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2023 Vol. 28, No. 2

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Regional Sensitivity of Surface Temperature to Nonuniform CO2 Concentration on the Century Scale
Jing PENG, Li DAN, Yongli WANG, Jinming FENG, Fuqiang YANG, Wei QI
2023, 28(2): 117-130. doi: 10.3878/j.issn.1006-9585.2022.21134
Abstract(101) HTML (14) PDF (7428KB)(31)
Simulations from Earth System Model show that the rapid increase in atmospheric CO2 concentration is one of the major reasons for climate change. Satellite data analysis shows that the atmospheric CO2 concentration is globally nonuniform. There are evident regional discrepancies, mainly caused by anthropogenic carbon emissions. The impact of this spatial difference on global warming has not been thoroughly studied. We evaluated simulation results using the BNU-ESM (Earth System Model of Beijing Normal University) and compared the results with observational datasets. The results show that within a threshold of 2℃ temperature increase between 1901 and 2100, the CO2 concentration increase forced by nonuniform CO2 concentration was less than that by uniform CO2 concentration, which was approximately 4.30 ppm. On the regional scale, the sensitivity of surface temperature to CO2 concentration in China is lower than that in the United States, Europe, and the Northern Hemisphere. This might result from the combined impacts of CO2-radiative forcing and climate feedback across these regions; however, this requires future investigation. The impact of nonuniform CO2 concentration on surface temperature sensitivity could provide scientific support for estimating future carbon sinks under a carbon-neutral target.
Circulation Characteristics of Winter Rainfall Interannual Variations over South China and Their Response to Preceding Sea Surface Temperature Anomalies
Chao LI, Yuan LI, Qian CHEN, Xunlai CHEN
2023, 28(2): 131-142. doi: 10.3878/j.issn.1006-9585.2022.21155
Abstract(113) HTML (17) PDF (4005KB)(24)
The characteristics of the interannual variability of winter (December–February) precipitation over South China and their association with atmospheric and preceding ocean conditions are analyzed using the observed precipitation data from 160 surface meteorological stations in China, the NCEP/NCAR reanalysis dataset, and the sea surface temperature (SST) dataset from the Met Office Hadley Center. The precipitation tends to be more (less) than the climatology under a southward (northward) shift of the East Asian jet stream, the weakened (strengthened) East Asian trough, and the enhanced (attenuated) transient eddy. The southwesterly winds from the Bay of Bengal and the South China Sea in the front of the southern branch trough favor more precipitation over South China. Further analysis suggests that the preceding SST anomalies (SSTAs) over the tropical Indian Ocean and western tropical Pacific in November have a closer relationship with the southern branch trough and low-level southwesterly winds associated with the variation in precipitation over South China, which could not be well explained by the ENSO-like SSTAs. The correlation coefficient between precipitation over South China and the derived index from the preceding SSTA is 0.44 and reaches a maximum when the SSTA index leads precipitation anomalies by approximately one month, which may act as a potential precursor for wintertime precipitation predictions.
Impacts of Intraseasonal Convection Activity over Maritime Continent on the Boreal Winter Precipitation over Southeastern China
Guiwan CHEN, Yuqing LONG, Xiong CHEN, Yuqing ZHAO, Jian LING, Chongyin LI
2023, 28(2): 143-159. doi: 10.3878/j.issn.1006-9585.2021.21156
Abstract(125) HTML (11) PDF (14874KB)(14)
This study assessed the effects of intraseasonal convection over the Maritime Continent on the boreal winter precipitation over Southeast China. The intraseasonal convection events were further classified into MJO (Madden-Julian Oscillation) events with continuous eastward propagation and non-MJO events with stationary oscillation. The outcomes suggest that the effects of the MJO and non-MJO events on the precipitation over Southeast China are quite distinct. The precipitation anomalies linked to MJO over Southeast China have a wider spatial range and demonstrate continuous southward propagation as the MJO propagates eastward, while the range of precipitation anomalies linked to the non-MJO is narrower, and the precipitation center shifts southward over time. When the convection is active (inactive) over the Maritime Continent, the MJO-induced precipitation anomalies over Southeast China reveal a northward positive-negative (negative-positive) dipolar distribution, while the non-MJO-induced precipitation anomalies demonstrate a negative (positive) pattern over Guangdong and Fujian. When the convection is transformed from the suppressed (active) to the active (suppressed) phase over the Maritime Continent, the MJO-induced precipitation anomalies are positive (negative) over Southeast China, while the non-MJO-induced precipitation anomalies indicate a negative (positive) pattern over northern Jiangxi, northwestern Fujian, and western Zhejiang. The moisture flux diagnosis indicates that both the MJO and non-MJO convection-induced precipitation anomalies over Southeast China are controlled by intraseasonal low-level circulations. Exclusively, the low-level meridional winds influenced by MJO and non-MJO convection are distinct over the sub-tropical region; this results in different gradients of the meridional winds on the moisture, which further leads to various moisture transport processes that identify the precipitation anomalies over Southeast China controlled by two types of intraseasonal convection events.
Process Classification Based on the Onset Date of the First Rainy Season and Meiyu over Southern China and Relevant Characteristic Analyses
Yingfa LI, Junhu ZHAO, Naihui ZANG, Fei JI, Peiyi FAN, Guolin FENG
2023, 28(2): 160-172. doi: 10.3878/j.issn.1006-9585.2022.22057
Based on the onset date of the first rainy season in South China (ODFRS_SC) from "South China flood season monitoring operational specifications" and Meiyu (OD_Meiyu) over the middle and lower reaches of the Yangtze River from "Meiyu monitoring operational specifications" released by China Meteorological Administration in 2014, rainy season processes over southern China are divided into four categories objectively from 1961 to 2021: Early type (early for ODFRS_SC and OD_Meiyu), late type (late for ODFRS_SC and OD_Meiyu), first-phase early and second-phase late type (early for ODFRS_SC and late for OD_Meiyu), and first-phase late and second-phase early type (late for ODFRS_SC and early for OD_Meiyu). In various types of rainy season processes, there are obvious differences in precipitation anomaly distribution in the spring and Meiyu periods over central and eastern China. Moreover, evolutions of east Asian atmospheric circulation anomaly and sea surface temperature (SST) in different rainy season processes have obvious differences. In the early type, from late March to early May, the East Asian subtropical jet (EASJ) was stronger, and the first northward jump was earlier. In June, the northward jump of the western Pacific subtropical high (WPSH) was obvious, and the anticyclone anomaly was located in the Philippines; the late type is the opposite of the early type in circulation terms. In the first-phase early and second-phase late type, the EASJ was stronger in the first stage and weaker in the second stage, the anticyclone (cyclone) anomaly in the first (second) stage was located at the Philippines, and the location of the WPSH was abnormally southward; the first-phase late and second-phase early type is the opposite of the former. The correlation between the rainy season process in southern China and the evolution of tropical SST is insignificant; especially, the relationships between the various progressions and evolutions of El Niño southern oscillation are complex.
Decomposition and Application of the Modified Moist Potential Vorticity Tendency Equation
Saisai LIU, Yanling ZHAO, Gui ZHANG, Kaicheng LU, Ming ZHANG
2023, 28(2): 173-182. doi: 10.3878/j.issn.1006-9585.2022.21164
In this study, the modified moist potential vorticity tendency equation is theoretically analyzed, discussed, and verified in a typhoon process. The main conclusions are as follows: The modified moist potential vorticity tendency equation can be decomposed into dry and moist component tendency equations. Without regard to the moisture species and friction, the dry component of the modified moist potential vorticity tendency equation is conservative, and it is the same as the Ertel potential vorticity tendency equation. The moisture gradient term has an obvious effect on the variation of the modified moist potential vorticity; thus, the tendency equation is more suitable for diagnosing and analyzing some mesoscale and microscale weather systems. With the same decomposition method, the upgraded virtual potential vorticity tendency equation and the upgraded equivalent moist potential vorticity tendency equation can be derived. After this upgrade, these equations now include the moisture gradient term, which potentially makes the potential vorticity diagnosis more precise. By analyzing the latent heat of condensation in various potential vorticity tendency equations, we determined that the Ertel potential vorticity tendency equation overestimates the effect of the latent heat of condensation, whereas the modified moist potential vorticity tendency equation can deduct some of the latent heat of condensation; thus, it should have a better diagnostic effect. The result of subtracting the modified moist potential vorticity tendency equation and the equivalent moist potential vorticity tendency equation can reasonably reflect the effect of the latent heat of condensation. Therefore, it can have a better diagnostic effect for the Meiyu front rainstorm and tropical cyclones, where the latent heat of condensation plays a major role.
Numerical Simulation Analysis on Ozone Source Apportionment in the Yinchuan Metropolitan Area in Summer
Li QIN, Xiao HAN, Meigen ZHANG, Jianjun LIU
2023, 28(2): 183-194. doi: 10.3878/j.issn.1006-9585.2022.21186
Under the current situation of combined pollution due to ozone and particulate matter in China, regional ozone pollution is prominent in Ningxia, northwestern China, in summer. Thus, the regional air quality modeling system RAMS-CMAQ (Regional Atmospheric Modeling System and Models-3 Community Multi-scale Air Quality) was applied to investigate ozone pollution in the Yinchuan metropolitan area (Yinchuan, Shizuishan, and Wuzhong) in June 2019. The contribution of ozone regional and vertical transmission was quantitatively discussed to provide scientific evidence for effective control of local ozone pollution. The results show that O3 concentration was high in the north and low in the middle of the area, which was not completely consistent with the distribution characteristics of ozone precursors, indicating a nonlinear effect of O3 and a potential contribution of background O3 transmission. In the horizontal direction, the contribution of local emission sources to near-surface O3 was mostly between 20%~30%, except in Lingwu, where it reached more than 40%, and the contribution of external transmission was more than 30%. In Yinchuan, the local contribution was relatively weak, and a transport effect occurred between adjacent areas, weakening the local contribution to some certain extent. Moreover, O3 was obviously transported from south to north in summer because of overall southerly winds. In the vertical direction, the variation in O3 concentration was basically similar to the suburban, urban, and industrial representative sites, while the contribution of each process differed. At night, O3 photochemical loss was the largest at industrial sites, followed by urban and suburban sites, and was the strongest near the ground at all sites. During the day, O3 was mainly photochemically generated in the upper and middle regions of the boundary layer at urban and industrial sites. Then, together with a remnant in the nocturnal residual layer, O3 was transported vertically to the ground and horizontally around. Meanwhile, some O3 in the free atmosphere was entrained down into the boundary layer. Conversely, at suburban sites, photochemical ozone generation occurred throughout the boundary layer and was the strongest near the ground, while the transport effect was relatively weak.
Exploration of the Meteorological Drivers of Extreme Wildfire Events in the Arctic during 2019–2020
Daofu PENG, Xu YUE, Jun ZHU, Chenguang TIAN, Cheng GONG, Yimian MA, Yadong LEI, Hao ZHOU
2023, 28(2): 195-206. doi: 10.3878/j.issn.1006-9585.2022.22011
Abstract(169) HTML (108) PDF (8146KB)(26)
Wildfire activities in the Arctic have increased in recent years, especially after the extraordinary explosions in 2019–2020. This study investigated the relationships between wildfire carbon emissions and meteorological factors in the key regions of the Arctic during 1997–2020, with the stepwise regression method using a series of meteorological variables (snowfall, precipitation, wind speed, relative humidity, 2-m air temperature, and daily maximum temperature) from MERRA-2 reanalyses and the Fire Weather Index (FWI). The authors further explored the dominant meteorological drivers for the large wildfires in the Arctic during 2019–2020. Results showed that in all three key regions, the Duff Moisture Code (DMC) from FWI makes the dominant contribution to wildfire emissions. The anomalously high geopotential height results in an extremely increased daily maximum temperature and significantly reduced precipitation, jointly leading to anomalously high DMC and consequent wildfire episodes during 2019–2020. This result suggests that climatic anomalies such as warming and drought promote frequent wildfire activities in the Arctic.
Mountain Terrain Effects on Lidar Accuracy for Turbulence Measurement
Zhi LIANG, Lei LIU, Yu SHI, Fei HU
2023, 28(2): 207-215. doi: 10.3878/j.issn.1006-9585.2022.22025
Lidar turbulence measurement in flat terrain and in mountainous terrain are compared, and the error source is discussed. The field data show that the correlation coefficients for wind speed, turbulence kinetic energy (TKE), and turbulence intensity (TI) are 0.995, 0.908, and 0.904; in flat terrain, respectively, 0.999, 0.917, and 0.900; the fitting results in flat terrain are y=1.003x+0.241, y=1.192x+0.091, and y=1.140x+0.006; the fitting results in mountain terrain are y=0.949x+0.119, y=1.606x+0.167, and y=1.131x+0.031. In flat terrain, lidar overestimates wind speed by 2.71%, TKE by 28.3%, and TI by 17%; in mountain terrain, lidar underestimates wind speed by 3.91%, TKE is overestimated by 77.3%, and TI is overestimated by 17.85%. In the line of sight of a laser beam, the correlation coefficient of lidar TI is 0.93, and the fitting formula is y=1.003x−0.003. The results of this paper show that mountain terrain has an effect on lidar measurement of wind speed and turbulence: Lidar overestimated the TKE and TI, while underestimated the wind speed.
Influence of Mixed Air Pollution on Surface Micrometeorological Characteristics in Autumn and Winter in the Nanjing Area —Taking 2018 as an Example
Jiaze WANG, Xiaolu LING, Xinsheng ZHU, Weidong GUO, Jun ZOU, Jianning SUN
2023, 28(2): 216-228. doi: 10.3878/j.issn.1006-9585.2022.22053
Abstract(126) HTML (11) PDF (7758KB)(22)
Multielement observation data from the Station for Observing Regional Processes of the Earth System (SORPES) from 27 November to 3 December 2018 were used to quantitatively analyze the influence of mixed air pollution conditions on surface micrometeorological elements and energy balance characteristics under the combined effects of long-distance sand and dust and local emission pollution. On this basis, the response characteristics of surface meteorological elements and energy distribution under different pollution conditions in autumn and winter in Nanjing are compared by synthetic analysis. The results showed a daytime temperature of approximately 1 °C lower on polluted days than on clear days and a night temperature of approximately 2 °C higher. The downward/upward shortwave radiation flux on polluted days decreased as high as 48.8% and 55.2%, and the downward/upward long-wave radiation flux at night increased by 15% and 5.1%. On clear days, the net radiation budget during the day was 45.6% higher than that of polluted days, and the surface sensible heat flux was 75.5% higher than that of polluted days, while the difference in the surface latent heat flux was relatively small. The average Bowen ratio at night was higher on polluted days than on clear days, indicating stronger nighttime sensible heat exchange. The results help understand the influence process and mechanism of air pollution from different sources and different properties on surface energy balance and local meteorological elements in urban agglomerations of the Yangtze River Delta, as well as provide a verification basis for the interaction between air pollution and meteorological conditions, air quality prediction, and corresponding countermeasures.