The characteristics of raindrop size distributions (DSDs) and vertical structures of rainfall during the Asian summer monsoon season in East China are studied using measurements from a ground‐based two‐dimensional video disdrometer (2DVD) and a vertically pointing Micro Rain Radar (MRR). Based on rainfall intensity and vertical structure of radar reflectivity, the observed rainfall is classified into convective, stratiform, and shallow precipitation types. Among them, shallow precipitation has previously been ignored or treated as outliers due to limitations in traditional surface measurements. Using advanced instruments of 2DVD and MRR, the characteristics of shallow precipitation are quantified. Furthermore, summer rainfall in the study region is found to consist mainly of stratiform rain in terms of frequency of occurrence but is dominated by convective rain in terms of accumulated rainfall amount. Further separation of the summer season into time periods before, during, and after the Meiyu season reveals that intrasummer variation of DSDs is mainly due to changes in percentage occurrence of the three precipitation types, while the characteristics of each type remain largely unchanged throughout the summer. Overall, higher raindrop concentrations and smaller diameters are found compared to monsoon precipitation at other locations in Asia. Higher local aerosol concentration is speculated to be the cause. Finally, rainfall estimation relationships using polarimetric radar measurements are derived and discussed. These new relationships agree well with rain gauge measurements and are more accurate than traditional relations, especially at high and low rain rates.

Numerical simulations of a convective boundary layer (CBL) are performed to investigate model behavior in the terra incognita, also known as the gray zone. The terra incognita of the CBL refers to a range of model grid spacing that is comparable to the size of the most energetic convective eddies, which are on the order of the boundary layer depth. Using the Rayleigh–Bénard thermal instability as reference, a set of idealized simulations is used to show that gray zone modeling is not only a numerical challenge, but also poses dynamical difficulties. When the grid spacing falls within the CBL gray zone, grid-dependent convection can occur. The size of the initial instability structures is set by the grid spacing rather than the natural state of the flow. This changes higher-order flow statistics and poses fundamental difficulties for gray zone modeling applications.

This study is the first attempt to investigate the characteristics of the drop size distribution (DSD) and drop shape relation (DSR) of seven typhoons after making landfall in China. Four typhoons were sampled by a C-band polarimetric radar (CPOL) and a two-dimensional video disdrometer (2DVD) in Jiangsu Province (East China) while three typhoons were sampled by two 2DVDs in Guangdong Province (south China). Although the DSD and DSR are different in individual typhoons, the computed DSD parameters in these two groups of typhoons possess similar characteristics. The DSR is more spherical, and the shape-slope (μ-Λ) relation has a significantly lower value of μ for a given Λ than that in typhoons in the Taiwan area, indicating different microphysical processes of typhoons between continental China and other regions (western Pacific and Atlantic). The convective precipitation of typhoons contains higher raindrop concentration and lower raindrop diameter than that of the maritime convection. A Z (reflectivity factor)-R (rain rate) relationship, Z = 147.28R 1.38 , is derived for typhoons over land in China. The contoured frequency by altitude diagrams of CPOL polarimeteric parameters and the vertical distributions of hydrometeors and retrieved DSD parameters are further investigated to better reveal the microphysical processes of two typhoons (Matmo and Soudelor). Despite the differences in DSDs and polarimetric parameters, microphysical characteristics in both typhoons are similar. The CPOL-derived microphysical properties, in conjunction with high freezing level, suggest that warm rain accretion processes dominate typhoon rainfall after landfall in China.In addition to the characteristics of the DSDs, the shapes of the raindrops (axis ratio) also vary a lot with different weather systems because of the oscillation and canting effect of raindrops (e.g., Gorgucci et al., 2000). Polarimetric radars make use of this axis ratio to measure the difference in backscatter reflectivity and the propagation phase (Thurai & Bringi, 2005). Drop shapes therefore play a crucial role in retrieving the DSD of the raindrops and the subsequent estimation of rainfall rates from the polarimetric radar measurements (e.g., Gorgucci et al., 2000). A small error in the axis ratio can lead to significant errors in the estimated DSD and rainfall rates (Bringi & Chandrasekar, 2001).

The precipitation in Sichuan Basin (SB), China, exhibits pronounced diurnal variation, including minimum rainfall in daytime and a prominent peak near midnight. This study investigates the primary mechanism of precipitation diurnal variation in SB using forecasts from three summer months of 2013 produced at a 4‐km grid spacing. The model forecasts reproduce the observed spatial distributions and diurnal cycles well, including the peak precipitation in SB at around 02 local solar time (LST). Contrary to the common belief that emphasizes the solenoidal effects associated with the Tibetan and Yunnan‐Guizhou Plateaus, prominent diurnal inertial oscillations of boundary layer south‐southwesterly low‐level jet into SB are shown to play more important roles in modulating the diurnal cycles of precipitation in SB. A basinwide moisture budget analysis is performed to reveal that the moisture flux from the southeast side of the basin dominates within the diurnal oscillations of the net moisture flux into the basin, and the much enhanced nocturnal low‐level jet plays a crucial role in the formation of nocturnal precipitation within the basin. The net moisture flux into SB reaches maximum at around 22 LST, the time boundary layer perturbation winds from the daily mean in the direction normal to the southeastern boundary of SB reach maximum, which is about 4 hr before precipitation peak at around 02 LST. Shallow thermally forced nighttime downslope flows and daytime upslope flows on the Tibetan Plateau and Yunnan‐Guizhou Plateau slopes contribute only a small portion of moisture fluxes through the basin boundaries.

Using operational Doppler radar and regional reanalysis data from 2007–2009, the climatology and physical mechanisms of the diurnal cycle and propagation of convection over the Pearl River Delta (PRD) region of China during the Mei‐Yu seasons are investigated. Analyses reveal two hot spots for convection: one along the south coastline of PRD and the other on the windward slope of mountains in the northeastern part of PRD. Overall, convection occurs most frequently during the afternoon over PRD due to solar heating. On the windward slope of the mountains, convection occurrence frequency exhibits two daily peaks, with the primary peak in the afternoon and the secondary peak from midnight to early morning. The nighttime peak is shown to be closely related to the nocturnal acceleration and enhanced lifting on the windward slope of southwesterly boundary layer flow, in the form of boundary layer low‐level jet. Along the coastline, nighttime convection is induced by the convergence between the prevailing onshore wind and the thermally induced land breeze in the early morning. Convection on the windward slope of the mountainous area is more or less stationary. Convection initiated near the coastline along the land breeze front tends to propagate inland from early morning to early afternoon when land breeze cedes to sea breeze and the prevailing onshore flow.

8367Acknowledgment. We thank the National Science Foundation into the effect of surface oxygen protonation on the photodynamic processes of semiconductor metal oxides. All the data reveal that the electronic and structural perturbations of the polyoxometalate complex induced by solvent, including the presence or absence of electron donor-acceptor interactions, salt effects, ion pairing effects, and other medium effects are substantially less important on the photoredox chemistry than those induced by protonation.(Grant CHE-9022317) for support of this work. Supplementary Material Available:Twelve figures addressing kinetics, quantum yield, electrochemical, and spectral (IE3W NMR and UV-visible) measurements (1 3 pages). Ordering information is given on any current masthead page.Polyene 21Ag and llBu States and the Photochemistry of Previtamin D3 Abstract: The quantum yields of the photoproducts from previtamin D3 were measured at different wavelengths with monochromatic irradiation. While the quantum yield for the cis-trans isomerization decreases with increasing wavelength near 303 nm, the ones for formation of the ring-closure products increase dramatically. This increase in photocyclization yield with decreasing photon energy is attributed to the involvement of both the 1B and 2A excited states of previtamin D3. This hypothesis is supported by measurements of the previtamin D3 fluorescence spectrum, fluorescence lifetime, wavelength dependence of the fluorescence quantum yield, and temperature dependence of fluorescence intensity. All of these data are integrated into a potential energy surface diagram that is consistent with both the photochemical and spectroscopic behavior. 'University of California, Berkeley. *Recipient of a Feodor-Lynen Fellowship of the Alexander von Humboldt i University of California, Riverside. Foundation, 1986-1987. Scheme I. Photoreactions of Previtamin D,In an earlier study at Berkeley: the calculated quantum yields for the formation of pro D3 and lumisterol3 (lumi,) from pre D3 (1) General reviews of the photochemistry related to the previtamin D3 system: (a) Dauben, W. G.; Mclnnis, D. M. Yamachuchi, H.; Ogata, Y.; Kunii, T.; Kagei, K.; Katsui, G.; Toyoshima, s.; Yasumura, M.; Kobayashi, T. J. Nut?. Sci. Vitaminol. 1980,26, 545. (d) Barton, D. H. R.; Hesse, R. H.; Pechet, M. M.; Rizzardo, E.

Forecasts at a 4 km convection‐permitting resolution over China during the summer season have been produced with the Weather Research and Forecasting model at Nanjing University since 2013. Precipitation forecasts from 2013 to 2014 are evaluated with dense rain gauge observations and compared with operational global model forecasts. Overall, the 4 km forecasts show very good agreement with observations over most parts of China, outperforming global forecasts in terms of spatial distribution, intensity, and diurnal variation. Quantitative evaluations with the Gilbert skill score further confirm the better performance of the 4 km forecasts over global forecasts for heavy precipitation, especially for the thresholds of 100 and 150 mm d−1. Besides bulk characteristics, the representations of some unique features of summer precipitation in China under the influence of the East Asian summer monsoon are further evaluated. These include the northward progression and southward retreat of the main rainband through the summer season, the diurnal variations of precipitation, and the meridional and zonal propagation of precipitation episodes associated with background synoptic flow and the embedded mesoscale convective systems. The 4 km forecast is able to faithfully reproduce most of the features while overprediction of afternoon convection near the southern China coast is found to be a main deficiency that requires further investigations.

Recent increases in computing power mean that atmospheric models for numerical weather prediction are now able to operate at grid spacings of the order of a few hundred meters, comparable to the dominant turbulence length scales in the atmospheric boundary layer. As a result, models are starting to partially resolve the coherent overturning structures in the boundary layer. In this resolution regime, the so‐called boundary layer “gray zone,” neither the techniques of high‐resolution atmospheric modeling (a few tens of meters resolution) nor those of traditional meteorological models (a few kilometers resolution) are appropriate because fundamental assumptions behind the parameterizations are violated. Nonetheless, model simulations in this regime may remain highly useful. In this paper, a newly formed gray zone boundary layer community lays the basis for parameterizing gray zone turbulence, identifies the challenges in high‐resolution atmospheric modeling and presents different gray zone boundary layer models. We discuss both the successful applications and the limitations of current parameterization approaches, and consider various issues in extending promising research approaches into use for numerical weather prediction. The ultimate goal of the research is the development of unified boundary layer parameterizations valid across all scales.