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Heat extremes including heatwaves have an adverse impact not only on ecosystems but also on human health. The impact can be seriously exacerbated when both spatial extension and compound factors (such as humidity) are included. However, a unified frame combining compound humidity-heat extremes with their regional extension has received little scientific attention. This study solves this problem by taking the evolution of daily mean 2 m air temperature (Tmean) and relative humidity (RH) over a large domain as two dynamical systems (DSs), then the instantaneous coupling index from the DS method combined with clustering analysis can sort out the regional compound humidity-heat extremes with distinct spatial organized structures. Among them, the compound humidity-heat extremes with dipole Tmean and RH patterns may be missed by the methods based on regional averaging or undiscerned by DS method. Moreover, the mechanisms behind these regional compound humidity-heat extremes with dipole pattern are distinctive on both dynamics and thermodynamics, with a dipole structure found in the atmospheric low-level circulation. These novel findings can contribute considerably to the in-depth understanding on the compound humidity-heat extremes and their mechanisms.

It is frequently observed in field experiments that the eddy-covariance heat fluxes are systematically underestimated compared to the available energy, a phenomenon known as the surface energy balance (SEB) closure problem. A large-eddy simulation (LES) study is presented that investigates the behavior of turbulent organized structures (TOS) and their impact on the SEB closure problem. LES experiments are conducted for the daytime atmospheric boundary layer heated over a flat surface with atmospheric stability parameters -zi/L ranging from 8 to 130. Local imbalance is defined as the deviation of the ‘observed’ heat flux at a grid point from the regionally ‘representative’ heat flux; systematic imbalance is defined as the horizontally averaged local imbalance. A thorough analysis of the correlation between local imbalance and various local variables is conducted. Local imbalance exhibited the most significant correlation with the variance of potential temperature, implying its potential usefulness in parameterizing local imbalance. In characterizing the vertical variation of systematic imbalance, the spatial variances of mean vertical velocity and potential temperature play key roles. Results reveal that TOS induced a correlation between the mean vertical velocity and potential temperature in a horizontal space, resulting in systematic imbalance. The local imbalance is further contributed by the inhomogeneous distribution of the observed heat flux. Our results advance the understanding of the SEB closure problem and pave a possible way for the development of parameterization schemes.

The effects of obstacle-height variability on spatial characteristics of turbulent organized structures were investigated with the use of a large-eddy simulation technique for airflows over roughness obstacles. Two-types simulation cases were considered: one is uniform-height case in which uniform-height obstacles are aligned in streamwise direction, the other is height-variability case with staggered higher-height obstacles. Streaky structures were observed above the roughness sublayer (RSL) regardless of obstacle-height variability. When obstacles are uniform, flow fields within the RSL contain low- and high-speed regions along the streamwise streets. When obstacle heights vary, airflow within the RSL collides with the front-facing surfaces of taller obstacles. The statistical features of low- and high-speed structures were examined using the spatial correlations of flow fields centering on strong ejection and sweep, respectively. The ejection– and sweep–center spatial correlations extend forward and backward in the streamwise direction, respectively. Length scales were obtained from the ejection–center and sweep–center spatial correlations. The streamwise lengths vary significantly below the canopy height when obstacles are uniform. In contrast, the streamwise length scales remain nearly constant when obstacle heights vary. The horizontal aspect ratios below the canopy heights indicate that turbulent organized structures over obstacles with variable heights are more isotropic than those over uniform obstacles. The inclination angles of the organized structures were also deduced using the spatial correlations. The angles of sweep–center structures are steeper than those of the ejection–center structures. The angles of the ejection–center structures at the RSL heights become larger with obstacle-height variability.

Abstract—Data of a numerical simulation of a stably stratified turbulent Couette flow are analyzed for various values of the Richardson number. Two different methods are used: direct numerical simulation (DNS) and large-eddy simulation (LES). It is shown that the flow contains large organized structures, along with chaotic turbulence, regardless of the simulation method. These structures appear as inclined layers in the temperature field with weakly stable stratification, separated by very thin layers with large temperature gradients. The existence of such layered structures in nature is indirectly confirmed by the analysis of data from field measurements on the meteorological mast, where temperature gradient histograms are found to be far from the normal distribution and similar to temperature gradient probability distributions obtained in numerical model data. The simulations indicate an increase in the turbulent Prandtl number with an increase in the gradient Richardson number. It is likely that the identified structures serve as efficient barriers for vertical turbulent heat flux without blocking the momentum transfer. We propose a hypothesis that it is these structures which serve as a physical mechanism for maintaining turbulence under supercritically stable stratification.

Cassava (Manihot esculenta) feeds c. 800 million people world-wide. Although this crop displays high productivity under drought and poor soil conditions, it is susceptible to disease, postharvest deterioration and the roots contain low nutritional content. Here, we provide molecular identities for 11 cassava tissue/organ types through RNA-sequencing and develop an open access, web-based interface for further interrogation of the data. Through this dataset, we consider the physiology of cassava. Specifically, we focus on identification of the transcriptional signatures that define the massive, underground storage roots used as a food source and the favored target tissue for transgene integration and genome editing, friable embryogenic callus (FEC). Further, we identify promoters able to drive strong expression in multiple tissue/organs. The information gained from this study is of value for both conventional and biotechnological improvement programs.

We examine the similarity of turbulent organized structures over smooth and very rough wall flows. Turbulent flow fields in horizontal cross-sections were measured using particle image velocimetry, and the characteristics of turbulent organized structures over four types of surfaces were investigated. Measurements were conducted at several measurement heights across the internal boundary layer. The length and width of turbulence structures were quantified using a two-point correlation method. We selected two thresholds of two-point correlation coefficients to consider both large-scale and small-scale structures; the validity of these choices was examined through the analyses using proper orthogonal decomposition. For large-scale structures, the length and aspect ratios (streamwise length/spanwise width) of structures were highly correlated with the velocity gradient for each measurement height and boundary-layer thickness. This relationship was also examined in the results of previous studies, and the scaling of the aspect ratio with the non-dimensional velocity gradient again showed the importance of the velocity gradient, with slight differences found between smooth and rough surfaces. In contrast, the small-scale structures exhibited weak dependency on the velocity gradient and boundary-layer thickness. Instantaneous snapshots of turbulent organized structures at the same shear level also displayed differences in small-scale structures, but the structures of the organized motions resembled each other, as in the results of the two-point correlation method.

Instantaneous flow structures “within” a cubical canopy are investigated via large-eddy simulation. The main topics of interest are, (1) large-scale coherent flow structures within a cubical canopy, (2) how the structures are coupled with the turbulent organized structures (TOS) above them, and (3) the classification and quantification of representative instantaneous flow patterns within a street canyon in relation to the coherent structures. We use a large numerical domain (2,560 m × 2,560 m × 1,710 m) with a fine spatial resolution (2.5 m), thereby simulating a complete daytime atmospheric boundary layer (ABL), as well as explicitly resolving a regular array of cubes (40 m in height) at the surface. A typical urban ABL is numerically modelled. In this situation, the constant heat supply from roof and floor surfaces sustains a convective mixed layer as a whole, but strong wind shear near the canopy top maintains the surface layer nearly neutral. The results reveal large coherent structures in both the velocity and temperature fields “within” the canopy layer. These structures are much larger than the cubes, and their shapes and locations are shown to be closely related to the TOS above them. We classify the instantaneous flow patterns in a cavity, specifically focusing on two characteristic flow patterns: flushing and cavity-eddy events. Flushing indicates a strong upward motion, while a cavity eddy is characterized by a dominant vortical motion within a single cavity. Flushing is clearly correlated with the TOS above, occurring frequently beneath low-momentum streaks. The instantaneous momentum and heat transport within and above a cavity due to flushing and cavity-eddy events are also quantified.

Collective constructions are marvels of complexity, composed of networks of tunnels and chambers. However, it is difficult to study subterranean nests without using invasive techniques because the nests are built within pieces of wood and/or in the soil. Using computerized tomography scans and medical imaging software (OsiriX), we were able to observe nest creation, constructions, and architecture of two subterranean termite species. We monitor the nests’ growth in three dimensions built by two Reticulitermes species: R. grassei , a species native to Europe, and R. flavipes , an invasive species introduced from North America, over a several month period. Doing so, we wanted to know whether the construction of the nest could participate to the invasive success of R. flavipes . Although the two species displayed some similarities (i.e., nest creation, chamber size, and levels of wood consumption), only R. flavipes built interior structures. Some of these structures changed over time and thus might play a role in the trade-off between wood consumption, colony protection, and environmental homeostasis.

The influence of the semialiphatic backbone on molecular ordering and proton conductivity was investigated in comparison to the rigid aromatic backbone in highly proton-conductive organized polyimide thin films. We newly synthesized two alkyl-sulfonated semialiphatic polyimides (ASSPIs) with different molecular weights and investigated their molecular organized structure, proton conductivity, water uptake, and the dissociation state of protons from sulfonic acid groups in thin films by in situ measurements for grazing incidence small-angle X-ray scattering (GISAXS), quartz crystal microbalance (QCM), fourier transform infrared (FT-IR) spectra, and impedance spectra. Declining planarity in the semialiphatic backbone reduced the aggregative character and molecular ordering in the lyotropic liquid-crystalline (LC) structure. However, the higher-molecular-weight ASSPI exhibited the oriented lamellar structure despite the lower planarity of the main chain. The proton conductivity of the oriented lamellar thin film had more than half an order of magnitude higher value of 1.5 × 10-1 S cm-1 than did the nonoriented lamellar thin film (3.0 × 10-2 S cm-1) at 25 °C and 95% RH. These results indicate that in sulfonated polyimide thin films, the lamellar orientation greatly contributes to the high proton conductivity in ASSPI thin films.

Turbulent organized structures (TOS) above building arrays were investigated using a large-eddy simulation (LES) model for a city (LES-CITY). Square and staggered building arrays produced contrasting behaviour in terms of turbulence that roughly corresponded to the conventional classification of 'D-type' and 'K-type' roughness, respectively: (1) The drag coefficients (referred to the building height) for staggered arrays were sensitive to building area density, but those for square arrays were not. (2) The relative contributions of ejections to sweeps (S sub(2)/S sub(4)) at the building height for square arrays were sensitive to building area density and nearly equalled or exceeded 1.0 (ejection dominant), but those for staggered arrays were insensitive to building area density and were mostly below 1.0 (sweep dominant). (3) Streaky patterns of longitudinal low speed regions (i.e., low speed streaks) existed in all flows regardless of array type. Height variations of the buildings in the square array drastically increased the drag coefficient and modified the turbulent flow structures. The mechanism of D-type and K-type urban-like roughness flows and the difference from vegetation flows are discussed. Although urban-like roughness flows exhibited mixed properties of mixing layers and flat-wall boundary layers as far as S sub(2)/S sub(4) was concerned, the turbulent organized structures of urban-like roughness flows resembled those of flat-wall boundary layers.