Future Atmospheric Rivers and Impacts on Precipitation: Overview of the ARTMIP Tier 2 High‐Resolution Global Warming Experiment

Atmospheric rivers (ARs) are long, narrow synoptic scale weather features important for Earth’s hydrological cycle typically transporting water vapor poleward, delivering precipitation important for local climates. Understanding ARs in a warming climate is problematic because the AR response to climate change is tied to how the feature is defined. The Atmospheric River Tracking Method Intercomparison Project (ARTMIP) provides insights into this problem by comparing 16 atmospheric river detection tools (ARDTs) to a common data set consisting of high resolution climate change simulations from a global atmospheric general circulation model. ARDTs mostly show increases in frequency and intensity, but the scale of the response is largely dependent on algorithmic criteria. Across ARDTs, bulk characteristics suggest intensity and spatial footprint are inversely correlated, and most focus regions experience increases in precipitation volume coming from extreme ARs. The spread of the AR precipitation response under climate change is large and dependent on ARDT selection

Reinforcement Learning-Based Formation Pinning and Shape Transformation for Swarms

Swarm models hold significant importance as they provide the collective behavior of self-organized systems. Boids model is a fundamental framework for studying emergent behavior in swarms systems. It addresses problems related to simulating the emergent behavior of autonomous agents, such as alignment, cohesion, and repulsion, to imitate natural flocking movements. However, traditional models of Boids often lack pinning and the adaptability to quickly adapt to the dynamic environment. To address this limitation, we introduce reinforcement learning into the framework of Boids to solve the problem of disorder and the lack of pinning. The aim of this approach is to enable drone swarms to quickly and effectively adapt to dynamic external environments. We propose a method based on the Q-learning network to improve the cohesion and repulsion parameters in the Boids model to achieve continuous obstacle avoidance and maximize spatial coverage in the simulation scenario. Additionally, we introduce a virtual leader to provide pinning and coordination stability, reflecting the leadership and coordination seen in drone swarms. To validate the effectiveness of this method, we demonstrate the model’s capabilities through empirical experiments with drone swarms, and show the practicality of the RL-Boids framework

Measurement errors induced by retardance deviation in a rotatable retarder fixed polarizer Stokes polarimeter

The retardance of an achromatic retarder may vary in the working frequency range and therefore deviate from its nominal value. In a rotatable retarder and fixed polarizer (RRFP) Stokes polarimeter, the retardance deviation of the retarder will result in significant measurement errors of the Stokes vector. The relationship between the retardance error and the measurement errors is theoretically derived in a RRFP Stokes polarimeter. Theoretical results show that the resultant measurement errors of the Stokes vector are determined by the retardance of the retarder, the retardance error and the Stokes vector under test, but are independent of the angular orientations of the retarder and the intensity measurements. Such measurement errors can not be reduced by choosing a set of optimum angular orientations or increasing the measurement number. To suppress such measurement errors in a complete RRFP Stokes polarimeter, the retarder with retardance from 110-deg to 135-deg is recommended. Simulation results in two measurement scenarios confirm the validity of the theoretical findings.Published versio

A 20-year database of MCSs in eastern China

This dataset contains the mesoscale convective systems (MCSs) over eastern China (20-42N, 95-125E) during the eight monsoon stages from 2001 to 2020. The zipped data are in netCDF format, each contains the brightness temperature (lon, lat, time) of an MCS event. Note that The time attribute shows "minutes since 2001-01-01 00:00" The lon, lat attributes are in degrees at the 4-km resolution For inquiries or potential collaborations, feel free to contact Dr. Tat Fan Cheng ([email protected]) or Prof. Mengqian Lu ([email protected]). If you find our dataset/analyses useful, please cite our recent paper (Thank you!). Cheng, T. F., Dong, Q., Dai, L., & Lu, M.* (2022). A Dual Regime of Mesoscale Convective Systems in the East Asian Monsoon Annual Cycle. Journal of Geophysical Research: Atmospheres, 127, e2022JD036523. https://doi.org/10.1029/2022JD03652

A staggered-grid lowrank finite-difference method for elastic wave extrapolation

Elastic wave extrapolation in the time domain is significant for an elastic wave equation-based processing. To improve the simulation reliability and accuracy of decoupled elastic P- and S- waves, we propose the staggered-grid lowrank finite-difference method based on the elastic wave decomposition. For elastic wave propagation, a lowrank finite-difference method based on the staggered grid is derived to improve the accuracy. Regarding the application of the decoupled elastic wave equation, we derive the finite-difference scheme coefficients which are dependent on velocity. Based on the elastic wave decomposition and plane wave theories, we formulate the elastic wave-extrapolation operators, which contain trigonometric adjustment factors. Accordingly, by applying the lowrank method to approximating the operators, the finite- difference scheme is designed to discretize the decoupled wave equation. The derivation processing implies the combination of elastic wave-mode decomposition and extrapolation. The proposed method enables elastic P- and S-waves to extrapolate in the time-space domain separately and produces accurate P-and S-wave components simultaneously. Dispersion analysis suggests that our proposed method is reliable and accurate in a wide range of wavenumber. Numerical simulation tests on a simple model and the Marmousi2 model validate the accuracy and effectiveness of the method, showing its ability in handling complex structures. Although the operators are accurate only when the medium is homogeneous, they are of high accuracy when the velocity gradient is quite small and are applicable when the velocity gradient is large. The subsequent results of reverse time migration for the Marmousi2 model also suggest that the proposed method is enough to serve as an extrapolator in elastic reverse time migration

Experimental and numerical studies on the thermal nonequilibrium behaviors of CO with Ar, He, and H₂

The time-dependent rotational and vibrational temperatures were measured to study the shock-heated thermal nonequilibrium behaviors of CO with Ar, He, and H-2 as collision partners. Three interference-free transition lines in the fundamental vibrational band of CO were applied to the fast, in situ, and state-specific measurements. Vibrational relaxation times of CO were summarized over a temperature range of 1110-2820 K behind reflected shocks. The measured rotational temperature instantaneously reached an equilibrium state behind shock waves. The measured vibrational temperature experienced a relaxation process before reaching the equilibrium state. The measured vibrational temperature time histories were compared with predictions based on the Landau-Teller model and the state-to-state approach. The state-to-state approach treats the vibrational energy levels of CO as pseudo-species and accurately describes the detailed thermal nonequilibrium processes behind shock waves. The datasets of state-specific inelastic rate coefficients of CO-Ar, CO-He, CO-CO, and CO-H-2 collisions were calculated in this study using the mixed quantum-classical method and the semiclassical forced harmonic oscillator model. The predictions based on the state-to-state approach agreed well with the measured data and nonequilibrium (non-Boltzmann) vibrational distributions were found in the post-shock regions, while the Landau-Teller model predicted slower vibrational temperature time histories than the measured data. Modifications were applied to the Millikan-White vibrational relaxation data of the CO-Ar and CO-H-2 systems to improve the performance of the Landau-Teller model. In addition, the thermal nonequilibrium processes behind incident shocks, the acceleration effects of H2O on the relaxation process of CO, and the characterization of vibrational temperature were highlighted

Experimental and numerical studies on the thermal nonequilibrium behaviors of CO with Ar, He, and H₂

The time-dependent rotational and vibrational temperatures were measured to study the shock-heated thermal nonequilibrium behaviors of CO with Ar, He, and H-2 as collision partners. Three interference-free transition lines in the fundamental vibrational band of CO were applied to the fast, in situ, and state-specific measurements. Vibrational relaxation times of CO were summarized over a temperature range of 1110-2820 K behind reflected shocks. The measured rotational temperature instantaneously reached an equilibrium state behind shock waves. The measured vibrational temperature experienced a relaxation process before reaching the equilibrium state. The measured vibrational temperature time histories were compared with predictions based on the Landau-Teller model and the state-to-state approach. The state-to-state approach treats the vibrational energy levels of CO as pseudo-species and accurately describes the detailed thermal nonequilibrium processes behind shock waves. The datasets of state-specific inelastic rate coefficients of CO-Ar, CO-He, CO-CO, and CO-H-2 collisions were calculated in this study using the mixed quantum-classical method and the semiclassical forced harmonic oscillator model. The predictions based on the state-to-state approach agreed well with the measured data and nonequilibrium (non-Boltzmann) vibrational distributions were found in the post-shock regions, while the Landau-Teller model predicted slower vibrational temperature time histories than the measured data. Modifications were applied to the Millikan-White vibrational relaxation data of the CO-Ar and CO-H-2 systems to improve the performance of the Landau-Teller model. In addition, the thermal nonequilibrium processes behind incident shocks, the acceleration effects of H2O on the relaxation process of CO, and the characterization of vibrational temperature were highlighted

Review of Specialty Fiber Based Brillouin Optical Time Domain Analysis Technology

Specialty fibers have introduced new functionalities and opportunities in distributed fiber sensing applications. Particularly, Brillouin optical time domain analysis (BOTDA) systems have leveraged the unique features of specialty fibers to achieve performance enhancement in various sensing applications. This paper provides an overview of recent developments of the specialty fibers based BOTDA technologies and their sensing applications. The specialty fibers based BOTDA systems are categorized and reviewed based on the new features or performance enhancements. The prospects of using specialty fibers for BOTDA systems are discussed

An Experimental Testbed for the Study of Visual Based Navigation Docking of Two Vertical Compound Aircraft

Compound aircraft, merging the advantages of two or more aircraft, is now a promising concept for designing modern aircraft. How to achieve successful docking of two aircraft in flight is an important issue for the applications of vertical compound aircraft. In order to resolve such an issue, this paper proposes a new visual based navigation docking scheme, which is different from rendezvous and docking operations in space applications. The present scheme uses a monocular camera mounted on the chaser aircraft with a certain installation angle to collect the visual features of the target aircraft, then the position and attitude of the landing gear of the target aircraft can be determined. Moreover, a six degrees of freedom docking mechanism mounted on the chaser aircraft is designed to catch hold of the landing gear tires of the target aircraft. In order to avoid undesired collision during the docking process, Z-direction position of the target landing gear is predicted and the proposed Z-direction speed control algorithm is applied to the chaser platform. The robustness of the present scheme has been validated numerically and experimentally by means of a chaser platform and a target platform on the ground testbed. Successful docking of the chaser platform and the target landing gear has been achieved, respectively, when the target platform performs a Z-direction movement and a compound movement