Low Latitudes Research Articles

Post-spawning migration and habitat use of adult Pacific bluefin tuna (Thunnus orientalis) in the western North Pacific

Pacific bluefin tuna (PBF, Thunnus orientalis), migrate widely throughout the north Pacific Ocean during all life stages. However, studies on the migration of adult fish in the northwestern Pacific Ocean, where spawning occurs, are limited. This study investigated the post-spawning migration and habitat use of PBF from the major spawning grounds of the Nansei Islands (approximately 23–31° N), Japan, using pop-up satellite archival transmission (PAT) tags. The PAT tags were deployed on 15 PBF individuals (estimated fork lengths: 170–260 cm) in the late spawning season (May–June) of 2021, and tracking data were collected for 3–103 days. Four tagged PBF individuals moved > 2,500 km north to the Kuroshio-Oyashio transition region at high latitudes (40° N) in July–September, immediately after the spawning season. During this northward movement, these PBF showed a spatiotemporal change in their vertical behavior, adapting to regional thermal habitat differences. At low latitudes near the spawning grounds (23.6–29.6° N), the PBF dived to deep depths (mean: 162.8 m) to avoid the warm surface layer (mean: 28.6 °C); however, once they reached higher latitudes (36.6–44.9° N), they spent most of their time in the cool surface layer (mean: 18.5 °C; 22.3 m). Our findings suggest that adult PBF move from spawning grounds to physiologically suitable low-temperature, food-rich waters through long-distance movements, and then exhibit a habitat preference behavior characterized by repeated short-distance movements in response to the feeding environments at high latitudes.

Nighttime Tweek Characteristics in Mid–Low Latitudes: Insights from Long-Term VLF Observations in China

An improved method for identifying nighttime tweek signals in WHU VLF measurements was developed by redesigning the extraction process and validated through comparison with World-Wide Lightning Location Network (WWLLN) data. Using the enhanced method, 1,728,032 tweek signals were identified from four years (2018–2021) of VLF data, forming the most comprehensive tweek dataset for the mid–low latitude region in China. Statistical analysis reveals distinct nighttime variations in tweek occurrence rates, which increase from 18:00 LT to 20:00 LT, remain high until 04:00 LT, and gradually decrease towards sunrise. Seasonal differences in propagation distance are evident, ranging from ~2000 km in summer to ~4000 km in winter, corresponding to the seasonal shift of lightning activity. The cutoff frequency showed apparent daily and seasonal fluctuations, and the trends of daily variation are opposite between winter and summer. The annual variation in cutoff frequency presents a pattern different from previous cognition, with a minimum of 1.62 kHz in summer and a maximum of 1.68 kHz in winter, influenced by the magnetic cyclotron frequency at ionospheric reflection points. These findings improve the understanding of nighttime tweek characteristics and ionospheric dynamics in East Asia, offering valuable insights for ionospheric research and VLF communication systems.

Mesosphere and Lower Thermosphere Temperature Responses to the May 2024 Mother's Day Storm

AbstractThe storm‐time temperature difference with respect to its quiet‐time expectation (ΔT) in the mesosphere and lower thermosphere were studied during the extreme storms on 2024 Mother's Day and 2003 Halloween Day. The storm‐time ΔT were determined by performing daily zonal running mean on the temperature profiles in the ascending and descending nodes separately. The storm‐time ΔT had peak values of ≥25 K and extended downward to ∼100 km globally. Above 105 km, the global mean ΔT had values of ≥20 K in the early morning and of ≥15 K in the late afternoon during storm‐time. At high latitudes, the storm‐time ΔT was larger in the late afternoon than in the early morning. This is opposite to that at middle and low latitudes. Adiabatic warming/cooling caused by the heating‐induced circulation changes outside of the auroral oval is likely responsible for the local time and latitude dependence of the storm‐time ΔT.

Correlation Study of Auroral Currents with External Parameters During 10–12 October 2024 Superstorm

This study investigated the correlations between field-aligned currents (FACs), polar electrojets (PEJs), and external solar and geomagnetic activity parameters during the intense geomagnetic storm that occurred from 10 to 12 October 2024. Notably, the merging electric field (Em) had a greater impact on FACs and PEJs compared to the May 2024 storm, while the influence of solar wind pressure (Pd) was equally important in both storms. The peak FAC densities in the northern dawn (southern dusk) and nighttime sectors correlate strongly with Em, whereas Pd dominates in the northern dusk (southern dawn) and daytime sectors. For PEJs, Em correlates strongly with current densities in the northern dawn–dusk and southern nighttime sectors, while Pd is the primary correlated parameter on the dayside. FAC (PEJ) latitudes are most strongly influenced by Em (Pd or Dst) on the dawnside–duskside. Additionally, FACs and PEJs are mostly more intense on the dawnside than on the duskside and extend to lower latitudes at dusk than at dawn. Analysis of the May and October 2024 storms reveals that FACs in the summer hemisphere are generally stronger and situated at more poleward latitudes than those in the winter hemisphere. This pattern is largely driven by summer–winter variations in ionospheric conductivity, with some differences also arising from the asymmetric magnetic field geometry between the two hemispheres.

Gut microbiomes are largely unchanged when exposed to their amphibian host's latitudinally variable upper thermal limit.

Climate change will increase the frequency and severity of temperature extremes. Links between host thermal physiology and their gut microbiota suggest that organisms' responses to future climates may be mediated by their microbiomes, raising the question of how the thermal environment influences the microbiome itself. Vertebrate gut microbiomes influence the physiological plasticity of their hosts via effects on immunity, metabolism, and nutrient uptake. The gut microbiota of ectothermic vertebrates in particular are responsive to long-term, sub-lethal gradual increases in environmental temperature. Whether and how the gut microbiota respond to brief exposure to temperatures at the upper limit of host physiological tolerance (CTmax) is poorly understood but could have downstream effects on host fitness. We assayed the CTmax of wood frogs (Lithobates sylvaticus) from 15 populations across a 10° latitudinal gradient. We then characterized the gut microbiota of juveniles at two time points following exposure to CTmax. Frogs from higher latitudes had lower thermal tolerance (lower CTmax) than those from lower latitudes. Unexpectedly, exposure to upper survivable temperature had little to no detectable effect on the frogs' microbiota richness, stability, or composition. Instead, we found a strong effect of time in which frogs kept in recovery conditions for four days had less diverse, but more stable gut microbiota than those that had recovered for only one day, regardless of CTmax exposure. We conclude that while wood frogs from higher latitudes have reduced thermal tolerances than those from lower latitudes, their microbial communities are largely unaffected by brief exposure to high temperatures at the edge of their physiological limits.

Ecological drivers of variation in the extent of the post‐fledging dependence period in the largest group of diurnal raptors

The post‐fledging dependence period (PFDP) is a fundamental stage in the life cycle of altricial birds that influences their long‐term survival and fitness. However, research on the duration of this period in raptors, and on the factors affecting it, is scarce. We performed the first literature review on the length of the PFDP in Accipitridae, the largest family among diurnal raptors, and a meta‐analysis examining the effects of breeding latitude and hemisphere, body weight and migratory status, controlling for species phylogeny. Hypotheses were tested at the levels of both species and populations. The length of the PFDP is known for less than half of Accipitridae species, with no data for two‐thirds of the threatened and near‐threatened species. Larger species and individuals breeding at lower latitudes showed a longer PFDP, as did non‐migrants and southern‐hemisphere breeders. The effect of latitude was more marked in larger species, in resident populations and in southern‐hemisphere breeders. This extended PFDP in larger and tropical raptors may promote juvenile survival. Migration timing and the effects of continentality in the northern hemisphere constrain the PFDP. These findings highlight the importance of encouraging the study of this key, but poorly known, life‐cycle stage of raptors.

Spatiotemporal patterns of annual clear-cutting distribution in tropical and subtropical regions of China with time series Landsat and CCDC

ABSTRACT Spatial and temporal clear-cutting distribution is an important data source for investigating forest dynamics and formulating policies related to timber production, land use, and sustainable development. Subtropical and tropical regions of China due to their favorable weather conditions for tree growth are important timber providers, but the spatial distribution of annual clear-cutting areas was unavailable. This research leveraged dense time-series Landsat images (1986–2022) and a novel approach combining Continuous Change Detection and Classification (CCDC) with Random Forest to produce the first annual 30 m resolution clear-cutting map for the China’s subtropical and tropical regions. The per-polygon approach based on the sub-compartment and field survey data was used to evaluate the developed clear-cutting product. The spatiotemporal distribution of clear-cutting areas was further analyzed along longitude and latitude as well as in different provinces. The results indicated that the combination of CCDC and Random Forest successfully detected spatial and temporal distribution of clear-cutting areas with an overall accuracy of 75.6% based on sub-compartments and 93.3% based on field polygons. The cumulative clear-cutting area between 1987 and 2021 was approximately 21.26 × 106 ha, with a mean annual clear-cutting area of 0.61 × 106 ha in China’s subtropics and tropics. About 10.24% of subtropical/tropical vegetation experienced clear-cutting and most areas (85.94%) were clear-cut once. Clear-cutting activities gradually clustered at low latitudes and moderate longitudes, represented by Guangxi Province. More frequent clear-cutting was observed during the later period (2001–2021). This research contributes to an improved understanding of forest dynamics over time at large scale, and provides scientific data to make proper decisions for forest sustainability.

First documented observation of feeding behaviour of humpback whales (Megaptera novaeangliae) in its breeding range off the southern coast of Tanzania

Feeding and breeding activities of humpback whales (Megaptera novaeangliae) are generally understood to be geographically and temporally separated, with feeding activities taking places in the higher latitudes and breeding in lower latitudes. However, humpback whales may supplement their energy budgets by feeding outside of their polar foraging grounds, with opportunistic feeding behaviour being observed in mid-to-low latitudes globally. The records of supplementary feeding during migration in the southern hemisphere have been documented for various breeding stocks, with no records for the East African stock. We present the first to our knowledge record of the humpback whales feeding events in the coastal waters of Tanzania, that have been recorded on the dedicated boat surveys conducted during the humpback whales breeding seasons in 2023 and 2024 off Mnazi Bay in Mtwara region. Demonstrated behavioural plasticity may play an important role in adaptation strategies to global environmental changes and prey availability fluctuations, all of which affect recovering populations. Mnazi Bay seascape and its vicinity is an important habitat for at least 11 species of cetaceans documented, all of which depend on its productive waters for foraging, socializing and as a nursery for migrating humpback whales. This record underpins the importance of the protection of this habitat. However, future studies are needed to confirm and understand the details of the observed supplementary feeding behaviour of the humpback whales and the potential reasons behind its occurrence in Tanzania.

Exploring daily fluctuations of cosmic ray muon components at a low latitude site and their associations with space weather variables

Exploring daily fluctuations of cosmic ray muon components at a low latitude site and their associations with space weather variables

Longer Duration of Extreme Cold Events Over East Asia Affected by the Stratospheric Polar Vortex Extension

AbstractUsing long‐term reanalysis data, extreme cold events (ECEs) over East Asia are categorized into long‐duration ECEs (L‐ECEs, lasting more than 7 days) and short‐duration ECEs (S‐ECEs, lasting 3–7 days) according to the duration of ECEs during boreal winters from 1959/1960 to 2019/2020. Our results show that L‐ECEs over East Asia exhibit greater intensity, higher frequency, and longer persistence than S‐ECEs. On annual average, L‐ECEs are 1.8 K colder, contribute over 60% of total ECE days, and dominate in longer durations, persisting beyond day 5 and lasting up to 12 days. L‐ECEs in East Asia are attributed to the extension of the stratospheric polar vortex (SPV) toward the Atlantic‐Euro region. This SPV extension tends to enhance the Atlantic‐Euro trough, which is coupled with a strengthened and persistent Eurasian teleconnection pattern and a strengthened Ural ridge and East Asia trough during the decay of ECEs (after day 3). The strengthened East Asia trough, accompanied with cyclonic circulation, facilitates the transport of cold air from higher to lower latitudes. This process makes the ECEs more persistent and longer in duration, potentially developing into L‐ECEs. The findings of this study provide valuable insights into the linkages between the extension of the SPV and ECEs over East Asia from a long‐term climate statistics perspective instead of relying solely on case‐by‐case analysis. This study may offer a valuable new predictor for forecasting long‐lasting ECE events over East Asia.

Climatological Investigation of Ionospheric Es Layer Based on Occultation Data

Sporadic E (Es) layers are irregular structures that occur at the E-layer height of the ionosphere, significantly affecting the reliability and accuracy of wireless communications, navigation, and satellite remote sensing. This study utilized the S4max data collected from the Constellation Observing System for the Meteorology, Ionosphere, and Climate (COSMIC) occultation observations from 2007 to 2016 to identify the Es layer and investigate its climatological variations. The Horizontal Wind Field model (HWM14), in conjunction with the International Geomagnetic Reference Field model (IGRF13), is used to calculate vertical ion convergence (VIC) and analyze its correlation to the Es layers. The results of this study showed that the occurrence of Es has apparent hemispheric asymmetry. In the mid- and low latitudes, Es layer activity is more intense in the summer hemispheres, with center peak altitudes of around 105 km. The summer hemisphere exhibits a semi-diurnal periodic pattern, whereas the winter hemisphere shows a weakened diurnal variation. Simulation studies indicate that VIC induced by neutral wind shear contributes to the asymmetry in Es layer activities observed between the Northern and Southern hemispheres, and the zonal wind shear plays a more critical role than the meridional wind one.

Emergent patterns of reef fish diversity correlate with coral assemblage shifts along the Great Barrier Reef

Escalating climate and anthropogenic disturbances draw into question how stable large-scale patterns in biological diversity are in the Anthropocene. Here, we analyse how patterns of reef fish diversity have changed from 1995 to 2022 by examining local diversity and species dissimilarity along a large latitudinal gradient of the Great Barrier Reef and to what extent this correlates with changes in coral cover and coral composition. We find that reef fish species richness followed the expected latitudinal diversity pattern (i.e., greater species richness toward lower latitudes), yet has undergone significant change across space and time. We find declines in species richness at lower latitudes in recent periods but high variability at higher latitudes. Reef fish turnover continuously increased over time at all latitudes and did not show evidence of a return. Altered diversity patterns are characterised by heterogeneous changes in reef fish trophic groups across the latitudinal gradient. Shifts in coral composition correlate more strongly with reef fish diversity changes than fluctuations in coral cover. Our findings provide insight into the extent to which classic macroecological patterns are maintained in the Anthropocene, ultimately questioning whether these patterns are decoupling from their original underlying drivers.

Increasing temporal stability of global tropical cyclone precipitation

Tropical cyclone (TC) precipitation has led to escalating urban flooding and transportation disruptions in recent years. The volatility of the TC rain rate (RR) over short periods complicates accurate forecasting. Here, we use satellite-based observational rainfall datasets from 1998 to 2019 to calculate changes in TC 24-h RR and quantify the temporal stability of TC precipitation. We demonstrate a significant global increase in the annual temporal stability of TC RR across the total rainfall area, inner-core, and rainband areas. Specifically, the probabilities of rapid RR increase and decrease events in the TC total rainfall area decreased at rates of –1.74 ± 0.57% per decade and –2.23 ± 0.55% per decade, respectively. Based on the reanalysis dataset, we propose that the synergistic effects of increased atmospheric stability and total column water vapor—both resulting from anthropogenic warming at low latitudes—are potentially associated with this trend.

A Comprehensive Assessment of the Economic Performance of an Innovative Solar Thermal System: A Case Study

An economic assessment of an innovative solar thermal system called Application to Solar Thermal Energy to Processes (ASTEP) was conducted. It considered its three main subsystems: a novel rotary Fresnel SunDial, Thermal Energy Storage (TES) and Control System. Current Fresnel collectors are unable to provide thermal energy above 150 °C in high-latitude locations. Therefore, the key contribution of this study is the assessment of the economic performance of the ASTEP system used to provide high-temperature process heat up to 400 °C for industries located at low and high latitudes. The ASTEP system is installed at two end-users: Mandrekas (MAND), a dairy factory located in Greece at a latitude of 37.93 N and ArcelorMittal (AMTP), a manufacturer of steel tubes located in Romania at a latitude of 47.1 N. The life cycle costs (LCC), levelised cost of energy (LCOE), energy cost savings, EU carbon cost savings and benefit–cost ratio (BCR) of the ASTEP system were assessed. The results showed that AMTP’s ASTEP system had higher LCC and LCOE than MAND. This can be attributed to the use of two TES tanks and a double-axis solar tracking system for AMTP’s ASTEP system due to its high latitude location, compared to a single TES tank and single-axis solar tracking system used for MAND at low latitude. The total financial savings of the ASTEP system were EUR 249,248 for MAND and EUR 262,931 for AMTP over a period of 30 years. This study demonstrates that the ASTEP system offers financial benefits through its energy and EU carbon cost savings for industries at different latitudes while enhancing their environmental sustainability.

Comment on “Io Hot Spot Distribution Detected by Juno/JIRAM” by Zambon et al.

AbstractThe distribution of volcanic thermal emission on Io might reflect the location and magnitude of tidal heating, so it is important to accurately identify Io’s volcanoes to enable robust interior modeling. Zambon et al. (2023, https://doi.org/10.1029/2022gl100597) “Io Hot Spot Distribution Detected by Juno/JIRAM,” Geophysical Research Letters, 50, e2022GL100597 (2023) report the positions of hot spots on Io at high latitudes that are apparently spurious. This appears to be due to mis‐registration of JIRAM images to a frame of reference, leading to the same hot spot being located in different positions on Io’s surface. Other hot spots are not identified. The outcome of these additional and missing detections is a skewing of volcanic activity toward high latitudes, suggesting more polar activity than that seen at lower latitudes. This distribution of thermal sources would support a preponderance of deep mantle tidal heating, a conclusion not supported by other analyses of the same data.

Brief Warm and Aldo-Keto Reductase Family AspiAKR1B1 Contribute to Cold Adaptation of Aleurocanthus spiniferus.

Aleurocanthus spiniferus not only damages plant leaves directly but also causes a sooty blotch due to the honeydew secreted by the nymphs and adults. This pest is widespread and seems to be spreading from low latitude to higher latitude areas where winters are typically colder, indicating an increase in its cold tolerance. Changes in temperature help insects to anticipate the arrival of winter, allowing them to take defensive measures in advance. This study examines the impacts of brief warm pulses on the low-temperature tolerance of A. spiniferus, and analyzes the physiological and biochemical mechanisms underlying its cold adaptation, utilizing seasonal differences in cold tolerance. Intermittent training at 25 °C significantly improved the survival rate of overwintering nymphs (third and fourth instar) at -7 °C. Analysis of seasonal differences in the supercooling point (SCP) and freezing point (FP) revealed that overwintering nymph had the highest cold tolerance in November. Seasonal variation in levels of cold-resistant substances were also observed, with moisture decreasing during overwintering, while fat and glycerol levels increased. Conversely, glucose, sorbitol, and trehalose levels rose significantly at the end of the overwintering period. The expression profile of cold-resistant genes indicated that the aldo-keto reductase family 1 member B1 in Aleurocanthus spiniferus (AspiAKR1B1) shows a significant decrease at the end of the overwintering period. Knocking down AspiAKR1B1 led to a marked reduction in the cold tolerance of A. spiniferus. Therefore, brief warm pulses and AspiAKR1B1 are key factors contributing to the enhanced cold tolerance of A. spiniferus. This research provides theoretical support for preventing the further spread of A. spiniferus to higher latitudes, and offers technical guidance for developing effective pest control measures.

Modeling of periodic input Ornstein-Uhlenbeck temperature-tick-borne disease transmission coupling mechanism under climate change.

Given the rapid increase in climate change, investigating the impact of climate change on the transmission mechanism of tick-borne diseases is imperative. In order to fully capture the influence of the seasonal variation of temperature, environmental disturbances and the co-feeding transmission on the spread of tick-borne diseases, we propose a novel stochastic dynamical model that couples the mean-reverting Ornstein-Uhlenbeck temperature equation with periodic input to the tick-borne disease model. Through theoretical analysis, we derive sufficient conditions for the extinction of tick populations and the eradication of tick-borne diseases, as well as the stochastic persistence conditions of the system. In numerical simulations, we find that the periodic Ornstein-Uhlenbeck temperature equation can effectively fit the actual temperature data in low, medium, and high latitude regions of China. In risk assessment, we find that at the spatial perspective, low-latitude areas have a higher risk of tick-borne diseases, requiring enhanced control measures; from a temporal perspective, compared to the past, the current stage presents a greater risk of tick-borne diseases when preventive measures are not implemented. Additionally, we observe that larger noise of environment for tick populations favors the extinction of tick populations, while smaller temperature fluctuations, noise on infected hosts and ticks, as well as higher temperature regression rate, are more likely to lead to the extinction of tick-borne diseases. These findings provide crucial insights into understanding the impact of climate change on the transmission mechanism of tick-borne diseases.

Latitudinal cline of ocean dependence in a diadromous fish.

Diadromous fishes exhibit latitudinal clines of ocean dependency at inter- and intra-species levels. A pattern of ocean dependence at high latitudes and river dependence at low latitudes is explained by relative aquatic productivity. Such latitudinal productivity clines may induce geographical variations in life-history diversity within migratory phenotypes. We hypothesized that the lifetime ocean dependency of a regional migratory salmonid would display a latitudinal cline that increased at higher latitudes. Freshwater growth rate decreased with higher latitudes, whereas marine growth rate was independent of latitude. The percentage of adult weight gain at sea was higher at higher latitudes. Relative weight gain (ln(ocean weight gain/freshwater weight gain)) decreased to zero at lower latitudes, indicating no growth benefit of going to sea at the southern distribution limit. These latitudinal variations in life history within salmonid migrants are consistent with the intra- and interspecific patterns and provide insight into the origin of diadromous migration but raise the question of whether the current definition of anadromy may be insufficient to fully capture the complexity and continuum of river-ocean migrations.

Reliability of Matching AMPERE Field‐Aligned Current Boundaries With SuperDARN Lower Latitude Ionospheric Convection Boundaries During Geomagnetic Storms

AbstractHigh‐latitude ionospheric convection is a useful diagnostic of solar wind‐magnetosphere interactions and nightside activity in the magnetotail. For decades, the high‐latitude convection pattern has been mapped using the Super Dual Auroral Radar Network (SuperDARN), a distribution of ground‐based radars which are capable of measuring line‐of‐sight (l‐o‐s) ionospheric flows. From the l‐o‐s measurements an estimate of the global convection can be obtained. As the SuperDARN coverage is not truly global, it is necessary to constrain the maps when the map fitting is performed. The lower latitude boundary of the convection, known as the Heppner‐Maynard boundary (HMB), provides one such constraint. In the standard SuperDARN fitting, the HMB location is determined directly from the data, but data gaps can make this challenging. In this study we evaluate if the HMB placement can be improved using data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), in particular for active time periods when the HMB moves to latitudes below . We find that the boundary as defined by SuperDARN and AMPERE are not always co‐located. SuperDARN performs better when the AMPERE currents are very weak (e.g., during non‐active times) and AMPERE can provide a boundary when there is no SuperDARN scatter. Using three geomagnetic storm events, we show that there is agreement between the SuperDARN and AMPERE boundaries but the SuperDARN‐derived convection boundary mostly lies equatorward of the AMPERE‐derived boundary. We find that disagreements primarily arise due to geometrical factors and a time lag in expansions and contractions of the patterns.

Intra‐, Inter‐ Seasonal and Inter‐Hemispheric Dynamical Changes in TEC in the Maximum and Minimum Years of Solar Cycle 24 at the Southern Low Latitude Station Cocos Islands Vis‐A‐Vis the Northern Magnetically Conjugate Station Dibrugarh

AbstractThe long‐term (2009–2019) TEC variation over a southern low latitude station Cocos Islands (12.2°S, 96.8°E) lying in edge of the Equatorial Ionization Anomaly (EIA) region and around the WN4 peak longitude are investigated and compared with its magnetic conjugate station Dibrugarh (27.5°N, 95°E). The causative mechanisms for the observed intra‐ and inter‐seasonal variations are explored via the study of EEJ, neutral O/N2 ratio, hmF2, meridional winds and IRI simulations. The month‐to‐month variation of the mean TEC showed a tendency of peaking in November (early summer) during 2009/2018 but in March (autumn) during 2014. In contrast, the seasonal maximum was always in March (spring equinox) over Dibrugarh. The hemispheric asymmetry was significant during the solar minimum period. The intra‐seasonal variation of the asymmetry showed a relation to the position of the sub‐solar point and solar activity. The equatorial anomaly was estimated by comparing it with equatorial TEC. The anomaly affected the stations only during respective summer of 2009/2018 whereas during 2014 the anomaly affected both stations from February to April. The monthly mean TEC over Cocos was well correlated with EEJ only during 2014. In contrast, the TEC was correlated with hmF2 in both 2009 and 2014. The IRI‐2020 mostly overestimated TEC with the exception of March equinox of 2014 when the EIA effect was strongest over the stations. The dynamics of TEC variation over Cocos seemed to vary from solar minimum to maximum, changing from being photo‐chemically driven to electric field driven with increase in solar activity.