Surface mean temperature from the observational stations and multiple reanalyses over the Tibetan Plateau

The Tibetan Plateau (TP), also called the “Third pole”, is sensitive to climate change due to extensive areas at high elevation presently dominated by snow and ice. In this study, observed surface temperature trends at 150 stations over the TP during 1979–2018 are analyzed and compared with surface temperatures from multiple reanalyses (NCEP1, NCEP2, ERA-Interim, MERRA, JRA55). Observed warming at the stations has a mean annual rate of 0.46 °C/decade during 1979–2018. Although all reanalyses underestimate observed temperatures (cold bias), most reproduce much of the inter-decadal variations of surface temperature shown in the observations. Absolute errors of mean surface temperature (reanalysis minus observation) are closely correlated with elevation errors, suggesting that parts of the cold bias can be interpreted by elevation errors of reanalysis. After elevation-temperature correction, about half of the cold bias is typically eliminated, more for both ERA-Interim and JRA55. Compared with the observations, corrected NCEP2 surface temperatures still have larger cold biases, and fail to capture the overall warming over the TP. Since the elevation-temperature correction fails to improve trend magnitudes even when a significant proportion of the bias has been removed, this suggests that a more sophisticated modeling of the lapse rate in each reanalysis is required to realistically model warming trends across complex topography.

     

地表反照率与高原夏季风爆发关系分析

利用2000～2016年MODIS地表反照率和ECMWF/ERA-Interim再分析资料,选取有代表性的高原季风指数DPMI,统计分析了青藏高原地表反照率与高原季风之间的联系,结果表明:1)11月高原地表反照率大小与次年高原夏季风爆发存在密切关系:11月高原地表反照率偏低(高),次年4月高原夏季风爆发偏早(晚),强度偏强(弱)。2)可能的影响机制为:当前期11月高原地表反照率偏低时,后期高原主体对大气的感热加热信号更强,从而引起4月高原上空近地面层上升运动明显加强,这有利于热量向高空传输,导致对流层加热作用加强,高原上空对流层温度偏高,使得高原季风环流系统加强,最终导致高原季风季节变化相应提前;反之亦然。     

On the Contrasting Decadal Changes of Diurnal Surface Temperature Range between the Tibetan Plateau and Southeastern China during the 1980s–2000s

The diurnal surface temperature range(DTR) has become significantly smaller over the Tibetan Plateau(TP) but larger in southeastern China, despite the daily mean surface temperature having increased steadily in both areas during recent decades.Based on ERA-Interim reanalysis data covering 1979–2012, this study shows that the weakened DTR over TP is caused by stronger warming of daily minimum surface temperature(Tmin) and a weak cooling of the daily maximum surface temperature(Tmax); meanwhile, the enhanced DTR over southeastern China is mainly associated with a relatively stronger/weaker warming of Tmax/Tmin. A further quantitative analysis of DTR changes through a process-based decomposition method—the Coupled Surface–Atmosphere Climate Feedback Response Analysis Method(CFRAM)—indicates that changes in radiative processes are mainly responsible for the decreased DTR over the TP. In particular, the increased low-level cloud cover tends to induce the radiative cooling/warming during daytime/nighttime, and the increased water vapor helps to decrease the DTR through the stronger radiative warming during nighttime than daytime. Contributions from the changes in all radiative processes(over-2?C) are compensated for by those from the stronger decreased surface sensible heat flux during daytime than during nighttime(approximately 2.5?C), but are co-contributed by the changes in atmospheric dynamics(approximately-0.4?C) and the stronger increased latent heat flux during daytime(approximately-0.8?C). In contrast, the increased DTR over southeastern China is mainly contributed by the changes in cloud, water vapor and atmospheric dynamics. The changes in surface heat fluxes have resulted in a decrease in DTR over southeastern China.     

Relationship between the increase temperature and variation of ozone level over the Antarctica and Tibetan plateau in spring

Based on the ozone and aerological sounding data at Syowa Station (69o 00'S, 39o35'E), Antarctica during 1966－1979 and Lhasa Station (39o40'N, 91o08'E), Tibetan Plateau during 1979－1983, the processes of temperature increase in spring over the Tibetan Plateau and the Antarctica are compared in this paper, and the relationship between the increase of air temperature and variation of total ozone and ozone partial pressure is analyzed. It is found that: (1) The process of temperature increase over the Tibetan Plateau is quite different from that over the Antarctica in spring. This is a proof that the heating effects of their ground surface on the atmosphere are of great difference; (2) Sudden increase of total ozone is always associated with sudden warming in the stratosphere over the Antarctica, but sudden decrease of total ozone is associated with sudden warming in the troposphere over the Tibetan Plateau in spring; and (3) There is a good positive correlation, with a correlation coefficient of about 0.85, between the temperature increase and variation of ozone partial pressure in the stratosphere over the Antarctica in spring.     

利用多种再分析资料对比分析青藏高原夏季大气水汽含量变化情况

利用ERA-Interim、MERRA和NCEP/NCAR三套再分析资料,分析1979~2014年夏季青藏高原大气水汽含量的时空变化特征,同时对比了各套资料异同点,结果表明:(1) ERA-Interim和MERRA资料均显示出夏季青藏高原大气水汽含量呈现显著的上升趋势,在1994~1995年前后发生明显突变,大气水汽含量由偏低时期向偏高时期转变;而NCEP/NCAR资料并没有出现类似的显著上升趋势和突变年份;ERA-Interim资料与MERRA资料的夏季青藏高原湿池指数之间的相关性明显强于NCEP/NCAR资料与它们任何一个之间的相关性。(2)夏季青藏高原大气水汽含量呈现出自高原东南边缘地区向西北部递减的分布形式。其中,MERRA与ERA-Interim资料显示的水汽含量分布更为相似,而NCEP/NCAR资料反映的水汽含量在高原中部往北递减不明显,湿度中心较为分散。(3)从空间分布上,MERRA与ERA-Interim资料显示青藏高原大部分地区夏季水汽含量均呈显著的增加趋势,而NCEP/NCAR资料仅在高原东北部小部分区域存在显著的增加趋势。(4)从夏季青藏高原大气水汽含量的年际变化特征分析来看,ERA-Interim和MERRA资料相对于NCEP/NCAR资料也更为接近。      

The Wave Train Characteristics of Teleconnection Caused by the Thermal Anomaly of the Underlying Surface of the Tibetan Plateau. Part Ⅰ: Data Analysis

探讨了前期青藏高原下垫面热力结构异常对后期长江中下游地区降水的影响。通过资料分析揭示出长江中下游地区夏季降水异常前期冬、春季青藏高原下垫面三维热力结构强信号特征,即长江中下游夏季旱涝前期高原南部和北部各层次的地温距平呈反位相分布。从地面0cm到地下320 cm的地温距平分布为:涝年高原偏南部(30°N以南)为正,中部和北部(30°N以北)为负,旱年时相反。其中地温距平的大值区在 40 cm到160 cm层之间。同时揭示了北半球环流型对青藏高原下垫面热力异常可能产生遥响应,并形成季尺度低频波的传播,从而影响长江中下游地区后期的降水,反映了遥相关是区域性旱涝形成的一个动力机制。资料分析结果表明前期青藏高原下垫面三维热力结构异常是后期长江中下游地区降水异常的重要原因之     

Climate-induced changes in river water temperature in North Iberian Peninsula

With the surface air temperature (SAT) data at 37 stations on Central Yunnan Plateau (CYP) for 1961–2010 and the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data, the temporal-spatial patterns of the SAT trends are detected using Sen’s Nonparametric Estimator of Slope approach and MK test, and the impact of urbanization on surface warming is analyzed by comparing the differences between the air temperature change trends of urban stations and their corresponding rural stations. Results indicated that annual mean air temperature showed a significant warming trend, which is equivalent to a rate of 0.17 °C/decade during the past 50 years. Seasonal mean air temperature presents a rising trend, and the trend was more significant in winter (0.31 °C/decade) than in other seasons. Annual/seasonal mean air temperature tends to increase in most areas, and higher warming trend appeared in urban areas, notably in Kunming city. The regional mean air temperature series was significantly impacted by urban warming, and the urbanization-induced warming contributed to approximately 32.3–62.9 % of the total regional warming during the past 50 years. Meantime, the urbanization-induced warming trend in winter and spring was more significant than that in summer and autumn. Since 1985, the urban heat island (UHI) intensity has gradually increased. And the urban temperatures always rise faster than rural temperatures on the CYP.     

青藏高原两类对流层顶频率的季节分布特征及其与同纬度地区的差异

基于1979~2014年ERA-Interim逐日再分析温度资料,依据温度递减率插值法,计算出北半球两类对流层顶(热带对流层顶和极地对流层顶)频率数据。对比分析了青藏高原与同纬度地区两类对流层顶频率在季节变化上的差异,并讨论了青藏高原两类对流层顶频率分布与高空温度的关系。结果表明:1)依据温度递减率插值法计算出的再分析两类对流层顶频率可以反映青藏高原两类对流层顶频率季节变化特征:热带对流层顶全年频率高,冷、暖季节差异不明显;极地对流层顶盛夏频率极低,冷、暖季节差异明显。与极地对流层顶频率相比,青藏高原热带对流层顶频率的可信度更高。2)青藏高原和同纬度地区热带(极地)对流层顶频率在暖季增加(减少),在冷季减少(增加)。相比同纬度地区,青藏高原热带(极地)对流层顶频率在冬季偏少(多),其他季节偏多(少)。青藏高原两类对流层顶频率等值线的梯度更大,表明青藏高原对流层顶更易断裂。3)青藏高原两类对流层顶频率与高空温度关系密切。青藏高原对流层中上层(平流层下部)温度升高(降低),有利于青藏高原热带对流层顶频率增加,极地对流层顶频率减少,反之亦然。     

青藏高原不同季节地表温度变化特征分析

基于欧洲中尺度气象预报中心(ECMWF)提供的ERA-Interim地表温度,利用经验正交函数(EOF)等方法,分析了青藏高原四季地表温度的时空变化特征.结果发现:青藏高原春、夏、冬季地表温度变化以整体型为主,并且大部地区地表温度呈现升高的趋势;秋季地表温度略有下降趋势,并且以东部和西部地表温度的反向型异常变化最为显著.此外还发现,青藏高原不同季节地表温度的异常变化具有一定的联系,其中整体型变化可以持续3个季节.     

青藏高原前期冬春季地面热源与我国夏季降水关系的初步分析

首先对青藏高原地表热通量再分析资料与自动气象站(AWS)实测资料进行对比, 结果表明: 相对于美国国家环境预报中心和国家大气中心20世纪90年代研制的NCEP/NCAR(Kalnay 等1996)和NCEP/DOE (Kanamitsu 等2002) 再分析资料, ECMWF(Uppala 等2004)资料在高原地区的地表热通量具有较好的代表性。进一步利用奇异值分解(SVD)方法分析了ECMWF资料反映的高原地面热源与我国夏季降水的关系, 发现前期青藏高原主体的冬季地面热源与长江中下游地区夏季降水量呈负相关, 与华北和东南沿海地区的夏季降水量呈正相关。而长江中下游地区夏季降水量还与春季高原南部的地面热源存在负相关、与高原北部的地面热源存在正相关。高原冬、春季地面热源场的变化是影响我国夏季降水的重要因子。     

1981—2010年青藏高原地区气温变化与高程及纬度的关系

基于青藏高原地区高质量、均一化的气象站点观测资料,研究1981—2010年青藏高原地区气温变化趋势特征。结果表明:1981—2010年青藏高原地区整体呈升温趋势,平均升温率为0.40℃/10a,冬春季升温率大于夏秋季节,以三江源区、西藏中西部和青海北部升温趋势最为显著。青藏高原地区年和冬、春、秋三季的升温率随海拔高度的升高而增大,海拔每升高1000 m,站点年平均气温倾向率增加0.1℃/10a,冬季更为显著。青藏高原地区夏季气温倾向率的空间分布具有显著的经向差异,纬度每增加10°,气温倾向率增加0.33℃/10a。     

Climatic timescale temperature and precipitation increases on long Island,New York

Abstract

Global warming due to increased greenhouse gases is believed to result in not only higher surface temperatures but also an acceleration of the hydrological cycle leading to increased precipitation. Although climate models consistently predict increases in global temperatures due to increasing greenhouse gases and the accompanying global warming, observations at the climatic timescales necessary to confirm the models are rare. Multidecadal studies at global and regional scales are necessary to determine whether the presently observed changes in temperature and precipitation are due to short‐term fluctuations or long‐term trends. In this study, we address this issue by examining changes in temperature and precipitation on Long Island, New York over a 74‐year time period (1931 to 2004) using a network of rain gauges and temperature measurements. The mean annual temperature on Long Island has increased at a rate of 0.05°C per decade, which is less than that of observed global values and is most likely due to the urban warming effects of New York City, not large‐scale climate change. The mean total annual precipitation has increased at a rate of 0.71 cm per decade during the study period, which is consistent with global observations. Intra‐annual temperature fluctuations are decreasing at a rate of 0.36% per decade, while precipitation variations are increasing at a rate of 0.91% per decade. Empirical orthogonal function analysis indicates that variations in temperature and precipitation on Long Island are dominated by island‐wide fluctuations that are directly related to the North Atlantic Oscillation, the Arctic Oscillation, and the El Niño Southern Oscillation.     

青藏高原热状况对南亚高压活动的影响

本文分析了青藏高原下垫面与高原上空热状况变化的异同及其二者与南亚高压的关系。指出青藏高原下垫面热状况与高原上空热状况年际变化的一致性及月际变化的差异——青藏高原下垫面从2月就开始大幅度增温,而高原上空5月才开始突发性增温。高原下垫面降温幅度最大的月份出现在11月,高原上空则出现在10月。分析还指出,青藏高原下垫面热状况与南亚高压南北振荡,青藏高原上空热状况与南亚高压东西振荡有密切关系。并且前期青藏高原上空热状况较高原下垫面热状况对南亚高压的预报更具有指示意义。     

Using a global climate model to evaluate the influences of water vapor, snow cover and atmospheric aerosol on warming in the Tibetan Plateau during the twenty-first century

We examine trends in climate variables and their interrelationships over the Tibetan Plateau using global climate model simulations to elucidate the mechanisms for the pattern of warming observed over the plateau during the latter half of the twentieth century and to investigate the warming trend during the twenty-first century under the SRES A1B scenario. Our analysis suggests a 4°C warming over the plateau between 1950 and 2100. The largest warming rates occur during winter and spring. For the 1961–2000 period, the simulated warming is similar to the observed trend over the plateau. Moreover, the largest warming occurs at the highest elevation sites between 1950 and 2100. We find that increases in (1) downward longwave radiation (DLR) influenced by increases in surface specific humidity (q), and (2) absorbed solar radiation (ASR) influenced by decreases in snow cover extent are, in part, the reason for a large warming trend over the plateau, particularly during winter and spring. Furthermore, elevation-based increases in DLR (influenced by q) and ASR (influenced by snow cover and atmospheric aerosols) appear to affect the elevation dependent warming trend simulated in the model.     

青藏高原气温变化趋势与同纬度带其他地区的差异以及臭氧的可能作用

利用台站探空观测资料和卫星观测资料,分析了1979—2002年青藏高原上空温度的变化趋势。结果表明:高原地区上空平流层低层和对流层上层的温度与对流层中低层具有反相变化趋势。平流层低层和对流层上层降温,温度出现降低趋势,降温幅度无论是年平均还是季节平均都比全球平均降温幅度更大。高原上空对流层中低层增温,温度显示出增加的趋势,并且比同纬度中国东部非高原地区有更强的增温趋势。对1979—2002年卫星臭氧资料的分析表明,青藏高原上空臭氧总量在每个季节都呈现出明显的下降趋势,并且比同纬度带其他地区下降得更快。由于青藏高原上空臭氧有更大幅度的减少,造成高原平流层对太阳紫外辐射吸收比其他地区更少,使进入对流层的辐射更多,从而导致高原上空平流层低层和对流层上层降温比其他地区更强,而对流层中低层增温更大。因此,高原上空比其他地区更大幅度的臭氧总量减少可能是造成青藏高原上空与同纬度其他地区温度变化趋势差异的一个重要原因。     

1971-2012年青藏高原春季风速的年际变化及对气候变暖的响应

利用青藏高原73个气象台站的观测资料和日本气象厅JRA-55再分析资料,通过引入年际增量和动能收支方程,分析了1971-2012年高原春季风速的年际变化特征及其对气候变暖的响应。结果表明,在气候变暖的背景下高原风速呈减弱的趋势,随着变暖趋缓风速的变化也趋于平稳。春季高原风速与气温的线性趋势是相反的,但在年际尺度上二者表现出同位相的变化,当青藏高原、中南半岛和印度半岛的地面气温偏高,北亚和东亚地区的地面气温偏低时,有利于高原地面风速增大,反之风速减小。20世纪末青藏高原及其周边地区的升温速率表现为北快南缓,高原南、北侧气温差异减小,而东、西向的气温差异增大,风速趋于减弱;21世纪初高原中部及其南侧地区以升温为主,高原东北侧和东亚地区以降温为主,南、北向气温差异较小,高原风速的变化也趋于平缓,东、西向气温差异有减小的趋势,对应高原东部风速有所增大。青藏高原及其邻近地区的热力差异及其变化速率的不均衡改变了对流层大气的斜压性,进而通过两种途径影响青藏高原的风速,一方面是近地面层气压梯度力的直接作用,另一方面是高层动能向低层的输送。此外,还指出JRA-55再分析风速资料比ERA-Interim和NCEP/NCAR资料在青藏高原的适用性更强。      

Improved estimation of average warming trend of China from 1951–2010 based on satellite observed land-use data

This paper provides new evidence of regional warming trends from local Chinese observations covering the period 1951–2010. We used satellite-derived land data and weighted urban and rural temperature records (a weighted method) and estimate the regional warming trend, which involves natural climate change and human impact. The annual warming rate over the whole of China is 0.21?±?0.02 °C/decade. The seasonal warming is 0.30?±?0.05 °C/decade (Winter), 0.24 °C?±?0.03 °C/decade (Spring); 0.16?±?0.02 °C/decade (Summer) and 0.21?±?0.03 °C/decade (Autumn). The mean warming trend is lower than previous estimates (e.g. NMIC, CRU-China) using un-weighted methods (arithmetic average of all records). The warming difference between the weighted and un-weighted accounts for 27 % (12 %) of the NMIC (CRU-China) un-weighted estimate on the total warming. This indicates that previous estimations overestimated a regional warming trend. The differences can be partly attributed to the weighting of the urban effect which is taken into consideration in this study, resulting in a much slower temperature increase. Spatially, the northern part of China shows a larger difference than the south especially for winter and spring. We argue that it is of importance to take into consideration the influence of urban land-use change to improve the physical understanding of surface warming in China over past decades.     

Evaluation of the trend uncertainty in summer ozone valley over the Tibetan Plateau in three reanalysis datasets

Trend uncertainty in the ozone valley over the Tibetan Plateau (OVTP) and the South Asian high (SAH) during 1979–2009 in ERA-Interim (interim reanalysis data from the ECMWF), JRA-55 (55-yr reanalysis data from the Japan Meteorological Agency), and NCEP-CFSR (Climate Forecast System Reanalysis) datasets was evaluated. The results showed that the NCEP-CFSR OVTP became strong in the summers of 1979–2009, whereas it became weak according to ERA-Interim and JRA-55. Satellite data merged with TOMS (Total Ozone Mapping Spectrometer) and OMI (Ozone Monitoring Instrument) agreed with the OVTP trend of NCEP-CFSR. The OVTP strengthening in NCEP-CFSR may have been caused by SAH intensification, a rising tropopause, and increasing ozone over non-TP (non-Tibetan Plateau) areas (27°–37°N, < 75°E and > 105°E). Analogously, the OVTP weakening in ERA-Interim and JRA-55 may have been affected by weakening SAH, descending tropopause, and decreasing non-TP ozone.     

基于多种资料的青藏高原地表感热的对比分析

青藏高原地表感热通量是高原热源的主要分量之一,对高原局地天气系统、我国天气气候以及亚洲季风等都有着重要影响。选取1980～2016年青藏高原的站点资料和ERA-Interim、NCEP1、NCEP2再分析资料,计算高原地表感热通量的分布状况和时间变化特征并对不同资料得到的结果进行比较分析,结果表明:4种资料在夏季的空间分布、年际变化,高原中部的年际变化,以及长期变化趋势上具有较好的一致性,其中ERA-Interim感热资料较优于其他两种再分析资料。青藏高原的地表感热通量分布呈西高东低的特征,年均最大值出现在柴达木盆地,最小值位于贡山;区域平均值春季最大,冬季最小。感热逐月变化呈单峰型分布,不同分区的年际变化均在2001年或2003年由减弱趋势转变为增强趋势。      

Underestimation of the Warming Trend over the Tibetan Plateau during 1998–2013 by Global Land Data Assimilation Systems and Atmospheric Reanalyses

Accurate surface air temperature (T2m) data are key to investigating eco-hydrological responses to global warming. Because of sparse in-situ observations, T2m datasets from atmospheric reanalysis or multi-source observation-based land data assimilation system (LDAS) are widely used in research over alpine regions such as the Tibetan Plateau (TP). It has been found that the warming rate of T2m over the TP accelerates during the global warming slowdown period of 1998–2013, which raises the question of whether the reanalysis or LDAS datasets can capture the warming feature. By evaluating two global LDASs, five global atmospheric reanalysis datasets, and a high-resolution dynamical downscaling simulation driven by one of the global reanalysis, we demonstrate that the LDASs and reanalysis datasets underestimate the warming trend over the TP by 27%–86% during 1998–2013. This is mainly caused by the underestimations of the increasing trends of surface downward radiation and nighttime total cloud amount over the southern and northern TP, respectively. Although GLDAS2.0, ERA5, and MERRA2 reduce biases of T2m simulation from their previous versions by 12%-94%, they do not show significant improvements in capturing the warming trend. The WRF dynamical downscaling dataset driven by ERA-Interim shows a great improvement, as it corrects the cooling trend in ERA-Interim to an observation-like warming trend over the southern TP. Our results indicate that more efforts are needed to reasonably simulate the warming features over the TP during the global warming slowdown period, and the WRF dynamical downscaling dataset provides more accurate T2m estimations than its driven global reanalysis dataset ERA-Interim for producing LDAS products over the TP.