scholarly journals Variations in the occurrence of SuperDARN F region echoes

2014 ◽  
Vol 32 (2) ◽  
pp. 147-156 ◽  
Author(s):  
M. Ghezelbash ◽  
R. A. D. Fiori ◽  
A V. Koustov
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Local Time ◽  
Northern Hemisphere ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Radar Data ◽  
Occurrence Rate ◽  
Major Focus ◽  
F Region

Abstract. The occurrence of F region ionospheric echoes observed by a number of SuperDARN HF radars is analyzed statistically in order to infer solar cycle, seasonal, and diurnal trends. The major focus is on Saskatoon radar data for 1994–2012. The distribution of the echo occurrence rate is presented in terms of month of observation and magnetic local time. Clear repetitive patterns are identified during periods of solar maximum and solar minimum. For years near solar maximum, echoes are most frequent near midnight during winter. For years near solar minimum, echoes occur more frequently near noon during winter, near dusk and dawn during equinoxes and near midnight during summer. Similar features are identified for the Hankasalmi and Prince George radars in the northern hemisphere and the Bruny Island TIGER radar in the southern hemisphere. Echo occurrence for the entire SuperDARN network demonstrates patterns similar to patterns in the echo occurrence for the Saskatoon radar and for other radars considered individually. In terms of the solar cycle, the occurrence rate of nightside echoes is shown to increase by a factor of at least 3 toward solar maximum while occurrence of the near-noon echoes does not significantly change with the exception of a clear depression during the declining phase of the solar cycle.

scholarly journals Unusual migration of the prominence activities in recent solar cycles

2013 ◽  
Vol 8 (S300) ◽  
pp. 161-167 ◽  
Author(s):  
Masumi Shimojo
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Radial Velocity ◽  
Northern Hemisphere ◽  
Solar Maximum ◽  
The Other ◽  
Occurrence Rate ◽  
Solar Cycles ◽  
Global Magnetic Field ◽  
Cycle 24

AbstractWe investigated the prominence eruptions and disappearances observed with the Nobeyama Radioheliograph during over 20 years for studying the anomaly of the recent solar cycle. Although the sunspot number of Cycle 24 is smaller than the previous one dramatically, the occurrence rate, size and radial velocity of the prominence activities are not changed significantly. We also found that the occurrence of the prominence activities in the northern hemisphere is normal from the duration of the cycle and the migration of the producing region of the prominence activities. On the other hand, the migration in the southern hemisphere significantly differs from that in the northern hemisphere and the previous cycles. Our results suggest that the anomalies of the global magnetic field distribution started at the solar maximum of Cycle 23.

scholarly journals North-South Distribution and Asymmetry of GOES SXR Flares during Solar Cycle 24

2020 ◽  
Vol 28 (1) ◽  
pp. 228-235
Author(s):  
Anita Joshi ◽  
Ramesh Chandra
Keyword(s):  
Data Analysis ◽  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Solar Maximum ◽  
X Ray ◽  
The North ◽  
Solar Cycle 24 ◽  
Cycle 24 ◽  
Second Peak

AbstractHere we present the results of the study of the north-south (N-S) distribution and asymmetry of GOES soft X-ray (SXR) flares during solar cycle 24. The period of study includes ascending, maximum and descending phases of the cycle. During the cycle double-peaked (2011, 2014) solar maximum has occurred. The cycle peak in the year 2011 is due to B-class flares excess activity in the northern hemisphere (NH) whereas C and M class flares excess activity in the southern hemisphere (SH) supported the second peak of the cycle in 2014. The data analysis shows that the SXR flares are more pronounced in 11 to 20 degree latitudes for each hemisphere. Cumulative values of SXR flare count show northern excess during the ascending phase of the cycle. However, in the descending phase of the cycle, southern excess occurred. In the cycle a significant SH dominated asymmetry exists. Near the maximum of the cycle, the asymmetry enhances pronouncedly and reverses in sign.

scholarly journals Model results for the ionospheric E region: solar and seasonal changes

1997 ◽  
Vol 15 (1) ◽  
pp. 63-78 ◽  
Author(s):  
J. E. Titheridge
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Electric Fields ◽  
Seasonal Changes ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Atmospheric Model ◽  
Reference Spectrum ◽  
Additional Increase ◽  
Model Calculations

Abstract. A new, empirical model for NO densities is developed, to include physically reasonable variations with local time, season, latitude and solar cycle. Model calculations making full allowance for secondary production, and ionising radiations at wavelengths down to 25 Å, then give values for the peak density NmE that are only 6% below the empirical IRI values for summer conditions at solar minimum. At solar maximum the difference increases to 16%. Solar-cycle changes in the EUVAC radiation model seem insufficient to explain the observed changes in NmE, with any reasonable modifications to current atmospheric constants. Hinteregger radiations give the correct change, with results that are just 2% below the IRI values throughout the solar cycle, but give too little ionisation in the E-F valley region. To match the observed solar increase in NmE, the high-flux reference spectrum in the EUVAC model needs an overall increase of about 20% (or 33% if the change is confined to the less well defined radiations at λ < 150 Å). Observed values of NmE show a seasonal anomaly, at mid-latitudes, with densities about 10% higher in winter than in summer (for a constant solar zenith angle). Composition changes in the MSIS86 atmospheric model produce a summer-to-winter change in NmE of about –2% in the northern hemisphere, and +3% in the southern hemisphere. Seasonal changes in NO produce an additional increase of about 5% in winter, near solar minimum, to give an overall seasonal anomaly of 8% in the southern hemisphere. Near solar maximum, reported NO densities suggest a much smaller seasonal change that is insufficient to produce any winter increase in NmE. Other mechanisms, such as the effects of winds or electric fields, seem inadequate to explain the observed change in NmE. It therefore seems possible that current satellite data may underestimate the mean seasonal variation in NO near solar maximum. A not unreasonable change in the data, to give the same 2:1 variation as at solar minimum, can produce a seasonal anomaly in NmE that accounts for 35–70% of the observed effect at all times.

The Hemispheric Sign Rule of Current Helicity during the Rising Phase of Cycle 23

2000 ◽  
Vol 179 ◽  
pp. 303-306
Author(s):  
S. D. Bao ◽  
G. X. Ai ◽  
H. Q. Zhang
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Active Regions ◽  
Hemispheric Preference ◽  
Current Helicity

AbstractWe compute the signs of two different current helicity parameters (i.e., αbestandHc) for 87 active regions during the rise of cycle 23. The results indicate that 59% of the active regions in the northern hemisphere have negative αbestand 65% in the southern hemisphere have positive. This is consistent with that of the cycle 22. However, the helicity parameterHcshows a weaker opposite hemispheric preference in the new solar cycle. Possible reasons are discussed.

Titan’s Ultraviolet Airglow Variability with Solar Cycle and Saturn Local Time

2020 ◽  
Author(s):  
Emilie Royer ◽  
Marielle Cooper ◽  
Joseph Ajello ◽  
Larry Esposito ◽  
Frank Crary
Keyword(s):  
Solar Cycle ◽  
Local Time ◽  
Solar Maximum ◽  
Incidence Angle ◽  
Upper Atmosphere ◽  
Particle Precipitation ◽  
Cassini Mission ◽  
Airglow Emissions ◽  
Airglow Intensity

&lt;p&gt;The Cassini spacecraft observed Titan&amp;#8217;s upper atmosphere and its airglow emissions from 2005 to 2017. It is now established that the solar XUV radiation is the main source of dayglow, while magnetospheric particle precipitation principally acts on the nightside of the satellite. Nevertheless, one of the questions remaining unanswered after the end of the Cassini mission concerns the role and quantification of the magnetospheric particle precipitation and other minor sources such as micrometeorite precipitation and cosmic galactic ray at Titan. We report here on enhancements observed in Ultraviolet (UV) observations of Titan airglow made with the Cassini-Ultraviolet Imaging Spectrograph (UVIS). Enhancements are correlated with magnetospheric changing conditions occurring while the spacecraft, and thus Titan, are known to have crossed Saturn&amp;#8217;s magnetopause and have been exposed to the magnetosheath environment. The processing and interpretation of 13+ years of airglow observations at Titan allows now for global studies of the upper atmosphere as a function of the Saturn Local Time (SLT) and the solar cycle.&lt;/p&gt;&lt;p&gt;Nitrogen airglow occur at about 1100 km of altitude in Titan&amp;#8217;s upper atmosphere. Observations by the Cassini-UVIS instrument revealed the emission of the LBH band system, VK band system as well as Nitrogen atomic emission lines at 1085&amp;#197; and 1493&amp;#197;, as the prominent features of airglow emissions at Titan, as shown in Figures 1 and 2. Measurements were made at a wide range of solar incidence angles and Saturn Local Time (SLT), during the entire Cassini mission, allowing for the investigation of the upper atmosphere response to the magnetospheric environment and energetic particle precipitation. Additionally, observations were taken in a variety of solar condition, from solar maximum to minimum. UVIS observations of Titan around 12PM SLT (near Saturn&amp;#8217;s magnetopause) present evidence of Titan&amp;#8217;s upper atmosphere response to a fluctuating magnetospheric environment.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.9617eca672fe56938492951/sdaolpUECMynit/0202CSPE&amp;app=m&amp;a=0&amp;c=975f92d7d9d43faa47cacd77ad47438f&amp;ct=x&amp;pn=gnp.elif&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Figure 1.&lt;/strong&gt; Airglow intensity as a function of the saturn Local Time (SLT), for observation taken close the Saturn&amp;#8217;s magnetopause (12PM SLT, labelled &amp;#8216;12h&amp;#8217;) and observations taken around miadnight SLT (labelled &amp;#8216;24h&amp;#8217;). Dayglow spectra exhibit higher averaged airglow intensity than Nightglow spectra.&lt;/p&gt;&lt;p&gt;We present here comparisons of the spectral emissions from the dayglow (Solar incidence angle &lt;110&amp;#176;) and nightglow (Solar incidence angle &amp;#8805;110&amp;#176;) between a rayheight of 900-1200 km around noon (&amp;#177;1 h) and around midnight (&amp;#177;1 h) SLT, during solar minima and maxima conditions (Fig. 2). Results show an enhancement of the airglow brightness with increasing particle precipitation, especially at SLT close to noon (i.e. close to the magnetopause), during solar maximum and minimum. Correlation between the ratio of the V-K, LBH, and NI-1493&amp;#197; emission peaks are also presented.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.2357e48772fe52168492951/sdaolpUECMynit/0202CSPE&amp;app=m&amp;a=0&amp;c=2c6d843782e300fc27ec3db3de320caf&amp;ct=x&amp;pn=gnp.elif&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Figure 2.&lt;/strong&gt; Dayglow intensity as a function of the saturn Local Time (SLT) and solar cycle. Observations have been dispatched in four groups as a function of Titan&amp;#8217;s orbital position within Saturn&amp;#8217;s magnetosphere and maximum oe minimum stage of the solar cycle. Results suggest that solar maximum conditions around midgnight SLT favor the apparition of the brightest dayglow.&lt;/p&gt;&lt;p&gt;In the past decade, results from the Cassini-UVIS instrument greatly improved our understanding of airglow production at Titan. However, combining remote-sensing datasets, such as Cassini-UVIS data, with in-situ measurements taken by the Cassini Plasma Spectrometer (CAPS) instrument can provide us with a more rigorous assessment of the airglow contribution and correlations between data from simultaneous observations of in-situ Cassini instruments (CAPS, RPWS and MIMI) has been possible on few occasions. UVIS results present here will be put in context with results from in-situ simultaneous observations.&lt;/p&gt;&lt;!-- COMO-HTML-CONTENT-END --&gt; &lt;p class=&quot;co_mto_htmlabstract-citationHeader&quot;&gt; &lt;strong class=&quot;co_mto_htmlabstract-citationHeader-intro&quot;&gt;How to cite:&lt;/strong&gt; Royer, E., Cooper, M., Ajello, J., Esposito, L., and Crary, F.: Titan&amp;#8217;s Ultraviolet Airglow Variability with Solar Cycle and Saturn Local Time, Europlanet Science Congress 2020, online, 21 September&amp;#8211;9 Oct 2020, EPSC2020-415, 2020 &lt;/p&gt;

scholarly journals Anomalous electron density events in the quiet summer ionosphere at solar minimum over Millstone Hill

1998 ◽  
Vol 16 (4) ◽  
pp. 460-469 ◽  
Author(s):  
A. V. Pavlo ◽  
M. J. Buonsanto
Keyword(s):  
Solar Minimum ◽  
Reduction Process ◽  
Radar Data ◽  
Molecular Ions ◽  
Ion Chemistry ◽  
Vibrationally Excited ◽  
F Region ◽  
Ion Chemistry And Composition ◽  
Density Results

Abstract. This study compares the observed behavior of the F region ionosphere over Millstone Hill with calculations from the IZMIRAN model for solar minimum for the geomagnetically quiet period 23-25 June 1986, when anomalously low values of hmF2(<200 km) were observed. We found that these low values of hmF2 (seen as a G condition on ionograms) exist in the ionosphere due to a decrease of production rates of oxygen ions resulting from low values of atomic oxygen density. Results show that determination of a G condition using incoherent scatter radar data is sensitive both to the true concentration of O+ relative to the molecular ions, and to the ion composition model assumed in the data reduction process. The increase in the O++ N 2 loss rate due to vibrationally excited N2 produces a reduction in NmF2 of typically 5-10% , but as large as 15% , bringing the model and data into better agreement. The effect of vibrationally excited NO+ ions on electron densities is negligible.Key words. Ionosphere (Ion chemistry and composition; Ionosphere-atmosphere interactions; Mid-latitude ionosphere).

A Search for Solar Cycle Variability in the Nightside Ionosphere of Mars

2020 ◽  
Author(s):  
Zachary Girazian ◽  
Jasper Halekas
Keyword(s):  
Solar Cycle ◽  
Ion Transport ◽  
Electron Impact ◽  
Solar Minimum ◽  
Impact Ionization ◽  
Solar Maximum ◽  
Electron Impact Ionization ◽  
Mars Atmosphere ◽  
Relative Contribution ◽  
Cyclical Variability

&lt;p&gt;The nightside ionosphere of Mars is mainly produced by a combination of electron impact ionization and day-to-night ion transport. The relative contribution of these two sources, and their variability over the solar cycle, has not been well established. To address this issue, we use Mars Atmosphere and Volatile EvolutioN (MAVEN) observations to search for cyclical variability in nightside ion densities over the solar cycle. We find that nightside densities (O&lt;sup&gt;+&lt;/sup&gt; in particular) were significantly higher during solar maximum (2014) than during solar minimum (2019). Our results suggest that, similar to the nightside ionosphere of Venus, day-to-night transport of O&lt;sup&gt;+&lt;/sup&gt; ions is more prominent during solar maximum.&lt;/p&gt;

scholarly journals Solar cycle and seasonal variations of the GPS phase scintillation at high latitudes

2018 ◽  
Vol 8 ◽  
pp. A48 ◽  
Author(s):  
Yaqi Jin ◽  
Wojciech J. Miloch ◽  
Jøran I. Moen ◽  
Lasse B.N. Clausen
Keyword(s):  
Solar Cycle ◽  
Seasonal Variations ◽  
Solar Maximum ◽  
Occurrence Rate ◽  
Local Minima ◽  
Magnetic Latitude ◽  
Latitude Range ◽  
Gps Scintillation ◽  
Gps Scintillations ◽  
The Impact

We present the long-term statistics of the GPS phase scintillation in the polar region (70°–82° magnetic latitude) by using the GPS scintillation data from Ny-Ålesund for the period 2010–2017. Ny-Ålesund is ideally located to observe GPS scintillations modulated by the ionosphere cusp dynamics. The results show clear solar cycle and seasonal variations, with the GPS scintillation occurrence rate being much higher during solar maximum than during solar minimum. The seasonal variations show that scintillation occurrence rate is low during summer and high during winter. The highest scintillation occurrence rate is around magnetic noon except for December 2014 (solar maximum) when the nightside scintillation occurrence rate exceeds the dayside one. In summer, the dayside scintillation region is weak and there is a lack of scintillations in the nightside polar cap. The most intriguing features of the seasonal variations are local minima in the scintillation occurrence rate around winter solstices. They correspond to local minima in the F2 peak electron density. The dayside scintillation region migrates equatorward from summer to winter and retreats poleward from winter to summer repetitively in a magnetic latitude range of 74°–80°. This latitudinal movement is likely due to the motion of the cusp location due to the tilt of the Earth’s magnetic field and the impact of the sunlight.

scholarly journals Why is there more ionosphere in January than in July? The annual asymmetry in the F2-layer

2006 ◽  
Vol 24 (12) ◽  
pp. 3293-3311 ◽  
Author(s):  
H. Rishbeth ◽  
I. C. F. Müller-Wodarg
Keyword(s):  
Electron Density ◽  
Southern Hemisphere ◽  
Solar Minimum ◽  
Annual Variation ◽  
Solar Maximum ◽  
Lower Atmosphere ◽  
Electron Content ◽  
Ion Production ◽  
The Asymmetry ◽  
June July

Abstract. Adding together the northern and southern hemisphere values for pairs of stations, the combined peak electron density NmF2 is greater in December-January than in June–July. The same applies to the total height-integrated electron content. This "F2-layer annual asymmetry" between northern and southern solstices is typically 30%, and thus greatly exceeds the 7% asymmetry in ion production due to the annual variation of Sun-Earth distance. Though it was noticed in ionospheric data almost seventy years ago, the asymmetry is still unexplained. Using ionosonde data and also values derived from the International Reference Ionosphere, we show that the asymmetry exists at noon and at midnight, at all latitudes from equatorial to sub-auroral, and tends to be greater at solar minimum than solar maximum. We find a similar asymmetry in neutral composition in the MSIS model of the thermosphere. Numerical computations with the Coupled Thermosphere-Ionosphere-Plasmasphere (CTIP) model give a much smaller annual asymmetry in electron density and neutral composition than is observed. Including mesospheric tides in the model makes little difference. After considering possible explanations, which do not account for the asymmetry, we are left with the conclusion that dynamical influences of the lower atmosphere (below about 30 km), not included in our computations, are the most likely cause of the asymmetry.

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