Solar cycle variations in F-region Te in the vicinity of the midlatitude trough based on AE-C measurements at solar minimum and DE-2 measurements at solar maximum

1990 ◽  
Vol 10 (11) ◽  
pp. 83-88 ◽  
Author(s):  
Larry H. Brace
Keyword(s):  
Solar Cycle ◽  
Solar Minimum ◽  
Solar Maximum ◽  
F Region

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.

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

<p>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<sup>+</sup> 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<sup>+</sup> ions is more prominent during solar maximum.</p>

scholarly journals A statistical study of diurnal, seasonal and solar cycle variations of F-region and topside auroral upflows observed by EISCAT between 1984 and 1996

1998 ◽  
Vol 16 (10) ◽  
pp. 1144-1158 ◽  
Author(s):  
C. Foster ◽  
M. Lester ◽  
J. A. Davies
Keyword(s):  
Solar Cycle ◽  
Statistical Study ◽  
Solar Maximum ◽  
Selection Criterion ◽  
Plasma Temperature ◽  
Threshold Values ◽  
Ion Temperature ◽  
F Region ◽  
Diurnal Distribution ◽  
Velocity Selection

Abstract. A statistical analysis of F-region and topside auroral ion upflow events is presented. The study is based on observations from EISCAT Common Programmes (CP) 1 and 2 made between 1984 and 1996, and Common Programme 7 observations taken between 1990 and 1995. The occurrence frequency of ion upflow events (IUEs) is examined over the altitude range 200 to 500 km, using field-aligned observations from CP-1 and CP-2. The study is extended in altitude with vertical measurements from CP-7. Ion upflow events were identified by consideration of both velocity and flux, with threshold values of 100 m s–1 and 1013 m–2 s–1, respectively. The frequency of occurrence of IUEs is seen to increase with increasing altitude. Further analysis of the field-aligned observations reveals that the number and nature of ion upflow events vary diurnally and with season and solar activity. In particular, the diurnal distribution of upflows is strongly dependent on solar cycle. Furthermore, events identified by the velocity selection criterion dominate at solar minimum, whilst events identified by the upward field-aligned flux criterion dominated at solar maximum. The study also provides a quantitative estimate of the proportion of upflows that are associated with enhanced plasma temperature. Between 50 and 60% of upflows are simultaneous with enhanced ion temperature, and approximately 80% of events are associated with either increased F-region ion or electron temperatures.Key words. Ionosphere (auroral ionosphere; particle acceleration)

scholarly journals Signature of the 27-day solar rotation cycle in mesospheric OH and H<sub>2</sub>O observed by the Aura Microwave Limb Sounder

2011 ◽  
Vol 11 (10) ◽  
pp. 28477-28498 ◽  
Author(s):  
A. V. Shapiro ◽  
E. Rozanov ◽  
A. I. Shapiro ◽  
S. Wang ◽  
T. Egorova ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Solar Irradiance ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Solar Rotation ◽  
Time Lag ◽  
Correlation Coefficients ◽  
Maximum Period ◽  
First Time ◽  
Zero Time

Abstract. The mesospheric hydroxyl radical (OH) is mainly produced by the water vapor (H2O) photolysis and could be considered as a proxy for the influence of the solar irradiance variability on the mesosphere. We analyze the tropical mean response of the mesospheric OH and H2O data as observed by the Aura Microwave Limb Sounder (MLS) to 27-day solar variability. The analysis is performed for two time periods corresponding to the different phases of the 11-yr cycle: from December 2004 to December 2005 ("solar maximum" period with a pronounced 27-day solar cycle) and from November 2008 to November 2009 ("solar minimum" period with a vague 27-day solar cycle). We demonstrate, for the first time, that in the mesosphere the daily time series of OH concentrations correlate well with the solar irradiance (correlation coefficients up to 0.79) at zero time-lag. At the same time H2O anticorrelates (correlation coefficients up to −0.74) with the solar irradiance at non-zero time-lag. We found that the response of OH and H2O to the 27-day variability of the solar irradiance is strong for the solar maximum and negligible for the solar minimum conditions. It allows us to suggest that the 27-day cycle in the solar irradiance and in OH and H2O are physically connected.

scholarly journals Radiative forcing from modelled and observed stratospheric ozone changes due to the 11-year solar cycle

2008 ◽  
Vol 8 (2) ◽  
pp. 4353-4371 ◽  
Author(s):  
I. S. A. Isaksen ◽  
B. Rognerud ◽  
G. Myhre ◽  
J. D. Haigh ◽  
S. T. Rumbold ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Radiative Forcing ◽  
Solar Minimum ◽  
Lower Stratosphere ◽  
Solar Maximum ◽  
Stratospheric Ozone ◽  
Satellite Observation ◽  
Model Studies ◽  
Northern Latitudes ◽  
Significant Disagreement

Abstract. Three analyses of satellite observations and two sets of model studies are used to estimate changes in the stratospheric ozone distribution from solar minimum to solar maximum and are presented for three different latitudinal bands: Poleward of 30° north, between 30° north and 30° south and poleward of 30° south. In the model studies the solar cycle impact is limited to changes in UV fluxes. There is a general agreement between satellite observation and model studies, particular at middle and high northern latitudes. Ozone increases at solar maximum with peak values around 40 km. The profiles are used to calculate the radiative forcing (RF) from solar minimum to solar maximum. The ozone RF, calculated with two different radiative transfer schemes is found to be negligible (a magnitude of 0.01 Wm−2 or less), compared to the direct RF due to changes in solar irradiance, since contributions from the longwave and shortwave nearly cancel each other. The largest uncertainties in the estimates come from the lower stratosphere, where there is significant disagreement between the different ozone profiles.

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)

scholarly journals foF2 Seasonal Asymmetry Diurnal Variation Study during Very Quiet Geomagnetic Activity at Dakar Station

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Sibri Alphonse Sandwidi ◽  
Doua Allain Gnabahou ◽  
Frédéric Ouattara
Keyword(s):  
Solar Cycle ◽  
Solar Radiation ◽  
Diurnal Variation ◽  
Geomagnetic Activity ◽  
Vertical Velocity ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Solar Cycles ◽  
Maximum Phase ◽  
Vertical Drift

This paper aims to study the foF2 seasonal asymmetry diurnal variation at Dakar station from 1976 to 1995. We show that equinoctial asymmetry is less pronounced and somewhere is absent throughout 21 and 22 solar cycles. The absence of equinoctial asymmetry may be due to Russell-McPherron mechanism and the vertical drift E × B . The solstice anomaly or annual anomaly is always observed throughout both 21 and 22 solar cycles as measured at Dakar ionosonde. The maximum negative value of σfoF2, fairly equal to -65%, is observed during the decreasing phase at solstice time; this value appeared usually at 0200 LT except during the maximum phase during which it is observed at 2300 LT. The maximum positive value, fairly equal to +94%, is observed at 0600 LT during solar minimum at solstice time. This annual asymmetry may be due to neutral composition asymmetric variation and solar radiation annual asymmetry with the solstice time. The semiannual asymmetry is also observed during all solar cycle phases. The maximum positive value (+73%) is observed at 2300 LT during solar maximum, and its maximum negative (-12%) is observed during the increasing phase. We established, as the case of annual asymmetry, that this asymmetry could not be explained by the asymmetry in vertical velocity E × B phenomenon but by the axial mechanism, the “thermospheric spoon” mechanism, and the seasonally varying eddy mixing phenomenon.

scholarly journals Solar cycle dependent characteristics of the equatorial blanketing E<sub><i>s</i></sub> layers and associated irregularities

2006 ◽  
Vol 24 (11) ◽  
pp. 2931-2947 ◽  
Author(s):  
C. V. Devasia ◽  
V. Sreeja ◽  
S. Ravindran
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Electric Field ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Dominant Role ◽  
Onset Time ◽  
Vhf Radar ◽  
Cycle Dependent ◽  
June July

Abstract. The occurrence of blanketing type Es (Esb) layers and associated E-region irregularities over the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip ~0.5°) during the summer solstitial months of May, June, July and August has been investigated in detail for the period 1986–2000 to bring out the variabilities in their characteristics with the solar cycle changes. The study has been made using the ionosonde and magnetometer data of Trivandrum from 1986–2000 along with the available data from the 54.95 MHz VHF backscatter radar at Trivandrum for the period 1995–2000. The appearance of blanketing Es layers during these months is observed to be mostly in association with the occurrence of afternoon Counter Electrojet (CEJ) events. The physical process leading to the occurrence of a CEJ event is mainly controlled by the nature of the prevailing electro dynamical/neutral dynamical conditions before the event. Hence it is natural that the Esb layer characteristics like the frequency of occurrence, onset time, intensity, nature of gradients in its top and bottom sides etc are also affected by the nature of the background electro dynamical /neutral dynamical processes which in turn are strongly controlled by the solar activity changes. The occurrence of Esb layers during the solstitial months is found to show very strong solar activity dependence with the occurrence frequency being very large during the solar minimum years and very low during solar maximum years. The intensity of the VHF radar backscattered signals from the Esb irregularities is observed to be controlled by the relative roles of the direction and magnitude of the prevailing vertical polarization electric field and the vertical electron density gradient of the prevailing Esb layer depending on the phase of the solar cycle. The gradient of the Esb layer shows a more dominant role in the generation of gradient instabilities during solar minimum periods while it is the electric field that has a more dominant role during solar maximum periods.

Sign in / Sign up

Export Citation Format

Share Document