Temporal and spatial variations of potential evaporation and the driving mechanism over Tibet during 1961–2001

Potential evaporation (PE) is the basic component of the global hydrological cycle and energy balance. This study detected the temporal and spatial variations of PE and related driving factors in Tibet, China, for the period 1961–2001, based on observed data recorded at 22 meteorological stations. The results showed that (1) Tibet experienced a statistically significant decrease of PE between 1961 and 2001, which started mainly in the 1980s, along with accelerated warming; (2) the mean annual PE in Tibet showed an east–west increasing trend, and the annual PE at most stations presented decreasing trends; (3) an inverse correlation of mean annual PE with elevation was detected (low–high decreasing trend), and the statistical equations to estimate PE were established based on longitude, latitude and elevation; and (4) PE in Tibet can be well expressed by related meteorological variables, with vapour pressure deficit the dominant factor in determining PE.

EDITOR Z. W. Kundzewicz ASSOCIATE EDITOR not assigned     

Spatial distribution and temporal variation of reference evapotranspiration during 1961–2006 in the Yellow River Basin,China

Abstract

To explore the spatial and temporal variations of the reference evapotranspiration (ET_ref) is helpful to understand the response of hydrological processes to climate changes. In this study, ET_ref was calculated by the Penman-Monteith method (P-M method) using air temperature, wind speed, relative humidity and sunshine hours at 89 meteorological stations during 1961–2006 in the Yellow River Basin (YRB), China. The spatial distribution and temporal variations of ET_ref were explored by means of the kriging method, the Mann-Kendall (M-K) method and the linear regression model, and the causes for the variations discussed. The contribution of main meteorological variables to the variations of ET_ref was explored. From the results we found that: (1) the spatial distributions of ET_ref display seasonal variation, with similar spatial patterns in spring, summer and autumn; (2) temporal trends for ET_ref showed large variation in the upper, middle and lower regions of the basin, most of the significant trends (P?=?0.05) were detected in the middle and lower regions, and, in particular, the upward and downward trends were mainly detected in the middle region and lower region of the basin, respectively; and (3) sensitivity analysis identified the most sensitive variable for ET_ref as relative humidity, followed by air temperature, sunshine hours and wind speed at the basin scale.

Citation Yang, Zhifeng, Liu, Qiang & Cui, Baoshan (2011) Spatial distribution and temporal variation of reference evapotranspiration during 1961–2006 in the Yellow River Basin, China. Hydrol. Sci. J. 56(6), 1015–1026.     

Supersubstorms during Storms of September 7–8, 2017

Geomagnetism and Aeronomy - The development of two supersubstorms (i.e., very intense substorms with an amplitude of more than 2000 nT) recorded in the main phase of two consecutive strong magnetic...     

Specific patterns of XCO2 observed by GOSAT during 2009–2016 and assessed with model simulations over China

Spatiotemporal patterns of column-averaged dry air mole fraction of CO2(XCO2)have not been well characterized on a regional scale due to limitations in data availability and precision.This paper addresses these issues by examining such patterns in China using the long-term mapping XCO2 dataset(2009-2016)derived from the Greenhouse gases Observing SATellite(GOSAT).XCO2 simulations are also constructed using the high-resolution nested-grid GEOS-Chem model.The following results are found:Firstly,the correlation coefficient between the anthropogenic emissions and XCO2 spatial distribution is nearly zero in summer but up to 0.32 in autumn.Secondly,on average,XCO2 increases by 2.08 ppm every year from2010 to 2015,with a sharp increase of 2.6 ppm in 2013.Lastly,in the analysis of three typical regions,the GOSAT XCO2 time series is inbetter agreement with the GEOS-Chem simulation of XCO2 in the Taklimakan Desert region(the least difference with bias 0.65±0.78 ppm),compared with the northern urban agglomerationregion(-1.3±1.2 ppm)and the northeastern forest region(-1.4±1.4 ppm).The results are likely attributable to uncertainty in both the satellite-retrieved XCO2 data and the model simulation data.     

Rapid improvement of PM_(2.5) pollution and associated health benefits in China during 2013–2017

Exposure to fine particulate matter(PM_(2.5)) is known to harm public health.In China,after implementation of aggressive emissions control measures under the Action Plan of Air Pollution Prevention and Control(2013-2017),air quality has significantly improved.In this work,we investigated changes in PM_(2.5) exposure and the associated health impacts in China for the period 2013-2017.We used an optimal estimator of PM_(2.5) combining in-situ observations,satellite measurements,and simulations from a chemical transport model to derive the spatial and temporal variations in PM_(2.5) exposure,and then used welldeveloped exposure-response functions to estimate the premature deaths attributable to PM_(2.5) exposure.We found that national population-weighed annual mean PM_(2.5) concentrations decreased from 67.4μgm~(-3) in 2013 to 45.5μgm~(-3) in 2017(32%reduction).This rapid decrease in PM_(2.5) pollution led to a 14% reduction in premature deaths due to long-term exposure.We estimated that,during 2013-2017,the premature deaths attributable to long-term PM_(2.5) exposure decreased from 1.2 million(95% CI:1.0,1.3;fraction of total mortality:13%) in 2013 to 1.0 million(95% CI:0.9,1.2;10%) in 2017.Despite the rapid decrease in annual mean PM_(2.5) concentrations,health benefits associated with reduced long-term exposure were limited,because for many cities,the PM_(2.5) levels remain at the portion where the exposure-response function is less steeper than that at the lowconcentration end.We also found that the deaths associated with acute exposure decreased by 61% during 2013-2017 due to rapid reduction in the number of heavily polluted days.Our results confirm that clean air policies in China have mitigated the air pollution crisis;however,continuous emissions reduction efforts are required to protect citizens from air pollution.     

Temporal characteristics of tropopause and lower stratosphere over Taiwan during 1990–1995

Temperature structures in the height range of 0–30 km over Pan Chiao (25°N, 121°E) in northern Taiwan were studied for the period 1990–1995 using radiosonde data. The purpose of this study is to see the annual variation of tropopause temperature and height and also to study local temperature perturbations caused by the series of volcanic eruptions at Mount Pinatubo in June 1991. While the annual variation in the tropopause height and temperature is clearly observed, we found a large increase in the temperature at the tropopause and in the lower stratospheric region during the year 1992. The tropopause is warm during the year 1992 and temperature increase at the tropopause is nearly 6°C in January 1992. The annual average temperature at the lower stratosphere during 1992 shows an increase of 2°C from the normal trend. The effects of Pinatubo are in general different in the troposphere and stratosphere.     

The changes of renewable water resources in China during 1956–2010

Water is a critical natural resource upon which all social and economic activities and ecosystem functions depend. With a surprising social and economic development in the past decades, water has become an important constraint for China’s sustainable development, and a matter concerning economic security, ecological security and national security of the country. Understanding the changes of water resources is greatly helpful in analyzing the impacts of climatic change, formulating plans for utilization and protection of water resources, and making water resource decisions. Based on China’s national water resources assessment, the Mann-Kendall’s test, and Morlet wavelet, we analyzed the changing trends and periods of China’s renewable water resources during 1956–2010. The results as following: (1) There is no significant change trend of water resources on the countrywide scale during the period 1956–2010, the total water resources show a slight increasing trend, and the national annual average water resources during the period 1991–2010 increased by 1% relative to that of the period 1961–1990. (2) The changes of water resources in different level-I water resource regions vary significantly. Annual average water resources of the Haihe River and Yellow River regions in the northern China decreased 19% and 17% respectively in the past 20 years. Water resource increased in Southern and Northwestern rivers regions, particularly in the Northwest rivers region, with the increasing amplitude by nearly 10% in the past 20 years. (3) The inter-annual variation of national water resource became larger in the past 20 years, as compared with that of the period 1961–1990. The coefficients of water resource variation increased in Northwestern and Southwestern rivers regions, while the inter-annual variation tended to decrease in the Haihe and the Yellow River regions where significant decline of water resources happened. (4) A 14-year quasi-periodicity of the national water resource variation was detected, overlapping with various periodicities of water resources of different level-I water resource regions. Remarkable uniformity exists between the first or secondary primary periodicity of water resource variation in adjacent level-I water resource regions.     

Climate change regionalization in China(1961–2010)

Since climatic condition is the important foundation for human subsistence and development and the key factor in sustainable development of economy and society, climate change has been a global issue attracting great attentions of politicians, scientists, governments, and the public alike throughout the world. Existing climate regionalization in China aims to characterize the regional differences in climate based on years of the mean value of different climate indexes. However, with the accelerating climate change nowadays, existing climate regionalization cannot represent the regional difference of climate change, nor can it reflect the disasters and environmental risks incurred from climate changes. This paper utilizes the tendency value and fluctuation value of temperature and precipitation from 1961 to 2010 to identify the climate change quantitatively, and completes the climate change regionalization in China(1961–2010) with county administrative regionalization as the unit in combination with China's terrain feature. Level-I regionalization divides China's climate change(1961–2010) into five tendency zones based on the tendency of temperature and precipitation, which are respectively Northeast China-North China warm-dry trend zone, East China-Central China wet-warm trend zone, Southwest China-South China dry-warm trend zone, Southeast Tibet-Southwest China wet-warm trend zone, and Northwest China-Qinghai-Tibet Plateau warm-wet trend zone; level-II regionalization refers to fourteen fluctuation regions based on level-I regionalization according to the fluctuation of temperature and precipitation.     

Climate-driven acceleration of glacier mass loss on global and regional scales during 1961–2016

During the past decades, glacier mass loss is becoming increasingly significant worldwide but knowledge about the acceleration is still limited despite its potentially profound impacts on sea level rise, water resources availability and glacial hazards. In this study, we analyzed the acceleration of glacier mass loss based on in-situ measurements and on the latest compilation dataset of direct and geodetic observations for the period 1961–2016. The results showed that the rate of glacier mass loss has increased worldwide during the past decades. At the global scale, the rate of glacier mass loss has been accelerating at 5.76±1.35 Gt a-2 as well as 0.0074±0.0016 m w.e.a-2 on mass balance(refer to the area-averaged mass change value) during the whole period. At regional scales, for mass change rate, the heavily glacierized regions excluding Antarctic and Subantarctic exhibited a larger acceleration compared to other regions. The highest acceleration of mass change was found in Alaska glaciers(1.33±0.47 Gt a-2) over the full period. As for mass balance, high acceleration occurred on the regions with small glaciers as well as on the heavily glacierized regions. Central Europe exhibited the highest acceleration(0.024±0.0088 m w.e.a-2) during 1961–2016. High level of consistency between the acceleration and temperature implies that climate warming had a significant effect on the accelerating of glacier mass loss. Moreover, acceleration of the contribution from the Greenland ice sheet(0.028 to0.070 mm a-2) and Antarctic ice sheet(0.023 to 0.058 mm a-2) to sea level rise exceeds acceleration of the contribution from global glaciers(0.019±0.013 mm a-2). These results will improve our understanding of the glacier retreat in response to climate change and provide critical information for improving mitigation strategies for impacts that may be caused by glacier melting.     

Regional difference of annual precipitation and discharge variation over west China during the last 50 years

Using annual precipitation and discharge data measured in the past five decades,this paper analyzed the regional differences over west China in terms of climate and discharge variations,and investigated the relationship between the regional characteristics and the activities of South and East Asian sum-mer monsoon. Results revealed that the precipitation and discharge in the upper reaches of the Yellow River (Central West China) have a negative correlation with those in Xinjiang (northwest China) and the Yarlung Zangbo River (the upper reaches of the Brahmaputra Rive,southwest China) regions. The geographical patterns of precipitation and discharge variations are different over west China,i.e. the regional climate displays the alteration of dry-wet-dry or wet-dry-wet from north to south in west China. The negative correlation of annual discharges between Xinjiang and the upper reaches of the Yellow River is found statistically significant in the decadal scale,and that between the Yarlung Zangbo River and the upper reaches of the Yellow River is found active in the interannual scale. The regional char-acteristics indicate that the discharge/precipitation variations in the upper reaches of the Yellow River are dominated by the East Asian summer monsoon while their variations in Xinjiang are affected by both the west wind and East Asian summer monsoon.     

Variability of aerosol properties during the 2007–2010 spring seasons over central Europe

Aerosol optical properties have been studied for spring seasons when increased values of PM10 are registered. Measurements of aerosol optical properties were taken by collocated lidar and sun-photometers at Belsk, Poland, and Minsk, Belarus. A significant increase of registered aerosol optical thickness (AOT) was found during episodes with elevated PM10 concentrations. An increase of AOT at 1020 nm amounted to 50% in the case of Minsk and 18% in the case of Belsk, while an increase of AOT at 400 nm was 66% and 33%, respectively. We noted an increase of Ångström exponent by 6% at both stations and no significant increase of single scattering albedo. The LIDAR measurements together with NAAPS model results and backtrajectory analysis suggest that both the biomass burning products and the Saharan dust are responsible for increased PM10 concentrations and large AOT values during spring time. The smoke aerosol is transported over Central Europe mainly in the boundary layer, increasing both PM10 concentration and AOT. The dust aerosol transported in the free troposphere slightly affects the AOT values only. Statistically significant correlation between PM10 concentration and AOT was found during reporting period.     

Study on spatial pattern of land-use change in China during 1995–2000

It is more and more acknowledged that land-use/cover dynamic change has become a key subject urgently to be dealt with in the study of global environmental change. Supported by the Landsat TM digital images, spatial patterns and temporal variation of land-use change during 1995 –2000 are studied in the paper. According to the land-use dynamic degree model, supported by the 1km GRID data of land-use change and the comprehensive characters of physical, economic and social features, a dynamic regionalization of land-use change is designed to disclose the spatial pattern of land-use change processes. Generally speaking, in the traditional agricultural zones, e.g., Huang-Huai-Hai Plains, Yangtze River Delta and Sichuan Basin, the built-up and residential areas occupy a great proportion of arable land, and in the interlock area of farming and pasturing of northern China and the oases agricultural zones, the reclamation of arable land is conspicuously driven by changes of production conditions, economic benefits and climatic conditions. The implementation of “returning arable land into woodland or grassland” policies has won initial success in some areas, but it is too early to say that the trend of deforestation has been effectively reversed across China. In this paper, the division of dynamic regionalization of land-use change is designed, for the sake of revealing the temporal and spatial features of land-use change and laying the foundation for the study of regional scale land-use changes. Moreover, an integrated study, including studies of spatial pattern and temporal process of land-use change, is carried out in this paper, which is an interesting try on the comparative studies of spatial pattern on change process and the change process of spatial pattern of land-use change.     

Monitoring temporal–spatial variations of AOD over the Yangtze River Delta,China

Aerosol can induce visibility reduction, affect radiation balance and modify cloud property on the environmental effect, and show the harmful effects on human health. Insight of aerosol becomes an integral task in the process of control measures for environmental pollution. The present study provided an analysis of temporal–spatial variations of aerosol optical depth (AOD) using the MOD04 level-2 in collection 6 (C6) with the deep blue retrieval algorithm from January 2005 to December 2015 over Yangtze River Delta (YRD) in China. The AOD validations between MODIS and Aerosol Robotic Network (AERONET) were estimated by the methods of regression, correlation. Then, the periodic features and trends of AOD and angstrom exponent (AE) were explored with the wavelet transformation (WT) procedure. Further, the variations of AOD and AE spatial distribution on multi-time scales (annual, monthly and season) were demonstrated. Meantime, the sources of AOD are discussed. It was found that the daily AOD from MODIS has a strong correlation relationship (slope?=?0.9838, r?=?0.84) with AERONET over YRD. The variations of both AOD and AE on time series have been distinct temporal periodic (12, 6 and 4 months) characteristics, and show the decreasing trends on annual and semi-annual periods. On annual, the AOD on spatial distribution is slowly declining from the northwest towards the southeast, and the AE on spatial distribution is gradually decreasing from the northwest to the southeast and from the land to the coast. The variations both inter-annual AOD and AE on spatial distribution show the inverse trends, respectively. On monthly, the means of AOD range from minimum 0.46 in January to maximum 0.90 in July, and the variations of spatial distribution mainly occur in the north parts of Yangtze River and some scattered areas with high terrain and south coast. The means of AE range from minimum 1.13 in October to maximum 1.58 in April, and the variations of spatial distribution are mainly found in the south of Henan, the north of Jiangsu, the coast belt and the riverside of Yangtze River and the high terrain regions. On seasonality, the means of AOD reaches its maximum 0.68 in summer and minimum 0.50 in winter, and the variations of spatial distribution mainly occur in the coast belt, the north parts of Hongze Lake and the south parts with high terrain. The means of AE reaches its maximum 1.48 in spring and minimum 1.25 in autumn, and the variations of spatial distribution were shown the similarity with that of monthly.     

Glacier runoff variation and its influence on river runoff during 1961–2006 in the Tarim River Basin, China

Using monthly precipitation and temperature data from national meteorological stations, 90 m resolution DEM and a digital vector map of modern glaciers from the Chinese Glacier Inventory, the glacier mass balance and glacier runoff in the Tarim River Basin (TRB), China, were estimated based on a monthly degree-day model for 1961–2006. The results suggest that the modified monthly degree-day model can simulate the long-term changes in glacier mass balance and glacier runoff, which have been confirmed by shor...     

Mechanism of the Spring Persistent Rains over southeastern China

The Spring Persistent Rains (SPR) in the areas to the south of middle and lower reaches of the Yangtze River or over southeastern China (SEC) is a unique synoptic and climatic phenomenon in East Asia. This study reveals a possible mechanism responsible for the climatic cause of SPR formation through climatic mean data analysis and sensitive numerical model experiments. SEC is located at the down-stream of the southwesterly velocity center (SWVC) which lies on the southeastern flank of the Tibetan Plateau (TP). As a result, there are strong southwesterly wind velocity convergence and moisture con-vergence over SEC. This is the immediate climatic cause of SPR formation. In spring, the seasonal evolution of the southwesterly velocity consists with the surface sensible heating over southeastern TP, indicating that the formation of SPR is related to not only the southwesterly wind of mechanical de-flected flow of TP, but also the southwesterly wind of thermal-forced cyclonic low circulation. Sensitive numerical experiments demonstrate that, without TP, both SWVC and the SPR rain belt will disappear. The southwesterly wind velocity increases almost linearly with the amount of the total diabatic heating with TP rising. Therefore, SWVC is the result of the mechanical forcing and thermal forcing of TP. All these strongly suggest that the presence of TP plays a primary role in the climatic formation of SPR.     

Characteristics of Changes in the Ozone Content in the Upper Stratosphere over Moscow during the Cold Half-Years of 2014–2015 and 2015–2016

Geomagnetism and Aeronomy - The results of ground-based microwave measurements of the stratospheric ozone profiles over Moscow during the cold half-years of 2014–2015 and 2015–2016 are...     

An observational analysis of the evolution of a mesoscale anti-cyclonic eddy over the Northern Bay of Bengal during May–July 2014

The Bay of Bengal (BoB) is a distinct oceanic region for mesoscale oceanic eddies. The sea level anomaly from the Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) help to identify an unusual anti-cyclonic eddy (ACE) over head BoB during May–July 2014. Two Indian moored buoys (BD08 and BD09) located over this region aided to study the subsurface thermohaline structures of the ACE. Compared to no-eddy environment, the temperature and salinity showed an increment of ~?3–4 °C and ~?1–2 PSU, respectively, during the ACE life period. The temperature and depth of the isothermal layer at genesis (peak) stages are increased to ~?30 °C (~?30.7 °C) and ~?20 m (30 m) when compared with no-eddy conditions (28.2 °C and 10 m). The thermocline depth is deepened to 75 m at the peak stage, while it is 50 m in no-eddy condition. A temperature difference of 3 °C between no-eddy and peak stages of ACE is observed up to 50 m. The ocean heat content (OHC) at BD08 (BD09) during genesis and peak stages has increased by ~?72% (~?50%) and ~?247% (~?181%), respectively, when compared with no-eddy conditions. Moreover, the MOHC also shows a similar increment of ~?125% (~?123%) and ~?258% (~?284%), respectively. A noticeable influence is seen in turbulent fluxes and lower atmospheric variables during eddy life. This study highlights the capability of moored buoys in understanding the subsurface thermohaline features of the eddies over northern BoB.