Pressure drag for shallow cumulus clouds: from thermals to the cloud ensemble

This study takes the first step to bridge the gap between the pressure drag of a shallow cloud ensemble and that of an individual cloud composed of rising thermals. It is found that the pressure drag for a cloud ensemble is primarily controlled by the dynamical component. The dominance of dynamical pressure drag and its increased magnitude with height are independent of cloud lifetime and are common features of individual clouds except that the total drag of a single cloud over life cycle presents vertical oscillations. These oscillations are associated with successive rising thermals but are further complicated by the evaporation-driven downdrafts outside the cloud. The horizontal vorticity associated with the vortical structure is amplified as the thermals rise to higher altitudes due to continuous baroclinic vorticity generation. This leads to the increased magnitude of local minima of dynamical pressure perturbation with height and consequently to increased dynamical pressure drag

Harms and benefits associated with psychoactive drugs: Findings of an international survey of active drug users

There have been several recent efforts in the UK and the Netherlands to describe the harms of psychoactive substances based on ratings of either experts or drug users. This study aimed to assess the perceived benefits as well as harms of widely used recreational drugs, both licit and illicit, in an international sample of drug users. The survey was hosted at https://www.internationaldrugsurvey.org/ and was available in three languages. Residents reported their experience of 15 commonly used drugs or drug classes; regular users then rated their harms and benefits. In all, 5791 individuals from over 40 countries completed the survey, although the majority were from English speaking countries. Rankings of drugs differed across 10 categories of perceived benefits. Skunk and herbal cannabis were ranked consistently beneficial, whilst alcohol and tobacco fell below many classified drugs. There was no correlation at all between users’ harm ranking of drugs and their classification in schedules of the USA or ABC system in the UK. Prescription analgesics, alcohol and tobacco were ranked within the top 10 most harmful drugs. These findings suggest that neither the UK nor US classification systems act to inform users of the harms of psychoactive substances. It is hoped the results might inform health professionals and educators of what are considered to be both the harms and benefits of psychoactive substances to young people

Magnitude, scale, and dynamics of the 2020 Mei Yu rains and floods over China

Large parts of East and South Asia were affected by heavy precipitation and flooding during early summer 2020. This study provides both a statistical and dynamical characterization of rains and floods affecting the Yangtze River Basin (YRB). By aggregating daily and monthly precipitation over river basins across Asia, it is shown that the YRB is one of the areas that was particularly affected. June and July 2020 rainfall was higher than in the previous 20 years, and the YRB experienced anomalously high rainfall across most of its sub-basins. YRB discharge also attained levels not seen since 1998/9. An automated method detecting the daily position of the East Asian Summer Monsoon Front (EASMF) is applied to show that the anomalously high YRB precipitation was associated with a halted northward progression of the EASMF and prolonged Mei Yu conditions over the YRB lasting more than one month. Two 5-day heavy-precipitation episodes (12-16 June and 4-8 July 2020) are selected from this period for dynamical characterisation, including Lagrangian trajectory analysis. Particular attention is devoted to the dynamics of the airstreams converging at the EASMF. Both episodes display heavy precipitation and convergence of monsoonal and subtropical air masses. However, clear differences are identified in the upper-level flow pattern, substantially affecting the balance of airmass advection towards the EASMF. This study contextualises heavy precipitation in Asia in summer 2020 and showcases a number of analysis tools developed by the authors for the study of such events

Sensitivity of simulated mesoscale convective systems over East Asia to the treatment of convection in a high-resolution GCM

Mesoscale convective systems (MCSs) downstream of the Tibetan Plateau (TP) exhibit unique precipitation features. These MCSs can have damaging impacts and there is a critical need for improving the representation of MCSs in numerical models. However, most global climate models are typically run at resolutions that are too coarse to reasonably resolve MCSs, and it is still unclear how well higher-resolution global models can reproduce the precipitation characteristics of MCSs. In this study, the sensitivity of MCSs simulated by a global high resolution (~ 10 km), atmosphere-only climate model to different treatments of convection (with and without parametrized convection, and a hybrid representation of convection) have been investigated. The results show that explicit convection (i.e., non-parameterized) can better reproduce the observed pattern of MCS precipitation over the East Asian Summer Monsoon region. In general, explicit convection better simulates the diurnal variability of MCSs over the eastern China, and is able to represent the distinctive diurnal variations of MCS precipitation over complex terrain particularly well, such as the eastern TP and the complex terrain of central-northern China. It is shown that explicit convection is better at simulating the timing of initiation and subsequent propagating features of the MCS, resulting in better diurnal variations and further a better spatial pattern of summer mean MCS precipitation. All three experiments simulate MCS rainfall areas which are notably smaller than those in observations, but with much stronger rainfall intensities, implying that these biases in simulated MCS morphological characteristics are not sensitive to the different treatment of convection

Multiscale digital Arabidopsis predicts individual organ and whole-organism growth

Understanding how dynamic molecular networks affect wholeorganism physiology, analogous to mapping genotype to phenotype, remains a key challenge in biology. Quantitative models that represent processes at multiple scales and link understanding from several research domains can help to tackle this problem. Such integrated models are more common in crop science and ecophysiology than in the research communities that elucidate molecular networks. Several laboratories have modeled particular aspects of growth in Arabidopsis thaliana, but it was unclear whether these existing models could productively be combined. We test this approach by constructing a multiscale model of Arabidopsis rosette growth. Four existing models were integrated with minimal parameter modification (leaf water content and one flowering parameter used measured data). The resulting framework model links genetic regulation and biochemical dynamics to events at the organ and whole-plant levels, helping to understand the combined effects of endogenous and environmental regulators on Arabidopsis growth. The framework model was validated and tested with metabolic, physiological, and biomass data from two laboratories, for five photoperiods, three accessions, and a transgenic line, highlighting the plasticity of plant growth strategies. The model was extended to include stochastic development. Model simulations gave insight into the developmental control of leaf production and provided a quantitative explanation for the pleiotropic developmental phenotype caused by overexpression of miR156, which was an open question. Modular, multiscale models, assembling knowledge from systems biology to ecophysiology, will help to understand and to engineer plant behavior from the genome to the field. (Résumé d'auteur

Intensification of mesoscale convective systems in the East Asian rainband over the past two decades

As one of the major producers of extreme precipitation, mesoscale convective systems (MCSs) have received much attention. Recently, MCSs over several hotpots, including the Sahel and US Great Plains, have been found to intensify under global warming. However, relevant studies on the East Asian rainband, another MCS hotpot, are scarce. Here, by using a novel rain-cell tracking algorithm on a high spatiotemporal resolution satellite precipitation product, we show that both the frequency and intensity of MCSs over the East Asian rainband have increased by 21.8% and 9.8% respectively over the past two decades (2000–2021). The more frequent and intense MCSs contribute nearly three quarters to the total precipitation increase. The changes in MCSs are caused by more frequent favorable large-scale water vapor-rich environments that are likely to increase under global warming. The increased frequency and intensity of MCSs have profound impacts on the hydroclimate of East Asia, including producing extreme events such as severe flooding

Designs for representing shear-induced cloud field organization in a convection parametrization scheme

The mesoscale organization of tropical convection is an important atmospheric phenomenon, which often goes untreated in Convection Parametrization Schemes (CPSs). A methodology for designing changes to CPSs so that they can represent some aspects of shear-induced organization is developed. A novel clustering procedure is used to produce a set of 10 Representative Wind Profiles (RWPs) based on wind profiles from a climate model. The RWPs are found to be associated with the organization of convection. Idealized radiative-convective equilibrium experiments with a cloud-resolving model are performed. The wind profiles in the experiments are varied to investigate the effect of shear and surface wind on the cloud field and mean atmospheric state. Convection is stimulated by prescribed cooling in forcing experiments, and by relaxation back to a reference state in relaxation experiments. From the forcing experiments we find that organization and cloud lifetimes are dependent on shear, and that thermodynamic properties of the atmosphere show some dependence on surface wind. A robust relationship between the low-level shear and the organization of the cloud field is found. Relationships between the organization and both the mean lifetime of clouds, and the mean mass flux per cloud are also found. The Convective Available Potential Energy (CAPE) is found to be related to the surface wind. Relaxation experiments provide information about the convective response as a function of the imposed wind profile. Contrary to our expectations, the organized convective response is found to produce upper-level cooling and lower-level heating. We determine that this is due to the CAPE in the reference profiles, and the need to maintain a fixed thermodynamic profile. The results are used to design changes to existing CPSs to make them “shear-aware”. Methods for assessing the “shear-aware” schemes, and their representation of organization, are also discussed

Data supporting 'Pressure drag for shallow cumulus clouds: from thermals to cloud ensemble'

This dataset is used to understand the pressure drag of shallow cumulus clouds, the relationship between the pressure drag of individual clouds and the cloud ensemble. We performed large eddy simulations of shallow cumulus clouds based on the Barbados Oceanographic and Meteorological Experiment (BOMEX) using the Met Office-NERC (National Environment Research Council) Cloud model (MONC). The grid spacing is 25 m in all directions and the domain size is (15X15X3) km^3. As the whole simulation has a huge dataset, we present a subset of the results that can be used to reproduce the figures in 'Pressure drag for shallow cumulus clouds: from thermals to cloud ensemble' (submitted to Geophysical Research Letters; 2020). Access to the all simulation data can be provided on request. The full dataset will be deposited in the CEDA Archive in due course. The dataset contains four sub-directories with generated data and another sub-directory with scripts for plotting the figures in the article. The generated data include: [1]. The conditionally averaged budget terms in vertical velocity equation for different parts of cloud ensemble; [2]. The conditionally averaged budget terms in vertical velocity equation for all tracked clouds; [3]. The conditionally averaged budget terms in vertical velocity equation for tracked clouds with different lifetime; [4]. The conditionally averaged budget terms in vertical velocity equation for each individually tracked cloud over its lifetime; [5]. The vertical cross section data of cloud structure; [6]. The positions of tracked clouds; [7]. The composited structure of clouds at 600m, 1000m and 1800m

Intraseasonal oscillations of the Silk Road pattern lead to predictability in East Asian precipitation patterns and the Mei Yu front

The Silk Road pattern (SRP) is analysed on intraseasonal timescales over summer using empirical orthogonal functions (EOFs) of the meridional wind at 200 hPa. The first two principal components explain almost equal amounts of variance, hence both are required to represent the intraseasonal SRP. The associated spatial loadings are 90◦ out of phase with each other, providing evidence that propagating oscillations are a natural mode of variability of the intraseasonal SRP. This is supported by Hovmöller diagrams of the meridional wind at 200 hPa and by phase diagrams of the first two EOFs, which both show a predominantly eastward-propagating oscillation. The oscillations are identified as plausibly being Rossby waves by means of waveguide theory. The subtropical westerly jet and East Asian rainfall patterns are found to be dependent on the phase of the oscillation: wet anomalies occur to the east of troughs in the jet, which are also regions where local jet entrances cause upper-level divergence via an ageostrophic circulation. Dry anomalies occur to the west of troughs, which are regions of upper-level convergence. The time-delayed location of the summer Mei Yu front relative to its climatology is dependent on the phase of the oscillation: when there is an upper-level trough located over the Korean Peninsula, the Mei Yu front is likely to be located further north than normal 3–8 days later, before returning to its climatological position. This suggests that the phase of the intraseasonal SRP acts as a potential source of predictability of the location of the Mei Yu front, which might allow for better prediction of the associated rains