Active Solar Periods Research Articles

SoloHI observations of coronal mass ejections observed by multiple spacecraft

Context. The Solar Orbiter Heliospheric Imager (SoloHI) instrument of the Solar Orbiter mission is a next-generation heliospheric imager. New observations from SoloHI demonstrate the improved spatial and temporal resolution compared to previous observations of the heliosphere and corona. At perihelion, the field of view (FoV) of SoloHI covers the transition between the coronagraph (COR2) and heliospheric imager (HI1) Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite. In this paper, we focus on an active solar period following the first Solar Orbiter science perihelion that resulted in a number of well-observed large coronal mass ejections (CMEs) in SoloHI data in March and April 2022. Specifically, we highlight a series of events produced by AR12795 between 28 March and 2 April and show overlapping observations with SECCHI/COR2 and HI1 and LASCO/C3. Aims. We compare the performance of the SoloHI instrument against similar observations from 1 au imagers. We describe CME observations, highlighting the unique structural features captured within the SoloHI FoV. These observations demonstrate that SoloHI will provide new insights into CME morphology and evolution from a unique vantage point. Methods. To provide a direct and relevant comparison, images from all the telescopes we used in the paper are presented in FoVs common to each and with minimal processing applied. The J-maps we used to highlight outflowing features are also presented to show that the CME kinematics can be tracked through the SoloHI FoV, and also to report how the rest of the Heliophysics Systems Observatory (HSO) can be used to support the SoloHI data. Results. The high-resolution SoloHI images of these eruptions, taken from ∼0.3 au, reveal a number of detailed structural CME features, including internal cavities or cores of the CME flux rope(s). They also show the surrounding material and associated sheath region of the compressed upstream solar wind plasma. Many features that could not have been observed by other instruments are highlighted and discussed. Conclusions. The SoloHI instrument is performing well and has already provided detailed observations of CMEs that can help us understand the details of the internal structure and magnetic field of CMEs. These new observations in combination with synoptic observations from 1 au offer new opportunities for CME propagation from the corona to the heliosphere.

Unleashing the power of the Sun: the increasing impact of the solar cycle on off-season super typhoons since the 1990s

The occurrence of super typhoons outside the normal typhoon season can result in devastating loss of life and property damage. Our research reveals that the 11-year solar cycle can affect the incidence of these off-season typhoons (from November to April) in the western North Pacific by influencing sea surface temperature (SST) through a footprint mechanism. The solar cycle, once amplified by atmospheric and ocean interactions, generates a noticeable SST footprint in the subtropical North Pacific during winter and spring, which eventually intrudes into the tropical central Pacific and affects the atmospheric conditions, resulting in an increase or decrease in the occurrence of super typhoons during active or inactive solar periods. This mechanism has become more effective since the Atlantic Multi-decadal Oscillation (AMO) shifted to a warm phase in the 1990s, intensifying the subtropical Pacific couplings. An example of this type of off-season super typhoon during an active solar period is Typhoon Haiyan in 2013. By incorporating information about the solar cycle, we can anticipate the likelihood of super typhoon occurrences, thus improving decadal disaster preparation and planning.

Influence of Solar Activity on Precise Orbit Prediction of LEO Satellites

The perturbations of low earth orbit (LEO) satellites operating in the orbit of 300 ∼ 2000 km are complicated. In particular, the atmospheric drag force and solar radiation pressure force change rapidly over a short period of time due to solar activities. Using spaceborne global positioning system (GPS) data of the CHAMP, GRACE and SWARM satellites from 2002 to 2020, this paper studies in depth the influence of solar activity on LEO satellites’ precise orbit prediction by performing a series of orbit prediction experiments. The quality of GPS data is more susceptible to being influenced by solar activity during years when this activity is high and the changes in dynamic parameters are consistent with those of solar activity. The effects of solar activity on LEO orbit prediction accuracy are analyzed by comparing the predicted orbits with the precise ones. During years of high solar activity, the average root-mean-squares prediction errors at 10, 20, and 30 minutes are 0.15, 0.20, and 0.26 m, respectively, which are larger than the corresponding values in low-solar-activity years by 59%, 63%, and 68%, respectively. These results demonstrate that solar activity has a great influence on the orbit prediction accuracy, especially during high-solar-activity years. We should strengthen the real-time monitoring of solar activity and geomagnetic activity, and formulate corresponding orbit prediction strategies for the active solar period.

In Situ Data and Effect Correlation During September 2017 Solar Particle Event

AbstractSolar energetic particles are one of the main sources of particle radiation seen in space. In the first part of September 2017 the most active solar period of cycle 24 produced four large X‐class flares and a series of (interplanetary) coronal mass ejections, which gave rise to radiation storms seen over all energies and at the ground by neutron monitors. This paper presents comprehensive cross comparisons of in situ radiation detector data from near‐Earth satellites to give an appraisal on the state of present data processing for monitors of such particles. Many of these data sets have been the target of previous cross calibrations, and this event with a hard spectrum provides the opportunity to validate these results. As a result of the excellent agreement found between these data sets and the use of neutron monitor data, this paper also presents an analytical expression for fluence spectrum for the event. Derived ionizing dose values have been computed to show that although there is a significant high‐energy component, the event was not particularly concerning as regards dose effects in spacecraft electronics. Several sets of spacecraft data illustrating single event effects are presented showing a more significant impact in this regard. Such a hard event can penetrate thick shielding; human dose quantities measured inside the International Space Station and derived through modeling for aircraft altitudes are also presented. Lastly, simulation results of coronal mass ejection propagation through the heliosphere are presented along with data from Mars‐orbiting spacecraft in addition to data from the Mars surface.

Comparisons of Characteristics of Magnetic Clouds and Cloud-Like Structures During 1995 – 2012

Using eighteen years (1995 – 2012) of solar wind plasma and magnetic field data (observed by the Wind spacecraft), solar activity (e.g. sunspot number: SSN), and the geomagnetic-activity index (Dst), we have identified 168 magnetic clouds (MCs) and 197 magnetic-cloud-like structures (MCLs), and we have made relevant comparisons. The following features are found during seven different periods (TP: total period during 1995 – 2012, P1 and P2: first and second half-period during 1995 – 2003 and 2004 – 2012, Q1 and Q2: quiet periods during 1995 – 1997 and 2007 – 2009, A1 and A2: active periods during 1998 – 2006 and 2010 – 2012). (1) During the total period, the yearly occurrence frequency is 9.3 for MCs and 10.9 for MCLs. (2) In the quiet periods 〈N MCs〉Q1 > 〈N MCLs〉Q1 and 〈N MCs〉Q2 > 〈N MCLs〉Q2, but in the active periods 〈N MCs〉A1 < 〈N MCLs〉A1 and 〈N MCs〉A2 < 〈N MCLs〉A2. (3) The minimum Bz (Bz min) inside of an MC is well correlated with the intensity of geomagnetic activity, Dstmin (minimum Dst found within a storm event) for MCs (with a Pearson correlation coefficient, $\mathrm{c.c.} =0.75$ , and the fitting function is Dstmin=0.90+7.78Bz min), but Bz min for MCLs is not well correlated with the Dst index ( $\mathrm{c.c.} =0.56$ , and the fitting function is Dstmin=−9.40+4.58Bz min). (4) MCs play a major role in producing geomagnetic storms: the absolute value of the average Dstmin (〈Dstmin〉MC=−70 nT) for MCs associated geomagnetic storms is twice as strong as that for MCLs (〈Dstmin〉MCL=−35 nT) because of the difference in the IMF (interplanetary magnetic field) strength. (5) The SSN is uncorrelated with MCs (〈N MCs〉TP, $\mathrm{c.c.} = 0.27$ ), but is well associated with MCLs (〈N MCLs〉TP, $\mathrm{c.c.} = 0.85$ ). Note that the c.c. for SSN vs. 〈N MCs〉P2 is higher than that for SSN vs. 〈N MCLs〉P2. (6) Averages of IMF, solar wind speed, and density inside of the MCs are higher than those inside of the MCLs. (7) The average of MC duration (≈ 18.82 hours) is ≈ 20 % longer than the average of MCL duration (≈ 15.69 hours). (8) There are more MCs than MCLs in the quiet solar period and more MCLs than MCs in the active solar period, probably as a result of the interaction between an MC and another significant interplanetary disturbance (including another MC), which could obviously change the character of an MC, but we speculate that some MCLs are no doubt due to other factors such as complex birth conditions at the Sun.

Spectral broadening and phase scintillation measurements using interplanetary spacecraft radio links during the peak of solar cycle 23

When an interplanetary spacecraft is in a solar superior conjunction configuration, the received radio signals are degraded by several effects that generally increase in magnitude as the angle between the spacecraft and the Sun (Sun‐Earth‐Probe or SEP angle) decreases as viewed by a terrestrial tracking station. During periods of quiescent solar activity, phase scintillation and spectral broadening follow well‐defined trends as a function of solar impact distance (SEP angle) and link frequency. During active solar periods, the magnitudes of these effects increase above background levels predicted by the quiet period models. Several such events were observed during the solar superior conjunction of the Cassini spacecraft during the peak of solar cycle 23 in May 2000. Pronounced features in the spectral broadening data above the quiet background appear to be associated with Coronal Mass Ejections (CMEs), and last for extended periods of time ranging from ∼30 min to ∼4 h. These features are coincident with periods of increased activity seen in the region of the spacecraft signal source on coronal white light images, and tend to be related or matched with EIT flare events and possibly long‐duration flare events seen in satellite X‐ray data. Several such features were captured in the May 2000 Cassini solar conjunction phase scintillation and spectral broadening data at X band (8.4 GHz) and Ka band (32 GHz) radio frequencies, and are presented here. Such characterizations are beneficial in understanding the impact of such events in future interplanetary communication scenarios during solar conjunction periods.

Relationships Among Magnetic Clouds, CMES, and Geomagnetic Storms

During solar cycle 23, 82 interplanetary magnetic clouds (MCs) were identified by the Magnetic Field Investigation (MFI) team using Wind (1995 – 2003) solar wind plasma and magnetic field data from solar minimum through the maximum of cycle 23. The average occurrence rate is 9.5 MCs per year for the overall period. It is found that some of the anomalies in the frequency of occurrence were during the early part of solar cycle 23: (i) only four MCs were observed in 1999, and (ii) an unusually large number of MCs (17 events) were observed in 1997, just after solar minimum. We also discuss the relationship between MCs, coronal mass ejections (CMEs), and geomagnetic storms. During the period 1996 – 2003, almost 8000 CMEs were observed by SOHO-LASCO. The occurrence frequency of MCs appears to be related neither to the occurrence of CMEs as observed by SOHO LASCO nor to the sunspot number. When we included “magnetic cloud-like structures” (MCLs, defined by Lepping, Wu, and Berdichevsky, 2005), we found that the occurrence of the joint set (MCs + MCLs) is correlated with both sunspot number and the occurrence rate of CMEs. The average duration of the MCL structures is ~40% shorter than that of the MCs. The MCs are typically more geoeffective than the MCLs, because the average southward field component is generally stronger and longer lasting in MCs than in MCLs. In addition, most severe storms caused by MCs/MCLs with Dst min≤ −100 nT occurred in the active solar period.

Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest

Abstract. The VHF amplitude scintillation recorded during the period January 1991 to December 1993 in the declining phase of a solar cycle and April 1998 to December 1999 in the ascending phase of the next solar cycle at Varanasi (geogr. lat.=25.3°, long.=83.0°, dip=37°N) have been analyzed to study the behavior of ionospheric irregularities during active solar periods and magnetic storms. It is shown that irregularities occur at arbitrary times and may last for &lt;30min. A rise in solar activity increases scintillations during winter (November-February) and near equinoxes (March-April; September-October), whereas it depresses the scintillations during the summer (May-July). In general, the role of magnetic activity is to suppress scintillations in the pre-midnight period and to increase it in the post-midnight period during equinox and winter seasons, whilst during summer months the effect is reversed. The pre-midnight scintillation is sometimes observed when the main phase of Dst corresponds to the pre-midnight period. The annual variation shows suppression of scintillations on disturbed days, both during pre-midnight and post-midnight period, which becomes more effective during years of high solar activity. It is observed that for magnetic storms for which the recovery phase starts post-midnight, the probability of occurrence of irregularities is enhanced during this time. If the magnetic storm occurred during daytime, then the probability of occurrence of scintillations during the night hours is decreased. The penetration of magnetospheric electric fields to the magnetic equator affects the evolution of low-latitude irregularities. A delayed disturbance dynamo electric field also affects the development of irregularities.

Compact Energetic Light Particle Detector and Spectrometer

We have developed a megaelectron-volt class energetic charged-particle spectrometer based on a novel configuration and processing algorithm. The National Space Development Agency of Japan has undertaken a program to develop a particle monitor capable of discriminating and measuring protons in the range from 0.9 to 150 MeV, electrons in the range from 0.5 to >10 MeV and alpha particles >8 MeV, all within a single sensor called the standard dose monitor. The goal is to utilize sensors with nearly identical design and performance on several simultaneous missions to develop a clearer understanding of particle energies and their variability as a function of solar activity, latitude, and altitude. To date, four flight model sensors have been delivered. The sensors are designed to detect accurately the higher-energy particles and high count rates present during active solar periods. In addition, this sensor exhibits extremely efficient discrimination between low-energy electrons and protons. The sensors have been calibrated over nearly their entire particle-energy range. The design is described and calibration data are compared with the results of a Monte Carlo sensor performance model.

Bursts of HF radio noises after irregularities of solar wind

We present analyses of HF radio emission spectra of magnetospheric origin, at frequencies of 150 and 500 MHz, collected with ground-based antennae at middle latitudes ( L=2) during the second half of 1999. We discover a large occurrence of short-time-scale (1–10 s) sporadic radio bursts during active solar periods. To identify the source of these bursts, we associate their occurrence and perform correlations with solar wind parameters and energetic particle fluxes in interplanetary space and in the outer magnetosphere. Solar wind parameters and energetic ion fluxes in interplanetary space are provided by the ACE satellite. GOES8 and GOES10 satellites provide electron fluxes with energy E>2 MeV at geosynchronous orbit. These data are analyzed in order to show a correlation between particle fluxes and high amplitude radio bursts. There is a delay between the initiations of high-amplitude, short-term, sporadic radio bursts (at a frequency 150 MHz) and the arrival of high-speed solar wind streams at Earth's magnetosphere. The temporal delay of a few hours from the start of these features in the temporal distribution of electron fluxes at L=6.6 is shown, too. We suggest the possibility that the sources of radio bursts are located in the inner parts of magnetosphere.

Solar activity dependence of trans-equatorial ion whistler

This paper describes occurrence probabilities and patterns of trans-equatorial proton (TEP), deuteron (TED) and helium (TEH) whistler from the ISIS-2 satellite in time compressed dynamic spectra. It is shown that the TEP whistlers have high occurrence probability in an active solar period, while the TED whistler has low occurrence probability. In a quiet solar period, the TEP whistler has a relatively lower occurrence probability than the TED whistler. The TEP whistler in a quiet solar period shows a strong seasonal variation. That is a higher occurrence probability in the winter than in the summer in the Northern Hemisphere. The curve of occurrence probability of the TED whistler has a valley (no occurrence) at the noon in a solar active period. The minimum occurrence probabilities, which depend on geomagnetic activity appear at about K P = 4-5. These phenomena seem to be explained by using the bouncing surface diagram of multicomponent and inhomogeneous plasmas with various proton density. The spectral pattern of trans-equatorial ion whistlers and calculation of an approximate equation with regard to deuteron effect show that relative proton densities to electrons N P / N e decrease with increasing solar activity.

Behavior of low-energy protons and alpha particles during a disturbed time period

The paper presents observations of 130- to 1200-keV protons and 40- to 420-keV/nucleon alpha particles made on the earth-orbiting spacecraft Imp 8 and Imp 7 during an active solar period in September 1974, concentrating, in particular, on an energetic storm particle (ESP) event observed in association with an interplanetary shock wave on September 21. It is found that the observed variations in the proton-to-alpha particle ratios and spectral indices can be explained either by 'pileup' or by acceleration models of ESP events. Several instances of local acceleration of particles in the near-earth environment are also discussed.

Effects of cosmic radiation on the extremely low-frequency properties of the mesosphere

At extremely low frequencies (1 to 3000 cps), relatively slight amounts of ionization can produce notable effects on electromagnetic phenomena in the terrestrial system. Representative atmospheric conditions are examined to find minimum conditions that can produce such strong ELF effects at geophysically quiet periods. On the basis of analyses of ion production parameters, it is found that even for quiet nights, when only cosmic radiation is important for producing ionization in the mesosphere, large refractivities can be produced in this portion of the atmosphere below the ionosphere. For even a minimum electron detachment condition the refractive index of the mesosphere has the large magnitude of 4 at an altitude 75 km. For a more inclusive ion production condition with a maximum detachment factor that collates with VLF observations, strong refractivity effects occur at quite low altitudes: 35 km at 1 cps, 50 km at 10 cps, 55 km at 100 cps, and 65 km at 1000 cps. At very low frequencies (10 kc/s and above) effective altitudes for the nighttime lower ionosphere take on values normally assumed. During daytime and active solar periods it is indicated that strong refractivity effects will occur at altitudes below 30 km.