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Heavy rainfall events causing floods and flash floods are examined in the context of solar wind coupling to the magnetosphere–ionosphere–atmosphere system. The superposed epoch (SPE) analyses of solar wind variables have shown the tendency of severe weather to follow arrivals of high-speed streams from solar coronal holes. Precipitation data sets based on rain gauge and satellite sensor measurements are used to examine the relationship between the solar wind high-speed streams and daily precipitation rates over several midlatitude regions. The SPE analysis results show an increase in the occurrence of high precipitation rates following arrivals of high-speed streams, including recurrence with a solar rotation period of 27 d. The cross-correlation analysis applied to the SPE averages of the green (Fe XIV; 530.3 nm) corona intensity observed by ground-based coronagraphs, solar wind parameters, and daily precipitation rates show correlation peaks at lags spaced by solar rotation period. When the SPE analysis is limited to years around the solar minimum (2008–2009), which was dominated by recurrent coronal holes separated by ∼ 120∘ in heliographic longitude, significant cross-correlation peaks are found at lags spaced by 9 d. These results are further demonstrated by cases of heavy rainfall, floods and flash floods in Europe, Japan, and the USA, highlighting the role of solar wind coupling to the magnetosphere–ionosphere–atmosphere system in severe weather, mediated by aurorally excited atmospheric gravity waves.

Simulations of the ionospheric response to solar flux changes driven by the 27 d solar rotation have been performed using the global 3-D Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) physics-based numerical model. Using the F10.7 index as a proxy for solar extreme ultraviolet (EUV) variations in the model, the ionospheric delay at the solar rotation period is well reproduced and amounts to about 1 d, which is consistent with satellite and in situ measurements. From mechanistic CTIPe studies with reduced and increased eddy diffusion, we conclude that the eddy diffusion is an important factor that influences the delay of the ionospheric total electron content (TEC). We observed that the peak response time of the atomic oxygen to molecular nitrogen ratio to the solar EUV flux changes quickly during the increased eddy diffusion compared with weaker eddy diffusion. These results suggest that an increase in the eddy diffusion leads to faster transport processes and an increased loss rate, resulting in a decrease in the ionospheric time delay. Furthermore, we found that an increase in solar activity leads to an enhanced ionospheric delay. At low latitudes, the influence of solar activity is stronger because EUV radiation drives ionization processes that lead to compositional changes. Therefore, the combined effect of eddy diffusion and solar activity leads to a longer delay in the low-latitude and midlatitude region.

This paper examines long-term (more than four solar cycles) temporal and spatial fluctuations in the solar rotation by investigating radio-emission escapes from various layers of the solar atmosphere during the years 1967–2010. The flux modulation approach can also be used to investigate variations in solar rotation, which is a contentious topic in solar physics. This study makes use of a time-series of radio flux data at various frequencies (245–15 400 MHz) obtained at Sagamore Hill Solar Radio Observatory in Massachusetts, USA, and at other observatories from 1967 to 2010. The periodicity present in the temporal variation of the time-series is estimated through a Lomb–Scargle periodogram. The rotation period estimated for five radio emissions (606, 1415, and 2695 MHz from the corona, and 4995 and 8800 MHz from the transition region) through a statistical approach shows continuous temporal and spatial variations throughout the years. The smoothed rotation period shows the presence of periodic ∼22-yr and ∼11-yr components. The 22-yr component could be linked to the reversal of the solar magnetic field (Hale) cycle, while the 11-yr component is most likely related to the sunspot (Schwabe) cycle. In addition to these two components, random components are also prominently present in the analysed data. The cross-correlation between the sunspot number and the rotation period obtained shows a strong correlation with the 11-yr Schwabe and 22-yr Hale cycle. The corona rotates faster or slower than the transition region in different epochs. The alternation of the faster rotation speed between the corona and transition region also follows the 22-yr cycle.

The solar gravitational moments $J_{2n}$ are important astronomical quantities whose precise determination is relevant for solar physics, gravitational theory and high precision astrometry and celestial mechanics. Accordingly, we propose in the present work to calculate new values of $J_{2n}$ (for $n$=1,2,3,4 and 5) using recent two-dimensional rotation rates inferred from the high resolution SDO/HMI helioseismic data spanning the whole solar activity cycle 24. To this aim, a general integral equation relating $J_{2n}$ to the solar internal density and rotation is derived from the structure equations governing the equilibrium of slowly rotating stars. For comparison purpose, the calculations are also performed using rotation rates obtained from a recently improved analysis of SoHO/MDI heliseismic data for solar cycle 23. In agreement with earlier findings, the results confirmed the sensitivity of high order moments ($n>1$) to the radial and latitudinal distribution of rotation in the convective zone. The computed value of the quadrupole moment $J_{2}$ ($n=1$) is in accordance with recent measurements of the precession of Mercury's perihelion deduced from high precision ranging data of the MESSENGER spacecraft. The theoretical estimate of the related solar oblateness $\Delta_{\odot}$ is consistent with the most accurate space-based determinations, particularly the one from RHESSI/SAS., Comment: 6 pages, 3 figures, 1 table

A real-time model for predicting the quasistationary solar wind speed at the near-Earth orbit is presented. The forecast of the high-speed solar wind stream velocity is obtained with an empirical model linking the areas of coronal holes to the solar wind speed. The forecast of the slow solar wind is based on data on the observed solar wind speed from the previous solar rotation. Over the whole analyzed period from May 2010 to December 2019, the coefficient of correlation between the observed and predicted solar wind speed values is 0.45, and the standard deviation is 88 km/s. The accuracy of forecasting the speed of quasistationary solar wind streams is comparable to the results of foreign models.

The magnetic field measurements of the Sun as a star initiated by academician A.B. Severny have been supported by six other observatories. The history of such investigations at CrAO and the basic results are briefly described. The synodic spin period of the gravitating solar mass P⊙ = 27.027(6) days is determined; the latter is shown to be linked to the Earth’s motion: the Sun makes 27 semi-revolutions over one terrestrial year, and the Earth – the same number of its revolutions with the period PD during one full solar rotation. The field changes with the Hale cycle PH ≈ 22 years and the cycle P7 = 7 years, whereas their ratio coincides with the Archimedes approximation, 22:7, for the π number, the timescale (π - 3)P7 = P⊙2/2PD – with the Earth’s orbital period. We provide arguments in favour of the cosmic origin of both cycles and holographic expressions, including PH, P7, π, and universal constants.

The traditional method considers the Sun as a rigid sphere and diffuse radiator, and neglects the solar characteristics. However, this leads to high bias in the measurement model. In this study, to build a more realistic bias model and a statistical model of noise, the authors consider three solar characteristics, including the solar differential rotation, Lambert radiator and small-scale solar activities. After mathematical derivation, the bias model of the solar Doppler difference measurement considering the solar differential rotation and Lambert radiator is built. Simulation results demonstrate that the difference between the proposed bias model and the traditional one is on the order of 0.1–1 m/s, which is slowly-varying and non-ignorable. Therefore, the bias model considering the solar differential rotation and Lambert radiator is meaningful. After mathematical analysis, they also find that small-scale solar activities cause an extremely low error in the solar Doppler difference measurement. Moreover, the noise of the Doppler difference is within 2 m/s. Due to the randomness of small-scale solar activities, the extremely low errors caused by activities can be regarded as noises. These results provide a reference for the measurement modelling of the solar Doppler difference velocimetry navigation.

Cosmic rays may have contributed to the start of life on Earth. Here, we investigate the evolution of the Galactic cosmic ray spectrum at Earth from ages $t = 0.6-6.0\,$Gyr. We use a 1D cosmic ray transport model and a 1.5D stellar wind model to derive the evolving wind properties of a solar-type star. At $t=1\,$Gyr, approximately when life is thought to have begun on Earth, we find that the intensity of $\sim$GeV Galactic cosmic rays would have been $\sim10$ times smaller than the present-day value. At lower kinetic energies, Galactic cosmic ray modulation would have been even more severe. More generally, we find that the differential intensity of low energy Galactic cosmic rays decreases at younger ages and is well described by a broken power-law in solar rotation rate. We provide an analytic formula of our Galactic cosmic ray spectra at Earth's orbit for different ages. Our model is also applicable to other solar-type stars with exoplanets orbiting at different radii. Specifically, we use our Galactic cosmic ray spectrum at 20$\,$au for $t=600\,$Myr to estimate the penetration of cosmic rays in the atmosphere of HR$\,$2562b, a directly imaged exoplanet orbiting a young solar-type star. We find that the majority of particles $, 15 pages, 10 figures, accepted for publication in MNRAS

The magnetic field measurements of the Sun as a star initiated by academician A.B. Severny have been supported by six other observatories. The history of such investigations at CrAO and the basic results are briefly described. The synodic spin period of the gravitating solar mass P⊙ = 27.027(6) days is determined; the latter is shown to be linked to the Earth’s motion: the Sun performs 27 semi-revolutions over one terrestrial year, and the Earth – the same number of its revolutions with period PD during one full solar rotation. The field is also changing with the Hale cycle PH ≈ 22 years and the cycle P7 = 7 years, whereas their ratio coincides with the Archimedes approximation, 22:7, for the π number, the timescale (π - 3)P7 = P⊙2/2PD – with the Earth’s orbital period. We provide arguments in favour of the cosmic origin of both cycles and holographic expressions, including PH, P7, π, and universal constants

We provide an analytical description of the method for the determination of the coordinates of solar radio sources from multi-azimuth observations on RATAN-600. We analyze models of the displacement of the object across the scan depending as a function of azimuth taking into account solar rotation and suggest a method for estimating the rate of displacement due to rotation. We demonstrate the results of the application of the method using the determination of the coordinates of a radio source in the active region NOAA 11 520 as example. After eliminating gross scan referencing errors we obtained the coordinates, which agree well with observational data. We discuss the scan coordinate reference errors.

Forecasting the thermosphere (the atmosphere's uppermost layer, from about 90 to 800 km altitude) is crucial to space-related applications, from space mission design to re-entry operations, space surveillance and more. Thermospheric dynamics is directly linked to the solar dynamics through the solar UV (ultraviolet) input, which is highly variable, and through the solar wind and plasma fluxes impacting Earth's magnetosphere. The solar input is non-periodic and non-stationary, with long-term modulations from the solar rotation and the solar cycle and impulsive components, due to magnetic storms. Proxies of the solar input exist and may be used to forecast the thermosphere, such as the F10.7 radio flux and the Mg II EUV (extreme-ultraviolet) flux. They relate to physical processes of the solar atmosphere. Other indices, such as the Ap geomagnetic index, connect with Earth's geomagnetic environment. We analyse the proxies' time series comparing them with in situ density data from the ESA (European Space Agency) GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) gravity mission, operational from March 2009 to November 2013, therefore covering the full rising phase of solar cycle 24, exposing the entire dynamic range of the solar input. We use empirical mode decomposition (EMD), an analysis technique appropriate to non-periodic, multi-scale signals. Data are taken at an altitude of 260 km, exceptionally low for a low-Earth-orbit (LEO) satellite, where density variations are the single most important perturbation to satellite dynamics. We show that the synthesized signal from optimally selected combinations of proxy basis functions, notably Mg II for the solar flux and Ap for the plasma component, shows a very good agreement with thermospheric data obtained by GOCE, during periods of low and medium solar activity. In periods of maximum solar activity, density enhancements are also well represented. The Mg II index proves to be, in general, a better proxy than the F10.7 index for modelling the solar flux because of its specific response to the UV spectrum, whose variations have the largest impact over thermospheric density.

By using atmospheric wind data in the mesopause and lower thermosphere (MLT) region, features of seasonal variations in the quasi-6-day wave (6DW) at different latitudes are analyzed, and modulation of the 6DW by the diurnal tide and solar 27-day period is discussed. The data used in the analysis are extracted from a wind dataset collected by a meteor radar chain from December 2008 to November 2017. The meteor radar chain includes four stations, in Mohe, Beijing, Wuhan, and Sanya. Features of seasonal variations in the 6DW indicate that in summer the 6DW is usually strongest during July and August, followed by stronger variations in January and April. At certain altitudes over Wuhan and Sanya, the 6DW is slightly different in different years and altitudes. In our analysis of seasonal variations in the 6DW, we find that it is generally affected by annual oscillations and semiannual oscillations. The annual oscillations of the 6DW in the mid-low latitudes are modulated by the quasibiennial oscillation in the diurnal tide, resulting in seasonal features that are different from those at other latitudes. In addition, the 6DW amplitude at mid-high latitudes has a significant 27-day solar rotation variation, which was prominent in 2016.

Numerous analyses suggest the existence of various quasi-periodicities in solar activity. The power spectrum of solar activity recorded in sunspot data is dominated by the $\sim$11-year quasi-periodicity, known as the Schwabe cycle. In the mid-term range (1 month -- 11 years) a pronounced variability known as a quasi-biennial oscillation (QBO) is widely discussed. In the shorter time scale a pronounced peak, corresponding to the synodic solar rotation period ($\sim$ 27 days) is observed. Here we revisited the mid-term solar variability in terms of statistical dynamic of fully turbulent systems, where solid arguments are required to accept an isolated dominant frequency in a continuous (smooth) spectrum. For that, we first undertook an unbiased analysis of the standard solar data, sunspot numbers and the F10.7 solar radioflux index, by applying a wavelet tool, which allows one to perform a frequency-time analysis of the signal. Considering the spectral dynamics of solar activity cycle by cycle, we showed that no single periodicity can be separated, in a statistically significant manner, in the specified range of periods. We examine whether a model of solar dynamo can reproduce the mid-term oscillation pattern observed in solar data. We found that a realistically observed spectrum can be explained if small spatial (but not temporal) scales are effectively smoothed. This result is important because solar activity is a it global feature, although monitored via small-scale tracers like sunspots., accepted in MNRAS

Long-term periodicities in the solar irradiance are often observed with periods proportional to the solar rotational period of 27 days. These periods are linked either to some internal mechanism in the Sun or said to be higher harmonics of the rotation without further discussion of their origin. In this article, the origin of the peaks in periodicities seen in the solar extreme ultraviolet (EUV) and ultraviolet (UV) irradiance around the 7, 9, and 14 days periods is discussed. Maps of the active regions and coronal holes are produced from six images per day using the Spatial Possibilistic Clustering Algorithm (SPoCA), a segmentation algorithm. Spectral irradiance at coronal, transition-region/chromospheric, and photospheric levels are extracted for each feature as well as for the full disk by applying the maps to full-disk images (at 19.3, 30.4, and 170 nm sampling in the corona/hot flare plasma, the chromosphere/transition region, and the photosphere, respectively) from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) from January 2011 to December 2018. The peaks in periodicities at 7, 9, and 14 days as well as the solar rotation around 27 days can be seen in almost all of the solar irradiance time series. The segmentation also provided time series of the active regions and coronal holes visible area (i.e. in the area observed in the AIA images, not corrected for the line-of-sight effect with respect to the solar surface), which also show similar peaks in periodicities, indicating that the periodicities are due to the change in area of the features on the solar disk rather than to their absolute irradiance. A simple model was created to reproduce the power spectral density of the area covered by active regions also showing the same peaks in periodicities. Segmentation of solar images allows us to determine that the peaks in periodicities seen in solar EUV/UV irradiance from a few days to a month are due to the change in area of the solar features, in particular, active regions, as they are the main contributors to the total full-disk irradiance variability. The higher harmonics of the solar rotation are caused by the clipping of the area signal as the regions rotate behind the solar limb.

The solar rotation period is the most prominent mid-term periodicity in the temporal behaviour of solar, heliospheric, and geomagnetic parameters. It is also a cause of the repeatedly appearing geomagnetic storms originating from the corotating interaction regions (CIRs). Since geomagnetic CIR-driven storms have a natural periodic character, and geomagnetic storms impact energy infrastructure via geomagnetically induced currents, it is of interest whether this periodic character is also noticeable in the temporal behaviour of electrical-grid failures (EGFs), which, at least to some extent, might be of solar origin.

A relationship between the heliospheric magnetic field, atmospheric electric field, lightning activity, and secondary cosmic rays measured on the high mount of Lomnický Štít (2,634 m a.s.l.), Slovakia, during the declining phase of the solar cycle 24 is investigated with a focus on variations related to solar rotation (about 27 days). The secondary cosmic rays are detected using a neutron monitor and the detector system SEVAN, which distinguishes between different particles and energies. Using spectral analysis, we found distinct ∼27-day periodicities in variations of Bx and By components of the heliospheric magnetic field and in pressure-corrected measurements of secondary cosmic rays. The 27-day variations of secondary cosmic rays, on average, advanced and lagged the variations of Bx and By components by about 40° and −140°, respectively. Distinct 27-day periodicities were found both in the neutron monitor and the SEVAN upper and middle detector measurements. A nondominant periodicity of ∼27 days was also found for lightning activity. A cross-spectral analysis between fluctuation of the lightning activity and fluctuation of the heliospheric magnetic field (HMF) showed that fluctuation of the lightning activity was in phase and in antiphase with Bx and By components of the HMF, respectively, which is in agreement with previous studies investigating the influence of solar activity on lightning. On the other hand, the ∼27-day periodicity was not significant in the atmospheric electric field measured in Slovakia and Czechia. Therefore, no substantial influence of Bx and By on the atmospheric electric field was observed at these middle-latitude stations.

It is necessary to better understand the dynamic process of solar differential rotation. Here the hand-drawing sunspot group records from 1958 to 2015 of Yunnan Observatories (YNAO) are used to study the solar rotation profile. Firstly, the rotation profile in each solar cycle 19-23 is calculated. Secondly, the rotation parameters (equatorial rotation velocity A and differential gradient B) of YNAO are compared with the well-known earlier results. Finally, the rotation parameters in the northern and southern hemispheres during each solar cycle 19-23 are summarized. The main conclusions we reached are as follows: (1) The average difference of the equatorial rotation velocity and differential gradient, between YNAO sunspot and other sunspot datasets, are 0.09 and 0.4, respectively. (2) The magnitudes of the gradient B in the northern hemisphere are larger than that in the southern hemisphere at even-number cycles, and it will approximately reverse at odd-number cycles.

Deep space exploration missions continue to become more ambitious, driving the need to investigate autonomous navigation systems that are accurate and timely. The solar Doppler difference navigation is a newly developed and promising celestial autonomous navigation method for use, particularly, in the crucial capture period. In this paper, we present novel analyses for three error sources for the solar Doppler difference navigation from the perspective of geometry, motivated with a Mars deep space exploration example. The geometry error sources include the area overlap rate of the direct and the reflected solar light sources, the spread effects related to the time difference of arrival (TDOA) of light, and the solar rotation Doppler difference error. The area overlap rate and the spread effects of the TDOA can be utilized to assess the overlap degree of the direct source and the reflected source in both space and time. Theoretical analyses and simulation results demonstrate that the direct and the reflected light sources can be accurately approximated as the same source. The solar rotation Doppler difference error is explored using a velocity error model. This model forms a hemi-ellipsoid that can be utilized to compensate the Doppler error caused by the solar rotation. The three errors decline with the deep space explorer approaching Mars, which means that the performance of the solar Doppler difference navigation method continuously improves in the critical capture period. These results can offer a reference for the system design of the solar Doppler difference navigation.

Solar oblateness has been the subject of several studies dating back to the nineteenth century. Despite difficulties, both theoretical and observational, tangible results have been achieved. However, variability of the solar oblateness with time is still poorly known. How the solar shape evolves with the solar cycle has been a challenging problem. Analysis of the helioseismic data, which are the most accurate measure of the solar structure up to now, leads to the determination of asphericity coefficients which have been found to change with time. We show here that by inverting even coefficients of f-mode oscillation frequency splitting to obtain the oblateness magnitude and its temporal dependence can be inferred. It is found that the oblateness variations lag the solar activity cycles by about 3 years. A major change occurred between solar cycles 23 and 24 is that the oblateness was greater in cycle 24 despite the lower solar activity level. Such results may help to better understand the near-subsurface layers as they strongly impacts the internal dynamics of the Sun and may induce instabilities driving the transport of angular momentum.

Properties of helioseismic acoustic oscillations (p modes) are modified by flows and magnetic fields in the solar interior, with frequencies, amplitudes and damping rates all varying systematically through the solar cycle. Crucially, now, we have a long enough baseline of helioseismic data to compare of the different activity cycles. We review recent efforts along these lines, from the impact of near-surface magnetic fields on p-mode frequencies to the evolution of the torsional oscillation and meridional circulation. We show that each activity cycle for which we have helioseismic data is slightly different in terms of the relationship between p mode frequencies and atmospheric proxies of activity, and in terms of the rotation and meridional circulation flows. However, many challenges remain, crucially including our ability to constrain flows and magnetic fields in the deep solar interior.

Sturrock et al. have published a “rebuttal” to a paper by Pomme et al. who refuted their claim that variations in a radon decay experiment at the Geological Survey of Israel (GSI) can be associated with solar rotation. Sturrock et al. misinterpret the variability of the decay rates in the gamma counter to assert influences by solar and cosmic neutrinos on beta decay and draw unsubstantiated conclusions about solar dynamics. Evidence suggests that the radon measurements were susceptible to solar irradiance and rainfall, whereas there is no indication that radioactive decay is influenced by the solar neutrino flux. In this reply to the rebuttal, the arguments raised by Sturrock et al. are scrutinised.

Heavy rainfall events causing floods and flash floods are examined in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere system. The superposed epoch (SPE) analyses of solar wind variables have shown a tendency of severe weather to follow arrivals of high-speed streams from solar coronal holes (Prikryl et al., 2018). Precipitation datasets based on rain-gauge and satellite sensor measurements are used to examine the relationship between the solar wind high-speed streams and daily precipitation rates over several mid-latitude regions. The SPE analysis results show an increase in occurrence of high precipitation rates following arrivals of high-speed streams, including recurrence with a periodicity of 27 days. The cross-correlation analysis applied to the SPE averages of the green (Fe XIV, 530.3 nm) corona intensity observed by ground-based coronagraphs, solar wind parameters and daily precipitation rates show correlation peaks at lags spaced by solar rotation period. When the SPE analysis is limited to years around the solar minimum (2008–2009), which was dominated by recurrent coronal holes separated by ~120˚ in heliographic longitude, significant cross-correlation peaks are found at lags spaced by 9 days. These results are further demonstrated by cases of heavy rainfall, floods and flash floods in Europe, Japan, and the U.S., highlighting the role of solar wind coupling to the magnetosphere-ionosphere-atmosphere system in severe weather, mediated by aurorally excited atmospheric gravity waves.

The plethora of photometric data collected by the Kepler space telescope has promoted the detection of tens of thousands of stellar rotation periods. However, these periods are not found to an equal extent among different spectral types. Interestingly, early G-type stars with near-solar rotation periods are strongly underrepresented among those stars with known rotation periods. In this study we investigate whether the small number of such stars can be explained by difficulties in the period determination from photometric time series. For that purpose, we generate model light curves of early G-type stars with solar rotation periods for different inclination angles, metallicities and (magnitude-dependent) noise levels. We find that the detectability is determined by the predominant type of activity (i.e. spot or faculae domination) on the surface, which defines the degree of irregularity of the light curve, and further depends on the level of photometric noise. These two effects significantly complicate the period detection and explain the lack of solar-like stars with known near-solar rotation periods. We conclude that the rotation periods of the majority of solar-like stars with near-solar rotation periods remain undetected to date. Finally, we promote the use of new techniques to recover more periods of near-solar rotators., Comment: 14 pages, 7 figures, accepted for publication in ApJL

The solar photosphere, chromosphere and corona are known to rotate differentially as a function of latitude. To date, it is unclear if the solar transition region also rotates differentially. In this paper, we investigate differential rotational profile of solar transition region as a function of latitude, using solar full disk (SFD) images at 30.4 nm wavelength recorded by Extreme Ultraviolet Imager (EUVI) onboard Solar Terrestrial Relations Observatory (STEREO) space mission for the period from 2008 to 2018 (Solar Cycle 24). Our investigations show that solar transition region rotates differentially. The sidereal rotation rate obtained at +/- 5 degree equatorial band is quite high (~ 14.7 degree/day), which drops to ~ 13.6 degree/day towards both polar regions. We also obtain that the rotational differentiality is low during the period of high solar activity (rotation rate varies from 14.86 to 14.27 degree/day) while it increases during the ascending and the descending phases of the 24th solar cycle (rotation rate varies from 14.56 to 13.56 degree/day in 2008 and 14.6 to 13.1 degree/day in 2018). Average sidereal rotation rate (over SFD) follows the trend of solar activity (maximum ~ 14.97 degree/day during the peak phase of the solar activity, which slowly decreases to minimum ~ 13.9 degree/day during ascending and the descending phases of the 24th solar cycle). We also observe that solar transition region rotates less differentially than the corona., Comment: 8 pages, 6 figures, 2 tables, Accepted for publication in MNRAS

The Solar Orbiter mission, with an orbit outside the Sun Earth line and leaving the ecliptic plane, opens up opportunities for the combined analysis of measurements obtained by solar imagers and spectrometers. For the first time, different space spectrometers will be located at wide angles to each other, allowing three-dimensional (3D) spectroscopy of the solar atmosphere. The aim of this work is to prepare the methodology to facilitate the reconstruction of 3D vector velocities from two stereoscopic LOS Doppler velocity measurements using the Spectral Imaging of the Coronal Environment (SPICE) onboard the Solar Orbiter and the near-Earth spectrometers, while widely separated in space. We develop the methodology using the libraries designed earlier for the STEREO mission but applied to spectroscopic data from the Hinode mission and the Solar Dynamics Observatory. We use well-known methods of static and dynamic solar rotation stereoscopy and the methods of EUV stereoscopic triangulation for optically thin coronal EUV plasma emissions. We develop new algorithms using analytical geometry in space to determine the 3D velocity in coronal loops. We demonstrate our approach with the reconstruction of 3D velocity vectors in plasma flows along "open" and "closed" magnetic loops. This technique will be applied to an actual situation of two spacecraft at different separations with spectrometers onboard (SPICE versus the Interface Region Imaging Spectrograph (IRIS) and Hinode imaging spectrometer) during the Solar Orbiternominal phase. We summarise how these observations can be coordinated., Comment: accepted to be published in Astronomy and Astrophysics

In this study the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) is used to describe the delayed ionospheric response to solar Extreme Ultraviolet (EUV) radiation and its varying relation to solar and geomagnetic activity (e.g. stronger impact of the solar wind during winter season in the northern hemisphere). Long-term changes, at time scales longer than the 27-day solar rotation cycle, are analyzed and the dependence of the ionospheric delay on the solar activity is presented based on calculations at a chosen location in the mid-latitudes. Ionospheric delays of 2, 11 and 20 h can be correlated to the mean solar radio flux index (F10.7) values of 95, 115 and 135 sfu. In addition, a possible relation of the delayed ionospheric response with the geomagnetic activity is analyzed with TIE-GCM model runs, that estimate an ionospheric delay of 15 h for a corresponding Kp-index of≈ 0.91 and an ionospheric delay of 17 h for a corresponding Kp-index of ≈ 2.88 (during December). These differences are related to changes in electron temperature and ion velocity perpendicular to the geomagnetic field lines. The results suggest a significant impact of transport processes on the delayed ionospheric response.

We apply the generalized Lomb–Scargle periodogram to the $${^{123}\text {I}}$$ 123 I and $${^{99\mathrm{m}}\text {Tc}}$$ 99 m Tc decay rate measurements based on data taken at the Bronson Methodist Hospital. The aim of this exercise was to carry out an independent search for sinusoidal modulation for these radionuclei (to complement the analysis in Borrello et al.) at frequencies for which other radionuclei have shown periodicities. We do not find such a modulation at any frequencies, including annual modulation or at frequencies associated with solar rotation. Our analysis codes and datasets have been made publicly available.

Galactic cosmic rays as observed by the Hermanus and Jungfraujoch Neutron Monitors between 1960 and 2018 have been analysed using various spectral analysis techniques. Daily mean neutron monitor measurements are used to identify how several harmonics of the roughly 27-day synodic rotation period change during each of these years. Spectral analysis using Lomb-Scargle and Morlet wavelet techniques of Hermanus and Jungfraujoch data revealed in particular that the fourth harmonic (∼7-day) of the solar rotation period is exceptionally strong during the minima of solar cycles when A 0 (solar dipole pointing north). The power spectrum results obtained in this investigation showed that galactic cosmic rays at both Hermanus and Jungfraujoch exhibit peculiar short-term periodicity behaviour as a result of solar polarity dependent magnetic drifts during negative minima.

Generally, the occurrence of F region irregularities associated with Equatorial Plasma Bubbles is considered difficult to predict due to its day-to-day variability. Recent investigation shows that the dominant period of variability of EPB can be > 25 days (quasi 27 day), presumably associated with solar rotation period. VHF scintillation recorded from Pingtung, Taiwan in 2015 indicated the coexistence of planetary scale variability (4-8 days), 10-15 days variability and quasi 27 day variability. Lomb-Scargle power spectrum of S4 time series indicated that the larger period variability (quasi 27 days) is much more dominant than the other scales (which includes day-to-day variability). Interestingly, the dominant period of S4 variability corresponded exactly with the dominant period of high-latitude geomagnetic variability. Continuous operation of Equatorial Atmosphere Radar (EAR) in 2012 also indicated similar observation. Dominant period of variability of EPB in EAR observations corresponded with the high-latitude geomagnetic variability. These observations reveal that EPB are controlled predominantly by geomagnetic activity through large period variability (quasi- 27 days).

Accurate measurements of the solar differential rotation parameters are necessary for understanding the solar dynamo mechanism. We use the orthogonalization process to estimate these parameters. The advantage of the orthogonalization of the data in the tracer motion statistical analysis is outlined. The differential rotation is represented in terms of various types of polynomials. We compare the quality of a set of models of the solar differential rotation using the Akaike information criterion and choose the best one. Applying the proposed method, we studied the solar differential rotation and its North-South asymmetry using observations of coronal holes. A statistical analysis of observations from the Atmospheric Imaging Assembly (AIA) on Solar Dynamics Observatory (SDO) reveals the differential rotation pattern of coronal holes and its North-South asymmetry. ispartof: Advances In Space Research vol:65 issue:7 pages:1843-1851 status: published

Forecasting the Thermosphere (Atmosphere's uppermost layer, from about 90 to 800 km altitude) is crucial to many space-related applications, from space mission design, to re-entry operations, to space surveillance. Thermospheric dynamics is directly linked to the solar dynamics through the solar UV input, which is highly variable, and through the solar wind and plasma fluxes, impacting Earth's magnetosphere. The solar input is non-periodic and non-stationary, with long-term modulations from the solar rotation and the solar cycle, and impulsive components, due to magnetic storms. Proxies of the solar input exist and may be used to forecast the thermosphere, such as the F10.7 radio flux and the MgII EUV flux. They relate to physical processes on the Solar atmosphere. Other indices, such as the Ap geomagnetic index, connect with Earth's geomagnetic environment. We analyse the proxies' time series comparing them with in-situ density data from the ESA/GOCE gravity mission, operational from March 2009 to November 2013, therefore covering the full rising phase of solar cycle XXIV, exposing the entire dynamic range of the solar input. We use Empirical Mode Decomposition (EMD), an analysis technique appropriate to non-periodic, multi-scale signals. Data are taken at an altitude of 260 km, exceptionally low for a LEO satellite, where density variations are the single most important perturbation to satellite dynamics. We show that the synthesized signal from optimally selected combinations of proxies's basis functions, notably Mg II for the solar flux and Ap for the plasma component, shows a very good agreement with thermospheric data obtained by GOCE, during low and medium solar activity periods. In periods of maximum solar activity, density enhancements are also well represented. The Mg II index proves to be, in general, a better proxy than the F10.7 one, to model the solar flux, because of its specific response to the UV spectrum, whose variations have the largest impact over thermospheric density.

Context. Results from global magnetoconvection simulations of solar-like stars are at odds with observations in many respects: They show a surplus of energy in the kinetic power spectrum at large scales, anti-solar differential rotation profiles, with accelerated poles and a slow equator, for the solar rotation rate, and a transition from axi- to non-axisymmetric dynamos at a much lower rotation rate than what is observed. Even though the simulations reproduce the observed active longitudes in fast rotators, their motion in the rotational frame (the so-called azimuthal dynamo wave, ADW) is retrograde, in contrast to the prevalent prograde motion in observations. Aims. We study the effect of a more realistic treatment of heat conductivity in alleviating the discrepancies between observations and simulations. Methods. We use physically-motivated heat conduction, by applying Kramers opacity law, on a semi-global spherical setup describing convective envelopes of solar-like stars, instead of a prescribed heat conduction profile from mixing-length arguments. Results. We find that some aspects of the results now better correspond to observations: The axi- to non-axisymmetric transition point is shifted towards higher rotation rates. We also find a change in the propagation direction of ADWs so that also prograde waves are now found. The transition from anti-solar to solar-like rotation profile, however, is also shifted towards higher rotation rates, leaving the models into an even more unrealistic regime. Conclusions. Although a Kramers-based heat conduction does not help in reproducing the solar rotation profile, it does help in the faster rotation regime, where the dynamo solutions now match better with observations., Comment: 10 pages, 6 figures, 1 appendix. Submitted to A&A

The dynamo mechanism, responsible for the solar magnetic activity, is still an open problem in astrophysics. Different theories proposed to explain such phenomena have failed in reproducing the observational properties of the solar magnetism. Thus, ab-initio computational modeling of the convective dynamo in a spherical shell turns out as the best alternative to tackle this problem. In this work we review the efforts performed in global simulations over the past decades. Regarding the development and sustain of mean-flows, as well as mean magnetic field, we discuss the points of agreement and divergence between the different modeling strategies. Special attention is given to the implicit large-eddy simulations performed with the EULAG-MHD code., Comment: 21 pages, 9 figures, proceedings of IAU symposium 354, Solar and Stellar Magnetic Fields: Origins and Manifestations

We continue our investigation into the nonlinear evolution of the Goldreich-Schubert-Fricke (GSF) instability in differentially rotating radiation zones. This instability may be a key player in transporting angular momentum in stars and giant planets, but its nonlinear evolution remains mostly unexplored. In a previous paper we considered the equatorial instability, whereas here we simulate the instability at a general latitude for the first time. We adopt a local Cartesian Boussinesq model in a modified shearing box for most of our simulations, but we also perform some simulations with stress-free, impenetrable, radial boundaries. We first revisit the linear instability and derive some new results, before studying its nonlinear evolution. The instability is found to behave very differently compared with its behaviour at the equator. In particular, here we observe the development of strong zonal jets ("layering" in the angular momentum), which can considerably enhance angular momentum transport, particularly in axisymmetric simulations. The jets are, in general, tilted with respect to the local gravity by an angle that corresponds initially with that of the linear modes, but which evolves with time and depends on the strength of the flow. The instability transports angular momentum much more efficiently (by several orders of magnitude) than it does at the equator, and we estimate that the GSF instability could contribute to the missing angular momentum transport required in both red giant and subgiant stars. It could also play a role in the long-term evolution of the solar tachocline and the atmospheric dynamics of hot Jupiters., Comment: Accepted for publication in MNRAS on 8th May 2020

With new space missions, such as Solar Dynamics Observatory (SDO), solar images are being produced in unprecedented volumes. To derive, as much as possible, information on evolution of solar activity from those huge datasets, the scientific community needs a new generation of software tools for automatic and efficient data processing. In the last decade, several research teams have been developing tools for obtaining more precise estimations of the solar rotation profile, but more are needed to improve knowledge about solar activity. We applied here a segmentation algorithm called Gradient Path Labelling (GPL), used originally to identify drusens in medical retinal images, to detect and track the coronal bright points (CBPs) using images from the AIA instrument onboard the SDO satellite. The CBPs have a tendency to change shape and size along time, to disappear and reappear at a corresponding heliographic position, therefore, decision trees were also included in the tracking solution. Since our CBP detection algorithm uses an active region mask to filter out the CBPs, whose centroid is inside the active regions, the number of identifications clearly depends on the level of solar activity. Our approach uses the commonly applied fitting relation to the latitudinal dependence of the rotational velocity, which resulted in calculation of the optimum fit parameters as well as the Gegenbauer orthogonal polynomials. Comparison of these parameters with the results presented in recent papers on this topic shows that our rotational velocity profile indicates slightly lower rotational velocities than the profiles obtained with other approaches. We also calculate the meridional motion of the CBPs, but comparison with other authors results, clearly show that a 3-day time interval is too short to estimate the latitudinal dependence of the CBP meridional motion. Distributions of the rotational velocity and meridional motion velocity uncertainties show that 85% of uncertainty values are lower than 1 degree/day. The evaluation of our test results shows that the applied algorithm is a promising tool that can help to refine the solar rotational profile.

Two intervals of exceptionally strong recurrence of galactic cosmic ray (GCR) intensity at solar rotation period stand out in recent history, one in 2007–2008 and the other in 2014–2015. We use neutron monitor data from Oulu and Hermanus, solar wind (SW) data, and coronal images to study these intervals. We find that in both cases the source of solar rotation period recurrence was a coronal hole (CH), but CH structures were different. While a large, longitudinally asymmetric CH existed at high southern latitudes in 2014–2015, a low‐latitude CH caused the recurrence in 2007–2008. Spectral properties of GCR and SW parameters reflect these differences. In 2014–2015 the GCR power spectrum density was broad and peaked at a period of 28.9 days, longer than the simultaneous recurrence period of SW speed. In 2007–2008 the GCR power spectrum was narrow and peaked at 27.5 days, exactly the same as for SW speed. The effect of CHs to GCRs was somewhat different in the two cases because of opposite solar polarities in the two intervals. In 2014–2015, during positive polarity when GCRs drift inward from high latitudes, the convection of fast SW from CH reduces the inward GCR drift over a wide range of high heliolatitudes at certain heliolongitudes. In 2007–2008, during negative polarity when GCRs drift inward via the heliospheric current sheet, a low‐latitude CH depletes the GCR flux not only by convection but also by the deflecting heliospheric current sheet away from the ecliptic, whence GCR drift to higher latitudes in a limited longitude range.

In the first article in this series, we reported an analysis of 29,000 hourly measurements of gamma radiation associated with the decay of radon gas in a sealed container at the Geological Survey of Israel (GSI) Laboratory in Jerusalem (Sturrock et al., 2012). We now report an analysis of a full 10 years of operation that yields over 85,000 hourly gamma measurements. To avoid possible confusion with seasonal environmental influences, we pay special attention to oscillations with frequencies in a band relevant to solar rotation, identifying two striking oscillations with frequencies 11.35 year−1 and 12.63 year−1, which we have found to be prominent also in decay data acquired at the Brookhaven National Laboratory (Sturrock et al., 2016). The 12.63 year−1 frequency agrees with the synodic rotational frequency (the frequency as observed on Earth) of the radiative zone as determined by helioseismology. Significantly, the more prominent rotational oscillations occur in pairs separated by 1 year−1, indicating that the solar sources of modulation rotate about axes that are oblique with respect to the normal to the ecliptic. It is notable that one of a triplet of such oscillations has exactly the same frequency (9.43 year−1) as the most significant oscillation in Super-Kamiokande measurements, suggesting that the experiment is responding to the influence of neutrinos. As found in our previous article, the annual oscillation is (counter-intuitively) stronger by day (with phase of maximum near 0.5, i.e. mid-year, suggestive of a cosmic source) than by night (with phase of maximum near zero, as expected for a solar source). This day-night asymmetry in the measurements may be understood in terms of a combined influence of asymmetries in the experiment and in the relevant nuclear processes. Spectrograms (with axes local hour of day and frequency) formed from the ambient temperature and pressure and the supply voltage differ significantly from the corresponding spectrogram formed from the gamma measurements. We have been unable to identify any environmental influence or experimental artifact, or any combination thereof, which can duplicate these statistically highly significant patterns found in the GSI data.

Thunderstorm and cloud activities sometimes show a 27-day period, and this has long been studied to uncover a possible important link to solar rotation. Because the 27-day variations in the solar forcing parameters such as solar ultraviolet and galactic cosmic rays become more prominent when the solar activity is high, it is expected that the signal of the 27-day period in meteorological phenomena may wax and wane according to the changes in the solar activity level. In this study, we examine in detail the intensity variations in the signal of the 27-day solar rotational period in thunder and lightning activity from the 18th to the 19th centuries based on 150-year-long records found in old diaries kept in Japan and discuss their relation with the solar activity levels. Such long records enable us to examine the signals of solar rotation at both high and low solar activity levels. We found that the signal of the solar rotational period in the thunder and lightning activity increases as the solar activity increases. In this study, we also discuss the possibility of the impact of the long-term climatological conditions on the signals of the 27-day period in thunder/lightning activities. Keywords. Meteorology and atmospheric dynamics (lightning)

To investigate the differential rotation of sunspot groups using the Greenwich data, we propose an approach based on a statistical analysis of the histograms of particular longitudinal velocities in different latitude intervals. The general statistical velocity distributions for all such intervals are shown to be described by two rather than one normal distribution, so that two fundamental rotation modes exist simultaneously: fast and slow. The differentiality of rotation for the modes is the same: the coefficient at sin2 in Faye’s law is 2.87–2.88 deg/day, while the equatorial rotation rates differ significantly, 0.27 deg/day. On the other hand, an analysis of the longitudinal velocities for the previously revealed two differing populations of sunspot groups has shown that small short-lived groups (SSGs) are associated with the fast rotation mode, while large long-lived groups (LLGs) are associated with both fast and slow modes. The results obtained not only suggest a real physical difference between the two populations of sunspots but also give new empirical data for the development of a dynamo theory, in particular, for the theory of a spatially distributed dynamo.

The study of solar rotation has a 150-year history. Early studies were restricted to looking at the movement of sunspots; much later came studies using other tracers such as supergranules, and spectroscopic measurements using Doppler shifts of spectral lines. These studies also found evidence of other large-scale flows, such as the meridional flows in the north-south direction and the zonal flows, or torsional oscillations, parallel to the equator. However, until the 1980s, the study of solar rotation and large-scale flows was restricted to what could be observed on the solar surface. The advent of good helioseismic data changed that and gave us the means to study flows in the solar interior. Instruments like GONG, MDI and HMI have now collected helioseismic data for two solar cycles and these also allow us to study the large scale flows and their variations with time and solar activity. We review what the long data sets tell us about the these flows and discuss some of the differences between solar cycles 23 and 24.

Claims were made by Sturrock et al. that radioactive decay can be induced by interaction of the nucleus with solar neutrinos and that cyclic modulations in decay rates are indicative of the dynamics of the solar interior. They analysed a series of measurements of gamma radiation associated with the emanation and decay of radon in a sealed container at the Geological Survey of Israel (GSI) laboratory. The integral count rates in the NaI detector showed strong variations in time of year and time of day. From time-series analysis, Sturrock et al. claim the presence of small oscillations at frequencies in a range between 7.4 a−1 and 12.5 a−1, which they speculatively associated with rotational influence on the solar neutrino flux. In this work, it is argued that the GSI radon measurements are unsuited for studying the variability of decay constants, because the data are strongly influenced by environmental conditions, such as solar irradiance and rainfall. At the JRC and PTB, decay rate measurements of the radon decay chain were performed with ionisation chambers, gamma-ray spectrometers and an alpha spectrometer. No deviation from the exponential-decay law was observed. The existence of cyclic variations in the decay constants is refuted, as well as the concept of measuring solar rotation through radioactive decay.

Context.Results from helioseismology indicate that the radial gradient of the rotation rate in the near-surface shear layer (NSSL) of the Sun is independent of latitude and radius. Theoretical models using the mean-field approach have been successful in explaining this property of the NSSL, while global direct or large-eddy magnetoconvection models have so far been unable to reproduce this.Aims.We investigate the reason for this discrepancy by measuring the mean flows, Reynolds stress, and turbulent transport coefficients under conditions mimicking those in the solar NSSL.Methods.Simulations with as few ingredients as possible to generate mean flows were studied. These ingredients are inhomogeneity due to boundaries, anisotropic turbulence, and rotation. The parameters of the simulations were chosen such that they matched the weakly rotationally constrained NSSL. The simulations probe locally Cartesian patches of the star at a given depth and latitude. The depth of the patch was varied by changing the rotation rate such that the resulting Coriolis numbers covered the same range as in the NSSL. We measured the turbulent transport coefficient relevant for the nondiffusive (Λ-effect) and diffusive (turbulent viscosity) parts of the Reynolds stress and compared them with predictions of current mean-field theories.Results.A negative radial gradient of the mean flow is generated only at the equator where meridional flows are absent. At other latitudes, the meridional flow is comparable to the mean flow corresponding to differential rotation. We also find that the meridional components of the Reynolds stress cannot be ignored. Additionally, we find that the turbulent viscosity is quenched by rotation by about 50% from the surface to the bottom of the NSSL.Conclusions.Our local simulations do not validate the explanation for the generation of the NSSL from mean-field theory where meridional flows and stresses are neglected. However, the rotational dependence of the turbulent viscosity in our simulations agrees well with theoretical predictions. Moreover, our results agree qualitatively with global convection simulations in that an NSSL can only be obtained near the equator.

Extreme weather events, such as heavy rainfall causing floods and flash floods continue to present difficult challenges in forecasting. Using gridded daily precipitation datasets in conjunction with solar wind data it is shown that high-rate precipitation occurrence is modulated by solar wind high-speed streams. Superposed epoch analysis shows a statistical increase in the occurrence of high-rate precipitation following arrivals of high-speed streams from coronal holes, including their recurrence with the solar rotation period of 27 days. These results are consistent with the observed tendency of heavy rainfall leading to floods and flash floods in Japan, Australia, and continental United States to follow arrivals of high-speed streams. A possible role of the solar wind–magnetosphere–ionosphere–atmosphere coupling in weather as mediated by globally propagating aurorally excited atmospheric gravity waves triggering conditional moist instabilities leading to convection in the troposphere that has been proposed in previous publications is highlighted.

Observations reveal a relatively small but statistically significant North-South (NS) asymmetry in sunspot activity varying on a time scale of several solar cycles. This paper proposes a dynamo model for the phenomenon of long-term NS asymmetry. The model separates dynamo equations for magnetic fields of dipolar and quadrupolar equatorial parity. The NS asymmetry results from the superposition of dipolar and quadrupolar fields. Model computations confirm the formerly proposed excitation of the quadrupolar dynamo mode by a dominant dipolar mode mediated by the equator-symmetric fluctuations in the $\alpha$-effect as a mechanism for the long-term NS asymmetry. An analytically solvable example of oscillations excited by short-term random forcing is given to justify the numerical result of NS asymmetry coherent on a time scale of several (about 6 in the present model) solar cycles resulting from random variations in the $\alpha$-effect on a time scale of one solar rotation. The model computations show the phase locking phenomenon of dipolar and quadrupolar fields oscillating predominantly in phase (northern type asymmetry) or in antiphase (southern type asymmetry) with relatively short irregular transitions between these two states. Large asymmetry in the simulated Grand minima is found and explained by weak magnetic quenching of the $\alpha$-effect during the minima. The possibility of polar field asymmetry in activity minima as a precursor of sunspot asymmetry in the following activity cycles is discussed based on the dynamo model and observations., Comment: 12 pages, 9 figures, accepted in ApJ

We present observations during the interval 2006–2014 of 27 day and 13.5 day periodic oscillations in the ionospheric sporadic E (Es) layer. This is a thin, dense layer composed of metallic ions in the Earth’s upper atmosphere between 90 and 130 km. Lomb–Scargle spectral and wavelet analyses reveal that these pronounced periodicities observed from ground-based ionosondes and GPS/GNSS radio occultations are associated with high-speed solar winds generated from persistent coronal holes on successive 27 day solar rotations. The 27 day and 13.5 day oscillations in the Es layers are dependent on latitude, showing a higher magnitude of periodicities at low latitudes between 0° and 15° and at high latitudes between 45° and 90° (10%–14%) than those at midlatitudes between 15° and 45° (4%–10%). The 27 day and 13.5 day oscillations in the high-latitude Es layers correlate well with the geomagnetic activity Dst and Ap indices, and these periodic oscillations become more significant at the solar maximum (2000–2003 and 2011–2014) than at the solar minimum.

Context. We study two coronal mass ejections (CMEs) observed between April 1-2, 2019 by both the inner Wide-Field Imager for Parker Solar Probe (WISPR-I) and the inner heliospheric imager (HI-1) on board STEREO-A. 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 understand how the PSP observations affect the CME kinematics, especially due to its proximity to the Sun. Methods. We estimate the CME positions, speeds, accelerations, propagation directions and longitudinal deflections using imaging observations from two spacecraft, and a set of analytical expressions that consider the CME as a point structure and take into account the rapid change in spacecraft position. Results. We find that both CMEs are slow ($< 400\ km\ s^{-1}$), propagating eastward of the Sun-Earth line. The second CME seems to accelerate between $\sim 0.1$ to $\sim 0.2\ au$ and deflect westward with an angular speed consistent with the solar rotation speed. We find some discrepancies in the CME solar distance (up to $0.05\ au$, particularly for CME \#1), latitude (up to $\sim10^{\circ}$) and longitude (up to $24^{\circ}$) when comparing results from different fit cases (different observations or set of free parameters). Conclusions. Discrepancies in longitude are likely due to the feature 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 to 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., 27 pages, 10 figures. Submitted for publication on Astronomy and Astrophysics