Shanghai is the biggest metropolis in China, and its local temperature change is affected not only by global warming but also by urbanization. Integrating the Mann-Kendall test, EMD (Empirical Mode Decomposition), Cross Wavelet Analysis and statistical methods, we studied the response of the local temperature change in Shanghai to global warming and urbanization. The results indicate that the local temperature at Shanghai present a significant warming trend under the background of global warming over the past 135 years. The local temperature at Shanghai displays 2-year, 6-year, 15-year, 23-year and 68-year periodic fluctuation, whereas global temperature shows 4-year, 9-year, 15-year, 23-year and 68-year cyclic variation. Although the two cycles are not exactly the same, they show some comparability. Urbanization facilitated the warming process of Shanghai. In the most recent 50 years, temperature difference between urban and suburban Shanghai has increased nearly 0.4 • C. The related indicators of urban development, such as population, built-up area, Gross Domestic Product (GDP), energy consumption and number of vehicles show significantly positive correlation with the temperature difference between urban and suburban area. In addition, the frequency of extreme high temperature has become higher, whereas the frequency of extreme low temperature has become lower over the most recent 55 years.
Stabilizing the atmosphere and ventilating the sub-cloud layer through vertical transport of moisture, moist convection is an important sub-grid scale process that still needs to be parameterized in general circulation models (GCMs) in the coming decades (Plant & Yano, 2016). The purpose of convection parameterization is to provide feedback on sub-grid scale convection to the large-scale fields as tendency terms. It is important to keep in mind that for achieving this goal, we do not have to introduce full details of convection into a parameterization. Rather, it must constitute a caricature of the reality of convection, as emphasized by Yano (2014b). Therefore, early convection schemes only considered the feedback without describing the convective clouds (e.g., the moist adjustment scheme of Manabe et al. (1965) or the moisture convergence scheme of Kuo (1965)). However, some shortcomings, including fixed tropical temperature profiles (Arakawa, 2004) and unreasonable convective moistening profiles (Emanuel, 1994), are related to such an oversimplified approach, indicating that an idealized caricature cannot encompass the collective effect of a series of complex processes during the convection. A practical way to mitigate this problem is to describe more basic features of convective clouds in detail in convection schemes. As a result, convection schemes started to adopt a bulk or spectrum mass-flux (plume) formulation (e.g.,
It has been confirmed that the karst rocky desertification (KRD) has severely changed the interactions between atmosphere and terrestrial ecosystem which would cause a significant effect on regional climate system. In this study, the Weather and Research Forecasting model was applied to investigate the biogeophysical impact on temperature and precipitation change by land use/land cover change data with different KRD conditions in 1993KRD conditions in , 2003KRD conditions in , and 2013 in Southwest China. The results showed that an improving trend of KRD has been found in Southwest China, especially in east Sichuan, Chungking, southwest Yunnan, and south Guangxi. The 2-m air temperature decreased by 0~− 1°C in general with this improving trend. The possible reason was the decreasing KRD accompanied by the decreasing albedo, causing the increasing net shortwave radiation and the increasing net radiation. Meanwhile, the increasing evaporation strengthened the latent heat flux and weakened the sensible heat flux so that decreased temperature was addressed in forest areas. The effect of KRD change transferred to the upper troposphere through atmosphere vertical convection, which made the subtropical high to be strengthened and westerly extended. Therefore, the upward moisture flux at the surface (QFX) was weakened in the central part of Guangxi, southern Guizhou, which led to the decrease of the precipitation. Moreover, the southwest monsoon was strengthened, which caused the increasing water vapor flux and led to the heavy rainfall in the west of Yunnan.
Performance of global climate models (GCMs) is strongly affected by their cumulus parameterizations (CP) used. Similar to the approach in GFDL AM4, a double-plume CP, which unifies the deep and shallow convection in one framework, is implemented and tested in NCAR Community Atmospheric Model version 5 (CAM5). Based on the University of Washington (UW) shallow convection scheme, an additional plume was added to represent the deep convection. The shallow and deep plumes share the same cloud model, but use different triggers, fractional mixing rates and closures. The scheme was tested in single column, short-term hindcast and AMIP simulations. Compared with the default combination of Zhang-McFarlane scheme and UW scheme in CAM5, the new scheme tends to produce a top-heavy mass flux profile during the active monsoon period in the single column simulations. The scheme increases the intensity of tropical precipitation, closer to TRMM observations. The new scheme increased subtropical marine boundary layer clouds and high clouds over the deep tropics, both in better agreement with observations. Sensitivity tests indicate that regime dependent fractional entrainment rates of the deep plume are desired to improve tropical precipitation distribution and upper troposphere temperature. This study suggests that a double-plume approach is a promising way to combine shallow and deep convections in a unified framework.
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