Diurnal Variation Research Articles

Long-term observations of cloud condensation nuclei (CCN) characteristics of atmospheric aerosols: Results from a rural location in India

Long-term measurement of cloud condensation nuclei (CCN) is essential to assess the role of seasonally varying aerosol sources and underlying synoptical meteorological conditions in aerosol-cloud interactions. However, long-term measurement of CCN is limited over the Indian region and globally. This study provides first-ever long-term observations of CCN concentrations at different supersaturation (SS) values ranging from 0.2 to 1.0% using a CCN counter from a rural location of Gadanki, India (13.5°N, 79.2°E, and 375 m AMSL) during October 2019–August 2023. The total CCN concentration (NCCN) was the highest during pre-monsoon season (2847 ± 1148 #/cc), followed by winter (2463 ± 1066 #/cc), post-monsoon (2124 ± 1145 #/cc), and monsoon (1099 ± 740 #/cc) at 0.4% SS. Diurnal variations in NCCN showed bi-modal distribution with a relatively weak peak at around 8:00 h (Local time, LT) and a substantial rise at about 20 h LT. However, a systematic increase in NCCN was observed during the daytime in all the seasons except for the monsoon. The two peaks in diurnal variation of NCCN were associated with CCN of sizes less than 2 μm. The peak diameter of the mono-modal size distribution of CCN shifted towards the higher SS, implying the growth of small aerosols and available CCN. The broad peak indicates that most aerosol particles over Gadanki grow at the SS of 0.4%. Estimates of the k-parameter (Twomey's empirical fit) show the aerosols over Gadanki are relatively more hygroscopic during the monsoon than in winter, with their respective k-values of 0.7 and 0.4. Further, the diurnal variation in the k-parameter suggests significant variability in hygroscopicity within a day during monsoon and winter. Comparison with other locations suggests the CCN concentrations over Gadanki lies between those of polluted urban, coastal, and high-altitude stations.

Gut Microbiota-Mediated Alterations of Hippocampal CB1R Regulating the Diurnal Variation of Cognitive Impairment Induced by Hepatic Ischemia-Reperfusion Injury in Mice.

Patients suffering from hepatic ischemia-reperfusion injury (HIRI) frequently exhibit postoperative cognitive deficits. Our previous observations have emphasized the diurnal variation in hepatic ischemia-reperfusion injury-induced cognitive impairment, in which gut microbiota-associated hippocampal lipid metabolism plays an important role. Herein, we further investigated the molecular mechanisms involved in the process. Hepatic ischemia-reperfusion surgery was performed under morning (ZT0, 08:00) and evening (ZT12, 20:00). Fecal microbiota transplantation was used to associate HIRI model with pseudo-germ-free mice. The novel object recognition test and Y-maze test were used to assess cognitive function. 16S rRNA gene sequencing and analysis were used for microbial analysis. Western blotting was used for hippocampal protein analysis. Compared with the ZT0-HIRI group, ZT12-HIRI mice showed learning and short term memory impairment, accompanied by down-regulated expression of hippocampal CB1R, but not CB2R. Both gut microbiota composition and microbiota metabolites were significantly different in ZT12-HIRI mice compared with ZT0-HIRI. Fecal microbiota transplantation from the ZT12-HIRI was demonstrated to induce cognitive impairment behavior and down-regulated hippocampal CB1R and β-arrestin1. Intraperitoneal administration of CB1R inhibitor AM251 (1mg/kg) down-regulated hippocampal CB1R and caused cognitive impairment in ZT0-HIRI mice. And intraperitoneal administration of CB1R agonist WIN 55,212-2 (1mg/kg) up-regulated hippocampal CB1R and improved cognitive impairment in ZT12-HIRI mice. In summary, the results suggest that gut microbiota may regulate the diurnal variation of HIRI-induced cognitive function by interfering with hippocampal CB1R.

Space‐Time Monitoring of Seafloor Velocity Changes Using Seismic Ambient Noise

AbstractWe use seismic ambient noise recorded by dense ocean bottom nodes (OBNs) in the Gorgon gas field, Western Australia, to compute time‐lapse seafloor models of shear‐wave velocity. The extracted hourly cross‐correlation (CC) functions in the frequency band 0.1–1 Hz contain mainly Scholte waves with very high signal‐to‐noise ratio. We observe temporal velocity variations (dv/v) at the order of 0.1% with a peak velocity change of 0.8% averaged from all station pairs, from the conventional time‐lapse analysis with the assumption of a spatially homogeneous dv/v. With a high‐resolution reference (baseline) model from full waveform inversion of Scholte waves, we present an elastic wave equation based double‐difference inversion (EW‐DD) method, using arrival time differences between the reference and time‐lapsed Scholte waves, for mapping temporally varying dv/v in the heterogeneous subsurface. The time‐lapse velocity models reveal increasing/decreasing patterns of shear‐wave velocity in agreement with those from the conventional analysis. The velocity variation exhibits a ∼24‐hr cycling pattern, which appears to be inversely correlated with the diurnal variations in sea level height, possibly associated with dilatant effects for porous, low‐velocity shallow seafloor and rising pore pressure with higher sea level. This study demonstrates the feasibility of using dense passive seismic surveys and wave‐equation time‐lapse inversion for quantitative monitoring of subsurface property changes in the horizontal and depth domain.

Comparison of Proxy-Shortwave Cloud Albedo from SBUV Observations with CMIP6 Models

Abstract We construct a long-term record of top of atmosphere (TOA) shortwave (SW) albedo of clouds and aerosols from 340-nm radiances observed by NASA and NOAA satellite instruments from 1980 to 2013. We compare our SW cloud+aerosol albedo with simulated cloud albedo from both AMIP and historical CMIP6 simulations from 47 climate models. While most historical runs did not simulate our observed spatial pattern of the trends in albedo over the Pacific Ocean, four models qualitatively simulate our observed patterns. Those historical models and the AMIP models collectively estimate an equilibrium climate sensitivity (ECS) of ∼3.5°C, with an uncertainty from 2.7° to 5.1°C. Our ECS estimates are sensitive to the instrument calibration, which drives the wide range in ECS uncertainty. We use instrument calibrations that assume a neutral change in reflectivity over the Antarctic ice sheet. Our observations show increasing cloudiness over the eastern equatorial Pacific and off the coast of Peru as well as neutral cloud trends off the coast of Namibia and California. To produce our SW cloud+aerosol albedo, we first retrieve a black-sky cloud albedo (BCA) and empirically correct the sampling bias from diurnal variations. Then, we estimate the broadband proxy albedo using multiple nonlinear regression along with several years of CERES cloud albedo to obtain the regression coefficients. We validate our product against CERES data from the years not used in the regression. Zonal mean trends of our SW cloud+aerosol albedo show reasonable agreement with CERES as well as the Pathfinder Atmospheres–Extended (PATMOS-x) observational dataset. Significance Statement Equilibrium climate sensitivity is a measure of the rise in global temperature over hundreds of years after a doubling of atmospheric CO2 concentration. Current state-of-the-art climate models forecast a wide range of equilibrium climate sensitivities (1.5°–6°C), due mainly to how clouds, aerosols, and sea surface temperatures are simulated within these models. Using data from NASA and NOAA satellite instruments from 1980 to 2013, we first construct a dataset that describes how much sunlight has been reflected by clouds over the 34 years and then we compare this data record to output from 47 climate models. Based on these comparisons, we conclude the best estimate of equilibrium climate sensitivity is about 3.5°C, with an uncertainty range of 2.7°–5.1°C.

Macro‐ and Microphysical Characteristics of Extreme Hourly Precipitation Over the Pearl River Delta on the Monsoon Coast (South China)

AbstractIn this study, the Extreme Hourly Precipitation Areas (EHPAs) of three extreme levels (i.e., between the 95th and 99th percentiles, between the 99th and 99.9th percentiles, beyond the 99.9th percentile) in the Pearl River Delta over South China are identified; then the related events and associated Convective Cores (CCs) are tracked, and their macro‐and‐microphysical characteristics are analyzed using multi‐year dual‐polarization radar observations. Results show that >90% of EHPAs are smaller than 10 km2, and 65%–75% of EHPA events last only one hour. They tend to be more localized and persist longer with increasing hourly‐precipitation extremity. The EHPAs overlap with the CCs during 50%–64% of the EHPAs' life span. Their occurrence frequencies are nearly quadrupled after the monsoon onset over South China Sea (SCS), with a major (secondary) peak at about 1400 LST (0600 LST) in the diurnal variations. The CCs are non‐linear shaped with about 65% being meso‐γ‐scale and embedded within mostly meso‐β or α‐scale 20 dBZ regions. The CCs generally contain active warm‐rain processes and about 70% possess moderate‐to‐intense mixed‐phase microphysical processes. The ratios of ice water path to liquid water path are about 0.37, and coalescence dominates (about 68%) the liquid‐phase processes. The average size of raindrop is slightly larger than the “maritime‐like” regime and the average concentration is much higher than the “continental‐like” regime. These CCs' characteristics roughly resemble those of the convection producing extreme instantaneous precipitation, except for a larger horizontal scale and less evident variations with the increasing hourly‐precipitation extremity.

Improving Diurnal Precipitation Forecasts Through Coherent Coupling of Cumulus and Planetary Boundary Layer Parameterizations

AbstractThis study explores the impact of coupling cumulus and planetary boundary layer (PBL) parameterizations on diurnal precipitation forecasting during the plum rainy season in Jiangsu Province, China, using a double grid‐nesting approach. Results show that coherent coupling of cumulus (only in the 15 km grid outer domain [O]) and PBL parameterizations leads to improved forecasting of diurnal variations in the morning, afternoon, and the evening. Increasing the frequency of the Kain‐Fritsch (KF) cumulus scheme in [O] enhances subgrid precipitation while reducing grid‐scale precipitation, resulting in a more accurate representation of daytime convective activities and a reduction in over‐forecasting of evening valley and early‐morning precipitation. Additionally, coupling a suitable PBL scheme mitigates the overpredicted afternoon peak by facilitating turbulent mixing to penetrate higher altitudes with a thicker layer, thereby reducing instability energy accumulation. A higher KF frequency in [O] retains less low tropospheric moisture, reducing moisture convergence into the 1 km grid inner domain [I] and decreasing overpredicted daytime precipitation in [I]. Various PBL schemes produce distinct vertical distributions of turbulent moisture and heat transport, impacting convection and precipitation in [I] resolved by cloud microphysics processes. The coherent coupling of these parameterizations maintains a balanced supply of convective energy and water vapor, significantly improving diurnal precipitation forecasts in [I]. Isolating these parameterizations between nested grids may undermine this improvement.

Fluctuations in the “static” atmosphere and their effects on tropospheric ozone distribution

Atmospheric fluctuation can be seen everywhere. This study focuses on the record-breaking increase of O3 concentration during the summer in some sensitive areas in recent years. The findings indicate that in the vicinity of the East Asian continent near western Pacific ocean, when the atmospheric conditions are stable or neutral, it is conducive to the maintenance and propagation of atmospheric oscillations near the height of the pollutant mixed layer (H_PML). Accompanied by the "peak-trough" effect of external gravity wave oscillations, due to the abundant water vapor of the cloud system (there are low pressure or typhoon disturbances in summer) near the large-scale cloud belt at the edge of the subtropical high in the western Pacific, the bright temperature at cloud top shows "light and dark changes" on satellite images, forming a wave-like cloud system. The novelty of this study lies in the fact that atmospheric fluctuations near the H_PML is not only related to the known aggravation of heavy rainfall, but also leads to the additional value-added effect of aerosols. Under static atmospheric conditions, the impact of atmospheric fluctuations near the H_PML on additional rise of O3 concentration helps us to deepen our understanding of the so-called "entrained ozone (EZ) effect" in the atmosphere. Due to the external gravity waves, the concentration of O3 increased further. Diurnal variations of solar zenith angle and H_PML are key meteorological factors influencing the significant increase in near-surface O3 concentration entrainment. The formation mechanism of solar photochemical O3 is further deepened and supplemented by analyzing the record-breaking increase of O3 concentration in summer observed in recent years.

Intra‐annual radial growth of Quercus acutissma and its response to hydrometeorological factors in the Nandadish experimental catchment, eastern China

AbstractInvestigating the relationship between tree growth within a year and environmental factors is crucial for understanding how climate change affects seasonal tree growth patterns. In this study, high‐resolution point dendrometers were used to monitor the stem radial changes of Oak trees (Quercus acutissma) over two years (2020 and 2021) in the eastern subtropical monsoon region of China. We find that the main growth period of Oak trees spans from March to September, and air temperature significantly affects the growth onset of Oak trees but with no clear impact on their growth cessation. The observations show that precipitation substantially affects daily stem radial increment (SRI), but the frequency of precipitation days plays a more crucial role in enhancing seasonal growth than the total precipitation amount. In the growing season, the stem radius of the Oak trees shows obvious diurnal cycles with shrinkage during the day and expansion at night, reflecting a delicate balance between canopy water loss and soil water absorption. The diurnal variations of the stem radius during the cold period (January and December) show an opposite pattern to that of the growing season, due to the sap's freezing under the condition of low air temperature at night as well as no or weak transpiration in the daytime. Because the temporal dynamics and intensity of tree activities significantly affect the timing and mechanisms of carbon assimilation in terrestrial ecosystems, our results are helpful to evaluate the carbon sequestration capacity of subtropical forests under the global climate change.

Characterization of Mineral Meposits Using the Magnetic Method: The Case of the Aïn Beida Mine in Bouarfa, Morocco

Abstract Geophysical methodologies represent a paramount approach for assessing the mining potential of a given area. Among these methodologies, the magnetic method stands out as indispensable for the exploration of metalliferous deposits. This method facilitates the characterization of both the lateral extent and vertical depth of anomalous bodies within the surveyed region, as discerned from their influence on the total magnetic field. In the case of the manganese-rich mining zone situated in Bouarfa, particularly in Aïn Beida, the mineral deposit genesis typically involves the association of manganese with ferruginous minerals, significantly perturbing the total magnetic field. However, the initial findings necessitate meticulous corrections to isolate the exclusive impact of anomalous bodies on the magnetic field. Accordingly, correction procedures must address diurnal variations prior to executing a Reduction to the Pole (RTP), enabling the identification of well-defined and unipolar anomalies crucial for precise delineation of potentially mineralized zones. Integration of spatially interpolated data yields comprehensive maps delineating areas of mining significance and elucidating pertinent geological phenomena within the study area. Subsequently, employing 2D modeling techniques on magnetic survey results facilitates accurate estimation of mineralized horizon extents and thicknesses. Ultimately, these synthesized maps serve as valuable guides for subsequent mechanical prospecting endeavors aimed at corroborating findings derived from geophysical methodologies.

Cholecystokinin receptor type A are involved in the circadian rhythm of the mouse retina

The retina is the only organ projecting external light to the suprachiasmatic nucleus. Cholecystokinin receptor type A (Cckar/Cckar) is one of the essential factors for light reception in retinal cells. As there was a lack of literature on the matter, we aimed to elucidate the cause of the time-dependent phase change in clock gene expression. We found that Cckar mRNA expression in retinal cells exhibited diurnal variations. The rhythm of expression of the clock gene Per1/Per2 in retinal cells was altered in Cckar−/− mice. The light sensitivity of retinal cells was evaluated in wild-type mice, which showed c-Fos was activated in the ganglion cell layer more than in the inner granular layer. This increase in the number of c-Fos-positive cells was suppressed by lorglumide, a Cckar antagonist. Treatment of rat retina primary cells with lorglumide suppressed Per2 transcription, which was altered in a time-dependent manner relative to the Per2 expression. Light irradiation studies in Cckar−/− mice did not exhibit an increase in Period expression in the suprachiasmatic nucleus. These results indicate that Cckar is among the factors that regulate the cycle of clock genes on the retina. Cckar knockout attenuates the light responsiveness of suprachiasmatic nucleus and reduces the expression amplitude of Period genes in the retina. Thus, Cckar may contribute to entrainment of the light environment and maintenance of the expression cycle of Period gene, which is one of the core clock genes.

Determining Suitable Sampling Times for Soil CO2 and N2O Emissions Helps to Accurately Evaluate the Ability of Rubber-Based Agroforestry Systems to Cope with Climate Stress

Agroforestry is known to significantly improve long-term land productivity, potentially enhancing the ability to cope with climate stress. However, there is limited information regarding the accurate monitoring of greenhouse gases (GHGs) in rubber-based agroforestry systems. Before GHGs can be accurately estimated, the diurnal variations and suitable sampling times must be studied to reduce the uncertainty of the manual static chamber method. In this study, the soil GHGs emitted from conventional single-row (SR) and improved double-row (DR) rubber plantations were compared across the dry and wet seasons in Hainan, China. A total of 1728 GHG samples from a field trial were collected, analyzed, and related to environmental factors. The results demonstrated that the diurnal fluxes of CO2 in rubber plantations were likely to remain fluctuating, with the maximum typically occurring during the night-time and daytime hours of the dry and wet seasons, respectively. A clearer double-peak (around 2:00 and 14:00) during the dry season and a daytime peak (14:00) during the wet season of the N2O were recorded. In addition to the commonalities, different seasons and different types of GHGs and rubber plantations also differed in their detailed fluctuation times and ranges; therefore, the determination of suitable sampling times should not ignore these factors in certain cases. Based on this study, it was determined that the late afternoon (16:00–18:00) was the suitable sampling time of soil GHGs in rubber plantations, instead of the most common morning times (with an underestimation of 25% on average). In addition, the air humidity during the dry season and the soil temperature during the wet season were both positively correlated with GHGs (p < 0.05). This study highlights the significance of accurately monitoring soil GHGs in rubber-based agroforestry systems, providing a basic reference for the development and management of climate-smart land use practices in rubber plantations.

Solar Activity and Cosmic Ray Intensity Variation with Geomagnetic Activity during 1996–2022

The average features of diurnal variation have been observed to change with different phases of the solar cycle, with the variance being substantially bigger at higher energies. The events were classified on the basis of different phases of solar cycles, i.e., the minimum solar activity time period, the maximum solar activity time period, and the declining phase of solar cycle. This research looks at the observed results and the influence of solar variability on cosmic rays and the geomagnetic field from 1996 to 2022. The occasional group includes a Forbush effect decline, transitory decrease, and a ground level enhancement (GLE). The 11-year fluctuation in Galactic Cosmic Rays is also known as the long-term variation, whereas the Forbush effect reduction is known as short-term variation. We investigated the long-term change in the cosmic ray intensity and its relationship to the number of Sun spots (Rz), solar wind speed (

Evaluation of Precipitation Forecast by the Operational China Meteorological Administration Mesoscale Model During the 2020 Meiyu Period

AbstractThis study evaluated the precipitation forecast produced by the operational China Meteorological Administration Mesoscale model (CMA‐MESO) during the “super violent” Meiyu season of 2020. Generally, CMA‐MESO, which runs with ∼3‐km‐grid resolution, is able to reproduce the distribution and diurnal variation of precipitation. However, the precipitation amount is greatly overestimated, especially in eastern coastal areas of China. Precipitation in that region usually occurs with two peaks: one in the morning that mostly reflects organized precipitation systems, and the other in the afternoon generated mostly by local convection. Analyses showed that overestimation of low‐level wind speed is the main reason for the overestimation of precipitation. CMA‐MESO produces low‐level winds that are overly strong, which greatly enhance the predicted convergence at night, leading to overestimation of precipitation. Additionally, the stronger wind speed increases the estimated transport of water vapor to the eastern coastal area, producing fake convection near the coastal mountains as the perturbed wind direction turns toward the mountain area in the afternoon. In comparison with ERA5, CMA‐MESO tends to overestimate (underestimate) the temperature in the northwest (southeast), and the larger temperature gradient increases the pressure gradient, resulting in the stronger low‐level wind speed.

Meteoropathy: myth or reality? Assessment of the relationship between cardiovascular diseases and weather conditions according to data from a Moscow hospital

Many patients and some doctors associate the worsening of cardiovascular diseases with meteoropathy (changes in atmospheric pressure and air temperature). Opinion about lack of weather influence on the increase in overall morbidity and the lack of related research data indicate the need to study the relationship between cardiovascular diseases and meteorological conditions.Aim. To assess the prevalence of hospitalizations with symptomatic increases in blood pressure (BP), atrial fibrillation (AF), and decompensated heart failure (HF) in a Moscow hospital depending on meteorological conditions.Material and methods. This retrospective analysis of the number of emergency hospitalizations of patients with symptomatic increases in blood pressure, AF, and decompensated HF in Moscow City Clinical Hospital № 24 was carried out in the period from October 1, 2018 to September 30, 2019. Information from the website www.weather.com was used as a source of meteorological data. The following indicators were assessed daily: daytime air temperature (t), nighttime air temperature, maximum diurnal air temperature variation, atmospheric pressure, maximum diurnal atmospheric pressure variation, amount of precipitation. To assess statistical significance, the Mann-Whitney and Kruskal-Wallis tests were used. A correlation analysis was carried out, and a prognostic model was created using multiple linear regression.Results. During the period from October 1, 2018 to September 30, 2019, 4354 patients were hospitalized at City Clinical Hospital № 24 with symptomatic BP increase and/or AF and/or decompensated HF. The highest number of hospitalizations occurred in November, December and January. The median number of admissions per day was 12 patients. When comparing the mean number of patients admitted to the hospital per day, depending on day- and nighttime air temperature, following statistically significant differences were obtained (p<0,001): with day- and nighttime air temperature ≥0о C, the number of admissions was less compared to sub-zero temperatures. Significant inverse correlations were established between the number of patients hospitalized with symptomatic BP increase, AF and HF per day, with air temperature at night (correlation coefficient r=-0,339; p<0,001), air t during the day (r=-0,316; p<0,001), temperature difference over 48 hours (r=-0,205; p<0,001); direct correlations with atmospheric pressure (r=0,106; p=0,044) and its changes (r=0,115; p=0,028) were identified. All identified relationships were of moderate strength. According to prognostic model, only nighttime air temperature turned out to be a significant indicator associated with the hospitalization rate per day. With a decrease in air temperature at night for every 7,5о C <0, one more patient is expected to be hospitalized with a symptomatic BP increase, decompensated HF, or paroxysmal AF.Conclusion. Negative air temperature in a metropolis is associated with an increase in hospitalizations for symptomatic BP increase, AF or decompensated HF. Atmospheric pressure and precipitation do not affect these conditions.

The impact of gaseous degradation on the gas–particle partitioning of methylated polycyclic aromatic hydrocarbons

Abstract. The partitioning of semi-volatile organic compounds (SVOCs) between gas and particle phases plays a crucial role in their long-range transport and health risk assessment. However, the accurate prediction of the gas–particle (G–P) partitioning quotient (KP′) remains a challenge, especially for the light-molecular-weight (LMW) SVOCs due to their upward deviation from equilibrium state. In this study, the phenomenon with the influence of gaseous degradation on G–P partitioning was observed. Based on the diurnal study of concentrations and KP′ values for methylated polycyclic aromatic hydrocarbons (Me-PAHs), it was found that the KP′ values of methylated naphthalenes (Me-Naps; one type of LMW SVOC) during the daytime were higher than during the nighttime, and the regression lines of log KP′ versus log KOA (octanol–air partitioning coefficient) for daytime and nighttime were non-overlapping, which were different from other Me-PAHs. Compared with other diurnal influencing factors, the higher gaseous degradation of Me-Naps in the daytime than in the nighttime should partially explain their special diurnal variation in KP′, which provided a new explanation for the non-equilibrium behavior of KP′ for LMW SVOCs. Moreover, the influence of gaseous degradation on the deviation of KP′ from equilibrium state was deeply studied based on the steady-state G–P partitioning model considering particulate proportion in emission (ϕ0). The increasing times of KP′ influenced by the gaseous degradation deviated from equilibrium state can be calculated by 1 + 13.2ϕ0 × kdeg (kdeg, gaseous degradation rate). The increase in KP′ along with the increase in kdeg proved that higher gaseous degradation in the daytime could increase the KP′ value. Furthermore, an amplification in KP′ ranging from 1.11 to 5.58 times (90 % confidence interval: 1.01 to 14.4) under different ϕ0 values (0 to 1) in the temperature range of −50 to 50 °C was estimated by the Monte Carlo analysis. In summary, it can be concluded that the influence of gaseous degradation should also be considered in the G–P partitioning models of SVOCs, especially for the LMW SVOCs, which provided new insights into the related fields.

Diurnal pattern and characteristic of soil respiration and net ecosystem carbon exchange in alpine meadow ecosystem on the northeastern Qinghai-Tibet Plateau

Analyzing the diurnal pattern of soil respiration is essential for understanding the potential mechanisms of carbon cycle. Additionally, long-term and high temporal frequency soil respiration observations are crucial and valuable at different time scales, particularly in alpine regions. Therefore, it is critical to conduct research on the diurnal pattern of soil respiration in areas sensitive to global warming. Here, four group (including soil respiration, heterotrophic respiration, net ecosystem carbon exchange, and net ecosystem carbon exchange under warming condition) of experiments were designed with a total 12 chambers, and data collected during growing season in 2023 (April to September) obtained by automatic observation system at hour-scale and four-parameter Gaussian equation were used to investigate the diurnal pattern of soil respiration and net ecosystem carbon exchange in alpine meadow ecosystem on the northeastern Qinghai-Tibet Plateau. The results indicated that: 1) the soil temperature was crucial factor for the variations in diurnal pattern of soil respiration and net ecosystem carbon exchange in four experiments. The response of the heterotrophic components to the diurnal variation in soil temperature induced diurnal lag between soil respiration and soil temperature, with mean lag time of 1.7 h. 2) The diurnal peak time of net ecosystem carbon exchange was 1–3 h earlier than respiration, and the diurnal variation of soil tempiration was one of the main driving forces. 3) Additionally, warming advanced the diurnal peak time of net ecosystem carbon exchange by 1.2–2 h through explaining the parameters of the Gaussian function. It also promoted microbial resistance, thereby limiting the increase in soil respiration during nighttime. The study suggested that temperature varied soil microenvironment and biochemical processes in alpine meadow ecosystem, thus affecting the diurnal pattern. Indeed, this study focused solely on traditional factors, and further investigations were needed, particularly from a biotic perspective, to validate these conclusions.

Hourly land-use regression modeling for NO2 and PM2.5 in the Netherlands.

Annual average land-use regression (LUR) models have been widely used to assess spatial patterns of air pollution exposures. However, they fail to capture diurnal variability in air pollution and consequently might result in biased dynamic exposure assessments. In this study we aimed to model average hourly concentrations for two major pollutants, NO2 and PM2.5, for the Netherlands using the LUR algorithm. We modelled the spatial variation of average hourly concentrations for the years 2016–2019 combined, for two seasons, and for two weekday types. Two modelling approaches were used, supervised linear regression (SLR) and random forest (RF). The potential predictors included population, road, land use, satellite retrievals, and chemical transport model pollution estimates variables with different buffer sizes. We also temporally adjusted hourly concentrations from a 2019 annual model using the hourly monitoring data, to compare its performance with the hourly modelling approach. The results showed that hourly NO2 models performed overall well (5-fold cross validation R2 = 0.50–0.78), while the PM2.5 performed moderately (5-fold cross validation R2 = 0.24–0.62). Both for NO2 and PM2.5 the warm season models performed worse than the cold season ones, and the weekends' worse than weekdays’. The performance of the RF and SLR models was similar for both pollutants. For both SLR and RF, variables with larger buffer sizes representing variation in background concentrations, were selected more often in the weekend models compared to the weekdays, and in the warm season compared to the cold one. Temporal adjustment of annual average models performed overall worse than both modelling approaches (NO2 hourly R2 = 0.35–0.70; PM2.5 hourly R2 = 0.01–0.15). The difference in model performance and selection of variables across hours, seasons, and weekday types documents the benefit to develop independent hourly models when matching it to hourly time activity data.

Exploring ionospheric plasma density trends in the Indian equatorial crest region under varying solar activity conditions

Long-term trends in the evolution of ionospheric plasma at Hyderabad (17.38∘N, 78.48∘E; 8.52∘N Magnetic Latitude), a near-equatorial anomaly (EIA) crest region of the Indian ionospheric sector, have been studied using 9 years of vertical Total Electron Content (TEC) data from 2004 to 2009 and 2011 to 2013 using global positioning satellites (GPS) measurements. The study examined the mean diurnal, monthly, seasonal, and yearly variations of TEC during geomagnetic quiet days in different seasons from 2004 to 2013. The findings reveal that the daytime TEC at the anomaly crest region exhibits semi-annual variations throughout the study period, while midnight TEC shows semi-annual variation only during the high solar activity years of 2011–2013. The winter anomaly was observed in 2004 and 2006. The study also assessed the performance of the International Reference Ionosphere (IRI) 2016 model in reproducing GPS TEC variability at the equatorial crest region. The diurnal and seasonal variation patterns in IRI-TEC show a good correlation with GPS TEC. However, the IRI 2016 model tends to overestimate TEC values during low solar activity conditions (2006–2009) but represents TEC variations reasonably well during high solar activity periods (2011–2013). Nevertheless, the IRI model fails to capture the wide plateau-like structure in the peak TEC, typically occurring between 1200–1600 IST at Hyderabad. Additionally, IRI-TEC consistently indicates very low TEC values during the early morning hours, whereas GPS-TEC measurements suggest a significant presence of plasma density. The study suggests a strong influence of the solar cycle on TEC variations at Hyderabad, evident from the positive correlation (R2= 0.71) with the F10.7 cm index. This characteristic is also well represented by the IRI 2016 model.

Ozone pollution aggravated by mountain-valley breeze over the western Sichuan Basin, Southwest China

The impact of thermally driven mountain-valley breezes (MVB) on the atmospheric environment remains poorly understood, especially in ozone (O3)-polluted regions with complex underlying topography. To address this knowledge gap, we focused on the western Sichuan Basin (SCB), situated immediately east of the Tibetan Plateau (TP), which is considered susceptible to MVB coupled with severe O3 pollution in southwest China. We revealed the MVB driving diurnal O3 variations and meteorological mechanisms using surface observations and ERA5 reanalysis data. Local MVB days accounted for up to 47% of cases in the summers of 2015–2022. Driven by the MVB, the near-surface O3 concentrations increased by 8.8%, with 12.7% and 50.0% deterioration in the O3 light and moderate exceedance rates, respectively, on the western SCB edge. The daytime upslope valley breeze with 20% higher wind speed drove the westward transport of rich O3 and precursors from the upwind-polluted inner SCB towards its western edge, and the O3 photochemical production, followed by intensifying solar radiation and air temperature, gave rise to 14.8% of surface O3 concentrations over the western SCB edge. The nighttime downward mountain breeze with a 20% increase in wind speed could transport the rich O3 in the mountainous area to the basin edge, causing O3 levels to increase by 2.8%. In summary, we quantitatively assessed the impacts of MVB on changes in O3 concentrations and air quality along with its meteorological mechanisms, facilitating a comprehensive understanding of meteorological drivers in the atmospheric environment.

The Afternoon/Morning Ratio of Tower-Based Solar-Induced Chlorophyll Fluorescence Can Be Used to Monitor Drought in a Chinese Cork Oak Plantation

Monitoring drought stress is crucial for estimating productivity and assessing the health status of forest ecosystems under global climate change. Solar-induced chlorophyll fluorescence (SIF) is mechanistically coupled to photosynthesis and has advantages over greenness-based vegetation indices in detecting drought. In recent years, SIF has commonly been used in monitoring drought stress in crop ecosystems. However, the response of tower-based SIF to drought stress in forest ecosystems remains unclear. In this study, we investigated the potential of tower-based SIF to monitor drought, which was quantified using the plant water stress index (PWSI) in a Chinese cork oak plantation. The results show the negative effect of drought on SIF, and afternoon depression of SIF emission under drought stress was observed. Canopy SIF (F) exhibited a nonlinear relationship with PWSI, while the quantum yield of SIF (ΦF) exhibited a significant linear relationship with PWSI at 687 nm and 760 nm (ΦF687: R2 = 0.90; ΦF760: R2 = 0.85). Incident radiation (PAR) and canopy structure affected the response of SIF to drought stress, with PAR as the main factor causing the nonlinear relationship between F and PWSI. Afternoon depression was described as the afternoon/morning ratio (AMR). AMRF and AMRΦF exhibited a negative linear response to PWSI. AMRF was less affected than F by PAR and canopy structures, and AMRΦF was more physiologically representative than ΦF. Moreover, AMRΦF was sensitive to VPD and REW, and it might be a good indicator of drought. Red SIF was more sensitive to drought than far-red SIF, as the R2 of PWSI with AMRΦF687 (R2 = 0.89) was higher than that with AMRΦF687 (R2 = 0.84). These results highlight the potential of tower-based SIF, especially red SIF, for drought monitoring in a plantation, and consideration of the physiological diurnal variation in SIF under drought stress is crucial for improving the accuracy of drought stress monitoring.