Comparison Between Computer Simulation of Transport and Diffusion of Cloud Seeding Material Within Stratiform Cloud and the NOAA-14 Satellite Cloud Track

A precipitation enhancement operation using an aircraft was conducted from 1415 to 1549 LST 14 March 2000 in Shaanxi Province. The NOAA-14 satellite data received at 1535 LST soon after the cloud seeding shows that a vivid cloud track appears on the satellite image. The length, average width and maximum width of the cloud track are 301 kin, 8.3 and 11 kin, respectively. Using a three-dimensional numerical model of transport and diffusion of seeding material within stratiform clouds, the spatial concentration distribution characteristics of seeding material at different times, especially at the satellite receiving time,are simulated. The model results at the satellite receiving time axe compared with the features of the cloud track. The transported position of the cloud seeding material coincides with the position of the track. The width, shape and extent of diffusion of the cloud seeding material are similar to that of the cloud track.The spatial variation of width is consistent with that of the track. The simulated length of each segment of the seeding line accords with the length of every segment of the track. Each segment of the cloud track corresponds to the transport and diffusion of each segment of the seeding line. These results suggest that the cloud track is the direct physical reflection of cloud seeding at the cloud top. The comparison demonstrates that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulated results are sound and trustworthy. The area, volume, width, depth, and lateral diffusive rate corresponding to concentrations 1, 4, and 10 L^-1 are simulated in order to understand the variations of influencing range.     

Simulation of East Asian Summer Monsoon by Using an Improved AGCM

The IAP 2-L AGCM is modified by introducing a set of climatological surface albedo data into the model for substituting the model’s original surface albedo parameterization. The comparison between the observations and the simulation results by the modified model shows that the general features of the East Asian summer monsoon can be well reproduced by the modified IAP 2-L AGCM. Especially for the simulation of monsoon precipitation, the modi-fied model can well reproduce not only the monthly mean features of the summer monsoon rainfall over East Asia, but also the stepwise advance and retreat of the East Asian summer monsoon rainbelt. Analysis results demonstrate that the good simulation of the monsoon rainfall is closely related to the reasonable simulation of the large scale gen-eral circulation over East Asian region, such as the western Pacific subtropical high, Asian monsoon low and the low level flows. The good performance of the modified model in the rainfall simulation shows its great potential to serve as a useful tool for the prediction of summer drought / flood events over East Asia.     

Numerical Simulation and Comparison Study of the Atmospheric Intraseasonal Oscillation

Daily mean outputs for 12 yr (1978-1989) from two general circulation models (SAMIL-R42L9 and CAM2.0.2) are analyzed and compared with the corresponding NCEP/NCAR reanalysis dataset, and results in two models show clearly that the root-mean square errors (RMSEs) from the simulation of intraseasonal oscillation can take 30-40 percent of the total RMSE, particularly, the distributions of the RMSE in simulating intraseasonal oscillation are almost identical with that of the total RMSE. The maximum RMSE of intraseasonal oscillation height at 500 hPa is shown in the middle latitude regions, but there are also large RMSEs of intraseasonal oscillation wind over the tropical western Pacific and tropical Indian Oceans. The simulated ISO energy in the tropic has very large difference from the result of the NCEP/NCAR reanalysis dataset which means the simulation of tropical atmospheric ISO still possesses serious insufficiency. Therefore, intraseasonal oscillation in the weather and climate numerical simulation is very important, and thus, how to improve the ability of the GCM to simulate the intraseasonal oscillation becomes very significant.     

The Seasonal Climatic Simulation of 9000 Years before Present by Using the IAP Atmospheric General Circulation Model

The seasonal cycle of the climate of 9000 years before present was simulated with the IAP two-level atmospheric general circulation model. The incoming solar radiation was specified from the orbital parameters for 9000 years ago. The boundary conditions of that time were prescribed to the present value because of the small differences between the two. The change in radiation makes temperature to be higher in summer and lower in winter over large areas of the land; and the increased temperature contrast between the land and the ocean strengthens the summer monsoon circulation and increases the precipitation over there. The asymmetry of temperature change between the Northern Hemisphere and the Southern Hemisphere and between summer and winter still exists, which agrees with that get from the previous perpetual experiments.     

Impact of Cloud Microphysical Processes on the Simulation of Typhoon Rananim near Shore.Part Ⅰ: Cloud Structure and Precipitation Features

By using the Advanced Regional Eta-coordinate Model (AREM),the basic structure and cloud features of Typhoon Rananim are simulated and verified against observations.Five sets of experiments are designed to investigate the effects of the cloud microphysical processes on the model cloud structure and precipitation features.The importance of the ice-phase microphysics,the cooling effect related to microphysical characteristics change,and the influence of terminal velocity of graupel are examined.The results indicate that the cloud microphysical processes impact more on the cloud development and precipitation features of the typhoon than on its intensity and track.Big differences in the distribution pattern and content of hydrometeors,and types and amount of rainfall occur in the five experiments,resulting in different heating and cooling effects.The largest difference of 24-h rain rate reaches 52.5 mm h-1.The results are summarized as follows:1) when the cooling effect due to the evaporation of rain water is excluded,updrafts in the typhoon's inner core are the strongest with the maximum vertical velocity of-19 Pa s-1 and rain water and graupel grow most dominantly with their mixing ratios increased by 1.8 and 2.5 g kg-1,respectively,compared with the control experiment; 2) the melting of snow and graupel affects the growth of rain water mainly in the spiral rainbands,but much less significantly in the eyewall area; 3) the warm cloud microphysical process produces the smallest rainfall area and the largest percentage of convective precipitation (63.19％),while the largest rainfall area and the smallest percentage of convective precipitation (48.85％) are generated when the terminal velocity of graupel is weakened by half.     

Comparison and Analysis of Two Different Calculation Schemes of SLEVE-Hybrid Coordinate in the GRAPES＿MESO Model

The calculation scheme of the smoothed-level and hybrid(SLEVE-hybrid for short) coordinates in numerical forecasting model is not limited in number. It is divided into the semi-analytical scheme and the finite differential scheme in terms of the various differential methods of the coordinate deformation variables. Having compared the dynamic equation and the long-time batch simulation results of the two schemes, the present study draws the following conclusions. The first-order finite difference accuracy of the coordinate deformation variables in the finite differential scheme is theoretically lower than that in the semi-analytical scheme. The larger the vertical gradient of the layer thickness is, the larger the relative errors of the finite differential scheme are. The long-time batch simulation test in the GRAPES model dynamic core demonstrates that the bias of the temperature and the geopotential height in the semianalytical scheme is smaller under the default layering, while the simulation difference of the two schemes is greatly reduced when the layering is more uniform.     

Simulation of the Electrification of a Tropical Cyclone Using the WRF-ARW Model：An Idealized Case

Evolution of the electrifi cation of an idealized tropical cyclone （TC） is simulated by using the Advanced Weather Research and Forecasting （WRF-ARW） model. The model was modifi ed by addition of explicit electrifi cation and a new bulk discharge scheme. The characteristics of TC lightning is further examined by analyses of the electrifi cation and the charge structure of the TC. The fi ndings thus obtained are able to unify most of the previous inconsisitent observational and simulation studies. The results indicate that the TC eyewall generally exhibits an inverted dipole charge structure with negative charge above the positive. In the intensifi cation stage, however, the extremely tall towers of the eyewall may exhibit a normal tripole structure with a main negative region between two regions of positive charge. The outer spiral rainband cells display a simple normal dipole structure during all the stages. It is further found that the diff erences in the charge structure are associated with diff erent updrafts and particle distributions. Weak updrafts, together with a coexistence region of diff erent particles at lower levels in the eyewall, result in charging processes that occur mainly in the positive graupel charging zone （PGCZ）. In the intensifi cation stage, the occurrence of charging processes in both positive and negative graupel charging zones is associated with strong updraft in the extremely tall towers. In addition, the coexistence region of graupel and ice crystals is mainly situated at upper levels in the outer rainband, so the charging processes mainly occur in the negative graupel charging zone （NGCZ）.     

Numerical Simulation Study on the Scientific and Methodological Aspects of the Brazilian Proposal

1. IntroductionObservations of surface air temperature indicatethat a significant global average warming has occurredduring the 20th century. The Intergovernmental Panelon Climate Change (IPCC, 2001) concludes that thereis new and stronger evidence that man has influencedthe climate. International negotiations have led to afirst step in combating climate change with the UnitedNations Framework Convention on Climate Change(UNFCCC) and the Kyoto Protocol, but further stepsare needed in …     

Assimilation and Simulation of Typhoon Rusa （2002） Using the WRF System

Using the recently developed Weather Research and Forecasting (WRF) 3DVAR and the WRF model, numerical experiments are conducted for the initialization and simulation of typhoon Rusa (2002).The observational data used in the WRF 3DVAR are conventional Global Telecommunications System (GTS) data and Korean Automatic Weather Station (AWS) surface observations. The Background Error Statistics (BES) via the National Meteorological Center (NMC) method has two different resolutions, that is, a 210-km horizontal grid space from the NCEP global model and a 10-km horizontal resolution from Korean operational forecasts. To improve the performance of the WRF simulation initialized from the WRF 3DVAR analyses, the scale-lengths used in the horizontal background error covariances via recursive filter are tuned in terms of the WRF 3DVAR control variables, streamfunction, velocity potential, unbalanced pressure and specific humidity. The experiments with respect to different background error statistics and different observational data indicate that the subsequent 24-h the WRF model forecasts of typhoon Rusa‘s track and precipitation are significantly impacted upon the initial fields. Assimilation of the AWS data with the tuned background error statistics obtains improved predictions of the typhoon track and its precipitation.     

On the Improvement of the DSAEF＿LTP Model to Heavy Precipitation Simulation of Landfalling Tropical Cyclones over China in 2018

In this study, the Dynamical-Statistical-Analog Ensemble Forecast model (DSAEF_LTP model) for landfalling tropical cyclone (LTC) precipitation was employed to simulate the precipitation of 10 LTCs that occurred Pover China in 2018. With adding parameter‘similarity region scheme’(SRS) values and introducing TC intensity into the generalized initial value (GIV), four groups of precipitation simulation experiments were designed to verify the forecasting ability of the improved model for more TC samples. Results show that the simulation ability of the DSAEF_LTP model can be optimized regardless of whether adding SRS values only, or introducing TC intensity into GIV, while the experiment with both the two improvements shows a more prominent advantage in simulating the heavier precipitation of LTCs. Compared with four NWP models (i.e., ECMWF, GFS, GRAPES and SMS-WARMS), the overall forecasting performance of the DSAEF_LTP model achieves a better result in simulating precipitation at the thresholds over 250 mm and performs slightly better than NWP models at the thresholds over 100 mm.     

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.     

Characteristic Study of the Boundary Layer Parameters over the Arabian Sea and the Bay of Bengal Using the QuikSCAT Dataset

The marine atmospheric boundary layer （MABL） plays a vital role in the transport of momentum and heat from the surface of the ocean into the atmosphere. A detailed study on the MABL characteristics was carried out using high-resolution surface-wind data as measured by the QuikSCAT （Quick scatterometer） satellite. Spatial variations in the surface wind, frictional velocity, roughness parameter and drag coefficient for the different seasons were studied. The surface wind was strong during the southwest monsoon season due to the modulation induced by the Low Level Jetstream. The drag coefficient was larger during this season, due to the strong winds and was lower during the winter months. The spatial variations in the frictional velocity over the seas was small during the post-monsoon season （-0.2 m s^-1）. The maximum spatial variation in the frictional velocity was found over the south Arabian Sea （0.3 to 0.5 m s^-1） during the southwest monsoon period, followed by the pre-monsoon over the Bay of Bengal （0.1 to 0.25 m s^-1）. The mean wind-stress curl during the winter was positive over the equatorial region, with a maximum value of 1.5×10^-7 N m^-3, but on either side of the equatorial belt, a negative wind-stress curl dominated. The area average of the frictional velocity and drag coefficient over the Arabian Sea and Bay of Bengal were also studied. The values of frictional velocity shows a variability that is similar to the intraseasonal oscillation （ISO） and this was confirmed via wavelet analysis. In the case of the drag coefficient, the prominent oscillations were ISO and quasi-biweekly mode （QBM）. The interrelationship between the drag coefficient and the frictional velocity with wind speed in both the Arabian Sea and the Bay of Bengal was also studied.     

Impact of Cloud Microphysical Processes on the Simulation of Typhoon Rananim near Shore.Part Ⅱ:Typhoon Intensity and Track

The impact of cloud microphysical processes on the simulated intensity and track of Typhoon Rananim is discussed and analyzed in the second part of this study.The results indicate that when the cooling effect due to evaporation of rain water is excluded,the simulated 36-h maximum surface wind speed of Typhoon Rananim is about 7 m s-1 greater than that from all other experiments; however,the typhoon landfall location has the biggest bias of about 150 km against the control experiment.The simulated strong outer rainbands and the vertical shear of the environmental flow are unfavorable for the deepening and maintenance of the typhoon and result in its intensity loss near the landfall.It is the cloud microphysical processes that strengthen and create the outer spiral rainbands,which then increase the local convergence away from the typhoon center and prevent more moisture and energy transport to the inner core of the typhoon.The developed outer rainbands are supposed to bring dry and cold air mass from the middle troposphere to the planetary boundary layer (PBL).The other branch of the cold airflow comes from the evaporation of rain water itself in the PBL while the droplets are falling.Thus,the cut-off of the warm and moist air to the inner core and the invasion of cold and dry air to the eyewall region are expected to bring about the intensity reduction of the modeled typhoon.Therefore,the deepening and maintenance of Typhoon Rananim during its landing are better simulated through the reduction of these two kinds of model errors.     

Determination of Intraseasonal Variation of Precipitation Microphysics in the Southern Indian Ocean from Joss–Waldvogel Disdrometer Observation during the CINDY Field Campaign

To date, the intraseasonal variation of raindrop size distribution(DSD) in response to the Madden–Julian Oscillation(MJO) has been examined only over the Indonesian Maritime Continent, particularly in Sumatra. This paper presents the intraseasonal variation of DSD over the Indian Ocean during the Cooperative Indian Ocean experiment on Intraseasonal Variability in the Year 2011(CINDY 2011) field campaign. The DSDs determined using a Joss–Waldvogel disdrometer,which was installed on the roof of the anti-rolling system of the R/V Mirai during stationary observation(25 September to 30 November 2011) at(8°S, 80.5°E), were analyzed. The vertical structure of precipitation was revealed by Tropical Rainfall Measuring Mission Precipitation Radar(version 7) data. While the general features of vertical structures of precipitation observed during the CINDY and Sumatra observation are similar, the intraseasonal variation of the DSD in response to the MJO at each location is slightly different. The DSDs during the active phase of the MJO are slightly broader than those during the inactive phase, which is indicated by a larger mass-weighted mean diameter value. Furthermore, the radar reflectivity during the active MJO phase is greater than that during the inactive phase at the same rainfall rate. The microphysical processes that generate large-sized drops over the ocean appear to be more dominant during the active MJO phase, in contrast to the observations made on land(Sumatra). This finding is consistent with the characteristics of radar reflectivity below the freezing level, storm height, bright band height, cloud effective radius, and aerosol optical depth.     

Runoff Simulation of Three Gorges Area in the Upper Yangtze River during 1998 Flood Season

The contribution of areal precipitation of the catchment from Cuntan to Yichang (Three Gorges area) to eight flood peaks of the Upper Yangtze River (the upper reaches of the Yangtze River) is diagnosed for 1998 flood season. A rainfall-runoff model is employed to simulate runoffs of-this catchment. Comparison of observed and simulated runoffs shows that the rainfall-runoff model has a good capability to simulate the runoff over a large-scale river and the results describe the eight flood peaks very well. Forecast results are closely associated with the sensitivity of the model to rainfall and the calibration processes. Other reasons leading to simulation errors are further discussed.     

Numerical Simulation of Global Temperature Change during the 20th Century with the IAP／LASG GOALS Model

The IAP/LASG GOALS coupled model is used to simulate the climate change during the 20th century using historical greenhouse gases concentrations, the mass mixing ratio of sulfate aerosols simulated by a CTM model, and reconstruction of solar variability spanning the period 1900 to 1997. Four simulations, including a control simulation and three forcing simulations, are conducted. Comparison with the observational record for the period indicates that the three forcing experiments simulate reasonable temporal and spatial distributions of the temperature change. The global warming during the 20th century is caused mainly by increasing greenhouse gas concentration especially since the late 1980s; sulfate aerosols offset a portion of the global warming and the reduction of global temperature is up to about 0.11℃ over the century; additionally, the effect of solar variability is not negligible in the simulation of climate change over the 20th century.     

A Numerical Simulation Study of Impacts of Historical Land-Use Changes on the Regional Climate in China Since 1700

By using the improved regional climate model (BCC_RegCM1.0), a series of modeling experiments are undertaken to investigate the impacts of historical land-use changes (LUCs) on the regional climate in China. Simulations are conducted for 2 years using estimated land-use for 1700, 1800, 1900, 1950, and 1990. The conversion of land cover in these periods was extensive over China, where large areas were altered from forests to either grass or crops, or from grasslands to crops. Results show that, since 1700, historical LUCs have significant effects on regional climate change, with rainfall increasing in the middle and lower reaches of the Yangtze River Basin, Northwest China, and Northeast China, but decreasing by different degrees in other regions. The air temperature shows significant warming over large areas in recent hundred years, especially from 1950 to 1990, which is consistent with the warming caused by increasing greenhouse gases. On the other hand, historical LUCs have obvious effects on mean circulation, with the East Asian winter and summer monsoonal flows becoming more intensive, which is mainly attributed to the amplifled temperature difference between ocean and land due to vegetation change. Thus, it would be given more attention to the impacts of LUCs on regional climate change.     

Simulation of the Ecosystem Productivity Responses to Aerosol Diffuse Radiation Fertilization Effects over the Pan-Arctic during 2001–19

The pan-Arctic is confronted with air pollution transported from lower latitudes. Observations have shown that aerosols help increase plant photosynthesis through the diffuse radiation fertilization effects(DRFEs). While such DRFEs have been explored at low to middle latitudes, the aerosol impacts on pan-Arctic ecosystems and the contributions by anthropogenic and natural emission sources remain less quantified. Here, we perform regional simulations at 0.2o×0.2ousing a well-validated vegetation ...     

Improving Simulation of a Tropical Cyclone Using Dynamical Initialization and Large-Scale Spectral Nudging： A Case Study of Typhoon Megi （2010）

In this study, an approach combining dynamical initialization and large-scale spectral nudging is proposed to achieve improved numerical simulations of tropical cyclones (TCs), including track, structure, intensity, and their changes, based on the Advanced Weather Research and Forecasting (ARW-WRF) model. The effectiveness of the approach has been demonstrated with a case study of Typhoon Megi (2010). The ARW-WRF model with the proposed approach realistically reproduced many aspects of Typhoon Megi in a 7-day-long simulation. In particular, the model simulated quite well not only the storm track and intensity changes but also the structure changes before, during, and after its landfall over the Luzon Island in the northern Philippines, as well as after it reentered the ocean over the South China Sea (SCS). The results from several sensitivity experiments demonstrate that the proposed approach is quite effective and ideal for achieving realistic simulations of real TCs, and thus is useful for understanding the TC inner-core dynamics, and structure and intensity changes.     

Retrieval of Upper Tropospheric Relative Humidity by the GMS-5 Water Vapor Channel： A Study of the Technique

This paper presents an analysis of a technique for retrieving upper tropospheric relative humidity through the GMS-5 satellite‘s 6.7-micron water vapor channel brightness temperature. NCEP analysis shows that a critical assumption of the retrieval theory, namely the constant temperature lapse rate,matches only in the tropical atmosphere. By statistical analyses of brightness temperature simulated by a radiative transfer model and of relative humidity, we examine the effect of lapse rate on this retrieval method and obtain retrieval parameters and error estimates applicable to the GMS-5 satellite over East Asia. If the retrieval parameters are properly chosen, the relative error of retrieving the upper tropospheric relative humidity in this region is less than 10%, and if applied to the low-latitude summer atmosphere, it is less than 5%.