Solar-Flux Variation in Helium Lines According to SDO/EVE Data in the 24th Cycle and the Forecast for Different Levels of Solar Activity. Lyman Decrements of Hydrogen and Helium Lines

2020 ◽  
Vol 60 (7) ◽  
pp. 966-973
Author(s):  
E. A. Bruevich ◽  
T. V. Kazachevskaya ◽  
G. V. Yakunina
Keyword(s):  
Solar Activity ◽  
Solar Flux ◽  
Flux Variation ◽  
24Th Cycle ◽  
Different Levels

scholarly journals Retrospective analysis of GLEs and estimates of radiation risks

2018 ◽  
Vol 8 ◽  
pp. A52 ◽  
Author(s):  
Leonty I. Miroshnichenko
Keyword(s):  
Solar Activity ◽  
Ground Level ◽  
Radiation Hazard ◽  
Occurrence Rate ◽  
Solar Cosmic Rays ◽  
Dose Rates ◽  
Recent Debate ◽  
Unique Distribution ◽  
Different Levels ◽  
Ground Level Enhancements

28 February 2017 marked 75 years since the first confident registration of solar cosmic rays (SCRs), i.e., accelerated solar particles with energies from about 106 to ~1010 ÷ 1011 eV. Modern state of the problems related to the studies of Ground Level Enhancements (GLEs) of relativistic SCRs is critically analyzed based on available direct and proxy data. We are also taking into account extremely large fluxes of non-relativistic solar energetic particles (SEPs). Both kinds of SCR events are of great astrophysical and geo-scientific (geophysical) interests. A number of the GLE properties (total statistics, occurrence rate, longitude distribution, ranking of GLEs, a number of specific GLEs – so-called “rogue” SEP events etc.) are discussed in some detail. We note also the problems of GLE identification (definition) by ground-based observations, the difficulties in the studies of weak (“hidden”, or sub-) GLEs etc. One of serious challenges to the problem of radiation hazard in space is a lack of a clear, unambiguous relation between the fluxes (fluences) of relativistic SCR and non-relativistic SEPs. Special attention is paid to the recent debate on the validity, origin and properties of the “ancient” events AD775, AD994, AD1859 (Carrington event) and BC3372. We demonstrate that, in spite of existing uncertainties in proton fluences above 30 MeV, all of them are fitted well by a unique distribution function, at least, with the present level of solar activity. Extremely large SEP events are shown to obey a probabilistic distribution on their fluences with a sharp break in the range of large fluences (or low probabilities). The studies of this kind may be extended for periods with different levels of solar activity in the past and/or in the future. Dose rates at aircraft altitudes are also demonstrated during some GLEs. Several examples of using the SCR data and GLE properties in radiation prediction schemes are considered.

scholarly journals Sensitivity of the MnI 539.47 nm spectral line to solar activity

2004 ◽  
pp. 47-52 ◽  
Author(s):  
Sanja Danilovic ◽  
Istvan Vince
Keyword(s):  
Solar Activity ◽  
Spectral Line ◽  
Equivalent Width ◽  
Astronomical Observatory ◽  
Solar Flux ◽  
Full Width ◽  
Half Maximum ◽  
Relative Variation ◽  
Ccd Observations ◽  
Central Depth

CCD observations of the MnI 539.47 nm spectral line in the solar flux made at the Astronomical Observatory in Belgrade between 1994 and 2003 have been reduced and certain line parameters, viz. the equivalent width, full width at half maximum and central depth have been derived. The variation of these parameters with the solar activity has been evaluated. The relative variation of the equivalent width from minimum to maximum of solar activity was found to be 1.4%, while the variation of the central depth is 2.3%. The full width at half maximum remains practically constant.

scholarly journals ASYMMETRY VARIATIONS IN THE 24TH CYCLE OF SOLAR ACTIVITY

2021 ◽  
Author(s):  
O.A. Andreeva ◽  
◽  
V.I. Abramenko ◽  
V.M. Malashchuk ◽  
◽  
...  
Keyword(s):  
Solar Activity ◽  
24Th Cycle

scholarly journals Evidence for charge drift modulation at intermediate solar activity from the flux variation of protons and α particles

2001 ◽  
Vol 106 (A12) ◽  
pp. 29355-29362 ◽  
Author(s):  
G. Boella ◽  
M. Gervasi ◽  
S. Mariani ◽  
P. G. Rancoita ◽  
I. G. Usoskin
Keyword(s):  
Solar Activity ◽  
Flux Variation ◽  
Α Particles

scholarly journals Lower-thermosphere response to solar activity: an empirical-mode-decomposition analysis of GOCE 2009–2012 data

2020 ◽  
Vol 38 (3) ◽  
pp. 789-800
Author(s):  
Alberto Bigazzi ◽  
Carlo Cauli ◽  
Francesco Berrilli
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Empirical Mode Decomposition ◽  
Dynamic Range ◽  
Extreme Ultraviolet ◽  
Lower Thermosphere ◽  
European Space Agency ◽  
Solar Flux ◽  
Specific Response ◽  
Mode Decomposition

Abstract. 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.

scholarly journals Role of eddy diffusion in the delayed ionospheric response to solar flux changes

2021 ◽  
Vol 39 (4) ◽  
pp. 641-655
Author(s):  
Rajesh Vaishnav ◽  
Christoph Jacobi ◽  
Jens Berdermann ◽  
Mihail Codrescu ◽  
Erik Schmölter
Keyword(s):  
Solar Activity ◽  
Extreme Ultraviolet ◽  
Solar Rotation ◽  
Eddy Diffusion ◽  
Transport Processes ◽  
Solar Flux ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Total Electron ◽  
Ionospheric Response

Abstract. 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.

scholarly journals Effect of solar cycle on topside ion temperature measured by SROSS C2 and ROCSAT 1 over the Indian equatorial and low latitudes

2012 ◽  
Vol 30 (12) ◽  
pp. 1645-1654 ◽  
Author(s):  
A. Borgohain ◽  
P. K. Bhuyan
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Significant Negative Correlation ◽  
Solar Flux ◽  
High Solar Activity ◽  
Topside Ionosphere ◽  
Ion Temperature ◽  
Ion Density ◽  
Positive Correlation ◽  
June Solstice

Abstract. The effect of solar activity on the diurnal, seasonal and latitudinal variations of ion temperature Ti and its relationship with corresponding ion density Ni over the Indian low and equatorial topside ionosphere within 17.5° S to 22.5° N magnetic latitudes are being investigated, combining the data from SROSS C2 and ROCSAT 1 for the 9-year period from 1995 to 2003 during solar cycle 23. Ti varies between 800 K and 1100 K during nighttime and rises to peak values of ~1800 K in the post sunrise hours. Daytime Ti varies from 1000 K to 1500 K. The time of occurrence, magnitude and duration of the morning enhancement show distinct seasonal bias. For example, in the June solstice, Ti increases to ~1650 K at ~06:00 h and exhibits a daytime plateau till 17:00 LT. In the equinoxes, enhanced ion temperature is observed for a longer duration in the morning. There is also a latitudinal asymmetry in the ion temperature distribution. In the equinoxes, the daytime Ti is higher at off equatorial latitudes and lower over the Equator, while in the solstices, Ti exhibits a north–south gradient during daytime. Nighttime Ti is found to be higher over the Equator. Daytime ion temperature exhibits insignificant positive correlation with F10.7 cm solar flux, while nighttime ion temperature decreases with increase in solar flux. Daytime ion temperature and ion density are negatively correlated during solar minimum, while nighttime Ti does not exhibit any correlation. However, during high solar activity, significant positive correlation of Ti with Ni has been observed over the Equator, while at 10° S and 10° N temperature and density exhibit significant negative correlation. The neutral temperature Tn derived from the MSISE 90 model is found to be higher than measured Ti during nighttime, while daytime Ti is higher than model Tn.

Solar cycle and seasonal variations in F-region vertical drifts over Kodaikanal, India

1995 ◽  
Vol 13 (6) ◽  
pp. 633-640 ◽  
Author(s):  
K. B. Ramesh ◽  
J. H. Sastri
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Seasonal Variations ◽  
Normal Incidence ◽  
Magnetic Activity ◽  
Solar Flux ◽  
Seasonal Trend ◽  
F Region ◽  
Phase Path ◽  
10.7 Cm Solar Flux

Abstract. Measurements of the changes in phase path of F-region reflections at normal incidence at Kodaikanal (77° 28'E, 10° 14'N, dip 3°N) from February 1991 to February 1993 are used to determine the variation of the equatorial evening F-region vertical drifts (V z) with season, solar and magnetic activity. It is found that on average, at Kodaikanal, the post-sunset peak in Vz(Vzp) is higher in equinox and local winter months than in local summer. The day-to-day variability in V zp is highest in summer and lowest in winter. This seasonal trend persists even on magnetically quiet days (Ap \\leq14). Vzp is found to increase with 10.7 cm solar flux in all three seasons but tends to saturate for large flux values (>230 units) during local summer and winter months. Magnetic activity [represented by Ap as well as the time-weighted accumulations of a p and ap (τ)] does not seem to have any statistically significant effect on Vzp , except during equinoctial months of moderate solar activity, when Vzp decreases as magnetic activity increases.

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