Solar Latitude Research Articles

An empirical model of electron temperatures in the Mars ionosphere based on Langmuir probe measurements in the descending phase of solar cycle 24

Mars ionospheric temperatures exhibit profound variability based on, for example, changes in solar irradiance, solar local time, season, and latitude. The close coupling between ionospheric temperatures and neutral thermospheric density is of even greater importance. To evaluate these effects and to quantify their contributions to electron temperature, we developed the Temperature of electrons Specification for the Mars Ionosphere (TeSMI). After identifying the strongest correlations between the model inputs and the observed electron temperatures, several additional corrections were examined and implemented. The primary source of climatological variability was related to neutral pressure, local solar time, and 17-22 nm irradiance. In addition to this, changes due to seasonal effects and latitude each required 5–10% of additional corrections. Evaluating the electron temperatures on which TeSMI is based provided an opportunity to study several relevant ionospheric phenomena. One of these is the solar cycle dependence of electron temperature which is found to be relatively small compared with other sources of variability. Solar minimum temperatures are on average 7–12% lower than those at solar maximum during solar cycle 24. The solar cycle dependence also appears stronger at aphelion than at other times. Furthermore, at Mars perihelion, electron temperatures seem to increase in response to a possible source of heating from the lower atmosphere. Furthermore, we identify cold and warm regions with respect to the TeSMI model that occur in specific aerographic locations. These regions of warmer and colder temperatures appear organized with respect to the crustal magnetic field locations at altitudes above 170 km. This is the first time that the effect of the crustal field is identified in the statistical electron temperature data below 200 km. Lastly, at the lowest altitudes (160–180 km) analyzed here, the equatorial ionosphere is colder than the polar regions by 5–15% which is interpreted to be a result of the atmospheric circulation pattern.

Giant white-light flares on fully convective stars occur at high latitudes

ABSTRACT White-light flares are magnetically driven localized brightenings on the surfaces of stars. Their temporal, spectral, and statistical properties present a treasury of physical information about stellar magnetic fields. The spatial distributions of magnetic spots and associated flaring regions help constrain dynamo theories. Moreover, flares are thought to crucially affect the habitability of exoplanets that orbit these stars. Measuring the location of flares on stars other than the Sun is challenging due to the lack of spatial resolution. Here we present four fully convective stars observed with the Transiting Exoplanet Survey Satellite that displayed large, long-duration flares in white-light which were modulated in brightness by the stars’ fast rotation. This allowed us to determine the loci of these flares directly from the light curves. All four flares occurred at latitudes between 55° and 81°, far higher than typical solar flare latitudes. Our findings are evidence that strong magnetic fields tend to emerge close to the stellar rotational poles for fully convective stars, and suggest that the impact of flares on the habitability of exoplanets around small stars could be weaker than previously thought.

Modeling the Observed Distortion of Multiple (Ghost) CME Fronts in STEREO Heliospheric Imagers

Abstract In this work we have, for the first time, applied the interpretation of multiple “ghost-fronts” to two synthetic coronal mass ejections (CMEs) propagating within a structured solar wind using the Heliospheric Upwind eXtrapolation time (HUXt) solar wind model. The two CMEs occurred on 2012 June 13–14 showing multiple fronts in images from Solar Terrestrial Relations Observatory Heliospheric Imagers (HIs). The HUXt model is used to simulate the evolution of these CMEs across the inner heliosphere as they interacted with structured ambient solar wind. The simulations reveal that the evolution of CME shape is consistent with observations across a wide range of solar latitudes and that the manifestation of multiple “ghost-fronts” within HIs’ field of view is consistent with the positions of the nose and flank of the same CME structure. This provides further confirmation that the angular separation of these features provides information on the longitudinal extent of a CME. For one of the CMEs considered in this study, both simulations and observations show that a concave shape develops within the outer CME front. We conclude that this distortion results from a latitudinal structure in the ambient solar wind speed. The work emphasizes that the shape of the CME cannot be assumed to remain a coherent geometrical shape during its propagation in the heliosphere. Our analysis demonstrates that the presence of “ghost” CME fronts can be used to infer the distortion of CMEs by ambient solar wind structure as a function of both latitude and longitude. This information has the potential to improve the forecasting of space weather events at Earth.

Coronal mass ejections observed by heliospheric imagers at 0.2 and 1 au

Context. We study two coronal mass ejections (CMEs) observed between April 1 to 2, 2019 by both the inner Wide-Field Imager for Parker Solar Probe (WISPR-I) onboard the Parker Solar Probe (PSP) spacecraft (located between about 46 and 38 solar radii during this period) and the inner heliospheric imager (HI-1) onboard the Solar Terrestrial Relations Observatory Ahead (STEREO-A) spacecraft, orbiting the Sun at about 0.96 au. This is the first study of CME observations from two viewpoints in similar directions but at considerably different solar distances. Aims. Our objective is to derive CME kinematics from WISPR-I observations and to compare them with results from HI-1. This allows us to understand how the PSP observations affect the CME kinematics, especially due to its proximity to the Sun. Methods. We estimated the CME positions, speeds, accelerations, propagation directions, and longitudinal deflections using imaging observations from two spacecrafts and a set of analytical expressions that consider the CME as a point structure and take the rapid change in spacecraft position into account. We derived the kinematics using each viewpoint independently and both viewpoints as a constraint. Results. We found that both CMEs are slow (<400 km s−1), propagating eastward of the Sun-Earth line (westward of PSP and STEREO-A). The second CME seems to accelerate between ~0.1 and ~0.2 au and deflect westward with an angular speed consistent with the solar rotation speed. We found some discrepancies in the CME solar distance (up to 0.05 au, particularly for CME #1), latitude (up to ~10°), and longitude (up to 24°) when comparing results from different fit cases (different observations or set of free parameters). Conclusions. Discrepancies in longitude are likely due to the feature that is tracked visually, rather than instrumental biases or fit assumptions. For similar reasons, the CME #1 solar distance, as derived from WISPR-I observations, is larger than the HI-1 result, regardless of the fit parameters considered. Error estimates for CME kinematics do not show any clear trend associated with the observing instrument. The source region location and the lack of any clear in situ counterparts (both at near-Earth and at PSP) support our estimate of the propagation direction for both events.

Higher latitude and lower solar radiation influence on hip fracture admissions in Chilean older population

Data linking solar radiation with fractures are lacking. We found that lower solar radiation was associated with higher hip fracture admission rates in men from Chile. This supports the idea that solar radiation, a surrogate of vitamin D, may be involved in the development of fractures in older population. INTRODUCTION : To explore the associations between solar radiation and latitude with hip fracture admission rates in people aged 65 years or older in Chile, the country with the greatest variation in solar radiation in the world. Methods In this ecological study, we investigated the associations between regional solar radiation and latitude with hospitalizations due to hip fracture in population aged 65 years or older, by reviewing national records between 2013 and 2018. We also evaluated the role of sociodemographic factors such as poverty, education, indigenous ethnicity, and rurality rates. Results Between 2013 and 2018, there were 44,328 admissions due to hip fracture in people aged 65 years or older; 77.5% were women and 65.1% were aged 80 years or older. The national admission rate was 389.3 per 100,000 inhabitants (95% CI: 382.4-396.2). The highest admission rate was registered in the Region IX (445.3 per 100,000, 95% CI: 398.3-492.4), which has the highest poverty rates, indigenous ethnicity rates, and rurality rates. We found a north-south increasing gradient of admission rates in men (β=1.5 [95% CI: 0 to 3], p=0.044) and a significant association between solar radiation and admission rates in men (β=-4.4 [95% CI: -8 to 0.8], p=0.02). Admission rates in men were also associated with sociodemographic variables such as poverty (β=2.4 [95% CI: 0 to 4.8], p=0.048) and rurality rates (β=1.2 [95% CI: 0.1 to 2.4], p=0.039). Conclusion Regional solar radiation and latitude were associated with hip fracture admission rates in men aged 65 years or older in Chile, with highest admission rates at higher latitudes and lower solar radiation.

Giant white-light flares on fully convective stars occur at high latitudes

White-light flares are magnetically driven localized brightenings on the surfaces of stars. Their temporal, spectral, and statistical properties present a treasury of physical information about stellar magnetic fields. The spatial distributions of magnetic spots and associated flaring regions help constrain dynamo theories. Moreover, flares are thought to crucially affect the habitability of exoplanets that orbit these stars. Measuring the location of flares on stars other than the Sun is challenging due to the lack of spatial resolution. Here we present four fully convective stars observed with the Transiting Exoplanet Survey Satellite (TESS) that displayed large, long-duration flares in white-light which were modulated in brightness by the stars' fast rotation. This allowed us to determine the loci of these flares directly from the light curves. All four flares occurred at latitudes between 55 deg and 81 deg, far higher than typical solar flare latitudes. Our findings are evidence that strong magnetic fields tend to emerge close to the stellar rotational poles for fully convective stars, and suggest that the impact of flares on the habitability of exoplanets around small stars could be weaker than previously thought.

Solar Orbiter: Mission and spacecraft design

The main scientific goal of Solar Orbiter is to address the central question of heliophysics: ‘how does the Sun create and control the heliosphere?’ To achieve this goal, the spacecraft carries a unique combination of ten scientific instruments (six remote-sensing instruments and four in-situ instruments) towards the innermost regions of the Solar System, to as close as 0.28 AU from the Sun during segments of its orbit. The orbital inclination will be progressively increased so that the spacecraft reaches higher solar latitudes (up to 34° towards the end of the mission), making detailed studies of the polar regions of the Sun possible for the first time. This paper presents the spacecraft and its intended trip around the Sun. We also discuss the main engineering challenges that had to be addressed during the development cycle, instrument integration, and testing of the spacecraft.

Novel Approach for Predicting Direct and Open Solar Drying Using Artificial Neural Network for Medicinal Plant

In this study, an artificial neural network (ANN) was developed to obtain a generalized model for predicting the direct and open sun drying process for some medicinal plants. Since the quality of the experimental dataset can lead to a very performant model, in this study the dataset was collected from previously published papers and divided randomly into three subsets, namely 70 %, 15 %, and 15 % for training, testing, and validation. Based on the complex solar drying behaviour, ten parameters were considered as inputs: time, global solar radiation (GSR), outside temperature, inclination, emissivity, altitude, longitude, latitude, inside temperature, and nutritional value, to predict moisture content (MC), and drying rate (DR). Based on a trial and error method, the best ANN model was found with a topology of 10-28-14-2, with regression coefficient and root mean square error of (R = 97.044 %. RMSE = 4.589 %) and (R = 99.968 %, RMSE = 1.185 %) for MC and DR, respectively. It can be concluded that the obtained ANN model provides the best method for solar dryer modelling which can be generalized for any location in the world.

Assessment of improvement of the IRI model for foF2 variability over three latitudes in different hemispheres during low and high solar activities

This paper discusses the diurnal and seasonal variations of the F2 layer critical frequency (foF2) and the improvement of performance of the IRI-2016 model in predicting foF2 over three latitudes in different hemispheres during low and high solar activities. We extracted the foF2 data from six ionosonde stations which are Manila (14.7oN, 121.1oE), Yamagawa (31.2oN, 130.6oE), Yakutsk (62.0oN,129.6oE), Townsville (19.6oS, 146.8oE), Hobart (42.9oS, 147.3oE) and Terre Adelie (66.6oS, 140.0oE). The data of both low solar activity (LSA) period and high solar activity (HSA) periods were divided into three seasons as Northern Summer (May, June, July and August), Equinoxes (March, April, September and October) and Northern Winter (November, December, January and February). The present study showed that the IRI-2016 performance is strongly dependent on the solar activity, latitude, season, local time and hemisphere. For both hemispheres, the foF2 values at low latitude station are larger than those at middle latitude station, whereas the foF2 values at middle latitude station are larger than those at high latitude station. The agreement between IRI2016-modelled foF2 and foF2 measurements on all stations selected in the northern hemisphere is best for North Summer and worst for North Winter. For northern hemisphere, the values of relative deviations during both solar activities are largest in high latitudes and smallest in middle latitudes. As for southern hemisphere, the values of relative deviations during LSA are largest in middle latitudes and smallest in high latitudes, whereas the values of relative deviations during HSA are largest in low latitudes and smallest in high latitudes. It is thought that the relative deviations in the observed foF2 values are caused by solar activity that strongly alter chemical and electromagnetic processes in the ionosphere. These results are important for future improvements depending on solar activity and seasons in the IRI model for foF2 values over three latitudes in different hemispheres.

An empirical model of energetic electrons in Saturn’s magnetosphere based on Cassini data

Based on one-hour average data observed by the MIMI/LEMMS instrument onboard the Cassini spacecraft from 2004 to 2017, we present an empirical model of energetic electrons (27 ​keV–1937 ​keV) in Saturn’s magnetosphere. This model distinguishes between two different regions. In the inner magnetosphere (<20RS, RS ​= ​60268 ​km is the radius of Saturn), this model is constructed based on L-shell and includes dayside-nightside asymmetry, which is caused by the interaction between solar wind and Saturn’s magnetosphere. This model is also adjusted for magnetodisk warping according to the seasonal variation of solar latitude. In the outer magnetosphere (>20RS), this model is constructed based on magnetodisk coordinates and represents the sheet-like structure at magnetotail. Gaussian distribution is used to fit the data along with the perpendicular distance to the warped magnetodisk. We also include a magnetopause model to filter the flux data. Finally, the results from this model are compared with those from SATRAD (SATurn RADiation model). Our new model based on Cassini data provides a picture of the energetic electron environment from 2.5 RS to 40 RS in Saturn’s magnetosphere.

Effect of wingtip connection on the energy and flight endurance performance of solar aircraft

This study explores the effects of wingtip connection on decreasing energy consumption and increasing flight endurance for solar aircraft. The Oswald efficiency factor, induced drag coefficient and power consumption are derived as the models of the number of wingtip connected aircraft. As the energy margin model is related to the number of connected solar aircraft, a flight endurance margin model is proposed to evaluate the advantages of wingtip connection quantitatively. With the numerical method developed, researches on the energy and flight endurance performance for a given example wingtip-connected solar aircraft are performed. Moreover, the impacts of solar cell efficiency, flight date and latitude on the advantages of wingtip connection for solar aircraft are explored. The results suggest that the wingtip connection design enables solar aircraft to decrease induced drag coefficient, increase flight endurance and range effectively when the aircraft is only powered by battery. The wingtip connection design is more effective to increase the flight endurance and improve the maximum perpetual flight latitude with more connected solar aircrafts and higher solar cell efficiency, especially in the flight condition with high solar elevation angle and more daylight hours. However, as the number of connected solar aircraft increases, the effect of one more connected aircraft on these advantages decreases because the effect of wingtip connection on decreasing induced drag coefficient decreases with increasing aspect ratio.

Spatial and Temporal Properties of the Solar Cycle from RATAN-600 Microwave Observations

The study involves the obtainment of regular tracers of the solar cycle in the radio range by activity manifestations in the chromosphere and corona. Our research method consists of the systematic processing of the RATAN-600 radio data at frequencies 3–18 GHz obtained during more than one cycle of solar activity and their comparison with other databases of time series characterizing the magnetic activity of the Sun at the photospheric level. In the first phase of this work, we identified an array of approximately 600 active regions that evenly covers all phases of solar cycle 24 in approximately 9 years, for which we reliably identified the local radio sources based on RATAN-600 data, as well as data from other databases, such as spacecraft of the Space Weather Prediction Center of the National Oceanic and Atmospheric Administration and the Solar Dynamics Observatory. The sample is statistically homogeneous and evenly distributed over solar latitudes in both hemispheres. The statistical relationships between the sunspot areas and the parameters of intensity and polarization of local radio sources are obtained. It is shown how the spectral flux density of local radio sources in the chromosphere and corona at different frequencies increases with the increase in the sunspot area (and, consequently, the magnetic flux). The estimates of exponents of this dependence are obtained.

A Methodology for Estimation of Hourly‐Monthly Stochastic Trend Characteristics of Midlatitude Ionosphere

AbstractSpatiotemporal variability of ionosphere poses a major challenge in characterization of observable parameters, critical frequency of F2 layer (foF2), maximum ionization height (hmF2), total electron content (TEC), and slab thickness. The nature of the multiscale space‐time variability of ionosphere can be modeled as a random field. In this study, as a first step in random field modeling of the trend, hourly‐monthly parametric probability density functions (PPDF) of foF2, hmF2, slab thickness, and TEC are obtained using IONOLAB‐PDF method for three midlatitude stations (namely, Juliusruh, Pruhonice, and Rome) for low, moderate, and high solar activity years of 2009, 2012, and 2014, respectively. foF2 and hmF2 are obtained from ionosondes. TEC is estimated from dual‐frequency Global Positioning System (GPS) receivers. It is observed that hourly‐monthly PPDFs of all ionospheric parameters at the three midlatitude stations can best be represented by lognormal and Weibull distributions. The estimates of mean and standard deviations of hourly‐monthly PPDFs indicate that the spatiotemporal stochastic trend variation of the midlatitude ionosphere differs in terms of foF2 and GPS‐TEC. The hourly‐monthly PPDF of foF2 represents all major anomalies as well as seasonal and hourly trends, whereas those of GPS‐TEC is highly dependent on solar activity level and latitude. The general statistical trend of hmF2 is anticorrelated with foF2 as expected. The mean of hourly‐monthly PPDF of slab thickness is around 400 km in 2012 and 2014 for all stations between 0200 UT and 1600 UT.

The Solar Orbiter Solar Wind Analyser (SWA) suite

The Solar Orbiter mission seeks to make connections between the physical processes occurring at the Sun or in the solar corona and the nature of the solar wind created by those processes which is subsequently observed at the spacecraft. The mission also targets physical processes occurring in the solar wind itself during its journey from its source to the spacecraft. To meet the specific mission science goals, Solar Orbiter will be equipped with both remote-sensing and in-situ instruments which will make unprecedented measurements of the solar atmosphere and the inner heliosphere. A crucial set of measurements will be provided by the Solar Wind Analyser (SWA) suite of instruments. This suite consists of an Electron Analyser System (SWA-EAS), a Proton and Alpha particle Sensor (SWA-PAS), and a Heavy Ion Sensor (SWA-HIS) which are jointly served by a central control and data processing unit (SWA-DPU). Together these sensors will measure and categorise the vast majority of thermal and suprathermal ions and electrons in the solar wind and determine the abundances and charge states of the heavy ion populations. The three sensors in the SWA suite are each based on the top hat electrostatic analyser concept, which has been deployed on numerous space plasma missions. The SWA-EAS uses two such heads, each of which have 360° azimuth acceptance angles and ±45° aperture deflection plates. Together these two sensors, which are mounted on the end of the boom, will cover a full sky field-of-view (FoV) (except for blockages by the spacecraft and its appendages) and measure the full 3D velocity distribution function (VDF) of solar wind electrons in the energy range of a few eV to ∼5 keV. The SWA-PAS instrument also uses an electrostatic analyser with a more confined FoV (−24° to +42° × ±22.5° around the expected solar wind arrival direction), which nevertheless is capable of measuring the full 3D VDF of the protons and alpha particles arriving at the instrument in the energy range from 200 eV/q to 20 keV/e. Finally, SWA-HIS measures the composition and 3D VDFs of heavy ions in the bulk solar wind as well as those of the major constituents in the suprathermal energy range and those of pick-up ions. The sensor resolves the full 3D VDFs of the prominent heavy ions at a resolution of 5 min in normal mode and 30 s in burst mode. Additionally, SWA-HIS measures 3D VDFs of alpha particles at a 4 s resolution in burst mode. Measurements are over a FoV of −33° to +66° × ±20° around the expected solar wind arrival direction and at energies up to 80 keV/e. The mass resolution (m/Δm) is &gt; 5. This paper describes how the three SWA scientific sensors, as delivered to the spacecraft, meet or exceed the performance requirements originally set out to achieve the mission’s science goals. We describe the motivation and specific requirements for each of the three sensors within the SWA suite, their expected science results, their main characteristics, and their operation through the central SWA-DPU. We describe the combined data products that we expect to return from the suite and provide to the Solar Orbiter Archive for use in scientific analyses by members of the wider solar and heliospheric communities. These unique data products will help reveal the nature of the solar wind as a function of both heliocentric distance and solar latitude. Indeed, SWA-HIS measurements of solar wind composition will be the first such measurements made in the inner heliosphere. The SWA data are crucial to efforts to link the in situ measurements of the solar wind made at the spacecraft with remote observations of candidate source regions. This is a novel aspect of the mission which will lead to significant advances in our understanding of the mechanisms accelerating and heating the solar wind, driving eruptions and other transient phenomena on the Sun, and controlling the injection, acceleration, and transport of the energetic particles in the heliosphere.

Thermal melanism explains macroevolutionary variation of dorsal pigmentation in Eurasian vipers

Colouration may endorse thermoregulatory and antipredatory functions in snakes. The thermal melanism hypothesis predicts that dark-coloured individuals are ecologically favoured in cool climates. However, the loss of aposematic and cryptic colourations may imply high predation for melanistic snakes. Here, we used the monophyletic group of Eurasian vipers (subfamily Viperinae) to test whether an increase in the extent of dark area inside the characteristic zigzag dorsal pattern is associated to colder environments. We measured two colouration traits in zigzag-patterned individuals (number of dorsal marks and weighted pigmentation index) and used a phylogenetic comparative approach to explore macroevolutionary patterns of dorsal pigmentation and test whether its extent is associated to ecogeographic characteristics of lineages’ ranges. Phylogenetically-naïve and phylogenetically-informed analyses yielded a significant association between the degree of pigmentation of the zigzag pattern and environmental variables such as solar radiation, elevation and latitude. The degree of pigmentation of the zigzag pattern is highlighted as an adaptive trait that matches range attributes mirroring cold environments irrespective of the phylogeny. These results constitute the first large-scale evidence supporting the thermal melanism hypothesis in snakes, opening new avenues of inquiry for the mechanisms that shape the evolution of colour phenotypes.

The Solar Orbiter EUI instrument: The Extreme Ultraviolet Imager

Context.The Extreme Ultraviolet Imager (EUI) is part of the remote sensing instrument package of the ESA/NASA Solar Orbiter mission that will explore the inner heliosphere and observe the Sun from vantage points close to the Sun and out of the ecliptic. Solar Orbiter will advance the “connection science” between solar activity and the heliosphere.Aims.With EUI we aim to improve our understanding of the structure and dynamics of the solar atmosphere, globally as well as at high resolution, and from high solar latitude perspectives.Methods.The EUI consists of three telescopes, the Full Sun Imager and two High Resolution Imagers, which are optimised to image in Lyman-αand EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere up to corona. The EUI is designed to cope with the strong constraints imposed by the Solar Orbiter mission characteristics. Limited telemetry availability is compensated by state-of-the-art image compression, onboard image processing, and event selection. The imposed power limitations and potentially harsh radiation environment necessitate the use of novel CMOS sensors. As the unobstructed field of view of the telescopes needs to protrude through the spacecraft’s heat shield, the apertures have been kept as small as possible, without compromising optical performance. This led to a systematic effort to optimise the throughput of every optical element and the reduction of noise levels in the sensor.Results.In this paper we review the design of the two elements of the EUI instrument: the Optical Bench System and the Common Electronic Box. Particular attention is also given to the onboard software, the intended operations, the ground software, and the foreseen data products.Conclusions.The EUI will bring unique science opportunities thanks to its specific design, its viewpoint, and to the planned synergies with the other Solar Orbiter instruments. In particular, we highlight science opportunities brought by the out-of-ecliptic vantage point of the solar poles, the high-resolution imaging of the high chromosphere and corona, and the connection to the outer corona as observed by coronagraphs.

Asymmetry in the Length Scales of the Solar Supergranulation Network

Abstract Supergranulation is the horizontal velocity pattern on the solar surface with a typical size of 30,000 km and a lifetime of 24 hr. The network structure seen in chromospheric lines, such as Ca ii K 3934 Å, is the manifestation of supergranulation. The network seen in the extreme-ultraviolet lines like He ii 304 Å is the extension of the chromospheric network into the upper solar atmosphere. We have obtained the length scales of the supergranulation network from the autocorrelation function of calcium ii K spectroheliograms from the Kodaikanal archival data. The behavior of the length scales in the horizontal (parallel to the direction of rotation) and vertical (perpendicular to the direction of rotation) have been obtained in different latitudes for a period of about 100 yr. The time-averaged length scales show a nearly symmetric variation in the northern and southern hemispheres. The length scales also show a profound asymmetry in the horizontal and vertical directions, which is dependent on solar latitude. A comparison reveals that both length scales are almost equal near the equatorial latitudes, but the vertical length scales relatively become smaller toward higher latitudes. The asymmetry is independently verified from He ii 304 Å images from the Solar Dynamic Observatory/Atmospheric Imaging Assembly. As the length scales are related to the width of the network, the results point to the asymmetry in the supergranular cell boundary. Supergranulation is one of the basic length scales of solar convection, hence these results can have implications for the convection in Sun-like stars.

Reconstruction of daytime land surface temperatures under cloud-covered conditions using integrated MODIS/Terra land products and MSG geostationary satellite data

There is considerable demand for satellite observations that can support spatiotemporally continuous mapping of land surface temperature (LST) because of its strong relationships with many surface processes. However, the frequent occurrence of cloud cover induces a large blank area in current thermal infrared-based LST products. To effectively fill this blank area, a new method for reconstructing the cloud-covered LSTs of Terra Moderate Resolution Imaging Spectroradiometer (MODIS) daytime observations is described using random forest (RF) regression approach. The high temporal resolution of the Meteosat Second Generation (MSG) LST product assisted in identifying the temporal variations in cloud cover. The cumulative downward shortwave radiation flux (DSSF) was estimated as the solar radiation factor for each MODIS pixel based on the MSG DSSF product to represent the impact from cloud cover on incident solar radiation. The RF approach was used to fit an LST linking model based on the datasets collected from clear-sky pixels that depicted the complicated relationship between LST and the predictor variables, including the surface vegetation index (the normalized difference vegetation index and the enhanced vegetation index), normalized difference water index, solar radiation factor, surface albedo, surface elevation, surface slope, and latitude. The fitted model was then used to reconstruct the LSTs of cloud-covered pixels. The proposed method was applied to the Terra/MODIS daytime LST product for four days in 2015, spanning different seasons in southwestern Europe. A visual inspection indicated that the reconstructed LSTs thoroughly captured the distribution of surface temperature associated with surface vegetation cover, solar radiation, and topography. The reconstructed LSTs showed similar spatial pattern according to the comparison with clear-sky LSTs from temporally adjacent days. In addition, evaluations against Global Land Data Assimilation System (GLDAS) NOAH 0.25° 3-h LST data and reference LST data derived based on in-situ air temperature measurements showed that the reconstructed LSTs presented a stable and reliable performance. The coefficients of determination derived with the GLDAS LST data were all above 0.59 on the four examined days. These results indicate that the proposed method has a strong potential for reconstructing LSTs under cloud-covered conditions and can also accurately depict the spatial patterns of LST.

Comparison of Latitude Distribution and Evolution of Even and Odd Sunspot Cycles

We study the latitudinal distribution and evolution of sunspot areas of Solar Cycles 12 – 23 (SC12–23) and sunspot groups of Solar Cycles 8 – 23 (SC8–23) for even and odd cycles. The Rician distribution is the best-fit function for both even and odd sunspots group latitudinal occurrence. The mean and variance for even northern/southern butterfly wing sunspots are 14.94/14.76 and 58.62/56.08, respectively, and the mean and variance for odd northern/southern wing sunspots are 15.52/15.58 and 61.77/58.00, respectively. Sunspot groups of even cycle wings are thus at somewhat lower latitudes on average than sunspot groups of the odd cycle wings, i.e. about 0.6 degrees for northern hemisphere wings and 0.8 degrees for southern hemisphere wings.The spatial analysis of sunspot areas between SC12–23 shows that the small sunspots are at lower solar latitudes of the Sun than the large sunspots for both odd and even cycles, and also for both hemispheres.Temporal evolution of sunspot areas shows a lack of large sunspots after four years (exactly between 4.2 – 4.5 years), i.e. about 40% after the start of the cycle, especially for even cycles. This is related to the Gnevyshev gap and is occurring at the time when the evolution of the average sunspot latitudes crosses about 15 degrees. The gap is, however, clearer for even cycles than odd ones. Gnevyshev gap divides the cycle into two disparate parts: the ascending phase/cycle maximum and the declining phase of the sunspot cycle.

A method of estimating the Martian neutral atmospheric density at 130 km, and comparison of its results with Mars Global Surveyor and Mars Odyssey aerobraking observations based on the Mars Climate Database outputs

Profiles of the Martian dayside ionosphere can be used to derive the neutral atmospheric densities at 130 km, which can also be obtained from the Mars Climate Database (MCD) and spacecraft aerobraking observations. In this research, we explain the method used to calculate neutral densities at 130 km via ionosphere observations and three long-period 130-km neutral density data sets at northern high latitudes (latitudes > 60°) acquired through ionospheric data measured by the Mars Global Surveyor (MGS) Radio Occultation Experiment. The calculated 130-km neutral density data, along with 130-km density data from the aerobraking observations of the MGS and Mars Odyssey (ODY) in the northern high latitudes, were compared with MCD outputs at the same latitude, longitude, altitude, solar latitude, and local time. The 130-km density data derived from both the ionospheric profiles and aerobraking observations were found to show seasonal variations similar to those in the MCD data. With a negative shift of about 2 × 1010 cm−3, the corrected 130-km neutral densities derived from MCD v4.3 were consistent with those obtained from the two different observations. This result means that (1) the method used to derive the 130-km neutral densities with ionospheric profiles was effective, (2) the MCD v4.3 data sets generally overestimated the 130-km neutral densities at high latitudes, and (3) the neutral density observations from the MGS Radio Science Experiment could be used to calibrate a new atmospheric model of Mars.