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- Author or Editor: Kaicun Wang x
- Bulletin of the American Meteorological Society x
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Abstract
Digital elevation models (DEMs) have important meteorological, hydrological, and climatological applications. This research studies the uncertainties of six widely accepted global DEM datasets over China and their derivative parameters, including slope and aspect, in calculating the surface-received solar radiation and extracting the river networks. The authors’ results indicate that, although the absolute height values of the six DEM data are nearly identical, substantial and significant differences are introduced when estimating the surface-received solar radiation. The extracted drainage streamflows of the Pearl River basin in South China are close to the actual river networks in general but are quite different in some details that cannot be ignored. Results herein highlight that the uncertainties of DEM themselves as well as their derived parameters must be considered in analogous study.
Abstract
Digital elevation models (DEMs) have important meteorological, hydrological, and climatological applications. This research studies the uncertainties of six widely accepted global DEM datasets over China and their derivative parameters, including slope and aspect, in calculating the surface-received solar radiation and extracting the river networks. The authors’ results indicate that, although the absolute height values of the six DEM data are nearly identical, substantial and significant differences are introduced when estimating the surface-received solar radiation. The extracted drainage streamflows of the Pearl River basin in South China are close to the actual river networks in general but are quite different in some details that cannot be ignored. Results herein highlight that the uncertainties of DEM themselves as well as their derived parameters must be considered in analogous study.
Abstract
The morphology of global precipitation systems can enhance our comprehension of precipitation patterns and the underlying physical processes. However, several unresolved issues remain in the existing studies of precipitation system morphology. This study employs IMERG-derived precipitation system dataset to investigate the climatological and changing characteristics of global precipitation system morphology from 2001 to 2022. The results show that precipitation systems with larger scales tend to be more flattened in morphology, while no clear differences in morphological characteristics are observed across systems with different intensities. In terms of geographic distributions, a notable land-sea contrast is observed, with land systems more circular than those over oceans. Due to the impact of the Coriolis force, the orientation distribution of precipitation systems shows obvious hemispherical contrast. Precipitation systems over tropical regions are more regular in shape and more likely to be organized convective systems. During the period of 2001-2022, there is a significant trend of global precipitation systems becoming more flattened and are more likely to manifest as organized convective systems. Our results also indicate that the precipitation system morphology is under combined influence of subtropical highs, lateral stretching influences of wind, and the organizing effects of moisture transport and convergence. Moreover, the increasing flattening of precipitation systems could be attributed to enhanced atmospheric stability which constrains vertical expansion, and increased moisture availability which favors wider horizontal extension. This study could provide new insights into precipitation changes under global warming.
Abstract
The morphology of global precipitation systems can enhance our comprehension of precipitation patterns and the underlying physical processes. However, several unresolved issues remain in the existing studies of precipitation system morphology. This study employs IMERG-derived precipitation system dataset to investigate the climatological and changing characteristics of global precipitation system morphology from 2001 to 2022. The results show that precipitation systems with larger scales tend to be more flattened in morphology, while no clear differences in morphological characteristics are observed across systems with different intensities. In terms of geographic distributions, a notable land-sea contrast is observed, with land systems more circular than those over oceans. Due to the impact of the Coriolis force, the orientation distribution of precipitation systems shows obvious hemispherical contrast. Precipitation systems over tropical regions are more regular in shape and more likely to be organized convective systems. During the period of 2001-2022, there is a significant trend of global precipitation systems becoming more flattened and are more likely to manifest as organized convective systems. Our results also indicate that the precipitation system morphology is under combined influence of subtropical highs, lateral stretching influences of wind, and the organizing effects of moisture transport and convergence. Moreover, the increasing flattening of precipitation systems could be attributed to enhanced atmospheric stability which constrains vertical expansion, and increased moisture availability which favors wider horizontal extension. This study could provide new insights into precipitation changes under global warming.
Abstract
The recent severe and frequent PM2.5 (i.e., fine particles smaller than 2.5 µm) pollution in China has aroused unprecedented public concern. The first two years of PM2.5 measurements in China are reported and compared with those of Europe and the United States. The average PM2.5 concentration in China is approximately 5 times that over Europe and America. The contribution of atmospheric dispersion to such air quality is evaluated in this study. Air stagnation or its absence is a good indicator of the atmosphere’s capability to disperse its pollutants, but the NOAA definition of an air stagnation event is found to not be applicable to China since it depends on vertical mixing that is weakened in China by the effects of terrain. To address this deficiency, a new threshold for air stagnation events is proposed that depends on the 10-m wind speed, boundary layer height, and occurrence of precipitation. This newly defined air stagnation closely tracks the day-to-day variation of PM2.5 concentrations. Such events are more frequent over China than over Europe and the United States during autumn and winter, especially over the Sichuan basin and Jing-Jin-Ji region of China. If China had the same frequency of air stagnation as the United States or Europe, 67% and 82% of its stations would improve their current air quality during autumn and winter (e.g., an average of 12% decrease in PM2.5 concentrations for the Jing-Jin-Ji region in wintertime). Its severe pollution and frequent air stagnation conditions make controls on emission less effective in China than elsewhere.
Abstract
The recent severe and frequent PM2.5 (i.e., fine particles smaller than 2.5 µm) pollution in China has aroused unprecedented public concern. The first two years of PM2.5 measurements in China are reported and compared with those of Europe and the United States. The average PM2.5 concentration in China is approximately 5 times that over Europe and America. The contribution of atmospheric dispersion to such air quality is evaluated in this study. Air stagnation or its absence is a good indicator of the atmosphere’s capability to disperse its pollutants, but the NOAA definition of an air stagnation event is found to not be applicable to China since it depends on vertical mixing that is weakened in China by the effects of terrain. To address this deficiency, a new threshold for air stagnation events is proposed that depends on the 10-m wind speed, boundary layer height, and occurrence of precipitation. This newly defined air stagnation closely tracks the day-to-day variation of PM2.5 concentrations. Such events are more frequent over China than over Europe and the United States during autumn and winter, especially over the Sichuan basin and Jing-Jin-Ji region of China. If China had the same frequency of air stagnation as the United States or Europe, 67% and 82% of its stations would improve their current air quality during autumn and winter (e.g., an average of 12% decrease in PM2.5 concentrations for the Jing-Jin-Ji region in wintertime). Its severe pollution and frequent air stagnation conditions make controls on emission less effective in China than elsewhere.
