A Statistical Analysis of Radar Blackouts at Mars: MARSIS, SHARAD and MAVEN Observations

We present an analysis of radar blackouts observed by MARSIS on Mars Express and SHARAD on Mars Reconnaissance Orbiter for the interval 2006 &#8211; 2017.&#160; The period of interest encompasses the extended solar minimum between solar cycles 23 and 24 as well as the solar maximum of cycle 24.&#160; Blackouts have been identified by eye through scanning daily plots of the surface reflection for both radars.&#160; A blackout occurs when, for no apparent instrumental reason, the surface reflection normally expected is either not observed (total) or when the surface reflection is seen for only part of the orbit or the surface reflection is both weaker and spread over a significant time delay (partial).&#160; Such blackouts are caused by enhanced ionisation at altitudes below the main ionospheric electron density peak resulting in increased absorption of the radar signal.&#160; There are more occurrences observed by MARSIS than SHARAD, which is expected due to the lower absorption at the higher operating frequency of SHARAD.&#160; We also observe more blackouts during solar maximum than solar minimum.&#160; Indeed, there are no total blackouts during the extended solar minimum, although both radars do have partial blackouts.&#160; There is no apparent relationship between blackout occurrence and crustal magnetic fields.&#160; Following previous work, which has indicated that solar energetic particles, specifically electrons are responsible for the enhanced ionisation in the atmosphere, we also present the analysis of the MAVEN SEP electrons between 20 keV and 2 MeV during events when all three spacecraft were operational.&#160; We find that the SEP electron flux-energy relationship is much enhanced during the total blackouts, in particular where both radars are impacted, while for partial blackouts the flux-energy spectrum is closer to those from orbits where no blackout occurs.&#160; We also find that for certain events, the average spectrum which result in a blackout is particularly enhanced at the higher energy end of the spectrum, above 50 keV. The average spectra from each condition is presented.&#160; We conclude that there is a higher probability of a radar blackout during solar maximum, that crustal magnetic fields play no apparent role in the their observational occurrence, that the higher energy (< 50 keV) electrons are responsible, and that for events where both radars observe a radar blackout the SEP electron fluxes are at their highest.

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Energetic particles and radar blackouts at Mars

10.5194/egusphere-egu21-11997 ◽

2021 ◽

Author(s):

Mark Lester ◽

Beatriz Sanchez-Cano ◽

Daniel Potts ◽

Rob Lillis ◽

Marco Cartacci ◽

...

Keyword(s):

Lower Ionosphere ◽

Solar Energetic Particle ◽

Lower Atmosphere ◽

Radar Signal ◽

Density Peak ◽

Surface Reflection ◽

Average Spectrum ◽

Apparent Relationship ◽

Radar Echo ◽

Human Exploration

We present the first long-term characterization of the lower ionosphere of Mars, a region previously inaccessible to orbital observations, based on an analysis of radar echo blackouts observed by MARSIS on Mars Express and SHARAD on the Mars Reconnaissance Orbiter from 2006 to 2017.&#160; A blackout occurs when the expected surface reflection is partly to fully attenuated for portions of an observation.&#160; Enhanced ionization at altitudes of 60 to 90 km, below the main ionospheric electron density peak, results in the absorption of the radar signal, leading to a radar blackout.&#160; MARSIS, operating at frequencies between 1.8 and 5 MHz suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz).&#160; More events are seen during solar maximum while&#160; there is no apparent relationship between blackout occurrence and crustal magnetic fields. Blackouts do occur during both nightside and dayside observations, and have an interesting variation with solar zenith angle.&#160; &#160;Analysis of MAVEN Solar Energetic Particle (SEP) electron counts between 20 and 200 keV during selected events demonstrates that these electrons are responsible for such events, and we investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce &#160;measurable attenuation.&#160; When both radars observe a radar blackout at the same time, the SEP electron fluxes are at their highest. For certain events, we find that the average spectrum responsible for a blackout is particularly enhanced at the higher energy end of the spectrum, i.e. above 70 keV .&#160; &#160;This study is, therefore, important for future communications for human exploration of Mars.

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

International Journal of Geophysics ◽

10.1155/2020/8896188 ◽

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.

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Dependence of solar cycles duration on the magnitude of the annual module of the sunspots magnetic field

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002251 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 71-72 ◽

Cited By ~ 2

Author(s):

Valery N. Krivodubskij ◽

Natalia I. Lozitska

Keyword(s):

Solar Cycle ◽

Magnetic Fields ◽

Large Scale ◽

Solar Maximum ◽

Dynamo Model ◽

Cycle Duration ◽

Solar Cycles ◽

Decline Phase ◽

Calculated Period ◽

Magnetic Index

AbstractThe dependence of the solar cycle duration, T, on the 3 years averaged module of the large-scale sunspots magnetic fields (30-60 arcsec), Bsp index, was investigated on the base of about 10,000 visual observations conducted during last eight (16-23) cycles. It was found that the duration T of the investigated cycles linearly depends on the index Bsp of the magnetic fields observed during 3 years on decline phase of the solar cycle (second, third and fourth years after solar maximum Tmax). Namely, the duration of the cycles T was varied between 9,5 and 12,5 years, when the magnetic index Bsp was ranged from 2450 to 2600 G. An explanation for this dependence is proposed within the framework of non-linear αΩ- dynamo model. We found the following equation for the dependence of solar dynamo-period on magnetic index: T ≈ Bsp3/2. Therefore, the large observed index Bsp, the longer calculated period T.

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Extreme Space-Weather Events and the Solar Cycle

Solar Physics ◽

10.1007/s11207-021-01831-3 ◽

2021 ◽

Vol 296 (5) ◽

Author(s):

Mathew J. Owens ◽

Mike Lockwood ◽

Luke A. Barnard ◽

Chris J. Scott ◽

Carl Haines ◽

...

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Space Weather ◽

Extreme Events ◽

Solar Minimum ◽

Geomagnetic Storms ◽

Extreme Event ◽

Solar Maximum ◽

Solar Cycles ◽

Event Occurrence

AbstractSpace weather has long been known to approximately follow the solar cycle, with geomagnetic storms occurring more frequently at solar maximum than solar minimum. There is much debate, however, about whether the most hazardous events follow the same pattern. Extreme events – by definition – occur infrequently, and thus establishing their occurrence behaviour is difficult even with very long space-weather records. Here we use the 150-year $aa_{H}$ a a H record of global geomagnetic activity with a number of probabilistic models of geomagnetic-storm occurrence to test a range of hypotheses. We find that storms of all magnitudes occur more frequently during an active phase, centred on solar maximum, than during the quiet phase around solar minimum. We also show that the available observations are consistent with the most extreme events occurring more frequently during large solar cycles than small cycles. Finally, we report on the difference in extreme-event occurrence during odd- and even-numbered solar cycles, with events clustering earlier in even cycles and later in odd cycles. Despite the relatively few events available for study, we demonstrate that this is inconsistent with random occurrence. We interpret this finding in terms of the overlying coronal magnetic field and enhanced magnetic-field strengths in the heliosphere, which act to increase the geoeffectiveness of sheath regions ahead of extreme coronal mass ejections. Putting the three “rules” together allows the probability of extreme event occurrence for Solar Cycle 25 to be estimated, if the magnitude and length of the coming cycle can be predicted. This highlights both the feasibility and importance of solar-cycle prediction for planning and scheduling of activities and systems that are affected by extreme space weather.

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Spectral analysis of auroral geomagnetic activity during various solar cycles between 1960 and 2014

Annales Geophysicae ◽

10.5194/angeo-34-1159-2016 ◽

2016 ◽

Vol 34 (12) ◽

pp. 1159-1164 ◽

Cited By ~ 2

Author(s):

Pieter Benjamin Kotzé

Keyword(s):

Spectral Analysis ◽

Geomagnetic Activity ◽

Solar Minimum ◽

High Speed ◽

Solar Rotation ◽

Pearson Correlation ◽

Coronal Holes ◽

Rotation Period ◽

Period Change ◽

Solar Cycles

Abstract. In this paper we use wavelets and Lomb–Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE (auroral electrojet) index during various phases of different solar cycles between 1960 and 2014. Previous investigations have revealed that the solar minimum of cycles 23–24 exhibited strong 13.5- and 9.0-day recurrence in geomagnetic data in comparison to the usual dominant 27.0-day synodic solar rotation period. Daily mean AE indices are utilized to show how several harmonics of the 27-day recurrent period change during every solar cycle subject to a 95 % confidence rule by performing a wavelet analysis of each individual year's AE indices. Results show that particularly during the solar minimum of 23–24 during 2008 the 27-day period is no longer detectable above the 95 % confidence level. During this interval geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics. A Pearson correlation analysis between AE and various spherical harmonic coefficients describing the solar magnetic field during each Carrington rotation period confirms that the solar dynamo has been dominated by an unusual combination of sectorial harmonic structure during 23–24, which can be responsible for the observed anomalously low solar activity. These findings clearly show that, during the unusual low-activity interval of 2008, auroral geomagnetic activity was predominantly driven by high-speed solar wind streams originating from multiple low-latitude coronal holes distributed at regular solar longitude intervals.

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The effect of the stratospheric QBO on the neutral density of the D region

Annals of Geophysics ◽

10.4401/ag-6491 ◽

2015 ◽

Vol 58 (3) ◽

Author(s):

Selçuk Sağır ◽

Ramazan Atıcı ◽

Osman Özcan ◽

Nurullah Yüksel

Keyword(s):

Statistical Analysis ◽

Solar Maximum ◽

Unit Root Test ◽

Multiple Regression Model ◽

Neutral Density ◽

Solar Cycles ◽

Ion Chemistry ◽

Integration Test ◽

D Region ◽

The Relationship

A multiple regression model, which defines relationship between two variables, is used to perform a statistical analysis of the relationship between the stratospheric QBO and the neutral density of the D region (NnD) at altitudes of 75 km and 90 km for Singapore station. While performing the analysis, the solar maxima and solar minima epochs of the sun for 21st, 22nd and 23rd solar cycles (SCs) are taken into account. Before applying the model for the statistical analysis of the relationship, the stationary of the variables is investigated by using the unit root test. The relationship between the variables is also investigated by using the co-integration test. The relationship between NnD measured at 75 km altitude and QBO obtained at altitude of 10 hPa is observed that it is positive for solar maximum epoch at 21st and 23rd SCs and for solar minimum epoch at 21st SC and is negative at the other epochs. The relationship between NnD measured at 90 km altitude and QBO is observed to be negative at both the solar maxima expect for solar maximum of 23rd SC and the solar minima epochs. The relationship between variables is positive for both phases (east and west) of QBO. Thus, QBO leads to a statistical change in the NnD. It may also give rise to changes on the ion chemistry of the D region.

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Elevation angles and attenuation of gravity waves in the ionosphere

10.5194/egusphere-egu21-866 ◽

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

&#160;&#160;&#160;&#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&#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.&#160;&#160;&#160;&#160;&#160;&#160;&#160; The results show that the distribution of elevation angles of wave vectors in the wind&#8211;rest frame is significantly narrower than in the Earth frame (observed elevations). Possible differences were also found between the wind&#8211;rest frame elevation angles obtained for the solar maximum (mean value (around -24&#176;) and solar minimum (mean value round -37&#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&#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.&#160;&#160;&#160;&#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.&#160;&#160;

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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

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-6991-2020 ◽

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.

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Investigating the foF2 variations at the Ionospheric Observatory of Rome during different solar cycles minimums and levels of geomagnetic activity

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2020054 ◽

2020 ◽

Vol 10 ◽

pp. 52

Author(s):

Alessandro Ippolito ◽

Loredana Perrone ◽

Christina Plainaki ◽

Claudio Cesaroni

Keyword(s):

Geomagnetic Activity ◽

Solar Minimum ◽

Critical Frequency ◽

Background Level ◽

Solar Cycles ◽

Physical Processes ◽

Minimum Duration ◽

Critical Frequency Fof2 ◽

Definition Of ◽

Low Activity

The variations of the hourly observations of the critical frequency foF2, recorded at the Ionospheric Observatory of Rome by the AIS-INGV ionosonde (geographic coordinates 41.82° N, 12.51° E; geomagnetic coordinates 41.69° N, 93.97° E) during the low activity periods at the turn of solar cycles 21–22, 22–23 and 23–24, are investigated. Deviations of foF2 greater than ± 15% with respect to a background level, and with a minimum duration of 3 h, are here considered anomalous. The dependence of these foF2 anomalies on geomagnetic activity has been accurately investigated. Particular attention has been paid to the last deep solar minimum 2007–2009, in comparison with the previous solar cycle minima. The lack of day-time anomalous negative variations in the critical frequency of the F2 layer, is one of the main findings of this work. Moreover, the analysis of the observed foF2 anomalies confirms the existence of two types of positive F2 layer disturbances, characterised by different morphologies and, different underlying physical processes. A detailed analysis of four specific cases allows the definition of possible scenarios for the explanation of the mechanisms behind the generation of the foF2 anomalies.

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

10.5194/acp-2018-799 ◽

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.

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