1,723,485 research outputs found
Microphysical Structure of Thunderstorms and Their Lightning Activity During the mei‐yu and Post‐mei‐yu Periods Over Nanjing, Yangtze River Delta
No full textAbstract Using polarimetric radar, cloud‐to‐ground (CG) lightning, and reanalysis data, this study examined the microphysical structures of thunderstorm and their environmental impact during two active monsoon periods over Nanjing, Yangtze River Delta. The results show that the mei‐yu thunderstorm presented a large area of radar echo and many graupels between 0 and −10°C levels; these were accompanied by large vertical wind shear, which was favorite for the organization of thunderstorm. Broad updrafts within the mei‐yu thunderstorms were hypothesized, causing lower amount of dilution and entrainment, facilitating transportation of supercooled liquid water to the mixed‐phase region and producing CG lightning. Due to large atmospheric instability, strong updrafts within the post‐mei‐yu thunderstorm were expected to supply supercooled liquid water for the riming process to form more graupel above −10°C level. These provided favorable conditions for electrification, resulting in more CG lightning during the post‐mei‐yu period than during the mei‐yu period
Prediction of a Mei-yu Frontal Cyclone and the Associated Torrential Rainfall over Southern Taiwan During 2008 Mei-yu Season
No full textA torrential rain episode (≥ 200 mm day-1) was observed over coastal regions of southern Taiwan (south of 23.0°N) on 5 June 2008 under the influence of a meso-scale frontal cyclone (MFC) formed along the western flank of a Mei-yu frontal zone. Through the incorporation of additional observations over the ocean collected during Southwest Monsoon Experiment (SoWMEX)/Terrain-influenced Monsoon Rainfall Experiment (TiMREX), the location of a Mei-yu frontal boundary, defined by the wind shift, is better identified over the open ocean by the data assimilation of dropsonde observations. Meanwhile, the low-level cyclonic vorticity and horizontal convergence are increased along the Mei-yu frontal zone, and an increment maximum center of cyclonic vorticity locates over the north of South China Sea (SCS), where the MFC subsequently forms
Comparison of Volatile Flavor Compounds and Qualities between Traditional Fermented and Inoculated Fermented of Mei yu
Full text linkObjective: To provide theoretical basis and basic research data for the technological development of inoculated Chinese traditional fermented fish, Mei yu, the effects of inoculated fermentation with Lactobacillus sake JXNU1-3 on the quality of Mei yu were investigated. Methods: The sensory evaluation, color, texture and composition of volatile flavor compounds of Mei yu prepared by traditional fermentation and inoculated fermentation with Lactobacillus sakei JXNU1-3 with different salt concentration during fermentation were compared by sensory evaluation, electronic nose, texture analyzer and solid phase micro-extraction and gas chromatography-mass spectrometry (SPEM/GC-MS). Result: It was showed that inoculated fermented Mei yu with a salt concentration of 2% and fermentation time of 3 days had better color, texture, and higher sensory score. The inoculated fermented Mei yu had lower response values to sulfides and methylated compounds compared with the traditional fermented Mei yu. Further, the main flavor substances and key flavor components of these two fermented fish samples were similar. However, compared with inoculated fermented Mei yu, isoamyl alcohol (sour odor) and 2-acetylpyrrole (musty odor) compounds were only detected in traditional fermented Mei yu. Conclusions: Compared with traditional fermentation, inoculated fermentation could reduce the corruption degree and improve the sensory quality of Mei yu, which indicated that Lactobacillus sakei JXNU1-3 could be used as a good starter culture for the development of inoculated fermentation technology of Mei yu
Extreme Mei-yu in 2020:Characteristics, causes, predictability and perspectives
Full text linkThe 2020 extreme rainfall was highly unusual with episodes of intensive rains and winds from the middle and lower reaches of the Yangtze River Valley to southern Japan. Given the severe implications and huge forecast spread among different models, the extreme Mei-yu has aroused widespread concern. This study is aimed at synthesizing the latest research on the characteristics and potential climate forcing factors of such extreme Mei-yu and discusses the challenges and outlooks for prediction and numerical modeling. The distinct characteristics of the Yangtze River Valley summer rainfalls in 2020 included record-breaking accumulated precipitation, longest duration, earliest onset, and highest intensity. We summarize the majority of the studies investigating the diverse coupled ocean-atmospheric processes at different timescales. The research consensus is that the anomalous anticyclone spanning the western North Pacific and the mid-high latitude trough-ridge patterns are the two critical circulation features carrying tropical and mid-high latitude signals, jointly affecting the extreme Mei-yu. Potential mechanisms based on the two essential atmospheric circulations during the Mei-yu period are then highlighted. In addition, different climate model simulations are also introduced to reach an inter-model agreement despite certain model biases on the response of atmospheric circulations to these potential forcings among the state-of-the-art atmospheric and coupled general circulation models. This study provides a synthesis to promote the understanding, prediction, and disaster prevention of extreme Mei-yu.</p
2009), Rainfall characteristics and convective properties of Mei‐Yu precipitation systems over south
No full textABSTRACT Rainfall characteristics and mesoscale properties of precipitation systems in mei-yu seasons over South China, Taiwan, and the South China Sea (SCS) during 1998-2007 are investigated in this study. Mei-yu rainbands are defined using the Tropical Rainfall Measuring Mission 3B42 rainfall product and then applied to divide the mei-yu season into the mei-yu and break periods. In the 10-yr ''climatology,'' on average, the mei-yu rainbands have a lifetime of 4-5 days and most frequently occur near the South China coast. During the mei-yu periods, rainfall maxima are found over the Pearl River Delta, the foothills of the Yun-Gui Plateau, and Wuyi Mountain, with the first two maxima corresponding to especially heavy rainfall. Intraseasonal variations on the convective structures, especially over land, are distinct among the mei-yu, break, pre-mei-yu, and post-mei-yu, based on analysis of convection intensity proxies and vertical radar reflectivity profiles of precipitation features. Lightning flash rates are consistent with the convective structure. The most frequent lightning over South China and Taiwan is in the pre-mei-yu and the least is during the mei-yu, which suggests different microphysical structures. Therefore, the discrimination of intraseasonal transitions on convective vertical structures may have important implications to the problems of cumulus parameterization, model validation, rainfall estimation, and latent heat retrievals. Intraseasonal variations of convective structures over the SCS are less evident than those over land. Storms over the SCS during the mei-yu are slightly convectively stronger than those in the break. Oceanic features with strong ice scattering have much lower lightning flash rates than their counterparts over land
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Contrasting Pre-Mei-Yu and Mei-Yu Extreme Precipitation in the Yangtze River Valley: Influencing Systems and Precipitation Mechanisms
No full textThe mei-yu season over the Yangtze-Huai Rivers basin, typically occurring from mid-June to mid-July, is one of three heavy-rainfall periods over China and can contribute 50% of the annual precipitation. In this study, the first and second heaviest daily precipitation events at the Wuhan station have been selected to represent typical mei-yu and pre-mei-yu precipitation events where the differences in the atmospheric thermodynamic characteristics, precipitation nature, influencing systems, and mechanisms are investigated. During the mei-yu case, moist air mainly came from the South China Sea. Precipitation occurred south of the mei-yu front where abundant moisture and favorable thermodynamic conditions were present. The main influencing systems include a stable blocking pattern and strong and stable western Pacific subtropical high in the midtroposphere, and a small yet intense mesoscale cyclonic vortex in the low troposphere. Rainfall in Wuhan was continuous, caused by a well-organized convective line. A heavy rainband was located along the narrow band between the elongated upper-level jet (ULJ) and the low-level jet (LLJ) where the symmetric instability was found in the midtroposphere near Wuhan. Quite differently, for the pre-mei-yu precipitation case, moist air primarily came from the Beibu Gulf and the Bay of Bengal. Precipitation happened in the low-level convective instability region, where a short-wave trough in the midtroposphere and a mesoscale cyclonic vortex in the low-troposphere were found. Precipitation in Wuhan showed multiple peaks associated with independent meso-beta-scale convective systems. A rainstorm occurred at the exit of the LLJ and the right entrance of the ULJ, where convective instability exited in the mid- to low troposphere.National Natural Science Foundation of ChinaNational Natural Science Foundation of China [41705019, 41620104009, 91637211]; IHR; U.S. National Science FoundationNational Science Foundation (NSF) [AGS-1354402, AGS-1445956]6 month embargo; published online: 16 November 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Modelling the Effects of Aerosol on Mei-Yu Frontal Precipitation and Physical Processes
No full textThe Mei-Yu front is a significantly important summer precipitation system in eastern Asia. In recent years, anthropogenic air pollution over the Yangtze-Huaihe region of China has been aggravating continuously. A cloud-resolving model coupled with an idealized frontal model is used to investigate the response of aerosols on the Mei-Yu frontal precipitation. The results indicate that increasing droplet concentrations lead to significant precipitation enhancement with the current pollution levels in Mei-Yu frontal system. Under the polluted conditions, the enhanced cold-cloud process is of great importance. Moreover, with the “towing” of active cold-cloud process, cold-cloud and warm-cloud processes developed mutually. These account for the complicated and special microphysical mechanism for aerosol impacts on Mei-Yu frontal system. Furthermore, two types of “microphysical-dynamic positive feedback loop” caused by the interactions of various physical processes and effects (direct dynamic effect, frontogenesis effect, and vapor pump effect) can be found in the Mei-Yu precipitation, which in turn reinforce the microphysical processes. The combined effect is to increase Mei-Yu front precipitation. The interaction of microphysical processes and dynamic processes, and the positive feedback loops they create are the main physical mechanisms behind the significant impacts of aerosol on Mei-Yu frontal precipitation. This may also be an important feature of climate change in eastern Asia
Improving Radar Rainfall Estimations with Scaled Raindrop Size Spectra in Mei-Yu Frontal Rainstorms
No full textHydrological calibration of raw weather radar rainfall estimation relies on in situ rainfall measurements. Raindrop size distribution (DSD) was collected during three typical Mei-Yu rainstorms in July 2014 using three particle size velocity (Parsivel) DSD sensors along the Mei-Yu front in Nanjing, Chuzhou, and the western Pacific, respectively. To improve the radar precipitation estimation in different parts of the Mei-Yu front, a scaling method was adopted to formulate the DSD model and further derive the Z–R relations. The results suggest a distinct variation of DSDs in different parts of the Mei-Yu front. Compared with statistical radar Z–ARb relations obtained by mathematical fitting techniques, the use of a DSD model fitting based on a scaling law formulation theoretically shows a significant improvement in both stratiform (33.9%) and convective (2.8%) rainfall estimations of the Mei-Yu frontal system, which indicates that using a scaling law can better reflect the DSD variations in different parts of the Mei-Yu front. Polarimetric radar has indisputable advantages with multiparameter detection ability. Several dual-polarization radar estimators are also established by DSD sensor data, and the R(ZH, ZDR) estimator is proven to be more accurate than traditional Z–R relations in Mei-Yu frontal rainfall, with potential applications for operational C-band polarimetric radar
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Interaction of the westerlies with the Tibetan Plateau in determining the mei-yu termination Interaction of the westerlies with the Tibetan Plateau in determining the mei-yu termination
Full text linkThis study explores how the termination of the mei-yu is dynamically linked to the westerlies impinging on the Tibetan Plateau. It is found that the mei-yu stage terminates when the maximum upper tropospheric westerlies shift beyond the northern edge of the Plateau, around 40°?. This termination is accompanied by the disappearance of tropospheric northerlies over northeastern China. The link between the transit of the jet axis across the northern edge of the Plateau, the disappearance of northerlies, and termination of mei-yu holds on a range of timescales from interannual through seasonal and pentad. Diagnostic analysis indicates that the weakening of meridional moisture contrast and meridional wind convergence, mainly resulting from the disappearance of northerlies, causes the demise of the mei-yu front. The authors propose that the westerlies migrating north of the Plateau and consequent weakening of the extratropical northerlies triggers mei-yu termination. Model simulations are employed to test the causality between the jet and the orographic downstream northerlies by repositioning the northern edge of the Plateau. As the Plateau edge extends northward, orographic forcing on the westerlies strengthens, leading to persistent strong downstream northerlies and a prolonged mei-yu. Idealized simulations with a dry dynamical core further demonstrate the dynamical link between the weakening of orographically forced downstream northerlies with the positioning of the jet from south to north of the Plateau. Changes in the magnitude of orographically forced stationary waves are proposed to explain why the downstream northerlies disappear when the jet axis migrates beyond the northern edge of the Plateau
On the Mei-Yu front and the associated potential vorticity anomaly
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University of TorontoThe Mei-Yu (called Baiu in Japanese) front is a particular atmospheric phenomenon in East Asia that occurs during the late spring and early summer period. This thesis presents a combination of theoretical and numerical studies of two important issues regarding the development of Mei-Yu fronts: (1) the initiation of mesoscale convective systems, and (2) the formation of the PV anomaly and its impact on the Mei-Yu frontogenesis. The organization mechanism of the mesoscale convective systems on the Mei-Yu front has been examined in the context of frontal stability. The results show that the Mei-Yu front itself is unstable due to the presence of a low-level PV anomaly. It is then proposed that the convective systems are organized by the instability of the low-level PV anomaly along the front. The growth rate of the most unstable mode depends on the intensity of cumulus heating, with the e-folding time of the order of less than one day. When the heating intensity is below a critical level, the wavelength is about 8-15 times the cross-front width scale of the PV anomaly, and the instability structure is of the barotropic type but modified by convection. When the heating intensity exceeds the critical level, the disturbance draws its energy almost entirely from heating and the instability structure resembles a system driven purely by cumulus heating. The most unstable wavelength is 1700-2100 km and bears no relationship to the scale of PV anomaly. The formation of the low-level PV anomaly and its impact on the Mei-Yu frontogenesis have been studied through the numerical simulation of an observed Mei-Yu front. The PV anomaly on the modeled Mei-Yu front is the result of condensational heating. While the PV anomaly on the central sector of the front was caused by stratiform clouds, the PV anomaly on the western sector was mostly caused by cumulus convection. The numerical simulations have verified that the western sector of the Mei-Yu front is intensified mainly by the low-level convergence flow of cumulus convection. The comparison between the numerical simulations, theoretical results and observations is also made in the thesis.Ph.D
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