Equatorial Region Research Articles

Morphology of equatorial F-region irregularities over the Indian longitude sector using GPS-derived ROTI observations

The occurrence characteristics of Equatorial F-region Irregularities (EFIs) along the Indian longitude sector are investigated using GPS-derived ROTI observations from 2010 to 2023, under both quiet and disturbed geomagnetic conditions. The analysis of the results emphasizes a strong dependence of EFIs occurrence on solar cycle variation. Additionally, the EFIs are more intense at the EIA regions under maximum solar activity periods attributed to the high ambient electron density in the F-layer. The occurrence of EFIs is found to be severe and frequently observed in equinox seasons in contrast to solstice seasons. Also, the occurrence of EFIs exhibits equinoctial asymmetry with more intense EFIs in the spring equinox than autumn equinox during the peak and declining periods of the solar cycle. Conversely, severe EFIs are observed during autumn equinox than spring equinox in the ascending phase of the solar cycle. The seasonal occurrence probability of EFIs is highest in the equinox seasons, following the winter solstice, and summer solstice in high solar activity conditions. Investigations of EFIs during two prominent geomagnetic storm events (17 March 2015 and 08 September 2017) during the study period show that the storm-induced Prompt Penetration Electric Fields (PPEFs) modulated the regular intensity of dusk time Pre-Reversal Enhancement (PRE), resulting in poleward expansion of ionospheric irregularities up to mid-latitude regions with spatial time lag. However, storm-induced westward electric fields and oscillating IMF Bz created Counter Electrojet (CEJ) like conditions, suppressing the dusk time ionospheric irregularities over dip equatorial and low-latitude regions on 17 March 2013. This study provides a comprehensive understanding of how ionospheric irregularities manifest under varying conditions, thereby supporting further research on substantiating the spatiotemporal EFIs characteristics and their predictions over the region.

Rainfall Estimation Model in Seasonal Zone and Non-Seasonal Zone Regions Using Weather Radar Imagery Based on a Gradient Boosting Algorithm

Indonesia, a country located in the equatorial region with hilly and valley lands surrounded by vast oceans, has complex rainfall patterns that can generally be classified into three types: equatorial, monsoon, and local. Rainfall estimates have only been derived based on local data and characteristics so far, and have not yet been developed based on universal data for all of Indonesia. This study aimed to develop a rainfall estimation model based on weather radar data throughout Indonesia using ensemble machine learning with the gradient boosting algorithm. The proposed rainfall estimation model is universal, can be applied to different rainfall pattern areas, and has a temporal resolution of 10 min. It is based on determining the root mean square error (RMSE) and R-squared (R2) values. Research was conducted in six areas with different rainfall patterns: Bandar Lampung and Banjarmasin with monsoon rain patterns, Pontianak and Deli Serdang with equatorial rain patterns, and the Gorontalo and Biak areas with local rain patterns. The analysis of the proposed model reveals that the best hyperparameters for the learning rate, maximum depth, and number of trees are 0.7, 3, and 50, respectively. The results demonstrate that the estimated rainfall in the six areas was very accurate, with RMSE < 2 mm/h and R2 > 0.7.

Morphology and ultrastructure of cicatricose spores found in an isolated sporangium-bearing structure of a schizaealean fern from the Lower Cretaceous rocks at Casal do Borracho, Torres Vedras, western Portugal

Fossil spores provide important insights into the evolutionary history of ferns, including their morphological changes and adaptations over time. The morphology and ultrastructure of trilete spores with cicatricose sculpture composed of sets of parallel or near-parallel ribs (muri) have been studied. Observations on the spores were performed using light microscopy, scanning electron microscopy, and transmission electron microscopy. The cicatricose spores were extracted from a single sporangium-bearing structure collected from Casal do Borracho mesofossil flora near Torres Vedras (Lusitanian Basin, western Portugal) from sediments belonging to the Almargem Formation, considered to be of late Barremian or early Aptian age (and possible younger than that). The sporangium-bearing structure of a schizaealean fern and in situ cicatricose spores are compared with the family Anemiaceae. On the basis of spore size and shape, laesura length, with about 20 proximal narrow ribs, oriented perpendicular to the spore sides, and three sets of distal ribs forming V-shaped patterns, the cicatricose spores in the present study are clearly assigned to the fossil-taxon Cicatricosisporites venustus. The spore ultrastructure includes a homogeneous exospore of a blechnoid type with a slight difference in the thickness in the proximal, distal, and equatorial regions. The morphology and ultrastructure of the studied spores are corresponded to Anemia type.

Retrieval of subsurface dissolved oxygen from surface oceanic parameters based on machine learning

Oceanic dissolved oxygen (DO) is crucial for oceanic material cycles and marine biological activities. However, obtaining subsurface DO values directly from satellite observations is limited due to the restricted observed depth. Therefore, it is essential to develop a connection between surface oceanic parameters and subsurface DO values. Machine learning (ML) methods can effectively grasp the complex relationship between input attributes and target variables, making them a valuable approach for estimating subsurface DO values based on surface oceanic parameters. In this study, the potential of ML methods for subsurface DO retrieval is analyzed. Among the selected ML methods, namely support vector regression (SVR), random forest (RF) regression, and extreme gradient boosting (XGBoosting) regression, the RF method generally demonstrates superior performance. As the depth increases, the accuracy of DO estimates tends to initially decrease, then gradually improve, with the poorest performance occurring at the depth of 600 dbar. The range of determination coefficients (R2) and root mean square error (RMSE) values based on the test dataset at different depths lies between 0.53 and 47.59 μmol/kg to 0.99 and 4.01 μmol/kg. In addition, compared to sea surface salinity (SSS) and sea surface chlorophyll-a (SCHL), sea surface temperature (SST) plays a more significant role in DO retrieval. Finally, compared to the pelagic interactions scheme for carbon and ecosystem studies (PISCES) model, the RF method achieves higher retrieval accuracies at depths above 700 dbar. In the deep ocean, the primary differences in DO values obtained from the RF method and the PISCES model-based method are noticeable in the vicinity of the equatorial region.

Data-driven modeling of equatorial atmospheric waves: The role of moisture and nonlinearity on global-scale instabilities and propagation speeds.

The equatorial region of the Earth's atmosphere serves as both a significant locus for phenomena, including the Madden-Julian Oscillation (MJO), and a source of formidable complexity. This complexity arises from the intricate interplay between nonlinearity and thermodynamic processes, particularly those involving moisture. In this study, we employ a normal mode decomposition of atmospheric reanalysis ERA-5 datasets to investigate the influence of nonlinearity and moisture on amplitude growth, propagation speed, and mode coupling associated with equatorially trapped waves. We focus our analysis on global-scale baroclinic Kelvin and Rossby waves, recognized as crucial components contributing to the variability of the MJO. We examine the dependence of wave amplitudes on the background moisture field in the equatorial region, as measured by total column water vapor. Our analysis demonstrates the crucial role of moisture in exciting these waves. We further investigate the dependence of the propagation speed of the waves on their amplitudes and the background moisture field. Our analysis reveals a robust correlation between the phase speed of the normal modes and their corresponding amplitude, whereas a weaker correlation is found between the eigenmodes' phase speed and the moisture field. Hence, our findings suggest that moisture plays a role in exciting the global-scale Rossby-Kelvin structure of the MJO. In this context, the propagation speed of the eigenmodes is mainly influenced by their amplitudes, underscoring the significant role of nonlinearity in wave propagation.

Comparative macroanatomical and scanning electron microscopy study of the eyeball in brachycephalic and mesocephalic dog breeds.

The anatomical structures forming the eyeball differ among dog breeds, both morphologically and morphometrically. This study was aimed at determining the morphometric values of the eyeball layers of different dog breeds and the morphological structures of these layers using scanning electron microscopy. Thirty-two eyeballs of 17 dogs belonging to 9 different breeds that died from traffic accidents, falling from a height, and naturally were used. These dog breeds were grouped according to their brachycephalic and mesocephalic skull structures, and morphometric measurements of the eyeballs of each group were obtained. Scanning electron microscopy was used to examine the morphological structure of the eyeball layers. The studied dogs' eyeballs comprised three layers: outer, middle, and inner. Thickness measurements obtained from three different regions of the eyeball indicated that the equatorial region was the thinnest among all dog breeds. Moreover, the cornea, which is covered by the sclera along its edges, was thicker at the corneal limbus than at the corneal vertex. A positive correlation was observed between lens thickness and the number of ciliary processes, which varied according to the dogs' head structures. Notably, depression was observed in the posterior surface of the lens in brachycephalic dogs. The morphometric values of the eyeball layers in the brachycephalic and mesocephalic dog breeds were also determined. These values will help researchers study this subject, and the determined morphometric and morphological values will contribute to the anatomy literature. RESEARCH HIGHLIGHTS: This comprehensive study investigates the morphometric and morphological variations in the eyeball layers of different dog breeds, utilizing scanning electron microscopy to analyze eyeballs. It reveals significant breed-specific differences, particularly between brachycephalic and mesocephalic dogs, regarding eyeball layer thickness, corneal structure, lens thickness, and the number of ciliary processes.

The impact of oceanographic factors on the composition and abundance of mesopelagic fish communities in the central and equatorial Atlantic

This paper presents an overview of the composition and abundance of pelagic fish communities collected during the 43rd cruise of the R/V ′Akademik Sergey Vavilov' on the transect in the central Atlantic, from the Azores to the Equator, in autumn 2016. Samples were taken only at night with a Samyshev-Aseev modified Isaacs-Kidd non-closing midwater pelagic trawl (SAMT) at 18 stations from two depth of 0–200 and 0–700 m. The study recorded 112 species of juvenile and adult mesopelagic fishes belonging to 20 families at the sampled stations. The statistical analysis indicated notable disparities in the fish communities that were caught at depths of 0–200 and 0–700 m. Our study suggests that there are notable differences in pelagic fish associations between the North Atlantic anticyclonic gyre zone and the equatorial jets region, at both depths analyzed. These differences are most likely the result of variations in hydro-physical and other environmental parameters. It has been observed that deep-sea fish communities in the equatorial and central North Atlantic are capable of inhabiting at the same time multiple habitats that exhibit varying physical and chemical structures of water masses. This phenomenon highlights the remarkable ecological adaptability of the species that make up mesopelagic deep-sea communities, as well as their wide geographical distribution. The higher abundance and diversity of mesopelagic fishes observed at stations located above the Mid-Atlantic Ridge may be due to a general decrease in depth over the ridge compared to the surrounding regions and/or local circulations occurring over its crests. Thus, the tops and slopes of seamounts may become unique concentrations of mesopelagic fishes for a limited time due to their topography.

Significant Reduction of Potential Exposure to Extreme Marine Heatwaves by Achieving Carbon Neutrality

AbstractMarine heatwave (MHW), a prolonged period of anomalously warm seawater, has a catastrophic repercussion on marine ecosystems. With global warming, MHWs have become increasingly frequent, intense, and prolonged. To avoid irreversible damages from such extreme events, net‐zero carbon emissions by the 2050s, called carbon neutrality, were proposed. Here, we evaluate the impact of carbon neutrality on MHWs in the late 21st century using multi‐model projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) Shared Socioeconomic Pathway (SSP) 1–1.9 and SSP3‐7.0 scenarios. It is found that if the current regional rivalry over carbon emissions continues (i.e., SSP3‐7.0), the MHWs in the late 21st century will become stronger and longer than historical ones, especially in the western boundary current and equatorial current regions. Approximately 68% of the global ocean will be exposed to permanent MHWs, regionally 93% in the Indian Ocean, 76% in the Pacific Ocean, 68% in the Atlantic Ocean, 65% in the Coastal Ocean, and 48% in the Southern Ocean. Such MHWs can be significantly reduced by achieving carbon neutrality (i.e., SSP1‐1.9). In particular, the spatial proportion of the ocean exposed to permanent MHWs can be reduced to as low as 0.02%–0.07%, depending on the regions. This result underscores the critical importance of ongoing efforts to achieve net‐zero carbon emissions to reduce the potential ecological risks induced by extreme MHWs.

Measurements of low-energy, re-entrant albedo protons by the HEPD-01 space-borne detector

Cosmic rays’ interactions with the residual atmosphere surrounding the Earth produce a variety of particles, like electrons, positrons, protons, anti-protons, and Helium nuclei that can be observed below the local geomagnetic cutoff. In this work, we present new measurements of downward-going, albedo proton fluxes with kinetic energy in the range ∼40–∼250 MeV, performed by the High-Energy Particle Detector (HEPD-01) on board of the China Seismo-Electromagnetic Satellite - CSES-01 - at an altitude of ∼500 km. Employing a dedicated trajectory-tracing simulation routine, the protons collected by HEPD-01 are classified into quasi-trapped (QT), long lifetime (≳10 s) particles concentrating in the equatorial region of the Earth, and un-trapped (UT), distributed at all latitudes; the latter includes both precipitating short lifetime particles (UTS) and pseudo-trapped long lifetime (UTL) populations, abundant in the so-called penumbra regions. The temporal trend of re-entrant protons between 2018 and 2022 is also reported, assessing the stability of such population during the data-taking period of HEPD-01; this highlights their independence from the long-term modulating effect of the solar activity.

Complexity and Nonlinear Dependence of Ionospheric Electron Content and Doppler Frequency Shifts in Propagating HF Radio Signals within Equatorial Regions

Complexity and Nonlinear Dependence of Ionospheric Electron Content and Doppler Frequency Shifts in Propagating HF Radio Signals within Equatorial Regions

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.

Predicted range expansion of Prostephanus truncatus (Coleoptera: Bostrichidae) under projected climate change scenarios.

The larger grain borer (Prostephanus truncatus [Horn] [Coleoptera: Bostrichidae]) is a wood-boring insect native to Central America and adapted to stored maize and cassava. It was accidentally introduced to Tanzania and became a pest across central Africa. Unlike many grain pests, P. truncatus populations can establish and move within forests. Consequently, novel infestations can occur without human influence. The objectives of our study were to (i) develop an updated current suitability projection for P. truncatus, (ii) assess its potential future distribution under different climate change scenarios, and (iii) identify climate variables that best inform the model. We used WALLACE and MaxEnt to predict potential global distribution by incorporating bioclimatic variables and occurrence records. Future models were projected for 2050 and 2070 with Representative Concentration Pathways (RCPs) 2.6 (low change) and 8.5 (high change). Distribution was most limited by high precipitation and cold temperatures. Globally, highly suitable areas (> 75%) primarily occurred along coastal and equatorial regions with novel areas in northern South America, India, southeastern Asia, Indonesia, and the Philippines, totaling 7% under current conditions. Highly suitable areas at RCPs 2.6 and 8.5 are estimated to increase to 12% and 15%, respectively, by 2050 and increase to 19% in 2070 under RCP 8.5. Centroids of highly suitable areas show distribution centers moving more inshore and away from the equator. Notably, the result is a range expansion, not a shift. Results can be used to decrease biosecurity risks through more spatially explicit and timely surveillance programs for targeting the exclusion of this pest.

PlanetiQ Radio Occultation: Preliminary Comparative Analysis of Neutral Profiles vs. COSMIC and NWP Models

Radio Occultation (RO) is pivotal for profiling the neutral and ionized atmosphere, with the PlanetiQ mission, via its GNOMES satellites, striving to establish an advanced atmospheric observing system. However, an assessment of the spatiotemporal distributions of PlanetiQ observations and comparisons with reliable datasets are lacking. This study addresses this gap by examining the temporal and spatial distribution of RO observations from PlanetiQ during its initial 198 operational days in 2023, alongside comparisons with COSMIC and Numerical Weather Prediction (NWP) models. Data from GN02, GN03, and GN04 satellites, yielding 1099, 1313, and 1843 RO events per day, respectively, were analyzed. The satellite constellation’s observations demonstrate a generally well-distributed pattern, albeit minor deficiencies in equatorial and polar regions. Single-profile comparisons with COSMIC data reveal strong correlations for pressure, temperature, Water Vapor Pressure (WVP), and refractivity profiles, with temperature exhibiting larger variations (RMSE = 1.24 °C). Statistical analyses confirm statistically insignificant differences between the PlanetiQ and COSMIC profiles at the same spatio-temporal coordinates. Comparisons with NWP models show slight differences with GFS, with overall RMSE values of 0.23 mb (WVP), 0.6 mb (pressure), 1.3 (refractivity), and 1.5 °C (temperature). However, assessments against GFS/ECMWF models indicate overall compatibility, with insignificant differences between PlanetiQ profiles and model observations.

Modeling microbial carbon fluxes and stocks in global soils from 1901 to 2016

Abstract. Soil microbes play a crucial role in the carbon (C) cycle; however, they have been overlooked in predicting the terrestrial C cycle. We applied a microbial-explicit Earth system model – the Community Land Model-Microbe (CLM-Microbe) – to investigate the dynamics of soil microbes during 1901 to 2016. The CLM-Microbe model was able to reproduce the variations of gross (GPP) and net (NPP) primary productivity, heterotrophic (HR) and soil (SR) respiration, microbial (MBC) biomass C in fungi (FBC) and bacteria (BBC) in the top 30 cm and 1 m, and dissolved (DOC) and soil organic C (SOC) in the top 30 cm and 1 m during 1901–2016. During the study period, simulated C variables increased by approximately 12 PgC yr−1 for HR, 25 PgC yr−1 for SR, 1.0 PgC for FBC and 0.4 PgC for BBC in 0–30 cm, and 1.2 PgC for FBC and 0.7 PgC for BBC in 0–1 m. Increases in microbial C fluxes and pools were widely found, particularly at high latitudes and in equatorial regions, but we also observed their decreases in some grids. Overall, the area-weighted averages of HR, SR, FBC, and BBC in the top 1 m were significantly correlated with those of soil moisture and soil temperature in the top 1 m. These results suggested that microbial C fluxes and pools were jointly governed by vegetation C input and soil temperature and moisture. Our simulations revealed the spatial and temporal patterns of microbial C fluxes and pools in response to environmental change, laying the foundation for an improved understanding of soil microbial roles in the global terrestrial C cycle.

The Signature of Sporadic E of an Equatorial Ionosphere of the Low Latitude Region

Sporadic E is usually referred to as the large unpredictable formation of regions of very high electron density in the E region as one of the anomalies that is present in the equatorial region. This work studies the variability of sporadic E in the region with respect to the propagation of low frequency communication and impact on the equatorial region during the occurrence of this anomaly. Hourly data for the year 2010, a year of low solar activity obtained in-situ from a Digisonde Portable Sounder (DPS-4) from the African sector, Ilorin, Nigeria (8.5oN, 4.5oE, -2.96 dip) and the Southern American sector online at Jicamarca, Peru (12 oS, 76.8 oW, 0.74 dip) and Fortaleza, Brazil (3 oS, 38 oW, -7.03dip) were used for this study. The result obtained shows that sporadic E is usually observed at the region during the daytime and early evening (0600- 1700 local time) and is more prevalent during solstice months. Two types of sporadic E were observed in the region: blanket and transparent sporadic E. 12% of the transparent sporadic E was observed during the March equinox while 9% of blanket sporadic E was observed during this period; September equinox shows 15% of transparent and 7% blanket sporadic E respectively, while June solstice has 21% transparent and 7% blanket sporadic E. During the December solstices, 14% transparent and 7% blanket sporadic E was observed. During the March equinox, the blanket sporadic E was observed around 0200 hour local time, and that of the transparent sporadic E at about 1000 hour local time. Observation during the September equinox shows that it occurs around 1100 hour and 0200 hour respectively. It was observed that there is no correlation between sporadic E and geomagnetic storm. Sporadic E has been observed to be one of the anomalies that are responsible for the scintillation and scattering of the lower frequency signal in the said region when present.

Seasonal to interannual variations of daily growth rate of a Tridacna shell from Palau Island, western Pacific, and paleoclimatic implications

Seasonal-interannual climate change is an important component of Earth's climate system and has a significant impact on ecosystems and social systems. However, the short-run of modern observational data limits our understanding of the seasonal-interannual climates on long-term timescales. The natural archives can provide information on climate change before the industrial period, but most of their temporal resolution is too low to capture the seasonal-interannual climate signals. Tridacna spp. is the largest marine bivalve, and its shell has the potential to trace climatic/environmental changes on a daily to interannual scale. In this study, we investigated the daily growth pattern of a modern Tridacna gigas shell (PL-1) from Palau based on laser scanning confocal microscopy images. The results showed that the growth pattern of PL-1 was affected by effective solar radiation primarily, followed by nutrients on the seasonal timescale. On the interannual timescale, the growth rate of the shell was modulated by ENSO, which affected the effective solar radiation and nutrients accepted by Tridacna. The growth rate of Tridacna PL-1 was accelerated during the ENSO positive phase, and vice versa. However, due to a lack of situ observations, the effects of nutrients on Tridacna and the symbiotic zooxanthella in detail need to be further investigated. This study indicates that the daily growth rate of Tridacna shells in equatorial regions may have the potential to reconstruct seasonal-interannual climate/environment variations.

Estimation and Evaluation of Ionospheric Scintillations at Various NavIC Signal Frequencies using Real Time Data

The ionospheric scintillations affect radio waves from the NavIC satellites through the ionosphere. The ionospheric scintillations lower receiver tracking accuracy, integrity, and continuity. This paper presents the computation of ionosphere parameters such as TEC, ROTI and scintillation index (S) using pseudo range and Carrier to Noise density ratio (C/No) measurements of NavIC L5 and S-band signals. Also, investigates the ionospheric scintillations, which are common in the equatorial and low latitude region. The correlation between the amplitude scintillation index S4 and ROTI is investigated using real data of NavIC receiver at Osmania University, Hyderabad. The results obtained confirm that the scintillations impact varies with radio signal frequency and it is severe on low frequencies during post sunset hours at low latitude regions.

Classification of eco-zones from the factors and processes controlling phytoplankton biomass

Phytoplankton is of utmost importance to the marine ecosystem and, subsequently, to the Blue Economy. This study aims to explain the reasons for variability of phytoplankton by estimating the dependency of Chlorophyll-a (Chl-a) on various limiting factors using statistics. The global oceans are classified into coherent units that display similar sensitivity to changing parameters and processes using the k-means algorithm. The resulting six clusters are based on the limiting factors (PAR, iron, or nitrate) that modulate Chl-a yield divisions of the oceans, similar to regions of different trophic statuses. The clusters range from the polar and equatorial regions with high nutrient values limited by light, to open oceanic regions in downwelling gyres limited by nutrients. Some clusters also show a high dependency on marine dissolved iron. Further, oceans are also divided into eight clusters based on the processes (stratification, upwelling, topography, and solar insolation) that impact ocean productivity. The study shows that considering temporal variations is crucial for segregating oceans into ecological zones by utilizing correlation of time-series data into classification. Our results provide valuable insights into the regulation of phytoplankton abundance and its variability, which can help in understanding the implications of climate change and other anthropogenic effects on marine biology.

Occurrence Characteristics of Nighttime Merged EIA Based on NASA GOLD Observations from 2018 to 2023

The ionosphere equatorial ionization anomaly (EIA) is usually characterized by two plasma density maxima in the Earth’s equatorial region. Merged EIA (MEIA) is a unique phenomenon in the evolution of the EIA. Currently, the occurrence characteristics of MEIA are still not well understood. In this study, we investigate the occurrence characteristics of nighttime MEIA using NASA Global-scale Observations of the Limb and Disk (GOLD) observations between October 2018 and the end of 2023. We found that the occurrence of nighttime MEIA exhibits solar cycle, seasonal, and local time variations. The occurrence rate of the MEIA is inversely dependent on solar activity. Occurrence of the MEIA maximizes near the equinoxes, with a primary (secondary) low occurrence rate near the June (December) solstice. In addition, occurrences of the MEIA are suppressed during the pre-reversal enhancement (PRE), resulting in relatively fewer events. Furthermore, it was found that the occurrence of the MEIA is not significantly dependent on the strength of geomagnetic activity. As far as we know, this study represents the first instance of utilizing observations from GOLD observations to investigate the characteristics of MEIA occurrences and their correlations with solar activity, season, and local time.

Characteristics of surface urban heat islands in global cities of different scales: Trends and drivers

Given the increasing severity of the surface urban heat island (SUHI) phenomenon, urban residents face heightened heat stress. Consequently, mitigating the effects of SUHI becomes critically important to improve urban livability. Previous studies often overlooked the influence of city size on SUHI, focusing on the correlational between SUHI and drivers and sidelining the synergistic effects of multiple factors on SUHI. To address this issue, we introduced a novel method, “geographical convergent cross-mapping”, coupled with the random forest and Shapley value theory. Our results indicated that: Globally, SUHI exhibited a decreasing trend during day and night, with significant spatiotemporal disparities, and in cities of varying sizes, the cooling capacity of vegetation for SUHI showed significant variation. Locally, in arid cities spanning 150–200 km², vegetation contributed to cooling SUHI by up to 61 %, but this effect lessened in larger cities. Notably, in equatorial cities larger than 200 km², this capability dropped drastically during summer, from 49 % to 7 %. Long-term trends showed an increase in daytime SUHI in equatorial regions and large cities along the southeastern coasts of China and the United States. This study provides key insights for precise urban climate adaptation and sustainable planning in cities of different sizes.