Variations in Surface Urban Heat Island and Urban Cool Island Intensity:A Review Across Major Climate Zones

The climate has an impact on the urban thermal environment,and the magnitude of the surface urban heat island(SUHI)and urban cool island(UCI)vary across the world’s climatic zones.This literature review investigated:1)the variations in the SUHI and UCI intensity under different climatic backgrounds,and 2)the effect of vegetation types,landscape composition,urban configuration,and water bodies on the SUHI.The SUHI had a higher intensity in tropical(Af(tropical rainy climate,Köppen climate classification),Am(tropical monsoon climate),subtropical(Cfa,subtropical humid climate),and humid continental(Dwa,semi-humid and semi-arid monsoon climate)climate zones.The magnitude of the UCI was low compared to the SUHI across the climate zones.The cool and dry Mediterranean(Cfb,temperate marine climate;Csb,temperate mediterranean climate;Cfa)and tropical climate(Af)areas had a higher cooling intensity.For cities with a desert climate(BWh,tropical desert climate),a reverse pattern was found.The difference in the SUHI in the night-time was greater than in the daytime for most cities across the climate zones.The extent of green space cooling was related to city size,the adjacent impervious surface,and the local climate.Additionally,the composition of urban landscape elements was more significant than their configuration for sustaining the urban thermal environment.Finally,we identified future research gaps for possible solutions in the context of sustainable urbanization in different climate zones.

Effects of Heat Intensity and Inflow Wind on the Reactive Pollution Dispersion in Urban Street Canyon

This paper investigates the impacts of heating intensity and inflow wind speed on the characteristics of reactive pollutant dispersion in street canyons using the computational fluid dynamic(CFD)model that includes the transportation of NO,NO_2,and O_3coupled with NO-NO_2-O_3photochemistry.The results indicated that the heat intensity and inflow wind speed have a significant influence on the flow field,temperature field and the characteristics of reactive pollutant dispersion in and above the street canyon.With the street canyon bottom heating intensity increasing,NO,NO_2and O_3concentrations in street canyon are decreased.The O_3concentration reductions are even more than the NO and NO_2concentrations.Improving the inflow wind speed can significantly reduce the NO and NO_2concentrations within street canyons.But the O_3concentrations have a slight rise with wind speed increasing.The results would be useful for understanding the interrelation among reactive vehicle emissions,and provide references for urban planners.

The shortest period of coal spontaneous combustion on the basis of oxidative heat release intensity

It’s necessary to forecast the shortest spontaneous combustion period for preventing and controlling the coal spontaneous combustion.During the experimental process,a calculating model of the SSCP is established on the basis of the oxidative heat release intensity and thermal capacity at different temperatures.According to the basic parameters of spontaneous combustion,heat of water evaporation and gas desorption,the SSCPs of different coals are further predicted.Finally,this study analyzed the relationships of the SSCP and the judging indexes of the self-ignite tendency.The result shows that the SSCP non-linearly increases with the decrease of dynamic oxygen adsorption and increase of activation energy.Compared with the practical fire situation of mine,this reliable method can meet the actual requirement of mine production.

Oxidative heat release intensity in coal at low temperatures measured by the hot-wire method

Directly measuring the oxidative heat release intensity at low temperatures is difficult at present.We developed a new method based on heat conduction theory that directly measures heat release intensity of loose coal at low temperatures.Using this method, we calculated the oxidative heat release intensity of differently sized loose coals by comparing the temperature rise of the coal in nitrogen or an air environment.The results show that oxidation heat release intensity of Shenhua coal sized 0～15 mm is 0.001～0.03 W/m3 at 30～90 °C and increases with increasing temperature.The heat release intensity at a given temperature is larger for smaller sized coal.The temperature effect on heat release intensity is muted as the coal size increases.At lower temperature the change in heat release intensity as a function of size becomes smaller.These results show that the test system is usable for practical applications and is easy to operate and is capable of measuring mass samples.

Impact of the Urban Heat Island Effect on Ozone Pollution in Chengdu City,China

With the advancement of urbanization,the urban heat island effect and ozone pollution have become hot issues in urban research.The urban heat island effect can impact ozone conversion,but its mechanism of action is unclear.In this study,the effects of the urban heat island effect on ozone concentration in Chengdu City,China,were investigated by comparing the ozone concentration under different heat island levels with ozone data from March 2020 to February 2021 and the temperature and wind field data of ERA5-Land during the same period.The results showed that:1)regarding the distribution characteristics,the ozone concentration in Chengdu presented a‘high in summer and low in winter’distribution.The ozone concentration in summer(189.54µg/m^(3))was nearly twice that in winter(91.99µg/m^(3)),and the ozone diurnal variation presented a‘single peak and single valley’distribution,with a peak at 16:00.2)For the characteristics of the heat island effect,the heat island intensity in Chengdu was obviously higher in spring than in other seasons,and the diurnal variation showed a‘single peak and single valley’distribution,with the peak and trough values appearing at 9:00 and 17:00,respectively.Spatially,the eastern part of Chengdu was a heat island,while the western and northwestern parts were mostly cold island.3)The correlation analysis between heat island intensity and ozone concentration showed a significant positive correlation but with a 7–8 h time lag.Ambient air temperature was not the main factor affecting ozone concentration.The heat island effect impacts the ozone concentration in two ways:changing the local heat budget to promote ozone generation and forming local urban wind,which promotes ozone diffusion or accumulation and forms different areas of low and high ozone values.

Urban Heat Island and Land Use/Cover Dynamics Evaluation in Enugu Urban, Nigeria

This study specifically estimated the effect of land use/cover change (LULC) processes on land surface temperature (LST) in Enugu urban and its suburbs. With Landsat images and supervised classification technique, four LULC classes comprising built-up areas, vegetation, rock outcrop, bare ground/farmland areas were delineated. The LST was extracted from the thermal bands of the images. The rate of change in land cover classes between 2009 and 2018 showed that from 2009 to 2013, built-up areas increased from 31.65% to about 47.5%, while vegetation cover decreased from 18.43% to 11.23%. Also, the periods witnessed about 8.69 km2 of vegetation being converted to other land surfaces. The trend in the LST in Enugu urban showed the highest mean temperatures of 34.5°C in 2018 and 32.26°C in 2015. However, in 2013 there was a slight decrease in mean LST to 31.65°C which further decreased to 31.26°C in 2009. This change in temperature suggests that urbanisation could have significant effect on the micro-climate of Enugu city. Result also revealed weak relationships between LULC classes and the LST throughout the years. The results of the surface heat intensity for the urban and rural areas showed general increase over the years and this suggests that rural areas are also experiencing high temperature which could be due to the loss of vegetation, increase in artificial surfaces and urban encroachment. Findings from this study could be useful for effective urban land-use planning, policy development and management in Nigeria, and elsewhere.

Numerical Study on the Impact of Ground Heating and Ambient Wind Speed on Flow Fields in Street Canyons

The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods. A series of numerical tests were performed, and three factors including height-to-width （H/W） ratio, ambient wind speed and ground heating intensity were taken into account. Three types of street canyon with H/W ratios of 0.5, 1.0 and 2.0, respectively, were used in the simulation and seven speed values ranging from 0.0 to 3.0 m s-1 were set for the ambient wind speed. The ground heating intensity, which was defined as the difference b-ween the ground temperature and air temperature, ranged from 10 to 40 K with an increase of 10 K in the tests. The results showed that under calm conditions, ground heating could induce circulation with a wind speed of around 1.0 m s-i, which is enough to disperse pollutants in a street canyon. It was also found that an ambient wind speed threshold may exist for street canyons with a fixed H/W ratio. When ambient wind speed was lower than the threshold identified in this study, the impact of the thermal effect on the flow field was obvious, and there existed a multi-vortex flow pattern in the street canyon. When the ambient wind speed was higher than the threshold, the circulation pattern was basically determined by dynamic effects. The tests on the impact of heating intensity showed that a higher ground heating intensity could strengthen the vortical flow within the street canyon, which would help improve pollutant diffusion capability in street canyons.

THERMAL EFFECTS OF BUILDING′S EXTERNAL SURFACES IN CITY——Characteristics of Heat Flux into and out of External Wall Surfaces

This study examined the thermal effects of building′s external wall surfaces, using observational data of spatial-temporal distribution of surface temperature, air temperature, and heat flux into and out of external surface. Results indicate that external wall surface temperature and nearby air temperature vary with the change of orientation, height and season. In general, the external wall surface temperature is lower near the ground, and is higher near the roof, than nearby air temperature. But north wall surface temperature is mostly lower than nearby air temperature at the same height; south wall surface temperature during the daytime in December, and west wall surface temperature all day in August, is respectively higher than nearby air temperature. The heat fluxes into and out of external wall surfaces show the differences that exist in the various orientations, heights and seasons. In December, south wall surface at the lower sites emits heat and north wall surface at the higher sites absorbs heat. In April, all external wall surfaces, emit heat near the ground and absorb heat near the roof. In August, west wall surface all day emits heat, and other wall surfaces just show the commensurate behavior with that in April.

Altitude and intensity characteristics of parametric instability excited by an HF pump wave near the fifth electron harmonic

An ionospheric heating experiment involving an O mode pump wave was carried out at European Incoherent Scatter Scientific Association site in Troms？. The observation of the ultra high frequency radar illustrates the systematic variations of the enhanced ion line and plasma line in altitude and intensity as a function of the pump frequency. The analysis shows that those altitude variations are due to the thermal effect, and the intensity variations of the enhanced ion line are dependent on whether or not the enhanced ion acoustic wave satisfy the Bragg condition of radar. Moreover, a prediction that if the enhancement in electron temperature is suppressed,those systematic variations will be absent, is given.

STUDY ON LOCATION OF HOT SPOT AT TUBE WALL FOR FIRED CYLINDRICAL FURNACE COMBUSTION

Based on the analysis of heat radiation intensity from flame, a new mathematical model ofthe tube-wall temperatmp of heated tubes is developed by taking down-fired, upright-tube cylindricalfurnace for example. The proposed mathematical model can be employed to indicate both the positionand size of the hot spot at fire-facing wall of heated tube of combustion chamber, and is characteristicof simplicity and efficiency If coupled with thermoelectric couple or infrared viewer, the presentedlocation method of combustion hot spot can offer engineers very valuable proposal to keep furnacerunning more safely The same is true for any other type of tubular furnaces.

Experimental simulation and numerical analysis of coal spontaneous combustion process at low temperature

The characteristic of coal spontaneous combustion includes oxidative property and exothermic capacity. It can really simulate the process of coal spontaneous combustion to use the large scale experimental unit loading coal 1 000 kg. According to the field change of gas concentration and coal temperature determined through experiment of coal self ignite at low temperature stage, and on the basis of hydromechanics and heat transfer theory, some parameters can be calculated at different low temperature stage, such as, oxygen consumption rate, heat liberation intensity. It offers a theoretic criterion for quantitatively analyzing characteristic of coal self ignite and forecasting coal spontaneous combustion. According to coal exothermic capability and its thermal storage surroundings, thermal equilibrium is applied to deduce the computational method of limit parameter of coal self ignite. It offers a quantitative theoretic criterion for coal self ignite forecasting and preventing. According to the measurement and test of spontaneous combustion of Haibei coal, some token parameter of Haibei coal spontaneous combustion is quantitatively analyzed, such as, spontaneous combustion period of coal, critical temperature, oxygen consumption rate, heat liberation intensity, and limit parameter of coal self ignite.

Spatial planning for urban ventilation corridors by urban climatology

Ventilation corridors in cities can decrease air pollution and alleviate heat island problems but there remains a need to fully assess their effectiveness.Few urban managers have been able to take city-scale approaches to the construction of urban ventilation corridors.This study aimed to introduced the Ventilation Corridor Planning(VCP)model,which is a multi-criteria evaluation method combined with a geographical information system(GIS)to determine where the ventilated environment is most appropriate.Specifically,the VCP model took Bozhou,China as the research object and contained two scales,including mesoscale and local scale.In mesoscale scale,we got three outputs to build urban ventilation corridors,including 1)background wind environment,2)ventilation potential,3)heat island intensity.In local scale,we used traditional computational fluid dynamics(CFD)model to verify the impact of VCP criteria.The results revealed that compared with the traditional CFD model,the proposed VCP model has advantages in establishing a comprehensive evaluation standard.In addition,the application of VCP model in macro and micro also enhances the efficiency of ventilation corridor construction.Overall,this study introduced a effective modeling method to urban ventilation corridors planning,and provide a way to study the urban climate.