Abstract:The contrails produced by the aviation activities of jet aircraft in the upper troposphere can affect the regional climate and have a positive contribution to global warming. The radiative forcing of contrails is closely related to the regional coverage, physical properties and optical properties of contrails. This paper reviews the related research progress in line-shaped contrails in recent decades and summarizes different methods for line-shaped contrails detection. Firstly, this paper discusses the mainstream Contrail Detection Algorithm (CDA) and its various extension algorithms in Europe and America, and summarizes the seasonal and diurnal variation characteristics of line-shaped contrails coverage over Western Europe, North America and other regions. Then this paper discusses several calculation schemes for the optical depth of line-shaped contrails and their calculation uncertainties. Finally, this paper analyses the radiative forcing of line-shaped contrails and its relationship with the coverage and optical thickness, and points out the problems existing in present studies of contrails and their future development direction.

Abstract:In this study, the features of intra-seasonal(10-30 d) precipitation variability over southern China during the autumn, winter and following spring season of different types of ENSO events are analyzed based on the Hadley Centre sea surface temperature(SST), National Centers for Environmental Prediction(NCEP) and National Center for Atmospheric Research(NCAR) atmospheric circulation data, and China daily rainfall station data. The results show that the impacts of different ENSO types on the intra-seasonal(10-30 d) precipitation variability over southern China vary with the different seasons. During the winter and following spring of EP El Niño events, the 10-30 d precipitation variability over southern China is significantly enhanced. Intra-seasonal precipitation variance is weakened during the CP El Niño autumn, yet strengthened during the CP El Niño winter, thus showing inverse features. The impacts of La Niña events on the 10-30 d precipitation variabilities are relatively minor and unstable. Further analyses show that the impact on the 10-30 d precipitation variability is closely related to the responses of seasonal atmospheric circulation anomalies over the western North Pacific associated with ENSO events. Compared with normal years, a strong anticyclonic circulation anomaly occurs over the Philippines during the EP El Niño years. The anomalous southerly winds on the western side of the anticyclone transport much greater amounts of water vapor northward to southern China, which favors the strengthened 10-30 d rainfall variability. However, an anomalous cyclonic circulation occurs in the western North Pacific during the CP El Niño autumn, which suppresses the tropical water vapor transporting northward to the East Asian continent. During CP El Niño winters, an anomalous anticyclone appears over the western North Pacific, and though its intensity is weak, it accounts for the inverse low frequency rainfall responses in autumn and winter. When La Niña occurs, the anomalous cyclonic circulation over the Philippines is weak, which results in the relatively weaker responses of the 10-30 d precipitation variability over southern China.

Abstract:The interdecadal variations of the relationship between the intense tropical cyclone(TC) over the western North Pacific Ocean(WNP) and the El Niño-Southern Oscillation(ENSO), were examined based on the TC Best Track data(JTWC, CMA, and JMA) and the reanalysis data of the NCAR/NCEP. It was determined that during the period ranging from 1960 to 1971(first examined period), the intense TC frequencies and the NDJ Niño3.4 were not statistically correlated. Meanwhile, during the period ranging from 1983 to 2014(second examined period), they were found to be closely correlated. Moreover, the differences in the life spans and genesis locations of TC45 between the El Niño developing years and the La Niña developing years had become enlarged in the more recent years, when compared to those during the prior period. The results of this study's analysis revealed that the westward extensions of the SSTA over the tropical Pacific Ocean during the more recent period were key factors in the enhancement of the relationship between the Niño3.4 index and the annual TC45 frequency. The extensions of the SSTA caused significant increases(decreases) of the relative humidity in the southeastern quadrant of the tropical WNP for the El Niño(La Niña) developing years during the period ranging from 1983 to 2014, which was favorable(unfavorable) to the TC genesis and affected the TC45 frequency variations with the ENSO events during the more recent period. This was due to the fact that the TC in southeastern quadrant was more likely to intensify into the TC45. During the period ranging from 1983 to 2014, more(less) TC45 occurred in the southeastern quadrant for the El Niño(La Niña) developing years.

Abstract:Based on the output data from 23 CMIP5 models, the evolution features of El Niño events were studied. The results showed that one third of the CMIP5 models can well demonstrate the evolution process of El Niño events while another one third of the models can not. Both dynamic and thermodynamic processes contributed to the fast decaying process of El Niño events. The former was related to wind responses in western Pacific whereas the latter was associated with cloud-radiation-SST feedback. The good models had the feature that a sea surface temperature anomaly center was located in the equatorial eastern Pacific region, while it tended to shift westward in the pool models. As a result, a strong negative SSTA tendency occurred during El Niño decaying phase in the good models and a much weaker SSTA tendency occurred in the pool models. Such a difference led to a SSTA sign change ñn next summer of El Niño events in the good models but there was no such sign change in pool models. A season-dependent coupled instability caused by sea-air interaction joined in autumn in northern hemisphere. Therefore, in good models, the negative SSTA developed and changed into a La Niña event and in pool models it maintained an El Niño episode. Results also showed that one third of the CMIP5 models could not well simulate the phase locking feature of El Niño events.

Abstract:The interannual fluctuations of atmospheric CO_2(IFAC), as an important signal of global carbon cycle research, are closely related to the El Niño-Southern Oscillation(ENSO). However, most studies regarding the impact of volcanic activities tend to focus merely on the post-Pinatubo eruption. By using monthly observational data of atmospheric CO₂ and δ¹³C at Mauna Loa and the South Pole from the period of 1959 to 2008, this study analyzes the features of IFAC. A positive correlation is found between IFAC and ENSO, and a negative correlation between IFAC and the volcanic eruption index. The massive eruptions could reduce the impact from strong ENSO on IFAC. The influence of volcanic activities is related to the eruption intensity, as well as the magnitude of eruptions and duration of eruption effects. ENSO and volcanic eruption work together on the IFAC. During the analysis period, the diversity of atmospheric CO₂ and δ¹³C variations after El Chichon and Pinatubo eruptions are related to the relative beginning time of both events. Using δ¹³C analysis and Keeling Plot calculation, ENSO exerts influence on IFAC through the changes of terrestrial biosphere, along with volcanic eruption, by means of oceanic uptake enhanced by the cooling and fertilization effects.

Abstract:In this study, based on the 10-15 day extended range ensemble forecasts of European Centre for Medium-Range Weather Forecasts(ECMWF), National Centers for Environmental Prediction (NCEP)and United Kingdom Met Office(UKMO)in the TIGGE dataset, the probabilistic forecasts of surface air temperature during the period from 1 June to 31 August 2013 were conducted using BMA(Bayesian Model Averaging). The results showed that the forecasting skill changed with the length of the training period, reaching its optimal value when the length of the training period was 30 days. BMA could provide full PDF(Probability Density Function), and quantitatively describe the forecast variance and uncertainty. The uncertainty and error on the land(higher latitude)were larger than those on the sea(lower latitude). Moving average methods improved the forecast skill of surface air temperature, and the longer the moving average period was, the better of the forecast performance would be.

Abstract:It has important significance if the surface automatic weather stations (AWS) data with high spatial and temporal resolution can be fully applied in the weather forecast, but it is hard to ensure the quality of data for various reasons. AWS data from 151 national AWS and 2 600 regional AWS in Jiangsu and Anhui Provinces are selected to discuss the quality of all kinds of AWS data and the quality control(QC) scheme. Based on the AWS data from 2012 to 2014, the missing rates are estimated respectively. A systematic and sophisticated QC scheme containing the missing data statistics, the climate limit check, the climate extreme value check, the internal consistency check, the second iterated space consistency check, the time consistency check, the continuous check and the comprehensive decision-making algorithm is designed for selecting out accurate information and rejecting abnormal information. What's more, the suspicious stations are marked according to the results of QC scheme. It turns out that not only the missing rates of national AWS data of various meteorological elements are apparently lower than the regional ones according to the statistics, but also the quality of national AWS data is obviously better than the regional ones in general. Among various elements, the quality of temperature and pressure data is best, the next is the quality of relative humidity data, and the quality of wind data is worst. The fail rates of all elements of regional AWS data are much higher than the national ones in the QC scheme, except for the wind field data in the second iterated space consistency check, which has little difference between the regional and national AWS data. If the results of QC scheme, especially the information of error data and suspicious stations can be provided to the corresponding stations in time, it is beneficial to the improvement of the real-time data quality and the maintenance and correction of corresponding instruments.

Abstract:Taking study on the simultaneous coupling temporal and spatial characteristics between temperature and precipitation of China as an example in winter and summer respectively, the correlation relationship and equilibrium of the main orthogonal modes of SVD and MEOF analysis are compared, and the superiority of SVD method in revealing correlation relationship between two element fields is demonstrated. The main conclusions are as follows:(1) Comparing the principle of SVD with that of MEOF, the direct decomposition object of SVD is more pure and only contains information reflecting correlation relationship between two element fields, while that of MEOF also includes the autocorrelation information of two element fields itself, respectively. (2) The positive and negative anomalous distributions of the spatial coupled modes between air temperature and precipitation revealed by MEOF and SVD are approximately similar, but the main MEOF orthogonal modes between air temperature and precipitation in winter and summer are unbalanced compared with those revealed by SVD. That is, one of the main MEOF orthogonal modes often focuses on describing one of the two anomalous element fields. This difference is especially pronounced in winter. The SVD method reveals that the local high temperature and less precipitation or low temperature and more precipitation are the main abnormal configurations between temperature and precipitation in winter and summer over the same period in China, and the correlation is strong in summer and weak in winter. (3) By comparing the correlation coefficients and equalization of the same order orthogonal modes of SVD with those of MEOF, it is found that the correlation coefficients of most orthogonal modes of SVD are larger and more stable than those of MEOF, and all pass the significance test, and part of correlation coefficients of MEOF orthogonal modes in winter do not pass the significance test. The equalization of SVD main orthogonal modes is superior to that of MEOF analysis in winter, and is superior to (for the first mode) or close to (for the second and third modes) that of MEOF in summer. So the SVD method is a better way to reveal the coupling relationship between the two elements.

Abstract:The inherent differences between observational topography and model terrain have seriously affected the verification accuracies of 2 m temperature levels. The traditional two-dimensional interpolation schemes are only able to ensure the forecasting elements and observational consistency in latitude and longitude locations of two-dimensional spaces, while ignoring the vertical direction consistency. This has the effect of the forecasting and observational verification results not originating from the same spatial positions, thereby causing misleading evaluations. The diurnal cycles are important features of the 2 m temperatures. However, due to the limitations of the physical processes(such as radiation), large bias have consistently appeared in the diurnal cycle forecasts. In this research study, three-dimensional forecast variables were combined with the near-surface elements of the forecasting products, and an advanced three-dimensional interpolation scheme was developed in order to ensure a consistency with the observations in the three-dimensional spatial forecasting processes. Then, based on topography correction methods, the monthly forecasting errors were used as reference bias products for the purpose of eliminating systematic errors and obtaining forecasting products with characteristic diurnal cycles. The abnormal datasets were rejected using a significance test in order to ensure the validity of the samples. In this study, using a classification analysis based on 27 typical observational gauges selected in the complex terrain of Shanxi Province, six major gauge stations were selected which were known to have different height biases between the model terrain and observational heights. The 48-hour forecasting products in August of 2016 were used for this study's comparison process. It was found that the three-dimensional interpolation scheme effectively solved the misleading evaluations caused by the height bias between the model terrain and observation topography, regardless of whether the large height bias gauge stations or small height bias gauge stations were examined. However, it was observed that the scheme had not effectively improved the diurnal cycle trends of 2 m temperature forecasting. Therefore, it was determined that the three-dimensional interpolation scheme could only modify the overall bias magnitude, and could not improve the forecasting abilities of the diurnal cycles. However, it was observed that after systematic error corrections were adopted, the diurnal cycle forecasting features had been obviously improved. In particular, it was found that a better consistency with the observations had been attained, as well as higher skill scores, particularly in the first 24 hours. The results of the seasonal statistical evaluation of the summer of 2016 indicated that, after the bias corrections, the 2 m temperatures could be effectively improve the oscillation of the periodic errors. Furthermore, the RMSE had been maintained at approximately 2 K, which indicated the obvious advantages of the improvements. This study focused on the effectiveness of the bias correction method, and was most concerned with the improvement trends. The systematic errors required monthly forecasting data for many years as reference errors, and the number of forecasting samples was found to restrict the bias correction effects to some extent. Therefore, it was concluded in this study that by increasing the forecasting samples, more reference samples could be added to ensure the error correction methods were perfected. In this way, the proposed bias correction effects could potentially be more significant in the future. At the same time, some of the related operational models have been running for long periods of time(such as the NCEPGFS, ECMWF, T639, and so on). A more ideal reference data base could be obtained using these long period forecasting products, which would potentially display superior effectiveness and applicability in 2 m temperature bias corrections in future studies.

Abstract:Expending 58 typhoon cases that had the considerable effect on Ningbo and had finish catastrophe records from 1949 to 2015. In view of the information of the calamity, the comprehensive correlation degree of typhoon disaster (R_oj) was set up by utilizing the grey relational investigation technique. Choosing the disaster-causing factors of typhoon and R_oj that point build disaster pre-assessment technique of typhoon disaster by utilizing BP neural network (BP). The outcomes demonstrated that, the severity of typhoon which evaluated by R_oj is reasonable and available. There is a significant correlation between typhoon disaster risk factors and disaster assessment indicators as well as R_oj. The pre-evaluation model of BP is useful for predicting typhoon disaster;the correlation coefficient linking the simulated value and the actual value of the training set and the test set respectively reached 0.94 and 0.896 and both achieved the confidence interval of 0.01. The consensus rate of the disaster level forecast of the training set and the test set is 85.3% and 77.8% respectively. This investigate outcomes could provide scientific premise to counter the typhoon work of government decision-making divisions.

Abstract:Currently, major challenges exist in the area of the quantitative precipitation estimations of convective short-term flooding caused by local heavy rainfall events. In this study, in order to improve the accuracy of the forecasting of the convective precipitation estimates, various currently used quantitative measurements methods for precipitation were summarized. Then, the limitations of these statistical methods for rainfall estimations were analyzed. It is known that different types of precipitation affect the accuracy of the precipitation estimates due to the variations in power, heat, and water vapor, which result in different micro-physical mechanisms and internal structures. Therefore, based on the physical mechanisms of the precipitation, along with the precipitation echo structures, the coefficient A and exponent b in the Z-I relationship become spatial functions rather than simple constants. Therefore, they can provide a theoretical basis for an adaptive method which can be effectively used to quantitatively estimate precipitation.
In this research study, the mechanisms of convective precipitation, mixed precipitation, and stratiform precipitation were examined, and the echo structural features, precipitation micro-physical characteristics, and echo extinction laws were analyzed. It is known that multiple parameters have certain impacts on precipitation, such as composite reflectivity factors (CR) and vertical liquid water content (VIL). Therefore, it was necessary to first distinguish the three different types of precipitation from the structure, and then use statistical methods for the fitting process. The lgR_C-lgI and R_C-I data pairs were respectively utilized. Then, depending on the type of rain event and the corresponding Z-I relationship, the precipitation measurement errors were reduced which had resulted from the unstable Z-I relationship caused by changes in the rain events, in order to solve the problem of the serious underestimations of heavy rainfall events. The results of this study showed that the lgR_C-lgI data pairs displayed better fitting results when fit by order, and R_C-I data pairs exhibited better results when fit by high-order. These findings indicated that the adaptive method which was used to quantitative estimate the precipitation was reasonable. Also, the instability of the Z-I relationship caused by the physical properties and structural characteristics of the precipitation was revealed.
This study also investigated the binary function relationships among the CR, VIL, and precipitation of convective and mixed precipitation. It was observed that there was a high correlation between the fitting results. The results confirmed that by taking the CR and VIL into account, the issue of significantly underestimating heavy rainfall events could be resolved.

Abstract:The cross-equatorial flow(CEF) plays an important role in the momentum, mass and water vapor exchange between the northern and southern hemispheres. It is one of important factors that reflect and affect the weather and climate anomalies in the northern and southern hemispheres, and especially has close connections with Asian monsoon, summer precipitation and typhoons. In recent years, the extensive research on the CEF has been conducted by domestic and foreign researchers. Previous studies have focused on the impact of CEF over the South China Sea(SCS) on Asian summer monsoon, especially on East Asian summer monsoon and South China Sea summer monsoon. However, there are few studies on the characteristics of SCS low-level CEF(SCEF) and the connection between SCEF variation and precipitation anomalies in the Asian-Australian monsoon region.
Therefore, according to the latest released Interim reanalysis data by ECMWF and the precipitation rate data by GPCP during 1979-2014, this paper analyzes the spatial structure and temporal variation of summer SCEF by using the correlation analysis and synthesis analysis methods. It discusses the relationship between SCEF and precipitation anomalies in the Asian-Australian monsoon region, and further presents the possible physical process of influence of SCEF variation on precipitation anomalies in the Asian-Australian monsoon region by analyzing characteristics of atmospheric circulation, water vapor transport and local Hadley circulation. Results show that the intensity of SCEF has a significant interannual variation in summer, with a 3-4 yr period. The intensity of SCEF in summer shows significant negative(positive) correlations with precipitation anomalies in the tropical eastern Indian Ocean and the maritime continent(the tropical western Pacific). In addition, the intensity of SCEF has a clearly negative correlation with precipitation anomalies in central China in summer. When the intensity of SCEF is stronger in summer, there are westerly wind anomalies from the Arabia Sea to the tropical western Pacific and easterly wind anomalies in the tropical eastern India Ocean at 850 hPa, leading to convergence(divergence) of water vapor in the tropical western Pacific(the tropical eastern India Ocean and the maritime continent). As a result, there are more(less) precipitation in the tropical western Pacific(the tropical eastern India Ocean and the maritime continent), and vice versa. When the intensity of SCEF is stronger(weaker) in summer, there is a cyclone(anticyclone) wind anomaly field in the southeast coast of China, which is unfavourable to(favourable to) water vapor transport from the tropical ocean to the central part of China, leading to less(more) precipitation in central China. When the intensity of SCEF is stronger in summer, the local Hadley circulation in East Asia is abnormally weaker. The anomalous SCEF converges with the cold air from the northern hemisphere around 20°N, and rises. There is an anomalous subsidence near the equator and 30-40°N area, making the precipitation in the tropical maritime continent and central China decrease;and vice versa.

Abstract:Based on the observed data and simulated results, this paper studies the structure characteristics and cause of catastrophic wind caused by super typhoon Meranti(typhoon "1614"). It is the strongest typhoon affecting Xiamen since typhoon "5903", and its impact radius is relatively small. Before landing, the local strong wind in typhoon circulation is characterized by periodic fluctuation. The azimuth change of the local strong wind relative to the typhoon first turns clockwise, then turns counterclockwise with the typhoon approaching. Simulated strength of typhoon Meranti based on the wind-pressure relation is in good agreement with the observed result. After landing, typhoon Meranti is affected by terrain friction, which makes the wind speed on the left side of typhoon stronger than that on the right side. Numerical simulation analysis shows that the horizontal advection of wind vector and the pressure gradient term are the main physical factors causing the local catastrophic wind. The strong wind area of typhoon Meranti shows obvious meso-scale characteristics. Wind around the eye wall is strengthened by the vertical air transportation with higher momentum and the momentum downward propagation effect.

Abstract:Using the hourly observation data of rain, relative humidity, wind direction, wind speed, and minimum visibility in the same period from 70 national weather stations in Jiangsu Province, the impacts of different rainfall intensities on visibility was analyzed, and the statistical characteristics of two types of rainfalls with different intensities, which caused low-visibility weather, were compared and analyzed. The results showed that rainfall was the major reason for low-visibility weather in Jiangsu(14.5%) besides fog. Stable weak rainfall and short-time heavy rainfall showed the most obvious impacts. Unlike the low-visibility weather events caused by fogs, those caused by rainfalls may occur at any time throughout the day usually with high wind speeds(>2 m/s). In 26.6% of these events, wind speed would be>4 m/s. Winter and spring were seasons with most frequent rain fog weather in Jiangsu, which was mainly affected by the duration of rainfalls. The corresponding low visibility range was 500-1 000 m with obvious diurnal variations. Short-time heavy rainfall fog weather was mainly affected by the intensity of rainfalls, which mostly occurred during June and September, and the corresponding low-visibility range was less than 200 m without obvious diurnal variations. There was obvious spatial distribution difference between the low visibility weather events caused by the two types of rainfalls. When the rain fog weather occurred, the northerly wind dominated;when the short-time heavy rainfall fog weather occurred, the easterly wind dominated.

Abstract:Haze has become one of the major weather disasters to harm social security and human health in the recent years and it reduces visibility and air quality for it contains a large number of pollutants and affects seriously the natural environment, human production and life. Satellite remote sensing data can make up for the shortage of manual field monitoring, which making full use of timeliness, reliability, wide range of satellite remote-sensing to monitor dynamically the distribution of a wide range of haze.
In this paper, MODIS_L1B data (MOD02_1KM-Collections 6) was used to inverse the air aerosol optical thickness (AOD) and the road visibility of a great haze weather event occurred in Beijing from March, 6th to March, 11th in 2012 combined with the retrieved data of AOD from AERONET (Aerosol Robotic Network) of NASA in USA, the observed data of visibility from the Ground Meteorological Observation Stations Network in Beijing and the observed data of visibility from the Road Automatic Weather Monitoring Stations Network and the relationship between the AOD and the visibility in this event was analyzed. Finally, the reasonable control measures were tried to put forward combined with the local traffic situation against haze. It can be provide reference for haze weather monitoring and early warning and traffic safety operation in the future (Inversion Comparison process time matches the satellite transit time from 10:00-12:00).
The results showed as follows:(1) Both of the retrieved AOD values from MODIS remote sensing and the ground observed values of AOD from AERONET had a change tendency of a single peak type. But the AOD inversion values were higher than the observed values for the deviation of observed times. (2) The visibility values calculated by the retrieved AOD values was basically consistent with the observed values, both the temporal and spatial variation trends were basically consistent and the correlation coefficient between the two was large than 0.6 (P<0.01). All of these inversions and calculation was consistent with the actual occurrence characteristics of this haze event, the errors between the inversion values and actual values of the visibility was small (<0.5km) in the urban area and the inversion effect was better, but this error was large (>1 km) in the suburban area and the inversion effect was poor. (3) Based on the distribution of expressway, and combined with different degrees of haze in different regions of Beijing, it can be seen that the haze pollution in the southeastern part of Beijing is the most serious. The sections of the expressway in the area are respectively:Beijing-Harbin Expressway (G1), Beijing-Shanghai high-speed (G2), Beijing-Taiwan high-speed (G3) and Beijing-Hong Kong and Macao high-speed (G4). In addition, it also included the Fifth Ring Road in Beijing.