By a simple method, that is, by heating raw materials in a flowing gas at ambient pressure, Si 3 N 4 , Ga 2 O 3 , and ZnO nanowires, SiC nanocables, and SiO 2 amorphous nanowires are synthesized without metal catalysts. The diameters of these one-dimensional nanoscale materials are greatly affected by synthesis temperatures. At suitable synthesis temperatures, their diameters are <100 nm. The growth mechanisms of these nanowires are discussed preliminarily.

Planetary boundary-layer (PBL) structure was investigated using observations from a Doppler lidar and the 325-m Institute of Atmospheric Physics (IAP) meteorological tower in the centre of Beijing during the summer 2015 Study of Urban-impacts on Rainfall and Fog/haze (SURF-2015) field campaign. Using six fair-weather days of lidar and tower data under clear to cloudy skies, we evaluate the ability of the Doppler lidar to probe the urban boundary-layer structure, and then propose a composite method for estimating the diurnal cycle of the PBL depth using the Doppler lidar. For the convective boundary layer (CBL), a threshold method using vertical velocity variance (σ 2 w > 0.1 m 2 s −2 ) is used, since it provides more reliable CBL depths than a conventional maximum wind-shear method. The nocturnal boundary-layer (NBL) depth is defined as the height at which σ 2 w decreases to 10 % of its near-surface maximum minus a background variance. The PBL depths determined by combining these methods have average values ranging from ≈270 to ≈1500 m for the six days, with the greatest maximum depths associated with clear skies. Release of stored and anthropogenic heat contributes to the maintenance of turbulence until late evening, keeping the NBL near-neutral and deeper at night than would be expected over a natural surface. The NBL typically becomes more shallow with time, but grows in the presence of low-level nocturnal jets. While current results are promising, data over a broader range of conditions are needed to fully develop our PBL-depth algorithms.

Abstract. Over the past decades, Beijing, the capital city of China, has encountered increasingly frequent persistent haze events (PHE). While the increased pollutant emissions are considered as the most important reason, changes in regional atmospheric circulations associated with large-scale climate warming also play a role. In this study, we find a significant positive trend of PHE in Beijing for the winters from 1980 to 2016 based on updated daily observations. This trend is closely related to an increasing frequency of extreme anomalous southerly episodes in North China, a weakened East Asian trough in the mid-troposphere and a northward shift of the East Asian jet stream in the upper troposphere. These conditions together depict a weakened East Asian winter monsoon (EAWM) system, which is then found to be associated with an anomalous warm, high-pressure system in the middle-lower troposphere over the northwestern Pacific. A practical EAWM index is defined as the seasonal meridional wind anomaly at 850 hPa in winter over North China. Over the period 1900-2016, this EAWM index is positively correlated with the sea surface temperature anomalies over the northwestern Pacific, which indicates a wavy positive trend, with an enhanced positive phase since the mid-1980s. Our results suggest an observation-based mechanism linking the increase in PHE in Beijing with large-scale climatic warming through changes in the typical regional atmospheric circulation.

The Ba(Ti1−xZrx)O3 (BTZ) system with x≤0.35 has been studied using a combination of x-ray diffraction, dielectric measurements, Raman spectroscopy, and electron diffraction with a view to better understand the changes in structure and correlation length of polar order as a function of composition and temperature. Careful fitting of Raman spectra has confirmed stabilization of the orthorhombic phase at room temperature in x=0.05 with mixed phase (orthorhombic and rhombohedral) present at 80 K. Raman data suggest that the rhombohedral phase is most likely to be present at low temperature for x=0.15 and 0.25 and that only short range polar order evolves in x=0.35. Interpretation of the Raman spectra is in broad agreement with the dielectric data as a function of composition and temperature. Diffuse scatter at room temperature in high order zone axis electron diffraction remains essentially identical for all compositions irrespective of structure and correlation length of polar order. The diffuse maxima are therefore considered not to relate directly to the correlation length of polar order in the BTZ system and therefore do not contribute to the dielectric behavior.

To investigate the effect of urban land surface on rainfall under different urban heat island intensity (UHII) conditions in Beijing, numerical simulation and sensitivity experiments on two individual summer convective rainfall events are performed, using the Weather Research and Forecasting/Noah/urban canopy model (UCM) model system. It is found that the cloud ice and cloud graupel formation processes in the microphysics parameterization scheme play a pivotal role in increasing the model's ability to simulate convective rainfall. When UHI is weak prior to the start of rainfall, urban land surface primarily affects rainfall through its dynamic action. Rainfall systems develop a tendency to bifurcate in the windward periphery of the urban area and move around it along both sides. Consequently, precipitation in the central urban area and its downstream area decreases, whereas precipitation in the suburban areas at the sides of the periphery of the urban area increases. When UHI is strong before rainfall begins, the thermal effect of the urban land surface is the main factor that affects rainfall. The lower atmosphere over urban area is more unstable, and horizontal convergence is enhanced, increasing the intensity of the convective system after it moves to the urban area. As a result, precipitation increases in the urban area. This study demonstrates that UHII can be used as an important factor for distinguishing the effect of urban land surface on rainfall.