The effects of forest litter on snow energy budget in the Tianshan Mountains,China

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 (T _s ), 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 T _s 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.     

SEASONAL HEAT BUDGET IN THE TROPICAL WESTERN PACIFIC OCEAN IN A GLOBAL GCM Ⅱ. IN FIVE SUBREGIONS

The general features of the seasonal suuface heat budget in the tropical western Pacific Ocean,20°S-20°N, western boundary-160°E, were documented by Qu (1995) using a high-resolution generalcirculation model (GCM, Semtner & Chervin,1992) ard existing observations.Close inspection of thesmaller areas, with the whole region further partitioned into six parts, showed different mechanisms balancethe seasonal surface heat budget in different parts of the region The results of study on five subregionsare detailed in this article. In the equatorial (3°S - 3°N) aed North Equatorial Countercurrent(3°N-9°N) region, the surface the flux the does not change significantly throughout the year, so the surface heat content is determined largely by vertical motion near the equator and roughly helf due to horizontal and halfdue to vertical circulation in the region of the North Equatorial Countercurrent(NECC). In the othersubregions (9°N-20°N, 20°S -11°S aed 11°S -3°S ), however, in addition to ocean dynamics     

Seasonal heat budget in the tropical Western Pacific Ocean in a global GCM II. In five subregions

The general features of the seasonal surface heat budget in the tropical western Pacific Ocean, 20° S–20°N, western boundary −160°E, were documented by Qu (1995) using a high-resolution general circulation model (GCM, Semtner & Chervin, 1992) and existing observations. Close inspection of the smaller areas, with the whole region further partitioned into six parts, showed different mechanisms balance the seasonal surface heat budget in different parts of the region. The results of study on five subregions are detailed in this article. In the equatorial (3°S–3°N) and North Equatorial Countercurrent (3°N–9°N) region, the surface heat flux does not change significantly throughout the year, so the surface heat content is determined largely by vertical motion near the equator and roughly half due to horizontal and half due to vertical circulation in the region of the North Equatorial Countercurrent (NECC). In the other subrigions (9°N–20°N, 20°S–11°S and 11°S–3°S), however, in addition to ocean dynamics, surface heat flux can also play a major role in the seasonal variation of sea surface temperature (SST). The remotely forced baroclinic waves and their effect on the surface heat storage in the model are also investigated. Comparison with observations indicates that the model wave activities are reasonably realistic. Contribution No. 2396 from the Institute of Oceanology, Chinese Academy of Sciences. This study was supported by the Australian CSIRO Division of Oceanography and the National Natural Science Foundation of China (No. 49176255)     

A 1-D model of the formation and evolution of Polar Stratospheric Clouds

A 1-D model of the formation and seasonal evolution of Polar Stratospheric Clouds (PSCs) is described. The model considers PSCs of types 1 and 2 in the vertical range from 8 to 30 km and utilizes real temperature data. The micro-physical processes included in the model are the heterogeneous nucleation and condensation (or evaporation), while sedimentation, gas diffusion and vertical wind velocity are the processes responsible for transport. Model simulations have been compared with PSC data obtained by lidar at the South Pole: results for the winter 1990 are discussed. The different contribution of type 1 and type 2 PSCs to the measured backscattering coefficient has been evidenced. In the simulations, layers of NAT particles form when low values of the backscattering coefficient are measured; similarly, ice particles form when sharper and rapidly changeable structures with higher values of the backscattering coefficient are observed. Significant results on the condensation and depletion of HNO₃ and H₂O are presented. Water vapor profiles measured during winter 1990 are reproduced quite well.     

Strategies for spatial and temporal extrapolation and interpolation of wet delay

. The excess radio-path delay due to the atmospheric water vapor, the wet delay, can be derived from water vapor radiometer (WVR) measurements. WVR data used for external calibration of space geodetic measurements are not always acquired in the directions of the space geodetic signal sources, thus extrapolation and interpolation methods for the wet delay are needed. We evaluate three different methods using approximately 10 days of WVR measurements. Two methods, the gradient method and turbulence method, use the directional information in the data, while the third method used is linear regression in time regardless of the direction of the observations. The turbulence method yielded at least 10% less RMS estimation error than the errors from the other two methods. Received: 20 May 1997 / Accepted: 15 December 1997     

THE APPROACH TO REMOTE SENSING OF WATER VAPOR BASED ON GPS AND LINEAR REGRESSION Tm IN EASTERN REGION OF CHINA

The approach to remote sensing of water vapor by using global positioning systems(GPS) isdiscussed.In order to retrieve the vertical integrated water vapor(IWV) or the precipitable water(PW),the weighted "mean temperature" of the atmosphere,T_m would be estimated to the specificarea and season.T_m depends on surface temperature,tropospheric temperature profile,and thevertical distribution of water vapor.The surface temperature dependence is borne out by acomparison of T_m and the values of surface temperature T_s using radiosonde profiles of BeijingStation(No.54511) throughout 1992.The analysis of radiosonde profiles spanning a one-yearinterval(1992) from sites in eastern region of China with a latitude range of 20-50°N and alongitude range of 100-130°E yields the coefficients a and b of a linear regression equation T_m=a+bT_s.     

一次飑线天气过程的卫星水汽图像特征

利用卫星水汽图像,结合雷达及常规天气资料,分析发生在山东省境内的一次飑线强天气过程,进一步分析水汽边界及附近的物理量条件,为短时天气预报提供一种思路。     

GMS-5 估计可降水量的研究

文章证明了由静止气象卫星GMS-5的分裂窗通道和水汽通道亮温反演可降水量的可行性,探讨了GMS-5红外通道亮温与可降水量的关系,建立了由3个通道亮温反演可降水量的经验公式。用60组大气平均廓线,对公式模拟检验误差为0.18 g/cm2,而用实际124组探空和对应的GMS-5亮温资料进行检验,误差0.40 g/cm2。用得到的经验公式可反演大范围的晴空可降水量分布。     

1995年6月梅雨期暴雨的水汽图像分析

文章利用GMS-5水汽图像及常规资料,分析1995年6月中旬至7月初梅雨期暴雨的水汽图像特征,指出水汽羽与强降水的关系,并概括出梅雨期暴雨的水汽图像概念模型。