Simulation of astronomical solar radiation over Yellow River Basin based on DEM

1IntroductionDistributed watershed hydrological model has become one of the hot topics in hydrology for its predominance in reflecting the influence of the spatial distributed features of terrains on hydrological processes (Wan etal., 2001; Abbott etal., 1986; Beven etal., 1992). However its demands on the spatio-temporal changeful surface elements such as solar radiation, precipitation, temperature etc. are strict. Being the limitations of observation techniques, data availability and study …     

The impact of changing subcanopy radiation on snowmelt in a disturbed coniferous forest

Understanding the role of forests on snowmelt processes enables better estimates of snow storages at a catchment scale and contributes to a higher accuracy of spring flood forecasting. A coniferous forest modifies the snowpack energy balance by reducing the total amount of solar shortwave radiation (SWR) and enhancing the role of longwave radiation (LWR) emitted by trees. This study focuses on changes in SWR and LWR at three sites with different canopy structure (Bohemian Forest, Czechia), including one site affected by the bark beetle (Ips typographus). Measurements of incoming and outgoing SWR and LWR were performed at all sites equipped with CNR4 Net Radiometers for three cold seasons. In addition to SWR and LWR, sensible and latent heat, and ground heat and energy supplied by liquid precipitation were calculated. The results showed that net SWR at the healthy forest site represented only 7% of the amount at the open site due to the shading effect of trees. In contrast, net LWR represented a positive component of the snowpack energy balance at the healthy forest site and thus contributed the most to snowmelt. However, the modelled snowmelt rates were significantly lower in the forest than in the open area since the higher LWR in the forest did not compensated for the lower SWR. The progressive decay of disturbed forest caused the decrease in mean net LWR from −3.1 W/m² to −12.9 W/m² and the increase in mean net SWR from 31.6 W/m² to 96.2 W/m² during the study period. These changes caused an increase in modelled snowmelt rates by 50% in the disturbed forest, compared to the healthy forest site, during the study period. Our findings have important implications for runoff from areas affected by land cover changes due to either human activity or climate change.     

全媒体时代地理信息传播模式的研究

全媒体时代的到来,实现了受众身份的重构,信息发布门槛的降低,让公众真正参与到信息的传播中。地理信息作为信息的种属分支,势必会在全媒体时代的浪潮中发生变化。本文针对全媒体时代下地理信息的传播模式进行了研究,从传播学的视角,以信息的传播理论为基础,对地理信息传播模式的变迁进行了分析,并构建了全媒体时代下去中心化、辐射扩散式的传播模式。结合全媒体的特点从传播主体、内容、形式、受众和方式上分析了地理信息的传播特征,对当下地理信息传播态势和所存在的问题进行了研究和展望。     

GRAPES中尺度模式中不同积云参数化方案预报性能对比研究

利用我国新一代中尺度数值模式GRAPES_Meso,采用KFeta和BMJ两种积云对流参数化方案,对我国2009年冬季(1月)和夏季(6—8月)天气进行批量回报试验。回报试验结果表明：在冬季,两种方案对GRAPES_Meso模式的预报性能影响差异较小。在夏季,两种方案对模式回报效果的影响表现明显。在低层BMJ方案对形势场的回报性能略优于KFeta方案,中层则是KFeta方案明显优于BMJ方案,而在高层KFeta方案略优于BMJ方案。TS评分检验表明KFeta方案对降水的预报总体上优于BMJ方案,特别是中雨到暴雨量级在华南地区KFeta方案有明显的优势。两个方案预报积云降水平均贡献率的空间分布差异主要表现在低纬度洋面上,BMJ方案的贡献率比KFeta方案大。两个方案积云降水贡献率的概率分布形态在小雨量级上都呈陡峭的“U”型分布。KFeta方案随着降水量级的增大逐渐向大贡献率偏移,特大暴雨量级时基本上是积云降水的贡献;而BMJ参数化方案则是随着降水量级的增大逐渐向小贡献率偏移,特大暴雨量级时基本上是格点降水的贡献。     

Performance of Convective Parameterization Schemes in Asia Using RegCM:Simulations in Three Typical Regions for the Period 1998–2002

This study discusses the sensitivity of convective parameterization schemes(CPSs) in the Regional Climate Model(version 4.3)(Reg CM4.3) over East/South Asia. The simulations using different CPSs in Reg CM are compared to discover a suitable scheme for this region, as the performance of different schemes is greatly influenced by region and seasonality. Over Southeast China and the Bay of Bengal, the Grell scheme exhibits the lowest RMSEs of summer precipitation compared to observed data. Moreover, the Emanuel over land and Grell over ocean(ELGO) scheme enhances the simulation, in comparison with any single CPS(Grell/Emanuel) over Western Ghats, Sri Lanka, and Southeast India. Over the Huang–Huai–Hai Plain(3H) and Tibetan Plateau(TP) regions of China, the Tiedtke scheme simulates the more reasonable summer precipitation with high correlation coefficient and comparable amplitude. Especially, it reproduces a minimum convective precipitation bias of 8 mm d-1and the lowest RMSEs throughout the year over East/South Asia. Furthermore, for seasonal variation of precipitation, the Tiedtke scheme results are closer to the observed data over the 3H and TP regions. However, none of the CPSs is able to simulate the seasonal variation over North Pakistan(NP). In comparison with previous research, the results of this study support the Grell scheme over South Asia. However, the Tiedtke scheme shows superiority for the 3H, TP and NP regions. The thicker PBL, less surface latent heat flux, the unique ability of deep convection and the entrainment process in the Tiedtke scheme are responsible for reducing the wet bias.     

Aerosol-Cloud-Precipitation Interactions in WRF Model: Sensitivity to Autoconversion Parameterization

Cloud-to-rain autoconversion process is an important player in aerosol loading, cloud morphology, and precipitation variations because it can modulate cloud microphysical characteristics depending on the participation of aerosols, and affects the spatio-temporal distribution and total amount of precipitation. By applying the Kessler, the Khairoutdinov-Kogan(KK), and the Dispersion autoconversion parameterization schemes in a set of sensitivity experiments, the indirect effects of aerosols on clouds and precipitation are investigated for a deep convective cloud system in Beijing under various aerosol concentration backgrounds from 50 to 10000 cm-3. Numerical experiments show that aerosol-induced precipitation change is strongly dependent on autoconversion parameterization schemes. For the Kessler scheme, the average cumulative precipitation is enhanced slightly with increasing aerosols, whereas surface precipitation is reduced significantly with increasing aerosols for the KK scheme. Moreover, precipitation varies non-monotonically for the Dispersion scheme, increasing with aerosols at lower concentrations and decreasing at higher concentrations.These different trends of aerosol-induced precipitation change are mainly ascribed to differences in rain water content under these three autoconversion parameterization schemes. Therefore, this study suggests that accurate parameterization of cloud microphysical processes, particularly the cloud-to-rain autoconversion process, is needed for improving the scientific understanding of aerosol-cloud-precipitation interactions.     

Sensitivity of Precipitation over China to Different Cumulus Parameterization Schemes in RegCM4

The effect of different cumulus parameterization schemes(CPSs) on precipitation over China is investigated by using the International Centre for Theoretical Physics(ICTP) Regional Climate Model version 4.3(Reg CM-4.3) coupled with the land surface model BATS1e(Biosphere-Atmosphere Transfer Scheme version1e). The ERA-interim data are utilized to drive a group of simulations over a 31-yr period from September1982 to December 2012. Two typically sensitive regions, i.e., the eastern Tibetan Plateau(TP; 29°–38°N,90°–100°E) and eastern China(EC; 26°–32°N, 110°–120°E), are focused on. The results show that all the CPSs have well reproduced the spatial distribution of annual precipitation in China. The simulation with the Emanuel scheme shows an overall overestimation of precipitation in China, different from the other three CPSs which only overestimate over northern and northwestern China but underestimate over southern China. Seasonally, the Tiedtke scheme shows the smallest overestimation in winter and summer, and the best simulation of the annual variance of precipitation. Interannual variations of precipitation among the four CPSs are generally simulated better in summer than in winter, and better for entire China than in the subregions of TP and EC. The precipitation trend is simulated better over EC than over TP, and better in summer than in winter. An overestimate(underestimate) of the East Asian summer monsoon index(EASMI) exists in the simulations with the Grell and the Emanuel(the Kuo and the Tiedtke) schemes.The smallest EASMI bias in the Tiedtke simulation could explain its small precipitation bias. A negative correlation between the EASMI and summer precipitation over the middle and lower reaches of Yangtze River is found in the Grell and the Emanuel simulations, but was missed by the simulations using the Kuo and the Tiedtke schemes.     

Sensitivity of the warm core of tropical cyclones to solar radiation

To investigate the impacts of solar radiation on tropical cyclone (TC) warm-core structure (i.e., the magnitude and height), a pair of idealized simulations are conducted by specifying different strengths of solar shortwave radiation. It is found that the TC warm core is highly sensitive to the shortwave radiative effect. For the nighttime storm, a tendency for a more intense warm core is found, with an elevated height compared to its daytime counterpart. As pointed out by previous studies, the radiative cooling during nighttime destabilizes the local and large-scale environment and thus promotes deep moist convection, which enhances the TC's intensity. Due to the different inertial stabilities, the diabatic heating in the eyewall will force different secondary circulations. For a strong TC with a deeper vertical structure, this promotes a thin upper-level inflow layer. This inflow carries the lower stratospheric air with high potential temperature and descends adiabatically in the eye, resulting in significant upper-level warming. The Sawyer-Eliassen diagnosis further confirms that the height of the maximum temperature anomaly is likely attributable to the balance among the forced secondary circulations.     

利用GPS卫星轨道确定地球二阶带谐系数的研究

重力恢复和气候实验(gravity recovery and climate experiment,GRACE)任务受限于卫星的低轨极地轨道性质和编队模式,确定的重力场模型C₂₀项存在不足。与之相比,全球定位系统(global positioning system,GPS)卫星为倾斜轨道,卫星数量多,将GPS卫星的精密轨道数据作为伪观测值,使用动力学方法进行C₂₀项确定的可行性研究。结果显示,2017年C₂₀项时间序列的平均值比GRACE更接近卫星激光测距(satellite laser ranging,SLR)的结果,且不存在明显的约160 d的周期信号,表明利用GPS卫星解算C₂₀项具有可行性。同时估计了光压模型P1参数,与GAMIT软件解算结果接近,进一步验证C₂₀项解算结果的可靠性。     

FY-3B TOU臭氧总量多元回归插值与验证

FY-3B TOU臭氧总量产品空间分辨率为50 km,在开展小区域或精细化的臭氧研究时,需要获得更高分辨率、更具有准确和可靠性的臭氧插值数据。常规的数据插值方法没有考虑TOU臭氧总量受短波辐射、海拔高度的影响,所得到的插值数据参考性不强。文中介绍TOU多元回归插值方法,方法采用程序设计方式,动态分析TOU与短波辐射、海拔高度之间的相关性,建立一元回归模型,并根据一元回归模型结构建立多元回归模型,再通过多元回归模型对TOU进行插值。使用OMI臭氧总量数据对插值结果开展验证,验证结果表明采用多元回归算法的插值具有较好的可行性。且该插值方法及程序设计对其他类似的数据插值、分析具有一定的借鉴和参考意义。