Diurnal Timing Research Articles

Diurnal timing of physical activity and risk of colorectal cancer in the UK Biobank

BackgroundPhysical activity reduces colorectal cancer risk, yet the diurnal timing of physical activity in colorectal cancer etiology remains unclear.MethodsThis study used 24-h accelerometry time series from UK Biobank participants aged 42 to 79 years to derive circadian physical activity patterns using functional principal component analysis. Multivariable Cox proportional hazard models were used to examine associations with colorectal cancer risk.ResultsAmong 86,252 participants (56% women), 529 colorectal cancer cases occurred during a median 5.3-year follow-up. We identified four physical activity patterns that explained almost 100% of the data variability during the day. A pattern of continuous day-long activity was inversely associated with colorectal cancer risk (hazard ratio (HR) = 0.94, 95% confidence interval (CI) = 0.89–0.99). A second pattern of late-day activity was suggestively inversely related to risk (HR = 0.93, 95% CI = 0.85–1.02). A third pattern of early- plus late-day activity was associated with decreased risk (HR = 0.89, 95% CI = 0.80–0.99). A fourth pattern of mid-day plus night-time activity showed no relation (HR = 1.02, 95% CI = 0.88–1.19). Our results were consistent across various sensitivity analyses, including the restriction to never smokers, the exclusion of the first 2 years of follow-up, and the adjustment for shift work.ConclusionsA pattern of early- plus late-day activity is related to reduced colorectal cancer risk, beyond the benefits of overall activity. Further research is needed to confirm the role of activity timing in colorectal cancer prevention.

How Well Does the DOE Global Storm Resolving Model Simulate Clouds and Precipitation Over the Amazon?

AbstractThis study assesses a 40‐day 3.25‐km global simulation of the Simple Cloud‐Resolving E3SM Model (SCREAMv0) using high‐resolution ground‐based observations from the Atmospheric Radiation Measurement (ARM) Green Ocean Amazon (GoAmazon) field campaign. SCREAMv0 reasonably captures the diurnal timing of boundary layer clouds yet underestimates the boundary layer cloud fraction and mid‐level congestus. SCREAMv0 well replicates the precipitation diurnal cycle, however it exhibits biases in the precipitation cluster size distribution compared to scanning radar observations. Specifically, SCREAMv0 overproduces clusters smaller than 128 km, and does not form enough large clusters. Such biases suggest an inhibition of convective upscale growth, preventing isolated deep convective clusters from evolving into larger mesoscale systems. This model bias is partially attributed to the misrepresentation of land‐atmosphere coupling. This study highlights the potential use of high‐resolution ground‐based observations to diagnose convective processes in global storm resolving model simulations, identify key model deficiencies, and guide future process‐oriented model sensitivity tests and detailed analyses.

Bedtime negative affect, sleep quality and subjective health in rural China

BackgroundThe overall level of negative affect (NeA) has been linked to impaired health. However, whether the diurnal timing of NeA matters and whether the NeA-health relationship is mediated by sleep quality remain unclear.MethodsUsing a longitudinal dataset (2006, 2009 and 2014 waves) consisting of 1959 participants, we examined the within-person impact of both bedtime NeA and non-bedtime NeA measured by Day Reconstruction Method (DRM) on subjective health measured by Visual Analogue Scale (VAS), and the mediating effect of sleep quality on the NeA-health relationships by fixed effect models.ResultsBedtime NeA predicted poorer health, while non-bedtime NeA was unrelated to health. The deleterious impact of bedtime NeA reduced and became non-significant after sleep quality was controlled for. Bedtime NeA also significantly predicted impaired sleep quality.ConclusionsBedtime NeA is a stronger predictor of poorer health than non-bedtime NeA, and the deleterious influence of bedtime NeA on health seems to operate through poor sleep quality. Therefore, interventions to reduce bedtime NeA could potentially improve subsequent sleep quality, thereby protecting people to some extent from impaired health status.

Evaluating Mesoscale Convective Systems Over the US in Conventional and Multiscale Modeling Framework Configurations of E3SMv1

AbstractOrganized mesoscale convective systems (MCSs) contribute a significant amount of precipitation in the Central and Eastern US during spring and summer, which impacts the availability of freshwater and flooding events. However, current global Earth system models cannot capture MCSs well and misrepresent the statistics of precipitation in the region. In this study, we investigate the representation of MCSs in three configurations of the Energy Exascale Earth System Model (E3SMv1) by tracking individual storms based on outgoing longwave radiation using a new application of TempestExtremes. Our results indicate that conventional parameterizations of convection, implemented in both low (LR; ∼150 km) and high (HR; ∼25 km) resolution configurations, fail to capture almost all MCS‐like events, in‐part because they underestimate high‐level cloud ice associated with deep convection. On the other hand, the multiscale modeling framework (MMF; cloud‐resolving models embedded in each grid‐column of ∼150 km resolution E3SMv1) configuration represents MCSs and their annual cycle better. Nevertheless, relative to observations, the E3SMv1‐MMF spatial distribution of MCSs and associated precipitation is shifted eastward, and the diurnal timing is lagged. A comparison between the large‐scale environment in E3SMv1‐MMF and ERA5 reanalysis suggests that the biases during the summer in E3SMv1‐MMF are associated with biases in low‐level humidity and meridional moisture transport within the low‐level jet. The fact that conventional parameterizations of convection, even with high‐resolution, cannot capture MCSs over the US suggests that methods with explicit representation of kilometer‐scale convective organization, such as the MMF, may be necessary for improving the simulation of these convective systems.

Association between circadian physical activity patterns and mortality in the UK Biobank

BackgroundThe benefit of physical activity (PA) for increasing longevity is well-established, however, the impact of diurnal timing of PA on mortality remains poorly understood. We aimed to derive circadian PA patterns and investigate their associations with all-cause mortality.MethodsWe used 24 h PA time series from 96,351 UK Biobank participants aged between 42 and 79 years at accelerometry in 2013–2015. Functional principal component analysis (fPCA) was applied to obtain circadian PA patterns. Using multivariable Cox proportional hazard models, we related the loading scores of these fPCs to estimate risk of mortality.ResultsDuring 6.9 years of follow-up, 2,850 deaths occurred. Four distinct fPCs accounted for 96% of the variation of the accelerometry data. Using a loading score of zero (i.e., average overall PA during the day) as the reference, a fPC1 score of + 2 (high overall PA) was inversely associated with mortality (Hazard ratio, HR = 0.91; 95% CI: 0.84–0.99), whereas a score of -2 (low overall PA) was associated with higher mortality (1.69; 95% CI: 1.57–1.81; p for non-linearity < 0.001). Significant inverse linear associations with mortality were observed for engaging in midday PA instead of early and late PA (fPC3) (HR for a 1-unit increase 0.88; 95% CI: 0.83–0.93). In contrast, midday and nocturnal PA instead of early and evening PA (fPC4) were positively associated with mortality (HR for a 1-unit increase 1.16; 95% CI: 1.08–1.25).ConclusionOur results suggest that it is less important during which daytime hours one is active but rather, to engage in some level of elevated PA for longevity.

Loss of control eating exhibits an evening diurnal shift among females with bulimia nervosa and binge-eating disorder.

Loss of control (LOC) is a hallmark feature of binge eating that is associated with significant distress and impairment. Despite the central role diurnal rhythms may play in the development and maintenance of LOC eating, diurnal patterns of LOC remain understudied and poorly characterised. We assessed the diurnal timing of LOC in a sample of females with bulimia nervosa and binge-eating disorder who participated in a study assessing the impact of bright light exposure on binge eating, hypothesising that higher ratings of LOC would be more likely to occur later in the day. Participants (N=34) completed a 22-day protocol during which they provided LOC ratings six times daily. Kernel density estimates describing LOC ratings across times of day were compared using permutation tests of equality. Results demonstrated an evening shift in LOC, wherein higher LOC was more likely to occur later in the day and lower LOC was more likely to occur earlier in the day. This study is the first to clearly depict the phenomenon that the likelihood of experiencing higher LOC increases throughout the day, pointing to the potential role diurnal rhythms, such as disrupted appetitive rhythms or mood variations, may play in maintaining binge eating.

Inbound arrivals: using weather surveillance radar to quantify the diurnal timing of spring trans‐Gulf bird migration

More than two billion birds migrate through the Gulf of Mexico each spring en route to breeding grounds in the USA and Canada. This region has a long history of complex natural and anthropogenic environments as the northern Gulf coast provides the first possible stopover habitats for migrants making nonstop trans‐Gulf crossings during spring migration. However, intense anthropogenic activity in the region, which is expanding rapidly at present, makes migrants vulnerable to a multitude of obstacles and increasingly fragments and alters these habitats. Understanding the timing of migrants' overwater arrivals has biological value for expanding our understanding of migration ecology relative to decision‐making for nonstop flights, and is imperative for advancing conservation of this critical region through the identification of key times in which to direct conservation actions (e.g. temporary halting of wind turbines, reduction of light pollution). We explored 10 years of weather surveillance radar data from five sites along the northern Gulf of Mexico coast to quantify the daily timing and intensity of arriving trans‐Gulf migrants. On a daily scale, we found that migrant intensity peaked an average of nine hours after local sunrise, occurring earliest at easternmost sites. On a seasonal level, the greatest number of arrivals occurred between late April and early May, with peak intensity occurring latest at westernmost sites. Overall intensity of migration across all 10 years of data was greatest at the westernmost sites and decreased moving farther to the east. These findings emphasize the differential spatial and temporal patterns of use of the Gulf of Mexico region by migrating birds, information that is essential for improving our understanding of the ecology of trans‐Gulf migration and for supporting data‐driven approaches to conservation actions for the migratory birds passing through this critical region.

Characterizing naturalistic meal timing, energy intake, and macronutrient intake among individuals with loss of control eating

Binge eating demonstrates an evening diurnal shift among individuals with eating disorders. Disruptions to diurnal appetitive rhythms may be somewhat chronic and set the stage for additional disruptions to prompt binge eating. Despite known diurnal shifts in binge eating and related constructs (e.g., mood) and detailed characterizations of binge-eating episodes, no findings to date describe the naturalistic diurnal timing and composition of energy and nutrient intake on days with and without loss of control eating. We aimed to characterize eating behaviors (i.e., meal timing, energy intake, and macronutrient composition) across seven days in individuals with binge-spectrum eating disorders, assessing differences between eating episodes and days with and without loss of control eating. Undergraduate students (N = 51; 76.5% female) who endorsed past 28-day loss of control eating completed a 7-day naturalistic ecological momentary assessment protocol. Participants completed daily food diaries and reported instances of loss of control eating across the 7-day period. Results indicated that episodes of loss of control were more likely to occur later in the day, but overall meal timing did not differ across days with and without loss of control. Similarly, greater caloric consumption was more likely for episodes with loss of control, but overall caloric consumption did not differ between days with and without loss of control. Analysis of nutritional content demonstrated differences between both episodes and days with and without loss of control for carbohydrates and total fats, but not for protein. Findings provide support for the hypothesized role disruptions in diurnal appetitive rhythms play in maintaining binge eating via consistent irregularities, underscoring the importance of examining treatment adjuncts that intervene on the regulation of meal timing to enhance eating disorder treatment outcomes.

Associations between diurnal timing of spinal cord injury and its etiology and co-morbidities.

Circadian rhythms play a role in time-of day differences in risk, presenting severity and outcomes of stroke. However, injury time of day effects on occurrence, presenting severity and acute hospital outcomes have not been yet reported in neurotrauma patients. Therefore, acute post-spinal cord injury hospitalization records of 759 patients from the prospective NACTN registry that contained information about the time of injury were analyzed. No major demographic differences were observed between groups with time of injury between 6:00-12:00, 12:00-18:00, 18:00-24:00 or 0:00-6:00. Two etiological factors including falls or sports/recreation-related accidents showed significant effects of time of injury with peaks in the 6:00-12:00 or 18:00-24:00 groups, respectively. History of diabetes or drug abuse was also significantly related to injury timing peaking in 6:00-12:00 or 18:00-24:00 groups, respectively. ASIA score-determined presenting severity during the first week post injury was not significantly affected by timing of injury. However, pairwise comparisons revealed worse motor but not sensory ASIA scores after injuries at 24:00-6:00 than any other group. These data suggest diurnal modulation of spinal cord injury risk due to specific mechanisms such as falls or sports-related accidents. Moreover, some co-morbidities may interact with those injury mechanisms as exemplified by the established risk elevation of falls in diabetics. Finally, while diurnal timing of the injury may modulate presenting severity, more patient records are needed to verify those effects.

Grassland productivity responds unexpectedly to dynamic light and soil water environments induced by photovoltaic arrays

AbstractAgrivoltaic (AV) systems are designed to coproduce photovoltaic (PV) energy on lands simultaneously supporting agriculture (food/forage production). PV infrastructure in agroecosystems alters resources critical for plant growth, and water‐limited agroecosystems such as grasslands are likely to be particularly sensitive to the unique spatial and temporal patterns of incident sunlight and soil water inherent within AV systems. However, the impact of resource alteration on forage production, the primary ecosystem service from managed grasslands, is poorly resolved. Here, we evaluated seasonal patterns of soil moisture (SM) and diurnal variation in incident sunlight (photosynthetic photon flux density [PPFD]) in a single‐axis‐tracking AV system established in a formerly managed semiarid C3 grassland in Colorado. Our goals were to (1) quantify dynamic patterns of PPFD and SM within a 1.2 MW PV array in a perennial grassland, and (2) determine how aboveground net primary production (ANPP) and photosynthetic parameters responded to the resource patterns created by the PV array. We hypothesized that spatial variability in ANPP would be strongly related to SM patterns, typical of most grasslands. We measured significant reductions in ANPP directly beneath PV panels, where SM and PPFD were both low. However, in locations with significantly increased SM from the shedding and redistribution of precipitation by PV panels, ANPP was not increased. Instead, ANPP was greatest in locations where plants were shaded in the afternoon but received high levels of PPFD in the morning hours, when air temperatures and vapor pressure deficits were relatively low. Thus, contrary to expectations, we found relatively weak relationships between SM and ANPP despite significant spatial variability in both. Further, there was little evidence that light‐saturated photosynthesis (Asat) and quantum yield of CO2 assimilation (ϕCO2) differed for plants growing directly beneath (lowest PPFD) versus between (highest PPFD) PV panels. Overall, the AV system established in this semiarid managed grassland did not alter patterns of ANPP in ways predictable from past studies of controls of ANPP in open grasslands. However, our results suggest that the diurnal timing of low versus high periods of PPFD incident on plants is an important determinant of productivity patterns in grasslands.

Impact of exercise timing on perceived appetite and food reward in early and late chronotypes: An exploratory study in a male Saudi sample

There is very limited evidence on the influence of diurnal exercise timing on appetite control, and none on food reward or how an individual's chronotype could moderate such effects. We examined the impact of acute exercise timing on perceived appetite and food reward in young Saudi adults with early or late chronotypes. Forty-five young adults (23 ± 4 years; BMI = 25.1 ± 4.0 kg/m2) completed the Morningness–Eveningness Questionnaire (MEQ) and were divided into early (score = 59 ± 5) or late (score = 41 ± 6) chronotypes. Participants attended the laboratory after ≥4 h fast on two occasions for an AM (8:00–10:00) and PM (17:00–19:00) 30-min moderate-intensity cycling bout in a randomized counterbalanced order. Appetite ratings and food reward (Arab Leeds Food Preference Questionnaire) were measured before and after exercise. An acute exercise-induced decrease in hunger was found, which appeared to be dependent upon diurnal timing and chronotype, with hunger being more suppressed after AM exercise in the early chronotypes and after PM exercise in the late chronotypes. There was greater wanting for low-fat sweet foods after AM exercise relative to PM exercise, whereas there was greater wanting for high-fat sweet food and sweet relative to savoury food after PM exercise compared to AM exercise. These preliminary findings suggest that diurnal timing of exercise impacts food preferences, and that chronotype may influence the appetite response to an exercise bout at different times of day.

High-resolution regional climate modeling of warm-season precipitation over the Tibetan Plateau: Impact of grid spacing and convective parameterization

The Tibetan Plateau (TP) features high elevation and complex terrain, which together shape the region's unique precipitation with high spatial heterogeneity and strong diurnal variations. Due to low spatial resolution, deficient convective parameterization (CP) and uncertainties in other physical assumptions, global climate models and traditional regional models tend to produce excessive precipitation with an earlier diurnal timing. In this work, two sets of numerical experiments with 4- and 10-km grid spacing, respectively, were performed using the Weather Research and Forecasting model to simulate the seasonal precipitation for an average warm season (April–September 2017) over the TP. Results showed that the 4-km experiment with microphysics only (i.e., without CP) reproduced the precipitation amount, frequency, intensity and diurnal cycle reasonably well on regional and local scales, as well as the nocturnal propagating convection at the lee side. The 10-km experiments with scale-aware CP schemes significantly overestimated the precipitation amount and frequency, underestimated the intensity, and failed to capture the diurnal propagation signature. The 10-km experiment with microphysics only had the poorest skill in representing the spatial distribution of precipitation. The scale-aware CP schemes on the 4-km grid caused a too-frequent occurrence of light precipitation even though their overall contribution to the total precipitation amount was rather small, and thus had little benefit to the model performance. A common deficiency in all experiments was excessive afternoon precipitation across the high elevation of the central Himalaya possibly due to the excessive surface insolation, but the satellite-based data may not accurately capture the afternoon precipitation. This research highlights the value of the 4-km model (the so-called convection-permitting model) and the limited benefit of the tested convective parameterizations over the TP.

Impact of urban aerosols on the cloud condensation activity using a clustering model

The indirect effect of aerosols on climate through aerosol-cloud-interactions is still highly uncertain and limits our ability to assess anthropogenic climate change. The foundation of this uncertainty is in the number of cloud condensation nuclei (CCN), which itself mainly stems from uncertainty in aerosol sources and how particles evolve to become effective CCN. We analyze particle number size distribution (PNSD) and CCN measurements from an urban site in a two-step method: (1) we use an unsupervised clustering model to classify the main aerosol categories and processes occurring in the urban atmosphere and (2) we explore the influence of the identified aerosol populations on the CCN properties. According to the physical properties of each cluster, its diurnal timing, and additional air quality parameters, the clusters are grouped into five main aerosol categories: nucleation, growth, traffic, aged traffic, and urban background. The results show that, despite aged traffic and urban background categories are those with lower total particle number concentrations (Ntot) these categories are the most efficient sources in terms of contribution to the overall CCN budget with activation fractions (AF) around 0.5 at 0.75 % supersaturation (SS). By contrast, road traffic is an important aerosol source with the highest frequency of occurrence (32 %) and relatively high Ntot, however, its impact in the CCN activity is very limited likely due to lower particle mean diameter and hydrophobic chemical composition. Similarly, nucleation and growth categories, associated to new particle formation (NPF) events, present large Ntot with large frequency of occurrence (22 % and 28 %, respectively) but the CCN concentration for these categories is about half of the CCN concentration observed for the aged traffic category, which is associated with their small size. Overall, our results show that direct influence of traffic emissions on the CCN budget is limited, however, when these particles undergo ageing processes, they have a significant influence on the CCN concentrations and may be an important CCN source. Thus, aged traffic particles could be transported to other environments where clouds form, triggering a plausible indirect effect of traffic emissions on aerosol-cloud interactions and consequently contributing to climate change.

The circadian clock sets a spatial-temporal window for recent thymic emigrants.

The diurnal timing system regulates multiple functions of lymphocytes in peripheral lymphoid organs. Whether T-cell development in the thymus and T-cell egress from the thymus are affected by the circadian clock is not clear. Herein, we used flow cytometry to examine the cell number and percentage of total thymocytes and various thymocyte subsets from Zeitgeber time (ZT) 1 to ZT21. CD4 and CD8 single-positive (SP) thymocytes, in particular, the mature CD4 SP4 thymocyte subset with emigration capability and P-phycoerythrin+ CD4 SP thymocytes in the perivascular space of the thymus, exhibited robust circadian oscillations. The diurnal expression of sphingosine-1-phosphate receptor-1 (S1PR1) and CCR2 on SP thymocytes and the rhythmic sphingosine-1-phosphate (S1P) and CCL2 gradient formed between peripheral blood and thymus likely promoted SP thymocyte egress in a circadian pattern. Switching the daylight cycle disturbed the rhythm of S1PR1 and CCR2 expression and subsequent thymocyte output. We further demonstrated that the core clock molecule BMAL1 had rhythmic binding of the promoters of Klf2, S1pr1 and Sphk2. Together, we elucidated the circadian dynamic characteristics of mature thymocyte egress, which coordinated with the diurnal changes in T-cell homing to the lymph nodes. The core rhythmic molecule BMAL1 likely promoted thymocyte emigration through transcriptional regulation of emigration-related molecules.

COP1 dynamics integrate conflicting seasonal light and thermal cues in the control of Arabidopsis elongation

As the summer approaches, plants experience enhanced light inputs and warm temperatures, two environmental cues with an opposite morphogenic impact. Key components of this response are PHYTOCHROME B (phyB), EARLY FLOWERING 3 (ELF3), and CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1). Here, we used single and double mutant/overexpression lines to fit a mathematical model incorporating known interactions of these regulators. The fitted model recapitulates thermal growth of all lines used and correctly predicts thermal behavior of others not used in the fit. While thermal COP1 function is accepted to be independent of diurnal timing, our model shows that it acts at temperature signaling only during daytime. Defective response of cop1-4 mutants is epistatic to phyB-9 and elf3-8, indicating that COP1 activity is essential to transduce phyB and ELF3 thermosensory function. Our thermal model provides a unique toolbox to identify best allelic combinations enhancing climate change resilience of crops adapted to different latitudes.

Exploring Hourly Updating Probabilistic Guidance in the 2021 Spring Forecasting Experiment with Objective and Subjective Verification

Abstract This study explored how forecasters can best use the two main forms of operational convection-allowing model guidance: the High-Resolution Ensemble Forecast (HREF) system and the hourly High-Resolution Rapid Refresh (HRRR). The former represents a wider range of possible outcomes, but the latter updates much more frequently and incorporates newer observations. HREF and time-lagged High-Resolution Rapid Refresh (HRRR-TL) probabilistic forecasts of reflectivity and updraft helicity, as well as two methods of combining HREF and HRRR into hourly updating blended guidance, were evaluated for the 2021 Spring Forecasting Experiment (SFE) period. In both objective skill and the subjective ratings of SFE participants, the 1200 UTC HREF proved difficult to outperform over this sample of events, even when incorporating HRRR initializations as late as 1800 UTC. It was usually better to use either of the experimental blending techniques than to simply discard the older HREF in favor of newer HRRR solutions. The greater model diversity and dispersion of solutions within the HREF is likely primarily responsible for this result. A possible bias in diurnal convection initiation timing and coverage in the newly upgraded HRRRv4 was also investigated, including on subdomains targeted to weakly forced diurnal initiation, and was found to have little or no systematic effect on HRRRv4’s operational utility.

A Systematic Review of Utilisation of Diurnal Timing Information in Clinical Trial Design for Long QT Syndrome

Diurnal oscillations in human cardiac electrophysiology are thought to be under the control of the endogenous circadian clock. The incidence of arrhythmic events in patients with Long QT syndrome (LQTS) varies diurnally. The diurnal variation in QT interval has previously been identified as a potential for error in clinical trials which utilise ECG measurement. We performed a systematic review of clinical trials for LQTS to identify practice around specification of timing information for point electrocardiogram (ECG) measurements, analysis of continual ECG recordings ≥24 h, and drug delivery. Despite guidelines having been issued around the analysis of 24-h ECG recordings, we identify a lack of usage of detailed time of day information in trial design for LQTS studies, which has the potential to affect the interpretation of the results of drug trials. We identify that, in contrast, clinical trials for QT prolonging drugs demonstrate increased incorporation of time of day information of both QT analysis and drug dosing. We provide a visual portal to allow trial designers and clinicians to better understand timing of common cardiac-targeting drugs, and to bear this concept in mind in the design of future clinical trials.

Assessing Two Approaches for Enhancing the Range of Simulated Scales in the E3SMv1 and the Impact on the Character of Hourly US Precipitation

AbstractImproving the representation of precipitation in Earth system models is essential for understanding and projecting water cycle changes across scales. Progress has been hampered by persistent deficiencies in representing precipitation frequency, intensity, and timing in current models. Here, we analyze simulated US precipitation in the low‐resolution (LR) configuration of the Energy Exascale Earth System Model (E3SMv1) and assess the effect of two approaches to enhance the range of explicitly resolved scales: high‐resolution (HR) and multiscale modeling framework (MMF), which incur similar computational expense. Both E3SMv1‐MMF and E3SMv1‐HR capture more intense and less frequent precipitation on hourly and daily timescales relative to E3SMv1‐LR. E3SMv1‐HR improves the intensity over the Eastern and Northwestern US during winter, while E3SMv1‐MMF improves the intensity over the Eastern US and summer diurnal timing over the Central US. These results indicate that both methods may be needed to improve simulations of different storm types, seasons, and regions.

A shift in the diurnal timing and intensity of deep convection over the Congo Basin during the past 40 years

The Congo Basin, one of the three most convective regions in the world, has recently experienced a large-scale drying trend accompanied by an increase in thunderstorm activity. This study analyzes changes in the diurnal variations of cloudiness and deep convection from 1979 to 2019 over the Congo, evaluates their associations with trends in precipitation efficiency, and explores their possible connections to the observed decrease in precipitation. Analyses of GridSat-B1 and MODIS satellite datasets in conjunction with ERA5 reanalysis data show that cloud cover has decreased, and brightness temperature (Tb) has increased during the morning hours, while convective activity has increased and Tb has decreased during the afternoon hours, possibly due to the observed warming and drying trend over the Congo. The combined effects of decreasing clouds during the morning and the subsequent increasing convection during the afternoon have led to an amplification of the diurnal amplitude in Tb over the Congo. Our results also indicate a decrease in precipitation efficiency and an increase in cloud base height. Such changes may be attributable to the Congo drought as increased surface temperatures and decreased surface relative humidity would raise the lifted condensation level, and thus increase the cloud base height and decrease the precipitation efficiency. This positive-feedback mechanism may ultimately result in the observed decrease of precipitation at the surface, further accelerating the drying trend over the Congo.

Light dominates the diurnal emissions of herbivore-induced volatiles in wild tobacco

BackgroundTiming is everything when it comes to the fitness outcome of a plant’s ecological interactions, and accurate timing is particularly relevant for interactions with herbivores or mutualists that are based on ephemeral emissions of volatile organic compounds. Previous studies of the wild tobacco N. attenuata have found associations between the diurnal timing of volatile emissions, and daytime predation of herbivores by their natural enemies.ResultsHere, we investigated the role of light in regulating two biosynthetic groups of volatiles, terpenoids and green leaf volatiles (GLVs), which dominate the herbivore-induced bouquet of N. attenuata. Light deprivation strongly suppressed terpenoid emissions while enhancing GLV emissions, albeit with a time lag. Silencing the expression of photoreceptor genes did not alter terpenoid emission rhythms, but silencing expression of the phytochrome gene, NaPhyB1, disordered the emission of the GLV (Z)-3-hexenyl acetate. External abscisic acid (ABA) treatments increased stomatal resistance, but did not truncate the emission of terpenoid volatiles (recovered in the headspace). However, ABA treatment enhanced GLV emissions and leaf internal pools (recovered from tissue), and reduced internal linalool pools. In contrast to the pattern of diurnal terpenoid emissions and nocturnal GLV emissions, transcripts of herbivore-induced plant volatile (HIPV) biosynthetic genes peaked during the day. The promotor regions of these genes were populated with various cis-acting regulatory elements involved in light-, stress-, phytohormone- and circadian regulation.ConclusionsThis research provides insights into the complexity of the mechanisms involved in the regulation of HIPV bouquets, a mechanistic complexity which rivals the functional complexity of HIPVs, which includes repelling herbivores, calling for body guards, and attracting pollinators.