Variability of thermosphere and ionosphere responses to solar flares (original) (raw)
Related papers
Ionospheric response to an intense solar flare in equatorial and low latitude region
Indian Journal of Physics, 2018
Multi-instrument data recorded at multi-stations are used to study the equatorial and low-latitude ionospheric response to an intense solar flare of class X7 (2B) in the current solar cycle 24 with the peak at 08:05 UT on 09 August 2011. Rapid changes in ionospheric total electron contents (TEC) measured by global positioning system (GPS) showed an enhancement of 2-3 TECU. The very low frequency (VLF) data recorded at a low latitude station Varanasi showed an enhancement of VLF signal amplitude during the solar flare period which is attributed to the sudden enhancement of D-region ionization. Ground based GPS measurements are also validated by analyzing the electron density profiles measured from COSMIC satellite mission. COSMIC-derived electron density profile shows a decrease below F2 peak altitude and increase above F2 peak. The D-region ionospheric perturbation observed during the solar flare could be caused by flare time enhanced level of photo-ionization due to X-ray flux enhancement, whereas for E and F-region ionosphere, enhanced EUV flux causes photo-ionization and hence perturbed the TEC.
2007
We examined the thermospheric and ionospheric responses to the solar flare on 28 October 2003, utilizing simultaneous observations of the electron and neutral density from the CHAMP satellite. Rapid thermospheric response within a few minutes was observed. In addition, the neutral and plasma perturbations contrasted each other remarkably. First, their temporal development differed. Though started nearly simultaneously, the plasma perturbation developed much faster and to a larger amplitude than its neutral counterpart. Second, their latitudinal distributions differed. At the initial stage of the response, the neutral density was enhanced by 20% almost homogeneously at all latitudes below 50°N/S. In comparison, the plasma disturbance exhibited a distinctive latitudinal structure, with largest density enhancements of 68% at the dip equator, moderate increase of $20% at midlatitudes, and depression up to 35% around 15°N/S. This suggests a decoupling between the neutral and plasma disturbances during this stage. The plasma-neutral coupling via ion drag was found to become important about 2-3 hours after the flare bursts. Another interesting feature is that the equatorial ionization anomaly was significantly weakened during the flare. The observations demonstrated that electrodynamics related to the equatorial fountain dominated the photochemistry in controlling the flare-induced plasma density disturbances on 28 October 2003. This differs considerably from the nearly linear cos(SZA) dependence of flare-induced total electron content enhancements.
Modeling the responses of the middle latitude ionosphere to solar flares
Journal of Atmospheric and Solar-Terrestrial Physics, 2007
In this paper, we investigate the solar flare effects of the ionosphere at middle latitude with a one-dimensional ionosphere theoretical model. The measurements of solar irradiance from the SOHO/Solar EUV Monitor (SEM) and GOES satellites have been used to construct a simple time-dependent solar flare spectrum model, which serves as the irradiance spectrum during solar flares. The model calculations show that the ionospheric responses to solar flares are largely related to the solar zenith angle. During the daytime most of the relative increases in electron density occur at an altitude lower than 300 km, with a peak at about 115 km, whereas around sunrise and sunset the strongest ionospheric responses occur at much higher altitudes (e.g. 210 km for a summer flare). The ionospheric responses to flares in equinox and winter show an obvious asymmetry to local midday with a relative increase in total electron content (TEC) in the morning larger than that in the afternoon. The flare-induced TEC enhancement increases slowly around sunrise and reaches a peak at about 60 min after the flare onset. r
Modeling the equatorial and low-latitude ionospheric response to an intense X-class solar flare
We have investigated the ionospheric response close to the subsolar point in South America due to the strong solar flare (X2.8) that occurred on 13 May 2013. The present work discusses the sudden disturbances in the D region in the form of high-frequency radio wave blackout recorded in ionograms, the E region disturbances in the form of the Sq current and equatorial electrojet intensifications, and the enhancement and decay in the ionospheric total electron content (TEC) as observed by a network of Global Navigation Satellite Systems receivers, the last of these manifestations constituting the main focuses of this study. The dayside ionosphere showed an abrupt increase of the TEC, with the region of the TEC increase being displaced away from the subsolar point toward the equatorial ionization anomaly (EIA) crest region. The decay in the ΔTEC following the decrease of the flare EUV flux varied at a slower ratio near the EIA crest than at the subsolar point. We used the Sheffield University Plasmasphere-Ionosphere Model to simulate the TEC enhancement and the related variations as arising from the flare-enhanced solar EUV flux and soft X-rays. The simulations are compared with the observational data to validate our results, and it is found that a good part of the observed TEC variation features can be accounted for by the model simulation. The combined results from model and observational data can contribute significantly to advance our knowledge about ionospheric photochemistry and dynamics needed to improve our predictive capability on the low-latitude ionospheric response to solar flares.
Ionospheric response to X-class solar flares in the ascending half of the subdued solar cycle 24
Journal of Earth System Science, 2016
The signature of 11 X-class solar flares that occurred during the ascending half of the present subdued solar cycle 24 from 2009 to 2013 on the ionosphere over the low-and mid-latitude station, Dibrugarh (27.5 • N, 95 • E; magnetic latitude 17.6 • N), are examined. Total electron content (TEC) data derived from Global Positioning System satellite transmissions are used to study the effect of the flares on the ionosphere. A nonlinear significant correlation (R 2 =0.86) has been observed between EUV enhancement (ΔEUV) and corresponding enhancement in TEC (ΔTEC). This nonlinearity is triggered by a rapid increase in ΔTEC beyond the threshold value ∼1.5 (×10 10 ph cm −2 s −1) in ΔEUV. It is also found that this nonlinear relationship between TEC and EUV flux is driven by a similar nonlinear relationship between flare induced enhancement in X-ray and EUV fluxes. The local time of occurrence of the flares determines the magnitude of enhancement in TEC for flares originating from nearly similar longitudes on the solar disc, and hence proximity to the central meridian alone may not play the dominating role. Further, the X-ray peak flux, when corrected for the earth zenith angle effect, did not improve the correlation between ΔX-ray and ΔTEC.
Journal of Scientific Research, 2013
We have investigated the response of ionosphere to major solar flare events that occurred during 1998 to 2011. The effect of enhanced radiation fluxes in the X-ray and EUV band on the GPS derived Total Electron Content (TEC) is examined. The data of X-ray flux from Geostationary Operational Environment Satellite (GOES) and EUV flux from Solar EUV Monitor (SEM) onboard SOHO spacecraft were correlated with the Total Electron Content (TEC) data of a high latitude station, Davis (68.570S, 77.960E). We found that peak intensities of X-ray and EUV flux correlate very well with the peak values of TEC. We also studied the correlation of peak enhancement of these fluxes with the peak enhancement of TEC and found that peak enhancement of these fluxes correlate highly with the peak enhancement of TEC than with the peak values themselves. It is also found that correlation is extraordinarily improved when these fluxes are multiplied by Cos(CMD) where CMD is Central Meridian Distance on the solar...
Journal of Geophysical Research: Space Physics, 2014
Based on the coordinated observations by the incoherent scatter radar (ISR), ionosonde, magnetometers and GPS receivers, the electrodynamic effects on the equatorial and low-latitude ionosphere have been investigated during the intense solar flare (X1.5/2B) on 13 September 2005. In the initial stage of the flare, the ISR and ionosonde measurements at Jicamarca show the decreases of 10.14 m/s and 20 km in the upward vertical E×B drift velocity and the F2-region peak height, respectively, while equatorial electrojet (EEJ) strength over American sector indicates a sudden increase of 53.7 nT. The decrease of the upward vertical E×B drift velocity reveals the weakening of eastward electric field during the flare, which is firstly and directly observed by instrument. It is well known that the variation of equatorial electric field is mainly attributed to the ionospheric dynamo electric field and partially affected by the penetration of interplanetary electric field. The observations during this flare suggest that the flare-induced increase of Cowling conductivity changes the ionospheric dynamo electric field and further results in the weakening of eastward electric field and the decrease of the upward vertical E×B drift velocity. Meanwhile, the upward vertical E×B drift velocity and the EEJ strength during the flare are negatively correlated, which is contrary to the knowledge established by Anderson et al. [2002] based on 10 days of observations in the Peruvian longitude sector. The difference may be caused by the flare-induced enhancement of Cowling conductivity. In addition, GPS total electron content (TEC) observations from six stations in the American equator and low latitudes show an enhancement of 1.47-3.09 TEC units. The measurements of GPS and ISR indicate the contribution of the enhanced photoionization to the increase of TEC is more than that of electrodynamic effect during the initial stage of the intense flare.
Journal of Geophysical Research: Space Physics, 2014
This study presents optical signatures of thermospheric OI 630.0 nm dayglow variability over a geomagnetic dip equatorial station Trivandrum (8.5°N, 77°E, 0.5° dip latitude), India, in response to solar flares of different ranks that occurred on 19 January 2005. It is found that over equator, the response of thermospheric dayglow to solar flares can be either prompt or delayed depending upon rank of the flare and dominant neutral/electrodynamical processes prevailing in the emission altitudes. This is strikingly in contrast to the earlier results, where prompt response of equatorial OI 630.0 nm dayglow to solar flares has been noticed. In addition, the flare‐induced changes at the E and F regions of the equatorial ionosphere are studied using high‐cadence measurements of the equatorial electrojet (EEJ) and total electron content (TEC) obtained from the ground‐based magnetometers and GPS receivers, respectively. The Hall/Pedersen conductivity measurements as inferred using the magnet...
A brief review of “solar flare effects” on the ionosphere
Radio Science, 2009
1] The study of solar flare effects (SFEs) on the ionosphere is having a renaissance. The development of GPS ground and satellite data for scientific use has opened up new means for high time resolution research on SFEs. At present, without continuous flare photon spectra (X rays, EUV, UV, and visible) monitoring instrumentation, the best way to model flare spectral changes within a flare is through ionospheric GPS studies. Flare EUV photons can increase the total electron content of the subsolar ionosphere by up to 30% in 5min.Energeticparticles(ions)of10keVtoGeVenergiesareacceleratedattheflaresite.ElectronswithenergiesuptoseveralMeVarealsocreated.Acoronalmassejection(CME)islaunchedfromtheSunatthetimeoftheflare.FastinterplanetaryCMEs(ICMEs)haveupstreamshockswhichaccelerateionsto5 min. Energetic particles (ions) of 10 keV to GeV energies are accelerated at the flare site. Electrons with energies up to several MeV are also created. A coronal mass ejection (CME) is launched from the Sun at the time of the flare. Fast interplanetary CMEs (ICMEs) have upstream shocks which accelerate ions to 5min.Energeticparticles(ions)of10keVtoGeVenergiesareacceleratedattheflaresite.ElectronswithenergiesuptoseveralMeVarealsocreated.Acoronalmassejection(CME)islaunchedfromtheSunatthetimeoftheflare.FastinterplanetaryCMEs(ICMEs)haveupstreamshockswhichaccelerateionsto10 keV to 10MeV.Bothsourcesofparticles,whenmagneticallyconnectedtotheEarth′smagnetosphere,enterthemagnetosphereandthehigh−latitudeandmidlatitudeionosphere.Thoseparticlesthatprecipitateintotheionospherecauserapidincreasesinthepolaratmosphericionization,disruptionoftranspolarcommunication,andcauseozonedestruction.Complicatingthepicture,whentheICMEreachesthemagnetosphere10 MeV. Both sources of particles, when magnetically connected to the Earth's magnetosphere, enter the magnetosphere and the high-latitude and midlatitude ionosphere. Those particles that precipitate into the ionosphere cause rapid increases in the polar atmospheric ionization, disruption of transpolar communication, and cause ozone destruction. Complicating the picture, when the ICME reaches the magnetosphere 10MeV.Bothsourcesofparticles,whenmagneticallyconnectedtotheEarth′smagnetosphere,enterthemagnetosphereandthehigh−latitudeandmidlatitudeionosphere.Thoseparticlesthatprecipitateintotheionospherecauserapidincreasesinthepolaratmosphericionization,disruptionoftranspolarcommunication,andcauseozonedestruction.Complicatingthepicture,whentheICMEreachesthemagnetosphere1 to 4 days later, shock compression of the magnetosphere energizes preexisting 10-100 keV magnetospheric electrons and ions, causing precipitation into the dayside auroral zone ($60°-65°MLAT) ionospheres. Shock compression can also trigger supersubstorms in the magnetotail with concomitant energetic particle precipitation into the nightside auroral zones. If the interplanetary sheath or ICME magnetic fields are southwardly directed and last for several hours, a geomagnetic storm will result. A magnetic storm is characterized by the formation of an unstable ring current with energetic particles in the range 10keVto10 keV to 10keVto500 keV. The ring current decays away by precipitation into the middle latitude ionosphere over timescales of $10 h. A schematic of a time line for the above SFE ionospheric effects is provided. Descriptions of where in the ionosphere and in what time sequence is provided in the body of the text. Much of the terminology presently in use describing solar, interplanetary, magnetospheric, and ionospheric SFE-related phenomena are dated. We suggest physics-based terms be used in the future.
Journal of Geophysical Research, 2006
Latitudinal and local time dependences of the sudden increase in total electron content (SITEC) of the ionosphere induced by solar flares were statistically studied. We analyzed 91 SITEC events associated with solar flares larger than M5 X-ray class from January 2000 to May 2005. Global total electron content (TEC) data from the Scripps Orbit and Permanent Array Center (SOPAC) GPS networks and X-ray flux data obtained by the Geosynchronous Operational Environmental Satellites (GOES) were used in this study. The global TEC maps revealed that the SITEC value basically depends on the cosine of solar zenith angle (SZA). However, we found that there were significant residuals d from the linear fitting to the SZA for almost all the flare events. The value of d is statistically larger in the winter hemisphere than in the summer hemisphere. The latitudinal difference of d is $0.5 TECU between 50°N and 50°S in the solstice. On the other hand, there was not a clear statistical difference in d between the morning and evening sectors. The similar summer-winter hemispheric asymmetry was also seen in the daytime distribution of the F region O/N 2 density ratio in the MSISE-90 model. This result indicates that the SITEC phenomena induced by solar flares depend not only on the SZA but also on the O/N 2 density ratio. The daytime F region electron density and the background TEC is well known to be determined basically by the O/N 2 ratio. It is reasonable that the O/N 2 ratio affects the sudden increase in TEC in the same sense as it determines the background TEC.