Construction and Application of a Regional Kilometer-Scale Carbon Source and Sink Assimilation Inversion System(CCMVS-R)

CO_(2)is one of the most important greenhouse gases(GHGs)in the earth’s atmosphere.Since the industrial era,anthropogenic activities have emitted excessive quantities of GHGs into the atmosphere,resulting in climate warming since the 1950s and leading to an increased frequency of extreme weather and climate events.In 2020,China committed to striving for carbon neutrality by 2060.This commitment and China’s consequent actions will result in significant changes in global and regional anthropogenic carbon emissions and therefore require timely,comprehensive,and objective monitoring and verification support(MVS)systems.The MVS approach relies on the top-down assimilation and inversion of atmospheric CO_(2)concentrations,as recommended by the Intergovernmental Panel on Climate Change(IPCC)Inventory Guidelines in 2019.However,the regional high-resolution assimilation and inversion method is still in its initial stage of development.Here,we have constructed an inverse system for carbon sources and sinks at the kilometer level by coupling proper orthogonal decomposition(POD)with four-dimensional variational(4DVar)data assimilation based on the weather research and forecasting-greenhouse gas(WRF-GHG)model.Our China Carbon Monito ring and Verification Support at the Regional level(CCMVS-R)system can continuously assimilate information on atmospheric CO_(2)and other related information and realize the inversion of regional and local anthropogenic carbon emissions and natural terrestrial ecosystem carbon exchange.Atmospheric CO_(2)data were collected from six ground-based monito ring sites in Shanxi Province,China to verify the inversion effect of regio nal anthropogenic carbon emissions by setting ideal and real experiments using a two-layer nesting method(at 27 and 9 km).The uncertainty of the simulated atmospheric CO_(2)decreased significantly,with a root-mean-square error of CO_(2)concentration values between the ideal value and the simulated after assimilation was close to 0.The total anthropogenic carbon emissions in Shanxi Province in 2019 from the assimilated inversions were approximately 28.6%(17%-38%)higher than the mean of five emission inventories using the bottomup method,showing that the top-down CCMVS-R system can obtain more comprehensive information on anthropogenic carbon emissions.

Connections between the Eurasian Teleconnection and Concurrent Variation of Upper-level Jets over East Asia

The variation of the East Asian jet stream （EAJS） associated with the Eurasian （EU） teleconnection pattern is investigated using 60-yr NCEP-NCAR daily reanalysis data over the period 1951-2010.The EAJS consists of three components：the polar front jet （PFJ）; the plateau subtropical jet （PSJ）; and the ocean subtropical jet （OSJ）.Of these three jets over East Asia,the EU pattern exhibits a significant influence on the PFJ and OSJ.There is a simultaneous negative correlation between the EU pattern and the PFJ.A significant positive correlation is found between the EU pattern and the OSJ when the EU pattern leads the OSJ by about 5 days.There is no obvious correlation between the EU pattern and the PSJ.The positive EU phase is accompanied by a weakened and poleward-shifted PFJ,which coincides with an intensified OSJ.A possible mechanism for the variation of the EAJS during different EU phases is explored via analyzing the effects of 10-day high-and low-frequency eddy forcing.The zonal wind tendency due to high-frequency eddy forcing contributes to the simultaneous negative correlation between the EU pattern and the PFJ,as well as the northward/southward shift of the PFJ.High-and low-frequency eddy forcing are both responsible for the positive correlation between the EU pattern and the OSJ,but only high-frequency eddy forcing contributes to the lagged variation of the OSJ relative to the EU pattern.The negative correlation between the EU pattern and winter temperature and precipitation anomalies in China is maintained only when the PFJ and OSJ are out of phase with each other.Thus,the EAJS plays an important role in transmitting the EU signal to winter temperature and precipitation anomalies in China.

New Method for Estimating Daily Global Solar Radiation over Sloped Topography in China

A new scheme for the estimation of daily global solar radiation over sloped topography in China is developed based on the Iqbal model C and MODIS cloud fraction. The effects of topography are determined using a digital elevation model. The scheme is tested using observations of solar radiation at 98 stations in China, and the results show that the mean absolute bias error is 1.51 MJ m-2 d-1 and the mean relative absolute bias error is 10.57%. Based on calculations using this scheme, the distribution of daily global solar radiation over slopes in China on four days in the middle of each season （15 January, 15 April, 15 July and 15 October 2003） at a spatial resolution of 1 km×1 km are analyzed. To investigate the effects of topography on global solar radiation, the results determined in four mountains areas （Tianshan, Kunlun Mountains, Qinling, and Nanling） are discussed, and the typical characteristics of solar radiation over sloped surfaces revealed. In general, the new scheme can produce reasonable characteristics of solar radiation distribution at a high spatial resolution in mountain areas, which will be useful in analyses of mountain climate and planning for agricultural production.

On the Relationship between the Winter Eurasian Teleconnection Pattern and the Following Summer Precipitation over China

The Eurasian teleconnection pattern （EU） is an important low-frequency pattern with well-known impacts on climate anomalies in Eurasia. The difference of low-level v-winds in several regions in the Eurasian mid-high latitudes is defined as the EU index （EUIv）. In this study, the relationship between the winter EUIv and precipitation in the following summer over China is investigated. Results show that there is a significant positive （negative） correlation between the winter EUIv and the following summer precipitation over North China （the Yangtze River-Huaihe River basins）. Meanwhile, an interdecadal variability exists in the interannual relationship, and the correlation has become significantly enhanced since the early 1980s. Thus, the proposed EUIv may have implications for the prediction of summer precipitation anomalies over China. In positive winter EUIv years, three cyclonic circulation anomalies are observed--over the Ural Mountains, the Okhotsk Sea, and the subtropical western North Pacific. That is, the Ural blocking and Okhotsk blocking are inactive, zonal circulation prevails in the mid-high latitudes, and the western Pacific subtropical high tends to be weaker and locates to the north of its normal position in the following summer. This leads to above-normal moisture penetrating into the northern part of East China, and significant positive （negative） precipitation anomalies over North China （the Yangtze River-Huaihe River basins）, and vice versa. Further examination shows that the SST anomalies over the Northwest Pacific and subtropical central North Pacific may both contribute to the formation of EUIv-related circulation anomalies over the western North Pacific.

Assessing the Ecological Quality of Nanjing during Its Urbanization Process by Using Satellite,Meteorological,and Socioeconomic Data

Assessing the ecological status of different districts within a city undergoing urbanization is challenging given their complex surface types and fast pace of development.In this study,we utilized satellite data obtained from Landsat5/TM(Thematic Mapper)and Landsat 8/OLI(Operational Land Imager)images in conjunction with meteorological and socioeconomic data to construct a remote sensing ecological index(RSEI)for monitoring the ecological quality of Nanjing,Jiangsu Province.A higher RSEI value corresponded to better ecological quality.Five ratings were associated with RSEI values of city districts:very poor,poor,average,good,and excellent.In Nanjing,the percentage of areas evidencing good RSEI ratings decreased from 55.9%in 2000 to 48.0%in 2018,whereas there was a slight increase in areas with very poor RSEI ratings during this period.Of the 11 city districts,16.8%,21.8%,and 61.4%respectively evidenced the increasing,decreasing,and stable ecological quality relative to their quality in 2000.Of the11 administrative districts in Nanjing,the main urban districts evidenced increased RSEI values in 2018 compared with those in 2000,with the improved areas exceeding the ones that had deteriorated in these districts.However,the ecological quality of new urban and ed because of the urban expansion,with areas that had deteriorated exceeding the improved ones.Of the three protected ecological zones,the quality of Zijin Mountain National Forest Park was considerably better than that of Laoshan and Jiangxinzhou.Overall,the urbanization rate and RSEI evidenced a high negative correlation coefficient value(-0.76).The urbanization process of Nanjing induced a declining trend for the ecological quality,indicating the need of strong protection measures for the maintenance or improvement of its ecological environment.

Classification of yearly extreme precipitation events and associated flood risk in the Yangtze-Huaihe River Valley

Fifty cases of regional yearly extreme precipitation events （RYEPEs） were identified over the Yangtze-Huaihe River Valley （YHRV） during 1979-2016 applying the statistical percentile method. There were five types of RYEPEs, namely Yangtze Meiyu （YM-RYEPE）, Huaihe Meiyu （HM-RYEPE）, southwest-northeast-oriented Meiyu （SWNE-RYEPE） and typhoon I and II （TC-RYEPE） types of RYEPEs. Potential vorticity diagnosis showed that propagation trajectories of the RYEPEs along the Western Pacific Subtropical High and its steering flow were concentrated over the southern YHRV. As a result, the strongest and most frequently RYEPEs events, about 16-21 cases with average rainfall above 100 mm, occurred in the southern YHRV, particularly in the Nanjing metropolitan area. There have been 14 cases of flood-inducing RYEPEs since 1979, with the submerged area exceeding 120 km2 as simulated by the FloodArea hydraulic model, comprising six HM-RYEPEs, five YM- RYEPEs, two TC-RYEPEs, and one SWNE-RYEPE. The combination of evolving RYEPEs and rapid expansion of urban agglomeration is most likely to change the flood risk distribution over the Nanjing metropolitan area in the future. In the RCP6.0 （RCPS.5） scenario, the built-up area increases at a rate of about 10.41 km2 （10 yr）-t（24.67 km2 （10 yr）-1） from 2010 to 2100, and the area of high flood risk correspondingly increases from 3.86 km2（3.86 km2） to 9.00 kin2（13.51 km2）. Areas of high flood risk are mainly located at Chishan Lake in Jurong, Lukou International Airport in Nanjing, Dongshan in Jiangning District, Lishui District and other low-lying areas. The accurate simulation of flood scenarios can help reduce losses due to torrential flooding and improve early warnings, evacuation planning and risk analysis. More attention should be paid to the projected high flood risk because of the concentrated population, industrial zones and social wealth throughout the Nanjing metropolitan area.

Transition of the annual cycle of precipitation from double-peak mode to single-peak mode in South China

Previous studies revealed the double-peak mode(DPM)in South China precipitation,corresponding to the two stages in the rainy season,i.e.the first rainy stage(FRS)and the second rainy stage(SRS).But observations in recent two decades show that the DPM has changed to a single-peak mode(SPM).Both the precipitation amount and the heavy rainfall event frequency enhanced significantly in the gap between the FRS and the SRS in 1991–2010,compared to those in 1961–1990.This change can be linked to the effects of the global warming.During the warmer period,the July sea surface temperature over the western Pacific has greater increases than that over the central and eastern Pacific,especially west of 140°E.It may generate more tropical cyclones(TCs)in the inshore areas and then more typhoon rainfall over South China.On the other hand,the increments of the air temperature over the East Asian continent are greater than those of the SST over the western Pacific under the global warming,which enlarges the land-ocean temperature/pressure contrast and leads to a trend of the earlier onset dates of the Asian summer monsoon(ASM)in recent two decades.Then,the earlier ASM will facilitate the western Pacific subtropical high(WPSH)to retreat earlier from the South China Sea and enhance the convective precipitation in South China between the FRS and the SRS.Also,due to the warmer ocean,the WPSH locates more westward in July,and more moisture will be transported to South China from the southwest side to the WPSTH.All these influences favor a remarkably increasing precipitation in the gap in the warmer period and changes the seasonal cycle from double-peak mode to single-peak mode.

Changed Relationships Between the East Asian Summer Monsoon Circulations and the Summer Rainfall in Eastern China

In previous statistical forecast models,prediction of summer precipitation along the Yangtze River valley and in North China relies heavily on its close relationships with the western Pacific subtropical high（WPSH）,the blocking high in higher latitudes,and the East Asian summer monsoon（EASM）.These relationships were stable before the 1990 s but have changed remarkably in the recent two decades.Before the 1990 s,precipitation along the Yangtze River had a significant positive correlation with the intensity of the WPSH,but the correlation weakened rapidly after 1990,and the correlation between summer rainfall in North China and the WPSH also changed from weak negative to significantly positive.The changed relationships present a big challenge to the application of traditional statistical seasonal prediction models.Our study indicates that the change could be attributed to expansion of the WPSH after around 1990.Owing to global warming,increased sea surface temperatures in the western Pacific rendered the WPSH stronger and further westward.Under this condition,more moisture was transported from southern to northern China,leading to divergence and reduced（increased） rainfall over the Yangtze River（North China）.On the other hand,when the WPSH was weaker,it stayed close to its climatological position（rather than more eastward）,and the circulations showed an asymmetrical feature between the stronger and weaker WPSH cases owing to the decadal enhancement of the WPSH.Composite analysis reveals that the maximum difference in the moisture transport before and after 1990 appeared over the western Pacific.This asymmetric influence is possibly the reason why the previous relationships between monsoon circulations and summer rainfall have now changed.

Impact of Multi-Scale Oscillations at High and Low Latitudes on Two Persistent Heavy Rainfall Events in the Middle and Lower Reaches of the Yangtze River

To investigate the multi-scale features in two persistent heavy rainfall （PHR） events in the middle and lower reaches of the Yangtze River （MLRYR） in June of 1982 and 1998, this study examines the impact of multi-scale oscillations in the north and south of 30°N on the PHR events by performing sensitivity experiments with the Weather Research and Forecast （WRF） model. It is found that the 60-day low- pass perturbation made a trivial contribution to the MLRYR precipitation during the PHR event in 1982. This PHR event resulted mainly from the combined effects of 30-60-day oscillation at low latitudes and 10-30-day oscillation at both high and low latitudes. The southwesterly anomalies associated with the 30- 60-day anticyclonic anomaly over the northwestern Pacific facilitated moisture transport from the ocean to the MLRYR and enhanced the low-level convergence and ascending motion in the MLRYR. This similarly occurred in the 10-30-day oscillation as well. Moreover, the 10 30-day anomalies at high latitudes played a role in strengthening the large-scale low-level convergence over the MLRYR. The PHR event in 1998 was mainly related to the 60-day oscillation at both high and low latitudes and 30-60-day oscillation at low latitudes. The 60-day low-pass filtered anomalous cyclone at high latitudes in the north of 30°N contributed to the development of low-level convergence and ascending motion in northern MLRYR while the anomalous anticyclone at low latitudes in the south of 30°N not only increased the moisture in the MLRYR but also preconditioned the dynamical factors favorable for PHR over the whole area. The 30-60-day perturbations located north and south of 30°N worked together producing positive moisture anomaly in the MLRYR. In addition, the anomalous circulation in the south of 30°N tended to favor the development of ascending motion and low-level convergence in the MLRYR.

Advances in Ecological Applications of Fengyun Satellite Data

In recent years,the remote sensing based on meteorological satellite observations has become an important tool for assessing global ecological conditions.Since the early 2000,Fengyun(FY)satellite data have been widely used to derive the key parameters of ecological environment in China.An integrated earth-observation system has been developed in China through using FY satellite data,including retrievals the key ecological parameters as well as to constructions of long-term data records of vegetation index,land surface temperature,net primary production,vegetation health index,and so on.Considerable progress has thus been made in the application and service for prevention of air pollution,management and control of ecological redline,ecological monitoring for the Belt and Road Initiative,and assessment of ecological environment for human settlement.In order to monitor the ecological parameters in real time and with a full dynamic coverage,it is necessary to improve the technology in application of ecological remote sensing from meteorological satellites,and further enhance the ecological meteorological service.

Comparison of the Multi-Scale Features in Two Persistent Heavy Rainfall Events in the Middle and Lower Reaches of Yangtze River

Two persistent heavy rainfall（PHR） events in the middle and lower reaches of Yangtze River（MLYR）occurring in June 1982 and 1998 are studied in this paper.Though both events happened in the Meiyu season,their large-scale background and developing processes were quite different.During the PHR event in 1982,the Lake Baikal area was occupied by a strong westerly trough and the western Pacific subtropical high（WPSH） was stronger and more westward-extending than the normal years.Under such a condition,the cold dry air and warm moist air were continuously transported to the MLYR and favored the PHR there.For the event in 1998,the WPSH was similar to that in 1982,while the westerly trough in the Lake Baikal area was comparatively weak and a shortwave trough situating in East China contributed to advect cold dry air to the MLYR.It is found that the high-latitude trough was closely related to the 1030-day low-frequency oscillation while the anomaly of WPSH was linked with the combined effect of both30 60- and 10 30-day low-frequency oscillations in the PHR event in 1982.By contrast,the 60-day low-pass perturbation demonstrated positive impact on the westward extension of WPSH and development of the Baikal trough while the 30 60-day oscillation played a role in strengthening the shortwave trough in East China and the WPSH in the case of 1998.Though the low-latitude 30 60-day oscillations contributed to the intensification and westward extension of the WPSH in both PHR events,their evolution exhibited evident differences.In the 1982 case,the 30 60-day anomalies originated from the western Indian Ocean were much more like the Madden Julian Oscillation,while its counterpart in the 1998 case was much more similar to the first mode of the boreal summer intraseasonal oscillation.

Estimation of Chlorophyll-a Concentration in Lake Taihu from Gaofen-1 Wide-Field-of-View Data through a Machine Learning Trained Algorithm

Wide-field-of-view(WFV) imager that observes the earth environment with four solar reflective bands in a spatial resolution of 16 m is equipped on board Gaofen-1(GF-1) satellite. Chlorophyll-a(Chl-a) concentration in Lake Taihu, China from 2018 to 2019 is collected and collocated with GF-1 satellite data. This study develops a general and reliable estimation of Chl-a concentration from GF-1 WFV data under turbid inland water conditions. The collocated data are classified according to season and used in random forest(RF) regression to train models for retrieving the lake Chl-a concentration. A composite index is developed to select the most important variables in the models. The models trained for each season show a better performance than the model trained by using the whole year data in terms of the coefficient of determination(R^(2)) between retrievals and observations. Specifically, the R2 values in spring, summer, autumn, and winter are 0.88, 0.88, 0.94, and 0.74, respectively;whereas that using the whole year data is only 0.71. The Chl-a concentration in Lake Taihu exhibits an obvious seasonal change with the highest in summer, followed by autumn and spring, and the lowest in winter. The Chl-a concentration also displays an obvious spatial variation with season. A high concentration occurs mainly in the northwest of the lake. The temporal and spatial changes of Chl-a concentration are almost consistent with the changes in the areas and times of cyanobacteria blooms based on Moderate Resolution Imaging Spectroradiometer(MODIS) data. The proposed algorithm can be operated without a priori knowledge on atmospheric conditions and water quality. Our study also demonstrates that GF-1 data are increasingly valuable for monitoring the Chl-a concentration of inland water bodies in China at a high spatial resolution.

Global Financial Crisis Making a V-Shaped Fluctuation in NO_2 Pollution over the Yangtze River Delta

The Yangtze River Delta（YRD）,China’s main cultural and economic center,has become one of the most seriously polluted areas in the world with respect to nitrogen oxides（NO_x）,owing to its rapid industrialization and urbanization,as well as substantial coal consumption.On the basis of nitrogen dioxide（NO_2）density data from ozone monitoring instrument（OMI）and ground-based observations,the effects of industrial fluctuations due to the financial crisis on local NO_2 pollution were quantitatively assessed.The results were as follows.（1）A distinct V-shaped fluctuation of major industrial products,thermal generating capacity,electricity consumption,and tropospheric NO_2 densities was associated with the global financial crisis from May 2007 to December 2009,with the largest anomalies 1.5 times more than standard deviations at the height of the crisis period from November 2008 to February 2009.（2）Among all industrial sectors,thermal power plants were mainly responsible for fluctuations in local NO_2 pollution during the crisis period.Thermal generating capacity had its greatest decrease of 12.10%at the height of the crisis compared with that during November 2007–February 2008,leading to local tropospheric NO_2 density decreasing by 16.97%.As the crisis appeased,thermal generating capacity increased by 29.63%from November 2009 to February 2010,and tropospheric NO_2 densities correspondingly increased by 30.07%.（3）Among all industrial sectors in the YRD,the thermal power sector has the greatest coal consumption of about 65.96%.A decline in thermal power of about 10% can induce a decrease of about 30%in NOx emissions and NO_2 densities,meaning that a relative small fluctuation in industrial production can lead to a large decrease in tropospheric NO_2 densities over industrially developed areas like the YRD region.Since electricity is mainly obtained from local coal-burning thermal plants without NO_x-processing equipment,installing NO_x-removal devices for all thermal power plants is an important and feasible way of controlling local NO_x pollution at present.