J. Meteor. Res.
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2018 Vol. 32, No. 2
Published: 2018-04-28

Investigation into the Formation, Structure, and Evolution of an EF4 Tornado in East China Using a High-Resolution Numerical Simulation
Dan YAO, Haile XUE, Jinfang YIN, Jisong SUN, Xudong LIANG, Jianping GUO
2018, 32(2): 157-171 [Abstract]( 118 ) HTML PDF (33810 KB)  ( 157 Supplemental Material
Abstract:Devastating tornadoes in China have received growing attention in recent years, but little is known about their formation, structure, and evolution on the tornadic scale. Most of these tornadoes develop within the East Asian monsoon regime, in an environment quite different from tornadoes in the U.S. In this study, we used an idealized, high-resolution (25-m grid spacing) numerical simulation to investigate the deadly EF4 (Enhanced Fujita scale category 4) tornado that occurred on 23 June 2016 and claimed 99 lives in Yancheng, Jiangsu Province. A tornadic supercell developed in the simulation that had striking similarities to radar observations. The violent tornado in Funing County was reproduced, exceeding EF4 (74 m s-1), consistent with the on-site damage survey. It was accompanied by a funnel cloud that extended to the surface, and exhibited a double-helix vorticity structure. The signal of tornado genesis was found first at the cloud base in the pressure perturbation field, and then developed both upward and downward in terms of maximum vertical velocity overlapping with the intense vertical vorticity centers. The tornado's demise was found to accompany strong downdrafts overlapping with the intense vorticity centers. One of the interesting findings of this work is that a violent surface vortex was able to be generated and maintained, even though the simulation employed a free-slip lower boundary condition. The success of this simulation, despite using an idealized numerical approach, provides a means to investigate more historical tornadoes in China.
Influence of the Northeast Cold Vortex on Flooding in Northeast China in Summer 2013
Jing GAO, Hui GAO
2018, 32(2): 172-180 [Abstract]( 84 ) HTML PDF (5132 KB)  ( 62 Supplemental Material
Abstract:Severe flooding occurred in Northeast China (NEC) in summer 2013. Compared with the rainfall climatology of the region, the rainy season began earlier in 2013 and two main rainy periods occurred from late June to early July and from mid July to early August, respectively. During the summer season of 2013, the western Pacific subtropical high (WPSH) was located farther westward, which strengthened the southerly winds on its west side in the lower troposphere. Under this circulation pattern, more water vapor was transported to North China and NEC. Another moisture transport pathway to NEC was traced to the cross-equatorial flow over the Bay of Bengal. In mid-high latitudes in summer 2013, the Northeast Cold Vortex (NECV) was much stronger and remained stable over NEC. Thus, the cold air flow from its northwest side frequently met with the warm and wet air from the south to form stronger moisture convergence at lower levels in the troposphere, resulting in increased precipitation over the region. Correlation analysis indicated that the NECV played a more direct role than the WPSH. Synoptic analyses of the two heaviest flood cases on 2 and 16 July confirmed this conclusion. The four wettest summers in NEC before 2000 were also analyzed and the results were consistent with the conclusion that both the WPSH and the NECV led to the intense rainfall in NEC, but the NECV had a more direct role.
Quasi-3-yr Cycle of Rainy Season Precipitation in Tibet Related to Different Types of ENSO during 1981-2015
Chunxue WANG, Zhenfeng MA
2018, 32(2): 181-190 [Abstract]( 51 ) HTML PDF (6215 KB)  ( 73 Supplemental Material
Abstract:The rainy season precipitation in Tibet (RSPT) is a direct cause for local floods/droughts. It also indirectly affects the thermal conditions of the Tibetan Plateau, which can result in anomalous patterns of atmospheric circulation over East Asia. The interannual variability of the RSPT is often linked with the El Niño-Southern Oscillation (ENSO), but the relevant mechanisms are far from being understood, particularly for different types of ENSO events. We investigated the interannual variation of the RSPT in association with different types of ENSO. A quasi-3-yr period of the RSPT (less-more-more precipitation) was significant at the 95% confidence level. A joint multi-taper method with singular value decomposition analysis of the coupled field between the RSPT and the sea surface temperature (SST) revealed that the developing eastern Pacific type El Niño was accompanied by a decrease in the RSPT. The shift from the central Pacific type El Niño to the eastern Pacific La Niña was accompanied by an increase in the RSPT. Weakening of the central Pacific La Niña was accompanied by an increase in the RSPT. Analysis of the mechanism of this coupling, using the same analysis method but other climatic factors, indicated that the gradually strengthening eastern Pacific El Niño can inhibit the Walker circulation, weakening the South Asian summer monsoon, and resulting in transport of less water vapor from the Bay of Bengal to Tibet. The change from the central Pacific El Niño to the eastern Pacific La Niña led to continued strengthening of the Walker circulation with westward movement of the ascending area. This enhanced the South Asian summer monsoon over the Arabian Sea and transported more water vapor to Tibet. The decreasing central Pacific La Niña accompanied by persistent cooling of SSTs in the equatorial Pacific led to a strong eastern North Pacific summer monsoon, causing an anomaly in the easterly transport of water vapor from the Sea of Japan to Tibet and increased RSPT.
Recent Rapid Decline of the Arctic Winter Sea Ice in the Barents-Kara Seas Owing to Combined Effects of the Ural Blocking and SST
Binhe LUO, Yao YAO
2018, 32(2): 191-202 [Abstract]( 70 ) HTML PDF (7793 KB)  ( 90 Supplemental Material
Abstract:This study investigates why the Arctic winter sea ice loss over the Barents-Kara Seas (BKS) is accelerated in the recent decade. We first divide 1979-2013 into two time periods:1979-2000 (P1) and 2001-13 (P2), with a focus on P2 and the difference between P1 and P2. The results show that during P2, the rapid decline of the sea ice over the BKS is related not only to the high sea surface temperature (SST) over the BKS, but also to the increased frequency, duration, and quasi-stationarity of the Ural blocking (UB) events. Observational analysis reveals that during P2, the UB tends to become quasi stationary and its frequency tends to increase due to the weakening (strengthening) of zo-nal winds over the Eurasia (North Atlantic) when the surface air temperature (SAT) anomaly over the BKS is posi-tive probably because of the high SST. Strong downward infrared (IR) radiation is seen to occur together with the quasi-stationary and persistent UB because of the accumulation of more water vapor over the BKS. Such downward IR favors the sea ice decline over the BKS, although the high SST over the BKS plays a major role. But for P1, the UB becomes westward traveling due to the opposite distribution of zonal winds relative to P2, resulting in weak downward IR over the BKS. This may lead to a weak decline of the sea ice over the BKS. Thus, it is likely that the rapid decline of the sea ice over the BKS during P2 is attributed to the joint effects of the high SST over the BKS and the quasi-stationary and long-lived UB events.
Atmospheric Circulation Patterns over East Asia and Their Connection with Summer Precipitation and Surface Air Temperature in Eastern China during 1961-2013
Shuping LI, Wei HOU, Guolin FENG
2018, 32(2): 203-218 [Abstract]( 62 ) HTML PDF (12506 KB)  ( 56
Abstract:Based on the NCEP/NCAR reanalysis data and Chinese observational data during 1961-2013, atmospheric circulation patterns over East Asia in summer and their connection with precipitation and surface air temperature in eastern China as well as associated external forcing are investigated. Three patterns of the atmospheric circulation are identified, all with quasi-barotropic structures:(1) the East Asia/Pacific (EAP) pattern, (2) the Baikal Lake/Okhotsk Sea (BLOS) pattern, and (3) the eastern China/northern Okhotsk Sea (ECNOS) pattern. The positive EAP pattern significantly increases precipitation over the Yangtze River valley and favors cooling north of the Yangtze River and warming south of the Yangtze River in summer. The warm sea surface temperature anomalies over the tropical Ind-ian Ocean suppress convection over the northwestern subtropical Pacific through the Ekman divergence induced by a Kelvin wave and excite the EAP pattern. The positive BLOS pattern is associated with below-average precipitation south of the Yangtze River and robust cooling over northeastern China. This pattern is triggered by anomalous spring sea ice concentration in the northern Barents Sea. The anomalous sea ice concentration contributes to a Rossby wave activity flux originating from the Greenland Sea, which propagates eastward to North Pacific. The positive ECNOS pattern leads to below-average precipitation and significant warming over northeastern China in summer. The reduced soil moisture associated with the earlier spring snowmelt enhances surface warming over Mongolia and northeastern China and the later spring snowmelt leads to surface cooling over Far East in summer, both of which are responsible for the formation of the ECNOS pattern.
Diurnal and Seasonal Variations of Thermal Stratification and Vertical Mixing in a Shallow Fresh Water Lake
Yichen YANG, Yongwei WANG, Zhen ZHANG, Wei WANG, Xia REN, Yaqi GAO, Shoudong LIU, Xuhui LEE
2018, 32(2): 219-232 [Abstract]( 79 ) HTML PDF (9769 KB)  ( 130 Supplemental Material
Abstract:Among several influential factors, the geographical position and depth of a lake determine its thermal structure. In temperate zones, shallow lakes show significant differences in thermal stratification compared to deep lakes. Here, the variation in thermal stratification in Lake Taihu, a shallow fresh water lake, is studied systematically. Lake Taihu is a warm polymictic lake whose thermal stratification varies in short cycles of one day to a few days. The thermal stratification in Lake Taihu has shallow depths in the upper region and a large amplitude in the temperature gradient, the maximum of which exceeds 5℃ m–1. The water temperature in the entire layer changes in a relatively consistent manner. Therefore, compared to a deep lake at similar latitude, the thermal stratification in Lake Taihu exhibits small seasonal differences, but the wide variation in the short term becomes important. Shallow polymictic lakes share the characteristic of diurnal mixing. Prominent differences on the duration and frequency of long-lasting thermal stratification are found in these lakes, which may result from the differences of local climate, lake depth, and fetch. A prominent response of thermal stratification to weather conditions is found, being controlled by the stratifying effect of solar radiation and the mixing effect of wind disturbance. Other than the diurnal stratification and convection, the representative responses of thermal stratification to these two factors with contrary effects are also discussed. When solar radiation increases, stronger wind is required to prevent the lake from becoming stratified. A daily average wind speed greater than 6 m s–1 can maintain the mixed state in Lake Taihu. Moreover, wind-induced convection is detected during thermal stratification. Due to lack of solar radiation, convection occurs more easily in nighttime than in daytime. Convection occurs frequently in fall and winter, whereas long-lasting and stable stratification causes less convection in summer.
Improving Representation of Tropical Cloud Overlap in GCMs Based on Cloud-Resolving Model Data
Xianwen JING, Hua ZHANG, Masaki SATOH, Shuyun ZHAO
2018, 32(2): 233-245 [Abstract]( 80 ) HTML PDF (8403 KB)  ( 78
Abstract:The decorrelation length (Lcf) has been widely used to describe the behavior of vertical overlap of clouds in gene-ral circulation models (GCMs); however, it has been a challenge to associate Lcf with the large-scale meteorological conditions during cloud evolution. This study explored the relationship between Lcf and the strength of atmospheric convection in the tropics based on output from a global cloud-resolving model. Lcf tends to increase with vertical velocity in the mid-troposphere (w500) at locations of ascent, but shows little or no dependency on w500 at locations of descent. A representation of Lcf as a function of vertical velocity is obtained, with a linear regression in ascending regions and a constant value in descending regions. This simple and dynamic-related representation of Lcf leads to a significant improvement in simulation of both cloud cover and radiation fields compared with traditional overlap treatments. This work presents a physically justifiable approach to depicting cloud overlap in the tropics in GCMs.
Applying the WRF Double-Moment Six-Class Microphysics Scheme in the GRAPES_Meso Model: A Case Study
Meng ZHANG, Hong WANG, Xiaoye ZHANG, Yue PENG, Huizheng CHE
2018, 32(2): 246-264 [Abstract]( 54 ) HTML PDF (6937 KB)  ( 116
Abstract:This study incorporated the Weather Research and Forecasting (WRF) model double-moment 6-class (WDM6) microphysics scheme into the mesoscale version of the Global/Regional Assimilation and PrEdiction System (GRAPES_Meso). A rainfall event that occurred during 3–5 June 2015 around Beijing was simulated by using the WDM6, the WRF single-moment 6-class scheme (WSM6), and the NCEP 5-class scheme, respectively. The results show that both the distribution and magnitude of the rainfall simulated with WDM6 were more consistent with the observation. Compared with WDM6, WSM6 simulated larger cloud liquid water content, which provided more water vapor for graupel growth, leading to increased precipitation in the cold-rain processes. For areas with the warm-rain processes, the sensitivity experiments using WDM6 showed that an increase in cloud condensation nuclei (CCN) number concentration led to enhanced CCN activation ratio and larger cloud droplet number concentration (Nc) but decreased cloud droplet effective diameter. The formation of more small-size cloud droplets resulted in a decrease in raindrop number concentration (Nr), inhibiting the warm-rain processes, thus gradually decreasing the amount of precipitation. For areas mainly with the cold-rain processes, the overall amount of precipitation increased; however, it gradually decreased when the CCN number concentration reached a certain magnitude. Hence, the effect of CCN number concentration on precipitation exhibits significant differences in different rainfall areas of the same precipitation event.
Simulating Aerosol Size Distribution and Mass Concentration with Simultaneous Nucleation, Condensation/Coagulation, and Deposition with the GRAPES-CUACE
Chunhong ZHOU, Xiaojing SHEN, Zirui LIU, Yangmei ZHANG, Jinyuan XIN
2018, 32(2): 265-278 [Abstract]( 108 ) HTML PDF (2122 KB)  ( 112
Abstract:A coupled aerosol-cloud model is essential for investigating the formation of haze and fog and the interaction of aerosols with clouds and precipitation. One of the key tasks of such a model is to produce correct mass and number size distributions of aerosols. In this paper, a parameterization scheme for aerosol size distribution in initial emission, which took into account the measured mass and number size distributions of aerosols, was developed in the GRAPES-CUACE[Global/Regional Assimilation and PrEdiction System-China Meteorological Administration (CMA) Unified Atmospheric Chemistry Environment model]—an online chemical weather forecast system that contains microphysical processes and emission, transport, and chemical conversion of sectional multi-component aerosols. In addition, the competitive mechanism between nucleation and condensation for secondary aerosol formation was improved, and the dry deposition was also modified to be in consistent with the real depositing length. Based on the above improvements, the GRAPES-CUACE simulations were verified against observational data during 1-31 January 2013, when a series of heavy regional haze-fog events occurred in eastern China. The results show that the aerosol number size distribution from the improved experiment was much closer to the observation, whereas in the old experiment the number concentration was higher in the nucleation mode and lower in the accumulation mode. Meanwhile, the errors in aerosol number size distribution as diagnosed by its sectional mass size distribution were also reduced. Moreover, simulations of organic carbon, sulfate, and other aerosol components were improved and the overestimation as well as underestimation of PM2.5 concentration in eastern China was significantly reduced, leading to increased correlation coefficient between simulated and observed PM2.5 by more than 70%. In the remote areas where bad simulation results were produced previously, the correlation coefficient grew from 0.35 to 0.61, and the mean mass concentration went up from 43% to 87.5% of the observed value. Thus, the simulation of particulate matters in these areas has been improved considerably.
Impact of Tropospheric Ozone on Summer Climate in China
Shu LI, Tijian WANG, Prodromos ZANIS, Dimitris MELAS, Bingliang ZHUANG
2018, 32(2): 279-287 [Abstract]( 67 ) HTML PDF (6999 KB)  ( 87
Abstract:The spatial distribution, radiative forcing, and climatic effects of tropospheric ozone in China during summer were investigated by using the regional climate model RegCM4. The results revealed that the tropospheric ozone column concentration was high in East China, Central China, North China, and the Sichuan basin during summer. The increase in tropospheric ozone levels since the industrialization era produced clear-sky shortwave and clear-sky longwave radiative forcing of 0.18 and 0.71 W m–2, respectively, which increased the average surface air temperature by 0.06 K and the average precipitation by 0.22 mm day–1 over eastern China during summer. In addition, tropospheric ozone increased the land-sea thermal contrast, leading to an enhancement of East Asian summer monsoon circulation over southern China and a weakening over northern China. The notable increase in surface air temperature in northwestern China, East China, and North China could be attributed to the absorption of longwave radiation by ozone, negative cloud amount anomaly, and corresponding positive shortwave radiation anomaly. There was a substantial increase in precipitation in the middle and lower reaches of the Yangtze River. It was related to the enhanced upward motion and the increased water vapor brought by strengthened southerly winds in the lower troposphere.
Oscillation of Surface PM2.5 Concentration Resulting from an Alternation of Easterly and Southerly Winds in Beijing: Mechanisms and Implications
Zhaobin SUN, Xiaoling ZHANG, Xiujuan ZHAO, Xiangao XIA, Shiguang MIAO, Ziming LI, Zhigang CHENG, Wei WEN, Yixi TANG
2018, 32(2): 288-301 [Abstract]( 49 ) HTML PDF (13454 KB)  ( 78
Abstract:We used simultaneous measurements of surface PM2.5 concentration and vertical profiles of aerosol concentration, temperature, and humidity, together with regional air quality model simulations, to study an episode of aerosol pollution in Beijing from 15 to 19 November 2016. The potential effects of easterly and southerly winds on the surface concentrations and vertical profiles of the PM2.5 pollution were investigated. Favorable easterly winds produced strong upward motion and were able to transport the PM2.5 pollution at the surface to the upper levels of the atmosphere. The amount of surface PM2.5 pollution transported by the easterly winds was determined by the strength and height of the upward motion produced by the easterly winds and the initial height of the upward wind. A greater amount of PM2.5 pollution was transported to upper levels of the atmosphere by upward winds with a lower initial height. The pollutants were diluted by easterly winds from clean ocean air masses. The inversion layer was destroyed by the easterly winds and the surface pollutants and warm air masses were then lifted to the upper levels of the atmosphere, where they re-established a multi-layer inversion. This region of inversion was strengthened by the southerly winds, increasing the severity of pollution. A vortex was produced by southerly winds that led to the convergence of air along the Taihang Mountains. Pollutants were transported from southern-central Hebei Province to Beijing in the boundary layer. Warm advection associated with the southerly winds intensified the inversion produced by the easterly winds and a more stable boundary layer was formed. The layer with high PM2.5 concentration became dee-per with persistent southerly winds of a certain depth. The polluted air masses then rose over the northern Taihang Mountains to the northern mountainous regions of Hebei Province.
Characteristics of Boundary Layer Structure during a Persistent Haze Event in the Central Liaoning City Cluster, Northeast China
Xiaolan LI, Yangfeng WANG, Lidu SHEN, Hongsheng ZHANG, Hujia ZHAO, Yunhai ZHANG, Yanjun MA
2018, 32(2): 302-312 [Abstract]( 64 ) HTML PDF (6520 KB)  ( 98
Abstract:The characteristics of boundary layer structure during a persistent regional haze event over the central Liaoning city cluster of Northeast China from 16 to 21 December 2016 were investigated based on the measurements of particulate matter (PM) concentration and the meteorological data within the atmospheric boundary layer (ABL). During the observational period, the maximum hourly mean PM2.5 and PM10 concentrations in Shenyang, Anshan, Fushun, and Benxi ranged from 276 to 355 μg m-3 and from 378 to 442 μg m-3, respectively, and the lowest hourly mean atmospheric visibility (VIS) in different cities ranged from 0.14 to 0.64 km. The central Liaoning city cluster was located in the front of a slowly moving high pressure and was mainly controlled by southerly winds. Wind speed (WS) within the ABL (< 2 km) decreased significantly and WS at 10-m height mostly remained below 2 m s-1 during the hazy episodes, which was favorable for the accumulation of air pollutants. A potential temperature inversion layer existed throughout the entire ABL during the earlier hazy episode from 0500 Local Time (LT) 18 December to 1100 LT 19 December, and then a potential temperature inversion layer developed with the bottom gradually decreased from 900 m to 300 m. Such a stable atmospheric stratification further weakened pollutant dispersion. The atmospheric boundary layer height (ABLH) estimated based on potential temperature profiles was mostly lower than 400 m and varied oppositely with PM2.5 in Shenyang. In summary, weak winds due to calm synoptic conditions, strong thermal inversion layer, and shallow atmospheric boundary layer contributed to the formation and development of this haze event. The backward trajectory analysis revealed the sources of air masses and explained the different characteristics of the haze episodes in the four cities.
Comparison of Two Air Pollution Episodes over Northeast China in Winter 2016/17 Using Ground-Based Lidar
Yanjun MA, Hujia ZHAO, Yunsheng DONG, Huizheng CHE, Xiaoxiao LI, Ye HONG, Xiaolan LI, Hongbin YANG, Yuche LIU, Yangfeng WANG, Ningwei LIU, Cuiyan SUN
2018, 32(2): 313-323 [Abstract]( 170 ) HTML PDF (6646 KB)  ( 213
Abstract:This study analyzes and compares aerosol properties and meteorological conditions during two air pollution epi-sodes in 19-22 (E1) and 25-26 (E2) December 2016 in Northeast China. The visibility, particulate matter (PM) mass concentration, and surface meteorological observations were examined, together with the planetary boundary layer (PBL) properties and vertical profiles of aerosol extinction coefficient and volume depolarization ratio that were measured by a ground-based lidar in Shenyang of Liaoning Province, China during December 2016-January 2017. Results suggest that the low PBL height led to poor pollution dilution in E1, while the high PBL accompanied by low visibility in E2 might have been due to cross-regional and vertical air transmission. The PM mass concentration decreased as the PBL height increased in E1 while these two variables were positively correlated in E2. The enhanced winds in E2 diffused the pollutants and contributed largely to the aerosol transport. Strong temperature inversion in E1 resulted in increased PM2.5 and PM10 concentrations, and the winds in E2 favoured the southwesterly transport of aerosols from the North China Plain into the region surrounding Shenyang. The large extinction coefficient was partially attributed to the local pollution under the low PBL with high ground-surface PM mass concentrations in E1, whereas the cross-regional transport of aerosols within a high PBL and the low PM mass concentration near the ground in E2 were associated with severe aerosol extinction at high altitudes. These results may facilitate better understanding of the vertical distribution of aerosol properties during winter pollution events in Northeast China.
Assessment of the GPM and TRMM Precipitation Products Using the Rain Gauge Network over the Tibetan Plateau
Sijia ZHANG, Donghai WANG, Zhengkun QIN, Yaoyao ZHENG, Jianping GUO
2018, 32(2): 324-336 [Abstract]( 115 ) HTML PDF (5173 KB)  ( 143
Abstract:Using high-quality hourly observations from national-level ground-based stations, the satellite-based rainfall products from both the Global Precipitation Measurement (GPM) Integrated MultisatellitE Retrievals for GPM (IMERG) and its predecessor, the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA), are statistically evaluated over the Tibetan Plateau (TP), with an emphasis on the diurnal variation. The results indicate that:(1) the half-hourly IMERG rainfall product can explicitly describe the diurnal variation over the TP, but with discrepancies in the timing of the greatest precipitation intensity and an overestimation of the maximum rainfall intensity over the whole TP. In addition, the performance of IMERG on the hourly timescale, in terms of the correlation coefficient and relative bias, is different for regions with sea level height below or above 3500 m; (2) the IMERG products, having higher correlation and lower root-mean-square error, perform better than the TMPA products on the daily and monthly timescales; and (3) the detection ability of IMERG is superior to that of TMPA, as corroborated by a higher Hanssen and Kuipers score, a higher probability of detection, a lower false alarm ratio, and a lower bias. Compared to TMPA, the IMERG products ameliorate the overestimation across the TP. In conclusion, GPM IMERG is superior to TRMM TMPA over the TP on multiple timescales.
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