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5. Singularity as a diagnostic for secondary eyewall occurrence in tropical cyclones

Author

Lu, Ping, Yang, Long, Zhang, Jishi, Wang, Danyang, and Lin, Yanluan

Subjects
Physics - Atmospheric and Oceanic Physics
Abstract

Secondary eyewalls occur in 70% of major tropical cyclones (TCs), and are associated with rapid changes in storm intensity and rapid broadening of strong winds. While mechanisms of secondary eyewall formation have been investigated from various perspectives, the explicit conditions on which secondary eyewalls occur in TCs remain veiled, leaving substantial uncertainties in TC intensity forecast, especially for the most extreme events. In this study, we present a simple diagnostic, in form of a singularity, for secondary eyewall occurrence in TCs. The diagnostic is solely dependent on three basic storm characteristics (the maximum wind speed, the radius of maximum wind, and the latitude) and shown to compare well with satellite observations. It provides a valuable tool to improve the understanding, modeling and risk assessment of secondary eyewall storms., Comment: 20 pages, 6 figures

Published
2022

11. Redefining climate index with sea surface temperature of key area can better express atmospheric physical activity

Author

Zhang, Jishi, Lu, Jingrong, Huang, Haidong, Liu, Xiaoning, Zhao, Yafeng, Wang, Zhiyang, and Mo, Jinlei

Subjects
Physics - General Physics
Abstract

Since the 1920s, when the three oscillations ENSO, NAO and NPO were found and defined, the theory of ocean-atmosphere coupling is particularly important in explaining the phenomena of atmospheric physics, then defined more than ten climate indexes, such as SOI, AO, AAO and Nino monitoring area and so on, the indexes usually adopt standardized sea level pressure (SLP) difference or standardized sea surface temperature anomaly (SSTA) difference definitions. The survey is carried out with seventy stations runoff of major rivers in the world shows that the correlation coefficient between these indexes and runoff is very low, most of which is between 0.1-0.2, the impact of the index on the hydrologic climate cannot be truly reflected, which has led to doubts about the clear physical mechanism and even questions of teleological authenticity. This is due to the fact that standardization is a nonlinear process, which changes the structure of the original data, causing the correlation coefficient to be low. Using sea surface temperature difference (SSTD) to define these climate indexes, the correlation coefficient is significantly improved, the Hankou station of Yangtze river, Darband station of Ind, Hope station of Fraser, Bangui station of Oubangui generally exceeds 0.8 strong degree, which prove that these relevant elements have a high resonance effect, there must be a common driving physical quantity. We find that the sun-earth distance has a very strong resonance effect, it is the earth's rotational orbit that determines their common activity intensity and cycle characteristics. The sun-earth distance can accurately calculate the tens and hundreds years of SST and SSTD, if using the SST or SSTD as the climate indicators, which express physical process of various ocean-atmosphere coupling, we can thoroughly solve long-term ultra-long-term forecast of international difficulty problems.

Published
2017

12. Atmospheric-river-induced precipitation in California as simulated by the regionally refined Simple Convective Resolving E3SM Atmosphere Model (SCREAM) Version 0.

Author

Bogenschutz, Peter A., Zhang, Jishi, Tang, Qi, and Cameron-Smith, Philip

Subjects
*ATMOSPHERIC models, *ATMOSPHERIC rivers, *TOPOGRAPHY, *EARTH (Planet)
Abstract

Using the regionally refined mesh (RRM) configuration of the US Department of Energy's Simple Cloud-Resolving Energy Exascale Earth System Model (E3SM) Atmosphere Model (SCREAM), we simulate and evaluate four meteorologically distinct atmospheric river events over California. We test five different RRM configurations, each differing in terms of the areal extent of the refined mesh and the resolution (ranging from 800 m to 3.25 km). We find that SCREAM RRM generally has a good representation of the AR-generated precipitation in CA, even for the control simulation which has a very small 3 km refined patch, and is able to capture the fine-scale regional distributions that are controlled largely by the fine-scale topography of the state. It is found that SCREAM generally has a wet bias over topography, most prominently over the Sierra Nevada mountain range, with a corresponding dry bias on the lee side. We find that refining the resolution beyond 3 km (specifically 1.6 km and 800 m) has virtually no benefit towards reducing systematic precipitation biases but that improvements can be found when increasing the areal extent of the upstream refined mesh. However, these improvements are relatively modest and only realized if the size of the refined mesh is expanded to the scale where employing RRM no longer achieves the substantial cost benefit it was intended for. [ABSTRACT FROM AUTHOR]

Published
2024
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15. Leveraging regional mesh refinement to simulate future climate projections for California using the Simplified Convection-Permitting E3SM Atmosphere Model Version 0.

Author

Zhang, Jishi, Bogenschutz, Peter, Tang, Qi, Cameron-smith, Philip, and Zhang, Chengzhu

Subjects
*ATMOSPHERIC models, *CLIMATE change models, *RADIATIVE forcing, *CLIMATE change, *TOPOGRAPHY, *STRATOCUMULUS clouds
Abstract

The spatial heterogeneity related to complex topography in California demands high-resolution (< 5 km) modeling, but global convection-permitting climate models are computationally too expensive to run multi-decadal simulations. We developed a 3.25 km California climate modeling framework by leveraging regional mesh refinement (CARRM) using the U.S. Department of Energy (DOE)'s global Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) version 0. Four 5-year time periods (2015–2020, 2029–2034, 2044–2049, and 2094–2099) were simulated by nudging CARRM outside California to 1° coupled simulation of E3SMv1 under the Shared Socioeconomic Pathways (SSP)5-8.5 future scenario. The 3.25 km grid spacing adds considerable value to the prediction of the California climate changes, including more realistic high temperatures in the Central Valley and much improved spatial distributions of precipitation and snowpack in the Sierra Nevada and coastal stratocumulus. Under the SSP5-8.5 scenario, CARRM simulation predicts widespread warming of 6–10 °C over most of California, a 38 % increase in statewide average 30 d winter–spring precipitation, a near-complete loss of the alpine snowpack, and a sharp reduction in shortwave cloud radiative forcing associated with marine stratocumulus by the end of the 21st century. We note a climatological wet precipitation bias for the CARRM and discuss possible reasons. We conclude that SCREAM RRM is a technically feasible and scientifically valid tool for climate simulations in regions of interest, providing an excellent bridge to global convection-permitting simulations. [ABSTRACT FROM AUTHOR]

Published
2024
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28. Critic Learning-Based Safe Optimal Control for Nonlinear Systems with Asymmetric Input Constraints and Unmatched Disturbances.

Author

Qin, Chunbin, Jiang, Kaijun, Zhang, Jishi, and Zhu, Tianzeng

Subjects
NONLINEAR systems, COST functions, ZERO sum games, DYNAMIC programming, LYAPUNOV stability
Abstract

In this paper, the safe optimal control method for continuous-time (CT) nonlinear safety-critical systems with asymmetric input constraints and unmatched disturbances based on the adaptive dynamic programming (ADP) is investigated. Initially, a new non-quadratic form function is implemented to effectively handle the asymmetric input constraints. Subsequently, the safe optimal control problem is transformed into a two-player zero-sum game (ZSG) problem to suppress the influence of unmatched disturbances, and a new Hamilton–Jacobi–Isaacs (HJI) equation is introduced by integrating the control barrier function (CBF) with the cost function to penalize unsafe behavior. Moreover, a damping factor is embedded in the CBF to balance safety and optimality. To obtain a safe optimal controller, only one critic neural network (CNN) is utilized to tackle the complex HJI equation, leading to a decreased computational load in contrast to the utilization of the conventional actor–critic network. Then, the system state and the parameters of the CNN are uniformly ultimately bounded (UUB) through the application of the Lyapunov stability method. Lastly, two examples are presented to confirm the efficacy of the presented approach. [ABSTRACT FROM AUTHOR]

Published
2023
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34. Vpliv toplotne obdelave na mikrostrukturo in lastnosti WC-10Co4Cr prevlek, izdelanih z zelo hitrim naprševanjem vplinski atmosferi mešanice propana in zraka

Author

Zhou, Xuedong, Liu, Haijun, Zhang, Jishi, Ji, Jinsheng, Zhao, Wensheng, Zhang, Zhimin, Wang, Qiang, and Xue, Yong

Subjects
odpornost proti abraziji, WC-10Co4Cr coatings, corrosion resistance, Polymers and Plastics, heat treatment, abrasion resistance, Metals and Alloys, toplotna obdelava, korozijska obstojnost, udc:66.040.4:620.1:621.793.7:620.193, prevleke na osnovi WC-10Co4Cr
Abstract

In this study a high-velocity air-fuel (HVAF) flame-sprayed WC-10Co4Cr coating was heat-treated at (240; 300; 400) °C for 2 h in an air atmosphere. The effect of the heat treatment on the hardness, fracture toughness, wear resistance, corrosion resistance, phase composition and microstructure behaviour of the coatings was investigated. It could be concluded from the X-ray diffraction (XRD) pattern that the phase of the coatings was mainly composed of tungsten carbide, an amorphous phase, a small amount of W2C and trace metal tungsten. However, the heat-treated coating had a small increase in W2C compared to the original coating, although the amount of amorphous phase did not decrease significantly. The results indicated that as the heat-treatment temperature increased, the hardness of the coating first increased and then decreased, while the fracture toughness increased. The polarization test confirmed that the heat-treated coating had higher corrosion resistance than the original coating. In addition, the results of the reciprocating friction and wear test indicated that small amounts of W2C strengthening phases were formed in the WC-10Co4Cr coating after heat treatment at 400 °C. This process did not eliminate many of the tougher Co and WC phases. Therefore, this coating had the best wear resistance among all the comparative coatings.

Published
2021

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