Modeling of Long-Periodic Changes in Atmospheric Motions Based on the Coupling of Simple Convective Systems

This paper focuses on quantitative calculation of longwave radiation and shortwave radiation from MODIS data in the Poyang Lake area of Jiangxi Province, China. The sum of the net longwave radiation and the shortwave radiation is the net radiation. These parameters are critical for the study of energy exchange in the lower boundary layer on land surface. Two of the most important factors for the retrieval of longwave radiation are the land surface temperature and emissivity. In this paper, the land surface temperature and emissivity were calculated from MODIS data using the regional self‐iterative split‐window method. The most important factor in the determination of the shortwave radiation is Earth surface albedo. The spectral reflectance and surface albedo were derived from MODIS data using the Synergy of TERRA and AQUA MODIS data (SYNTAM) algorithm. The net shortwave and longwave radiation were calculated and compared with the in situ measurement data. Our results indicate that the methods for quantitative calculation of net longwave radiation, shortwave radiation and net radiation from MODIS data can have a good accuracy. The relative errors are between 2.1% to 9.72% for longwave radiation, 0.15% to 10.48% for shortwave radiation and 0.64% to 13.7% for net radiation. We can conclude that a good accuracy can be achieved for deriving longwave radiation, shortwave radiation and net radiation, which are helpful for heat exchange, environmental, hydrology and ecology research in land areas.

Modeling the incoming all-wave radiation in a planted trench system

Complex interactions between the land surface and atmosphere and the exchange of water and energy have a significant impact on climate. The Tibetan Plateau is the highest plateau in the world and is known as “Earth’s third pole”. Because of its unique natural geographical and climatic characteristics, it directly affects China’s climate, as well as the world’s climate, through its thermal and dynamic roles. In this study, the BCCCSM1.1 model for the simulation results of CMIP5 is used to analyze the variation of the land surface processes of the Tibetan Plateau and the possible linkages with temperature change. The analysis showed that, from 1850 to 2005, as temperature increases, the model shows surface downward short-wave radiation, upward short-wave radiation, and net radiation to decrease, and long-wave radiation to increase. Meanwhile, latent heat flux increases, whereas sensible heat flux decreases. Except for sensible heat flux, the correlation coefficients of land surface fluxes with surface air temperature are all significant at the 99 % significance level. The model results indicate rising temperature to cause the ablation of ice (or snow) cover and increasing leaf area index, with reduced snowfall, together with a series of other changes, resulting in increasing upward and downward long-wave radiation and changes in soil moisture, evaporation, latent heat flux, and water vapor in the air. However, rising temperature also reduces the difference between the surface and air temperature and the surface albedo, which lead to further reductions of downward and upward short-wave radiation. The surface air temperature in winter increases by 0.93 °C/100 years, whereas the change is at a minimum (0.66 °C/100 years) during the summer. Downward short-wave and net radiation demonstrate the largest decline in the summer, whereas upward short-wave radiation demonstrates its largest decline during the spring. Downward short-wave radiation is predominantly affected by air humidity, followed by the impact of total cloud fraction. The average downward short-wave and net radiation attain their maxima in May, whereas for upward short-wave radiation the maximum is in March. The model predicts surface temperature to increase under all the different representative concentration pathway (RCP) scenarios, with the rise under RCP8.5 reaching 5.1 °C/100 years. Long-wave radiation increases under the different emission scenarios, while downward short-wave radiation increases under the low- and medium-emission concentration pathways, but decreases under RCP8.5. Upward short-wave radiation reduces under the various emission scenarios, and the marginal growth decreases as the emission concentration increases.

A two-dimensional cloud model is used to study the interrelationships among cloud microphysics, radiation, and dynamics in a midlatitude broken-line squall system. The impact of the ice phase, longwave and shortwave radiation on the dynamic and microphysical structures of this multicellular storm, the thermodynamic properties of the cloud ensemble, and their cloud-radiative feedback to the modeled squall line system is investigated in detail. In addition, partitioned heat, moisture, and water budgets are used to assess quantitatively the role of anvil clouds on the modeled squall line system. The major conclusions are as follows. 1) Both ice phase and radiation have little influence on the multicellular characters of the modeled squall line system. However, the ice phase and longwave radiation significantly impact the mesoscale structure and lead to a more realistic feature having an evident transition zone between the bright melting band and the convective region in the model-derived radar reflectivity. 2) The development of rear inflow in the modeled squall line system is attributed to the upshear tilt of the convective system. The intensity of rear inflow is also modulated by the ice phase and radiation. This rear inflow is found to play an important role in the cloud-radiative feedback to the modeled squall line system. 3) For this type of squall line system, the ice phase and radiation do not considerably change the heating and drying profiles of the cloud ensemble (10% ∼ 20% difference in the maximum heating and drying). Due to the dominance of convective clouds, the contributions of stratiform clouds to the total heat and moisture budgets of the cloud ensemble account for only a relatively small portion (10% and 20% ∼ 30% for the maximum heat and moisture budgets, respectively). 4) Horizontal transport of hydrometeors from deep convection is the primary source (∼2/3) of the water budget for anvil clouds in ice simulations; the rest (∼1/3) is contributed by the mesoscale lifting associated with the tilting convective system. 5) Longwave optical properties of anvils are insensitive to the ice phase. However, the ice phase can significantly impact shortwave optical properties of anvils. In contrast to the destabilization of longwave radiation, shortwave radiation acts to stabilize the stratiform and convective clouds. 6) Model simulations imply that the feedback of anvil clouds to the large-scale system is most likely dominated by radiative processes. Owing to the large coverage of convectively generated anvil clouds, the present study suggests that the missing physics of cumulus-anvil interactions in general circulation models may result in an underestimated cloud albedo and an overestimated surface insolation.

Background: Sunscreen products aim to help protect the skin against UV radiation and consequently reduce the risk of early skin ageing and skin cancer. However, it is well known that some sunscreen ingredients are not photostable, but this usually refers to irradiation with UV light. Moreover, it has to be mentioned that a relative cumulative erythema effectiveness compliant light source is used for the in vivo sun protection factor (SPF) testing. Here, UV simulators equipped with a xenon arc lamp use filters such as WG320 and UG11 (thickness 1 mm) to minimize infrared (IR) radiation and wavelength below 300 nm. However, under practical conditions, the sunscreen product is not only exposed to UVA/B light, but also to visible light (VIS) and IR light. In fact, the spectrum of solar radiation is composed of approximately 7% UV, 39% VIS and 54% IR. Aims: To investigate the influence of short-wave and long-wave radiation on the photostability of sunscreens. Methods: Irradiation was performed with the Suntest CPS+ that is considered to closely imitate solar radiation. The filter UG11 (thickness 1 mm), which absorbs much of the VIS and IR light, and the glass filter WG320 (thickness 2 mm), which effectively absorbs radiation of wavelengths less than 300 nm, were used in the Suntest CPS+ both individually and in combination and were inserted between the light source and the samples. The following transmission measurements were carried out with Labsphere’s UV-2000s device. Here, the effectiveness (percentage change of SPF before irradiation to SPF after irradiation) as a measure of the photostability was calculated. Results:As expected after total solar spectrum irradiation, the effectiveness in all tested sunscreens is lower compared to relative cumulative erythema effectiveness light used for in vitro testing of SPF. In the reference sunscreen formula S2 as well as in the two different sunscreen products, especially long-wave radiation (>400 nm) had an effect on photostability, whereas short-wave radiation had only a minor impact. In contrast, in the BASF sun care gel line only short-wave radiation below 300 nm had an effect on photostability, and blocking VIS and IR light had no effect at all. Conclusion:Based on these data, we can conclude that short waves and/or VIS + IR light have an influence on the photostability of sunscreens.

Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect effects of topographic dynamic forcing on the atmosphere. The one-dimensional weighted-average spatial spectral analysis method is used to explore topographic forcing on precipitation distribution in Sichuan. Results indicate that spectral distributions of terrain and winter precipitation in zonal direction present a typical resonance coupling pattern, while that of terrain and precipitation in other seasons drifts toward the smaller scale. In meridional direction, spectral distributions of terrain and precipitation in each season present the large-scale drift pattern. Different patterns are probably relevant to the change of circulations. In winter, due to strong zonal circulation and weak meridional circulation, atmospheric fluctuations caused by zonal topographic forcing show the most significant impact on precipitation. After that season, the zonal circulation weakens gradually in agreement with the decrease of zonal topographic forcing while the meridional flow enhances, leading to the increase of the damping of the zonal wind disturbance caused by terrain, and the pattern transforms from resonance to drift. Summer rainfall is produced by interaction among different scale systems, and terrain is one of the most important factors. The maximum topographic spectral energy in zonal direction is about an order of magnitude larger than that in meridional direction, implying that effects of topographic dynamic forcing are zonally stronger than that in meridional direction. Values of meridional and zonal topographic characteristic scales are 296.8 km and 475.8 km, respectively, which reflects the characteristic of the mesoscale topographic forcing coincident with the frequent mesoscale systems in Sichuan. The peak of the precipitation spectral energy in summer is about two orders of magnitude larger than that in winter and one order of magnitude larger than that in spring or autumn, and the characteristic scale in summer is about 150 km smaller than that in winter. It illustrates that the intensity of the zonal topographic dynamic forcing in summer is significantly increased when the scale of precipitation systems decreases, which explains the high frequency of mesoscale convective precipitation, and implies the significant impact of topographic dynamic forcing on atmosphere as well. The strongest summer precipitation in Sichuan is located at Ya'an, where larger-scale topographic perturbation is more significant than other region in Sichuan. The terrain spectra and summer precipitation spectra in meridional direction are phase-locked in identical wavelength (37.1 km), implying the critical role of terrain on the occurrence of heavy rainfall, and the effect of topographic dynamic forcing in meridional direction is dominant.

Ground-based, subcanopy measurements of incoming shortwave and longwave radiation are frequently used to drive and validate energy balance and snowmelt models. These subcanopy measurements are frequently obtained using different configurations (linear or distributed; stationary or moving) of radiometer arrays that are installed to capture the spatial and temporal variability of longwave and shortwave radiation. Three different radiometer configurations (stationary distributed, stationary linear, and moving linear) were deployed in a spruce forest in the eastern Swiss Alps during a 9-month period, capturing the annual range of sun angles and sky conditions. Results showed a strong seasonal variation in differences between measurements of shortwave transmissivity between the three configurations, whereas differences in longwave enhancement appeared to be seasonally independent. Shortwave transmissivity showed a larger spatial variation in the subcanopy than longwave enhancement at this field site. The two linear configurations showed the greatest similarity in shortwave transmissivity measurements, and the measurements of longwave enhancement were largely similar between all three configurations. A reduction in the number of radiometers in each array reduced the similarities between each stationary configuration. The differences presented here are taken to reflect the natural threshold of spatial noise in subcanopy measurements that can be expected between the three configurations.

Net radiation (Rn) is the balance between the incoming and outgoing radiation fluxes of longwave and shortwave radiations. As an essential parameter for surface energy budgets, Rn has been widely applied to weather prediction, agriculture evaluation, and regional water resource management. However, the traditional methods for estimating the net radiation are inadequate at the local to regional scales because of their spatial discontinuity and the uneven distribution of radiation sites. With high temporal and spatial resolutions, moderate resolution imaging spectroradiometer data provide numerous terrestrial and atmosphere products, which can help to estimate the shortwave and longwave radiations with limited measured meteorological data. Although many studies have calculated the radiation budget, most of them were applied in North America, where extensive ground validation data are available. In northeastern China, research on the radiation budget was rare, and ground validation data were difficult to acquire, which made our study meaningful and significant. In our work, we have experimented with different parameterization schemes of the components of the radiation budget in our study area and chose the most suitable one to estimate the instantaneous net radiation flux and its components for the study area. The results showed that the RMSE of the downwelling shortwave radiation flux, downwelling longwave radiation flux, upwelling longwave radiation flux, and instantaneous Rn were 31.5, 22.36, 20.61, and 34.32 W/m2, respectively. The sinusoidal model of the diurnal cycle and instantaneous Rn were used to calculate the daily average Rn, and the resulting RMSE was 47.67 W/m2. Finally, the variation of the monthly average Rn of northeastern China in 2011 was analyzed, and the result showed that the temporal and spatial distributions of the monthly average net radiation might be closely related to the land cover types, specifically the seasonal snow cover changes.

Adaptation and validation of a voxel based energy transport model for conifer species

Field evaluation of the efficacy of passive radiative cooling infrastructure: A case study in Phoenix Arizona

Radiative processes are substantially altered by the presence of forest canopies, further affecting snow energetics during wintertime. In situ measurements of subcanopy radiation can help improve process‐scale understanding of these complex interactions, which are needed to further constrain and improve land surface models. In this study, a custom‐made cable car was used to measure incoming and outgoing, shortwave and longwave radiation below an evergreen forest stand. Hemispherical photographs taken concurrently from the cable car measured view fractions of shaded snow, sunlit snow, and bare ground. With this setup it was possible to quantify diurnal and seasonal radiation patterns together with their potential drivers at high spatiotemporal resolution. Measurements were performed between January and May 2018, along a 48‐m transect in a discontinuous needleleaf forest in the Swiss Alps. Analysis of diurnal radiation patterns revealed a strong linear relationship (R = 0.94) between outgoing shortwave radiation and sunlit snow‐view fraction, highlighting shading as the main control on the subcanopy shortwave radiation budget. Measurements of outgoing longwave radiation were strongly controlled by the snow cover extent, with locations of diminished snow cover showing an increase in outgoing longwave radiation of up to 60 W/m2. The subcanopy radiation budget was shown to be dominated by shortwave radiation when surrounding canopy structure and the position of the sun allowed for direct insolation of the forest floor, but longwave radiation was the dominating component in the absence of direct insolation.

Forest litter exerts an impact on the energy budget of snow surfaces, which lie beneath forest canopies. In this study, we measured shortwave and longwave radiation levels, as well as quantities of Asian spruce (Picea schrenkinan) forest litter, over 3 snow study plots that representing an open environment, 20% forest canopy openness (20% FCO), and 80% forest canopy openness (80% FCO). The fractional litter coverage (lc) was obtained through the binarization of digital photographs of forest litter. The effects of forest litter on snow surface albedo (α), snow surface temperature (Ts), upward shortwave and longwave radiation (K↑ and L↑), and sensible heat flux (H) were then analyzed. According to our results, the energy budget over snow surface influenced by forest litter principally due to forest litter forcing α decrease and Ts increase. The effects of forest litter on the energy budget increased with time and lc. We found that forest litter exerted the most significant impact on K↑ and L↑ at daytime during the latter stages of the snowmelt period. The influence of forest litter on H was more apparent on windy days. The presence of forest litter increased gains in shortwave radiation and losses in longwave radiation and decreased gains in H. Compared to the simulated energy (K↑ + L↑ + H) over a snow surface without litter, the calculated energy decreased by −13.4 W/m2 and increased by 9.0 W/m2, respectively, at the 20% FCO and 80% FCO sites during the latter stages of the snowmelt period. Overall, forest litter facilitated snow surface energy gains at the 80% FCO site and impeded them at the 20% FCO site during the latter stages of the snowmelt period.

Simulation of within-canopy radiation exchange

A neighbourhood-scale multi-layer urban canopy model of shortwave and longwave radiation exchange that explicitly includes the radiative effects of tall vegetation (trees) is presented. Tree foliage is permitted both between and above buildings, and mutual shading, emission and reflection between buildings and trees are included. The basic geometry is a two-dimensional canyon with leaf area density profiles and probabilistic variation of building height. Furthermore, the model accounts for three-dimensional path lengths through the foliage. Ray tracing determines the receipt of direct shortwave irradiance by building and foliage elements. View factors for longwave and shortwave diffuse radiation exchange are computed once at the start of the simulation using a Monte Carlo ray tracing approach; for subsequent model timesteps, matrix inversion rapidly solves infinite reflections and interception of emitted longwave between all elements. The model is designed to simulate any combination of shortwave and longwave radiation frequency bands, and to be portable to any neighbourhood-scale urban canopy geometry based on the urban canyon. Additionally, the model is sufficiently flexible to represent forest and forest-clearing scenarios. Model sensitivity tests demonstrate the model is robust and computationally feasible, and highlight the importance of vertical resolution to the performance of urban canopy radiation models. Full model evaluation is limited by the paucity of within-canyon radiation measurements in urban neighbourhoods with trees. Where appropriate model components are tested against analytic relations and results from an independent urban radiation transfer model. Furthermore, system response tests demonstrate the ability of the model to realistically distribute shortwave radiation among urban elements as a function of built form, solar angle and tree foliage height, density and clumping. Separate modelling of photosynthetically-active and near-infrared shortwave bands is shown to be important in some cases. Increased canyon height-to-width ratio and/or tree cover diminishes the net longwave radiation loss of individual canyon elements (e.g., floor, walls), but, notably, has little effect on the net longwave loss of the whole urban canopy. When combined with parametrizations for the impacts of trees on airflow and hydrological processes in the urban surface layer, the new radiation model extends the applicability of urban canopy models and permits more robust assessment of trees as tools to manage urban climate, air quality, human comfort and building energy loads.

In this paper, based on the data of 17 stations (including scientific experiment data) on the Qinghai-Xizang Plateau covering the period June–August 1979, those components such as longwave radiation, shortwave radiation, latent heat and flux of sensible heat, are calculated by a direct method. On the basis of the above calculations, the average atmospheric heat budget over the Plateau is obtained. Compared with the results obtained from the indirect method, our results show that the main contribution to the atmospheric heat source comes from the longwave radiation. In addition, the relations of the atmospheric heating field with the circulation of pre-and post-monsoons, and with the circulation of active and non-active monsoons over the Plateau are discussed. The power spectra of radiative heating are also computed. It is confirmed that the oscillations within a period of 8–12 days do exist in both longwave and shortwave radiation.