Quiet Solar Periods Research Articles

Impact of flight route changes on cosmic ray exposure: consequences of the conflict between Ukraine and the Russian federation.

This work investigates the impact on cosmic ray exposures to aircrew due to changing flight routes operated in the context of the recent conflict between Ukraine and the Russian Federation. All analyses were done based on Paris-Tokyo and Tokyo-Paris flights taken as examples, and differences in radiation exposures were quantified by comparing the situation before and after the beginning of the conflict. Regarding space weather scenarios, a quiet solar period and an extreme solar event (ground level enhancement (GLE) 5) were considered in the study. Analyses showed that the new Paris-Tokyo flight route established after the beginning of the conflict results in a smaller radiation dose to aircrew than that operated before the conflict, particularly during solar events. In contrast, for Tokyo-Paris flights the new high-latitude route crossing the Atlantic Ocean and North America increases the dose significantly (+ 50% in the worst case). Although this analysis is limited only to flights connecting Paris and Tokyo, it allowed for an evaluation of the consequences of new routes (particularly polar ones) on ambient dose equivalent values.

Propagation Effects in Quiet Sun Observations at Meter Wavelengths

Abstract Quiet Sun meterwave emission arises from thermal bremsstrahlung in the MK corona, and can potentially be a rich source of coronal diagnostics. On its way to the observer, it gets modified substantially due to propagation effects—primarily refraction and scattering—through the magnetized and turbulent coronal medium, leading to the redistribution of the intensity in the image plane. By comparing the full-disk meterwave solar maps during a quiet solar period and the modeled thermal bremsstrahlung emission, we characterize these propagation effects. The solar radio maps between 100 MHz and 240 MHz come from the Murchison Widefield Array. The FORWARD package is used to simulate thermal bremsstrahlung images using the self-consistent Magnetohydrodynamic Algorithm outside a Sphere coronal model. The FORWARD model does not include propagation effects. The differences between the observed and modeled maps are interpreted to arise due to scattering and refraction. There is a good general correspondence between the predicted and observed brightness distributions, though significant differences are also observed. We find clear evidence for the presence of significant propagation effects, including anisotropic scattering. The observed radio size of the Sun is 25–30% larger in area. The emission peak corresponding to the only visible active region shifts by 8–11ʹ and its size increases by 35–40%. Our simple models suggest that the fraction of scattered flux density is always larger than a few tens of percent, and varies significantly between different regions. We estimate density inhomogeneities to be in the range 1–10%.

Modeling inner boundary values at 18 solar radii during solar quiet time for global three-dimensional time-dependent magnetohydrodynamic numerical simulation

We develop an empirical model of the solar wind parameters at the inner boundary (18 solar radii, Rs) of the heliosphere that can be used in our global, three-dimensional (3D) magnetohydrodynamic (MHD) model (G3DMHD) or other equivalent ones. The model takes solar magnetic field maps at 2.5 R, which is based on the Potential Field Source Surface, PFSS model and interpolates the solar wind plasma and field out to 18 Rs using the algorithm of Wang and Sheeley (1990). A formula (V18Rs = V1 + V2fsα) is used to calculate the solar wind speed at 18 Rs, where V1 is in a range of 150–350 km s−1, V2 is in the range of 250–500 km s−1, and “fs” is the magnetic flux expansion factor derived from the Wang and Sheeley (WS) algorithm at 2.5 R. To estimate the solar wind density and temperature at 18 Rs, we assume an incompressible solar wind and a constant total pressure. The three free parameters are obtained by adjusting simulation results to match in-situ observations (Wind) for more than 54 combinations of V1, V2 and α during a quiet solar wind interval, i.e., the Carrington Rotation (CR) 2082. We found that VBF = (200 ± 50) + (400 ± 100) fs−0.4 km/s is a good formula for the quiet solar wind period. The formula was also good to use for the other quiet solar periods. Comparing results between WSA (Arge et al. 2000, 2004) and our model (WSW-3DMHD), we find the following: i) The results of using VBF with the full rotation (FR) data as input to drive the 3DMHD model is better than the results of WSA using FR, or daily updated. . ii) The WSA model using the modified daily updated 4-day-advanced solar wind speed predictions is slightly better than that for WSW-3DMHD. iii) The results of using VBF as input to drive the 3DMHD model is much better than the using the WSA formula with an extra parameter for the angular width (θb) from the nearest coronal hole. The present study puts in doubt in the usefulness of θb for these purposes.

Analysis of Exposure to Solar and Galactic Cosmic Radiations of Flights Representative of the European International Air Traffic.

This study analyzed the impact of galactic and solar cosmic rays on ambient dose equivalent during airline travel. A high statistic of flights are considered, which is representative of European international air traffic. Flight paths are based on the Eurocontrol Demand Data Repository and consider realistic flight plans with and without regulations or updated with radar data from the Central Flow Management Unit. Ambient dose equivalent during flights was investigated during quiet solar periods and extreme solar flare events. Thus, the statistical analyses presented here take into account route characteristics (departure, arrival, continent, etc.) and space weather conditions. The findings of this work show the important influence of flight path, particularly the latitude, which drives the cutoff rigidity variations. Moreover, dose values vary drastically during ground level enhancement events, with the route path (latitude, longitude and altitude) and the phasing of the solar event. This study highlights the importance of monitoring these solar events and developing a physical approach to obtain reliable assessment of ambient dose equivalents.

Charged particle spectra measured during the transit to Mars with the Mars Science Laboratory Radiation Assessment Detector (MSL/RAD)

The Mars Science Laboratory (MSL) started its 253-day cruise to Mars on November 26, 2011. During cruise the Radiation Assessment Detector (RAD), situated on board the Curiosity rover, conducted measurements of the energetic-particle radiation environment inside the spacecraft. This environment consists mainly of galactic cosmic rays (GCRs), as well as secondary particles created by interactions of these GCRs with the spacecraft. The RAD measurements can serve as a proxy for the radiation environment a human crew would encounter during a transit to Mars, for a given part of the solar cycle, assuming that a crewed vehicle would have comparable shielding. The measurements of radiological quantities made by RAD are important in themselves, and, the same data set allow for detailed analysis of GCR-induced particle spectra inside the spacecraft. This provides important inputs for the evaluation of current transport models used to model the free-space (and spacecraft) radiation environment for different spacecraft shielding and different times in the solar cycle. Changes in these conditions can lead to significantly different radiation fields and, thus, potential health risks, emphasizing the need for validated transport codes. Here, we present the first measurements of charged particle fluxes inside a spacecraft during the transit from Earth to Mars. Using data obtained during the last two month of the cruise to Mars (June 11–July 14, 2012), we have derived detailed energy spectra for low-Z particles stopping in the instrument’s detectors, as well as integral fluxes for penetrating particles with higher energies. Furthermore, we analyze the temporal changes in measured proton fluxes during quiet solar periods (i.e., when no solar energetic particle events occurred) over the duration of the transit (December 9, 2011–July 14, 2012) and correlate them with changing heliospheric conditions.

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.

Energy release in the solar corona from spatially resolved magnetic braids

It is now apparent that there are at least two heating mechanisms in the Sun's outer atmosphere, or corona. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000 K (refs 1-3). The active corona needs additional heating to reach 2,000,000-4,000,000 K; this heat has been theoretically proposed to come from the reconnection and unravelling of magnetic 'braids'. Evidence favouring that process has been inferred, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought to have an angular width of about 0.2 arc seconds have not been resolved. Fine-scale braiding has been seen in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2 arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000 K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.

A Dynamic Model for the Validation of Cosmic Rays Anisotropy at Low Earth Orbit

The International Space Station (ISS) provides the proving ground for future long duration human activities in space. Ionizing radiation measurements at low Earth orbit (LEO) in general, and at ISS in particular, form the ideal tool for the experimental validation of radiation environmental models, nuclear transport code algorithms and nuclear reaction cross sections. Indeed, prior measurements onboard the space transportation system (STS; shuttle) have provided vital information impacting both the environmental models and the nuclear transport code development by requiring dynamic (time dependent) models of the LEO environment. In addition, past studies using computer aided design (CAD) models of ISS have demonstrated that the ion specific based flux or cumulative based dose exposure prediction for a spacecraft at LEO requires the description of an environmental model with accurate anisotropic (directional) as well as dynamic behavior. Within the framework of an environment code named GEORAD (GEOmagnetic RADiation), this paper describes the dynamic and anisotropic capabilities of GEORAD as applied to the interaction of galactic cosmic rays (GCR) with the geomagnetic field at LEO. The described model is a component of GEORAD which computes anisotropic cutoff rigidity and the corresponding transmission coefficient, both of which are used as input into a deterministic particle transport algorithm for exposure estimation within ISS. The GEORAD capability to compute anisotropic cutoff rigidity and transmission coefficient provides a useful tool to validate GCR exposure measurements by solid state particle telescopes which inherently have strong directional sensitivity. While this paper concentration is on the anisotropic characteristics of GCR ions at LEO, GEORAD suite is applicable to radiation environment prediction at LEO, medium Earth orbit (MEO) and geosynchronous Earth orbit (GEO) at quiet solar periods. GEORAD interest is in the study of the geomagnetic environment from a long term point of view (i.e., a meaningful portion of solar cycle), and therefore it does not account for any short term distortion of the geomagnetic field due to solar activity. With the concentration of the paper on the study of GCR ions at LEO, for the formation flying ISS, the paper presents the anisotropic profile of GCR ions at different angular distribution with respect to zenith. While the magnitude of the GCR anisotropy at LEO depends on a multitude of factors such as the ions rigidity, transmission, attitude and orientation of the spacecraft along the velocity vector, the paper draws quantitative conclusions on the effect of GCR anisotropy at LEO.

A low earth orbit dynamic model for the proton anisotropy validation

Ionizing radiation measurements at low earth orbit (LEO) form the ideal tool for the experimental validation of radiation environmental models, nuclear transport code algorithms and nuclear reaction cross sections. Indeed, prior measurements on the space transportation system (STS; shuttle) have provided vital information impacting both the environmental models and the nuclear transport code development by requiring dynamic models of the LEO environment. Previous studies using computer aided design (CAD) models of the international space station (ISS) have demonstrated that the dosimetric prediction for a spacecraft at LEO requires the description of an environmental model with accurate anisotropic as well as dynamic behavior. This paper describes such a model for the trapped proton. The described model is a component of a suite of codes collectively named GEORAD (GEOmagnetic RADiation) which computes cutoff rigidity, trapped proton and trapped electron environments. The web version of GEORAD is named OLTARIS (On-line Tool for the Assessment of Radiation in Space). GEORAD suite is applicable to radiation environment prediction at LEO, medium earth orbit (MEO) and geosynchronous earth orbit (GEO) at quiet solar periods. GEORAD interest is in the study of long term effect of the trapped environment and therefore it does not account for any short term external field contribution due to solar activity. With the concentration of the paper on the LEO protons only, the paper presents the validation of the trapped proton model within GEORAD with reported measurements from the compact environment anomaly sensor (CEASE) science instrument package, flown onboard the tri-service experiment-5 (TSX-5) satellite during the period of June 2000 to July 2006. The spin stabilized satellite was flown in a 410 × 1710 km, 69° inclination elliptical orbit, allowing it to be exposed to a broad range of the LEO regime. The paper puts particular emphasize on the validation of the differential at 40 MeV, and integral at >40 MeV proton flux profiles, in the vicinity of the south Atlantic anomaly (SAA) region where protons exhibit east–west (EW) anisotropy and have a relatively narrow pitch angle distribution. Within SAA, the EW anisotropy results in different level of exposure to different sections of a formation flying spacecraft such as TSX-5 or ISS. While the magnitude of the EW effect at LEO depends on a multitude of factors such as trapped proton energy, orientation of the spacecraft along the velocity vector and altitude of the spacecraft, the paper draws quantitative conclusions on the combined effect of proton pitch angle and EW anomaly.

The Low Earth Orbit validation of a dynamic and anisotropic trapped radiation model through ISS measurements

The International Space Station (ISS) provides the proving ground for future long duration human activities in space. Ionizing radiation measurements in ISS form the ideal tool for the experimental validation of radiation environmental models, nuclear transport code algorithms and nuclear reaction cross sections. Indeed, prior measurements on the Space Transportation System (STS; Shuttle) have provided vital information impacting both the environmental models and the nuclear transport code development by requiring dynamic models of the Low Earth Orbit (LEO) environment. Previous studies using Computer Aided Design (CAD) models of the evolving ISS configurations with Thermo-Luminescent Detector (TLD) area monitors, demonstrated that computational dosimetry requires environmental models with accurate non-isotropic as well as dynamic behavior, detailed information on rack loading, and an accurate six degree of freedom (DOF) description of ISS trajectory and orientation. It is imperative that we understand ISS exposures dynamically for crew career planning, and insure that the regulatory requirements of keeping exposure as low as reasonably achievable (ALARA) are adequately implemented. This is especially true as ISS nears some form of completion with increasing complexity, resulting in a larger drag coefficient, and requiring operation at higher altitudes with increased exposure rates. In this paper ISS environmental model is configured for 11A (circa mid 2005), and uses non-isotropic and dynamic geomagnetic transmission and trapped proton models. ISS 11A and LEO model validations are important steps in preparation for the design and validation for the next generation manned vehicles. While the described cutoff rigidity, trapped proton and electron formalisms as coded in a package named GEORAD (GEOmagnetic RADiation) and a web interface named OLTARIS (On-line Tool for the Assessment of Radiation in Space) are applicable to the LEO, Medium Earth Orbit (MEO) and Geosynchronous Earth Orbit (GEO) at quiet solar periods, in this report, the validation of the models using available measurements are limited to STS and ISS nominal operational altitudes (300–400 km) range at LEO where the dominant fields within the vehicle are the trapped proton and attenuated Galactic Cosmic Ray (GCR) ions. The described formalism applies to trapped electron at LEO, MEO and GEO as well. Due to the scarcity of available electron measurements, the trapped electron capabilities of the GEORAD are not discussed in this report, but are accessible through OLTARIS web interface. GEORAD and OLTARIS interests are in the study of long term effects (i.e. a meaningful portion of solar cycle). Therefore, GEORAD does not incorporate any short term external field contribution due to solar activity. Finally, we apply these environmental models to selected target points within ISS 6A (circa early 2001), 7A (circa late 2001), and 11A during its passage through the South Atlantic Anomaly (SAA) to assess the validity of the environmental models at ISS altitudes.

An Extended Solar Cycle 23 with Deep Minimum Transition to Cycle 24: Assessments and Climatic Ramifications

Abstract The extended length of solar cycle 23 and the associated deep quiet period (QP) between cycles 23 and 24 have been examined using the international sunspot record from 1755 to 2010. This study has also introduced a QP definition based on a (beginning and ending) mean monthly threshold value of less than 10 for the sunspot number. Features addressed are the length and intensity of cycle 23, the length of the QP and the associated number of spotless days, and the respective relationships between cycle intensity, length, and QP. The length of cycle 23 (153 months) is second only to cycle 4 (164 months), with an average of 132.5 months for the 11-yr cycle. The length of the QP between cycles 23 and 24 ranks eighth, extending from October 2005 through November 2009 (but subject to continued weakness in cycle 24). The number of spotless days achieved within this QP was 751 (and for all days within the transition from cycle 23 to cycle24, a record number of 801 spotless days had been observed through May 2010). Shortcomings of solar-convection-model predictions of sunspot activity and intensity are also noted, including the failure in the initial predictions of cycle-24 onset. The relevance of an extended quiet solar period and the potential reduction of total solar irradiance (TSI) are also discussed, both in the context of climate-model simulations of future climate change as well as with regard to future satellite measurements of TSI.

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.

Low energy gamma radiation in the atmosphere during active and quiet periods on the Sun

Gamma ray pulse height spectra during active and quiet solar periods from midlatitude balloon flights

The neutron flux in space after the November 15, 1960, polar cap neutron event

Low latitude neutron fluxes for PCN and quiet solar period, noting solar proton production of neutrons