Seasonal Term Research Articles

Experimental assessment of impact of different ventilation modes on cognitive and academic performance: A study based on classrooms in Türkiye

In closed spaces, such as classrooms, poor ventilation, indoor exposure to CO2, and non-optimal humidity and temperature conditions are global concerns associated with health and performance. This study experimentally assesses the effects of different ventilation modes on the air quality parameters and cognitive and academic performances of 120 s-grade primary school children in two buildings with different characteristics during heating and non-heating seasons. Based on a retrospective analysis of 455 primary schools in Türkiye during 2017–2018, the study was conducted in six classrooms of the two representative school buildings. Indoor air quality monitoring and performance (of the students) assessment was carried out from December 9, 2019, to September 28, 2020. The non-heating season measurements were conducted during the COVID-19 pandemic. According to our findings, the traditionally constructed school without energy efficiency regulations exhibited the worse scenario. The success percentages of arithmetic attention in both traditional and natural ventilation modes were significantly lower in the non-heating season than in the heating season, which indicates the impact of using a facemask inside a classroom during cognitive tasks. This study demonstrated that the heating season is more critical than the non-heating season in terms of ventilation of closed spaces.

Seasonal acclimation of energy and water balance in desert‐dwelling rodents of South America

AbstractSeasonal changes in environmental conditions may induce reversible physiological adjustments in organisms. We studied the acclimatization for multiple stressors in energy expenditure and water balance in Galea leucoblephara, a diurnal hystricognath rodent native to South America that experiences significant changes in temperature, precipitation, and food availability among seasons. We conducted a field study in the Monte Desert of Mendoza, Argentina, where we evaluated adult individuals' physiological status during two contrasting seasons in terms of climate and primary productivity. Reduced temperature, rainfall, and primary productivity during winter were associated with a decrease of 70% in basal metabolic rate (BMR), 30% in total evaporative water loss (TEWL), and 9% in body mass (Mb). In contrast, higher water availability, high temperature, and primary productivity during summer, induced significant increases in energy expenditure and evaporative water loss. As expected, the proportion of dietary items consumed by G. leucoblephara varied seasonally, resulting in a more diverse diet during summer. Our results illustrate how G. leucoblephara can cope with high seasonal contrasts in water availability, temperature, and food availability by modifying its physiological performance. Our data provide support for the hypothesis of physiological flexibility in energetic traits and water balance in response to the environmental challenges of the Monte Desert.

Comparative Analysis of the Nutritional Quality of Zizania latifolia Cultivars Harvested in Different Growing Seasons.

Zizania latifolia (Z. latifolia) is a popular aquatic vegetable with various nutrients in south China, but little is known about its cultivars and growing seasons in terms of the nutritional components. This work aims to characterize the nutrients of five Z. latifolia cultivars in different growing seasons. The results showed that Z. latifolia samples differed in terms of chemical parameters, which were significantly affected by variety, growing season, and their interaction. Zhejiao No. 8, harvested in the autumn, stood out with the highest levels of vitamin C. Tangxiajiao and Zhejiao No. 1 contained the highest values of total soluble solids, reducing sugar, soluble proteins, and amino acids. Significant differences were observed between the autumn Z. latifolia and spring samples; the former were of higher quality than the latter based on hierarchical clustering analysis and principal component analysis. Moreover, total amino acids (TAA) and glutamic acid (GLU) were selected as the key indicators for Z. latifolia comprehensive quality by multiple linear regression analysis. This study provides essential information on Z. latifolia quality characteristics corresponding to cultivars and growing seasons, which lays the foundation for promoting the quality improvement of Z. latifolia scientifically.

Trophic status of a shallow lake in Inner Mongolia: long-term, seasonal, and spatial variation

The study of lake-trophic status drivers and their variable effects over space and time can assist in the management of lake eutrophication. Winter dynamics in lake trophic status are rarely evaluated, yet they could vary drastically from the more commonly sampled summer patterns. This represents a key blindspot in our knowledge because ice sheets affect nutrient distribution (e.g., nitrogen and phosphorus), light infiltration (translucency), and phytoplankton propagation (Chl-a concentration). We examined long-term (2011–2020) changes in the trophic status (trophic level index; TLI) of Lake Wuliangsuhai, a shallow lake situated in a cold and arid region, using Generalized Additive Models (GAMs). The results suggested a significant decrease in eutrophication of Wuliangsuhai Lake over the study period, with TLI decreasing from 61.7 (moderately eutrophic) in 2011 to 49.9 (mesotrophic) in 2020. TLI was significantly higher over winter (p < 0.05), with the rank of seasons in terms of TLI of: winter (58.7) > summer (54.7) > autumn (54.2) > spring (54.0). TLI of the ice-covered period (58.7) significantly exceeded that of the ice-free period (54.3) (p < 0.05). There were also significant spatial differences in TLI (p < 0.05). Factors driving the spatial and temporal heterogeneity in lake trophic levels included the water supplement, water depth, water temperature, external inputs of nutrients, hydrodynamic conditions (flow velocity), distribution of phragmites, and the location of the main diversion channel.

Effects of Biochar and Compost Application on Soil Properties and on the Growth and Yield of Hot Pepper (Capsicum annuum L.)

Improper depositions of organic waste threaten the environment. On the other hand, intensive soil cultivation, inappropriate utilization of inorganic fertilizers, and inadequate soil management practices in the study area resulted in soil fertility reduction and poor crop growth. The addition of organic fertilizers from organic waste (biochar and compost) to soil can be considered an environmental-friendly and climate-smart practice able to improve soil properties and the yield of crops. Thus, this study aimed at evaluating the potential of organic amendment with coffee pulp compost (CPC), coffee pulp biochar (CPB), and their combination (CPC_CPB) on selected soil properties and hot pepper yield. The field experiment was conducted in the 2020 and 2021 growing seasons by adopting a randomized complete block design with a factorial experiment using CPC, CPB, and CPC_CPB treatments in different application rates. Results indicated that, in both years, the maximum dose (4 t/ha) of biochar significantly improved the yield of hot pepper and some soil chemical properties such as pH, OC, TN, P, K, Ca2+, Mg2+ contents, and CEC. When 2021 is compared with the 2020 growing season in terms of hot pepper yield, the treatments 4 CPB, 10 CPC, and 7 CPC_CPB increased the yield by 4.61, 1.62, and 1.55%, respectively. Thus, an application rate of CPB at the rate of 4 t/ha is considered suitable to improve hot pepper yield and soil properties. Therefore, the highest dose of CPB, followed by CPC_CPB and CPC can be considered as suitable to improve both soil fertility and hot pepper yield.

Monitoring Extreme Floods and Droughts in the Amazon Basin with Surface-Water-Based Indices

Abstract Extreme droughts and floods in the Amazon have great implications for ecosystems and societies. Over the last decade, the region has undergone major extreme events with no equivalent in the previous 100 years. Wetlands have been greatly impacted by these events. This study aims at presenting new indicators for wetlands based on water surface extent (WSE): duration of the flooded and nonflooded season, number of days of extreme events, delay of the start of the flooded season, and severity for each season. These indicators are more adapted for monitoring of wetlands than those based on precipitation, discharge, or groundwater information. They are computed for seven major Amazon subbasins for flooded and nonflooded seasons. These indicators improve our knowledge of the temporal behavior of the water surface during different extreme events, such as the 2015/16 drought and the 2014 flood that occurred in the Madeira basin. For the Negro basin and from the point of view of wetlands, the 2015 nonflooded season was 55% more severe than the average of the nonflooded season during the 2011–18 period. For the Paru, Trombetas, Negro, and Solimões basins, we found that a delay in the arrival of the flooded season led to a weak flood season in terms of severity. No correlation between the onset of the flooded season and its severity was found for the Madeira, Xingu, and Tapajós basins. Future hydrometeorological monitoring systems would benefit from including, in addition to variables such as river discharge and water elevation, precipitation, and vegetation dynamics, a severity index based on water surfaces as proposed in this study.

Soil Sustainability Assessment for Rice Cropping Recommendations: A Case Study in An Giang Province, Vietnam

Background: The study aimed to identify the sustainability of soil fertility and social-economic factors for major rice cropping and offer suggestions for sustainable rice cropping. Methods: The kite sustainability assessment is a multi-objective assessment method based on standardized scoring formulas built on land assessment criteria with limiting factors. It used the AHP method to determine how different critical factors affect whether a place is good for growing rice. The soil fertility, economics, and social factors were also significant in determining whether or not rice could grow there and how well it might do. Results: The soil fertility status of the two main rice cropping in the study area has low pH, high organic matter content, high cation exchange capacity, and high clay content. Besides, the soil has a good water-holding capacity, high total N content, and average total P content. Utilizing the AHP method, it was determined that soil fertility, economic, and social factors were the second-most significant factors in determining the suitability of land for agriculture as well as the possibility and performance of rice. While the double-rice cropping model is only sustainable regarding fertility, the triple-rice cropping model achieves the sustainability goal of economic, social, and soil fertility indicators. Two rice cropping seasons, lWS-mSA (double rice) and mWS-eSA-eAW (triple rice), achieve a balanced level in all indicators of level 2 of soil fertility. Therefore, in both models, a system that reaches a sustainable level exists. Even so, the lWS-mSA cropping season could be less harmful to the environment than the mWS-eSA-eAW season in terms of the environmental group.

Deriner Baraj Gölü Zooplanktonu (Artvin-Türkiye)

This study was carried out seasonally at 8 stations determined in Deriner Dam Lake between 2020 and 2021. In order to determine the seasonal zooplankton taxon diversity and richness at the determined stations, the samples were collected in the surface water with a plankton net with a pore size of 55 µm. In the zooplankton distribution of Deriner Dam Lake, more zooplankton was recorded in autumn and spring seasons compared to other seasons in terms of both the number of species and the number of individuals. Although the number of Rotifera species is high, the most common species in terms of individual numbers belong to the Copepoda group. Asplanchna sieboldi from Rotifera, Acanhopdiaptomus denticornis from Copepoda and Daphnia cucullata from Cladocera were the dominant species of their groups

Model-simulated hydroclimate in the East Asian summer monsoon region during past and future climate: a pilot study with a moisture source perspective

Abstract. Here we present a pilot study of the sensitivity of summer monsoon precipitation in the Yangtze River Valley (YRV; 110–122∘ E and 27–33∘ N, eastern China) to climatic boundary conditions from the Last Glacial Maximum (LGM), pre-industrial conditions, and the Representative Concentration Pathway 6 emission scenario from two different climate models. Using a quantitative Lagrangian moisture source diagnostic based on backward trajectories, we are able to interpret changes in precipitation amount and seasonality in terms of processes at the source regions and during transport that contribute to YRV precipitation. Thereby, we gain insight into influential processes and characteristics related to precipitation variability and the sensitivity of the summer monsoon hydroclimate in East Asia to boundary-condition changes in models. Comparing 10-year time slices similar to present-day conditions from the NorESM1-M and CAM5.1 models to reanalysis data reveals overall similar moisture source regions, albeit with a tendency for a more local precipitation origin in the climate models. The general characteristics of the moisture sources and moisture transport in the YRV are relatively stable across different climate forcings, both concerning the mean location of source regions, transport distance, and the relative contributions of moisture from land and ocean areas. Changes regarding regional precipitation contributions from the East Asian continent indicate that precipitation recycling responds to different climate forcings. We interpret these findings such that models to first order respond with a scaling rather than reorganisation of the hydroclimate to climatic forcing, while land–atmosphere interactions play an important, but secondary, role. If the model simulations are accurate, the moisture source regions and thus the general processes of precipitation in the YRV could remain relatively stable across different climates. However, some differences in moisture source conditions are larger between the different climate models than between different climatic boundary conditions in the same model. It may therefore be possible that current climate models underestimate the potential for non-linear responses to changing boundary conditions, for example due to precipitation recycling. Although limited by the relatively short analysis period, our findings demonstrate that the diagnosis of moisture sources provides a useful additional perspective for understanding and quantifying precipitation mechanisms and the hydroclimate simulated by models and enables more detailed evaluation of model simulations, for example using paleoclimate records.

Atmospheric Mercury Isotope Shifts in Response to Mercury Emissions from Underground Coal Fires.

Pollutant emissions from coal fires have caused serious concerns in major coal-producing countries. Great efforts have been devoted to suppressing them in China, notably at the notorious Wuda Coalfield in Inner Mongolia. Recent surveys revealed that while fires in this coalfield have been nearly extinguished near the surface, they persist underground. However, the impacts of Hg volatilized from underground coal fires remain unclear. Here, we measured concentrations and isotope compositions of atmospheric Hg in both gaseous and particulate phases at an urban site near the Wuda Coalfield. The atmospheric Hg displayed strong seasonality in terms of both Hg concentrations (5-7-fold higher in fall than in winter) and isotope compositions. Combining characteristic isotope compositions of potential Hg sources and air mass trajectories, we conclude that underground coal fires were still emitting large amounts of Hg into the atmosphere that have been transported to the adjacent urban area in the prevailing downwind direction. The other local anthropogenic Hg emissions were only evident in the urban atmosphere when the arriving air masses did not pass directly through the coalfield. Our study demonstrates that atmospheric Hg isotope measurement is a useful tool for detecting concealed underground coal fires.

Repeated UAV Observations and Digital Modeling for Surface Change Detection in Ring Structure Crater Margin in Plateau

As UAV technology has been leaping forward, small consumer-grade UAVs equipped with optical sensors are capable of easily acquiring high-resolution images, which show bright prospects in a wide variety of terrains and different fields. First, the crater rim landscape of the Dinosaur Valley ring formation located on the central Yunnan Plateau served as the object of the surface change detection experiment, and two repetitive UAV ground observations of the study area were performed at the same altitude of 180 m with DJI Phantom 4 RTK in the rainy season (P1) and the dry season (P2). Subsequently, the UAV-SfM digital three-dimensional (3D) modeling method was adopted to build digital models of the study area at two points in time, which comprised the Digital Surface Model (DSM), Digital Orthomosaic Model (DOM), and Dense Image Matching (DIM) point cloud. Lastly, a quantitative analysis of the surface changes at the pit edge was performed using the point-surface-body surface morphological characterization method based on the digital model. As indicated by the results, (1) the elevation detection of the corresponding check points of the two DSM periods yielded a maximum positive difference of 0.2650 m and a maximum negative value of −0.2279 m in the first period, as well as a maximum positive difference of 0.2470 m and a maximum negative value of −0.2589 m in the second period. (2) In the change detection of the two DOM periods, the vegetation was 9.99% higher in the wet season than in the dry season in terms of coverage, whereas the bare soil was 10.54% more covered than the wet season. (3) In general, the M3C2-PM distances of the P1 point cloud and the P2 point cloud were concentrated in the interval (−0.2,0.2), whereas the percentage of the interval (−0.1,0) accounted for 26.69% of all intervals. The numerical model of UAV-SfM was employed for comprehensive change detection analysis. As revealed by the result of the point elevation difference in the constant area, the technique can conform to the requirements of earth observation with certain accuracy. The change area suggested that the test area can be affected by natural conditions to a certain extent, such that the multi-source data can be integrated to conduct more comprehensive detection analysis.

Sympatric rodents in a desert shrubland differ in arthropod consumption

The foraging ecology of sympatric mammals within xeric habitats is poorly understood. In this study, we surveyed the diets of two sympatric woodrat species, Neotoma bryanti, N. lepida and their hybrids in a desert shrubland during the dry season using stable isotope analyses of hair and arthropod DNA metabarcoding of feces. We found that woodrats regardless of their ancestry fed on similar plants during the same season across multiple years. However, stable isotope analyses and arthropod metabarcoding were consistent with greater arthropod ingestion by N. bryanti compared to N. lepida or hybrids. These results suggest that while the diets of these sympatric woodrats largely overlap during the dry season in terms of the plant components, they differ in terms of arthropod ingestion. This arthropod feeding may serve to reduce interspecific competition or act as dietary supplementation during nutritionally challenging periods. These results demonstrate that integrating DNA metabarcoding approaches with stable isotope tracers enables a more rigorous evaluation of animal foraging behavior.

Changes in ecological and health risk assessment indices of potentially toxic elements associated with ambient air particulate matters (PM2.5) in response to source, land use and temporal variation in Isfahan city, Iran

Fine particles and their associated compounds such as potentially toxic elements (PTEs) are critical pollutants in ambient air of industrialized urban areas that adversely affect human health. The aim of this study was to determine the pollution, ecological and human health risk assessment of potentially toxic elements in PM2.5 using various indices spatiotemporally, in case of Isfahan city, Iran. Besides, the manuscript objective was to identify an overview and a comprehensive perspective of the potentially toxic elements pollution and risk in PM2.5, affected by anthropogenic and natural source and inversion time using various ecological and health risk assessment indices. The concentrations of 17 PTEs associated with PM2.5 from 40 sampling sites in ambient air of Isfahan city, Iran, were measured. Then their ecological risks (including individual and overall indices) and human health risks (carcinogenic and non-carcinogenic) were assessed. The results of the ecological risk analyses revealed traffic (particularly diesel vehicles) and industrial activities (metal smelting plants, brick and cement factories) together with natural sources (dust storms) affected the risk of PTEs. Among the elements, As, Pb, Cr, and Cd showed the highest health risk, respectively, and only As, Pb, and Cd crossed the carcinogenicity threshold in some sites. Cu, As, and Cd showed the level of highest, average, and potential ecological risk, respectively. Although fall was the most critical season in terms of PTEs ecological risk due to temperature inversion, the human health risk was the highest in summer mainly because of PTEs associated with dust storms. This revealed that health and ecological risk indices vary depending on the source of PM2.5, type and concentration of associated PTEs at different times. The risk trend for different sampling sites was urban > industrial > bus terminal showing the necessity of air pollution control in urban areas with a high population density.

THE USE OF CORRELATION ANALYSIS IN ASSESSING THE UNCERTAINTY OF THE INFLUENCE OF EXTERNAL FACTORS ON THE RESULT OF THERMAL CONTROL OF BIOLOGICAL OBJECTS

Research task. The paper considers the solution of the scientific and practical problem of determining the influence of external factors on the result of non-contact thermal control of biological objects. Object of study. A human was chosen as a biological object. Research progress. Establishing the correlation dependence was carried out in the two most opposite seasons in terms of climate parameters – winter and summer. One person was taken for the study, whose temperature was measured using a FLIR Vue Pro R 640 thermal imager mounted on a Cheerson CX-20 quadcopter at one-hour intervals throughout the day. The data were obtained in the summer period on August 10, 2022. In the winter period, measurements were carried out on January 20, 2022. Research results. Conclusions were made about the absence of a linear correlation between humidity, air temperature and body temperature of BO in the summer period. On the contrary, a high correlation was established between all the indicated parameters in the winter period. Conclusions were made about the need to develop a mathematical model of the factor influence on the thermal control result of the BO in order to obtain analytical ratios for evaluating the quantitative information on each of the temperature control indicators under the factor influence on the conversion function of these indicators. It is noted that such a model will make it possible to rank the indicators of temperature control according to the decrease in their sensitivity to changes in the levels of the temperature control parameter. Usage suggestions. It is proposed to calculate the correcting coefficients to determine the exact value of the body temperature, because it was experimentally established that the values of the body temperature in the winter period differ from the actual values precisely due to the influence of the temperature of the external environment.

Seasonal distribution of phytoplankton in river Gauthami-Godavari, Andhra Pradesh

The present study was investigated to evaluate the seasonal variability of phytoplankton species at the places Vruddha and Bhairavapalem along the stretch of river Godavari in Konaseema region, Andhra Pradesh. A total of 123 phytoplankton species were identified during the study period (2015-2017) in which diatoms contributes 91, dinoflagellates -26, Blue Green Algae-1 chlorphyceae-4. Dissimilarity in phytoplankton species composition was noticed in all seasons. Diatoms found as the dominant prevailing phytoplankton group in all seasons in terms of number of species and abundance. Diatom species viz., Coscinodiscus sp., Thalassiothrix sp., Skeletonema costatus were ubiquitous off Godavari estuary throughout the year. Diatoms are the most abundant group dominated in late winter and early spring bloom whereas dinoflagellates, dominate during the late spring blooms.

Seasonal and climatic factors have a significant influence on fertility associated sperm phenomic attributes in crossbred breeding bulls (Bos taurus × Bos indicus).

Although seasonal variations in semen quality and fertility have been studied to a considerable extent in breeding bulls, the effect of climatic variables on sperm functional competency has not been understood in detail. The present study analyzed sperm functional parameters in breeding bulls, over a period of 1year, and assessed the effect of climatic variables on fertility associated sperm parameters. Seasons were categorized into summer, rainy, autumn, and winter based on the meteorological data. Semen was collected from crossbred bulls (n = 7) across the seasons and evaluated for functional membrane integrity, acrosome reaction status, protamine deficiency, capacitation, and lipid peroxidation status using specific fluorescent probes. The results of the present study revealed that bulls produced higher (p < 0.05) viable and acrosome intact spermatozoa during the autumn. The proportion of uncapacitated spermatozoa was also higher (p < 0.05) during autumn. Further, correlation of sperm functional attributes with environmental variables revealed that sperm viability was significantly (p < 0.05) and negatively correlated with daylength and temperature; acrosomal integrity was significantly (p < 0.05) and negatively correlated with day length; and protamine deficiency had significant (p < 0.05) positive correlation with day length and average temperature, and negative correlation with relative humidity. It was concluded that semen produced during autumn was superior to the semen produced during other seasons in terms of sperm functional competencies required for fertility.

Effects of different levels of metal exposure and precipitation regimes on chlorophyll a fluorescence parameters in a coastal Brazilian restinga species

This work aimed to investigate whether there was a relationship between precipitation regimes and concentrations of trace elements (Cu, Mn, Fe and Zn) deposited on the coast from ore tailings released in the Mariana disaster (Minas Gerais, Brazil) in 2015. We also sought to answer if there would be a synergistic effect of increased precipitation and trace element levels affecting photosynthesis. The combination of these factors was evaluated using the dynamics of chlorophyll a fluorescence in plants of Byrsonima sericea, a shrub species, used as a model in restinga studies. In situ studies showed that, throughout the year, the photosynthetic performance of B. sericea exhibited seasonal variability. The combination of both trace elements in soil and leaves and precipitation regimes drives the variability of the chlorophyll fluorescence parameters on restinga vegetation. Significant negative correlations were observed between the high concentrations of metals (mainly Cu and Fe) and photosynthetic performance indices and the oxygen evolving complex (OEC) activity in PSII. Combined effects of high concentrations of Cu, Fe, Mn and Zn and different rainfall regimes were manifested in the alteration of Chlorophyll a Fluorescence parameters related to quantum efficiency, specific energy fluxes and performance indices. Data presented in this study conclusively proved that Byrsonima sericea respond to different environmental conditions and that the dry season was more damaging to plants than the rainy season in terms of the impacts of both the rain regime and metal availability; metal availability also varied according to rainfall patterns and transport via marine aerosols.

Indoor environmental quality in naturally ventilated schools of a dusty region: Excess health risks and effect of heating and desert dust transport.

Indoor air quality (IAQ) is impacted by polluted outdoor air in naturally ventilated schools, especially in places where both anthropogenic and natural sources of ambient air pollution exist. CO2 , PM2.5 , PM10 , temperature, relative humidity (RH), and noise were measured in five naturally ventilated primary schools in City of Sanliurfa, in a dusty region of Turkey, Southeast Anatolia. Excess risk levels were estimated for particulate matter. Investigation was conducted through an educational year including two seasons in terms of anthropogenic effect, that is, heating/non-heating, and natural effect, that is, desert dust transport/non-dust transport. The median CO2 concentration was measured to be >1000 ppm in all seasons/schools. Temperature and RH fell out of the comfort zone in October-December, during which pollutant concentrations were considerably increased, specifically in November, that heating and dust transport periods coincide. The overall mean indoor PM10 and PM2.5 levels were 58 and 31.8μg/m3 , respectively. Risk assessment indicate that both short (incidence of asthma symptoms in asthmatic children) and long-term (prevalence of bronchitis) effects are considerable with 10.9 (2.4-19.6)% and 19.5 (2.2-38.8)%, respectively. The findings suggest that mechanical ventilation retrofitting with particle filtration is needed to mitigate potential negative health consequences on children.

Combined role of ENSO and IOD on compound drought and heatwaves in Australia using two CMIP6 large ensembles

Compound drought and heatwaves (CDHWs) can cause significant socio-economic and ecological impacts. A better understanding of historical spatiotemporal changes of Australian CDHWs and their underlying physical mechanisms can help improve their predictability. We analyse changes in Australian CDHW metrics in the extended summer season (November to March) during the period 1958–2020. Our results suggest that CDHWs increased significantly in terms of their frequency, duration, amplitude, and severity in the recent period (1989/90–2019/20) relative to a historical period (1958/59–1988/89), particularly in eastern Australia. We further analysed the influence of co-occurring modes of El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on the frequency and severity of Australian CDHWs using two Coupled Model Intercomparison Project phase 6 (CMIP6) single model initial-condition large ensembles. We found that frequency, duration, and severity of CDHWs are significantly increased during strong El Niño phases across northeast Australia compared to neutral ENSO and IOD conditions. This increase is widespread over northeast and southeast Australia during the concurrence of strong El Niños and moderate-strong positive IOD events. Our results show that an extreme CDHW season in terms of their frequency, duration, and severity occurs one out of every two seasons of strong El Niño over the northeast Australia. Moreover, the same applies for the co-occurring strong El Niño and positive IOD over the northeast and southeast Australia as well. Our results highlight the importance of ENSO and IOD combinations for Australian CDHW events. Our findings provide insights into the importance of climate variability in driving Australian CDHWs.

Seasonal Variation of Thermospheric Composition Observed by NASA GOLD.

We examine characteristics of the seasonal variation of thermospheric composition using column number density ratio ∑O/N 2 observed by the NASA Global Observations of Limb and Disk (GOLD) mission from low‐mid to mid‐high latitudes. We also use ∑O/N 2 derived from the Global Ultraviolet Imager (GUVI) limb measurements onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and estimated by the NRLMSISE‐00 empirical model to aid our investigation. We found that the ∑O/N 2 seasonal variation is hemispherically asymmetric: in the southern hemisphere, it exhibits the well‐known annual and semiannual pattern, with highs near the equinoxes, and primary and secondary lows near the solstices. In the northern hemisphere, it is dominated by an annual variation, with a minor semiannual component with the highs shifting toward the wintertime. We also found that the durations of the December and June solstice seasons in terms of ∑O/N 2 are highly variable with longitude. Our hypothesis is that ion‐neutral collisional heating in the equatorial ionization anomaly region, ion drag, and auroral Joule heating play substantial roles in this longitudinal dependency. Finally, the rate of change in ∑O/N 2 from one solstice season to the other is dependent on latitude, with more dramatic changes at higher latitudes.