High Elevation Energy and Water Balance:the Roles of Surface Albedo and Temperature

Observation and modeling of the coupled energy and water balance is the key to understand hydrospheric and cryospheric processes at high elevation.The paper summarizes the progress to address this aspect in relation with different earth system elements,from glaciers to wetlands.The energy budget of two glaciers,i.e.Xiao Dongkemadi and Parlung No.4,was studied by means of extended field measurements and a distributed model of the coupled energy and mass balance was developed and evaluated.The need for accurate characterization of surface albedo was further documented for the entire Qinghai Tibet Plateau by numerical experiments with Weather Research and Forecast(WRF)on the sensitivity of the atmospheric boundary layer to the parameterization of land surface processes.A new approach to the calibration of a coupled distributed watershed model of the energy and water balance was demonstrated by a case study on the Heihe River Basin in northwestern China.The assimilation of land surface temperature did lead to the retrieval of critical soil and vegetation properties as the soil permeability and the canopy resistance to the exchange of vapour and carbon dioxide.The retrievals of actual Evapo-Transpiration(ET)were generated by the ETMonitor system and evaluated against eddy covariance measurements at sites spread throughout Asia.As regards glacier response to climate variability,the combined findings based on satellite data and model experiments showed that the spatial variability of surface albedo and temperature is significant and controls both glacier mass balance and flow.Experiments with both atmospheric and hydrosphere-cryosphere models documented the need and advantages of using accurate retrievals of land surface albedo to capture lan-atmosphere interactions at high elevation.

Inter-comparisons of thermodynamic sea-ice modeling results using various parameterizations of radiative flux

Radiative fluxes are of primary importance in the energy and mass balance of the sea-ice cover. Various parameterizations of the radiative fluxes are studied in a thermodynamic sea-ice model. Model outputs of the surface radiative and heat fluxes and mass balance are compared with observations. The contribution of short-wave radiation is limited to a long part of winter. Therefore, simple schemes are often sufficient. Errors in estimations of the short-wave radiation are due mainly to cloud effects and occasionally to multi-reflection between surface and ice crystals in the air. The long-wave radiation plays an important role in the ice surface heat and mass balance during most part of a winter. The effect of clouds on the accuracy of the simple radiative schemes is critical, which needs further attention. In general, the accuracy of an ice model depends on that of the radiative fluxes.

海冰热力模式的辐射参数化方案在渤海和波罗的海应用的比较

研究了海冰热力模式中的各种辐射参数化方案,对比了模式计算的太阳短波辐射、大气长波辐射以及海冰热力变化,并利用渤海和波罗的海观测资料进行比较和误差分析.冬季大部分时间太阳短波辐射对海冰热力过程的作用有限.简单计算方案一般满足海冰模式要求.误差主要受云和冰雪表面与大气之间的多重反射影响.长波辐射对表面热平衡和海冰质量变化起重要作用.长波辐射参数化方案的计算结果受环境因素影响.云量参数化有待进一步改进.海冰模式计算结果的精度与长波辐射计算精度有一致性.

An improved algorithm to estimate the surface soil heat flux over a heterogeneous surface: A case study in the Heihe River Basin

Surface soil heat flux(G0) is an indispensable component of the surface energy balance and plays an important role in the estimation of surface evapotranspiration(ET). This study calculated G0 in the Heihe River Basin based on the thermal diffusion equation, using the observed soil temperature and moisture profiles, with the aim to analyze the spatial-temporal variations of G0 over the heterogeneous area(with alpine grassland, farmland, and forest). The soil ice content was estimated by the difference in liquid soil water content before and after the melting of the frozen soil and its impact on the calculation of G0 was further analyzed. The results show that:(1) the diurnal variation of G0 is obvious under different underlying surfaces in the Heihe River Basin, and the time when the daily maximum value of G0 occurs is a few minutes to several hours earlier than that of the net radiation flux, which is related to the soil texture, soil moisture, soil thermal properties, and the vegetation coverage;(2) the net radiation flux varies with season and reaches the maximum in summer and the minimum in winter, whereas G0 reaches the maximum in spring rather than in summer, because more vegetation in summer hinders energy transfer into the soil;(3) the proportions of G0 to the net radiation flux are different with seasons and surface types, and the mean values in January are 25.6% at the Arou site, 22.9% at the Yingke site and 4.3% at the Guantan site, whereas the values in July are 2.3%, 1.6% and 0.3%, respectively; and(4) G0 increases when the soil ice content is included in thermal diffusion equation, which improves the surface energy balance closure by 4.3%.