Shortwave radiation balance modulates potential evapotranspiration over China

Shortwave radiation is an influential driver of global hydrological cycle,as its variation will alter evapotranspiration(ET).While climate change discussion extensively examined ET response to temperature,wind speed and land use/cover variations,little is known about the contribution of shortwave radiation balance on ET partly because of data availability.In this study,we applied the newly-released Global LAnd Surface Satellite(GLASS)products to detect changes in shortwave radiation and albedo for 2003–2018 over China,and quantified their contributions on potential evapotranspiration(PET)which is the upper limit of ET and generally the basis to estimate it.The results showed that downward shortwave radiation declined,together with a slight decrease in albedo,causing a decrease of net shortwave radiation.While climate change affected PET,the decreased net shortwave radiation reduced PET during the period.We identified a hotspot area in the north China plain that is one of the main agricultural production regions,as the radiation balance induced a contrasting effect on PET for the warm and the cold seasons.Our study indicates that it is important to consider shortwave radiation balance when estimating PET and ET to make reliable evaluation of climate change on hydrological cycle and ecosystem response.

RADIATION BALANCE AND TURBULENT FLUX CHARACTERISTICS OVER MIZUHO STATION IN ANTARCTICA

In this paper,by using measurements in micrometeorology and radiation balance in the surface layer(Yamanouchi et al.,1981;Wada et al.,1981;Ishikawa et al.,1982;Ohata et al.,1983),we have analyzed the diurnal and annual varia- tion characteristics of radiation balance in spring,summer,autumn and winter,and calculated the momentum flux and sensible heat flux with the aerodynamic method and profile gradient alternate method in different seasons.We have also obtained the diurnal variation characters of the latent heat flux from the equation for energy balance.The results from the calculation are compared.Finally,the relationship between the turbulent heat and momentum exchange coefficient and the diurnal variation of the Richardson number is discussed.

Study on the Influence of Piloti on Mean Radiant Temperature in Residential Blocks by 3-D Unsteady State Heat Balance Radiation Calculation

Piloti is commonly used in tropical and subtropical climate zones to get high wind velocity and create shadowed areas in order to optimize the living environment of residential blocks,but there are few studies to reveal the influence of piloti on the radiant environment of residential blocks systematically. Taking the city of Guangzhou as an example,using 3-D Unsteady State Heat Balance Radiation Calculation Method,this paper shows that the mean radiant temperature( MRT) under piloti area increases with the increase of piloti ratio,and especially when piloti ratio is equal to 100%,the MRT increase trend becomes sharp. The MRT of exposed area decreases with the increase of piloti ratio,especially when piloti ratio reaches 100%,the decrease trend of MRT becomes sharp,which offers the reference for the study on piloti design in subtropical climate zones and further research on living environment by CFD simulation in residential blocks.

Satellite-Based Estimation of Daily Average Net Radiation under Clear-Sky Conditions

ABSTRACT Daily average net radiation （DANR） is an important variable for estimating evapotranspiration from satellite data at regional scales, and is used for atmospheric and hydrologic modeling, as well as ecosystem management. A scheme is proposed to estimate the DANR over large heterogeneous areas under clear-sky conditions using only remotely sensed data. The method was designed to overcome the dependence of DANR estimates on ground data, and to map spatially consistent and reasonably distributed DANR, by using various land and atmospheric data products retrieved from MODIS （Moderate Resolution Imaging Spectroradiometer） data. An improved sinusoidal model was used to retrieve the diurnal variations of downward shortwave radiation using a single instantaneous value from satellites. The downward shortwave component of DANR was directly obtained from this instantaneous value, and the upward shortwave component was estimated using satellite-derived albedo products. Four observations of air temperature from MOD07_L2 and MYD07_L2 data products were used to derive the downward longwave component of DANR, while the upward longwave component was estimated using the land surface temperature （LST） and the surface emissivity from MOD1 l_L2. Compared to in situ observations at the cropland and grassland sites located in Tongyu, northern China, the root mean square error （RMSE） of DANR estimated for both sites under clear-sky conditions was 37 W m-2 and 40 W m-2, respectively. The errors in estimation of DANR were comparable to those from previous satellite-based methods. Our estimates can be used for studying the surface radiation balance and evapotranspiration.

Calculation of Solar Albedo and Radiation Equilibrium over the Qinghai-Xizang Plateau and Analysisof Their Climatic Features

Using radiation data from the Automatic Weather Stations (AWSs) for thermal balance obser-vations, which were set up at Lhasa, Nagqu, Xigaze and Nyingchi by the Sino-Japanese Asian Monsoon Mechanism Co-operative Project in 1993–1996, and 1985–1989 Earth Radiation Balance Experiment (ERBE) measurements of Langley Research Center/NASA of US, and 1961–1996 monthly mean data from 148 surface stations over the Qinghai-Xizang Plateau (QXP) and its neighborhood, study is performed on empirical calculation methods of surface albedo, surface total radiation, planetary albedo and outgoing longwave radiation with the climatic features of radiation balance at the surface and the atmospheric top examined. Evidences suggest that the empirical formulae for surface albedo, planetary albedo, surface to-tal radiation and outgoing longwave radiation from the atmospheric top are capable of describing their seasonal and interannual variations over the QXP. The surface albedo is marked by noticeable seasonal variation and yearly mean of 0.22 with the maximum of 0.29 in January and minimum of 0.17 in July and August; in winter the albedo has great horizontal difference, bigger in the moun-tains than in the river valleys, and small in summer. The planetary albedo shows a smaller range of its annual variation with the yearly mean of 0.37, the maximum (minimum) occurring in February and March (autumn). In winter its high-value regions are mainly at Gar (Shiquanhe) in the western QXP and from the southwestern Qinghai to the northeastern Tibet and the low-value area at the northern slope of the central Himalayas; in summer, however, the albedo distribution displays clear-ly a progressive decrease from southeast to northwest. As for the surface total radiation, its values and annual varying range are smaller in the east than in the southwest. Its high-value center is at the southern slope of the Himalayas in winter and makes a conspicuous westward migration in spr-ing, remaining there for a long time, and it begins to retreat eastward in autumn. Monthly mean values of the surface net radiation are all positive and larger in summer than in winter. The net ra-diation is significantly intensified under the combined effect of surface total radiation and surface albedo from spring to early summer, resulting in the strongest sector in the mid plateau with its center staying nearly motionless from March to September, and is reduced in autumn dominantly by surface effective radiation. The earth-atmosphere system loses heat outward from October to next February and gains in other months. On an average, the plateau gains heat of 15 W m-2 on an annual basis. Key words The Qinghai-Xizang Plateau - Albedo - Radiation balance - Climatic feature (1)This work was supported under the auspices of the National (G1998040800) and CAS’s Key Project for Basic Research on Tibetan Plateau (KZ951-A1-204; KZ95T-06).

SOME CHARACTERISTICS OF THE SURFACE RADIATION COMPONENTS AT ZHONGSHAN STATION

A preliminary analysis of some characteristics of the radiation components is made by using the surface radiation data obtained from February 1990 to January 1991 at Zhongshan Station. The result shows that the fluxes of direct radiation and global radiation are strong with higher atmospheric transparency, and the surface can absorb large amount of radiation energy in warm season. The surface loses heat energy in cold season due to the seasonal variations of the surface albedo and shortwave radiation. The variation of net longwave radiation is related to cloud amount and surface air temperature. The property of net radiation is similar to other Antarctic coastal stations but differs greatly from Antarctic inland area.

Continued Study on Hohlraum Radiation Source with Approximately Constant Radiation Temperature

An experiment was performed on the Shenguang III prototype laser facility to continue the study on hohlraum radiation source with approximately constant radiation temperature using a continuously shaped laser pulse.A radiation source with a flattop temperature of about130 e V that lasted about 5 ns was obtained.The previous analytical iteration method based on power balance and self-similar solution of ablation was modified taking into account the plasma movements and it was used to design the laser pulse shape for experiment.A comparison between experimental results and simulation is presented and better agreement was achieved using the modified method.Further improvements are discussed.

ELEMENTARY VIEW OF GREENHOUSE EFFECT OF THE ATMOSPHERES OF VARIOUS PLANETS

The global mean temperatures of the atmosphere and the surface of various planets of the solar system are deter- mined by taking the system as in radiative equilibrium,with the atmosphere taken as transparent to solar radiation but with an albedo α,and composed of N layers each of which absorbs all infrared radiation that falls on it,and a top layer of partial absorptivity a,while the surface is taken as black.It is found that,for the earth's atmosphere with α=0.33, N=0,a=0.83,it gives the current observed mean surface temperature T_s=15℃ and the effective mean radiative temper- ature of the atmosphere T_a=242.6K.On the other hand;the atmosphere of Venus is characterized by α=0.70 and N=70,which yields a surface temperature of about 700K. It is also found that surface evaporation and absorption of solar radiation by the atmosphere tend to lower the sur- face temperature.