Flux Variations Research Articles

Differences in the Sensitivity of Gross Primary Productivity and Ecosystem Respiration to Precipitation

The spatiotemporal variability of precipitation profoundly influences terrestrial carbon fluxes, driving shifts between carbon source and sink dynamics through gross primary productivity (GPP) and ecosystem respiration (ER). As a result, the sensitivities of GPP and ER to precipitation (SGPP and SER), along with their differential responses, are pivotal for understanding ecosystem reactions to precipitation changes and predicting future ecosystem functions. However, comprehensive evaluations of the spatiotemporal variability and differences in SGPP and SER remain notably scarce. In this study, we utilized eddy covariance flux data to investigate the spatial patterns, temporal dynamics, and differences in SGPP and SER. Spatially, SGPP and SER were generally strongly correlated. Among different ecosystems, the correlation between SGPP and SER was lowest in mixed forest and highest in broadleaf and needleleaf forest. Within the same ecosystem, SGPP and SER exhibited considerable variation but showed no significant differences. In contrast, they differed significantly across ecosystems, with pronounced variability in their magnitudes. For example, shrubland exhibited the highest values for SGPP, whereas needleleaf forest showed the highest values for SER. Temporally, SER demonstrated more pronounced changes than SGPP. Different ecosystems displayed distinct trends: shrubland exhibited an upward trend for both metrics, while grassland showed a downward trend in both SGPP and SER. Forest, on the other hand, maintained stable SGPP but displayed a downward trend in SER. Additionally, SGPP and SER exhibited a notable non-linear response to changes in the aridity index (AI), with both showing a rapid decline followed by stabilization. However, SER demonstrated a wider adaptive range to precipitation changes. Generally, this research enhances our understanding of the spatiotemporal variations in ecosystem carbon fluxes under changing precipitation patterns.

PAStar : A model for stellar surface from the Sun to active stars

The characterisation of exoplanets requires a good description of the host star. Stellar activity acts as a source of noise, which can alter planet radii as derived from the transit depth or atmospheric characterisation. Here, we propose PAStar a model to describe photospheric activity in the form of spots and faculae, which could be applied to a wide range of stellar observations, from photometric to spectroscopic time series, making it possible to correctly extract planetary and stellar properties. The adopted stellar atmosphere is a combination of three components: the quiet photosphere, spots, and faculae. The model takes into account the effects of star inclination and Doppler shifts due to stellar rotation and limb darkening, which is independent for each component. Several synthetic products have been presented to show the capabilities of the model. The model is able to retrieve the input surface-inhomogeneity configuration through photometric or spectroscopic observations. The model has been validated against optical solar data and compared to alternative stellar surface activity models; for example SOAP code . The Sun is a unique laboratory to test stellar models because of the possibility to unambiguously relate flux variations to surface inhomogeneities' configuration. This validation has been done by analysing a photometric time series from the Variability of Solar Irradiance and Gravity Oscillations (VIRGO) photometer on-board Solar and Heliospheric Observatory (SOHO) mission. Results have been compared to real solar images from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to confirm the goodness of the results in terms of surface inhomogeneities' positions and dimensions. The description of stellar activity is a fundamental step in several astrophysical contexts and it is covered by the method we present. Our model offers a flexible and valuable tool to describe the activity of stars when it is dominated by spots and faculae.

Detection of ultrafast electron energization by whistler-mode chorus waves in the magnetosphere of Earth

Electromagnetic whistler-mode chorus waves are a key driver of variations in energetic electron fluxes in the Earth’s magnetosphere through the wave-particle interaction. Traditionally understood as a diffusive process, these interactions account for long-term electron flux variations (> several minutes). However, theories suggest that chorus waves can also cause rapid (< 1 s) electron acceleration and significant flux variations within less than a second through a nonlinear wave-particle interaction. Detecting these rapid accelerations has been a great challenge due to a limited time resolution of conventional particle instruments. Here, we employ an analysis technique to enhance the time resolution of the particle measurements, revealing rapid electron flux variations within less than one second associated with chorus waves. This technique exposes short-lived flux increases significantly larger than those observable with the standard time resolution. Our findings indicate that these transient flux variations result from the nonlinear acceleration of electrons induced by the chorus waves, highlighting the importance of nonlinear wave-particle interactions in creating high energy electrons in the Earth’s magnetosphere. The same acceleration mechanism should operate in the magnetospheres of Jupiter and Saturn where chorus waves are present, and in laboratory plasma environments when chorus-like waves are excited.

High-Frequency High-Magnetic Flux Variation Foil Winding AC Inductor Design with the Vertical Penetrating Magnetic Field Elimination

In traditional inductor design with planar windings, the magnetic field distribution may not be well-organized, leading to significant winding loss, particularly at high switching frequencies. This study explores the relationship between current distribution and magnetic field distribution in the winding region. Unlike conventional magnetic flux distribution, which directs a large portion of the magnetic field vertically through the windings in the winding region, this work introduces a structure that maintains most of the magnetic flux parallel to the foil windings through the application of quasi-distributed air gaps. This paper presents a design methodology for a high-frequency foil winding inductor with high flux variation. Building on this concept, a high-power density, low loss inductor with foil windings is designed based on the four-switch buck-boost (FSBB) converter. Experimental results demonstrate that the proposed inductor design significantly reduces winding loss in inductors with planar windings.

Mixed Bioconvection Flow Around a Vertical Thin Needle with Variable Surface Fluxes

This study investigates mixed convection flow over a vertical thin needle with variable surface heat, mass, and microbial flux, incorporating the influence of gyrotactic microorganisms. The governing partial differential equations are transformed into ordinary differential equations using appropriate similarity transformations and then solved numerically by employing MATLAB’s Bvp4c solver. The primary focus lies in examining the influence of various dimensionless parameters, including the mixed convection parameter, power-law index, buoyancy parameters, bioconvection parameters, and needle size parameters, on the velocity, temperature, concentration, and microbe profiles. The results indicate that these parameters significantly affect the surface (wall) temperature, fluid concentration, and motile microbe concentration, as well as the corresponding velocity, temperature, concentration, and microorganism profiles. The findings provide insights into the intricate dynamics of mixed convection flow with bioconvection and have potential applications in diverse fields such as biomedicine and engineering.

X-ray timing and spectral characteristics of compact symmetric objects

ABSTRACT Compact Symmetric Objects (CSOs) are a distinct category of jetted active galactic nuclei whose high-energy emission is not well understood. We examined the X-ray characteristics of 17 bona fide CSOs using observations from Chandra, XMM–Newton, and NuSTAR. Among the sources with XMM–Newton observations, we found two sources, J0713+4349 and J1326+3154 to show clear evidence of variations in the soft (0.3–2 keV), the hard (2–10 keV), and the total energy (0.3–10 keV) bands with the normalized excess variance (F$_{\mathrm{ var}}$) as large as 1.17$\pm$0.27. Also, the F$_{\mathrm{ var}}$ is found to be larger in the hard band relative to the soft band for J1326+3154. From the analysis of the hardness ratio (HR) with count rate, we found both sources to show a harder when brighter (HWB) trend. Similarly, in the Chandra observations, we found one source, J0131+5545, to show flux variations in the total energy band (0.5–7 keV). We discuss possible reasons for about 82 per cent of the CSOs being non-variable. From spectral analysis, carried out in a homogeneous manner, we found the existence of obscured as well as unobscured CSOs. Three CSOs, J0111+3906, J1407+2827, and J2022+6136, were found to have the intrinsic neutral hydrogen column density N$_{\rm H,z} \gt 10^{23}$ cm$^{-2}$, consistent with earlier analyses. For the majority of the CSOs, the observed hard X-ray emission is expected to be dominated by their mildly relativistic jet emission. For the sources, J0713+4349, J1347+1217, J1407+2827, J1511+0518, and J2022+6136, the confirmed detection of Fe K $\alpha$ emission line suggests a significant contribution from the disc/corona. Our results point to diverse X-ray characteristics of CSOs.

Multi-scale temporal and spatial variations of soil heat flux under varying riparian forests: From a day to a year.

This study delves into the multi-scale temporal and spatial variations of soil heat flux (G) within riparian zones and its correlation with net radiation (Rn) across six riparian woodlands in Shanghai, each characterized by distinct vegetation types. The objective is to assess the complex interrelations between G and Rn, and how these relationships are influenced by varying vegetation and seasons. Over the course of a year, data on G and Rn is collected to investigate their dynamics. The multi-scale temporal patterns of G and its relationship with Rn are significantly influenced by both vegetation type and season, with the most pronounced variability observed seasonally, exhibiting distinct cycles for both broadleaf and conifer forests. The presence of shrubs is found to increase G, and the dominant temporal scales were found to vary within broadleaf forests. Additionally, G demonstrates a non-linear gradient with respect to the proximity to the river, with the river's influence on G diminishing at distances less than 11m in broadleaf and 6m in conifer woodlands. While the river enhances G and its hysteresis with Rn, vegetation characteristics dominate in dense canopies. This study underscores the importance of understanding the spatio-temporal variation patterns of soil heat flux and their response to different vegetation attributes. Such knowledge is vital for developing riparian soil heat flux models and informing riparian forest management strategies, especially in the context of climate change. The results provide insights into the complex interactions between soil heat flux, net radiation, and vegetation, offering a foundation for future research and management practices aimed at preserving and enhancing the ecological functions of riparian ecosystems.

Spatiotemporal variability of air-sea CO2 fluxes in response to El Niño-related marine heatwaves in the tropical Pacific Ocean.

The tropical Pacific is the largest oceanic source of carbon dioxide (CO2) emissions, where persistent marine heatwaves (MHWs) frequently occur. During persistent MHW events which are associated with strong El Niño events, CO2 outgassing is notably reduced, however, its detailed spatiotemporal response to MHWs has not been fully characterized. In this study, we showed a high degree of consistency between CO2 source regions in the central and eastern tropical Pacific Ocean and the occurrence regions with average annual MHW days exceeding 45 days (co-occurring area covers 80% of the area where MHWs occur). The spatiotemporal variability of the air-sea CO2 flux on interannual and longer timescales can be reconstructed from annual MHW days and occurrence frequency, respectively, in the central and eastern Pacific Ocean of the co-occurring region. In this region, El Niño-related MHWs reduce the air-sea CO2 flux density up to 0.4-0.8 molC/m2/yr per 100 MHW days, corresponding to a reduction of CO2 emissions by approximately 0.1 PgC per 100 MHW days. This is a 10%-40% reduction in CO2 emissions during MHW periods, with the strongest impact (30%-40% CO2 emission reduction) in the equatorial Pacific (5°S-5°N) of the central and eastern Pacific Ocean. In contrast, air-sea CO2 flux variations in coastal eastern upwelling region of the co-occurring region are mainly subjected to seasonal mixed layer variations, and thus not notably affected by El Niño-related MHWs on interannual timescales. By establishing the reproducibility between MHWs and air-sea CO2 flux variations, our results pave a way for detailed future spatiotemporal evolutions of MHW-induced changes in air-sea CO2 flux in the tropical Pacific Ocean.

Reliability assessments of using different heavy metals from remote sediment records to reconstruct historical pollution.

Interpreting heavy metal variations in sedimentary records is an important approach to understand historical pollution. However, few studies have investigated the reliability of different heavy metals in sedimentary records for reconstructing historical pollution. This study retrieved two adjacent lakes' sediment cores from a remote area in North China and investigated their temporal changes in excessive metal fluxes. Combined with a novel index of the ratios of atmospheric emissions of anthropogenic metals to background metal values in lake sediments, the reliability and influencing factors of eight metals (Cr, Co, Ni, Cu, As, Zn, Cd, and Pb) in sediments to reconstruct historical pollution were studied. Vertical As variations in the sediments were controlled mainly by early diagenesis effects, although anthropogenic pollution might also have had an impact. Consequently, As profiles in lake sediment records are usually difficult to reflect historical pollution. (2) Among the eight metals, Zn, Cd, and Pb in both lakes have been affected mainly by human pollution and insignificantly by natural factors. Their excessive flux variations in the two records were highly consistent with the historical trend of economic/industrial development. Relatively, these three metals can reliably reflect historical pollution. (3) Compared with Zn, Cd, and Pb, Cr, Co, Ni, and Cu in the two lakes have been relatively less affected by anthropogenic pollution. During the period of relatively high anthropogenic metal emissions (post-∼1980), they could roughly reflect historical pollution in the region; however, during the period of relatively low emissions (before ∼1980), they appeared to exhibit no signs of pollution. This suggests the complexity of using them in remote records to reconstruct historical pollution. The importance of this study lies in its potential to provide critical guidance for the use of aquatic sediment records from relatively remote areas in reconstructing the historical metal pollution.

Dynamic massive star formation: Radio flux variability in UCHII regions

Theoretical models of early accretion during the formation process of massive stars have predicted that regions exhibit radio variability on timescales of decades. However, large-scale searches for such temporal variations with sufficient sensitivity have not yet been carried out. Our aim is to identify regions with variable radio wavelength fluxes and to investigate the properties of the identified objects, especially those with the highest level of variability. We compared the peak flux densities of 86 ultracompact regions measured by the GLOSTAR and CORNISH surveys and identified variables that show flux variations higher than 30% over the ∼8 yr timespan between these surveys. We found a sample of 38 variable regions, which is the largest sample identified to date. The overall occurrence of variability is 44±5%, suggesting that variation in regions is significantly more common than prediction. The variable regions are found to be younger than nonvariable regions, all of them meeting the size criterion of hypercompact (HC) regions. We studied the seven regions that show the highest variability (the ``Top7'') with variations &gt; 100%. The Top7 variable regions are optically thick at 4--8 GHz and compact, suggesting they are in a very early evolutionary stage of or regions. There is a significant correlation between variability and the spectral index of the radio emission. No dependence is observed between the variations and the properties of the sources' natal clumps traced by submillimeter continuum emission from dust, although variable regions are found in clumps at an earlier evolutionary stage.

Geomagnetic dipole stability and zonal flows controlled by mantle heat flux heterogeneities

Abstract Palaeomagnetic evidence shows that the behaviour of the geodynamo has changed during geological times. These changes are visible through variations in the strength and stability of the magnetic dipole. Variations in the heat flux at the core-mantle boundary (CMB) due to mantle convection have been suggested as one possible mechanism capable of driving such a change of behaviour. This work aims at acquiring a more complete understanding of how lateral heterogeneities of the CMB heat flux affect the geodynamo while other relevant parameters are pushed towards realistic values. For this purpose, we ran geodynamo simulations with degree 1 and 2 spherical harmonic patterns of heat flux at the CMB. Several geodynamo models are used, ranging from standard numerical dynamos to more extreme parameters, including strong field cases and turbulent cases. We show that heat flux heterogeneities with amplitudes compatible with our knowledge of mantle convection history can favour multipolar dynamos. The multipolar transition is associated with a disruption of westward flows either through eastward thermal winds or through a loss of equatorial symmetry. Strong field dynamo models are found to have larger westward flows and are less sensitive to heat flux heterogeneities. Furthermore, we find that the dipolar fraction of the magnetic field correlates with $M_{Za}^*=\dfrac{\Lambda _{Za}}{Rm_{Za}^2}$ where ΛZa is the zonal antisymmetric Elsasser number and RmZa is the zonal antisymmetric magnetic Reynolds number. Importantly, $M_{Za}^*$ estimated for the Earth’s core is consistent with a reversing dipolar magnetic field. Within the range of $M_{Za}^*$ susceptible to reversals, breaking the equatorial symmetry or forcing eastward zonal flows through an equatorial cooling of the core consistently triggers reversals or a transition towards multipolar dynamos in our simulations. Our results support that time variations of heat-flux heterogeneities driven by mantle convection through Earth’s history are capable of inducing the significant variations in the reversal frequency observed in the palaeomagnetic record.

Characteristics of Energy Fluxes and Cold Frontal Effects on Energy Exchange over a Boreal Lake

Understanding the characteristics and variations of heat exchange and evaporation of lakes is important for regional water resource management and sustainable development. Based on eddy covariance measurements over Lake Vanajavesi in southern Finland, characteristics of energy fluxes and cold frontal effects on energy exchange were investigated. The lake acted as a heat sink in spring and summer and a heat source in winter. The latent heat flux reached its minimum value in the morning and peaked in the afternoon. The diurnal variation of sensible heat flux was opposite to that of latent heat flux. Impact factors for the sensible heat flux were mainly the lake-air temperature difference and the product of lake-air temperature difference and wind speed. The latent heat flux was mainly affected by the vapor pressure deficit and the product of vapor pressure deficit and wind speed. The annual mean values of bulk transfer coefficients for momentum, heat, and water vapor were 1.98 × 10−3, 1.62 × 10−3, and 1.31 × 10−3, respectively. Bulk transfer coefficients for heat and water vapor were not equal, indicating that the parameterization of energy exchange in numerical models, where the assumption that the heat coefficient equals the water vapor coefficient needs improvement. During the ice-free season, cold fronts resulted in 28 sensible heat pulses and 17 latent heat pulses, contributing to 50.59% and 34.89% of sensible and latent heat exchange in Lake Vanajavesi. These results indicate that cold fronts significantly impact the surface energy budget and evaporation over lakes.

Interstellar scintillation of sources B0821+394 and B1812+412 according to observations on the LPA LPI radio telescope

The search for long-term variability of compact components of radio sources B0821+394 and B1812+412 over an interval of 10 years was carried out. The LPA LPI radio telescope with an operating frequency of 111 MHz was used for observations. According to our estimates, the characteristic time of variability for both sources is 1.5–2.5 years. It is shown that the observed variability is not related to intrinsic variations in the radiation flux, but is due to refractive scintillation on inhomogeneities of the interstellar medium. From the obtained upper estimates of the apparent angular dimensions of the sources, it follows that the main contribution to the scattering of radio emission is made by turbulent plasma concentrated in sufficiently thin screens, the distance to which does not exceed 300–400 pc.

On the gravity dynamics of objects in space and time

Existing theories of gravity encompass Newton's law of universal gravitation and Einstein's general relativity; however, they fail to fully elucidate the nature of gravity and the mechanisms by which it influences the motion of objects. This article presents a new gravitational theory model proposed by the author, introducing the concept of gravitational line flux. By employing mathematical methods such as Gauss's theorem and Stokes's theorem, the study investigates how variations in gravitational flux through a closed spatial surface affect the motion of objects. The following laws are proposed: (1) The gravitational flux through a closed surface is directly proportional to the mass m of the enclosed celestial body. (2) Changes in gravitational flux through a semiclosed surface in the direction of an object's motion alter the object's motion state in space, while concurrently, the object's motion induces variations in the gravitational flux through the surface. (3) The time variation increment of gravitational flux through a semiclosed surface in the direction of the object's motion is proportional to the object's acceleration. Furthermore, the motion equations of gravitational fields for celestial bodies or matter in local inertial and noninertial frames are derived.

Novel approach for modelling low enthalpy geothermal in deep sedimentary aquifers: a case study of 40 years of production data in the Dogger formation

Geothermal energy in the Paris urban area has been exploited since the early 1970s. Deep drilling in the Paris sedimentary basin has targeted hot brine in the Dogger formations from a mid-Jurassic carbonate rocks series. More than a hundred wells have been drilled to depths ranging from 1400 to 2000 m and decades of production and reinjection have resulted in variations in the aquifer pressure and temperature in some areas. The regional numerical model discussed herein is aimed at assessing the potential interactions between doublets and for assessing the impact of the addition of more wells in the future. While the integration of a 3D refined geological model into a large-scale reservoir model needs heavy computational resources, local models simplifying the main productive areas into one or two layers surrounded by impermeable units can be used to approximately assess the reservoir characteristics. The modelling of a semi-regional area of the Dogger reservoir in the Southern part of Paris (Cachan/Orly) has been performed, using a conventional double-layer approach to simulate the natural state and production history of the area using the simulator Waiwera, a fast parallel open-source geothermal simulator from the University of Auckland in New-Zealand. Calibration of a natural state model, which describes the conditions before any geothermal operations, has been performed, including an analysis of the impact of boundary condition values on the ability of the model to match the data available in the public domain. The temperature and pressure distributions, instead of being based on geostatistical mapping methods have been obtained from a calibrated natural state model. The implementation of a regional lateral cross flow observed from past studies proved to be essential for matching the measured temperatures and pressures along with variations in the deep heat flux. A calibrated model has been obtained from matching the available production data with mismatches of no more than 1.5 °C. The modelling results confirm the dominance of the shallower productive zone in the aquifers and give insights into the extent of the cooler areas created by the long-term operations. Thus we have used the Dogger reservoir, with multiple data sets available, as a case study for calibrating a semi regional numerical model of a deep sedimentary aquifer used for geothermal direct-use. Our modelling study accounts for the conceptual understanding of the sedimentary aquifer with its heterogeneities and calibrates the numerical model against the measured historical data. Based on the calibrated reservoir model, the pressure and temperature responses in deep productive areas can be determined enabling operators or decision makers to test future strategies for sustainably operating the geothermal resource.

Morphological evolution of the Qingshuigou subaqueous delta of the Yellow River before and after the operation of the Xiaolangdi Reservoir (1997-2007)

The Modern Yellow River Delta has a rich history of geomorphological transformations shaped by frequent avulsions and rapid progradation. However, the delta entered a phase of altered morphodynamics following the construction of the Xiaolangdi Reservoir, which fundamentally restructured sediment transport regimes and seasonal hydrological patterns. These changes have amplified challenges in predicting long-term deltaic evolution under evolving boundary conditions. The Qingshuigou Subaqueous Delta, as a major depositional zone, provides a compelling lens to examine these morphodynamic processes. However, seasonal variations in riverine sand transport fluxes driven by the water-sand regulation scheme that accompanied the construction of the Xiaolangdi Reservoir and its impact on the evolution of the delta front are particularly understudied. This study developed a simplified long-term morphodynamic model of the Qingshuigou Subaqueous Delta to investigate its response to riverine water and sediment discharges from 1997 to 2007. The findings are as follows: (1) The morphological evolution of the Qingshuigou Subaqueous delta has gradually changed from the pattern of “leading edge deposition and localized near-shore erosion” before the construction of the Xiaolangdi Reservoir to the pattern of “enhanced leading edge deposition and increased near-shore erosion” after the construction. (2) The construction of Xiaolangdi Reservoir has weakened the spatial distribution of the erosion process to a certain extent, changing the spatial distribution dominated by the erosion process (63.8% of area) before the construction to the spatial distribution dominated by the accretion process (More than 50% of area) after the construction. (3) The spatial and temporal variability of the incoming sediments leads to a significant coarsening of the grain size of the tidal flats in the southern part of the abandoned delta, which in turn maintains a relatively steady state of the shoreline variability. In contrast, the abandoned sand spit experiences severe erosion and depositional fluctuations due to intensified wave action. (4) The study emphasizes the importance of considering seasonal variations in unsteady discharge in modeling the long-term evolution of the delta. It provides new insights into the spatial and temporal differentiation of the geomorphic equilibrium of the Yellow River Delta and contributes to a broader understanding of delta evolution.

Changes in high-latitude surface energy balance driven by snowpack and vegetation dynamics under warmer climate

Abstract With rapid climate warming, expected changes in snowpack and vegetation will alter the seasonal surface albedo of high-latitude ecosystems. The extent to which these albedo changes may affect surface energy balances and thus soil temperatures is uncertain, but represents a potentially important component of ecosystem feedbacks to climate change. Here, we apply a well-tested process-rich ecosystem model, ecosys, to examine changes in seasonal surface albedo and soil temperature driven by climate-induced snowpack and vegetation changes across Alaska under a warmer twenty-first century climate. Under the Representative Concentration Pathway 8.5 climate change scenario, the modeled changes in surface albedo exhibited large seasonal and spatial variations. We found spring albedo decreases driven by increases in snow-free periods (&gt;20 d) and an extended growing season length that resulted in greater gains in leaf area index (LAI) in most parts of Alaska. In contrast, we modeled increases in summer and winter albedo (despite modeled increases in LAI) across much of the boreal forest due to an increased proportion of aspen, which has a higher leaf albedo than the currently dominant black spruce. Modeled latent heat fluxes generally increase across the twenty-first century, particularly during the spring and summer. Overall, climate warming and changes in surface energy fluxes resulted in a 3.5 ± 0.50 °C increase in spatial- and annual-averaged top 10 cm surface soil temperatures across Alaskan ecosystems by the year 2100, with larger increases in tundra than boreal forest regions. We conclude that under warmer climates, seasonal variations in albedo and surface energy fluxes are particularly pronounced during the spring and summer, driven by changes in snowpack and vegetation dynamics.

Constraining net long-term climate feedback from satellite-observed internal variability possible by the mid-2030s

Abstract. Observing climate feedbacks to long-term global warming, which are crucial climate regulators, is not feasible within the observational record. However, linking them to top-of-the-atmosphere flux variations in response to natural surface temperature fluctuations (internal variability feedbacks) is a viable approach. We explore the use of relating internal variability to forced climate feedbacks in models and applying the resulting relationship to observations to constrain forced climate feedbacks. Our findings reveal strong longwave and shortwave feedback relationships in models during the 14-year overlap with the Clouds and the Earth's Radiant Energy System (CERES) record. Yet, due to the weaker relationship between internal variability and forced climate longwave feedbacks, the net feedback relationship remains weak, even over longer periods beyond the CERES record. However, after about half a century, this relationship strengthens, primarily due to reinforcements of the internal variability and forced climate shortwave feedback relationship. We therefore explore merging the satellite records with reanalysis to establish an extended data record. The resulting constraint suggests a stronger negative forced climate net feedback than the model's distribution and an equilibrium climate sensitivity of about 2.59 K (1.95 to 3.12 K, 5 %–95 % confidence intervals). Nevertheless, this method does not account for certain factors like biogeophysical–chemical feedbacks, inactive on short timescales and not represented in most models, along with differences in historical warming patterns, which may lead to misrepresenting climate sensitivity. Additionally, continuous satellite observations until at least the mid-2030s are essential for using purely observed estimates of the net internal variability feedback to constrain the net forced climate feedback and, consequently, climate sensitivity.

Fermi-LAT Detection of the Low-luminosity Radio Galaxy NGC 4278 during the LHAASO Campaign

Abstract We present a study of the high-energy properties of the compact symmetric object NGC 4278, recently associated with a TeV source by the Large High Altitude Air Shower Observatory (LHAASO) collaboration. We conducted a dedicated analysis of a Fermi Large Area Telescope (LAT) region around NGC 4278, limited to the LHAASO campaign conducted from 2021 March to 2022 October. A statistically significant emission (∼4.3σ) was revealed, spatially consistent with the radio position of NGC 4278 and the LHAASO source. The Fermi-LAT source is detected above 8 GeV, exhibiting a hard spectrum (photon index Γ = 1.3 ± 0.3) and a γ-ray luminosity of L &gt;100 MeV ≃ 4 × 1041 erg s–1. A serendipitous Swift X-Ray Telescope (XRT) observation of NGC 4278 during the TeV campaign reveals the source in a high state, with a flux F 0.5 − 8 ke V = 5 − 2 + 3 × 1 0 − 12 erg s − 1 cm − 2 , compatible with the highest luminosity level observed in previous Chandra pointings. The high-energy spectral energy distribution of the source and the intense flux variation observed in the X-ray band support a jet origin for the observed radiation. We suggest that the significant enhancement of the high-energy flux observed during the LHAASO campaign is due to a transient, highly energetic perturbation in the jet. The detection of NGC 4278 at both high and very high energies opens new frontiers in studying particle acceleration processes. It reveals that even compact, low-power radio galaxies can exceed the sensitivity thresholds of GeV and TeV instruments, becoming promising targets for the upcoming Cherenkov Telescope Array Observatory.

Magnetic Dipolarizations and Energetic Electron Flux Variations at the Nightside Geostationary Orbit

AbstractWe consider energetic electron (EE, 30–600 keV) flux variations, connected with magnetic dipolarizations, at geosynchronous orbit. Two types of these variations, due to injections and drift shell crossing (DSC), have been known since the 1960s, but no methods to separate them were suggested. To reach this goal we apply the hodogram Je(Bz) technique (EE flux vs. local magnetic field) to data of three spacecraft, GOES‐15 observing a sharp dipolarization and thus being in the injection region, and GOES‐13, GOES‐14, being inside the drifting electron cloud (DEC). Analysis of 45 sharp dipolarizations and corresponding EE flux variations in 2013–2017 showed that hodograms look quite different (a) inside and outside of the injection region and (b) for medium (30–200 keV) and high (200–600 keV) energies, allowing to identify the variation type as either DSC or true injection. EE fluxes and energy spectra were compared inside the injection region and in the DEC 4 hours eastward. EE fluxes are well correlated before the injection, but strongly scattered at its peak suggesting a highly structured drifting injected cloud. Spectra at the injection peak appeared similar, demonstrating hardening with increased geomagnetic activity. The best correlations between different injection and dipolarization measures are observed between peak Je values and ∆(MPB)1/2, where MPB is the ground mid‐latitude positive bay index; correlations of approximately 0.7 are attained inside the injection region, being lower in the DEC. The peak injected EE flux increases by ∼1–1.5 orders of magnitude with increase in dipolarization strength from low to high geomagnetic activity.