Applying Anomaly-based Weather Analysis to the Prediction of Low Visibility Associated with the Coastal Fog at Ningbo-Zhoushan Port in East China

Low visibility episodes (visibility < 1000 m) were studied by applying the anomaly-based weather analysis method. A regional episode of low visibility associated with a coastal fog that occurred from 27 to 28 January 2016 over Ningbo- Zhoushan Port, Zhejiang Province, East China, was first examined. Some basic features from the anomalous weather analysis for this case were identified:(1) the process of low visibility mainly caused by coastal fog was a direct response to anomalous temperature inversion in the lower troposphere, with a warm center around the 925 hPa level, which was formed by a positive geopotential height (GPH) anomaly in the upper troposphere and a negative GPH anomaly near the surface;(2) the positive humidity anomaly was conducive to the formation of coastal fog and rain;(3) regional coastal fog formed at the moment when the southwesterly wind anomalies transferred to northeasterly wind anomalies. Other cases confirmed that the low visibility associated with coastal fog depends upon low-level inversion, a positive humidity anomaly, and a change of wind anomalies from southwesterly to northeasterly, rain and stratus cloud amount. The correlation coefficients of six-hourly inversion, 850?925-hPa-averaged temperature, GPH and humidity anomalies against visibility are ?0.31, 0.40 and ?0.48, respectively, reaching the 99% confidence level in the first half-years of 2015 and 2016. By applying the anomaly-based weather analysis method to medium-range model output products, such as ensemble prediction systems, the anomalous temperature?pressure pattern and humidity?wind pattern can be used to predict the process of low visibility associated with coastal fog at several days in advance.

Constraining Anthropogenic CH_4 Emissions in Nanjing and the Yangtze River Delta,China,Using Atmospheric CO_2 and CH_4 Mixing Ratios

Methane （CH4） emissions estimated with the Intergovernmental Panel on Climate Change （IPCC） inventory method at the city and regional scale are subject to large uncertainties.In this study,we determined the CH4：CO2 emissions ratio for both Nanjing and the Yangtze River Delta （YRD）,using the atmospheric CH4 and CO2 concentrations measured at a suburban site in Nanjing in the winter.The atmospheric estimate of the CH4：CO2 emissions ratio was in reasonable agreement with that calculated using the IPCC method for the YRD （within 20％）,but was 200％ greater for the municipality of Nanjing.The most likely reason for the discrepancy is that emissions from unmanaged landfills are omitted from the official statistics on garbage production.

OPERATIONAL ENSEMBLE FORECASTING AND ANALYSIS OF TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC(INCLUDING THE SOUTH CHINA SEA)

Based on the tropical cyclone data from the Central Meteorological Observatory of China, Japan Meteorological Agency, Joint Typhoon Warning Center and European Centre for Medium-Range Weather Forecasts （ECMWF） during the period of 2004 to 2009, three consensus methods are used in tropical cyclone （TC） track forecasts. Operational consensus results show that the objective forecasts of ECMWF help to improve consensus skill by 2%, 3%-5% and 3%-5%, decrease track bias by 2.5 kin, 6-9 km and 10-12 km for the 24 h, 48 h and 72 h forecasts respectively over the years of 2007 to 2009. Analysis also indicates that consensus forecasts hold positive skills relative to each member. The multivariate regression composite is a method that shows relatively low skill, while the methods of arithmetic averaging and composite （in which the weighting coefficient is the reciprocal square of mean error of members） have almost comparable skills among members. Consensus forecast for a lead time of 96 h has negative skill relative to the ECMWF objective forecast.

A STUDY ON THE MECHANISM OF RAPID WEAKENING OF TYPHOON XANGSANE (0020) OVER THE EAST CHINA SEA

： Using the National Center for Environmental Prediction reanalysis data on 1.0°×l.0° grids and data from theTropical Cyclone yearbook （2000）, a diagnostic analysis and numerical simulation were performed to investigate the characteristics and mechanism underlying the rapid weakening of typhoon Xangsane. The results show that a sharp decline in the intensity of typhoon Xangsane resulted from its movement into the cool sea surface temperature area in the East China Sea, the intrusion of cold air from the mainland into the typhoon, and a rapid increase of the vertical wind shear in the surrounding environment. An important factor that led to the demise of the typhoon was a significant decrease in the moisture transport into the typhoon. Furthermore, the results of the numerical simulation and sensitivity experiments indicate that sea surface temperature largely modulated the rapid weakening of typhoon Xangsane.

NUMERICAL SIMULATION STUDY ON THE RAPID INTENSIFICATION OF TYPHOON HAIKUI(1211) OFF THE SHORE OF CHINA

Forecasting the rapid intensification of tropical cyclones over offshore areas remains difficult. In this article,the Weather Research and Forecast(WRF) model was used to study the rapid intensification of Typhoon Haikui(1211)off the shore of China. After successful simulation of the intensity change and track of the typhoon, the model output was further analyzed to determine the mechanism of the rapid change in intensity. The results indicated that a remarkable increase in low-level moisture transportation toward the inner core, favorable large-scale background field with low-level convergence, and high-level divergence played key roles in the rapid intensification of Typhoon Haikui in which high-level divergence could be used as an indicator for the rapid intensity change of Typhoon Haikui approximately 6 h in advance. An analysis of the typhoon structure revealed that Typhoon Haikui was structurally symmetric during the rapid intensification and the range of the eyewall was small in the low level but extended outward in the high level. In addition, the vertically ascending motion, the radial and tangential along wind speeds increased with increasing typhoon intensity, especially during the process of rapid intensification. Furthermore, the intensity of the warm core of the typhoon increased during the intensification process with the warm core extending outward and toward the lower layer. All of the above structural changes contributed to the maintenance and development of typhoon intensity.

LOW-DEFORMATION VORTICITY AREAS IN SYNOPTIC-SCALE DISTURBANCES FOR TROPICAL CYCLOGENESIS：AN OBSERVATIONAL ANALYSIS

It has long been known that incipient tropical cyclones(TCs) always occur in synoptic-scale disturbances or tropical cyclogenesis precursors, and the disturbances can intensify only within a limited area during tropical cyclogenesis. An observational analysis of five tropical cyclogenesis events over the western North Pacific during 11 August to 10 September 2004 is conducted to demonstrate the role of synoptic-scale disturbances in establishing a limited area of low-deformation vorticity for tropical cyclogenesis.The analysis of the five tropical cyclogenesis events shows that synoptic-scale tropical cyclogenesis precursors provide a region of low-deformation vorticity, which is measured with large positive values of the Okubo-Weiss(OW) parameter.The OW concentrated areas are within the tropical cyclogenesis precursors with a radius of about 400-500 km and can be found as early as 72 hours prior to the formation of the tropical depression. When the TCs reached the tropical storm intensity, the concentrated OW is confined to an area of 200-300 radius and the storm centers are coincident with the centers of the maximum OW. This study indicates that the tropical cyclogenesis occurs in the low-deformation 18-72 hours prior to the formation of tropical depressions, suggesting the importance of low-deformation vorticity in pre-existent synoptic-scale disturbances. Although the Rossby radius of deformation is reduced in TC genesis precedes,the reduction does not sufficiently make effective conversion of convective heating into kinetic energy within the low-deformation area. Further analysis indicates that the initial development of four of the five disturbances is coupled with the counterclockwise circulation of the mixed Rossby-Gravity(MRG) wave.

CAUSE OF THE RAPID WEAKENING OF TYPHOON BEBINCA(0021)IN THE SOUTH CHINA SEA

The cause of the rapid weakening of Typhoon“Bebinca”was analyzed in this paper,by using the NCEP FNL(Final)Operational Global Analysis data on 1°×1°grids and the Tropical Cyclone(TC)Annual Report.The result shows that during the middle to late stage of its life cycle,the meteorological environments did not sustain“Bebinca”to maintain its intensity:the water vapor transport at low level decreased significantly;cold air intruded from north at low to middle level;both the divergence at high level and the convergence at low level reduced at the same time in the late stage.All these above factors restrained the development of“Bebinca”.In particular,the rapid reduction of sea surface temperature(SST)was the main factor that induced the rapid weakening of the Typhoon,which occurred about 6 hour ahead of its weakening.Compared to the 500-850 hPa vertical wind shear,which shows a relatively high correlation with the weakening,the impact of the 200-850 hPa vertical wind shear on the intensity change was not significant.Therefore,the Typhoons in the South China Sea would possibly weaken and disappear rapidly in fall and winter.So we have to pay more attention to the time effectiveness of the forecasting and correct the results in time.