Orographic Effects of the Tibetan Plateau on the East Asian Summer Monsoon: An Energetic Perspective

This paper investigates the dynamical processes through which the Tibetan Plateau (TP) influences the East Asian summer monsoon (EASM) within the framework of the moist static energy (MSE) budget, using both observations and atmospheric general circulation model (AGCM) simulations. The focus is on the most prominent feature of the EASM, the so-called meiyu–baiu (MB), which is characterized by a well-defined, southwest–northeast elongated quasi-stationary rainfall band, spanning from eastern China to Japan and into the northwestern Pacific Ocean between mid-June and mid-July. Observational analyses of the MSE budget of the MB front indicate that horizontal advection of moist enthalpy, and primarily of dry enthalpy, sustains the front in a region of otherwise negative net energy input into the atmospheric column. A decomposition of the horizontal dry enthalpy advection into mean, transient, and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection. Numerical simulations in which the TP is either retained or removed show that the TP influences the stationary enthalpy flux, and hence the MB front, primarily by changing the meridional stationary eddy velocity, with reinforced southerly wind over the MB region and northerly wind to its north. Changes in the longitudinal thermal gradient are mainly confined to the near downstream of the TP, with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended MB region

A matrix-free parallel solution method for the three-dimensional heterogeneous Helmholtz equation

The Helmholtz equation is related to seismic exploration, sonar, antennas, and medical imaging applications. It is one of the most challenging problems to solve in terms of accuracy and convergence due to the scalability issues of the numerical solvers. For 3D large-scale applications, high-performance parallel solvers are also needed. In this paper, a matrix-free parallel iterative solver is presented for the three-dimensional (3D) heterogeneous Helmholtz equation. We consider the preconditioned Krylov subspace methods for solving the linear system obtained from finite-difference discretization. The Complex Shifted Laplace Preconditioner (CSLP) is employed since it results in a linear increase in the number of iterations as a function of the wavenumber. The preconditioner is approximately inverted using one parallel 3D multigrid cycle. For parallel computing, the global domain is partitioned blockwise. The matrix-vector multiplication and preconditioning operator are implemented in a matrix-free way instead of constructing large, memory-consuming coefficient matrices. Numerical experiments of 3D model problems demonstrate the robustness and outstanding strong scaling of our matrix-free parallel solution method. Moreover, the weak parallel scalability indicates our approach is suitable for realistic 3D heterogeneous Helmholtz problems with minimized pollution error.Comment: 25 pages, 15 figures, manuscript submitted to a special issue of conference NMLSP202

Early Summer Response of the East Asian Summer Monsoon to Atmospheric CO_2 Forcing and Subsequent Sea Surface Warming

The early summer regional climate change of the East Asian summer monsoon (EASM) is investigated in the phase 5 of the Coupled Model Intercomparison Project (CMIP5) archive. In the greenhouse gas–forced scenario, reduction of radiative cooling and increase in continental surface temperature occur much more rapidly than changes in sea surface temperatures (SSTs). Without changes in SSTs, the early summer rainfall in the monsoon region decreases (increases) over ocean (land) in most models. On longer time scales, as SSTs increase, rainfall changes are opposite. The total response to atmospheric CO_2 forcing and subsequent SST warming is a large (modest) increase in rainfall over ocean (land) in the EASM region. Dynamic changes, in spite of significant contributions from the thermodynamic component, play an important role in setting up the spatial pattern of precipitation changes. Early summer rainfall anomalies over east China are a direct consequence of local land–sea contrast, while changes in the large-scale oceanic rainfall band are closely associated with the displacement of the larger-scale North Pacific subtropical high (NPSH). Ad hoc numerical simulations with the AM2.1 general circulation model show that topography and SST patterns play an important role in early summer rainfall changes in the EASM region

Negative Selection by Clustering for Contrastive Learning in Human Activity Recognition

Contrastive learning has been applied to Human Activity Recognition (HAR) based on sensor data owing to its ability to achieve performance comparable to supervised learning with a large amount of unlabeled data and a small amount of labeled data. The pre-training task for contrastive learning is generally instance discrimination, which specifies that each instance belongs to a single class, but this will consider the same class of samples as negative examples. Such a pre-training task is not conducive to human activity recognition tasks, which are mainly classification tasks. To address this problem, we follow SimCLR to propose a new contrastive learning framework that negative selection by clustering in HAR, which is called ClusterCLHAR. Compared with SimCLR, it redefines the negative pairs in the contrastive loss function by using unsupervised clustering methods to generate soft labels that mask other samples of the same cluster to avoid regarding them as negative samples. We evaluate ClusterCLHAR on three benchmark datasets, USC-HAD, MotionSense, and UCI-HAR, using mean F1-score as the evaluation metric. The experiment results show that it outperforms all the state-of-the-art methods applied to HAR in self-supervised learning and semi-supervised learning.Comment: 11 pages, 5 figure

Intermodel spread of East Asian summer monsoon simulations in CMIP5

In this paper we diagnose the intermodel spread in the Coupled Model Intercomparison Project Phase 5 (CMIP5) East Asian summer monsoon (EASM) simulations in the context of the moist static energy and moisture budgets. We find that the spatial distribution of the EASM precipitation simulated by different models is highly correlated with the meridional stationary eddy velocity, defined as the deviation from the long-term zonal mean. The correlation becomes more robust when energy fluxes into the atmospheric column are considered, consistent with recent observational analyses. The spread in the area-averaged rainfall amount can be partially explained by the spread in the simulated globally averaged precipitation, with the rest primarily due to the lower level meridional wind convergence. Clear relationships between precipitation and zonal and meridional eddy velocities are observed

Photothermal catalysis: From fundamentals to practical applications

Photothermal catalysis is an innovative approach that integrates photochemical and thermocatalytic processes to enable an efficient use of full-spectrum sunlight in catalyzing various chemical reactions for energy conversion and environmental governance. This approach has demonstrated competitive performance and energy efficiency compared to conventional techniques, making it suitable for large-scale applications. In this review, we will comprehensively examine the fundamentals and classification of photothermal catalysis and discuss detailed design principles of various types of photothermal catalysts, focusing on enhancing solar light absorption, improving internal electric field for more energetic hot carriers (EHC) and localized thermal energy (LTE), interfacial engineering for robust and directed EHC transferring, and regulating EHC and LTE for continuous 24/7 operation. We will also report photothermal catalysis in a diverse range of chemical reactions. Moreover, we will introduce the latest technologies for synthesizing robust photothermal catalysts and advanced solar concentrators for pilot testing in the production of solar fuels at scale. Finally, the future opportunities and challenges of the promising but fledging field will be discussed, which is expected to transform conventional chemical industries into a clean and sustainable manner