Modeling the effects of changes in air temperature and precipitation on heterotrophic respiration in the central Tibetan Plateau

Theoretical and Applied Climatology - The performance of the operational extended-range forecast (ERF) issued by IMD is evaluated for the southwest monsoon 2020. The normal onset of monsoon over...     

Properties of cloud and precipitation over the Tibetan Plateau

The characteristics of seasonal precipitation over the Tibetan Plateau(TP) were investigated using TRMM(Tropical Rainfall Measuring Mission) precipitation data(3B43). Sensitive regions of summer precipitation interannual variation anomalies were investigated using EOF(empirical orthogonal function) analysis. Furthermore, the profiles of cloud water content(CWC) and precipitable water in different regions and seasons were analyzed using TRMM-3A12 data observed by the TRMM Microwave Imager. Good agreement was found between hydrometeors and precipitation over the eastern and southeastern TP, where water vapor is adequate, while the water vapor amount is not significant over the western and northern TP.Further analysis showed meridional and zonal anomalies of CWC centers in the ascending branch of the Hadley and Walker Circulation, especially over the south and east of the TP. The interannual variation of hydrometeors over the past decade showed a decrease over the southeastern and northwestern TP, along with a corresponding increase over other regions.     

青藏高原感热与黄土高原春季降水异常关系研究

利用1961～2000年黄土高原56站的春季降水、气温资料,用SVD方法分析了其与青藏高原感热场的关系。结果表明,降水量与青藏高原感热场的前两模态代表了两场间的主要耦合特征;上年冬季和秋季青藏高原感热场的异常通过影响大气环流,能够导致次年黄土高原春季降水异常;青藏高原感热对黄土高原西部和南部、北部的部分地区影响较显著,而对陕西北部、山西中部影响不明显。前期高原感热场SVD第一、二模态的变化,可以作为黄土高原春季降水异常的预测信号。     

青藏高原季风期降水的日变化

利用1998年夏季GAME－TIBET IOT期间的探空、降水和雷达资料分析了季风期降水和CAPE、LCL热力参量的日变化及其之间的关系。降水的日变化很明显，最大的降水和CAPE的最大值出现在同一时间段。6km和8.5km高度内的大气层结在大部分时间是不稳定的。0400－0800时间内6km以下9km以上的稳定层结阻碍了对流系统的发展，降水的日变化与这些热力参数的日变化有关。同时，利用三维云模式模拟了降水的日变化和水汽及温度对降水的影响，云模式再现了降水和回波强度的最大和最小值，晚上低层的高湿度是影响降水的重要因素。     

Characteristics of the precipitation over the eastern edge of the Tibetan Plateau

Variations of precipitation over the eastern edge of the Tibetan Plateau are analyzed by using data over station Yaan including daytime, nighttime, and daily-mean precipitation and satellite-derived information. A comparison of some features over Yaan and other stations is also carried out. Over Yaan, light-moderate precipitation contributes significantly to both the number of rainy days (96.9%) and the amount (66.9%) of total precipitation. The light-moderate precipitation occurs more frequently at nighttime than at daytime (by 44.5 days, or 33.4%, and by 520.6 mm, or 134.4%, each year), and the nighttime precipitation is mainly in the form of light-moderate precipitation. The number of rainy days and the amount of total precipitation have decreased from the 1950s to the 1970s and during the recent 20 years, associated with negative trends of light-moderate precipitation. Similar features are also found in the Tropical Rainfall Measuring Mission satellite data. Local convective precipitation is the main form of the light-moderate precipitation over Yaan. The absorption of latent heat at the lower troposphere and the release of latent heat at the upper troposphere are larger at nighttime than at daytime by 1–2 times and 2–3 times, respectively. Both the peak value and the total release of latent heat over Yaan are significantly larger than those over the Tibetan Plateau, eastern China, and the western Pacific warm pool. These distinct local characteristics of the “rain city” Yaan are closely related to the interaction between the atmospheric circulation and the steep topography on the eastern edge of the Tibetan Plateau.     

青藏高原中东部夏季极端降水年代际变化特征

基于中国国家级地面气象站基本气象要素日值数据集得到的均一化降水序列,计算了夏季极端降水指数,分析青藏高原中东部1961—2014年夏季极端降水年代际变化趋势。结果表明:青藏高原中东部地区夏季降水量占全年总降水的50%以上,且夏季降水的变化趋势存在区域性差异,北部站点主要为增加趋势,南部增加和减少趋势的站点相当。夏季极端降水除西藏东部主要为减少趋势外,其他地区主要为增加趋势,且极强降水量的年代际变化趋势显著。大部分夏季极端降水指数的变化趋势在1970s发生转折,在此之前表现为减少的趋势,之后为增加趋势。通过Mann-Kendall趋势检验,在2000年之后强降水量和极强降水量出现突变。     

青藏高原东部冬季降水对北极涛动异常的响应

基于1979—2015年中国区域CN05.1格点降水以及全球降水气候中心(GPCC)降水等数据资料,采用回归、合成分析等方法,分析了青藏高原东部(简称高原)冬季降水的南、北区域性差异及其年际变化对北极涛动(AO)异常的响应.结果表明:(1)高原北部和南部冬季降水都与AO异常存在密切关系,但降水的年际变化并不一致,对AO...     

1967—2008年青藏高原汛期不同强度降水日数变化

利用1967—2008年青藏高原68个台站逐日降水资料,按照《气象规范》对不同等级降水的定义,对青藏高原汛期（5—9月）不同强度的降水日数进行分析。结果表明：1967—2008年青藏高原汛期总降水日数及各强度降水日数均呈现出由东南向西北递减的空间分布特征,降水总日数和小雨日数以减少趋势为主,最显著的区域位于青藏高原东北和东南部,中雨日数以增加为主,大雨日数变化趋势的区域差异显著。青藏高原汛期各强度降水日数存在明显的年际变化,总降水日数的变化主要受小雨日数影响。汛期降水各旬分布上,各强度降水日数主要集中在夏季（6—8月）,小雨日数越少（多）的旬内其占总降水日数的比例就越大（小）,中雨和大雨日数越少（多）的旬内占总降水日数的比例就越小（大）;小雨和中雨日数均在1978年发生突变,突变前后,青藏高原东南部小雨和中雨日数差异最为明显。     

1967—2008年青藏高原汛期不同强度降水日数变化

利用1967—2008年青藏高原68个台站逐日降水资料,按照《气象规范》对不同等级降水的定义,对青藏高原汛期（5—9月）不同强度的降水日数进行分析。结果表明：1967—2008年青藏高原汛期总降水日数及各强度降水日数均呈现出由东南向西北递减的空间分布特征,降水总日数和小雨日数以减少趋势为主,最显著的区域位于青藏高原东北...     

Impact of the anomalous thawing in the Tibetan Plateau on summer precipitation in China and its mechanism

The impact of the anomalous thawing of frozen soil in the late spring on the summer precipitation in China and its possible mechanism are analyzed in the context of the frozen soil thawing date data of the 50 meteorological stations in the Tibetan Plateau, and the NCEP/NCAR monthly average reanalysis data.Results show that the thawing dates of the Tibetan Plateau gradually become earlier from 1980 to 1999,which is consistent with the trend of global warming in the 20th century. Because differences in the thermal capacity and conductivity between frozen and unfrozen soils are larger, changes in the freezing/thawing process of soil may change the physical properties of the underlying surface, thus affecting exchanges of sensible and latent heat between the ground surface and air. The thermal state change of the plateau ground surface must lead to the thermal anomalies of the atmosphere over and around the plateau, and then further to the anomalies of the general atmospheric circulation. A possible mechanism for the impact of the thawing of the plateau on summer (July) precipitation may be as follows. When the frozen soil thaws early (late) in the plateau, the thermal capacity of the ground surface is large (small), and the thermal conductivity is small (large), therefore, the thermal exchanges between the ground surface and the air are weak (strong). The small (large) ground surface sensible and latent heat fluxes lead to a weak (strong) South Asian high, a weak (strong) West Pacific subtropical high and a little to south (north) of its normal position. Correspondingly, the ascending motion is strengthened (weakened) and precipitationin creases (decreases) in South China, while in the middle and lower reaches of the Changjiang River, the ascending motion and precipitation show the opposite trend.     

青藏高原气温和降水近期、中期与长期变化的预估及其不确定性来源

采用第五次耦合模式比较计划（Coupled Model Intercomparison Project Phase 5,CMIP5）高分辨率全球统计降尺度预估数据集,针对近期（2020—2039年）、中期（2040—2059年）和长期（2080—2099年）,以及全球1.5℃和2℃温升阈值,预估了青藏高原地区平均气温和降水、极端气温和极端降水的变化,定量估算了预估结果的不确定性来源。结果表明：（1）在RCP4.5和RCP8.5情景下,21世纪青藏高原地区平均气温和降水、极端气温和极端降水强度均显著增加,最长连续干旱天气减少。高原气候变化幅度超全球平均,至21世纪末,模式集合预估的气候变化幅度介于全球平均的1.5~3倍。（2）青藏高原地区受0.5℃额外增温的显著影响,年均气温、极端高温和极端低温均显著升高,平均及极端强降水均显著增加。（3）排放情景的选择对近期气候预估影响小,但对长期影响大。在相同排放情景下,内部变率主导了近期高原平均气温预估的不确定性,但至长期其贡献降至10%以下。模式和内部变率的不确定性对降水预估均有贡献,且都随时间减小,最大不确定性中心位于西部和北部边缘,噪声与信号比大于6。     

Quantifying recent precipitation change and predicting lake expansion in the Inner Tibetan Plateau

Lake expansion since the middle of the 1990s is one of the most outstanding environmental change events in the Tibetan Plateau (TP). This expansion has mainly occurred in the Inner TP, a vast endorheic basin with an area of about 708,000 km² and containing about 780 lakes larger than 1 km². The total lake area of the Inner TP has increased from 24,930 km² in 1995 to 33,741 km² in 2015. The variability of the lake area in the coming decades is crucial for infrastructure planning and ecology policy for this remote region. In this study, a lake mass balance model was developed to describe the lake area response to climate change. First, the model was used to inversely estimate the change in precipitation from the change in lake volume. The result shows that precipitation has increased by about 21?±?7% since the middle of the 1990s, as seen in GPCC global data set. Then, the lake size in the coming two decades was predicted by the model driven with either current climate or a projected future climate, showing the lake area would expand continuously, but at a lower rate than before. Both predictions yield a total lake area of 36150?±?500 km² in 2025 and a rise of average lake level by about 6.6?±?0.3 m from 1995 to 2025. However, the two predictions become disparate in the second decade (2026–2035), as the future climate is more warming and wetting than the current climate. It is noted that the prediction of lake expansion is robust for the entire inner TP lake system but not always applicable to individual subregions or specific lakes due to their spatiotemporal heterogeneity.     

青藏高原春季土壤湿度与夏季降水的关系

应用SVD方法对1981-2018年青藏高原春季土壤湿度和高原地区夏季降水进行诊断.结果表明:土壤湿度前两个模态累积协方差百分比达到了 61.15％,左右场展开序列的时间相关系数均为0.7 8,反映两场关系的主要特征.土壤湿度场表现出南北相的一致性,而降水场的一致性较差.第一模态说明青藏高原北部春季土壤湿度较大时,对应...     

三种再分析气温降水资料在青藏高原的适用性评价

基于青藏高原61个区域级气象站的气温降水地面观测数据,对CMFD(中国区域高分辨率地区驱动数据集)、CRA(全球大气和陆面再分析资料)以及MERRA-2(大气再分析资料)数据集的日、月、季节以及年气温、降水数据进行精度对比分析,评估3套数据的准确性以及在青藏高原的适用性,结果表明：(1)3套年平均气温资料70%的R_MSE<4℃,其中CMFD拟合精度最高,2/3的站点R_MSE<2℃;CMFD和CRA对年降水的拟合精度较高,MERRA-2低估了高原中部的年降水量。(2)CMFD对季节平均气温整体拟合结果最好,尤其是气温较高的夏季和秋季;CRA在降水较为集中的夏季和秋季拟合结果最接近观测值,而在降水较少的春季和冬季CMFD拟合结果最好。(3)CMFD对月平均气温拟合结果整体上最接近观测值;月降水拟合结果与季节降水结果相似,CMFD对降水偏少月份拟合结果较好,CRA在降水偏多月份最接近观测值。(4)对61个区域站进行日尺度平均气温和降水数据精度评估,发现CMFD和CRA拟合效果最好,CMFD拟合趋势一致性好。     

Simulation of summer precipitation diurnal cycles over the Tibetan Plateau at the gray-zone grid spacing for cumulus parameterization

Climate Dynamics - The Tibetan Plateau (TP) is often referred to as the “water tower of Asia” or the “Third Pole”. It remains a challenge for most global and regional models...     

Diurnal variations of circulation and precipitation in the vicinity of the Tibetan Plateau in early summer

A regional climate model (RCM) has been applied to simulate the diurnal variations of the Asian summer monsoon during the early summer period. The ERA40 reanalysis data and the TRMM precipitation data are used to evaluate the performance of the model. The 5-year simulations show that the RCM could simulate well the diurnal cycle of the monsoon circulation over the region. A strong diurnal variation of circulation over the Tibetan Plateau (TP) can be observed at the 500-hPa level, with strong convergence and upward motion in the late afternoon. The diurnal variation of the 500-hPa relative vorticity over the TP associated with the corresponding diurnal variation of convergence may lead to the formation of a prominent plateau-scale cyclonic circulation over the TP during the evening to midnight period. The simulated diurnal variation of precipitation over land is generally better than that over the ocean, particularly over the regions close to the TP such as the Bangladesh region in the southern flank of the TP, where the well-known nocturnal maximum in precipitation is well captured by the RCM. However, the late-afternoon maximum in precipitation over the Southeast Asia region is not well simulated by the RCM. The model results suggest that the diurnal variation of precipitation over the southern flank of the TP is associated with the strong diurnal variation in the circulation over the TP.     

青藏和伊朗高原热力异常与北疆夏季降水的关系

青藏高原和伊朗高原热力异常对其周边地区天气气候有重要影响,已有研究多关注东部季风区,而对干旱区关注较少.针对这一不足,利用美国国家环境预测中心/美国国家大气研究中心(NCEP/NCAR)再分析月平均资料和北疆43站降水资料,分析了1961-2007年5月青藏高原和伊朗高原地表感热异常与北疆夏季降水的关系.奇异值分解(SVD)分析发现,5月青藏高原地表感热与北疆夏季降水呈负相关,伊朗高原为正相关.青藏高原和伊朗高原感热异常的大尺度对比,要比仅考虑单一高原的感热异常与北疆夏季降水有更密切的联系.定义了一个热力差异指数来表征这种地表感热异常的对比程度,相关分析发现,当5月伊朗高原地表感热偏强,青藏高原地表感热偏弱时,500hPa中亚上空和贝加尔湖上空分别为异常气旋和反气旋环流,在二者共同作用下,新疆上空盛行异常的偏南气流,有利于低纬度的暖湿气流北上,形成有利于降水的环流形势,同时越赤道索马里急流偏强,低纬度水汽被接力输送至中亚和新疆地区,为降水的发生提供了有利的水汽条件.进一步分析发现,青藏高原热力异常主要影响中高层大气环流,伊朗高原则主要影响水汽通量输送.