Latitudinal Profiles Research Articles

SIMULATION OF GEOELECTRIC STRUCTURE OF NORTHERN VIETNAM BY 3D INVERSION OF MAGNETOVARIATIONAL TIPPERS

This paper presents the results of constructing a model of the geoelectric structure of Northern Vietnam obtained by 3D inversion of magnetovariational tippers calculated for 13 values of variation periods in a range of 40–10047 s at 12 points where geomagnetic variations are recorded. Inversion is performed using the ModEM software, which makes it possible to construct a model in a 400 × 400 × 200-km spatial region with the center at the Hanoi Observatory (PHU). The resulting model of the geoelectric structure contains two regional blocks separated by the Red River fault region. A conductive block is located in the southwest of the fault region, and a high-resistivity block is located in the northeast. The boundary of the blocks, inclined to the northeast at an angle of about 45°, is visible to a depth of 150 km. The conductive block occupies the region between the Red River and Song Ma faults. Its western boundary could not be localized due to insufficient data in this region. Highly conductive local blocks stand out against the background of the regional conductive block. They usually gravitate toward the faults and are located in a depth range of 10–20 km with a slight inclination to the west on latitudinal profiles and to the south on meridional ones. In a depth range of 12–14 km, they merge into one highly conductive band extending in the northwest and marking the Red River fault system connected to the Gulf of Tonkin waters. Also, there are more massive highly conductive blocks in depth intervals of 20–50 km, which are often associated with upper crustal ones. There is a highly conductive block observed on the latitudinal profile, passing through the central region of the Hanoi Basin, and steeply dipping to the east (75°) to depths of more than 100 km. The deep geoelectric features of the Red River fault system are compared with the geoelectric section under their continuation in Southern Tibet in the adjacent territory in China.

A new approach to three-dimensional monitoring of surface changes in lakes: application of three-way data analysis model in Lake Burdur, Turkey.

Lakes are areas of ecological significance that host a wide range of living species. Therefore, monitoring changes in lake surfaces is critical for ecosystem preservation. Since conventional methods based on one-dimensional data analysis have limited capacity to analyze complex systems, they may not always produce the desired results in examining surface change. In this regard, a novel approach based on a three-way analysis model of a multi-temporal dataset was improved for the first time to monitor surface changes in Lake Burdur between 2014 and 2023 in terms of latitude, longitude, and year modes. The newly proposed approach, based on the deconvolution of a multi-temporal data series, provided a new way and an alternative approach with a three-dimensional perspective for the simultaneous prediction of changes in latitude, longitude, and relative quantity profiles of Lake Burdur between 2014 and 2023. The proposed approach is based on the parallel factor analysis (PARAFAC) modeling of the multi-temporal datasets. The change in the lake surface as water levels were monitored from latitudinal and longitudinal profiles was obtained by applying the PARAFAC model to the multi-temporal data array. In the same model, the change in lake water surface over the years was determined from the relative quantity profile. The results obtained from the three-way analysis model were compared with the results provided by the conventional method. It was concluded that the findings of this study could provide valuable information to researchers and policymakers in developing effective strategies to analyze changes in lake surfaces in future studies.

Investigation of the global climatologic performance of ionospheric models utilizing in-situ Swarm satellite electron density measurements

The Swarm constellation is a triplet of satellites, flying, since their final configuration reached in April 2014, at altitudes of about 420 to 490 km (the lower pair) and about 500 to 530 km (the upper satellite). All the three satellites provide in-situ measurements of the plasma density in the topside ionosphere using Langmuir Probe sensors onboard the Electrical Field Instrument. The present study is a comprehensive investigation into the climatologic performance of three ionospheric models when compared to the Swarm satellite in-situ measurements. The models are the International Reference Ionosphere (IRI) model, a quick run ionospheric electron density model (NeQuick), and a 3-dimensional electron density model based on artificial neural network training of COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellites radio occultation measurements (3D-NN). The mean monthly quiet-time latitudinal profile of Swarm measurements was computed by binning the Swarm electron density measurements in 15-degree longitudes starting from longitude −180° in steps of 15° to 180°, and corresponding model predictions were obtained. The data used in the study covers the years 2014, 2016, 2019, and 2022, capturing various phases of the solar activity cycle. Results from the study show that modelled electron density predictions from all three climatologic models are fairly good representations of the Swarm satellite measurements, with some exceptions in which the models underestimate or overestimate the Swarm satellite values. The IRI model performed best at the northern hemisphere mid latitude, and it overestimated the Swarm measurements at altitudes of ∼ 450 km, especially at the southern hemisphere mid and high latitudes. The NeQuick performed best during the night times, and it overestimated the Swarm measurements, especially at the mid latitudes. The NeQuick was also observed to overestimate the Swarm measurements during the winter solstices at both hemispheres, which is June solstice in the southern hemisphere and December solstice in the northern hemisphere. Overall, the 3D-NN model most often performed better than the IRI model and the NeQuick, especially during the day times and during the high solar activity year (2014), but it underestimated the Swarm measurements, especially at the low and mid latitudes. For all categories explored in the study, the 3D-NN consistently performed better than the other two models. The NeQuick performed better than the IRI model at altitude of satellite B, while the IRI model performed slightly better than the NeQuick at altitude of satellites A and C. The NeQuick also performed better than the IRI model in the local time category, whereas the IRI model performed better than the NeQuick in categories of season, solar activity, and longitudinal sector.

Longitudinal filtering, sponge layers, and equatorial jet formation in a general circulation model of gaseous exoplanets

ABSTRACT General circulation models are a useful tool in understanding the three dimensional structure of hot Jupiter and sub-Neptune atmospheres; however, understanding the validity of the results from these simulations requires an understanding of the artificial dissipation required for numerical stability. In this paper, we investigate the impact of the longitudinal filter and vertical ‘sponge’ used in the Met Office’s unified model when simulating gaseous exoplanets. We demonstrate that excessive dissipation can result in counter-rotating jets and a catastrophic failure to conserve angular momentum. Once the dissipation is reduced to a level where a super-rotating jet forms, however, the jet and thermal structure are relatively insensitive to the dissipation, except in the nightside gyres where temperatures can vary by $\sim 100\, \mathrm{K}$. We do find, however, that flattening the latitudinal profile of the longitudinal filtering alters the results more than a reduction in the strength of the filtering itself. We also show that even in situations where the temperatures are relatively insensitive to the dissipation, the vertical velocities can still vary with the dissipation, potentially impacting physical processes that depend on the local vertical transport.

Daily geomagnetic variations under variable IMF/solar conditions and their connection with underground conductivity changes in Japan

Fluctuations in Solar Wind (SW) and Interplanetary Magnetic Field (IMF) significantly affect the Geomagnetic Field (GF) measurements particularly during extreme space weather events. The current study investigates the variations of horizontal (H), vertical (Z) geomagnetic components under quiet and disturbed IMF and solar conditions as well as the effect of underground conductivity on the stationary geomagnetic measurements in Japan. Results of data analysis show that the response of the GF to IMF and solar parameters fluctuations is variable. The H- and Z-components were in good harmony with high visual correlation along a latitudinal profile across Japan during quiet times. On the other hand, during the disturbed times related to a Coronal Mass Ejection (CME) launched on 13 May 2005, the GF components varied with the disturbance of IMF and solar parameters. The H-components showed highly correlated variations with a significant reduction along the examined profile due to intensified ionospheric currents, while the Z-components recorded in the northern part of Japan showed abnormal daily variations pattern (positive daily variations) with an enhanced amplitude which is opposite to the normal behavior of daily variations recorded in the central and southern parts of Japan (negative daily variations). The observed enhanced and abnormal daily variation of Z-components in north Japan, which we consider a remarkable observation here, is possibly linked with underground conductivity anomaly in this region.

Large‐Scale Wave‐Driven Interactions and Plasma‐Neutral Coupling in the Low‐Latitude Ionosphere‐Thermosphere

AbstractThe plasma and neutral density variations, interactions and coupling processes within ±30° latitudes are examined concurrently by the DMSP‐F18 and Swarm‐C satellite during geomagnetically quiet years in 2020–2021. The wavenumber (WN) patterns are computed in the form of neutral and electron density for two altitudes and their latitudinal profiles are analyzed. We observe that the WN1 structure of the electron density has a significant seasonal dependence in the topside ionosphere and dominates all other structures but WN2 neutral density amplitude dominates all other structures in the middle thermosphere (∼440 km). Additionally, we analyze vertical‐temporal‐latitudinal tidal structures from the Climatological Tidal Model of the Thermosphere (CTMT) to find evidence for the modulation of the large‐scale waves (LSWs) neutral density structures. Through the examination of the in situ observational and modeling approaches, we show that the tidal contributors of WN structures obtained from CTMT can capture the influence of terrestrial sources on the WN structures of plasma‐neutral density and imprint the corresponding vertical coupling in the IT system. Correlation analysis reveals that the amplitudes of the WN1 and WN3 structures of electron density in topside ionosphere and those of neutral density in the middle thermosphere show intermittent but significant correlations with each other, unlike the WN2 and WN4 structures. This study provides new insights into the topside ionospheric response to wave driving in the lower atmosphere, which ultimately improves our capability to understand the interaction and vertical coupling of large‐scale structures, thereby advancing our predictive capabilities of space weather critical for satellite operations.

Coriolis darkening in late-type stars

Context. Modeling the surface brightness distribution of stars is of prime importance to interpret the large amount of available interferometric, spectropolarimetric, or photometric observations. Beyond stellar physics, this is also a prerequisite to characterize exoplanets or our Galaxy. Nevertheless, this remains quite challenging for cool stars as it requires one to model the magnetohydrodynamic turbulence that develops in their convective envelope. Aims. In Paper I (Raynaud, R., Rieutord, M., Petitdemange, L., Gastine, T., & Putigny, B. 2018, A&A, 609, A124), the effect of the Coriolis acceleration on the surface heat flux has been studied by means of hydrodynamic simulations. In this paper, we aim to investigate the additional effect of dynamo magnetic fields that can be generated in the thick convective envelopes of cool stars. We focus on an envelope thickness that is representative of either a ∼0.35 M⊙ M dwarf, a young red giant star or a pre-main sequence star. Methods. We performed a parametric study using numerical magnetohydrodynamic simulations of anelastic convection in thick rotating spherical shells. The stratification in density ranges from a few tens to a few hundreds. The setup assumes a constant entropy jump between the inner and outer layers to force convection, with stress-free boundary conditions for the velocity field. The magnetic Prandtl number was systematically varied in order to vary the magnetic field intensity. For each model, we computed the azimuthally and temporally averaged surface distribution of the heat flux, and examined the leading-order effect of the magnetic field on the obtained latitudinal luminosity profile. Results. We identify three different regimes. Close to the onset of convection, while the first unstable modes tend to convey heat more efficiently near the equator, magnetic fields are shown to generally enhance the mean heat flux close to the polar regions (and the tangent cylinder). By progressively increasing the Rayleigh number, the development of a prograde equatorial jet was previously shown to make the equator darker when no magnetic field is taken into account. For moderate Rayleigh numbers, magnetic fields can instead inverse the mean pole-equator brightness contrast (which means going from a darker to a brighter equator when a dynamo sets in) and finally induce a similar regime to that found close to the onset of convection. For more turbulent models with larger Rayleigh numbers, magnetic fields alternatively tend to smooth out the brightness contrast. This general behavior is shown to be related to the quenching of the surface differential rotation by magnetic fields and remains valid regardless of the magnetic morphology. Conclusions. Mean global trends regarding the impact of rotation and magnetic fields on the surface brightness distribution of cool stars are theoretically depicted and need to be tested by future observations. This work opens the door to more detailed theoretical studies including the effect of nonaxisymmetric and time-variable surface features associated with magnetic activity.

WawHelioIonMP: A Semiempirical Tool for the Determination of Latitudinal Variation in the Ionization Rate of Interstellar Hydrogen and the Solar Wind

The latitudinal structure of the solar wind varies during the cycle of solar activity. Analysis of this variation is important for understanding the solar activity and interpretation of observations of heliospheric energetic neutral hydrogen atoms and interstellar neutral (ISN) atoms inside the heliosphere, which yield information on the heliosphere and its interaction with the interstellar medium. Existing methods of retrieving this information from indirect remote-sensing measurements of phenomena, including the heliospheric backscatter glow and interplanetary scintillations of remote radio sources, are challenging to apply in real time. Here, we propose a method WawHelioIonMP of approximate retrieval of latitudinal profiles of the ionization rates of ISN H using a machine-learning-based interpretation of the helioglow. Assuming that we know their history during two past solar cycles and have observations of the helioglow for close-to-circumsolar circles with a radius close to 90°, we derive statistically an algebraic relation between the ionization profiles and lightcurves. With the relation reversed, we are then able to derive the ionization rate profiles based on observed light curves, such as those planned for the GLObal solar Wind Structure (GLOWS) experiment on the forthcoming NASA mission Interstellar Mapping and Acceleration Probe (IMAP). The application of this method is straightforward and rapid because complex simulations are no longer needed. We present the method of retrieval of the profiles of the ionization rates, leaving the discussion of details of the decomposition of the retrieved ionization rate profiles into profiles of the solar wind speed and density to a future paper.

A Comparison of Auroral Oval Proxies With the Boundaries of the Auroral Electrojets

AbstractThe boundaries of the auroral oval and auroral electrojets are an important source of information for understanding the coupling between the solar wind and the near‐earth plasma environment. Of these two types of boundaries the auroral electrojet boundaries have received comparatively little attention, and even less attention has been given to the connection between the two. Here we introduce a technique for estimating the electrojet boundaries, and other properties such as total current and peak current, from 1‐D latitudinal profiles of the eastward component of equivalent current sheet density. We apply this technique to a preexisting database of such currents along the 105° magnetic meridian, estimated using ground‐based magnetometers, producing a total of 11 years of 1‐min resolution electrojet boundaries during the period 2000–2020. Using statistics and conjunction events we compare our electrojet boundary data set with an existing electrojet boundary data set, based on Swarm satellite measurements, and auroral oval proxies based on particle precipitation and field‐aligned currents. This allows us to validate our data set and investigate the feasibility of an auroral oval proxy based on electrojet boundaries. Through this investigation we find the proton precipitation auroral oval is a closer match with the electrojet boundaries. However, the bimodal nature of the electrojet boundaries as we approach the noon and midnight discontinuities makes an average electrojet oval poorly defined. With this and the direct comparisons differing from the statistics, defining the proton auroral oval from electrojet boundaries across all local and universal times is challenging.

Ionospheric response of the March 2023 geomagnetic storm over European latitudes

The present study describes a spatial and temporal analysis of the ionospheric variability over the European sector during a major storm event from 23 to 24 March 2023. The analysis is mainly based on ionospheric characteristics such as foF2, hmF2 and Vertical Total Electron Content (VTEC) over ten Digisondes and co-located GNSS receivers. The event started at 12:00UT on 23 March as a positive ionospheric storm followed by a negative ionospheric storm to 04:00 UT on the next day SYM-H<-183nT. A notable latitude dependence of the ionospheric response is more prominent over the northern mid-latitude region attributed to the equatorward displacement of the Midlatitude Ionospheric Trough (MIT). To verify this hypothesis, Swarm latitudinal electron density profiles from in-situ Langmuir probe measurements over Europe were considered. These profiles demonstrate a clear MIT displacement from ∼65°N on 22 March to ∼55°N on 23 March with a subsequent recovery around ∼65°N on 25 March.

Local variations of the cross-field transversal anisotropy orientation and drift direction in the F-region of the mid-latitude ionosphere

Analysis of fluctuations of the satellite radio-signals scattered on small-scale irregularities in F-region of the ionosphere and obtained recorded by a terrestrial ground-based receiver in Moscow showed has shown that often two or three maxima are present in the latitudinal profile of amplitude dispersion variance. The orientation of the cross-field transverse or transversal anisotropy of the irregularities was determined and compared with the drift direction obtained by the ionosonde DPS-4 using the LocalDrift program.

An Analytic Theory of Near-Surface Relative Humidity over Land

Abstract There is no simple explanation for the spatial structure of near-surface relative humidity over land. We present a diagnostic theory for zonally and temporally averaged near-surface relative humidity (RH) over land based on energy budgets of an atmospheric column in radiative–convective equilibrium. The theory analytically relates RH to the surface evaporative fraction (EF), has no calibrated parameters, and is quantitatively accurate when compared with RH from a reanalysis, and with cloud-permitting simulations over an idealized land surface. The theory is used to answer two basic questions. First, why is RH never especially low (e.g., 1%)? The theory shows that established lower bounds on EF over land and ocean are equivalent to lower bounds on RH that preclude particularly low values, at least for conditions typical of the modern Earth. Second, why is the latitudinal profile of RH over land shaped like the letter W, when both specific humidity and saturation specific humidity essentially decline monotonically from the equator to the poles? The theory predicts that the latitudinal profile of RH should look more like that of water stored in the soil (which also exhibits a W-shaped profile) than in the air (which does not).

Toroidal Magnetic Flux Budget in Mean-field Dynamo Model of Solar Cycles 23 and 24

We study the toroidal magnetic flux budget of the axisymmetric part of a data-driven 3D mean-field dynamo model of Solar Cycles 23 and 24. The model simulates the global solar dynamo that includes the effects of the formation and evolution of bipolar magnetic regions (BMRs) emerging on the solar surface. By applying Stokes’s theorem to the dynamo induction equation, we show that the hemispheric magnitude of the net axisymmetric toroidal magnetic field generation rate in the bulk of the convection zone can only partially be estimated from the surface parameters of the differential rotation and the axisymmetric radial magnetic field. The contribution of the radial integral along the equator, which is mostly due to the rotational radial shear at the bottom of the convection zone, has the same magnitude and is nearly in phase with the effect of the surface latitudinal differential rotation. Also, the toroidal field generation rate estimate strongly depends on the latitudinal profile of the surface radial magnetic field near the poles. This profile in our dynamo models significantly deviates from the polar magnetic field distribution observed during the minima of Solar Cycles 22, 23, and 24. The cause of this discrepancy requires further observational and theoretical studies. Comparing the 2D axisymmetric and the 3D nonaxisymmetric dynamo models, we find an increase in the toroidal field generation rate in the 3D model due to the surface effects of BMRs, resulting in an increase in the axisymmetric poloidal magnetic field magnitude.

Lithospheric underthrusting beneath the northern Eastern Cordillera plateau, Colombian Andes: Insights from analyzing tomographic inversion using local earthquake travel time and gravity data

The northern Eastern Cordillera in the Colombian Andes is a wide (~200 km) high-elevation (>2.5 km) subduction-related asymmetric plateau. This plateau is currently subjected to shortening and magmatic addition, and yet the nature of the lowermost crust and its transition to the underlying mantle remains poorly constrained. To improve our knowledge about the structure of the deep crust beneath the EC plateau, we conducted a joint inversion of travel times of local earthquakes and gravity data. Gravity contributes to up to 0.5% in dVp and dVs with no affectation of the shape or location of the discussed anomalies. Along the latitudinal profile with the highest resolution (~5.7°N), two anomalies are identified at depths of 40–60 km beneath the plateau. A western low-velocity anomaly is interpreted as crustal material underthrust eastward beneath the northwestern EC. This process is triggering the abrupt change in topography between the adjacent low-elevation basin and the orogenic plateau. Additionally, a high-velocity anomaly beneath the eastern flank of the EC is likely related to mantle metasomatism and westward underthrusting of the foreland lithosphere. This metasomatism is either related to the interaction between mafic magmas and the uppermost mantle or silica enrichment that occurred during a past episode of flat subduction. Evidence for foreland underthrusting includes relocated earthquakes at 33–42 km depth within the thrust system between the EC and the foreland, along with increased shortening in the eastern part of the plateau, an increase in exhumation rates, the eastward migration of deformation towards the foreland, and dominated thick-skinned deformation in the upper crust of the foreland with an eastward vergence of thrusts and related folds. Furthermore, within the central part of the plateau, our results show low velocities between 30 and 40 km depth, consistent with previous constraints, suggesting magmatic underplating beneath the Paipa-Iza volcanic complex.

Strong Resemblance between Surface and Deep Zonal Winds inside Jupiter Revealed by High-degree Gravity Moments

Jupiter’s atmosphere interior is a coupled fluid dynamical system strongly influenced by the rapid background rotation. While the visible atmosphere features east–west zonal winds on the order of ∼100 m s−1, zonal flows in the dynamo region are significantly slower, on the order of ∼cm s−1 or less, according to the latest magnetic secular variation analysis. The vertical profile of the zonal flows and the underlying mechanism remain elusive. The latest Juno radio tracking measurements afforded the derivation of Jupiter’s gravity field to spherical harmonic degree 40. Here, we use the latest gravity solution to reconstruct Jupiter’s deep zonal winds without a priori assumptions about their latitudinal profile. The pattern of our reconstructed deep zonal winds strongly resemble that of the surface wind within ±35° latitude from the equator, in particular the northern off-equatorial jet (NOEJ) and the southern off-equatorial jet. The reconstruction features larger uncertainties in the southern hemisphere due to the north–south asymmetric nature of Juno's trajectory. The amplitude of the reconstructed deep NOEJ matches that of the surface wind when the wind is truncated at a depth ∼2500 km, and becomes twice that of the surface wind if the truncation depth is reduced to ∼1500 km. Our analysis supports the physical picture in which a prominent part of the surface zonal winds extends into Jupiter’s interior significantly deeper than the water cloud layer.

Jupiter’s Atmosphere Dynamics Based on High-Resolution Spectroscopy with VLT/ESPRESSO

We present a new study of Jupiter’s atmosphere dynamics using for the first time the extremely high-resolution capabilities of VLT/ESPRESSO to retrieve wind velocities in Jupiter’s troposphere, with a dedicated ground-based Doppler velocimetry method. This work is primarily a proof-of-concept for retrieving Jupiter’s winds using VLT/ESPRESSO Doppler velocities. These results are complemented by a re-analysis of Cassini’s data from its fly-by of Jupiter in December 2000, performing cloud tracking at visible wavelengths, for cross comparison with Doppler velocimetry results, along with previous cloud-tracking results. We explore the effectiveness of this refined method to measure winds in Jupiter, using high-resolution spectroscopy data obtained from ESPRESSO observations performed in July 2019, with a Doppler velocimetry method based on backscattered solar radiation in the visible range. Coupled with our ground-based results, we retrieved a latitudinal and longitudinal profile of Jupiter’s winds along select bands of the atmosphere. Comparing the results between cloud-tracking methods, based on previous reference observations, and our new Doppler velocimetry approach, we found a good agreement between them, demonstrating the effectiveness of this technique. The winds obtained in this exploratory study have a two-fold relevance: they contribute to the temporal and spatial variability study of Jupiter’s troposphere dynamics, and the results presented here also validate the use of this Doppler technique to study the dynamics of Jupiter’s atmosphere and pave the way for further exploration of a broader region of Jupiter’s disk for a more comprehensive retrieval of winds and to evaluate their spatial and temporal variability.

Latituditual Structure of Dayside Polar Cusp Precipitation

The results of observations of low-altitude spacecraft crossing the daytime sector of the auroral zone and of high-apogee spacecraft in the equatorial plane of the magnetosphere were analyzed in order to identify the main processes leading to the formation of dayside polar cusps. Observations from the DMSP F7 spacecraft were used to analyze the latitudinal characteristics of ion precipitation in the cusp region and to study the latitudinal profile of ion pressure in the cusp depending on the IMF parameters. A significant difference was found in identifying the cusp boundaries using an automated data processing system and direct analysis of spacecraft observations. It is shown that for small negative values of the Bz-component of the IMF (〈Bz〉 = –3.0 nT), an ordinary feature of the cusp is the latitudinal profile of the ion pressure (Pi) with a width of ~1° of latitude with two maxima, one of which is located in the equatorward and the other in the poleward of the cusp. For large negative Bz values (–6, –8 nT), the polar maximum in the latitudinal profile Pi disappears; only the equatorial maximum remains, the Pi level at the maximum increases, and the width of the cusp decreases to ~0.7°. For Bz IMF 0, the most characteristic is the Pi profile with a maximum ion pressure in the polar part of the cusp. The cusp for Bz 0 is located at higher latitudes than for Bz 0, and its average latitudinal width increase to ~1.4° of latitude. In the prenoon sector MLT, the most typical for periods with a large negative By-component of the IMF (〈By〉 = –6.3 nT, 〈Bz〉 = –1.7 nT) is a cusp with a width of ~1.4° of latitude with a flat top in the latitudinal Pi profile. Comparison of the pressure distributions observed at low heights with data from high-apogee satellites confirmed the possibility of describing the formation of the cusp as a diamagnetic cavity and using observations in the cusp to determine the ion pressure in the magnetosheath.

Do satellite-based products suffice for rainfall observations over data-sparse complex terrains? Evidence from the North-Western Himalayas

Remotely sensed observations are crucial for conducting meteorological studies, particularly over complex mountainous terrains such as, the North-Western Himalayas (NWH), which are characterized by a very sparse and uneven distribution of ground observatories. These complex terrains are subject to huge inter-basin climatic and topographic heterogeneity, which often induces large inconsistencies in the form of varying rainfall estimations and observations among the satellite-based gridded precipitation products (GPPs). This underpins the need for a detailed sub-regional validation of GPPs and attribution of the observed discrepancies over such complex terrains. This study provides a comprehensive validation analysis of four major high-resolution GPPs (TMPA-3B42V7, CHIRPS-V2.0, CMORPH-CDR, and PERSIANN-CDR) against the in-situ gridded observations provided by IMD, across the six sub-basins of NWH. Utilizing various descriptive, statistical, and categorical metrics, we evaluated the daily, seasonal, and annual rainfall climatology for each dataset and also extracted their longitudinal and latitudinal error profiles and detection capabilities as a function of elevation and local relief. High inconsistencies were observed among the datasets, with each dataset performing differently over different sub-basins. All the datasets underperformed IMD over higher elevations, while TMPA-3B42V7 performed better even over the Upper Indus sub-basin. CHIRPS-V2.0 performed well over Jhelum, and Chenab sub-basins, whereas the CDR version of CMORPH, performed well over the flatter terrains of Ravi, Beas, and Satluj sub-basins, particularly during the summer monsoons. The IR-based PERSIANN-CDR, on the other hand, failed to capture the daily rainfall estimates and underperformed IMD throughout NWH. The findings further highlight low detection capability of datasets at higher rainfall thresholds, indicating underestimation of extreme rainfall. With respect to the relationship between GPPs performance and topographic components, the results showed that the occurrence frequency of rain detection in GPPs decreases, while the occurrence frequency of over-detection increases with increase in elevation and local relief. Although, the performance of GPPs co-varies with both topographic components, local relief governed by the multi-step topographic gradients comprising valleys, orographic fronts, and orographic interiors was observed to have a more profound effect on error profiles. Lastly, the study identifies and discusses the probable regional (e.g., rainfall structure, orographic influence, biophysical, data scarcity, spatial resolution), and product-specific (e.g., source of generation, remote sensing instrumentation, satellite algorithms, data assimilation techniques) factors attributing to the inconsistencies observed among the datasets. The findings from the present research offer insights to the algorithm developers for improving product accuracy and hydro-meteorologist for utilizing appropriate GPP over respective sub-basin.

Temporal and spatial variability of EUV flux at 094 Å and its relationship with sunspot activity

We study temporal and spatial variability of coronal EUV flux/emission/intensity at 094 Å and investigate latitudinal profiles of the EUV flux from centre to poles of solar disc based on daily image obtained from the SDO/AIA for the period from 10 February 2011 to 20 November 2021. Solar coronal activities (regions of high EUV flux) patterns of latitudinal EUV flux, latitudinal north-south asymmetry of EUV flux and relationship between EUV flux and sunspot numbers are discussed. The disc-integrated normalized EUV flux is found positive correlated with SDO/EVE normalised solar irradiance. It is shown that there are two kinds of migration of solar coronal activities in distribution of EUV flux at 094 Å during the rising phase of solar cycle 24: one towards the equator and another towards the poles in both hemispheres. The peaks of EUV flux occur in the region −25∘ to +25∘ solar latitudes in the years 2011 and 2014. The latitudinal EUV flux in northern and southern hemispheres have asymmetrical behaviour. The dominancy of EUV flux in northern hemisphere is found only at 5∘, 15∘, and 75∘ solar latitudes whereas the dominancy of EUV flux in southern hemisphere is found at the rest of the solar latitudes. We found that the dominancy of EUV flux in both the hemispheres is a function of time and solar latitude. The EUV flux is dominated in the southern hemisphere during the entire period. The EUV flux is positive correlated with sunspot numbers for full disc, northern and southern hemispheres and their relationship is found linear and significant.

Geoinduced currents on Karelian-Kola power line and finnish gas pipeline on september, 12–13 2017

Geomagnetic activity and occurrence of large values of geoinduced currents (GICs) during a moderate magnetic storm (SYM/H ∼ −65 nT) on September, 12–13 2017 have been studied. Two intense substorms (AL ∼600 nT and ∼1200 nT) were observed within the period of this magnetic storm. Amplification and motion of electrojets during substorms is known to be one of the important sources of GIC value increase in the auroral zone. The fine spatial temporal structure of westward electrojet has been analyzed using the latitudinal profiles of the IMAGE network and the equivalent currents of the MIRACLE system data. GICs activity were monitored by EURISGIC from Russian stations Vykhodnoy (VKH) and Revda (RVD) in the North-West of Russia (eurisgic.ru) and Mäntsälä station (MAN) in South Finland. The data from these stations are convenient to track GIC from ∼60° to ∼69° geographical latitudes. It has been shown that the increase in GIC amplitudes at different latitudes was associated with the poleward movement of the westward electrojet during the expansion phase of the substorm. Besides, it has been found that the source of the GICs at the recovery phase of the second substorm appeared to be a short pulse of Pc5 pulsations and the amplitudes of GICs were comparable with substorms one. It is also shown that the increase in GIC amplitude are in good agreement with the increase in the Wp- and IL-geomagnetic indices used for global and local control over the substorm appearance.