease daily fluctuations of external building envelope temperatures and as a consequence to reduce fluctuations of conductive heat fluxes reaching the building envelope. This effect is all the more important that the substrate is deep, in link with its heat capacity and thermal inertia. Yet, no significant effect of the green roofs on surface urban heat island has been observed on average despite a surface cooling during daytime. It is concluded that the green roofs can be suitable urban greening solutions since they do not have negative effect on surface urban heat island during winter, provide cooling during summer, and contribute to building insulation inducing therefore building energy savings.
•Conventional, extensive and semi-intensive green roofs have been compared.•Green roofs reduced temperature and heat flux fluctuations at the building surface.•Deeper substrates reduced the temperature and heat flux fluctuations of the building surface.•On average there was no or only slight effects on winter surface urban heat island.
Electron heat flux is an important value for ionospheric space weather modeling networks. Utilizing the 2D array of Time History of Events and Macroscale Interactions during Substorms all-sky-imager ...(ASI) observations, Gabrielse et al. (2021, https://doi.org/10.3389/fphy.2021.744298) described a new method that estimates the auroral scale sizes of intense precipitating electron energy fluxes and their mean energies during two substorms on 16 February 2010. These parameters in combination with SuperThermal Electron Transport code were used to develop a new methodology to calculate electron thermal fluxes from data inputs in 2D during one of the substorms at 09:40:00 UT across Canada and Alaska. To test the effect of various precipitation lifetimes on electron heat flux values, boxcar averages ranging from 0 to 900 s were applied to the ASI data. These data are then combined with the newly developed kinetic simulation to determine the thermal fluxes associated with the observed diffuse and discrete precipitation.
ABSTRACT
Cold air outbreaks (CAOs) are the dominant cause of intense wintertime upward heat fluxes in the Irminger Sea. In this study, the climatological pathways of Irminger Sea CAO airmasses and ...the evolution of airmass properties, as well as the large‐scale synoptic environments leading to CAO formation are examined for winter. To that end, a comprehensive, multi‐decadal climatology of Irminger Sea CAO airmasses using kinematic trajectories is presented, complemented by a composite analysis of the large‐scale synoptic environment for intense CAO events.
The following three synoptic environments conducive for CAO formation are identified: (1) The westerly environment is characterized by an upper‐level trough crossing Greenland and inducing strong westerly winds at crest level, accompanied by either cyclogenesis or the intensification of an existing cyclone in the lee of Greenland. The associated CAO airmasses originate in the Canadian Arctic, overflow southern Greenland, and descend into the Irminger Sea with an according imprint in their thermodynamic evolution. (2) In the easterly cyclonic environment, one or multiple cyclones in the Nordic Seas induce northerly winds along Greenland's eastern coast that transport Arctic airmasses from Fram Strait to Denmark Strait. (3) The easterly anti‐cyclonic environment, finally, is dominated by an anti‐cyclone over Greenland with similar airmass origins and pathways as in the easterly cyclonic environment. The two easterly environments represent the limiting cases of an intermediate spectrum, whereas in contrast the westerly environment is clearly distinct. Katabatic drainage from northern Greenland contributes to the CAO airmasses in both easterly environments, whereas in the easterly cyclonic environment also marine airmasses from the Nordic Seas are involved. An important conclusion of this study is that the amount of heat extracted from the ocean by a CAO airmass depends critically on its pathway, and thus on the synoptic environment.
This paper examines the interannual variability of latent (LE) and sensible (H) heat fluxes over the North Indian Ocean for the summer season (June, July, August), that show positive linear trends ...during 1958–2017. Using Air-Sea Flux (OAFlux) from NCEP/NCAR reanalysis-I, the variability and trends in LE and H heat fluxes are compared with changes in the position and pressure of the South Asia Low (SAL). Investigation of interactions between the air-sea heat fluxes and SAL pressure center through correlations analysis and with analysis of composites of humidity gradient, temperature gradient and vector wind fields is carried out. The results show that the SAL plays an important role in the variability of air-sea heat fluxes over North Indian Ocean. There is a negative correlation between SAL pressure and its latitude position. A change of the SAL from a north location to a south location induces changes in North Indian Ocean surface winds, humidity and temperature. These, combined with sea surface warming trends, produce trends in summer latent and sensible heat fluxes.
•Latent and sensible heat fluxes over north Indian Ocean show positive linear trends during summer rainy season.•Correlations between detrended monthly mean heat fluxes and detrended South Asia low (SAL) indices have been calculated.•The correlations show that the latitudinal movement of SAL play a significant role in the variability of heat fluxes.•Composite analysis of various meteorological fields for different states of SAL have been performed.•The composite analysis indicate a strong connection between trends in SAL and trends in the Indian Ocean heat fluxes.
Magnetospheric whistler waves, chorus and hiss, can't provide the resonance heating of the core electron plasma population. However, these whistler-mode branches, can implicitly participate in the ...heating processes of the core plasma thermal electron population by triggering the electron precipitation over a broad energy range from the magnetosphere and subsequent atmospheric ionization processes leading to the production of superthermal electron population. These superthermal electrons play a large role in the magnetosphere-ionosphere-atmosphere energy interplay with participation of both magnetically conjugate hemispheres, and their Coulomb interaction with background magnetospheric thermal electrons. Using strong hiss and chorus wave events measured by the Van Allen Probes and SuperThermal Electron Transport code, we evaluate the formation of electron heat fluxes at the upper ionospheric altitudes and discuss their consequences on the formation of electron temperature. It is found that chorus and hiss waves that initiate the precipitation of magnetospheric electrons with energies below 30 keV and the follow-up production of secondary electrons play an important role in the energy balance of ionosphere-magnetosphere system.
The Rice Convection Model-Equilibrium (RCM-E) and SuperThermal Electron Transport (STET) are combined to investigate electron heat flux formation in the region of the diffuse aurora for the ...geomagnetic storms of 17 March 2013 and 17 March 2015. The primary electron precipitation into the atmosphere resulting from wave particle scattering in the magnetosphere are simulated by the magnetically and electrically RCM-E during these two geomagnetic storms. The primary precipitating electron fluxes are modified by the STET model by taking into account atmospheric backscatter processes. The modified electron energy fluxes and their mean energies are coupled to the STET code to calculate electron thermal fluxes associated with diffuse aurora on a global scale. We use the simulated heat flux to estimate electron temperatures at the upper ionospheric altitudes and compare them with corresponding observations from the Defense Meteorological Satellite Program satellite.
In this work, we exploit nanosecond laser irradiation as a compact solution for investigating the thermomechanical behavior of tungsten materials under extreme thermal loads at the laboratory scale. ...Heat flux factor thresholds for various thermal effects, such as melting, cracking and recrystallization, are determined under both single and multishot experiments. The use of nanosecond lasers for mimicking thermal effects induced on W by fusion-relevant thermal loads is thus validated by direct comparison of the thresholds obtained in this work and the ones reported in the literature for electron beams and millisecond laser irradiation. Numerical simulations of temperature and thermal stress performed on a 2D thermomechanical code are used to predict the heat flux factor thresholds of the different thermal effects. We also investigate the thermal effect thresholds of various nanostructured W coatings. These coatings are produced by pulsed laser deposition, mimicking W coatings in tokamaks and W redeposited layers. All the coatings show lower damage thresholds with respect to bulk W. In general, thresholds decrease as the porosity degree of the materials increases. We thus propose a model to predict these thresholds for coatings with various morphologies, simply based on their porosity degree, which can be directly estimated by measuring the variation of the coating mass density with respect to that of the bulk.
Within the last decades, the water temperature of several European lakes has risen. It is assumed that these temperature increases are due to a reconfiguration of the heat‐balance components. This ...study explores the dominant modifications of heat exchange with the atmosphere and their temporal evolutions. The objective is to identify the primary changes in heat fluxes and the sequence of events of the reconfiguration for the period 1984–2011. For this purpose, a model was applied to Lake Constance to estimate the contributions of the individual heat fluxes to the total heat balance. The results show that increasing absorption of solar radiation (+0.21 ± 0.13 W m−2 yr−1) and of longwave radiation (+0.25 ± 0.11 W m−2 yr−1) was responsible for the lake surface warming of 0.046 ± 0.011°C yr−1. Heat losses to the atmosphere by longwave emission (−0.24 ± 0.06 W m−2 yr−1) and by latent heat flux (−0.27 ± 0.12 W m−2 yr−1) have intensified in parallel due to higher lake surface temperatures. The heat budget is in a quasi‐steady state, whereas incoming solar radiation and the warmer atmosphere increased the lake surface temperature; the warmer surface emits more longwave radiation and more water is evaporated. At each level of the slowly increasing water temperature, the heat fluxes are balanced. The overall change of the total heat content, however, is relatively little. Although the cooling effect of inflowing rivers decreased, this contribution is also small.
Key Points
Estimation of trends in surface heat fluxes in Lake Constance over three decades
Increased shortwave and longwave radiation cause higher water temperatures
Increased heat loss by nonradiative fluxes maintain a constant heat content in the lake
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