A total of 4967 observations of 385 tropical cyclones (TCs) in the Northwest Pacific Ocean from 2001 to 2014 from the Best Track data, the Tropical Rainfall Measuring Mission (TRMM) satellite data and the National Centers for Environmental Prediction (NCEP) reanalysis data were classified to compare and analyze the response of environmental vertical wind shear and water vapor field on TC structural change. The results show that intensify TCs are mainly accompanied by east wind shear, and weaken TCs are mainly accompanied by west wind shear. Under the strong vertical wind shear (v > 5 m/s), there is no obvious water vapor anomaly on TC structural change. Under the weak vertical wind shear (v ≤ 5 m/s), the intensify (weaken) TC is accompanied by positive (negative) water vapor anomaly.

A wide range of radiation fog shrouded North China at 18:00 on January 21, 2013. Based on mesoscale model of WRF (the Weather Research and Forecasting Model) V3.5.1, the predictability of this case is discussed, through comparison between different horizontal resolution of the boundary layer scheme (BLS) and large eddy simulation (LES) scheme. The results indicate that there exists a certain capability to simulate this fog through the BLS, but also exists a delay of 3 hours; however, through LES, both of the occurrence time and distribution of fog can be well simulated. More accurate results can be obtained by improving the horizontal resolution, which makes the occurrence time and distribution closer to the observation. Further analysis shows that, compared with BLS, LES simulates lower temperature of the surface, more water vapor, higher relative humidity and earlier occurrence of the temperature inversion. As a result, in this example, LES is capable of significantly improving the forecast skill of the mesoscale model for radiation fog in North China.

A squall line hit Beijing on Sept. 14, 2008 when thunder, light and strong winds was observed in the urban areas, however, the weather forecast for that day failed. The weather research and forecasting model (WRF) and the ARPS (advanced regional prediction system) data assimilation system (ADAS) are used to analyze the sensitivity of model horizontal resolution and initial condition contributed by different kinds of observations (FY2C satellite data, MICAPS data and GTS (global telecommunication system) data). Results show that there is no precipitation at all in Beijing in the simulation with a horizontal resolution of 15 km. While, for the simulation with a horizontal of 5 km, the precipitation can be simulated except that the area and intensity of the rainfall is different. There is no precipitation in the urban area in the control experiment without data assimilation. The simulated precipitation location is improved after using the ADAS data assimilation system. A MICAPS sounding in the Hetao area brings stronger northeast winds at lower level in the initial condition compared with control run in which the simulated squall line moves to the north of Beijing.

Interaction of tropical cyclone and South China Sea (SCS) summer monsoon, especially the mechanism for intensification of low level jet over SCS caused by tropical cyclone landfall, is discussed base on case study and statistical analysis. In case study, different sets of numerical experiments during the landfall of tropical storm BILIS (0604) are carried out using mesoscale model MM5. Result shows that the moist southwestly summer monsoon retarded the decay of tropical cyclone and enhanced the rainfall. On the other hand, the backward reaction from tropical cyclone to low level jet over SCS cannot be ignored. Mesoscale convection systems accompanied with tropical cyclone landfall would enhance the pressure gradient force in low atmosphere over SCS, which would lead to intensification of the low level jet in summer monsoon. Statistical analysis of 30 tropical cyclones with similar track as BILIS dating from 1950 to 2009 also shows that 80% tropical cyclone activities accompany with positive low level wind speed anomaly in SCS.

Based on the Tropical Storm and Hurricane WX products ( WX-TROPL) , 596 tropical disturbances generated over the Northwestern Pacific during 2000-2008 are analyzed, 456 of which occur in summer half year (May to October). The frequency peaks in August ( 11. 6 per year in average) . There are 369 disturbances generated in the monsoon trough. The average development rate of disturbances is 43. 8% , while the peak value 54. 8% appears in August, and the neap value 20% appears in February. The ENSO3. 4 index at the end of year has a high negative correlation with the frequency of disturbances in the next summer half year, and the coefficient reaches 76. 1% . The stronger peak value of La Nina's signal appears, and the longer it lasts, the higher frequency of disturbances in the next summer half year turns up. Over the Northwestern Pacific, most disturbances generate in the South of 15°N in winter half year, and scatter between 0°-35°N in summer half year. Using data derived from satellites, it is implied that the tropical disturbances over the Northwestern Pacific all generate in the high value areas of lower level vorticity and latent heat release.

SAGEⅡ( stratospheric aerosol and gas experiment Ⅱ) data extending as long as 20 years was used to study both the spatial and temporal distributions and the trend of column aerosol between 5.0 and 15.0 km over East Asia. The transport of aerosol to the upper level and downstream areas by dust activities was also studied. It's found that there are three different kinds of horizontal distributions. In the low level of 5.0 -8.5 km, the high-value area is just above the dust source of aerosol, e.g. Tibetan Plateau, deserts in the northwest of China; in the middle level of 9.0-10.0 km, the high-value area is consistent with the area with high extratropical cyclone frequency; in the high level of 10.5 - 15.0 km, the value in low-latitude is significantly higher than that in high-latitude. Upper level aerosol distributions in all the three levels significantly vary seasonally resulting from different synoptic systems. A downward trend of upper air aerosol is found in recent ten years over East Asia and the aerosol optical depth (AOD) between 5.0 and 15.0 km has decreased by 0.016. It is also found that aerosol between 5. 0 and 11. 5 km has significant positive correlation with the dust storm activity, which infers the injection of surface dust to all the altitude in troposphere. Upper-air-effect-index of dust storm was defined to study the impact of dust storms in East Asia on the downstream areas. The movement of dust towards the east was observed; and the dust could reach the Atlantic Ocean in about 12 days.

The Fifth generation NCAR/PSU mesoscale nonhydrostatic model(MM5) was used to simulate the process that a tropical disturbance developed into a strong typhoon WUKONG over the South China Sea in September 2000 The MM5 model could forecast the maximum wind and intensity of the typhoon with considerable accuracy The natural developing characteristics of South China Sea Typhoon which involved step-by-step deepening and drastic strengthening were also well simulated Based on some diagnostic variable analysis, the potential factors on typhoon structure as well as the genesis of typhoon eye were briefly analyzed Sensitivity experiments on sea surface temperature (SST) effect indicate that the SST is of vital importance to the genesis and development of typhoon over South China Sea If SST is degraded by 1 degree, the simulated typhoon would have a decrease of 10m/s on maximum wind and a nearly seven-hour delay to reach typhoon level intensity (surpass 328m/s) If SST is degraded by 2 degree (with SST still being between 26 and 27 degree), the initial tropical disturbance could hardly develop into typhoon

High, resolution numerical simulation scheme is used to study the physical mechanism of the intensification of Typhoon LEO (1999), which develops from a tropical storm in South Chine Sea. The results show the transition from a tropical storm to a typhoon is caused by convective bursts near the storm center. The convective condensation heating effect helps to form a warm core and also a cyclonic circulation at upper levels. The merger of mesoscale vortices or the injection of mesoscale vortices to the storm center at lower levels might be the trigger of convective bursts.

Mesoscale model MM5 is used to examine the orographic effect to the precipitation caused by a Mesoscale Convective System (MCS) over Taiwan. A series of sensitive simulations are carried out to investigate the sensitivity of model resolution and orographic accuracy to precipitation. The results show that model resolution is crucial to the precipitation forecast, and orographic accuracy is found to be essential to both the location and the amount of the precipitation for this case. In order to get reasonable prediction, 6km model grid resolution and 18km accuracy of orography are needed.
      Sensitivity simulations with and without orography of Central Mountain Range (CMR) in the model show there are two kinds of orographic effects to the precipitation in this case, which can be called as "induced" and "modified" effects. CMR in Taiwan blocks the movement of mesoα scale low that associated with the MCS in the lower troposphere, and help to generate local mesoβ scale lows interacting with the mesoα scale vortex at the north of CMR. Severe rainfall brought by these local stationary mesoscale circulation systems is "induced" in northern Taiwan. At the central CMR, where the MCS landed, both rainfall area and its intensity are increased. That means the central CMR only "modified" the rainfall.

The evolution and structure of two organized meso-α-scale convective systems developed sequentially on the landfall typhoon low during 3-5 August 1996 are simulated successfully using Penn State/NCAR mesoscale model version 5(MM5). The simulated cloud and precipitation are coincident with the satellite and conventional precipitation observations, respectively. Based on the model output, the detail structure and characteristic of MCS are studied, and the air trajectories around these MCSs are also calculated. Finally, a concept model of MCS in landfall typhoon was given out; In mature stage, the mesoscale Low-Level Jets (mLLJs) act as mesoscale disturbances that embedded in the synoptic-scale Low-Level Jets (LLJs) at the low-level. Strong convergence and upward motion occurred on the left-front of the mLLJ. Mesoscale Upper-Level Jets (mULJs) was found in the upper level outflow caused by upward motion. This mULJ can be verified from conventional upper-air soundings. Strong divergence happened in the right-rear of the mULJ in simulation.

This paper discusses some theoretical issues in the following aspects: methodology, climatic model, climatic change and climate prediction.