Abstract:esearch in precipitation enhancement around the world has a history of over sixty years. Over those decades, there have been significant development and progress in precipitation enhancement. However, until now, many scientific and technological problems associated with precipitation enhancement demand urgent solution. Hence, we have to improve the scientific and technological level. First of all, research in some critical technologies such as prediction of seeded clouds, indexes for selecting clouds, and optimization of seeding methods needs to be emphasized so as to reduce the degree of blindness to the utmost. In addition, the evaluation of weather modification attainments has been perplexing scientists without an ideal solution. Scientific reserves including understanding of basic cloud seeding technology, modern observational equipment, and hightech talent are not enough as well. At present, to make breakthrough in weather modification, we have to reform in terms of strategy and technology application and avoid following the old routine. Four critical technologies of developing precipitation enhancement are proposed in the present study, including conduct shorttime, local prediction of clouds and precipitation, having a good indexes to identify and selecting clouds suitable for rain enhancement, optimizing methods of artificial seeding, and conducting evaluation through control observations and comparative analysis scientifically.

Abstract:The anomaly mode of the Asia-Pacific (20°N-70°N, 40°E-120°W) sea level pressure in winter is studied, using the methods of rotated empirical orthogonal function decomposition (REOF), Morlet wavelet analysis, correlation analysis, and synthesis analysis on the global monthlyaverage Sea Level Pressure (SLP) and Sea Surface Temperature (SST). Then the relationship between SLP anomaly (SLPA) and SST anomaly (SSTA) is studied. The results show: The Asia-Pacific winter SLP has a nearly-zonal dipole (anti-phase) distribution, as well as an obvious meridional dipole (anti-phase) distribution. The most significant anomalies of winter SLP are in the four areas which locate in Northeast Asia (60°N-70°N, 110°E-150°E), subtropical North Pacific (25°N-35°N, 150°E-170°W), northwest of China (35°N-45°N,85°E-110°E), and the Aleutian Islands (50°N-60°N, 170°E-165°W). There is a significant negative correlation of SLP between Northeast Asia and the subtropical North Pacific, as well as Northwest China and the Aleutian Islands, which shows the existence of meridional dipole oscillation and zonal dipole oscillation. Two dipoles obviously change at interannual scale with a period of 3-4 a, while zonal dipole index has a cycle of 16 a or so at interdecadal scale in addition.

Abstract:The zonal wind variation in the lower and middle stratosphere (from 300 hPa to 10 hPa) of the Northern Hemisphere (NH) is analyzed using the NCEP/NCAR reanalysis data during 1979-2005. Because the reversal of zonal wind direction mainly occurs during the stratospheric seasonal transition period, the classification of the seasonal change in stratosphere is necessary. To determine the seasonal transition in stratosphere, a method named similarity coefficient is used. The atmospheric general circulation in the stratosphere is of bimodal, i.e. winter and summer modes, with abrupt change during the winter-summer transition. Analyses show that in the zonal direction, the seasonal transition is synchronous; in the meridional direction, however, it is nonsynchronous, and the winter-summer and summer-winter transitions are both earlier in higher latitudes than that in lower latitudes. In the middle stratosphere (10-70 hPa) the seasonal change begins from the higher levels downward to the lower levels, but the seasonal transition in lower stratosphere (100-200 hPa) is complex. In the extra-tropical stratosphere of the NH, the onset date and withdrawal date of stratospheric easterly have good correlation with the seasonal transition date in stratosphere determined by the measure of similarity coefficient. In general, there is a period of ten days with zero zonal wind (weak wind) before and after stable easterly period in the middle stratosphere.

Abstract:Based on the spectral characteristics of the InfraRed Atmospheric Sounder (IRAS) channel, an atmospheric radiative transfer model for IRAS is developed. Using the HIgh resolution TRANsmission（HITRAN）2004 molecular spectroscopic database, the sensitivity to changes in atmospheric CO2 concentration of the measured radiance for ten channels of IRAS during the CO2 absorption bands were calculated to explore the feasibility of monitoring atmospheric CO2 concentration from Fengyun-3 (FY-3) meteorological satellite, and the uncertainties due to the errors of the atmospheric temperature, water vapor, and minor constituent concentrations were compared. It shows that the channel number 4 is the first choice to monitor atmospheric CO2 concentrations, and the ability to identify the changes in CO2 concentration is about 10×10-6 for the currently planned instrument noise.

Abstract:Using the observational air and surface temperature datasets of 112 stations in the Tibetan Plateau (TP) and around areas, the temporalspatial evolution characteristics of the difference of temperature between surface and atmosphere （Ts-Ta) over Tibetan Plateau in the early stage of East Asian Summer Monsoon(EASM) onset and its connections with the EASM are analyzed by EOF(Empirical Orthogonal Function), REOF (Rotated Empirical Orthogonal Function), and other methods. The results show that, the time when Ts-Ta in TP reach the peak value of the year is one month ahead of that of the air and surface temperature, and about two months earlier than that of the same latitude in the middle and eastern China. During the transition season, the sensitive area of Ts-Ta in TP gradually shifts from the central in March to the southeast part in April, and after its 〖JP〗range expands in May, it maintains a stable state in the southeast part of TP. In April and May, the early stage of EASM, snowmelt and thawingfreezing processes of soil over TP have significant effects on the sensitive distribution of Ts-Ta. The trend of Ts-Ta in TP in April is entirely different from that in May. In April, the radiation cooling caused by snow albedo has affected on the change of surface ground, leading to Ts-Ta of TP decreases from the 1960s to the mid-1970s, afterwards it always keeps a rising trend from the late 1970s through the 1990s. During a period from the 1960s to the 1990s, Ts-Ta of TP in May more reflects the effect of diabatic heating over TP, and appears the decreasing trend.

Abstract:Based on the NCAR CAM3.1 model and the distribution of heat sources calculated by NCEP/NCAR (version 1) reanalysis datasets, the impact of atmospheric heat source (sink) distribution over Asia and the Southern Hemisphere on East Asian summer monsoon and Indian summer monsoon is investigated. The results show that: Firstly, the distribution of atmospheric heat source over East Asian region and heat sink over Australia have close relations with East Asian summer monsoon, the heating over the East Asian continent and West Pacific can induce the subtropical monsoon system over the Northern Hemisphere (for example the subtropical high), and the heating over the South China Sea and the cooling over the North Australia are the major mechanism for the tropical Southwestlies monsoon over the South China Sea, the anticyclone over Australia, and the crossequatorial flow; Secondly, the heating over the western part of Asian region and Indian Ocean and that south of the equator connect with Indian summer monsoon very well, however, the impact on East Asian summer monsoon is weak. Heating over the Bay of Bengal can induce Indian southwestlies monsoon to extend eastwardly, heating over the subtropical continent is the major mechanism for the subtropical high over the Northern Hemisphere.

Abstract:A modified automatic cloud-screening method is developed using 1-min measurement of surface downwelling shortwave global and diffuse irradiance. Clear skies are detected firstly by peak frequency density of ratio (PFDR) method. Then the detected clear-sky irradiance measurements are used to fit the expected clear-sky irradiance as the function of the cosine of the solar zenith angle by the least squares fitting method. Afterwards, the PFDR method is applied to the ratio of observed total shortwave irradiance to the predicted values for the cloud-free sky condition with the fitting expression. The clear sky detection method is verified using Total Sky Imager data and observer reports. The result shows that the average accuracy is 90.9% for the solar zenith angle less than 75°. For the modified cloud-screening method, the uncertainties due to both diurnal changes in such variables as column water vapor，aerosol loading，systematic pyranometer offsets，and solar zenith variables are diminished. Cloud occurring frequency and cloud radiative forcing (CRF) on downward shortwave irradiance at ground are calculated based on the clear sky detection results for Xianghe and Taihu. The cloud occurring frequency and the CRF show a distinct seasonal variation with maximum in summer and minimum in winter. The annual average of CRF is -39.5 W·m-2 in Xianghe and -66.2 W·m-2 in Taihu. The seasonal average of CRF in Xianghe is -25.9 W·m-2 in spring, -70.9 W·m-2 in summer, -51.1 W·m-2 in autumn, and -10.8 W·m-2 in winter. And the seasonal average of CRF in Taihu is -84.6 W·m-2，-89.1 W·m-2，-50.2 W·m-2，and -44.1 W·m-2, respectively, from spring to winter.

Abstract:The visibility rules in Beijing were analyzed on the basis of historic data from 2005 to 2009, it showed that the annual mean visibility in Beijing was 10.17 km in the past five years and experienced a significant increasing trend, approximately 0.69 km·a-1(R2=0.99,p<0.01), and at the same time haze days decreased rapidly in the past four years. The decreased annual concentrations of PM2.5 (aerodynamic diameter ≤2.5 μm) were the main reason for the increased visibility. Visibility was the best in spring, better in winter and the worst in summer. In order to understand the causes of the low visibility in Beijing, the characteristics of the low visibility through a selected case in which the visibility rapidly changed to low visibility was analyzed. In this analysis visibility showed a negative correlation with relative humidity and a positive or negative correlation with wind speed, which suggested that the influence of wind speed to visibility was two-sidedness. The analysis also suggested that high concentration of aerosol particles (PM2.5) was a major cause for the visibility degradation. There was a significant anticorrelation between the concentrations of aerosol and the ranges of visibility (R2=0.93,p<0.01), which indicated that the concentration of PM2.5 should firstly be controlled below 30 μg·m-3 to keep a good visibility (>10 km) in Beijing, and the further reduction in aerosol concentrations will lead to an acceleration in improvement in visibility due to the non-linear relationship between aerosols and visibility. According to the diagnostic analysis result of environment process with weather pattern, PM2.5 and visibility had good relationship with the synoptic situation evolution. When the North China region was influenced by the high pressure gradient field after the front, the area of Beijing was affected by northerly winds. With a strong surface wind, atmospheric conditions favored for the diffusion of pollutants, resulting a lower concentration of particulate matter and a higher visibility. By contrast, when a mainland high pressure covered this area, the ground wind speed was weak and not conducive to the diffusion of pollutants. With accumulated local source and regional transportation, PM2.5 accumulated day after day from the valley value to the peak value, while the visibility decreased constantly. This study suggested the primary pollutant which should be controlled was PM2.5 to increase the visibility in Beijing.

Abstract:Based on the annual total solar radiation and related meteorological data of monitoring stations of Ganzhou and Nanchang from 1960 to 2000, the annual total solar radiation of the two stations were calculated with six net long wave radiation formulas combinated with Penman equation. The Method of Absolute Errors (MAE), aiming at estimating the total solar radiation in the region, was proposed with the annual weight coefficients of MAE. The annual total solar radiation of the other 76 stations in Jiangxi Province was calculated with this method. Through the analysis of the temporal-spatial distribution and the trend of the annual total solar radiation of the province, the authors found that: (1) During 1961 to 2000, the value of the total solar radiation in the most parts of Jiangxi Province was 3800-4400 MJ·m-2·a-1. The total solar radiation was high in the southeast region, where there was a large value center. The west part had a lower value than the other parts of the province; (2) For the whole province, the total solar radiation decreased in the past 40 years with the ratio of 143.70 MJ·m-2·(10 a)-1. Among the total 78 stations, 63 stations passed the 0.05 significance level and six stations presented an upward trend. The total solar radiation showed a relatively larger decline in the northern and southern region than in the center part. And there was a low value center on the east side of Poyang Lake.

Abstract:The absorption and scattering coefficients of atmospheric aerosols were measured continuously using the Photo Acoustic Soot Spectrometer (PASS) during May to July in 2008 at the Guangmingding meteorological observatory on Huangshan Mountains. The characteristics of absorption and scattering coefficients, such as the diurnal variation and the relationships to meteorological factors were analyzed. The results show that, under the relative dry conditions (with the relative humidity lower than 60%), the absorption and scattering coefficients are larger during the daytime than that at night. It is found that both of these two coefficients are well correlated with relative humidity (with the correlation coefficients of 0.87 and 0.80, respectively), and are negatively correlated with the local wind speed (with the correlation coefficients of -0.53 and -0.78, respectively). It is also shown that both the absorption and scattering coefficients are remarkably reduced due to precipitation or fog. Compared with the properties measured in Nanjing, it is found that the values of absorption and scattering coefficients measured on Huangshan Mountains are order of magnitude smaller, and that the daily cycle is almost opposite to that in Nanjing. The possible reasons for this are explored.

Abstract:Using thunderstorm data from 1961 to 2007 in Beijing, statistical of tendency rate, polynomial curve fitting, and Morlet wavelet method, comparison analyses of the climate characteristics of thunderstorm and the trend of climate change were given. The results show that: 1）Thunderstorm occurring from March to November had obvious monthly variation and daily variation, which increased abruptly in May, decreased abruptly in September, and reached maximum in July. 2）In contrast to the rural area, the urban area had more obvious phenonmenon that the first day of thunderstorm advanced, the terminal day of thunderstorm delayed, and the period of thunderstorm extented. 3）Annual average days of thunderstorm in the urban area had an extreme opposite variation tendency to the rural area. Although more annual average days of thunderstorm occurred in the rural area, it decreased in a fluctuating tendency. And although less annual average days of thunderstorm occurred in the urban area, it increased in a fluctuating tendency. The increment tendency of annual average days of thunderstorm in urban area was possibly related to greenhouse effection and the increment of days on which relative humidity≥85％. The decrement tendency of annual average days of thunderstorm in the rural area is possibly related to the evident decrement of relative humidity. 4）The variations of annual average days of thunderstorm had multiple period oscillations in both the urban and rural areas, among which 16-18-year and 3-5-year period oscillations were especially obvious.

Abstract:The variation characteristics of the global radiation and the meteorological factors such as cloud cover, humidity, wind speed, visibility, and sunshine duration which may impact the global radiation over the Yunnan-Guizhou Plateau in the southwestern part of China were studied by mathematical statistics method, with which the data of nine radiation observation stations and about 200 weather stations from 1961 to 2005 were involved. The results show that the spatial distribution characteristics of annual global radiation are higher in the western part than the eastern part, and the highest is at Lijiang station(6207 MJ·m-2·a-1), the lowest is at Zunyi station(3340 MJ·m-2·a-1). The global radiations in six out of nine stations have no significant linear trend (P>0.1) in interannual variation, but the other three stations (Mengzi, Guiyang, and Zunyi) have a significant decline (P<0.001) from the 1960s to the 1980s, and then followed by slight (Mengzi) or significant increasing (Guiyang). The main reason of the global radiation declining in Mengzi may owe to the visibility decreasing, and that in Guiyang is concerned with the increasing total cloud cover which result in sunshine duration decreasing. The cloud cover increasing and visibility decreasing are the reasons of the global radiation decline in Zunyi. Overall, interannual or decada1 time scale variations of the global radiation are relative to the cloud cover and sunshine duration on the Yunnan-Guizhou Plateau during 1961-2005. The sunshine duration at city stations (Kunming and Guiyang) decreased with visibility reducing.

Abstract:The impact of the 500-hPa high over the Tibetan Plateau (the 500-hPa high for short) on the heat wave in the eastern part of Sichuan-Chongqing area was studied on the basis of case study and composite circulation anomaly evolution. According to its impact on the heat wave, there are two types of the 500-hPa high. One type dominates over the western and northern parts of the Tibetan Plateau, leading to the northwesterlies prevailing over the northeastern and eastern parts of the Tibetan Plateau, and favoring the heat wave in the eastern part of Sichuan-Chongqing area. Another type is caused by the subtropical high over the western Pacific. As the subtropical high extends westward on the Tibetan Plateau, the 500hPa high forms, and heat wave strikes the areas along the Changjiang River including the eastern part of Sichuan-Chongqing area. As the subtropical high moves eastward, the 500-hPa high still affects the eastern part of Sichuan-Chongqing area. Thus, the heat wave in the eastern part of Sichuan-Chongqing area lasts while the heat wave in the middle and low branch of the Changjiang River ends.