Upward Radiation Research Articles

Development of a Physically Based Soil Albedo Parameterization for the Tibetan Plateau

Core Ideas Liquid soil moisture controls seasonal variations in soil albedo. Solar zenith angle determines diurnal variations in soil albedo. Soil optical parameter values can be reasonably estimated from soil composition. The simulated surface energy budget in summer is considerably improved. Soil albedo controls the surface energy budget on the Tibetan Plateau (TP); however, estimates of the soil albedo include substantial uncertainties. This study presents a physically based soil albedo parameterization that includes the effects of the solar zenith angle and liquid soil moisture. The parameter values are calibrated and validated using the measurements from the Global Energy and Water Cycle Experiment–Asian Monsoon Experiment and the Coordinated Enhanced Observing Period Asia–Australia Monsoon Project (CAMP‐Tibet). Because few measurements of albedo are available from the TP, a transfer equation was built to estimate the parameter values through their inverse physical links with the soil composition. Compared with previous parameterizations, the parameter values from the transfer equation reduce the simulated mean bias and RMSE values by nearly 50%. Comparisons of the observed albedos and simulated values obtained using the new parameterization show that the correlation values are >0.5 and that the absolute errors (dimensionless) are within ±0.05. The new parameterization captures the diurnal and seasonal variations better than the previous schemes and shows that the diurnal and seasonal variations in soil albedo are controlled by the solar zenith angle and liquid soil moisture, respectively. This new parameterization scheme was incorporated into the Geomorphology‐Based Eco‐Hydrological Model and run for the CAMP‐Tibet stations. The inclusion of this new parameterization significantly improved the simulated surface energy budget in summer; the deviations in the upward shortwave radiation decreased by 81%, and the accuracy of the simulated Bowen ratio increased substantially.

Feasibility study of multi-pixel retrieval of optical thickness and droplet effective radius of inhomogeneous clouds using deep learning

Abstract. Three-dimensional (3-D) radiative-transfer effects are a major source of retrieval errors in satellite-based optical remote sensing of clouds. The challenge is that 3-D effects manifest themselves across multiple satellite pixels, which traditional single-pixel approaches cannot capture. In this study, we present two multi-pixel retrieval approaches based on deep learning, a technique that is becoming increasingly successful for complex problems in engineering and other areas. Specifically, we use deep neural networks (DNNs) to obtain multi-pixel estimates of cloud optical thickness and column-mean cloud droplet effective radius from multispectral, multi-pixel radiances. The first DNN method corrects traditional bispectral retrievals based on the plane-parallel homogeneous cloud assumption using the reflectances at the same two wavelengths. The other DNN method uses so-called convolutional layers and retrieves cloud properties directly from the reflectances at four wavelengths. The DNN methods are trained and tested on cloud fields from large-eddy simulations used as input to a 3-D radiative-transfer model to simulate upward radiances. The second DNN-based retrieval, sidestepping the bispectral retrieval step through convolutional layers, is shown to be more accurate. It reduces 3-D radiative-transfer effects that would otherwise affect the radiance values and estimates cloud properties robustly even for optically thick clouds.

New theoretical formulation for the determination of radiance transmittance at the water-air interface.

Radiative transfer across the water-air interface has important implications for optics and remote sensing of natural waters. The upward radiance emerging from the water suffers a critical change when it passes through the water-air interface. Upwelling radiance transmittance τw,a is an optical process occurring at the water-air interface that determines the in-water radiances propagating through the interface. In previous studies, τw,a was successfully derived for determining the water-leaving radiances in open ocean waters, despite being oversimplified with a constant value. The constant τw,a value becomes rapidly invalid in high scattering and absorbing waters within nearshore and inland environments. In this study, we attempt to quantitatively solve the upwelling radiance transmittance τw,a (i.e., the percentage of in-water photons that escape through the water-air interface) for varying coefficients of scattering and absorption within the range of natural waters. The two important optical phenomena which are ignored in the previous studies have been fully accounted: (i) the particulate contribution to the refractive index (RI) of seawater and (ii) the multiple interactions of the upwelling photons with the water-air interface. As a result, this study leads to a new theoretical formulation of the upwelling radiance transmittance applicable to all natural waters. The effect and variation of the new formulation on the water-leaving radiance and remote sensing reflectance is further studied for coastal and inland waters. Particular attention is also focused on the conversion of sub-surface remote sensing reflectance (rrs) to above-surface remote sensing reflectance (Rrs), which is important for calibration and validation of the remote sensing algorithms. The results show substantial improvement in the ocean color quantities (Lw and Rrs) by up to factor 33% for scattering waters and <5% for absorbing waters.

Vegetation-cloud feedbacks to future vegetation changes in the Arctic regions

This study investigates future changes in the Arctic region and vegetation-cloud feedbacks simulated using the National Center for Atmospheric Research Community Atmosphere Model Version 3 coupled with a mixed layer ocean model. Impacts of future greening of the Arctic region are tested using altered surface boundary conditions for hypothetical vegetation distributions: (1) grasslands poleward of 60°N replaced by boreal forests and (2) both grasslands and shrubs replaced by boreal forests. Surface energy budget analysis reveals that future greening induces a considerable surface warming effect locally and warming is largely driven by an increase in short wave radiation. Both upward and downward shortwave radiation contribute to positive surface warming: upward shortwave radiation decreases mainly due to the decreased surface albedo (a darker surface) and downward shortwave radiation increases due to reduced cloud cover. The contribution of downward shortwave radiation at surface due to cloud cover reduction is larger than the contribution from surface albedo alone. The increased roughness length also transported surface fluxes to upper layer more efficiently and induce more heating and dry lower atmosphere. A relatively smaller increase in water vapor compared to the large increase in low-level air temperature in the simulation reduces relative humidity and results in reduced cloud cover. Therefore, vegetation-cloud feedbacks induced from land cover change significantly amplify Arctic warming. In addition to previously suggested feedback mechanisms, we propose that the vegetation-cloud feedback should be considered as one of major components that will give rise to an additional positive feedback to Arctic amplification.

Impact of fire on global land surface air temperature and energy budget for the 20th century due to changes within ecosystems

Fire is a global phenomenon and tightly interacts with the biosphere and climate. This study provides the first quantitative assessment and understanding of fire’s influence on the global annual land surface air temperature and energy budget through its impact on terrestrial ecosystems. Fire impacts are quantified by comparing fire-on and fire-off simulations with the Community Earth System Model (CESM). Results show that, for the 20th century average, fire-induced changes in terrestrial ecosystems significantly increase global land annual mean surface air temperature by 0.18 °C, decrease surface net radiation and latent heat flux by 1.08 W m−2 and 0.99 W m−2, respectively, and have limited influence on sensible heat flux (−0.11 W m−2) and ground heat flux (+0.02 W m−2). Fire impacts are most clearly seen in the tropical savannas. Our analyses suggest that fire increases surface air temperature predominantly by reducing latent heat flux, mainly due to fire-induced damage to the vegetation canopy, and decreases net radiation primarily because fire-induced surface warming significantly increases upward surface longwave radiation. This study provides an integrated estimate of fire and induced changes in ecosystems, climate, and energy budget at a global scale, and emphasizes the importance of a consistent and integrated understanding of fire effects.

Potential of remote sensing of cirrus optical thickness by airborne spectral radiance measurements at different sideward viewing angles

Abstract. Spectral radiance measurements collected in nadir and sideward viewing directions by two airborne passive solar remote sensing instruments, the Spectral Modular Airborne Radiation measurement sysTem (SMART) and the Differential Optical Absorption Spectrometer (mini-DOAS), are used to compare the remote sensing results of cirrus optical thickness τ. The comparison is based on a sensitivity study using radiative transfer simulations (RTS) and on data obtained during three airborne field campaigns: the North Atlantic Rainfall VALidation (NARVAL) mission, the Mid-Latitude Cirrus Experiment (ML-CIRRUS) and the Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems (ACRIDICON) campaign. Radiative transfer simulations are used to quantify the sensitivity of measured upward radiance I with respect to τ, ice crystal effective radius reff, viewing angle of the sensor θV, spectral surface albedo α, and ice crystal shape. From the calculations it is concluded that sideward viewing measurements are generally better suited than radiance data from the nadir direction to retrieve τ of optically thin cirrus, especially at wavelengths larger than λ = 900 nm. Using sideward instead of nadir-directed spectral radiance measurements significantly improves the sensitivity and accuracy in retrieving τ, in particular for optically thin cirrus of τ ≤ 2. The comparison of retrievals of τ based on nadir and sideward viewing radiance measurements from SMART, mini-DOAS and independent estimates of τ from an additional active remote sensing instrument, the Water Vapor Lidar Experiment in Space (WALES), shows general agreement within the range of measurement uncertainties. For the selected example a mean τ of 0.54 ± 0.2 is derived from SMART, and 0.49 ± 0.2 by mini-DOAS nadir channels, while WALES obtained a mean value of τ = 0.32 ± 0.02 at 532 nm wavelength, respectively. The mean of τ derived from the sideward viewing mini-DOAS channels is 0.26 ± 0.2. For the few simultaneous measurements, the mini-DOAS sideward channel measurements systematically underestimate (−17.6 %) the nadir observations from SMART and mini-DOAS. The agreement between mini-DOAS sideward viewing channels and WALES is better, showing the advantage of using sideward viewing measurements for cloud remote sensing for τ ≤ 1. Therefore, we suggest sideward viewing measurements for retrievals of τ of thin cirrus because of the significantly enhanced capability of sideward viewing compared to nadir measurements.

The variability of surface radiation fluxes over landfast sea ice near Zhongshan station, east Antarctica during austral spring

ABSTRACTSurface radiative fluxes over landfast sea ice off Zhongshan station have been measured in austral spring for five springs between 2010 and 2015. Downward and upward solar radiation vary diurnally with maximum amplitudes of 473 and 290 W m−2, respectively. The maximum and minimum long-wave radiation values of the mean diurnal cycle are 218 and 210 W m−2 for downward radiation, 277 and 259 W m−2 for upward radiation and 125 and −52 W m−2 for net radiation. The albedo has a U-shaped mean diurnal cycle with a minimum of 0.64 at noon. Sea ice thickness is in the growth phase for most spring days, but can be disturbed by synoptic processes. The surface temperature largely determines the occurrence of ice melting. Surface downward and upward long-wave radiation show synoptic oscillations with a 5–8 day period and intraseasonal variability with a 12–45 day period. The amplitudes of the diurnal, synoptic and intraseasonal variability show some differences during the five austral springs considered here. The intraseasonal and synoptic variability of downward and upward long-wave radiation are associated with the variability of cloud cover and surface temperature induced by the atmospheric circulation.

Directional, horizontal inhomogeneities of cloud optical thickness fields retrieved from ground-based and airbornespectral imaging

Abstract. Clouds exhibit distinct horizontal inhomogeneities of their optical and microphysical properties, which complicate their realistic representation in weather and climate models. In order to investigate the horizontal structure of cloud inhomogeneities, 2-D horizontal fields of optical thickness (τ) of subtropical cirrus and Arctic stratus are investigated with a spatial resolution of less than 10 m. The 2-D τ-fields are derived from (a) downward (transmitted) solar spectral radiance measurements from the ground beneath four subtropical cirrus and (b) upward (reflected) radiances measured from aircraft above 10 Arctic stratus. The data were collected during two field campaigns: (a) Clouds, Aerosol, Radiation, and tuRbulence in the trade wind regime over BArbados (CARRIBA) and (b) VERtical Distribution of Ice in Arctic clouds (VERDI). One-dimensional and 2-D autocorrelation functions, as well as power spectral densities, are derived from the retrieved τ-fields. The typical spatial scale of cloud inhomogeneities is quantified for each cloud case. Similarly, the scales at which 3-D radiative effects influence the radiance field are identified. In most of the investigated cloud cases considerable cloud inhomogeneities with a prevailing directional structure are found. In these cases, the cloud inhomogeneities favour a specific horizontal direction, while across this direction the cloud is of homogeneous character. The investigations reveal that it is not sufficient to quantify horizontal cloud inhomogeneities using 1-D inhomogeneity parameters; 2-D parameters are necessary.

Study on the local climatic effects of large photovoltaic solar farms in desert areas

Large-scale solar power plants are rapidly increasing in size and number across the world. However, the surface heat balance is altered when a photovoltaic (PV) power plant is operating. Modifications to the surface albedo through the deployment of photovoltaic arrays have the potential to change radiative forcing, surface temperatures and local weather patterns. In this work, the field observation data from a large solar farm and a region without PV array in Golmud are used to study the impact of large solar farms in desert areas on the local meteorology. The results show that the total daily values of upward shortwave radiation and net radiation in the two sites are significantly different. The mean daily albedo in the solar farm is 0.19, while it is 0.26 in the region without PV. The annual mean net radiation in the solar farm is evidently higher than that of the region without PV. The daily range of soil temperatures at a depth of 5–10cm in the solar farm is lower than that in the region without a PV farm. The annual range of soil temperatures at a depth of 5–180cm in the solar farm is higher than that in the region without PV. The soil temperatures at different depths in winter in the solar farm are clearly lower than those in the region without PV. The daily mean of soil temperatures at a depth of 5–80cm from October 2012 to March 2013 is clearly lower than that in the region without a PV array. The 2-m daytime air temperature in the two sites is essentially the same during winter, while during the other seasons, the daytime air temperature in the PV farm is higher than that in the region without PV, with the maximum difference appearing during the summer. The nighttime air temperatures at a height of 2m during the four seasons in the solar farm are higher than those in the region without PV. The monthly average 2-m air temperature in the solar farm is higher than that in the region without PV.

Peculiarities of slick formation on the sea surface

This paper deals with surface slicks, their nature, and causes of formation in context of the development of remote detection methods and investigation of dynamic processes in the ocean and at the air–ocean interface. A simplified formalism is introduced for slick–sea surface contrast formation which takes into account the upward sea radiation and qualitatively explains in situ measurement results. The results of a detection of slicks on the coastal water surface are also described, which, together with the simplified formalism suggested, provide optimal experimental conditions for slick–sea surface contrast measurements; i.e., the contrast of the P component of reflected radiation is measured at viewing angles close to the horizon.

A shift in the upper-ocean temperature trends in the South China Sea since the late 1990s

In this paper, the interdecadal variability of upper-ocean temperature in the South China Sea (SCS) is investigated based on several objectively analyzed data sets and two reanalysis data sets. The trends of the SCS sea surface temperature (SST) have changed from warming to cooling since the late 1990s. A heat budget analysis suggests that the warming of the surface mixed layer during 1984–1999 is primarily attributed to the horizontal heat advection and the decrease of upward long wave radiation, with the net surface heat flux playing a damping role due to the increase of upward latent and sensible heat fluxes. On the other hand, the cooling of the surface mixed layer during 2000–2009 is broadly controlled by net surface heat flux, with the radiation flux playing the dominant role. A possible mechanism is explored that the variation of a sea level pressure (SLP) over the North Pacific Ocean may change the prevailing winds over the SCS, which contributes to the change of the SST in the SCS through the horizontal heat advection and heat fluxes.

Comparison of land–atmosphere interaction at different surface types in the mid- to lower reaches of the Yangtze River valley

Abstract. The mid- to lower reaches of the Yangtze River valley are located within the typical East Asian monsoon zone. Rapid urbanization, industrialization, and development of agriculture have led to fast and complicated land use and land cover change in this region. To investigate land–atmosphere interaction in this region where human activities and monsoon climate have considerable interaction with each other, micrometeorological elements over four sites with different surface types around Nanjing, including urban surface at Dangxiao (hereafter DX-urban), suburban surface at Xianling (XL-suburb), and grassland and farmland at Lishui County (LS-grass and LS-crop), are analyzed and their differences are revealed. The impacts of surface parameters of different surface types on the radiation budget and land surface–atmosphere heat, water, and mass exchanges are investigated and compared. The results indicate the following. (1) The largest differences in daily average surface air temperature (Ta), surface skin temperature (Ts), and relative humidity (RH), which are found during the dry periods between DX-urban and LS-crop, can be up to 3.21 °C, 7.26 °C, and 22.79 %, respectively. The diurnal ranges of the above three elements are the smallest at DX-urban and the largest at LS-grass, XL-suburb, and LS-crop. (2) Differences in radiative fluxes are mainly reflected in upward shortwave radiation (USR) that is related to surface albedo and upward longwave radiation (ULR) that is related to Ts. When comparing four sites, it can be found that both the smallest USR and the largest ULR occur at the DX-urban site. The diurnal variation in ULR is same as that of Ts at all four sites. (3) The differences in daily average sensible heat (H) and latent heat (LE) between DX-urban and LS-crop are larger than 45 and 95 Wm−2, respectively. The proportion of latent heat flux in the net radiation (LE/Rn) keeps increasing with the change in season from the spring to summer. (4) Human activities have obvious effects on microclimate. The urban heat island (UHI) effect results in a Ta 2 °C higher at the urban site than other sites in the nighttime. At the crop site, LE is dominant due to irrigation, and negative H is observed since evaporation cooling leads to low Ts. Although Ts is higher at XL-suburb than that at LS-grass, there is no large difference in Ta between the two sites due to the distinct effects of the planted forest.

Revisiting the climate impacts of cool roofs around the globe using an Earth system model

Solar reflective ‘cool roofs’ absorb less sunlight than traditional dark roofs, reducing solar heat gain, and decreasing the amount of heat transferred to the atmosphere. Widespread adoption of cool roofs could therefore reduce temperatures in urban areas, partially mitigating the urban heat island effect, and contributing to reversing the local impacts of global climate change. The impacts of cool roofs on global climate remain debated by past research and are uncertain. Using a sophisticated Earth system model, the impacts of cool roofs on climate are investigated at urban, continental, and global scales. We find that global adoption of cool roofs in urban areas reduces urban heat islands everywhere, with an annual- and global-mean decrease from 1.6 to 1.2 K. Decreases are statistically significant, except for some areas in Africa and Mexico where urban fraction is low, and some high-latitude areas during wintertime. Analysis of the surface and TOA energy budget in urban regions at continental-scale shows cool roofs causing increases in solar radiation leaving the Earth–atmosphere system in most regions around the globe, though the presence of aerosols and clouds are found to partially offset increases in upward radiation. Aerosols dampen cool roof-induced increases in upward solar radiation, ranging from 4% in the United States to 18% in more polluted China. Adoption of cool roofs also causes statistically significant reductions in surface air temperatures in urbanized regions of China (−0.11 ± 0.10 K) and the United States (−0.14 ± 0.12 K); India and Europe show statistically insignificant changes. Though past research has disagreed on whether widespread adoption of cool roofs would cool or warm global climate, these studies have lacked analysis on the statistical significance of global temperature changes. The research presented here indicates that adoption of cool roofs around the globe would lead to statistically insignificant reductions in global mean air temperature (−0.0021 ± 0.026 K). Thus, we suggest that while cool roofs are an effective tool for reducing building energy use in hot climates, urban heat islands, and regional air temperatures, their influence on global climate is likely negligible.

Broadband fiber-chip zero-order surface grating coupler with 0.4 dB efficiency.

Surface grating couplers enable efficient coupling of light between optical fibers and nanophotonic waveguides. However, in conventional grating couplers, the radiation angle is intrinsically wavelength dependent, thereby limiting their operation bandwidth. In this Letter, we present a zero-order surface grating coupler in silicon-on-insulator which overcomes this limitation by operating in the subwavelength regime. By engineering the effective refractive index of the grating region, both high coupling efficiency and broadband operation bandwidth are achieved. The grating is assisted by a silicon prism on top of the waveguide, which favors upward radiation and minimizes power losses to substrate. Using a linear apodization, our design achieves a coupling efficiency of 91% (-0.41 dB) and a 1-dB bandwidth of 126 nm.

Sulfate Aerosols from Non-Explosive Volcanoes: Chemical-Radiative Effects in the Troposphere and Lower Stratosphere

SO2 and H2S are the two most important gas-phase sulfur species emitted by volcanoes, with a global amount from non-explosive emissions of the order 10 Tg-S/yr. These gases are readily oxidized forming SO42− aerosols, which effectively scatter the incoming solar radiation and cool the surface. They also perturb atmospheric chemistry by enhancing the NOx to HNO3 heterogeneous conversion via hydrolysis on the aerosol surface of N2O5 and Br-Cl nitrates. This reduces formation of tropospheric O3 and the OH to HO2 ratio, thus limiting the oxidation of CH4 and increasing its lifetime. In addition to this tropospheric chemistry perturbation, there is also an impact on the NOx heterogeneous chemistry in the lower stratosphere, due to vertical transport of volcanic SO2 up to the tropical tropopause layer. Furthermore, the stratospheric O3 formation and loss, as well as the NOx budget, may be slightly affected by the additional amount of upward diffused solar radiation and consequent increase of photolysis rates. Two multi-decadal time-slice runs of a climate-chemistry-aerosol model have been designed for studying these chemical-radiative effects. A tropopause mean global net radiative flux change (RF) of −0.23 W·m−2 is calculated (including direct and indirect aerosol effects) with a 14% increase of the global mean sulfate aerosol optical depth. A 5–15 ppt NOx decrease is found in the mid-troposphere subtropics and mid-latitudes and also from pole to pole in the lower stratosphere. The tropospheric NOx perturbation triggers a column O3 decrease of 0.5–1.5 DU and a 1.1% increase of the CH4 lifetime. The surface cooling induced by solar radiation scattering by the volcanic aerosols induces a tropospheric stabilization with reduced updraft velocities that produce ice supersaturation conditions in the upper troposphere. A global mean 0.9% decrease of the cirrus ice optical depth is calculated with an indirect RF of −0.08 W·m−2.

Estimating the Thermal Radiative Properties of Shading Nets Under Natural Outdoor Conditions

The perforated nature of nets makes it impossible to measure the thermal radiative properties (emittance, εn, transmittance, τn, and reflectance, ρn) correctly by using any measuring device under natural conditions. In this study, a theoretical model was developed and validated to predict εn, τn, and ρn precisely by solving the model equations simultaneously. The net was tacked onto a wooden frame; thermal radiation balance was applied below and above the net surfaces and above a black substrate underneath the frame. The downward and upward thermal radiation fluxes were measured below and above the net to be used as input parameters to the simulation. Nets with different porosities (ϕ) and colors were used for the study. The results showed that the estimated εn ranged from 0.41 to 0.82 and τn ranged from 0.16 to 0.55 for the nets tested, whereas the reflectances were very low (ρn≤0.08). The color and porosity together affect the properties of the net. Even though under equilibrium conditions of a net with the surrounding environment, the emittance of the net is equal to its absorptance. However, the absorbed thermal radiation by the net dose not equal to the emitted radiation and the difference is a convected heat.

An Automated Comparative Observation System for Sun-Induced Chlorophyll Fluorescence of Vegetation Canopies.

Detecting sun-induced chlorophyll fluorescence (SIF) offers a new approach for remote sensing photosynthesis. However, to analyse the response characteristics of SIF under different stress states, a long-term time-series comparative observation of vegetation under different stress states must be carried out at the canopy scale, such that the similarities and differences in SIF change law can be summarized under different time scales. A continuous comparative observation system for vegetation canopy SIF is designed in this study. The system, which is based on a high-resolution spectrometer and an optical multiplexer, can achieve comparative observation of multiple targets. To simultaneously measure the commonly used vegetation index and SIF in the O2-A and O2-B atmospheric absorption bands, the following parameters are used: a spectral range of 475.9 to 862.2 nm, a spectral resolution of approximately 0.9 nm, a spectral sampling interval of approximately 0.4 nm, and the signal-to-noise ratio (SNR) can be as high as 1000:1. To obtain data for both the upward radiance of the vegetation canopy and downward irradiance data with a high SNR in relatively short time intervals, the single-step integration time optimization algorithm is proposed. To optimize the extraction accuracy of SIF, the FluorMOD model is used to simulate sets of data according to the spectral resolution, spectral sampling interval and SNR of the spectrometer in this continuous observation system. These data sets are used to determine the best parameters of Fraunhofer Line Depth (FLD), Three FLD (3FLD) and the spectral fitting method (SFM), and 3FLD and SFM are confirmed to be suitable for extracting SIF from the spectral measurements. This system has been used to observe the SIF values in O2-A and O2-B absorption bands and some commonly used vegetation index from sweet potato and bare land, the result of which shows: (1) the daily variation trend of SIF value of sweet potato leaves is basically same as that of photosynthetically active radiation (PAR); and (2) the bare land is a non-fluorescent emitter, the SIF of which is significantly smaller than that of sweet potato; and (3) analysis result based on the measured data is basically same as that based on simulated data. The above results verified the reliability of the SIF extracted from the measured data and the feasibility of comparatively observing the SIF value and the commonly used vegetation index of multiple vegetation canopy with this continuous observation system. This approach is beneficial for comprehensively analysing the stress response characteristics of vegetation canopies.

A comparison between energy transfer and atmospheric turbulent exchanges over alpine meadow and banana plantation

Banana plantation and alpine meadow ecosystems in southern China and the Tibetan Plateau (TP) are unique in the underlying surfaces they exhibit. In this study, we used eddy covariance and a micrometeorological tower to examine the characteristics of land surface energy exchanges over a banana plantation in southern China and an alpine meadow in the Tibetan Plateau from May 2010 to August 2012. The results showed that the diurnal and seasonal variations in upward shortwave radiation flux and surface soil heat flux were larger over the alpine meadow than over the banana plantation surface. Dominant energy partitioning varied with season. Latent heat flux was the main consumer of net radiation flux in the growing season, whereas sensible heat flux was the main consumer during other periods. The Monin-Obukhov similarity theory was employed for comparative purposes, using sonic anemometer observations of flow over the surfaces of banana plantations in the humid southern China monsoon region and the semi-arid areas of the TP, and was found to be applicable. Over banana plantation and alpine meadow areas, the average surface albedo and surface aerodynamic roughness lengths under neutral atmospheric conditions were ∼0.128 and 0.47 m, and ∼0.223 and 0.01 m, respectively. During the measuring period, the mean annual bulk transfer coefficients for momentum and sensible heat were 1.47 × 10−2 and 7.13 × 10−3, and 2.91 × 10−3 and 1.96 × 10−3, for banana plantation and alpine meadow areas, respectively.

Surface energy budget changes over Central Australia during the early 21st century drought

Satellite observations are used to investigate surface energy budget variability over central Australia during the early 21st century drought. Over a large expanse of open shrubland and savanna, surface albedo exhibits a multiyear increase of 0.06 during the drought followed by a sharp decline of 0.08 after heavy rainfall in 2010 broke the drought. The surface albedo variations are associated with increased normalized difference vegetation index (NDVI) during wet years before and after the drought and decreased NDVI during drought years. During the worst drought years (2002–2009), the surface albedo increase is most pronounced in the shortwave infrared region (wavelengths between 1 and 3 µm), implying soil moisture content variability is the likely cause of the albedo changes. At interannual timescales, surface albedo variability is associated with near-surface soil moisture, controlled by episodic precipitation events, whereas the multiyear increase in surface albedo is more closely linked with decreases in soil moisture in deeper surface layers. In addition to a higher surface albedo and lower soil moisture content during the drought, the observations show less evaporation, enhanced reflected shortwave radiation, increased upward emission of thermal infrared radiation, lower downwelling longwave (LW) radiation, reduced net total downward radiation, and higher sensible heating compared with the rainy period following the drought. Upward emission of thermal infrared radiation decreases sharply after the drought with increased surface evaporation. However, the surface energy budget changes during the worst drought years show a stronger relationship between upward emission of thermal radiation and reflected shortwave flux. During this period, evaporative fraction is extremely low and surface albedo is steadily increasing. In such extreme conditions, the surface albedo appears to modulate surface upward LW radiation, preventing it from getting too high. The change in upward LW radiation thus represents a negative feedback as it offsets further decreases in surface net radiation.

Clinical trial design of Boron Neutron Capture Therapy on breast cancer using D-D coaxial compact neutron generator as neutron source and Monte Carlo N-Particle simulation method

&lt;span&gt;A clinical trial simulation of Boron Neutron Capture Therapy (BNCT) for breast cancer was conducted at National Nuclear Energy Agency Yogyakarta, Indonesia. This was motivated by high rate of breast cancer in the world, especially in Indonesia. BNCT is a type of therapy by nuclear reaction &lt;/span&gt;&lt;sup&gt;10&lt;/sup&gt;&lt;span&gt;B(n,α)&lt;/span&gt;&lt;sup&gt;7&lt;/sup&gt;&lt;span&gt;Li that produces kinetic energy totaling 2.79 MeV. High Linear Energy Transfer (LET) radiation of α-particle and recoil &lt;/span&gt;&lt;sup&gt;7&lt;/sup&gt;&lt;span&gt;Li would locally deposit their energy in a range of 5-9 μm, which corresponds to the human cell diameter. Fast neutron coming out of Compact Neutron Generator (CNG) was moderated using Fe and MgF&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt; material. A collimator, along with breast cancer and the corresponding organ at risk were designed compatible to Monte Carlo N-Particle X (MCNPX). The radiation were simulated by the MCNPX software and the physical quantities were counted by tally MCNPX codes. The highest neutron thermal flux was found at a depth of 1.4 cm on fat tissue. En face and upward intersection radiation techniques were adopted for the breast cancer radiation. The average dose rate of radiation used on breast cancer was 1.72×10&lt;/span&gt;&lt;sup&gt;-5 &lt;/sup&gt;&lt;span&gt;Gy/s for the en face method and 8.98×10&lt;/span&gt;&lt;sup&gt;-6 &lt;/sup&gt;&lt;span&gt;Gy/s for the upward intersection method. Dose 50±3 Gy was given into cancer cell, (4.18±0.06) ×10&lt;/span&gt;&lt;sup&gt;-2&lt;/sup&gt;&lt;span&gt; Gy into heart and (8.16±0.06) ×10&lt;/span&gt;&lt;sup&gt;-2&lt;/sup&gt;&lt;span&gt;Gy into lung for 806.34 hours irradiation.&lt;/span&gt;