scholarly journals Role of eddy diffusion in the delayed ionospheric response to solar flux changes

2021 ◽  
Vol 39 (4) ◽  
pp. 641-655
Author(s):  
Rajesh Vaishnav ◽  
Christoph Jacobi ◽  
Jens Berdermann ◽  
Mihail Codrescu ◽  
Erik Schmölter
Keyword(s):  
Solar Activity ◽  
Extreme Ultraviolet ◽  
Solar Rotation ◽  
Eddy Diffusion ◽  
Transport Processes ◽  
Solar Flux ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Total Electron ◽  
Ionospheric Response

Abstract. Simulations of the ionospheric response to solar flux changes driven by the 27 d solar rotation have been performed using the global 3-D Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) physics-based numerical model. Using the F10.7 index as a proxy for solar extreme ultraviolet (EUV) variations in the model, the ionospheric delay at the solar rotation period is well reproduced and amounts to about 1 d, which is consistent with satellite and in situ measurements. From mechanistic CTIPe studies with reduced and increased eddy diffusion, we conclude that the eddy diffusion is an important factor that influences the delay of the ionospheric total electron content (TEC). We observed that the peak response time of the atomic oxygen to molecular nitrogen ratio to the solar EUV flux changes quickly during the increased eddy diffusion compared with weaker eddy diffusion. These results suggest that an increase in the eddy diffusion leads to faster transport processes and an increased loss rate, resulting in a decrease in the ionospheric time delay. Furthermore, we found that an increase in solar activity leads to an enhanced ionospheric delay. At low latitudes, the influence of solar activity is stronger because EUV radiation drives ionization processes that lead to compositional changes. Therefore, the combined effect of eddy diffusion and solar activity leads to a longer delay in the low-latitude and midlatitude region.

scholarly journals Role of Eddy Diffusion in the Delayed Ionospheric Response to Solar Flux Changes

2021 ◽  
Author(s):  
Rajesh Vaishnav ◽  
Christoph Jacobi ◽  
Jens Berdermann ◽  
Mihail Codrescu ◽  
Erik Schmölter
Keyword(s):  
Solar Activity ◽  
Solar Rotation ◽  
Rotation Period ◽  
Eddy Diffusion ◽  
Transport Processes ◽  
Solar Flux ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Total Electron ◽  
Ionospheric Response

Abstract. Simulations of the ionospheric response to solar flux changes driven by the twenty-seven days solar rotation have been performed using the global 3-D Coupled Thermosphere/Ionosphere Plasmasphere electrodynamics (CTIPe) physics- based numerical model. Using the F10.7 index as a proxy for solar EUV variations in the model, the ionospheric delay at the solar rotation period is well reproduced and amounts to about 1 day, which is consistent with satellite and in-situ measurements. From mechanistic CTIPe studies with reduced and increased eddy diffusion, we conclude that the eddy diffusion is a primary factor that influences the delay of the ionospheric total electron content (TEC). We observed the peak response time of atomic oxygen to the molecular nitrogen ratio to solar EUV flux changes quickly during the increased eddy diffusion compared with weaker eddy diffusion. These results suggest that an increase in the eddy diffusion leads to faster transport processes and an increased loss rates resulting in a decrease of the ionospheric time delay. Furthermore, we found that an increase in solar activity leads to an enhanced ionospheric delay. At low latitudes, the influence of solar activity is stronger, as EUV radiation drives ionization processes that lead to composition changes. Hence, the combined effect of eddy diffusion and solar activity lead to longer delay in the low and mid latitude region.

scholarly journals Ionospheric response to solar EUV variations: Preliminary results

2018 ◽  
Vol 16 ◽  
pp. 157-165 ◽  
Author(s):  
Rajesh Vaishnav ◽  
Christoph Jacobi ◽  
Jens Berdermann ◽  
Erik Schmölter ◽  
Mihail Codrescu
Keyword(s):  
Extreme Ultraviolet ◽  
Solar Rotation ◽  
Rotation Period ◽  
Transport Processes ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Delay Model ◽  
Total Electron ◽  
Ionospheric Response ◽  
Preliminary Results

Abstract. We investigate the ionospheric response to solar Extreme Ultraviolet (EUV) variations using different proxies, based on solar EUV spectra observed from the Solar Extreme Ultraviolet Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, the F10.7 index (solar irradiance at 10.7 cm), and the Bremen composite Mg-II index during January 2003 to December 2016. The daily mean solar proxies are compared with global mean Total Electron Content (GTEC) values calculated from global IGS TEC maps. The preliminary analysis shows a significant correlation between GTEC and both the integrated flux from SEE and the Mg II index, while F10.7 correlates less strongly with GTEC. The correlations of EUV proxies and GTEC at different time periods are presented. An ionospheric delay in GTEC is observed at the 27 days solar rotation period with the time scale of about ∼1–2 days. An experiment with the physics based global 3-D Coupled Thermosphere/Ionosphere Plasmasphere electrodynamics (CTIPe) numerical model was performed to reproduce the ionospheric delay. Model simulations were performed for different values of the F10.7 index while keeping all the other model inputs constant. Preliminary results qualitatively reproduce the observed ∼1–2 days delay in GTEC, which is might be due to vertical transport processes.

scholarly journals Long-term trends in the ionospheric response to solar EUV variations

2019 ◽  
Author(s):  
Rajesh Vaishnav ◽  
Christoph Jacobi ◽  
Jens Berdermann
Keyword(s):  
Solar Activity ◽  
Time Delay ◽  
Variance Estimation ◽  
Solar Rotation ◽  
Estimation Method ◽  
Electron Content ◽  
Eof Analysis ◽  
Total Electron ◽  
Ionospheric Response ◽  
Wavelet Variance

Abstract. The thermosphere-ionosphere system shows high complexity due to interaction with the continuously varying solar radiation flux. We investigate the ionospheric response to the temporal and spatial dynamics of the solar activity using 18 years (1999–2017) of total electron content (TEC) maps provided by the international GNSS service (IGS) and twelve solar proxies (F10.7, F1.8, F3.2, F8, F15, F30, He-II, MG-II index, Ly-α, Ca K, DSA and SSN). Cross-wavelet and Lomb Scargle periodogram (LSP) analysis are used to evaluate the different solar proxies in respect to their impact on the global mean TEC (GTEC), which is important for improved ionosphere modelling and forecasts. A 16–32 days period in all the solar proxies and GTEC has been identified. The maximum correlation at this time scale is observed between the He-II, Mg-II, and F30 with respect to GTEC, with an effective time delay of about one day. LSP analysis shows that the most dominant period is 27 days, which is based on mean solar rotation, followed by a 44-day periodicity. In addition, a semi-annual and an annual variation has been observed in GTEC, with the strongest correlation near the equator region where a time delay about 1–2 days exists. The wavelet variance estimation method is used to find the variance in the maximum of the solar cycles (SC) 23 (2000–2002) and 24 (2012–2014), for GTEC and F10.7 index, respectively. Wavelet variance estimation suggests that GTEC variance is highest for the seasonal timescale followed by the 16–32 days period, similar to the F10.7 index highest variance for the 16–32 days period. Variance during SC 23 is larger than during SC 24. The most suitable proxy to represent the solar activity at the time scales of 16–32 days and 32–64 days is He-II. The MG-II index, Ly-α, and F30 may be placed at the second as these indices show the strongest correlation with GTEC, but there are some differences between solar maximum and minimum. The F1.8 and DSA are of limited use to represent the solar impact on GTEC. Empirical orthogonal function (EOF) analysis of the TEC data shows that the first EOF components capture more than 86 % of the variance, and the first three EOF components explain 99 % of the total variance. EOF analysis suggests that the first component is associated with the solar flux.

scholarly journals Spatial and seasonal effects on the delayed ionospheric response to solar EUV changes

2020 ◽  
Vol 38 (1) ◽  
pp. 149-162
Author(s):  
Erik Schmölter ◽  
Jens Berdermann ◽  
Norbert Jakowski ◽  
Christoph Jacobi
Keyword(s):  
Geomagnetic Activity ◽  
Extreme Ultraviolet ◽  
Ionospheric Delay ◽  
Seasonal Effects ◽  
Electron Content ◽  
Average Delay ◽  
Total Electron ◽  
Ionospheric Response ◽  
The Impact ◽  
Northern And Southern Hemispheres

Abstract. This study correlates different ionospheric parameters with the integrated solar extreme ultraviolet radiation (EUV) radiation to analyze the delayed ionospheric response, testing and improving upon previous studies on the ionospheric delay. Several time series of correlation coefficients and delays are presented to characterize the trend of the ionospheric delay from January 2011 to December 2013. The impact of the diurnal variations of ionospheric parameters in the analysis at an hourly resolution for fixed locations are discussed and specified with calculations in different timescales and with comparison to solar and geomagnetic activity. An average delay for the total electron content (TEC) of ≈18.7 h and for foF2 of ≈18.6 h is calculated at four European stations. The difference between the Northern and Southern hemispheres is analyzed by comparisons with the Australian region. A seasonal variation of the delay between the Northern and Southern hemispheres is calculated for TEC with ≈5±0.7 h and foF2 with ≈8±0.8 h. The latitudinal and longitudinal variability of the delay is analyzed for the European region, and found to be characterized by a decrease in the delay from ≈21.5 h at 30∘ N to ≈19.0 h at 70∘ N for summer months. For winter months, a roughly constant delay of ≈19.5 h is calculated. The results based on solar and ionospheric data at an hourly resolution and the analysis of the delayed ionospheric response to solar EUV show seasonal and latitudinal variations. Results also indicate a relationship of the ionospheric delay with geomagnetic activity and a possible correlation with the 11-year solar cycle in the analyzed time period.

scholarly journals Long-term trends in the ionospheric response to solar extreme-ultraviolet variations

2019 ◽  
Vol 37 (6) ◽  
pp. 1141-1159 ◽  
Author(s):  
Rajesh Vaishnav ◽  
Christoph Jacobi ◽  
Jens Berdermann
Keyword(s):  
Solar Activity ◽  
Time Delay ◽  
Variance Estimation ◽  
Extreme Ultraviolet ◽  
Solar Rotation ◽  
Estimation Method ◽  
Electron Content ◽  
Eof Analysis ◽  
Total Electron ◽  
Wavelet Variance

Abstract. The thermosphere–ionosphere system shows high complexity due to its interaction with the continuously varying solar radiation flux. We investigate the temporal and spatial response of the ionosphere to solar activity using 18 years (1999–2017) of total electron content (TEC) maps provided by the international global navigation satellite systems service and 12 solar proxies (F10.7, F1.8, F3.2, F8, F15, F30, He II, Mg II index, Ly-α, Ca II K, daily sunspot area (SSA), and sunspot number (SSN)). Cross-wavelet and Lomb–Scargle periodogram (LSP) analyses are used to evaluate the different solar proxies with respect to their impact on the global mean TEC (GTEC), which is important for improved ionosphere modeling and forecasts. A 16 to 32 d periodicity in all the solar proxies and GTEC has been identified. The maximum correlation at this timescale is observed between the He II, Mg II, and F30 indices and GTEC, with an effective time delay of about 1 d. The LSP analysis shows that the most dominant period is 27 d, which is owing to the mean solar rotation, followed by a 45 d periodicity. In addition, a semi-annual and an annual variation were observed in GTEC, with the strongest correlation near the equatorial region where a time delay of about 1–2 d exists. The wavelet variance estimation method is used to find the variance of GTEC and F10.7 during the maxima of the solar cycles SC 23 and SC 24. Wavelet variance estimation suggests that the GTEC variance is highest for the seasonal timescale (32 to 64 d period) followed by the 16 to 32 d period, similar to the F10.7 index. The variance during SC 23 is larger than during SC 24. The most suitable proxy to represent solar activity at the timescales of 16 to 32 d and 32 to 64 d is He II. The Mg II index, Ly-α, and F30 may be placed second as these indices show the strongest correlation with GTEC, but there are some differences in correlation during solar maximum and minimum years, as the behavior of proxies is not always the same. The indices F1.8 and daily SSA are of limited use to represent the solar impact on GTEC. The empirical orthogonal function (EOF) analysis of the TEC data shows that the first EOF component captures more than 86 % of the variance, and the first three EOF components explain 99 % of the total variance. EOF analysis suggests that the first component is associated with the solar flux and the third EOF component captures the geomagnetic activity as well as the remaining part of EOF1. The EOF2 captures 11 % of the total variability and demonstrates the hemispheric asymmetry.

scholarly journals Ionospheric response to solar extreme ultraviolet radiation variations: comparison based on CTIPe model simulations and satellite measurements

2021 ◽  
Vol 39 (2) ◽  
pp. 341-355
Author(s):  
Rajesh Vaishnav ◽  
Erik Schmölter ◽  
Christoph Jacobi ◽  
Jens Berdermann ◽  
Mihail Codrescu
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Extreme Ultraviolet ◽  
Electron Content ◽  
Solar Dynamics Observatory ◽  
International Gnss Service ◽  
Average Delay ◽  
Total Electron ◽  
Ionospheric Response ◽  
Flux Model

Abstract. The ionospheric total electron content (TEC) provided by the International GNSS Service (IGS) and the TEC simulated by the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model have been used to investigate the delayed ionospheric response against solar flux and its trend during the years 2011 to 2013. The analysis of the distinct low-latitude and midlatitude TEC response over 15∘ E shows a better correlation of observed TEC and the solar radio flux index F10.7 in the Southern Hemisphere compared to the Northern Hemisphere. Thus, a significant hemispheric asymmetry is observed. The ionospheric delay estimated using model-simulated TEC is in good agreement with the delay estimated for observed TEC against the flux measured by the Solar Dynamics Observatory (SDO) extreme ultraviolet (EUV) Variability Experiment (EVE). The average delay for the observed (modeled) TEC is 17(16) h. The average delay calculated for observed and modeled TEC is 1 and 2 h longer in the Southern Hemisphere compared to the Northern Hemisphere. Furthermore, the observed TEC is compared with the modeled TEC simulated using the SOLAR2000 and EUVAC flux models within CTIPe over northern and southern hemispheric grid points. The analysis suggests that TEC simulated using the SOLAR2000 flux model overestimates the observed TEC, which is not the case when using the EUVAC flux model.

scholarly journals Weak ionization of the global ionosphere in solar cycle 24

2014 ◽  
Vol 32 (7) ◽  
pp. 809-816 ◽  
Author(s):  
Y. Q. Hao ◽  
H. Shi ◽  
Z. Xiao ◽  
D. H. Zhang
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Critical Frequency ◽  
Extreme Ultraviolet ◽  
Maximum Level ◽  
Electron Content ◽  
Total Electron ◽  
Weakly Ionized ◽  
Critical Frequency Fof2 ◽  
Cycle 24

Abstract. Following prolonged and extremely quiet solar activity from 2008 to 2009, the 24th solar cycle started slowly. It has been almost 5 years since then. The measurement of ionospheric critical frequency (foF2) shows the fact that solar activity has been significantly lower in the first half of cycle 24, compared to the average levels of cycles 19 to 23; the data of global average total electron content (TEC) confirm that the global ionosphere around the cycle 24 peak is much more weakly ionized, in contrast to cycle 23. The weak ionization has been more notable since the year 2012, when both the ionosphere and solar activity were expected to be approaching their maximum level. The undersupply of solar extreme ultraviolet (EUV) irradiance somewhat continues after the 2008–2009 minimum, and is considered to be the main cause of the weak ionization. It further implies that the thermosphere and ionosphere in the first solar cycle of this millennium would probably differ from what we have learned from the previous cycles of the space age.

scholarly journals Multifractal analysis of vertical total electron content (VTEC) at equatorial region and low latitude, during low solar activity

2013 ◽  
Vol 31 (1) ◽  
pp. 127-133 ◽  
Author(s):  
M. J. A. Bolzan ◽  
A. Tardelli ◽  
V. G. Pillat ◽  
P. R. Fagundes ◽  
R. R. Rosa
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
Solar Rotation ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
X Rays ◽  
Equilibrium System ◽  
Equatorial Anomaly ◽  
Total Electron ◽  
Small Scales

Abstract. This paper analyses the multifractal aspects of the GPS data (measured during a period of low solar activity) obtained from two Brazilian stations: Belém (01.3° S, 48.3° W) and São José dos Campos (SJC) (23.2° S, 45.9° W). The results show that the respective geographic sites show important scaling differences as well as similarities when their multifractal signatures for vertical total electron content (VTEC) are compared. The f(α) spectra have a narrow shape for great scales, which indicates the predominance of deterministic phenomena, such as solar rotation (27 days) over intermittent phenomena. Furthermore, the f(α) spectra for both sites have a strong multifractality degree at small scales. This strong multifractality degree observed at small scales (1 to 12 h) at both sites is because the ionosphere over Brazil is a non-equilibrium system. The differences found were that Belém presented a stronger multifractality at small scales (1 h to 12 h) compared with SJC, particularly in 2006. The reason for this behaviour may be associated with the location of Belém, near the geomagnetic equator, where at this location the actions of X-rays, ultraviolet, and another wavelength from the Sun are more direct, strong, and constant throughout the whole year. Although the SJC site is near ionospheric equatorial anomaly (IEA) peaks, this interpretation could explain the higher values found for the intermittent parameter μ for Belém compared with SJC. Belém also showed the presence of one or two flattening regions for f(α) spectra at the same scales mentioned before. These differences and similarities also were interpreted in terms of the IEA content, where this phenomenon is an important source of intermittence due the presence of the VTEC peaks at ±20° geomagnetic latitudes.

scholarly journals Delayed response of the global total electron content to solar EUV variations

2016 ◽  
Vol 14 ◽  
pp. 175-180 ◽  
Author(s):  
Christoph Jacobi ◽  
Norbert Jakowski ◽  
Gerhard Schmidtke ◽  
Thomas N. Woods
Keyword(s):  
Total Electron Content ◽  
Time Scales ◽  
Extreme Ultraviolet ◽  
Solar Rotation ◽  
Time Lag ◽  
Delayed Response ◽  
Electron Content ◽  
Solar Dynamics Observatory ◽  
Total Electron ◽  
Tec Variability

Abstract. The ionospheric response to solar extreme ultraviolet (EUV) variability during 2011–2014 is shown by simple proxies based on Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment solar EUV spectra. The daily proxies are compared with global mean total electron content (TEC) computed from global TEC maps derived from Global Navigation Satellite System dual frequency measurements. They describe about 74 % of the intra-seasonal TEC variability. At time scales of the solar rotation up to about 40 days there is a time lag between EUV and TEC variability of about one day, with a tendency to increase for longer time scales.

Ionospheric Variability: Response to Sudden Stratospheric Warming events during Solar Cycle 24

2021 ◽  
Author(s):  
Sumedha Gupta ◽  
Arun Kumar Upadhayaya ◽  
Devendraa Siingh
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Total Electron ◽  
Ionospheric Response ◽  
Solar Cycle 24 ◽  
Cycle 24

<p>With low solar activity and unusual progression, Solar Cycle 24 lasted from December 2008 to December 2019 and is considered to be the weakest cycle in the last 100 years. During such quiet solar background conditions, the wave forcing from lower atmosphere will have a perceivable effect on the ionosphere. This study examines the ionospheric response to meteorological phenomenon of Sudden Stratospheric Warming (SSW) events during Solar Cycle 24 (Arctic winter 2008/09 to 2018/19). Ionospheric response to each of these identified warming periods is quantified by studying ground – based Global Positioning System (GPS) derived vertical Total Electron Content (VTEC) and its deviation from monthly median (ΔVTEC) for four longitudinal chains, selected from worldwide International GNSS service (IGS) stations. Each chain comprises of eight stations, chosen in such a way as to cover varied latitudes both in Northern and Southern Hemispheres. A strong latitude – dependent response of VTEC perturbations is observed after the peak stratospheric temperature anomaly (ΔT<sub>max</sub>). The semidiurnal behaviour of VTEC, with morning increase and afternoon decrease, is mostly observed at near-equatorial stations. This vertical coupling between lower and upper atmosphere during SSW is influenced by prominent 13-14 days periodicities in VTEC observations, along with other periodicities of 7, 5, and 3 days. It is seen that the ionospheric response increases with increase in solar activity. Further, under similar ionizing conditions, quite similar ionospheric response is observed, irrespective of ΔT<sub>max</sub> and type of SSW event being major or minor. However, under similar SSW strength (ΔT<sub>max</sub>), no prominent pattern in ionospheric response is observed. The causative mechanism for the coupling processes in the atmosphere during these SSW events is discussed in detail.</p>

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