A new approach to identify the sensitivity and importance of physical parameters combination within numerical models using the Lund–Potsdam–Jena (LPJ) model as an example

Daily global solar irradiation (R _s) is one of the main inputs in environmental modeling. Because of the lack of its measuring facilities, high-quality and long-term data are limited. In this research, R _s values were estimated based on measured sunshine duration and cloud cover of our synoptic meteorological stations in central and southern Iran during 2008, 2009, and 2011. Clear sky solar irradiation was estimated from linear regression using extraterrestrial solar irradiation as the independent variable with normalized root mean square error (NRMSE) of 4.69 %. Daily R _s was calibrated using measured sunshine duration and cloud cover data under different sky conditions during 2008 and 2009. The 2011 data were used for model validation. According to the results, in the presence of clouds, the R _s model using sunshine duration data was more accurate when compared with the model using cloud cover data (NRMSE = 11. 69 %). In both models, with increasing sky cloudiness, the accuracy decreased. In the study region, more than 92 % of sunshine durations were clear or partly cloudy, which received close to 95 % of total solar irradiation. Hence, it was possible to estimate solar irradiation with a good accuracy in most days with the measurements of sunshine duration.     

Carbon and water flux responses to physiology by environment interactions: a sensitivity analysis of variation in climate on photosynthetic and stomatal parameters

Sensitivity of carbon uptake and water use estimates to changes in physiology was determined with a coupled photosynthesis and stomatal conductance (g _s) model, linked to canopy microclimate with a spatially explicit scheme (MAESTRA). The sensitivity analyses were conducted over the range of intraspecific physiology parameter variation observed for Acer rubrum L. and temperate hardwood C₃ (C₃) vegetation across the following climate conditions: carbon dioxide concentration 200–700 ppm, photosynthetically active radiation 50–2,000 μmol m^?2 s^?1, air temperature 5–40 °C, relative humidity 5–95 %, and wind speed at the top of the canopy 1–10 m s^?1. Five key physiological inputs [quantum yield of electron transport (α), minimum stomatal conductance (g ₀), stomatal sensitivity to the marginal water cost of carbon gain (g ₁), maximum rate of electron transport (J _max), and maximum carboxylation rate of Rubisco (V _cmax)] changed carbon and water flux estimates ≥15 % in response to climate gradients; variation in α, J _max, and V _cmax input resulted in up to ~50 and 82 % intraspecific and C₃ photosynthesis estimate output differences respectively. Transpiration estimates were affected up to ~46 and 147 % by differences in intraspecific and C₃ g ₁ and g ₀ values—two parameters previously overlooked in modeling land–atmosphere carbon and water exchange. We show that a variable environment, within a canopy or along a climate gradient, changes the spatial parameter effects of g ₀, g ₁, α, J _max, and V _cmax in photosynthesis-g _s models. Since variation in physiology parameter input effects are dependent on climate, this approach can be used to assess the geographical importance of key physiology model inputs when estimating large scale carbon and water exchange.     

基于多源卫星资料的中国地区云宏微观特征研究

利用2007—2016年国际卫星云气候计划（International Satellite Cloud Climatology Project,ISCCP）、云和地球辐射能量系统（Clouds and the Earth''s Radiant Energy System,CERES）和中分辨率成像光谱仪（Moderate Resolution Imaging Spectroradiometer,MODIS）卫星反演云产品,对比分析了不同数据反演的中国地区云系结构的宏微观特征,并采用复合评价指标定量评估了不同数据之间时间和空间上的一致性。结果表明：三套卫星数据都能较好地反演出中国地区总云量呈南高北低、东高西低、夏高冬低的分布特征,但通过比较时间技巧（Temporal Skill,S_T）及空间技巧（Spatial Skill,S_S）复合评价指标及其各项分量发现,与MODIS相比,CERES与ISCCP数据反演的总云量时间序列演变特征明显更为一致,且其评分均有南方优于北方,夏季优于冬季的特征;进一步分析不同高度云量的S_T评分发现,CERES和ISCCP两套数据在南方地区的总云量差异主要来自于低云量的绝对偏差,而北方地区的偏差则同时存在于低云和中云;对比分析MODIS和CERES反演的云滴有效半径发现,高云对应的冰相云一致性较高,而中低云相对应的液相云的偏差则有夏季高于冬季的规律。针对夏季液相和冰相云滴粒径及概率密度分析则表明,相比CERES数据,MODIS对夏季液水和冰水粒子的有效半径在不同地区均有不同程度的高估,液（冰）水谱宽则更宽（窄）。     

Peculiarities of climatic changes in cloud cover over the Russian Federation

Modern climatic changes in cloud cover over Russia are analyzed from standard ground-based meteorological observations in 1951–2000 and information on cloudiness obtained from the actinometrical observations in 1976–2000. In addition to studies of changes in total cloud amount, a special attention is paid to the distribution of basic forms of cloudiness with respect to their frequency. A spatial generalization of the results for large-scale regions (the European and Asian parts of Russia) allowed revealing dominant tendencies in cloud cover changes that are slightly related to seasons of year and reflect large-scale changes in cloud characteristics in the second half of the 20th century.     

ASC200型地基双波段全天空云量自动观测仪云量比对分析

采用ASC200型地基双波段全天空云量自动观测仪2019年2—5月在中国气象局长沙国家综合气象观测试验基地和上海宝山国家基本气象站的连续观测数据,分别与人工观测云量及器测云量参考标准进行比对,从综合云量、可见光云量及红外云量3方面初步探究其云量观测能力。比对结果显示：该设备长沙站和宝山站综合云量样本与人工云量参考标准差值在±20%以内的样本分别占总量的92.2%和79.4%,长沙站综合云量样本与器测云量参考标准差值在±20%以内的占样本总量的90.5%,差值在±10%以内的占样本总量的86%。结论如下：①ASC200综合云量样本与人工及器测云量参考标准一致性良好;②验证了可见光云量观测系统在雾霾等天气条件下观测能力较弱,红外云量观测系统对卷云的观测能力较弱;③在能见度良好的观测条件下,双波段云量观测系统的云量观测能力优于单一波段云量观测系统。     

云量的时间精细化预报研究-以榆中为例

利用2001年7月至2011年7月甘肃省榆中县地面测站的每日8次云量资料和同期NCEP每日4次等压面资料,由NCEP资料构造预报因子,以总云量和低云量为预报对象,分析预报因子和预报对象的相关性,采用逐步回归方法建立榆中县逐月8个时次的云量预报方程并进行回代;并利用2012年的资料检验预报方程的预报效果。结果表明：云量主要受整层湿度、垂直运动、不稳定能量、槽强度指数和700 hPa水汽通量散度影响,其中湿度状况和垂直运动是重要因素。建立的预报方程对总云量的预报效果比低云量好;总云量平均预报误差在2成左右,低云量平均预报误差在3成左右;预报值变化趋势可以部分地反映实际云量的变化趋势。     

Spatiotemporal Variations of Cloud Amount over the Yangtze River Delta, China

Based on the NOAA's Advanced Very High Resolution Radiometer(AVHRR) Pathfinder Atmospheres Extended(PATMOS-x) monthly mean cloud amount data, variations of annual and seasonal mean cloud amount over the Yangtze River Delta(YRD), China were examined for the period 1982–2006 by using a linear regression analysis. Both total and high-level cloud amounts peak in June and reach minimum in December, mid-level clouds have a peak during winter months and reach a minimum in summer, and lowlevel clouds vary weakly throughout the year with a weak maximum from August to October. For the annual mean cloud amount, a slightly decreasing tendency(–0.6% sky cover per decade) of total cloud amount is observed during the studying period, which is mainly due to the reduction of annual mean high-level cloud amount(–2.2% sky cover per decade). Mid-level clouds occur least(approximately 15% sky cover) and remain invariant, while the low-level cloud amount shows a significant increase during spring(1.5% sky cover per decade) and summer(3.0% sky cover per decade). Further analysis has revealed that the increased low-level clouds during the summer season are mainly impacted by the local environment. For example,compared to the low-level cloud amounts over the adjacent rural areas(e.g., cropland, large water body, and mountain areas covered by forest), those over and around urban agglomerations rise more dramatically.     

Cloud vertical distribution from radiosonde,remote sensing,and model simulations

Knowledge of cloud vertical structure is important for meteorological and climate studies due to the impact of clouds on both the Earth’s radiation budget and atmospheric adiabatic heating. Yet it is among the most difficult quantities to observe. In this study, we develop a long-term (10 years) radiosonde-based cloud profile product over the Southern Great Plains and along with ground-based and space-borne remote sensing products, use it to evaluate cloud layer distributions simulated by the National Centers for Environmental Prediction global forecast system (GFS) model. The primary objective of this study is to identify advantages and limitations associated with different cloud layer detection methods and model simulations. Cloud occurrence frequencies are evaluated on monthly, annual, and seasonal scales. Cloud vertical distributions from all datasets are bimodal with a lower peak located in the boundary layer and an upper peak located in the high troposphere. In general, radiosonde low-level cloud retrievals bear close resemblance to the ground-based remote sensing product in terms of their variability and gross spatial patterns. The ground-based remote sensing approach tends to underestimate high clouds relative to the radiosonde-based estimation and satellite products which tend to underestimate low clouds. As such, caution must be exercised to use any single product. Overall, the GFS model simulates less low-level and more high-level clouds than observations. In terms of total cloud cover, GFS model simulations agree fairly well with the ground-based remote sensing product. A large wet bias is revealed in GFS-simulated relative humidity fields at high levels in the atmosphere.     

黄河上游玛曲地区近40a云量的变化特征

利用玛曲国家基本气象观测站1971—2010年的总云量、低云量等观测数据,用线性趋势分析、小波分析等方法对玛曲地区近40 a总云量、低云量的月、季、年际、年代际变化和周期性变化特征进行分析。研究表明,近40 a来,平均总云量距平在-0.1%～0.1%之间,保持了很好的稳定性,平均低云量以4.0%/10 a的速率递增;春、夏、秋季低云量呈现出不同程度的增多趋势,夏季增加趋势非常明显达7.3%/10 a。平均总云量周期变化不明显,平均低云量有明显的6～7 a的周期。玛曲地区在总云量保持稳定的情况下低云量不断增多,夏季低云量的增多趋势非常明显,且积雨云的增多是主要特征,是对玛曲草原气候变化的一种响应机制,反映出在气候变暖的大背景下,玛曲草原对流性天气活动频繁。     

Decomposition of Fast and Slow Cloud Responses to Quadrupled CO2 Forcing in BCC–AGCM2.0 over East Asia

In this study, the decomposed fast and slow responses of clouds to an abruptly quadrupled CO₂ concentration (approximately 1139 ppmv) in East Asia (EA) are obtained quantitatively by using a general circulation model, BCC–AGCM2.0. Our results show that in the total response, the total cloud cover (TCC), low cloud cover (LCC), and high cloud cover (HCC) all increased north of 40°N and decreased south of 40°N except in the Tibetan Plateau (TP). The mean changes of the TCC, LCC, and HCC in EA were –0.74%, 0.38%, and –0.38% in the total response, respectively; 1.05%, –0.03%, and 1.63% in the fast response, respectively; and –1.79%, 0.41%, and –2.01% in the slow response, respectively. By comparison, we found that changes in cloud cover were dominated by the slow response in most areas in EA due to the changes in atmospheric temperature, circulation, and water vapor supply together. Overall, the changes in the cloud forcing over EA related to the fast and slow responses were opposite to each other, and the final cloud forcing was dominated by the slow response. The mean net cloud forcing (NCF) in the total response over EA was –1.80 W m^–2, indicating a cooling effect which partially offset the warming effect caused by the quadrupled CO₂. The total responses of NCF in the TP, south China (SC), and northeast China (NE) were –6.74 W m^–2, 6.11 W m^–2, and –7.49 W m^–2, respectively. Thus, the local effects of offsetting or amplifying warming were particularly obvious.     

Sea surface winds derived from cloud motion vectors over the tropical Atlantic

The relationship between satellite-derived low-level cloud motion, surface wind and geostrophic wind vectors is examined using GATE data. In the trades, surface wind speeds can be derived from cloud motion vectors by the linear relation: V = 0.62 V _s + 1.9 m s^–1 with a mean scatter of ±1.3 m s^–1. The correlation coefficient between surface and satellite wind speed is 0.25. Considering baroclinicity, i.e., the influence of the thermal wind, the correlation coefficient does not increase, because of the uncertainty of the thermal wind vectors. The ratios of surface to geostrophic wind speed and surface to satellite wind speed are 0.7 and 0.8, respectively, with a statistical uncertainty of ±0.3. Calculations of the ratio of surface to geostrophic wind speed on the basis of the resistance law yield V/V _g = 0.8 ± 0.2, in agreement with experimental results. The mean angle difference between the surface and the satellite wind vectors amounts to - 18 °, taking into account baroclinicity. This value is in good agreement with the mean ageostrophic angle - 25 °.     

The radiative influence of aerosol effects on liquid-phase cumulus and stratiform clouds based on sensitivity studies with two climate models

Aerosol effects on warm (liquid-phase) cumulus cloud systems may have a strong radiative influence via suppression of precipitation in convective systems. A consequence of this suppression of precipitation is increased liquid water available for large-scale stratiform clouds, through detrainment, that in turn affect their precipitation efficiency. The nature of this influence on radiation, however, is dependent on both the treatment of convective condensate and the aerosol distribution. Here, we examine these issues with two climate models—CSIRO and GISS, which treat detrained condensate differently. Aerosol–cloud interactions in warm stratiform and cumulus clouds (via cloud droplet formation and autoconversion) are treated similarly in both models. The influence of aerosol–cumulus cloud interactions on precipitation and radiation are examined via simulations with present-day and pre-industrial aerosol emissions. Sensitivity tests are also conducted to examine changes to climate due to changes in cumulus cloud droplet number (N _c); the main connection between aerosols and cumulus cloud microphysics. Results indicate that the CSIRO GCM is quite sensitive to changes in aerosol concentrations such that an increase in aerosols increases N _c, cloud cover, total liquid water path (LWP) and reduces total precipitation and net cloud radiative forcings. On the other hand, the radiative fluxes in the GISS GCM appear to have minimal changes despite an increase in aerosols and N _c. These differences between the two models—reduced total LWP in the GISS GCM for increased aerosols, opposite to that seen in CSIRO—appear to be more sensitive to the detrainment of convective condensate, rather than to changes in N _c. If aerosols suppress convective precipitation as noted in some observationally based studies (but not currently treated in most climate models), the consequence of this change in LWP suggests that: (1) the aerosol indirect effect (calculated as changes to net cloud radiative forcing from anthropogenic aerosols) may be higher than previously calculated or (2) lower than previously calculated. Observational constrains on these results are difficult to obtain and hence, until realistic cumulus-scale updrafts are implemented in models, the logic of detraining non-precipitating condensate at appropriate levels based on updrafts and its effects on radiation, will remain an uncertainty.     

Changes in the cloud properties in response to El Niño: a bivariate approach

We analyse the dependence of the cloud radiative effect (CRE) and cloud amount on mid-tropospheric pressure velocity (ω ₅₀₀) and sea surface temperature (SST) and point out the shortcomings of using these two proxies separately as means to separate cloud regimes. A bivariate approach is proposed to overcome these shortcomings and it is used to systematically investigate marine cloud properties at different spatial and time scales in the present-day (1985–2001) tropical climate. During the 1997–1998 El Niño, the greatest regional change in CRE and cloud cover coincides with the greatest local change in circulation and SST. In addition, we find that the cooling effect of the stratiform low clouds reduces at the rate of approximately 1 W/m² per percent of cloudiness reduction in the subsident cold pools of the Pacific ocean. During El Niño, the transition between different cloud regimes gives rise to opposing cloud feedbacks. The sign of the total feedback is controlled by the cloud optical thickness. More generally, we find that the largest part of the cloud response to El Niño, when averaged over the tropical Pacific, is not directly associated with ω ₅₀₀ and SST changes, so other factors must play a role as well.     

Ground observed climatology and trend in snow cover phenology across China with consideration of snow-free breaks

Accurate understanding of snow cover phenology and its changes is important to hydrological processes and climate system. Having recognized the potential uncertainties in remote sensing snow cover products, we used daily snow depth observations from 514 meteorological stations across China to investigate the spatiotemporal variations in snow cover phenology during 1970–2014. Climatologically, the snow cover onset date (D_o) and end date (D_e) as well as the number of snow cover days (D_s) depended on latitude at most stations outside of the Tibetan Plateau (TP). For the high-elevation stations, which were mainly in the TP, multiple snow-free breaks (SFBs) during the cold season made D_s insensitive to D_o and D_e. Furthermore, the number of SFBs (D_b) increased significantly with the rise in elevation, explaining why higher altitudes in TP did not necessarily have greater D_s values despite the earlier D_o and later D_e values. From 1970 to 2014, most stations in China exhibited delayed D_o and advanced D_e due mainly to the increased temperature, but such trends were significant at only 10.5% and 15.4% of the stations, respectively. During the same period, shortened D_s primarily occurred south of ~ 40° N, whereas the opposite ones dominated north of ~ 40° N. Most stations (except those in Hexi Corridor) with significant growth in D_s were characterized by delayed D_o and advanced D_e. Such a phenomenon of “increased snow cover days during shortened cold season” was due to the significant shrinkage in D_b values. The spatial pattern of the trends in annual total snow depth overall follows that of D_s, suggesting that the D_s, when takes SFBs into consideration, could be an indicator of variations of snow water resources in China. The trends in D_o, D_e and D_s were not elevation dependent in TP.

     

中国夏季云和降水的定量关系及其成因分析

云的形成是产生降雨的必要条件,云和降水之间存在着极为密切而复杂的联系。利用常规站点数据和ISCCP卫星数据等资料分析了夏季中国地区云的多种特征参数的变化与降水变化在时空分布上的联系。站点数据结果表明总云量、低云量与降水的距平在全国范围内表现出显著的正相关关系;在通过0.05水平显著性检验的站点上,云量和降水距平百分率之间的线性关系较明显,总云量每增加1.00%降水增加2.23%,低云量每增加1.00%降水增加0.46%。ISCCP数据结果显示总云云量、光学厚度和云水路径以及高云中的卷层云和深对流云云量与降水距平呈非常好的正相关关系。采用K-means聚类分析方法并参考中国地理气候分布特点,将中国分为9个气候区,以小波相干分析和交叉小波分析对各个气候区夏季云量和降水距平百分率序列在时频域内多尺度特征的关系做了进一步研究。结果显示9个气候区夏季白天总云量和低云量与降水变化在2~4年(a)和5~8a的尺度周期都具有较强的相干性与共振周期,且处于正相关位相。在时空分布和时频域上,中国地区夏季云和降水的变化之间都存在非常显著的正相关关系,尤其是低云量。云和降水变化之间具有强相干性与共振周期是两者之间正相关联系的原因。     

Ground-based measurements of local cloud cover

Clouds are believed to reflect temporal climate changes through variations in their amounts, characteristics, and occurrence. In addition, they reflect both weather and climate in a region. In this work, a methodology to determine the local cloud cover (LCC) is proposed using sky images obtained from a ground-based instrument. Three years of sky images from an urban, tropical site were obtained and analyzed through that methodology. Monthly average LCC varied from 3 to 96 %, while seasonal average values were 68 % for summer, 54 % for spring, 46 % for fall, and 23 % for winter. LCC results show a clear seasonal dependence and a fair agreement (r ² = 0.72) with satellite data, which typically underestimate the cloud cover in relation to LCC. Our analysis also suggests the possibility of a measurable link between LCC and natural events like the El Niño Southern Oscillation.     

Current and projected water demand and water availability estimates under climate change scenarios in the Weyib River basin in Bale mountainous area of Southeastern Ethiopia

ENSO has been known to influence the trends of summer warming over Southern Africa. In this work, we used observational and reanalysis data to analyze the relationship between ENSO and maximum surface air temperature (SAT_max) trends during the three epochs created by the ENSO phase shifts around 1977 and 1997 for the period 1960 to 2014. We observed that while ENSO and cloud cover remains the dominant factor controlling SAT_max variability, the first two epochs had the predominant La Niña (El Niño)-like events connected to robust positive (negative) trends in cloud fraction. However, this established relationship reversed in the post-1997 La Niña-like dominated epoch which coincided with a falling cloud cover trend. It is established that this deviation from the previously established link within the previous epochs could be due to the post-1998 era in which SAT_min was suppressed while SAT_max was enhanced. The resulting increase in diurnal temperature range (DTR) could have discouraged the formation of low-level clouds which have relatively more extensive areal coverage and hence allowing more solar energy to reach the surface to boost daytime SAT_max. It is noted that these relationships are more pronounced from December to March.     

“碧利斯”（2006）暴雨过程降水强度和降水效率分析

利用2006年第4号强热带风暴“碧利斯”登陆过程的高分辨率数值模拟资料,结合三维地面降水诊断方程和降水效率公式,研究了“碧利斯”登陆后引发的局地暴雨过程,重点分析了此次局地暴雨过程的降水强度和降水效率及其与宏微观物理因子的联系。结果表明,降水强度越强,降水效率越高,但两者并非一一对应的线性关系,随着降水强度增大,降水效率增高的趋势逐渐变缓;伴随暴雨系统快速发展,降水强度和降水效率均显著增强,而主要降水源/汇项的时间变化要复杂得多;暴雨发生前时段与发生时段降水物理过程存在显著差异,发生前,较明显的水汽辐合显著加湿局地大气,并通过微物理转化支持降水云系发展,液相水凝物辐合对降水云系快速发展贡献明显,固相水凝物辐合贡献不显著,较强的“云滴与雨滴碰并（P_racw）”微物理过程同液相水凝物明显辐合可能有直接关系,“霰融化造成雨滴增长（P_gmlt）”仅为P_racw的27%,发生时段,进一步明显加强的水汽辐合依旧是主要降水来源,而汇项发生了明显变化,同时,微物理转化过程与发生前比更活跃,尤其是P_racw和P_gmlt,其中,P_gmlt增强更明显,其值接近P_racw的50%。     

卫星遥感结合气象资料计算的青藏高原地面感热特征分析

本文选取1981年7月至2012年12月美国国家航空和航天局（NASA）制作的归一化的动态植被指数（NDVI）资料、根据NDVI值计算地表热力输送系数（C_H）的参数化关系式（C_H-I_NDV）和青藏高原70个常规气象观测资料,计算了青藏高原全区的逐月地表热力输送系数（C_H）,讨论了其时空分布特征,并在此基础上计算了高原70个常规台站的感热通量（SSHF）序列,并与已有感热资料进行了对比。随后,探讨了地面感热通量的气候特征及其年际变化与气候因子的关系。结果表明:高原地区的C_H值具有明显的空间差异和季节差异,表现为东高西低、夏季大、冬季小的特点。感热的年际变化在冬季主要响应于地气温差的变化,夏季则受地面风速影响较大;由于风速减小趋缓,地气温差增大,变化趋势在2003年前后由减弱趋势转变为增强趋势,这种趋势的转变最早发生在2001年秋季,且在高原全区具有较好的一致性。