ATMOSPHERIC BOUNDARY LAYER CONCEPT MODEL OF THE PEARL RIVER DELTA AND ITS APPLICATION

Based on the geographical circumstance, climate and the boundary layer meteorology features of the Pearl River Delta, a boundary layer concept model of the Pearl River Delta was built. The concept model consists of four fundamental factors that affect the boundary layer meteorology of the Pearl River Delta and can convincingly explain the reason of the air quality change in the Pearl River Delta. The model can be used to the diffusion capability analysis, the air pollution potential forecasting or haze forecasting, etc.

THE RELATIONSHIP BETWEEN EXTREME PRECIPITATION ANOMALY IN SOUTH OF CHINA AND ATMOSPHERIC CIRCULATION IN THE SOUTHERN HEMISPHERE

Based on the daily rainfall datasets of 743 stations in China and the NCEP/NCAR monthly reanalysis data during the period of 1960-2003,the relationship between the anomalous extreme precipitation(EP) in the south of China and atmospheric circulation in the Southern Hemisphere is analyzed.The phenomenon of opposite changes in the sea level pressure and geopotential height anomalies over the Ross Sea and New Zealand is defined as RN,and the index which describes this phenomenon is expressed as RNI.The results show that the RN has barotropic structure and the RNI in May is closely related to the June EP amount in the south of China(SCEP) and the East Asian summer monsoon(EASM).The positive correlations between the May RNI at each level and the June SCEP are significant,and the related simultaneous correlations between the RNI and the June SCEP are also positive,suggesting that the potential impact of RN on the SCEP persists from May to June.Therefore,RN in May can be taken as one of the predictive factors for the June SCEP.Furthermore,one possible physical mechanism by which the RN affects the June SCEP is a barotropic meridional teleconnection emanating from the Southern Hemisphere to the western North Pacific.

Observation-based Estimation of Aerosol-induced Reduction of Planetary Boundary Layer Height

Radiative aerosols are known to influence the surface energy budget and hence the evolution of the planetary boundary layer. In this study, we develop a method to estimate the aerosol-induced reduction in the planetary boundary layer height （PBLH） based on two years of ground-based measurements at a site, the Station for Observing Regional Processes of the Earth System （SORPES）, at Nanjing University, China, and radiosonde data from the meteorological station of Nanjing. The observations show that increased aerosol loads lead to a mean decrease of 67.1 W m-2 for downward shortwave radiation （DSR） and a mean increase of 19.2 W m-2 for downward longwave radiation （DLR）, as well as a mean decrease of 9.6 W m-2 for the surface sensible heat flux （SHF） in the daytime. The relative variations of DSR, DLR and SHF are shown as a function of the increment of column mass concentration of particulate matter （PM2.5）. High aerosol loading can significantly increase the atmospheric stability in the planetary boundary layer during both daytime and nighttime. Based on the statistical relationship between SHF and PM2.5 column mass concentrations, the SHF under clean atmospheric conditions （same as the background days） is derived. In this case, the derived SHF, together with observed SHF, are then used to estimate changes in the PBLH related to aerosols. Our results suggest that the PBLH decreases more rapidly with increasing aerosol loading at high aerosol loading. When the daytime mean column mass concentration of PM2.5 reaches 200 mg m-2, the decrease in the PBLH at 1600 LST （local standard time） is about 450 m.

K-MEANS CLUSTERING FOR CLASSIFICATION OF THE NORTHWESTERN PACIFIC TROPICAL CYCLONE TRACKS

Based on the Joint Typhoon Warning Center(JTWC) best-track dataset between 1965 and 2009 and the characteristic parameters including tropical cyclone(TC) position,intensity,path length and direction,a method for objective classification of the Northwestern Pacific tropical cyclone tracks is established by using k-means Clustering.The TC lifespan,energy,active season and landfall probability of seven clusters of tropical cyclone tracks are comparatively analyzed.The characteristics of these parameters are quite different among different tropical cyclone track clusters.From the trend of the past two decades,the frequency of the western recurving cluster(accounting for 21.3% of the total) increased,and the lifespan elongated slightly,which differs from the other clusters.The annual variation of the Power Dissipation Index(PDI) of most clusters mainly depended on the TC intensity and frequency.However,the annual variation of the PDI in the northwestern moving then recurving cluster and the pelagic west-northwest moving cluster mainly depended on the frequency.

Environmental impact of aquaculture-sedimentation and nutrient loadings from shrimp culture of the southeast coastal region of the Bay of Bengal

Nutrient loadings were measured for surface seawater and bottom sediments of semi intensive and improved extensive shrimp culture pond, adjacent estuary, and fallow land in the south east coastal region of Bangladesh during August, 2000—January, 2001 to evaluate the impact of shrimp culture. The mean levels of nutrients found in the pond surface water were 108 780 mg/L for CaCO 3, 0 526 mg/L for NH + 4 N, 3 075 wt% for organic carbon, 7 00 mg/L for PO 4 P, 5 57 mg/L for NO 3 N, and 7 33 mg/L for chlorophyll a. The maximum mean value of H 2S(0 232 mg/L) was found in estuarine water. Nutrients loading were found to be decreased with distance from the shrimp farm discharge unit in estuarine water. The mean level of organic matter, total nitrogen, and organic carbon were found in higher concentrations in sediments of cultured pond compared to bottom soil of adjacent fallow land at the same elevation. Extractable Ca values were found in higher concentration(550 33 ppt) in adjacent fallow land, as the shrimps for molting in shrimp ponds use extractable Ca. The relation between seawater H 2S value and sediment pH ( r= -0 94); sediment organic carbon and sediment pH values ( r= -0 76), sediment total nitrogen and sediment pH ( r= - 0 74) were found to be highly negatively correlated. Whereas the relation between seawater H 2S value and sediment total nitrogen ( r= 0 92), water NH + 4 N and sediment pH ( r= 0 66) were found to be positively correlated. The results revealed that load of nutrients at eutrophic level in estuarine water, and decrease of soil pH; leading to acid sulphate soil formation indicates a negative impact of shrimp culture.

APPLICATION OF BDA SCHEME IN TYPHOON TRACK PREDICTION

The MM5, which is the PSU/NCAR mesoscale nonhydrostatic limited-area ,nodel, and its adjoining modeling system are used in this paper. Taking T106 analysis data as background field the authors generate an optimal initial condition of a typhoon by using two bogus data assimilation schemes, and conduct some numerical simulating experiments. The results ofno.9608 typhoon （Gloria） show that the optimal initial tield have some dramatic improvements, such as inaccurate position of typhoon center, weaker typhoon circulation and incomplete inner structure of the typhoon, which are caused by shortage of data over the sea. Some improvements have been made in the track forecast. Through several comparing experiments, the initialization optimized by BDA scheme is found to be more reasonable than GFDL scheme and its typhoon track forrecast is better.

Impact of Land Use Changes on Surface Warming in China

Land use changes such as urbanization, agriculture, pasturing, deforestation, desertification and irrigation can change the land surface heat flux directly, and also change the atmospheric circulation indirectly, and therefore affect the local temperature. But it is difficult to separate their effects from climate trends such as greenhouse-gas effects. Comparing the decadal trends of the observation station data with those of the NCEP/NCAR Reanalysis (NNR) data provides a good method to separate the effects because the NNR is insensitive to land surface changes. The effects of urbanization and other land use changes over China are estimated by using the difference between the station and the NNR surface temperature trends. Our results show that urbanization and other land use changes may contribute to the observed 0.12℃ (10yr)-1 increase for daily mean surface temperature, and the0.20℃ (10yr)-1 and 0.03℃ (10 yr)-1 increases for the daily minimum and maximum surface temperatures, respectively. The urban heat island effect and the effects of other land-use changes may also play an important role in the diurnal temperature range change. The spatial pattern of the differences in trends shows a marked heterogeneity. The land surface degradation such as deforestation and desertification due to human activities over northern China, and rapidly-developed urbanization over southern China, may have mostly contributed to the increases at stations north of about 38°N and in Southeast China, respectively. Furthermore, the vegetation cover increase due to irrigation and fertilization may have contributed to the decreasing trend of surface temperature over the lower Yellow River Basin. The study illustrates the possible impacts of land use changes on surface temperature over China.

Oil Spill Risk Assessment of Offshore Pipeline in the Bohai Sea Under the Perspective of Ecological Protection

In recent decades,the exploration and development of marine oil and gas resources have increased significantly to meet the increasing energy demand of mankind.The Bohai Sea is a semi-closed continental sea that has a weak water exchange capacity and high ecological fragility.However,at present,more than 200 oil platforms have been built in the Bohai Sea,with more than 270 offshore oil pipelines having a length exceeding 1600 km.The oil spill pollution of offshore platforms has a great impact on the marine environment and ecosystems.Therefore,a comprehensive assessment of its risks is of great practical significance.This paper systematically constructs a comprehensive oil spill risk assessment model that combines the oil spill risk probability model and the ocean hydrodynamic model.This paper uses the Bohai Sea offshore pipeline as an example to assess its oil spill risk.The high-risk-value areas of the Bohai Sea offshore pipeline are mainly distributed at the bottom of Liaodong Bay,the bottom of Bohai Bay,near the Caofeidian area,and the northern part of the Yellow River Estuary.

Convective Rainfall in Amazonia and Adjacent Tropics

Hourly rainfall estimates from integrated satellite data are used to build a dynamically based climatology of convectively generated rainfall across South America, including tropical, sub-tropical and oceanic regions. Herein, we focus on 0S to 15S, including greater Amazon and NE Brazil leeward of the South Atlantic Ocean. Emphasis is placed on rainfall resulting from organized convective regimes, which are known to produce the majority of seasonal rainfall in various parts of South America and other continents. The statistical characteristics of individual events are quantified and examined with respect to regional atmospheric conditions. Among the factors considered are steering winds and wind shear, convective available potential energy (CAPE), sea and land breezes, and the occurrence of transient disturbances such as Kelvin Waves and Easterly Waves. Forcing and convective triggering mechanisms are inferred from the diagnosis of systematic patterns as evidenced in the continental diurnal cycle and longer periods of natural variability. The episodes of organized convection are analyzed in terms of their duration, span, phase speed, starting and ending time, starting and ending longitude, month and year through frequency distribution analysis. Most episodes of organized convection tend to move westward across the Amazon Basin. Descriptive statistics indicate average phase speed of westward and eastward episodes of convection in the Amazon basin at -11.8 m.s-1 and 13.0 m.s-1, respectively. Eastward propagating systems are influenced by northeastward moving cold fronts in Southern South America and tend to trigger and to organize convection across the Amazon Basin. Hourly rainfall analyses indicate that convection over the Amazon region is often organized.

Simulation and Analysis of Back Siltation in a Navigation Channel Using MIKE 21

The channel back-siltation problem has been restricting the development of channels,and its monitoring is limited by funds and natural conditions.Moreover,predicting the channel back-siltation situation in a timely and accurate manner is difficult.Hence,a numerical simulation of the back-siltation problem in the sea area near the channel is of great significance to the maintenance of a channel.In this study,the back siltation of a deep-water channel in the Lanshan Port area of the Port of Rizhao after dredging is predicted.This paper relies on the MIKE 21 software to establish the wave,tidal current,and sediment numerical models and uses measured data from two observation stations in the study area for verification.On this basis,taking one month as an example,the entire project channel was divided into five sections,and three observation points were set on each section.The results show that the area with offshore siltation is located in the northerly direction of the artificial anti-wave building.Siltation occurred on the northern seabed in the sea a little farther from the shore.Siltation occurred on the seabed surface far away from the shoreline,and with the increase in the distance from the shoreline,the amount of siltation in the south,center,and north became gradually closed,and the results can be used to guide actual engineering practices.This study will play a positive role in promoting the dredging project of Rizhao Lanshan Port.

Main Characteristics of Dust Storms and Their Radiative Impacts: With a Focus on Tajikistan

known aridity of the region is a major factor in promoting numerous dust storms. They have many diverse impacts on the environment and the climate of the region. The classification of dust storms and synoptic conditions related to their formation in Central Asia are discussed in the content of their diverse impact. We address dust optical properties that are representative of the region. Dust storms significantly reduce visibly and pose a human health threads. They also cause a significant impact on the radiative regime. As a result, dust storms may cause a decrease in temperature during daytime of up to 16℃ and an increase in temperature during night time from up to 7℃ compared to a clear day.

Preyminary Investigations on the Global Summer Monsoonal Drought Mechanics and the Latitudinal Teleconnections

The question of possible teleconnections between the middle latitude general circulation and the Indian south-west monsoon was investigated in this paper. Within the framework of a simple model it was shown that there can exist such an interaction via the ultra-long Rossby waves.

Meshless Surface Wind Speed Field Reconstruction Based on Machine Learning

We propose a novel machine learning approach to reconstruct meshless surface wind speed fields,i.e.,to reconstruct the surface wind speed at any location,based on meteorological background fields and geographical information.The random forest method is selected to develop the machine learning data reconstruction model(MLDRM-RF)for wind speeds over Beijing from 2015-19.We use temporal,geospatial attribute and meteorological background field features as inputs.The wind speed field can be reconstructed at any station in the region not used in the training process to cross-validate model performance.The evaluation considers the spatial distribution of and seasonal variations in the root mean squared error(RMSE)of the reconstructed wind speed field across Beijing.The average RMSE is 1.09 m s^(−1),considerably smaller than the result(1.29 m s^(−1))obtained with inverse distance weighting(IDW)interpolation.Finally,we extract the important feature permutations by the method of mean decrease in impurity(MDI)and discuss the reasonableness of the model prediction results.MLDRM-RF is a reasonable approach with excellent potential for the improved reconstruction of historical surface wind speed fields with arbitrary grid resolutions.Such a model is needed in many wind applications,such as wind energy and aviation safety assessments.

Precipitation Patterns in Cape Verde Islands:Santiago Island Case Study

The Cape Verde archipelago is located between 14。N - 18。N and 22。W - 28。W in the Atlantic Ocean. Previous studies associated Cape Verde’s rainfall regime with ITCZ and African squall lines. This hypothesis is revisited here using rainfall time series?of the 4 Santiago Island station network of Cape Verde National Institute of Meteorology and Geophysics. Rainfall monthly totals are standardized to produce indices in the 1981-2009 period. Time section plots of zonal and meridional wind components anomalies are made using reanalysis data from ESRL/PSD/NOAA website. Daily outgoing long wave radiation and sea level pressure time section plots are also made as proxies for weather systems propagation. Results show that Santiago presents a seasonal rainfall regime characterized by dry (November-June) and wet (July-October) seasons, with short transition period. In general, rainfall totals increase with altitude. Weather systems within a wet year rainy season were associated with positive anomalies of zonal and meridional wind components of relative short duration, while negative anomalies dominated in dry years. These results suggest that winds coming from southwestern quadrant over warm Atlantic Ocean, associated with frontal systems traveling eastward, are the rain-producing events in wet years, not ITCZ or African squall lines. Winds coming from the northeastern quadrant produce dry years. Apparently, decadal-long wet periods are related to PDO cold phase. In the current PDO cold phase, there is only one year (2002) slightly dry. Considering that each PDO phases lasts 25 to 30 years and the current PDO cold phase started in 1999, it is possible that wet years predominate in the next 10 to 15 years.

Hydrometeorological Modeling of Limpopo River Basin in Mozambique with TOPMODEL and Remote Sensing

The Limpopo River basin (LRB) is known for its vulnerability to floods, high rates of evapotranspiration, and droughts that cause significant losses to the local community. The present study aimed to perform simulations of flood events occurring in two Mozambican sub-basins of LRB, namely Chókwè and Xai-Xai from 2000 to 2015 with TOPography-based hydrological MODEL (TOPMODEL) and satellite remote sensing data. As input in TOPMODEL, data from two high-resolution global satellite-based precipitation products: Climate Prediction Center MORPHing technique (CMORPH) and Integrated Multi-Satellite Retrievals for the Global Precipitation Mission (GPM) algorithm (IMERG), 8-day MOD16 evapotranspiration product and surface runoff data estimated by Global Land Data Assimilation System (GLDAS) were used. The sensitivity tests of TOPMODEL parameters were applied using the Monte Carlo simulation. Calibration and validation of the model were performed by the Shuffled Complex Evolution (SCE-UA) method and were evaluated with the Kling-Gupta Efficiency (KGE) index. The results indicated that simulations with the GPM-IMERG (KGE: 0.59 and 0.65) tended to underestimate the stream flows, while with the CMORPH product the performance was much better (KGE: 0.66 and 0.77) in both sub-basins. Thus, TOPMODEL can help to develop flood monitoring systems from satellite remotely sensed data in similar regions of Mozambique.

Numerical Analysis of Effects of Atmospheric Ice Nuclei Concentrations on Radiant Properties of Cold Clouds

Numerical simulations of 18 precipitation days from June to September in 1996with the 3D convective cloud model of CAMS (Chinese Academy of Meteorological Sciences, Version2000) were conducted. In these simulations, the concentration of IN (ice nuclei) was assumed toincrease by 5 times. The results show that when IN concentrations increase, the amounts ofprecipitation decrease, cloud tops heighten and the areas of cloud tops increase in 80 percentsimulated clouds. Moreover, in 95 percent simulated clouds, the sizes of ice crystals in cloudsdecrease and quantities increase. These results mean that the physical properties of clouds willchange when IN concentration increases. The radiant properties of clouds and climate may also changedirectly and indirectly.

Relationship between the simulated East Asian westerly jet biases and seasonal evolu-tion of rainbelt over eastern China

A possible reason for the unreasonable simula- tion of maximum rainfall location, intensity and seasonal evolution over eastern China in CCM3 has been investigated. The analyses focus on the relationship between the simulated East Asian subtropical westerly jet biases and the seasonal evolution of rainbelt over eastern China. Comparisons of the simulated and observed precipitation distributions indicate that the simulated maximum rainfall location, intensity and seasonal evolution are inconsistent with reality. The simu- lated westerly jet center is located to the north of 40°N, which shifts eastward and northward and strengthens, com- pared with NCEP/NCAR reanalysis. The correlation analysis shows that there exists a significant positive correlation be- tween the maximum rainfall amount and zonal wind at 200 hPa over the Great Bend of the Huanghe River. Thus the simulated unrealistic heavy precipitation in the inland area of western China is related to the biases in the location and intensity of the East Asian subtropical westerly jet. Further analysis indicates that the temperature differences from south to north in the lower troposphere and the larger sensi- ble heating over the southeast Tibetan Plateau are responsi- ble for the westerly jet location and intensity biases. There- fore, much more attention should be paid to the accurate simulation of the surface heating near the Tibetan Plateau and the location and intensity of the East Asian subtropical westerly jet for the improvement of precipitation simulation over East Asia.

Statistical characteristics of the double ridges of subtropical high in the Northern Hemisphere

The generality and some climatological charac- teristics of the double ridge systems of subtropical high (SH) are investigated statistically by using the daily NCEP/NCAR reanalysis data from 1958 to 1998. The results show that the SH double-ridge event is a common phenomenon in the Northern Hemisphere, with the distinct seasonal and re- gional features, that is, the majority of SH double-ridge geneses concentrate over the eastern North India Ocean- western North Pacific as well as the central North Pacific in the period from mid-July to mid-September. Especially over the western North Pacific subtropics, the SH double-ridge events are extremely active. It is found that the life cycle of most double-ridge events of western Pacific subtropical high (WPSH) is shorter but some still last longer. The WPSH dou- ble-ridge events occur most frequently from July to Septem- ber, while there is a paucity of occurrences during Novem- ber-March. Also, it is shown that the WPSH double-ridge events have a strong interannual variation with a certain periodicity which possesses a remarkably abrupt change in the mid-1970s. Additionally, the relationship between the WPSH double ridges and the meridional movement of WPSH is discussed.

Definition and Features of the North Edge of the East Asian Summer Monsoon

By using daily total precipitable water（TPW） amount from the ECMWF reanalysis（ERA-44a） data in 1958-2001,the north edge of the Asian sub-tropical summer monsoon is defined by a normalized precipitable water index（NPWI）,and its climatology and interannual/interdecadal variability are examined.The results show that two monsoon systems（the Indian and East Asian monsoon systems） can be identified in terms of monsoon edge defined by the NPWI over Asia.The mean north edge goes in the west-east direction along the south side of the Tibetan Plateau over the area west of 100°E,and then turns northeastward along the northeast side of the Tibetan Plateau via the east of Northwest China,the north of North China, the west of Northeast China to Northeast Asia over the region east of 100°E.The north edge of the East Asian monsoon system has distinct interannual and interdecadal variabilities in the area east of 100°E while that of the Indian monsoon does not show obvious interannual or interdecadal variation in the area west of 100°E.

Characteristics of Secondary Circulations in the Convective Boundary Layer over Two-Dimensional Heterogeneous Surfaces

Large-eddy simulations are conducted to investigate the impacts of the scale of chessboard-like heteroge- neous surface heating and the background wind on secondary circulations （SCs） in the convective boundary layer （CBL）. When the wind blows along the diagonal of the chessboard pattern, the cases with different heterogeneity length scales （λ = 1.2, 2.4, and 4.8 km） and weak background wind （U = 2.5 m s-1） suggest that there exists a threshold for the roll-like SCs, which is satisfied when the heterogeneity length scale is 1.6 times the boundary layer height （λ = 1.6zi）. During the CBL development, the SC intensity increases before this threshold is met, whereas it decreases thereafter. The cases with different background wind speeds （U = 2.5, 5.0, and 10.0 m s-1） and relatively large heterogeneity length scale （λ = 4.8 km） show that the SCs are strengthened by larger wind speeds when the heterogeneity length scale is so large that the threshold cannot be met during the CBL development. Another case with wind direction along neither the diagonal nor the side of the chessboard pattern shows that the roll-like SCs can still be triggered, but the roll axes are orientated along the diagonal of the chessboard pattern rather than along the wind direction.