Impacts of Weather Conditions Modified by Urban Expansion on Surface Ozone： Comparison between the Pearl River Delta and Yangtze River Delta Regions

In this paper, the online weather research and forecasting and chemistry (WRF-Chem) model is used to explore the impacts of urban expansion on regional weather conditions and its implication on surface ozone concentrations over the Pearl River Delta(PRD) and Yangtze River Delta(YRD) regions. Two scenarios of urban maps are used in the WRF-Chem to represent the early 1990s (pre-urbanization) and the current urban distribution in the PRD and the YRD. Month-long simulation results using the above land-use scenarios for March 2001 show that urbanization increases both the day- and night-time 2-m temperatures by about 0.6^oC and 1.4^oC, respectively. Daytime reduction in the wind speed by about 3.0 m s^-1 is larger than that for the nighttime (0.5 to 2 m s^-1). The daytime increase in the PBL height (> 200 m) is also larger than the nighttime (50--100 m). The meteorological conditions modified by urbanization lead to detectable ozone-concentration changes in the PRD and the YRD. Urbanization increases the nighttime surface-ozone concentrations by about 4.7%--8.5% and by about 2.9%--4.2% for the daytime. In addition to modifying individual meteorological variables, urbanization also enhances the convergence zones, especially in the PRD. More importantly, urbanization has different effects on the surface ozone for the PRD and the YRD, presumably due to their urbanization characteristics and geographical locations. Even though the PRD has a smaller increase in the surface temperature than the YRD, it has (a) weaker surface wind speed, (b) smaller increase in PBL heights, and (c) stronger convergence zones. The latter three factors outweighed the temperature increase and resulted in a larger ozone enhancement in the PRD than the YRD.     

Relevance of ion-induced nucleation of sulfuric acid and water in the lower troposphere over the boreal forest at northern latitudes

The relevance of ion-induced nucleation of sulfuric acid and water (IINSW) in the troposphere over the boreal forest at northern latitudes is investigated by combining two existing and previously published models (MALTE — model to predict new aerosol formation in the lower troposphere; PARNUC — a parameterized steady-state model of neutral and ion-induced nucleation of sulfuric acid and water for atmospheric conditions). Simulations were performed for 4 days with observed new particle formation at ground level by using input data from the SMEAR II station in Hyytiälä, Finland. The selected days were chosen to cover a wide range of values of the parameters most relevant for IINSW. The results showed that ion-induced nucleation of sulfuric acid and water can contribute up to 15% to the total amount of newly formed particles in the size range of 3–10 nm inside the mixed layer at the Hyytiälä site. The importance of IINSW seemed to increase in the free troposphere above the boundary layer, however, lack of measurements in the vertical structure of the input parameters suggest that the model results are burdened with high uncertainties.     

Modeling the impacts of climate change on China''s agriculture

1 Introduction Since recognition of the potential climate change [IPPC, 1990], efforts have been made to estimate the economic impacts of projected changes in climate on important sectors, such as agriculture, forestry and ecosystem, coastal zones and fisheries, water resource, and energy development. Although several sectors have been studied, none have received more attention than agriculture. Countrywide economic analysis has been completed for the United States[1-4], India[5] and Brazil…     

An analytic solution to the wave bottom boundary layer governing equation under arbitrary wave forcing

Existing models of the wave bottom boundary layer have focused on the vertical and temporal dynamics associated with monochromatic forcing. While these models have made significant advances, they do not address the more complicated dynamics of random wave forcing, commonly found in natural environments such as the surf zone. In the closed form solution presented here, the eddy viscosity is assumed to vary temporally with the bed shear velocity and linearly with depth, however, the solution technique is valid for any eddy viscosity which is separable in time and space. A transformation of the cross-shore velocity to a distorted spatial domain leads to time-independent boundary conditions, allowing for the derivation of an analytic expression for the temporal and vertical structure of the cross-shore velocity under an arbitrary wave field. The model is compared with two independent laboratory observations. Model calculations of the bed shear velocity are in good agreement with laboratory measurements made by Jonsson and Carlsen (1976, J. Hydraul. Res., 14, 45–60). A variety of monochromatic, skewed, and asymmetric wave forcing conditions, characteristic of those found in the surf zone, are used to evaluate the relative effects on the bed shear. Because the temporal variation of the eddy viscosity is assumed proportional to the bottom shear, a weakly nonlinear interaction is created, and a fraction of the input monochromatic wave energy is transferred to the odd harmonics. For a monochromatic input wave, the ratio of the third harmonic of velocity at the bed to the first is <10%. However, for a skewed and asymmetric input wave, this ratio can be as large as 30% and is shown to increase with increasing root-mean-square input wave acceleration. The work done by the fluid on the bed is shown to be a maximum under purely skewed waves and is directed onshore. Under purely asymmetric waves, the work done is significantly smaller and directed offshore.     

Relaxed Eddy Accumulation Simulations of Aerosol Number Fluxes and Potential Proxy Scalars

Direct eddy-covariance measurements of aerosol number fluxes obtained during the 2007 CHATS field experiment in Dixon, California, USA are compared with relaxed eddy accumulation simulations using temperature and water vapour concentration as proxy scalars. After a brief discussion of the limited time response of the aerosol measurement, the applicability of temperature and water vapour concentration as proxy scalars for aerosol number concentration is investigated by evaluating scalar and spectral correlation coefficients as simple measures of scalar similarity. In addition, the proportionality factor b, which compensates for the use of a constant sampling flow in relaxed eddy accumulation, is derived from the time series of aerosol number, temperature and water vapour, and its variability is analyzed. The reduction of the b factor due to application of a deadband, i.e. the rejection of data when the vertical wind speed is close to zero, is evaluated for all three studied scalars, and compared with published functional relationships. In this study, using temperature or water vapour as proxy scalars for aerosol number shows no advantage over the use of a constant b factor. Thus, it is suggested to apply a deadband H _REA  = w′/σ _w  = 0.6 to 0.8 (where w′ is the vertical velocity fluctuation and σ _w is its standard deviation), to use a theoretical b factor based on a parameterization that includes a stability dependence, and to calculate the deadband effect according to a derived relation for aerosol relaxed eddy accumulation.     

The power of low‐resolution spectroscopy: On the spectral classification of planet candidates in the ground‐based CoRoT follow‐up

Planetary transits detected by the CoRoT mission can be mimicked by a low‐mass star in orbit around a giant star. Spectral classification helps to identify the giant stars and also early‐type stars which are often excluded from further follow‐up. We study the potential and the limitations of low‐resolution spectroscopy to improve the photometric spectral types of CoRoT candidates. In particular, we want to study the influence of the signal‐to‐noise ratio (SNR) of the target spectrum in a quantitative way. We built an own template library and investigate whether a template library from the literature is able to reproduce the classifications. Including previous photometric estimates, we show how the additional spectroscopic information improves the constraints on spectral type. Low‐resolution spectroscopy (R ≈ 1000) of 42 CoRoT targets covering a wide range in SNR (1–437) and of 149 templates was obtained in 2012–2013 with the Nasmyth spectrograph at the Tautenburg 2 m telescope. Spectral types have been derived automatically by comparing with the observed template spectra. The classification has been repeated with the external CFLIB library. The spectral class obtained with the external library agrees within a few sub‐classes when the target spectrum has a SNR of about 100 at least. While the photometric spectral type can deviate by an entire spectral class, the photometric luminosity classification is as close as a spectroscopic classification with the external library. A low SNR of the target spectrum limits the attainable accuracy of classification more strongly than the use of external templates or photometry. Furthermore we found that low‐resolution reconnaissance spectroscopy ensures that good planet candidates are kept that would otherwise be discarded based on photometric spectral type alone. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling the impacts of climate change on China’s agriculture

The impacts of climate change on China’s agriculture are measured based on Ricardian model. By using county-level cross-sectional data on agricultural net revenue, climate, and other economic and geographical data for 1275 agriculture-dominated counties in the period of 1985-1991, we find that both higher temperature and more precipitation will have overall positive impact on China’s agriculture. However, the impacts vary seasonally and regionally. Higher temperature in all seasons except spring increases agricultural net revenue while more precipitation is beneficial in winter but is harmful in summer. Applying the model to five climate scenarios in the 2020s and 2050s shows that the North, the Northeast, the Northwest, and the Qinghai-Tibet Plateau would always benefit from climate change while the South and the Southwest may be negatively affected. For the East and the Central China, most scenarios show that they may benefit from climate change. In conclusion, climate change would be beneficial to the whole China.     

Surface inhomogeneities and line variability on DF Tau

We have mapped surface inhomogeneities on the classical T Tauri star DF Tau, using the Li  i doublet at 670.8 nm, the Ca  i lines at 612.2 nm and 643.9 nm and a calcium and iron blend at 646.3 nm. We find compelling evidence that there are hotspots with temperatures of more than 5000 K. Two of the hotspots produce line-profile deformations that can be traced as they move through the cross-correlated profiles. When one of the hotspots crosses the stellar disc, redshifted absorption components appear in the Na D lines. As these redshifted absorption features are usually tracers for mass-infall we interpret this hotspot as an accretion shock close to the stellar surface.   Parts of the surface of DF Tau are covered with a hot chromosphere that is visible in the Ca  ii infrared triplet lines and the narrow component of He  i . We find no correlation between the veiling and the lines that originate from the hot chromosphere, suggesting that the veiling and the chromospheric emission are produced in physically distinct regions.