scholarly journals High-latitude Ulysses observations of the H/He intensity ratio under solar minimum and solar maximum conditions

2001 ◽  
Author(s):  
D. Lario
Keyword(s):  
High Latitude ◽  
Intensity Ratio ◽  
Solar Minimum ◽  
Solar Maximum

scholarly journals Climatology of ionospheric slab thickness

2004 ◽  
Vol 22 (1) ◽  
pp. 25-33 ◽  
Author(s):  
B. Jayachandran ◽  
T. N. Krishnankutty ◽  
T. L. Gulyaeva
Keyword(s):  
High Latitude ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Magnetic Activity ◽  
Slab Thickness ◽  
Electron Content ◽  
Night Time ◽  
Total Electron ◽  
Ionospheric Physics ◽  
F Region

Abstract. The ionospheric slab thickness τ defined as a ratio of the total electron content (TEC) to the F-region peak electron density (NmF2) has been analysed during the solar maximum (1981) and minimum (1985) phases of an intense, the 21st, solar cycle. Hourly values of TEC and NmF2 collected at Hawaii (low-latitude), Boulder (mid-latitude) and Goosebay (high-latitude) are used in the study. Climatology of the slab thickness is described by the diurnal, seasonal, solar and magnetic activity variations of τ for the different latitude zones. It is found that, for magnetically quiet days of solar maximum, increased ionization of NmF2 and TEC during the daytime is accompanied by an increased thickness of the ionosphere compared to the night-time for non-auroral latitudes. However, the reverse is found to be true during the solar minimum compensating TEC against a weak night-time ionization of NmF2. For the high-latitude the night-time slab thickness is higher compared to the daytime for both the solar phases. Ratios of daily peak to minimum values of slab thickness vary from 1.3 to 3.75 with the peaks of τ often observed at pre-sunrise and post-sunset hours. The average night-to-day ratios of τ vary from 0.68 to 2.23. The day-to-day variability of τ, expressed in percentage standard deviation, varies from 10% by day (equinox, high-latitude) to 67% by night (summer, mid-latitude) during solar minimum and from 10% by day (winter and equinox, mid-latitude) to 56% by night (equinox, high-latitude) during solar maximum. A comprehensive review of slab thickness related literature is given in the paper. Key words. Ionospheric physics

scholarly journals Solar cycle variations of the energetic H/He intensity ratio at high heliolatitudes and in the ecliptic plane

2003 ◽  
Vol 21 (6) ◽  
pp. 1229-1243 ◽  
Author(s):  
D. Lario ◽  
E. C. Roelof ◽  
R. B. Decker ◽  
G. C. Ho ◽  
C. G. Maclennan ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Intensity Ratio ◽  
Energetic Particle ◽  
Solar Minimum ◽  
High Speed ◽  
Solar Maximum ◽  
Ecliptic Plane ◽  
Interplanetary Shocks ◽  
Interplanetary Physics

Abstract. We study the variability of the heliospheric energetic proton-to-helium abundance ratios during different phases of the solar cycle. We use energetic particle, solar wind, and magnetic field data from the Ulysses, ACE and IMP-8 spacecraft to compare the H/He intensity ratio at high heliographic latitudes and in the ecliptic plane. During the first out-of-ecliptic excursion of Ulysses (1992–1996), the HI-SCALE instrument measured corotating energetic particle intensity enhancements characterized by low values (< 10) of the 0.5–1.0 MeV nucleon-1 H/He intensity ratio. During the second out-of-ecliptic excursion of Ulysses (1999–2002), the more frequent occurrence of solar energetic particle events resulted in almost continuously high (< 20) values of the H/He ratio, even at the highest heliolatitudes reached by Ulysses. Comparison with in-ecliptic measurements from an identical instrument on the ACE spacecraft showed similar H/He values at ACE and Ulysses, suggesting a remarkable uniformity of energetic particle intensities in the solar maximum heliosphere at high heliolatitudes and in the ecliptic plane. In-ecliptic observations of the H/He intensity ratio from the IMP-8 spacecraft show variations between solar maximum and solar minimum similar to those observed by Ulysses at high heliographic latitudes. We suggest that the variation of the H/He intensity ratio throughout the solar cycle is due to the different level of transient solar activity, as well as the different structure and duration that corotating solar wind structures have under solar maximum and solar minimum conditions. During solar minimum, the interactions between the two different types of solar wind streams (slow vs. fast) are strong and long-lasting, allowing for a continuous and efficient acceleration of interstellar pickup He +. During solar maximum, transient events of solar origin (characterized by high values of the H/He ratio) are able to globally fill the heliosphere. In addition, during solar maximum, the lack of strong recurrent high-speed solar wind streams, together with the dynamic character of the Sun, lead to weak and short-lived solar wind stream interactions. This results in a less efficient acceleration of pickup He +, and thus a higher value of the H/He intensity ratio.Key words. Interplanetary physics (energetic particles, interplanetary shocks; solar wind plasma)

Energetic intensity ratio under solar maximum and solar minimum conditions: Ulysses observations

2003 ◽  
Vol 32 (4) ◽  
pp. 585-590 ◽  
Author(s):  
D. Lario ◽  
E.C. Roelof ◽  
R.B. Decker ◽  
G.C. Ho ◽  
C.G. Maclennan ◽  
...  
Keyword(s):  
Intensity Ratio ◽  
Solar Minimum ◽  
Solar Maximum

Elevation angles and attenuation of gravity waves in the ionosphere

2021 ◽  
Author(s):  
Jaroslav Chum ◽  
Kateřina Podolska ◽  
Jiri Base ◽  
Jan Rusz
Keyword(s):  
Gravity Waves ◽  
Solar Minimum ◽  
Rest Frame ◽  
Solar Maximum ◽  
Three Dimensional ◽  
Mean Value ◽  
3D Analysis ◽  
Doppler Shifts ◽  
Wind Velocities ◽  
One Year

&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Characteristics of gravity waves (GWs) are studied from multi-point and multi-frequency continuous Doppler sounding in the Czech Republic. Three dimensional (3D) phase velocities of GWs are determined from phase shifts between the signals reflecting from the ionosphere at different locations that are separated both vertically and horizontally; the reflection heights are determined by a nearby ionospheric sounder located in Pr&amp;#367;honice. Wind-rest frame (intrinsic) velocities are calculated by subtracting the neutral wind velocities, obtained by HWM-14 wind model, from the observed GW velocities. In addition, attenuation of GWs with height was estimated from the amplitudes (Doppler shifts) observed at different altitudes. A statistical analysis was performed over two one-year periods: a) from July 2014 to June 2015 representing solar maximum b) from September 2018 to August 2019 representing solar minimum.&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160; The results show that the distribution of elevation angles of wave vectors in the wind&amp;#8211;rest frame is significantly narrower than in the Earth frame (observed elevations). Possible differences were also found between the wind&amp;#8211;rest frame elevation angles obtained for the solar maximum (mean value (around -24&amp;#176;) and solar minimum (mean value round -37&amp;#176;). However, it is demonstrated that the elevation angles partly depended on the daytime and day of year. As the distribution of the time intervals suitable for the 3D analysis in the daytime&amp;#8211;day of year plane was partly different for solar maximum and minimum, no reliable conclusion about the possible dependence of elevation angles on the solar activity can be drawn.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160; It is shown that the attenuation of GWs in the ionosphere was in average smaller at the lower heights. This is consistent with the idea that mainly viscous damping and losses due to thermal conductivity are responsible for the attenuation.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&lt;/p&gt;

scholarly journals Quantifying uncertainties of climate signals in chemistry climate models related to the 11-year solar cycle – Part 1: Annual mean response in heating rates, temperature, and ozone

2020 ◽  
Vol 20 (11) ◽  
pp. 6991-7019
Author(s):  
Markus Kunze ◽  
Tim Kruschke ◽  
Ulrike Langematz ◽  
Miriam Sinnhuber ◽  
Thomas Reddmann ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Solar Minimum ◽  
Climate Model ◽  
Solar Maximum ◽  
Sunspot Cycle ◽  
Spectral Irradiance ◽  
Data Sets ◽  
Reference Spectrum ◽  
Heating Rates ◽  
Data Set

Abstract. Variations in the solar spectral irradiance (SSI) with the 11-year sunspot cycle have been shown to have a significant impact on temperatures and the mixing ratios of atmospheric constituents in the stratosphere and mesosphere. Uncertainties in modelling the effects of SSI variations arise from uncertainties in the empirical models reconstructing the prescribed SSI data set as well as from uncertainties in the chemistry–climate model (CCM) formulation. In this study CCM simulations with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and the Community Earth System Model 1 (CESM1)–Whole Atmosphere Chemistry Climate Model (WACCM) have been performed to quantify the uncertainties of the solar responses in chemistry and dynamics that are due to the usage of five different SSI data sets or the two CCMs. We apply a two-way analysis of variance (ANOVA) to separate the influence of the SSI data sets and the CCMs on the variability of the solar response in shortwave heating rates, temperature, and ozone. The solar response is derived from climatological differences of time slice simulations prescribing SSI for the solar maximum in 1989 and near the solar minimum in 1994. The SSI values for the solar maximum of each SSI data set are created by adding the SSI differences between November 1994 and November 1989 to a common SSI reference spectrum for near-solar-minimum conditions based on ATLAS-3 (Atmospheric Laboratory of Applications and Science-3). The ANOVA identifies the SSI data set with the strongest influence on the variability of the solar response in shortwave heating rates in the upper mesosphere and in the upper stratosphere–lower mesosphere. The strongest influence on the variability of the solar response in ozone and temperature is identified in the upper stratosphere–lower mesosphere. However, in the region of the largest ozone mixing ratio, in the stratosphere from 50 to 10 hPa, the SSI data sets do not contribute much to the variability of the solar response when the Spectral And Total Irradiance REconstructions-T (SATIRE-T) SSI data set is omitted. The largest influence of the CCMs on variability of the solar responses can be identified in the upper mesosphere. The solar response in the lower stratosphere also depends on the CCM used, especially in the tropics and northern hemispheric subtropics and mid-latitudes, where the model dynamics modulate the solar responses. Apart from the upper mesosphere, there are also regions where the largest fraction of the variability of the solar response is explained by randomness, especially for the solar response in temperature.

scholarly journals Solar 27-day signatures in standard phase height measurements above central Europe

2018 ◽  
Author(s):  
Christian von Savigny ◽  
Dieter H. W. Peters ◽  
Günter Entzian
Keyword(s):  
Central Europe ◽  
Time Scale ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Solar Forcing ◽  
Superposed Epoch Analysis ◽  
Height Change ◽  
Underlying Mechanisms ◽  
Epoch Analysis ◽  
Good Agreement

Abstract. We report on the effect of solar variability at the 27-day and the 11-year time scale on standard phase height measurements carried out in central Europe. Using the superposed epoch analysis (SEA) method, we extract statistically highly significant solar 27-day signatures in standard phase heights. The 27-day signatures are roughly anti-correlated to solar proxies, such as the F10.7 cm radio flux or the Lyman-α flux. The sensitivity of standard phase height change to solar forcing at the 27-day time scale is found to be in good agreement with the sensitivity for the 11-year solar cycle, suggesting similar underlying mechanisms. The amplitude of the 27-day signature in standard phase height is larger during solar minimum than during solar maximum, indicating that the signature is not only driven by photo-ionisation of NO. We identified statistical evidence for an influence of ultra-long planetary waves on the quasi 27-day signature of standard phase height in winters of solar minimum periods.

scholarly journals On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

2007 ◽  
Vol 25 (4) ◽  
pp. 855-861 ◽  
Author(s):  
G. Manju ◽  
C. V. Devasia ◽  
R. Sridharan
Keyword(s):  
Solar Minimum ◽  
Solar Maximum ◽  
Decisive Role ◽  
Meridional Wind ◽  
Equatorial Spread F ◽  
Clear Cut ◽  
Meridional Winds ◽  
Different Seasons ◽  
Spread F ◽  
Bottom Side

Abstract. A study has been carried out on the occurrence of bottom side equatorial spread F (ESF) and its dependence on the polarity and magnitude of the thermospheric meridional wind just prior to ESF occurrence during summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5° N, 76.5° E, dip=0.5° N) and SHAR (13.7° N, 80.2° E, dip ~5.5° N) in the Indian longitude sector. In this study, we have examined the changes in the threshold height of the base of the F layer for the triggering of ESF, irrespective of the magnitude and polarity of the meridional winds during the above periods. The study indicates that the threshold height above which ESF triggering is entirely controlled only by the collisional R-T instability is least for summer months, with higher values for winter and equinox, during the solar minimum period, whereas for the solar maximum period the threshold height is least for winter, with higher values for summer and equinox. But the range over which the threshold height varies is very narrow (<15 km) for solar minimum in relation to the large range of variation (>50 km) in the solar maximum epoch. Further to this, the study also reveals a clear-cut increase in threshold height with solar activity for all seasons. Clear-cut seasonal variability is also observed in the threshold height, especially for solar maximum. The study quantifies the level of the base of the F layer below which neutral dynamical effects play a decisive role in the triggering of ESF during different seasons and solar epochs.

scholarly journals Latitudinal and radial variation of >2 GeV/n protons and alpha-particles at solar maximum: ULYSSES COSPIN/KET and neutron monitor network observations

2003 ◽  
Vol 21 (6) ◽  
pp. 1295-1302 ◽  
Author(s):  
A. V. Belov ◽  
E. A. Eroshenko ◽  
B. Heber ◽  
V. G. Yanke ◽  
A. Raviart ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Neutron Monitor ◽  
Solar Minimum ◽  
Latitudinal Gradient ◽  
Solar Maximum ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Alpha Particles ◽  
Polar Regions

Abstract. Ulysses, launched in October 1990, began its second out-of-ecliptic orbit in September 1997. In 2000/2001 the spacecraft passed from the south to the north polar regions of the Sun in the inner heliosphere. In contrast to the first rapid pole to pole passage in 1994/1995 close to solar minimum, Ulysses experiences now solar maximum conditions. The Kiel Electron Telescope (KET) measures also protons and alpha-particles in the energy range from 5 MeV/n to >2 GeV/n. To derive radial and latitudinal gradients for >2 GeV/n protons and alpha-particles, data from the Chicago instrument on board IMP-8 and the neutron monitor network have been used to determine the corresponding time profiles at Earth. We obtain a spatial distribution at solar maximum which differs greatly from the solar minimum distribution. A steady-state approximation, which was characterized by a small radial and significant latitudinal gradient at solar minimum, was interchanged with a highly variable one with a large radial and a small – consistent with zero – latitudinal gradient. A significant deviation from a spherically symmetric cosmic ray distribution following the reversal of the solar magnetic field in 2000/2001 has not been observed yet. A small deviation has only been observed at northern polar regions, showing an excess of particles instead of the expected depression. This indicates that the reconfiguration of the heliospheric magnetic field, caused by the reappearance of the northern polar coronal hole, starts dominating the modulation of galactic cosmic rays already at solar maximum.Key words. Interplanetary physics (cosmic rays; energetic particles) – Space plasma physics (charged particle motion and acceleration)

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