2020 Vol. 26, No. 2

Article
The Relationship Between Abnormal Meiyu and Medium-Term Scale Wave Perturbation Energy Propagation Along the East Asian Subtropical Westerly Jet
JIN Rong-hua, YANG Ning, SUN Xiao-qing, LIU Si-jia, YIN Shan
2020, 26(2): 125-136. doi: 10.46267/j.1006-8775.2020.012
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Abstract:
The East Asian subtropical westerly jet (EASWJ) is one of the most important factors modulating the Meiyu rainfall in the Yangtze-Huaihe River Basin, China. This article analyzed periods of the medium-term EASWJ variation, wave packet distribution and energy propagation of Rossby waves along the EASWJ during Meiyu season, and investigated their possible influence on abnormal Meiyu rain. The results showed that during the medium-term scale atmospheric dynamic process, the evolution of the EASWJ in Meiyu season was mainly characterized by the changes of 3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves. The strong perturbation wave packet and energy propagation of the 3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves are mostly concentrated in the East Asian region of 90°-150°E, where the two wave trains of perturbation wave packets and wave-activity flux divergence coexist in zonal and meridional directions, and converge on the EASWJ. Besides, the wave trains of perturbation wave packet and wave-activity flux divergence in wet Meiyu years are more systematically westward than those in dry Meiyu years, and they are shown in the inverse phases between each other. In wet (dry) Meiyu year, the perturbation wave packet high-value area of the 10-15 d low-frequency variability is located between the Aral Sea and the Lake Balkhash (in the northeastern part of China), while over eastern China the wave-activity flux is convergent and strong (divergent and weak), and the high-level jets are strong and southward (weak and northward). Because of the coupling of high and low level atmosphere and high-level strong (weak) divergence on the south side of the jet over the Yangtze-Huaihe River Basin, the low-level southwest wind and vertically ascending motion are strengthened (weakened), which is (is not) conducive to precipitation increase in the Yangtze-Huaihe River Basin. These findings would help to better understand the impact mechanisms of the EASWJ activities on abnormal Meiyu from the perspective of medium-term scale Rossby wave energy propagation.
Resonance Effect in Interaction Between South Asian Summer Monsoon and ENSO During 1958-2018
YUAN Shuai, XU Jian-jun, CHAN J C L, CHIU Long-sang, PAN Yu-shan
2020, 26(2): 137-149. doi: 10.46267/j.1006-8775.2020.013
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Abstract:
The study has shown that the shear component of the vertical integrated kinetic energy (Ks) over the box (40ºE-100ºE, 0-20ºN) can be used to measure the intensity of the South Asian summer monsoon (SASM). Based on its value averaged between June and August, the SASM can be divided into strong and weak monsoon episodes. Between 1958 and 2018, there existed 16 (16) strong (weak) monsoon episodes. Based on the calendar year, the relationship between the SASM and ENSO episodes can be grouped into six patterns: weak monsoon - El Niño (WM-EN), normal monsoon - El Niño (NM-EN), weak monsoon - non ENSO (WM-NE), strong monsoon - La Niña (SM-LN), normal monsoon - La Niña (NM-LN) and strong monsoon - non ENSO (SM-NE). Previous studies suggest that the WM-EN and SM-LN patterns reflect the correlated relationship between the SASM and El Niño/Southern Oscillation (ENSO) events. Therefore, we name these two strongly coupled categories WM-EN and SM-LN as the resonance effect. Two important circulations, i.e., Walker circulation (WC) and zonal Asian monsoon circulation (MC), in the vertical plane are found to be not always correlated. The MC is controlled by thermal gradients between the Asian landmass and the tropical Indian Ocean, while the WC associated with ENSO events is primarily the east-west thermal gradient between the tropical South Pacific and the tropical Indian Ocean. Furthermore, the gradient directions caused by different surface thermal conditions are different. The main factor for the resonance effect is the phenomenon that the symbols of SSTA in the tropical Indian Ocean and the equatorial eastern Pacific are the same, but are opposite to that of the SSTA near the maritime continent.
A Precipitation Detection Method for MWTS-Ⅱ Radiance Assimilation in Typhoon Simulation
YUAN Bing, MA Gang, ZHANG Peng, XI Shuang, WANG Ting-fang
2020, 26(2): 150-160. doi: 10.46267/j.1006-8775.2020.014
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Abstract:
FY-3C Microwave Temperature Sounder Ⅱ (MWTS-Ⅱ) lacks observations at 23.8 GHz, 31 GHz and 89 GHz, making it difficult to remove the data contaminated by precipitation in assimilation. In this paper, a fast forward operator based on the Community Radiative Transfer Model (CRTM) was used to analyze the relationship between the observation minus background simulation (O-B) and the cloud fractions in different MWTS-Ⅱ channels. In addition, based on the community Gridpoint Statistical Interpolation (GSI) system, the radiation brightness temperature of the MWTS-Ⅱ was assimilated in the regional Numerical Weather Prediction (NWP) model. In the process of assimilation, Visible and Infrared Radiometer (VIRR) cloud detection products were matched to MWTS-Ⅱ pixels for precipitation detection. For typhoon No. 18 in 2014, impact tests of MWTS-Ⅱ data assimilation was carried out. The results show that, though the bias observation minus analysis (O-A) of assimilated data can be reduced by quality control only with | O-B | < 3K; however, the O-A becomes much smaller while the precipitation detection is performed with Fvirr < 0.9 (VIRR cloud fraction threshold of 0.9). Besides, the change of the environmental field around the typhoon is more conducive to make the simulated track closer to the observation. The 72-hour typhoon track simulation error also shows that, after the precipitation detection, the error of simulated typhoon track is significantly reduced, which reflects the validity of a precipitation detection method based on a double criterion of | O-B | < 3K and Fvirr < 0.9.
A Study of the Impacts of the Spatial Differences in Climate Engineering Programs on the Intensities of Extreme High-Temperature Events in China Under A 1.5℃ Temperature Control Target
KONG Feng
2020, 26(2): 161-175. doi: 10.46267/j.1006-8775.2020.015
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Abstract:
Based on the daily maximum temperature data and average temperature data prediction for the period ranging from 2020 to 2099 under the scenario of BNU-ESM climate engineering (G4 test) and non-climate engineering (RCP4.5), the regional differences in the extreme high-temperature intensities in China during the implementation of climate engineering programs (2020 to 2069) and after the implementation of those programs (2070 to 2099) were analyzed using the Weibull Distribution Theory. The results are as follows. (1) The comparison of the two scenarios shows that climate engineering has not fundamentally changed the spatial variation of the intensity of extreme hightemperature events in different recurring periods in China. It was found that in both scenarios, the extreme hightemperature intensities were characterized by the spatial differentiations of low-temperature intensities on the QinghaiTibet Plateau, and high-temperature intensities in the eastern and northwestern region. (2) The comparison of the two scenarios shows that climate engineering in the two study periods could help mitigate the extreme high-temperature intensities with different recurrence periods in China, and the mitigation effects during the implementation period would be significantly higher than those after the implementation. (3) The comparison between the periods ranging from 2020 to 2069 and 2070 to 2099 under the proposed climate engineering scenarios suggests that there would be no strong rebounding of extreme high-temperatures following the implementation of climate engineering programs. Moreover, the mitigation effect of extreme high-temperature intensity during the implementation of climate engineering is significantly higher than that after the completion of climate engineering. (4) According to the comparison between the average temperature changes in China before and after the implementation of the climate project, the average temperature in China has been reduced by at least 1.25 ℃, which effectively alleviates global warming and is conducive to the realization of the 1.5 ℃ temperature control target of the Paris Agreement.
Operational Evaluation of the Quantitative Precipitation Estimation by a CINRAD-SA Dual Polarization Radar System
CHEN Chao, LIU Li-ping, HU Sheng, WU Zhi-fang, WU Chong, ZHANG Yang
2020, 26(2): 176-187. doi: 10.46267/j.1006-8775.2020.016
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Abstract:
In this paper, a quantitative precipitation estimation based on the hydrometeor classification (HCA-QPE) algorithm was proposed for the first operational S band dual-polarization radar upgraded from the CINRAD/SA radar of China. The HCA-QPE algorithm, localized Colorado State University-Hydrometeor Identification of Rainfall (CSUHIDRO) algorithm, the Joint Polarization Experiment (JPOLE) algorithm, and the dynamic Z-R relationships based on variational correction QPE (DRVC-QPE) algorithm were evaluated with the rainfall events from March 1 to October 30, 2017 in Guangdong Province. The results indicated that even though the HCA-QPE algorithm did not use the observed rainfall data for correction, its estimation accuracy was better than that of the DRVC-QPE algorithm when the rainfall rate was greater than 5 mm h-1; and the stronger the rainfall intensity, the greater the QPE improvement.Besides, the HCA-QPE algorithm worked better than the localized CSU-HIDRO and JPOLE algorithms. This study preliminarily evaluated the improved accuracy of QPE by a dual-polarization radar system modified from CINRAD-SA radar.
Comparison of Liquid Water Content Retrievals for Airborne Millimeter-Wave Radar with Different Particle Parameter Schemes
CUI Xin-dong, YAO Zhi-gang, ZHAO Zeng-liang, WANG Min-wei, FAN Chun-hui, SU Tao
2020, 26(2): 188-198. doi: 10.46267/j.1006-8775.2020.017
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Abstract:
In the application of the physical iterative method to retrieve millimeter-wave radar liquid water content (LWC) and liquid water path (LWP), particle parameter scheme is the main factor affecting retrieval performance. In this paper, synchronous measurements of an airborne millimeter-wave radar and a hot-wire probe in stratus cloud are used to compare the LWC retrievals of the oceanic and continental particle parameter scheme with diameter less than 50μm and the particle parameter scheme with diameter less than 500μm and 1500μm (scheme 1, scheme 2, scheme 3, and scheme 4, respectively). The results show that the particle parameter scheme needs to be selected according to the reflectivity factor when using the physical iterative method to retrieve the LWC and LWP. When the reflectivity factor is less than - 30dBZ, the retrieval error of scheme 1 is the minimum. When the reflectivity factor is greater than -30dBZ, the retrieval error of scheme 4 is the minimum. Based on the reflectance factor value, the LWP retrievals of scheme 4 are closer to the measurements, the average relative bias is 5.2%, and the minimum relative bias is 4.4 %. Compared with other schemes, scheme 4 seems to be more useful for the LWC and LWP retrieval of stratus cloud in China.
Long-Term Trends in the Probability of Different Grades of Haze Days in China from 1960 to 2013
FU Chuan-bo, DAN Li
2020, 26(2): 199-207. doi: 10.46267/j.1006-8775.2020.018
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Abstract:

The number of haze days and daily visibility data for 543 stations in China were used to define the probabilities of four grades of haze days: slight haze (SLH) days; light haze (LIH) days; moderate haze (MOH) days; and severe haze (SEH) days. The change trends of the four grades of haze were investigated and the following results were obtained. The highest probability was obtained for SLH days (95.138%), which showed a decreasing trend over the last 54 years with the fastest rate of decrease of?0.903% · (10 years)?1 and a trend coefficient of?0.699, passing the 99.9% confidence level. The probabilities of LIH and MOH days increased steadily, whereas the probability of SEH days showed a slight downward trend during that period. The increasing probability of SLH days was mainly distributed to the east of 105°E and the south of 42°N and the highest value of the trend coefficient was located in the Pearl River Delta and Yangtze River Delta regions. The increasing probability of LIH days was mainly distributed in eastern China and the southeastern coastal region. The probabilities of MOH and SEH days was similar to the probability of LIH days. An analysis of the four grades of haze days in cities with different sizes suggested that the probability of SLH days in large cities and medium cities clearly decreased during the last 54 years. However, the probabilities of LIH days was < 10% and increased steadily. The probability of MOH days showed a clear interdecadal fluctuation and the probability of SEH days showed a weak upward trend. The probability of SLH days in small cities within 0.8° of large or medium cities decreased steadily, but the probability of LIH and MOH days clearly increased, which might be attributed to the impact of large and medium cities. The probability of SLH days in small cities >1.5° from a large or medium city showed an increasing trend and reached 100% after 1990; the probability of the other three grades was small and decreased significantly.

Sensitivity Analysis of Ensemble Simulations on a Torrential Rainfall Case over South China Using Multiple PBL and SL Parameterizations
HUANG Ling
2020, 26(2): 208-222. doi: 10.46267/j.1006-8775.2020.019
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Abstract:

A good representation of the interaction between the planetary boundary layer (PBL) and the surface layer (SL) in numerical models is of great importance for the prediction of the initiation and development of convection. This study examined an ensemble that consists of the available suites of PBL and SL parameterizations based on a torrential rainfall event over south China. The sensitivity of the simulations was investigated against objective measurements using multiple PBL and SL parameterization schemes. The main causes of the bias from different parameterization schemes were further analysed by comparing the good and bad ensemble members. The results showed that good members tended to underestimate the rainfall amount but presented a decent evolution of mesoscale convective systems that were responsible for the torrential rainfall. Using the total energy mass flux (TEMF) scheme, the bad members overestimated the amount and spatial coverage of rainfall. The failure of the bad member was due to a spurious convection initiation (CI) resulting from the overestimated high-θe elevated air. The spurious CI developed and expanded rapidly, causing intensive and extensive rainfall over south China. Consistent with previous studies, the TEMF scheme tends to produce a warmer and moister PBL environment. The detailed sensitivity analysis of this case may provide reference for the operational forecast of rainfall over south China using multiple PBL and SL parameterizations.

Different Summer Rainfall Anomaly Patterns in Northeast China Associated with Two Kinds of El Niño Events
WANG Qin, LI Shuang-lin
2020, 26(2): 223-230. doi: 10.46267/j.1006-8775.2020.020
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Abstract:

The relationship between summer rainfall anomalies in northeast China and two types of El Niño events is investigated by using observation data and an atmospheric general circulation model (AGCM). It is shown that, for different types of El Niño events, there is different rainfall anomaly pattern in the following summer. In the following year of a typical El Niño event, there are remarkable positive rainfall anomalies in the central-western region of northeast China, whereas the pattern of more rainfall in the south end and less rainfall in the north end of northeast China easily appears in an El Niño Modoki event. The reason for the distinct difference is that, associated with the different sea surface temperature anomalies (SSTA) along the equatorial Pacific, the large-scale circulation anomalies along east coast of East Asia shift northward in the following summer after El Niño Modoki events. Influenced by the anomalous anticyclone in Philippine Sea, southwesterly anomalies over eastern China strengthen summer monsoon and bring more water vapor to northeast China. Meanwhile, convergence and updraft is strengthened by the anomalous cyclone right in northeast China in typical El Niño events. These moisture and atmospheric circulation conditions are favorable for enhanced precipitation. However, because of the northward shift, the anomalous anticyclone in the Philippine Sea in typical El Niño cases shifts to the south of Japan in Modoki years, and the anomalous cyclone in northeast China in typical El Niño cases shifts to the north of northeast China, leading to the"dipole pattern"of rainfall anomalies. According to the results of numerical experiments, we further confirm that the tropical SSTA in different types of El Niño event can give rise to observed rainfall anomaly patterns in northeast China.

Characteristics of Aerosol Pollution Under Different Visibility Conditions in Winter in a Coastal Mega-City in China
YANG Hong-long, ZHANG Yong, LI Lei, CHAN PAK WAI, LU Chao, ZHANG Li
2020, 26(2): 231-238. doi: 10.46267/j.1006-8775.2020.021
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Abstract:

To investigate chemical profiles and formation mechanisms of aerosol particles in winter haze events, comprehensive measurements including hourly concentrations of PM2.5 and water-soluble inorganic ions and related gas-phase precursors were conducted via an online monitoring system from January to March of 2016 in Shenzhen, a coastal mega-city in south China. In this study, high concentrations of PM2.5, NO2 and lower levels of O3 were observed during haze periods in comparison with clear days (Visibility > 15km). The major secondary ionic species were

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-, which varied significantly on haze and clear days. The ratio of

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in haze days was greater than that on clear days and tended to be larger when air pollution became more serious. At the same time, compared with previous studies, it has been found that the ratio has been increasing gradually in Shenzhen, indicating that the motor vehicle exhaust emissions have a more and more important impact on air quality in Shenzhen. Sulfur oxidation rate(SOR) and nitrogen oxidation rate(NOR) was higher during the haze period than that in clean days, indicating efficient gas to particle conversion. Further analysis shows that high concentrations of sulfate might be explained by aqueous oxidation, but gas-phase reactions might dominate nitrate formation. This study also highlights that wintertime nitrate formation can be an important contributor to aerosol particles, especially during haze periods.

Impact of Dynamic and Thermal Forcing on the Intensity Evolution of the Vortices over the Tibetan Plateau in Boreal Summer
GAO Yuan, YAO Xiu-ping
2020, 26(2): 239-252. doi: 10.46267/j.1006-8775.2020.022
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Abstract:

The Tibetan Plateau Vortex (TPV) is one of the main weather systems causing heavy rainfall over the Tibetan Plateau in boreal summer. Based on the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) reanalysis datasets provided by the National Aeronautics and Space Administration (NASA), 8 cases of TPV over the Tibetan Plateau generated in June-August with a lifetime of 42 hours are composited and analyzed to reveal the impact of dynamic and thermal forcing on the intensity evolution of TPVs. The results are as follows. (1) The TPVs appear obviously at 500 hPa and the TPVs intensity (TPVI) shows an obvious diurnal variation with the strongest at 00LT and the weakest at 12LT (LT=UTC+6h). (2) A strong South Asia High at 200 hPa as well as a shrunken Western Pacific Subtropical High at 500 hPa provide favorable conditions for the TPVI increasing. (3) The vorticity budget reveals that the divergence is indicative of the variation of the TPVI. The TPVI decreases when the convergence center at 500 hPa and the divergence center at 200 hPa lie in the east of the TPVs center and increases when both centers coincide with the TPVs center. (4) Potential vorticity (PV) increases with the enhancement of the TPVI. The PV budget shows that the variation of the TPVI is closely related to the diabatic heating over the Tibetan Plateau. The increased sensible heating and radiative heating in the boundary layer intensify the ascent and latent heating release. When the diabatic heating center rises to 400 hPa, it facilitates the development of the TPVs.