Abstract:The earth system model (ESM) is an important tool for analyzing global climate and ecological environment changes. The Aerosol and Atmospheric Chemistry Model (AACM) enables the simulation of gases and aerosols associated with the effects of climate change for further processing using the Atmospheric General Circulation Model (AGCM). On the basis of the Global Nested Grid Air Quality Prediction Model System, a simplified version of the AACM of the Institute of Atmospheric Physics (IAP-AACM) suitable for the ESM of the Chinese Academy of Sciences (CAS-ESM) is developed using a simplified gas-phase chemical mechanism. Not only anthropogenic aerosols but also natural aerosols and its precursors (e.g., sea salt, dust, and dimethyl sulfide) are considered. The evaluation showed that the IAP-AACM with simplified gas-phase chemical mechanism can reasonably simulate the spatial distribution of aerosols and precursor gases. The difference between the simplified version and the standard version with CBM-Z mechanism is small. The comparison of the obtained values with the observations shows that the simplified version captured the spatial distribution of aerosols and its precursors well and provided a reliable aerosol simulation for the IAP-AGCM in favor of two-way feedback. Furthermore, the simplified version can significantly improve the calculation efficiency and well satisfy the need for long-range integration of the CAS-ESM. To provide a more comprehensive aerosol simulation in the research on global climate change, the mechanism of nitrogen chemistry and the stratospheric chemistry of ozone will be considered in the IAP-AACM in the future.

Abstract:Correctly understanding the hydrological impacts of forest vegetation and climate change is of considerable significance for forestry management and watershed ecological restoration. To investigate the effects of climate and vegetation cover changes on carbon-water cycles, the biophysical/dynamic vegetation model SSiB4/TRIFFID (Simplified Simple Biosphere model version 4, coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics model) was coupled with the TOPMODEL (Topographic Index Model) based on the catchment scheme partitions between saturated and unsaturated zones. The coupled model (hereinafter SSiB4T/TRIFFID) was employed to perform long-term dynamic simulations of vegetation succession and carbon-water circulations under different climate scenarios for a subalpine basin (the Soumou River basin that is a tributary of the Yangtze River located in the mountain region of southwestern China). The results of all tests indicate that vegetation fractions initially undergo changes from C3 grass dominance to tundra shrub dominance and then gradually approach equilibrium forest dominance. The results of the control test show that evapotranspiration of the basin increases and reaches its maximum value and runoff reaches its minimum value during the succession period of C3 grasses into tundra shrubs. Additionally, evapotranspiration decreases and runoff increases during the succession period of tundra shrubs into forests. An increase in temperature by 2 ℃ enhances the rate of transpiration and canopy interception evaporation of forests more than those of grasses and tundra shrubs. As a result, the role of forests in increasing runoff is reduced. An increase in temperature by 5 ℃ accompanied by an increase in precipitation by 40% [T+5, (1+40%)P test] will cause forests to reduce runoff because of the considerable increase in water loss through canopy interception evaporation and transpiration of forests. The results indicate that sensitivity to temperature changes of canopy interception evaporation and transpiration of forests are more than those of grasses and shrubs. Such a mechanism of temperature change causes the forest-runoff relationship to change. From the control test to the T+5, (1+40%)P test, the forest net primary productivity (NPP) increases with the increase in temperature. By contrast, the increase in temperature has a slight effect on the NPP of grasses and tundra shrubs. The water use efficiency (WUE), which characterizes the coupling relationship between carbon and water, considerably decreases with the increase in temperature. As elevation decreases (temperature increases) in the mountain region of southwestern China, WUE decreases with the decrease in altitude. Moreover, the role of forests to increase runoff changes to decrease runoff. The vertical zonality of climate controls the spatial variation of the forest-runoff relationship and WUE.

Abstract:On the basis of the topography and historical seismic information of the South China Sea, many scholars at home, and abroad have investigated the source area of possible earthquakes and tsunamis on the South China Sea. In this study, on the basis of previous research results, the authors analyze the areas that may be a tsunami source, select a group of typical tsunami sources, simulate these tsunami sources with the COMCOT model, and assess the damage to coastal areas and reefs of the South China Sea from in terms of tsunami propagation time, wave height, and energy distribution. The sensitivity test confirmed that the intensity of the tsunami wave is considerably influenced by the magnitude of the earthquake. If a local tsunami is triggered by a strong earthquake, then it will cause considerable damage to different parts of the coastal areas and reefs of the South China Sea.

Abstract:In this paper, Ka band radar data from January 2014 to December 2017 are used to statistically analyze the macro-physical characteristics of cloud in Beijing. The average cloud occurrence frequency during the four years is 36.3%. The maximum monthly averaged cloud occurrence frequency occurs in September, and the minimum is in December. Cloud occurrence frequency has significant daily variation in spring and summer, increasing by up to 15% from 1100 LST to 1700 LST and then decreasing gradually. The mean cloud base height (CBH) is 4.9 km, and cloud top height (CTH) is 7.2 km. The CBH and CTH rise from January gradually, reach the peak in June, and fall to minimum in December. From March to October, high-level clouds (CBH > 5 km) account for 50% of all clouds. Clouds with cloud thickness (CT) < 1 km are the majority in each month; from April to September, clouds with CT > 4 km account for the second-top proportion. Statistics show that single-layer clouds account for 66.7%, double-layers clouds account for 25.2%, and 8.1% are multiple-layers clouds. About 80% of clouds are single-layer in winter. The climatological characteristics, especially the vertical distribution of clouds in Beijing, are characterized numerically based on radar data in high temporal and spatial resolution. Results from this work will further clarify regional cloud climatic characteristics as well as cloud parameterization in climate models.

Abstract:East China was dominated by a strongly intense, long-duration, and extensive-coverage haze in December 2013. The synoptic characteristics, persistent mechanism, and precursory oceanic conditions for the persistent haze in December 2013 are studied using a monthly NCEP/NCAR reanalysis dataset, particulate matter observations in Huadong, and other regular observational data during 1981-2014. This persistent haze may be closely related to the activity of blocking over East Asia. The blocking over the Bering Sea-Okhotsk Sea, weakened transient eddy over East Asia, persistent trough over Lake Baikal, and attenuated northerly winds over east China would favor a worse diffusion condition for local accumulation and more transportation of particulate matter to East China in December 2013. Moreover, the enhanced blocking over Okhotsk Sea in December 2013 is probably related to the warm sea surface temperature over the tropical Indian Ocean.

Abstract:The NO₂ photolysis frequency j(NO₂) is an important parameter in tropospheric chemistry. It is one of the key factors affecting the formation of ozone and OH radicals in the troposphere. The variations of j(NO₂) and solar radiation and the correlation between photolysis rate and sub-band solar radiation were analyzed using the observational data in Xianghe from November 2017 to January 2018. On this basis, a parameterized scheme suitable for reconstructing j(NO₂) in the Xianghe area was constructed. The results indicate that the variation trends of j(NO₂) and solar radiation in Xianghe are basically the same, and the diurnal variations are all unimodal with high noon and small morning and evening. The variation range of j(NO₂) in winter is 0.00046-0.0044 s^-1, with a mean of 0.0029 s^-1. Since j(NO₂) correlates well with the clear sky index (K_S) and transmittance of ultraviolet radiation (K_UV), an experimental estimating equation based on K_UV was established using the correlation between j(NO₂), air mass number, and clear air index. Considering the clear sky index K_S is more easily obtained and global radiation is a conventional observation of meteorological stations, an experimental estimating equation was established based on K_S. The instantaneous value of j(NO₂) can be estimated by the equations established using K_UV and Ks, and the mean absolute percentage errors between the instantaneous values obtained by the two equations and the observed value are 6.5% and 13.9%, and the root mean square errors are 0.00029 and 0.00051, respectively.

Abstract:On the basis of the Level 2 product data of Aqua MODIS satellite and CloudSat satellite from 2013 to 2016, precipitating and nonprecipitating ice clouds that occurred in the Beijing-Tianjin-Hebei region in summer were counted. Moreover, the cloud feature parameters, cloud layer numbers, and cloud phase of the two types of ice clouds are compared and analyzed. The differences between the two in the vertical structure are investigated and the relative sizes of the cloud parameters in different channels are examined. Results show that precipitating ice clouds are dominated by deep convective and nimbostratus clouds, accounting for 48.63% and 34.65%, respectively. The mean cloud top temperature, cloud top height, cloud optical thickness, cloud water path, and effective particle radius are 230.99 K, 10.90 km, 53.26, 937.98 g/m², and 31.45 μm, respectively. Meanwhile, nonprecipitating ice clouds are dominated by altocumulus and cirrus clouds, accounting for 55.62% and 31.58%, respectively. The mean cloud top temperature, cloud top height, cloud optical thickness, cloud water path, and effective particle radius are 236.17 K, 10.10 km, 12.81, 209.00 g/m², and 27.54 μm, respectively. Precipitating ice clouds mainly consist of single-layer clouds (80.39%). However, double-layer clouds still account for a large proportion (18.75%) and are higher than nonprecipitating ice clouds. Moreover, nonprecipitating ice clouds still consist of single-layer clouds (85.35%) and double-layer clouds (14.38%). Compared with nonprecipitating ice clouds, the position of cirrus and altocumulus clouds, which are higher than 1-9 and 0-1.5 km, respectively, in precipitating ice clouds is higher, whereas the position of altostratus and deep convective clouds, which are lower than 0-0.5 and 0.5-3 km, respectively, are lower. The ice water content of nonprecipitating ice clouds varies with height as a double-peak structure, whereas that of precipitating ice clouds is a single-peak structure. The particle number concentrations of precipitating and nonprecipitating ice clouds vary slightly with height. The particle effective radius of nonprecipitating ice clouds varies slightly with height from 5 to 7.5 km, whereas that of precipitating ice clouds decrease with height. The ratio of the cloud water path, optical thickness, and particle effective radius of precipitating ice clouds >≥ mode [where , , and represent the values of the cloud parameters at 1.6, 2.1, and 3.7 μm, respectively; when n=1, 2, 3, they represent the optical thickness (b₁), total amount of integrated cloud water (b₂), and effective radius (b₃)] is higher than that of nonprecipitating ice clouds. Moreover, the ratio of the cloud parameters in the ≥ ≥ mode is different.

Abstract:The West China (25°N-35°N, 100°E-110°E) is one of the main autumn precipitation regions in China. In this study, the monthly precipitation data of 72 stations in West China, NCEP/NCAR reanalysis data, and sea surface temperature and sea ice data of Hadley Centre were analyzed. Accordingly, the interdecadal variability of autumn rain in West China from 1961 to 2014 and its relationship with atmospheric circulation and sea surface temperature were found through correlation and regression methods. The decadal variability of autumn precipitation in West China was decomposed into two periods P1 (1964-1998) with a significant downward trend and P2 (1998-2014) with an upward trend. Results show that the anomalous field of the atmospheric geopotential height, corresponding to the downtrend of the precipitation in P1, has a structure of the positive to negative in west to east inside the study region. The large-scale circulation field shows the quasi-zonal wave train originating from the eastern Atlantic Ocean to East Asia via the Barents-Kara Seas and Kara Sea areas, which reflects the modulation effect of the upstream negative-phase NAO. In P2, the geopotential height field configuration related to the downward precipitation trend is opposite to that in P1.The large-scale wave train structure shows a westward-shifting northwest-southeast pathway over Eurasia, which reflects the modulation effect of positive-phase NAO at the upstream. This circulation structure leads to the formation of a negative anomaly center over the northwest of West China, which is favorable for the southwest warm and humid airflow to enter the study area. The key SST zones that influence the autumn rain in West China are located in central and eastern tropical Pacific and Indian Ocean. In P1, the precipitation trend of autumn rain transition in West China was positively correlated with the SST over tropical Middle East Pacific and Indian Ocean during the same period. In P2, there exists a significant negative correlation between the autumn rain and SST in the tropical Middle East Pacific and Indian Ocean during the last winter. In addition, the positive SST anomaly in the northwest Pacific Ocean during the previous winter also affects the increasing trend of the autumn rain in West China.

Abstract:The spatial and temporal variations of persistent haze events and their related impact factors were analyzed by using 324 stations in the central and eastern China during 1980-2014. The results show that the annual average frequency of persistent haze events and their contributions to total haze events increase year by year, with growth rates of 0.79 (10 a)^-1 and 2.7% (10 a)^-1, respectively. It is represented by three large-value areas: The North China Plain (including Shanxi Province, Beijing-Tianjin-Hebei region), the Yangtze River Delta, and the eastern Sichuan Basin. The most significant increase appears mainly in Huang-Huai area, with a growth rate of 6.3 (10 a)^-1 and 13.95 d (10 a)^-1. At the same time, persistent haze events show obvious seasonal and monthly changes. January is the highest incidence month with 2.56 d, meanwhile high frequency appears in summer and autumn, with a growth rate of 0.38 (10 a)^-1 and 0.46 (10 a)^-1. Unfavorable meteorological conditions, such as increasing windless days, decreasing wind speed and gale days, and adverse circulation situations, such as the weakening of the East Asian winter monsoon, have resulted in an increase in persistent hazy days and its abnormal maintenance.