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Motuo and Naqu are two typical regions of the Tibetan Plateau with different geographical locations and climate regimes. These differences may lead to discrepancies in the raindrop size distributions (DSDs) and precipitation microphysical processes between the two regions. This paper investigates discrepancies in the DSDs using disdrometer data obtained during the rainy season in Motuo and Naqu. The DSD characteristics are studied under five different rainfall rate categories and two precipitation types (stratiform and convective). For the total data sets, the number concentrations of drops with diameters D > 0.6 (D < 0.6) mm are higher (lower) in Naqu than in Motuo. The fitted normalized gamma distributions of the averaged DSDs for the five rainfall rate categories show that Naqu has a larger (lower) mass-weighted mean diameter Dm (normalized intercept parameter, log10Nw) than does Motuo. The difference in Dm between Naqu and Motuo increases with the rainfall rate. Convective clusters in Naqu could be identified as continental-like, while convective precipitation in Motuo could be classified as maritime-like. The relationships between the shape factor μ and slope parameter Λ of the gamma distribution model, the radar reflectivity Z and the rainfall rate R are also derived. Furthermore, the possible causative mechanism for the notable DSD variation between the two regions during the rainy season is illustrated using reanalysis data and automated weather station observations. Cold rain processes are mainly responsible for the low concentrations of large drops observed in Naqu, whereas warm rain prevails in Motuo, producing abundant small drops.

The Sichuan Basin (SCB), in southwest China, is characterized by a high frequency of heavy precipitation (HP) events in the boreal summer. In this study, the top 50 HP events that occurred in the SCB were selected, based on daily precipitation gauge data during 1980–2013, and the moisture sources for these events have been identified. Taking advantage of the Lagrangian approach, we particularly examined the spatiotemporal structure of the moisture sources, both in their magnitude and temporal sequence. The results of this study can be summarized as follows: (1) the quantification of the contribution of the moisture sources indicated that the remote sources of moisture originating from the Tibetan Plateau, Indian Peninsula, Bay of Bengal and the Arabian Sea made considerable contributions to the moisture in the HP events; however, these areas were only the third most important factor in climatology, following the stronger influence of moisture uptake from the SCB local regions and the nearby Indo-China Peninsula and South China Sea regions; (2) the time that moisture involved in the HP events varies between a few hours to more than a week before the HP events. Most of the moisture uptakes happened 1–5 days before the events, with maximum uptake occurring about 1 day before; (3) individual event-to-event variability of moisture sources was apparent. However, in contrast to the primary moisture contributors, this event-to-event variation depended largely on the externally imported moisture, particularly water vapor conveyed by both dominant southwest circulations and the moisture exported from the Tibetan Plateau, rather than the local SCB region. These results have established the atmospheric flow patterns that are prerequisites for HP events; meanwhile, regional moisture availability over the SCB region could also be an essential component of forecasting the HP events and needs to be better understood.

This study presented a quantitative climatology of atmospheric moisture affecting the Yangtze River Basin (YRB) region in boreal summer season, as well as the spatial evolution of atmospheric moisture passage towards the target regions. A three-dimensional Lagrangian particle dispersion model FLEXPART was driven by the National Centers for Environmental Prediction Final Operational Global Analysis data combined with a backtracking scheme, and the transport contributions to the moisture budget over the YRB region was identified through the continuous calculation of changes in specific humidity along the FLEXPART back trajectories of all air masses residing over this region for a period of six summers of year 2004–2009. The back trajectory analysis revealed four major moisture sources contributed to the YRB summer water vapour with different transport timescales: the East China Sea (17.5%), South China Sea (26.6%), Indian peninsula and the Bay of Bengal (20.5%) and Arabian Sea (13.6%). The properties of moisture sources and its transport processes are dominated by the Asian Summer Monsoon regimes. The Tibetan Plateau also acts as an effective barrier for the meridional moisture transport, leading to distinct moisture sinks at the southern slope. In contrast to the previous results, the tropical western Pacific only plays a minor role in the water vapour contributors. The importance of the four source areas varies over the summer: East and South China Sea sources persist throughout the summer, whereas the Indian peninsula, the Bay of Bengal and Arabian Sea sources reach the strongest moisture supply to the YRB region only in high summer (July), showing a close association with the March of Asian monsoon. The further evaluation shows that the inter-annual variability of precipitation over YRB is strongly related to the moisture sources in the Bay of Bengal and Arabian Sea. Copyright © 2012 Royal Meteorological Society

The diurnal variations of gaseous pollutants and the dynamical and thermodynamic structures of the atmospheric boundary layer (ABL) in the Beijing area from January to March 2001 are analyzed in this study using data from the Beijing City Air Pollution Observation Field Experiment (BECAPEX). A heavy pollution day (22 February) and a good air quality day (24 February) are selected and individually analyzed and compared to reveal the relationships between gaseous pollutants and the diurnal variations of the ABL. The results show that gaseous pollutant concentrations exhibit a double-peak-double-valley-type diurnal variation and have similar trends but with different magnitudes at different sites in Beijing. The diurnal variation of the gaseous pollutant concentrations is closely related to (with a 1–2 hour delay of) changes in the atmospheric stability and the mean kinetic energy in the ABL.

Based on 1961–2000 NCEP/NCAR monthly mean reanalysis datasets, vapor transfer and hydrological budget over the Tibetan Plateau are investigated. The Plateau is a vapor sink all the year round. In summer, vapor is convergent in lower levels (from surface to 500 hPa) and divergent in upper levels (from 400 to 300 hPa), with 450 hPa referred to as level of non-divergence. Two levels have different hydrologic budget signatures: the budget is negative at the upper levels from February to November, i.e., vapor transfers from the upper levels over the plateau; as to the lower, the negative (positive) budget occurs during the winter (summer) half year. Evidence also indicates that Tibetan Plateau is a “vapor transition belt”, vapor from the south and the west is transferred from lower to upper levels there in summer, which will affect surrounding regions, including eastern China, especially, the middle and lower reaches of the Yangtze. Vapor transfer exerts significant influence on precipitation in summertime months. Vapor transferred from the upper layers helps humidify eastern China, with coefficient −0.3 of the upper budget to the precipitation over the middle and lower reaches of the Yangtze (MLRY); also, vapor transferred from east side (27.5°–32.5°N) of the upper level has remarkable relationship with precipitation, the coefficient being 0.41. The convergence of the lower level vapor has great effects on the local precipitation over the plateau, with coefficient reaching 0.44, and the vapor passage affects the advance and retreat of the rainbelt. In general, atmospheric hydrologic budget and vapor transfer over the plateau have noticeable effects on precipitation of the target region as well as the ambient areas.

This paper explores the impact of the convective action over the low-latitude region; the water vapor transport around the West Pacific subtropical high (WPSH), and its convective action on the seasonal northward jump and southward withdrawal of the WPSH in summer by using the daily data set of NCEP and T BB for 1998. The research shows that in summer, the WPSH moves northward when the convection over the low-latitude tropical region intensifies and the subsidence region of the meridional vertically vertical circulation in meridional direction circulation over the region of 110°–150°E moves northward. Furthermore, as revealed by diagnostic analysis, the subtropical high moves northward after the obvious weakening of the longitudinal water vapor transport over the region around the subtropical high, but withdraws southward a pentad after the reduction of the latitudinal water vapor transport over the tropical West Pacific region. The research results show that the northward jump and southward withdrawal of the WPSH are closely related to the release of the convective latent heat at low latitudes and the water vapor transport at boundaries around WPSH and its convective action. The numerical simulation further validates the above-mentioned correlation between the variation of the action of the subtropical high and the preceding water vapor transport along with the convection characteristics.

The water vapor transport model at the regional boundary in the Meiyu period is put forward through diagnostic analysis. The numerical simulation on the water vapor transport at the boundary of China in the heavy rainfall period during June–July 1998 shows that the feature of water vapor transport in June is different from that in July. The main body of the water cycle that forms the torrential rain in the Yangtze River Valley is made up of water vapor transport at the western and southern boundaries of the China region in June, whereas the water vapor flow at the western boundary in middle Tibet turns out to be the main body of water vapor sources in July. The water vapor transport at the western boundary of the Tibetan Plateau and the southern boundary of China plays an important role in the torrential rain in the Yangtze River Valley. The temporal and spatial distribution characteristics of water vapor flow at the regional boundary and their theoretical model would provide the scientific proof for the heavy rain forecasts in the Yangtze River Valley.

The effect of the thermal anomaly of the underlying surface of the Tibetan Plateau in the previous winter and spring on the precipitation over the middle and lower reaches of the Yangtze River (MRYR) in the subsequent summer was investigated. Through data analysis, the influence of “strong signal” features of the three-dimensional thermal anomaly of the Plateau upon the precipitation anomaly over MRYR in the subsequent summer was revealed. This feature of the signal shows that from 0 cm to 320 cm under the surface of the ground, the soil temperature anomalies of the Tibetan Plateau manifest out of phase distribution in flood years and drought years over MRYR. In flood years over MRYR, there is a positive soil temperature anomaly in the region of the southern Tibetan Plateau (to the south of 30°N) and a negative anomaly in the region of the middle and northern Tibetan Plateau (to the north of 30°N), while in drought years the distribution of the soil temperature anomaly is opposite to the one in flood years. The maximum value of the soil temperature anomaly lies in the levels between 40 cm and 160 cm under the surface of the ground. Meanwhile, the data analysis also shows that the general circulation in the Northern Hemisphere may respond to the thermal anomaly of the Tibetan Plateau and form the propagation of a low frequency wave train with a seasonal time scale, and this wave train may affect the precipitation over MRYR in the subsequent summer. Analyses reveal that the thermal anomaly of the underlying surface of the Tibetan Plateau in the previous winter and spring is one of the key influencing factors for the subsequent summer precipitation over MRYR.

This paper summarizes main progresses made in tropical cyclone research field in China in the past few years after the 8th five year program of China. New achievements have been made on tropical cyclone (hereafter referred as TC) structure, numerical prediction, evaluation of operational numerical model, TC–caused heavy rain, TC climate features and disasters, etc.

The data of the meteorological elements in the surface layer have been analyzed which were obtained during the IOP of TIPEX from May to July 1998 inGěrzě, Damxung and Qamdo. The characteristics of the diurnal variations and the vertical profiles of the wind velocity, temperature and humidity in the surface layer have been investigated. Some interesting results have been obtained. The moisture inversion phenomena occured during the daytime in the surface layer have also been discussed.

This paper studies correlations between the spatial structure character of thermal forcing and deformation and the amplitude of rays of meridional wave train. It is shown that if thermal forcing appears a meridional linear variation the rays of quasi-stationary planetary wave may propagate along oblique lines and if the meridional variability of heat source has second order term the rays show distinct deformation as a great circular route. Additionally, the inhomogeneous distribution may cause lower frequency oscillations in mid- and low-latitudes. The combination of zonal and meridional wave numbers and distributive character of heat source may form an inverse mechanism of variational trend of generized wave energy, reflecting in some degree the physical process of transition between meridional and zonal flow patterns.