scholarly journals A statistical study of the geoeffectiveness of magnetic clouds during high solar activity years

2004 ◽  
Vol 109 (A9) ◽  
Author(s):  
Jichun Zhang
Keyword(s):  
Solar Activity ◽  
Statistical Study ◽  
Magnetic Clouds ◽  
High Solar Activity

scholarly journals Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

2009 ◽  
Vol 27 (4) ◽  
pp. 1363-1375 ◽  
Author(s):  
A. V. Pavlov ◽  
N. M. Pavlova
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Conditional Probability ◽  
Statistical Study ◽  
Expected Value ◽  
Diurnal Variations ◽  
High Solar Activity ◽  
Winter Anomaly ◽  
Anomalous Feature ◽  
The Mean

Abstract. We present a statistical study of variations in the F2-layer peak electron density, NmF2, and altitude, hmF2, over the Argentine Islands ionosonde. The critical frequencies, foF2, and, foE, of the F2 and E-layers, and the propagation factor, M(3000)F2, measured by the ionosonde during the 1957–1959 and 1962–1995 time periods were used in the statistical analysis to determine the values of NmF2 and hmF2. The probabilities to observe maximum and minimum values of NmF2 and hmF2 in a diurnal variation of the electron density are calculated. Our study shows that the main part of the maximum diurnal values of NmF2 is observed in a time sector close to midnight in November, December, January, and February exhibiting the anomalous diurnal variations of NmF2. Another anomalous feature of the diurnal variations of NmF2 exhibited during November, December, and January when the minimum diurnal value of NmF2 is mainly located close to the noon sector. These anomalous diurnal variations of NmF2 are found to be during both geomagnetically quiet and disturbed conditions. Anomalous features are not found in the diurnal variations of hmF2. The statistical study of the NmF2 winter anomaly phenomena over the Argentine Islands ionosonde was carried out. The variations in a maximum daytime value, R, of a ratio of a geomagnetically quiet daytime winter NmF2 to a geomagnetically quiet daytime summer NmF2 taken at a given UT and for approximately the same level of solar activity were studied. The conditional probability of the occurrence of R in an interval of R, the most frequent value of R, the mean expected value of R, and the conditional probability to observe the F2-region winter anomaly during a daytime period were calculated for low, moderate, and high solar activity. The calculations show that the mean expected value of R and the occurrence frequency of the F2-region winter anomaly increase with increasing solar activity.

MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

2021 ◽  
Vol 44 ◽  
pp. 85-91
Author(s):  
V.N. Obridko ◽  
◽  
D.D. Sokoloff ◽  
V.V. Pipin ◽  
A.S. Shibalova ◽  
...  
Keyword(s):  
Solar Activity ◽  
Activity Cycle ◽  
Solar Interior ◽  
Local Fields ◽  
Lower Atmosphere ◽  
High Solar Activity ◽  
Dynamo Model ◽  
Sunspot Activity ◽  
Geomagnetic Variations ◽  
Near Surface

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

scholarly journals A Neural Network-Based TEC Model Capable of Reproducing Nighttime Winter Anomaly

2021 ◽  
Vol 13 (22) ◽  
pp. 4559
Author(s):  
Marjolijn Adolfs ◽  
Mohammed Mainul Hoque
Keyword(s):  
Neural Network ◽  
Solar Activity ◽  
Geomagnetic Latitude ◽  
Machine Learning Techniques ◽  
High Solar Activity ◽  
Electron Content ◽  
Solar Cycles ◽  
Total Electron ◽  
The Neural Network ◽  
Winter Anomaly

With the availability of fast computing machines, as well as the advancement of machine learning techniques and Big Data algorithms, the development of a more sophisticated total electron content (TEC) model featuring the Nighttime Winter Anomaly (NWA) and other effects is possible and is presented here. The NWA is visible in the Northern Hemisphere for the American sector and in the Southern Hemisphere for the Asian longitude sector under solar minimum conditions. During the NWA, the mean ionization level is found to be higher in the winter nights compared to the summer nights. The approach proposed here is a fully connected neural network (NN) model trained with Global Ionosphere Maps (GIMs) data from the last two solar cycles. The day of year, universal time, geographic longitude, geomagnetic latitude, solar zenith angle, and solar activity proxy, F10.7, were used as the input parameters for the model. The model was tested with independent TEC datasets from the years 2015 and 2020, representing high solar activity (HSA) and low solar activity (LSA) conditions. Our investigation shows that the root mean squared (RMS) deviations are in the order of 6 and 2.5 TEC units during HSA and LSA period, respectively. Additionally, NN model results were compared with another model, the Neustrelitz TEC Model (NTCM). We found that the neural network model outperformed the NTCM by approximately 1 TEC unit. More importantly, the NN model can reproduce the evolution of the NWA effect during low solar activity, whereas the NTCM model cannot reproduce such effect in the TEC variation.

scholarly journals Characterization of ionospheric irregularities over Vietnam and adjacent region for the 2008-2018 period

2021 ◽  
Author(s):  
Dung Nguyen Thanh ◽  
Minh Le Huy ◽  
Christine Amory-Mazaudier ◽  
Rolland Fleury ◽  
Susumu Saito ◽  
...  
Keyword(s):  
Solar Activity ◽  
Correlation Coefficients ◽  
Rate Of Change ◽  
Occurrence Rate ◽  
High Solar Activity ◽  
Electron Content ◽  
Total Electron ◽  
Plasma Irregularities ◽  
Almost All ◽  
Continuous Gps

This paper presents the variations of the rate of change of Total Electron Content (TEC) index (ROTI), characterizing the occurrence of ionospheric plasma irregularities over Vietnam and neighboring countries in the Southeast Asian region using the continuous GPS data during the 2008-2018 period. The results showed that the occurrence of strong ROTI in all stations is maximum in equinox months March/April and September/October and depends on solar activity. The ROTI is weak during periods of low solar activity and strong during periods of high solar activity. There is an asymmetry between the two equinoxes. During maximum and declining phases of 2014-2016, occurrence rates in March equinox are larger than in September equinox, but during the descending period of 2010-2011, the occurrence rates in September equinox at almost all stations are larger than in March equinox. The correlation coefficients between the monthly occurrence rate of irregularities and the F10.7 solar index at the stations in the equatorward EIA crest region are higher than at those in the magnetic equatorial and the poleward EIA crest regions. The irregularity occurrence is high in the pre-midnight sector, maximum between 2000 LT to 2200 LT. The maximum irregularity occurrence is located around 4-5° degrees in latitude equator-ward away from the anomaly crests.

scholarly journals New possibilities of the PCA-Seq method in the analysis of time series (on the example of solar activity)

2021 ◽  
Vol 2099 (1) ◽  
pp. 012034
Author(s):  
V M Efimov ◽  
K V Efimov ◽  
D A Polunin ◽  
V Y Kovaleva
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Maunder Minimum ◽  
High Solar Activity ◽  
External Influence ◽  
Average Period ◽  
Time Axis ◽  
Constant Amplitude ◽  
The Impact ◽  
Analysis Of Time Series

Abstract When analyzing a 1D time series, it is traditional to represent it as the sum of the trend, cyclical components and noise. The trend is seen as an external influence. However, the impact can be not only additive, but also multiplicative. In this case, not only the level changes, but also the amplitude of the cyclic components. In the PCA-Seq method, a generalization of SSA, it is possible to pre-standardize fragments of a time series to solve this problem. The algorithm is applied to the Anderson series – a sign alternating version of the well-known Wolf series, reflecting the 22-year Hale cycle. The existence of this cycle is not disputed at high solar activity, but there are doubts about the constancy of its period at this time, as well as its existence during the epoch of low solar activity. The processing of the series by the PCA-Seq method revealed clear oscillations fluctuations of almost constant amplitude with an average period of 21.9 years, and it was found that the correlation of these oscillations with the time axis for 300 years does not differ significantly from zero. This confirms the hypothesis of the existence of 22-year oscillations in solar activity even at its minima, like the Maunder minimum.

M(3000)F2 and IRI-2012 model at an equatorial latitude in the African sector

2021 ◽  
Vol 16 (3) ◽  
pp. 49-54
Author(s):  
A.O. Olawepo ◽  
J.O. Adeniyi ◽  
A. Afolabi
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Correlation Coefficient ◽  
High Solar Activity ◽  
Equatorial Latitude ◽  
Magnetic Declination ◽  
Two Peaks

We have used ionosonde data from Ouagadougou (Geo. Lat.12.40 N, Long. 358.50, Magnetic declination -5.1320) to study the morphology of M(3000)F2 and to investigate the performance of IRI-12 during 1991 and 1995, years of high and low solar activities respectively. Results show that M(3000)F2 exhibits diurnal and solar cycle characteristics with no distinctive monthly/seasonal features. The two peaks which characterize the diurnal M(3000)F2 during high solar activity (HSA) are reduced to just one (the sunrise peak) during low solar activity (LSA). The study also shows that IRI-12 gives good representations of the observed values of M(3000)F2 with high correlation coefficient, R ranging between 0.9 and 0.95 during LSA and 0.94 and 0.99 during HSA. The model gives its best performance in the months of April irrespective of the solar activity. It either under-estimates or over-estimates the observed values of M(3000)F2 during other months.

Observational evidence of solar activity interaction with chlorine chemistry curbing Antarctic ozone loss

2021 ◽  
Author(s):  
Annika Seppälä ◽  
Emily Gordon ◽  
Bernd Funke ◽  
Johanna Tamminen ◽  
Kaley Walker
Keyword(s):  
Solar Activity ◽  
Observational Evidence ◽  
High Solar Activity ◽  
Quasi Biennial Oscillation ◽  
Ozone Loss ◽  
Reservoir Species ◽  
Antarctic Ozone ◽  
Catalytic Ozone Destruction ◽  
The Antarctic ◽  
The Impact

&lt;p&gt;We present the impact of the so-called energetic particle precipitation (EPP), part of natural solar forcing on the atmosphere, on polar stratospheric NO&lt;sub&gt;x&lt;/sub&gt;, ozone, and chlorine chemistry in the Antarctic springtime, using multi-satellite observations covering the overall period of 2005&amp;#8211;2017. We find consistent ozone increases when high solar activity occurs during years with easterly phase of the quasi biennial oscillation. These ozone enhancements are also present in total O&lt;sub&gt;3&lt;/sub&gt; column observations. We find consistent decreases in springtime active chlorine following winters of elevated solar activity. Further analysis shows that this is accompanied by increase of chemically inactive chlorine reservoir species, explaining the observed ozone increase. This provides the first observational evidence supporting the previously proposed mechanism relating to EPP modulating chlorine driven ozone loss. Our findings suggest that solar activity via EPP has played an important role in modulating Antarctic ozone depletion in the last 15 years. As chlorine loading in the polar stratosphere continues to decrease in the future, this buffering mechanism will become less effective and catalytic ozone destruction by EPP produced NO&lt;sub&gt;x&lt;/sub&gt; will likely become a major contributor to Antarctic ozone loss.&lt;/p&gt;

scholarly journals Comparison of IRI-2016 model with IGS VTEC maps during low and high solar activity period

2019 ◽  
Vol 12 ◽  
pp. 555-561 ◽  
Author(s):  
Chuang Shi ◽  
Tao Zhang ◽  
Cheng Wang ◽  
Zhipeng Wang ◽  
Lei Fan
Keyword(s):  
Solar Activity ◽  
Activity Period ◽  
High Solar Activity ◽  
Solar Activity Period
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