F 2 region response to geomagnetic disturbances across Indian latitudes: O( 1 S) dayglow emission

The 2015 St. Patrick's Day geomagnetic storm with SYM‐H value of −233 nT is an extreme space weather event in the current 24th solar cycle. In this work, we investigated the main mechanisms of the profound ionospheric disturbances over equatorial and low latitudes in the Asian‐Australian sector and the American sector during this super storm event. The results reveal that the disturbed electric fields, which comprise penetration electric fields (PEFs) and disturbance dynamo electric fields (DDEFs), play a decisive role in the ionospheric storm effects in low latitude and equatorial regions. PEFs occur on 17 March in both the American sector and the Asian‐Australian sector. The effects of DDEFs are also remarkable in the two longitudinal sectors. Both the DDEFs and PEFs show the notable local time dependence, which causes the sector differences in the characteristics of the disturbed electric fields. This differences would further lead to the sector differences in the low‐latitude ionospheric response during this storm. The negative storm effects caused by the long‐duration DDEFs are intense over the Asian‐Australian sector, while the repeated elevations of hmF2 and the equatorial ionization anomaly intensifications caused by the multiple strong PEFs are more distinctive over the American sector. Especially, the storm time F3 layer features are caught on 17 March in the American equatorial region, proving the effects of the multiple strong eastward PEFs.

Section: Resultsmentioning

confidence: 99%

Effects of disturbed electric fields in the low‐latitude and equatorial ionosphere during the 2015 St. Patrick's Day storm

Kuai

Liu

et al. 2016

“…It has been reported that the geomagnetic storms show a delayed ionospheric effect at low‐mid latitude Indian station, Delhi, a comprehensive analysis of which is recently presented by Upadhayaya et al . []. In this case, on 31 December 2015, due to a possible effect of geomagnetic storm, the electron density increased by ~154%.…”

Section: Discussionmentioning

confidence: 99%

“…This variation observed in O/N 2 in either case is not very prominent despite an increase in O/N 2 was observed on the precursor day in one of the earthquake events. However, with limited observations during these earthquake events, it appears that the thermospheric neutral composition (O/N 2 ) was not adequately modified during the earthquake period, as normally observed in case of the geomagnetic storms [ Zhang et al ., ; Lee et al ., ; Upadhayaya et al ., ]. These results further indicate towards possible different sources of origin of ionospheric perturbations during the geomagnetic storms and earthquakes.…”

Section: Discussionmentioning

confidence: 99%

Preearthquake anomalous ionospheric signatures observed at low‐mid latitude Indian station, Delhi, during the year 2015 to early 2016: Preliminary results

Gupta

Upadhayaya

2017

Self Cite

We have analyzed five major earthquake events measuring greater than 6 on Richter scale (M > 6) that occurred during the year 2015 to early 2016, affecting Indian region ionosphere, using F2 layer critical parameters (foF2, hmF2) obtained using Digisonde from a low‐mid latitude Indian station, Delhi (28.6°N, 77.2°E, 19.2°N geomagnetic latitude, 42.4°N dip). Normal day‐to‐day variability occurring in ionosphere is segregated by calculating F2 layer critical frequency and peak height variations (ΔfoF2, ΔhmF2) from the normal quiet time behavior apart from computing interquartile range. We find that the ionospheric F2 region across Delhi by and large shows some significant perturbations 3–4 days prior to these earthquake events, resulting in a large peak electron density variation of ~200%. These observed perturbations indicate towards a possibility of seismo‐ionospheric coupling as the solar and geomagnetic indices were normally quiet and stable during the period of these events. It was also observed that the precursory effect of earthquake was predominantly seen even outside the earthquake preparation zone, as given by Dobrovolsky et al. (1979). The thermosphere neutral composition (O/N2) as observed by Global Ultraviolet Imager, across Delhi, during these earthquake events does not show any marked variation. Further, the effect of earthquake events on ionospheric peak electron density is compared to the lower atmosphere meteorological phenomenon of 2015 sudden stratospheric warming event.

“…At the end of warming period (day 34), there exists an enhancement from 0900 to 1200 LT and at 1800 LT, followed by prominent enhancements for the next 3 days. A variation of not more than 30% is expected in the electron density because of a geomagnetic storm of moderate strength [ Upadhayaya et al , ]. The latitudinal response to SSW can be seen in Figures (b), (c), and (d), for the other low midlatitude stations, Yamagawa, Kokubunji, and Wakkanai, respectively.…”

Section: Observations and Analysismentioning

confidence: 99%

Morphology of ionospheric F₂ region variability associated with sudden stratospheric warmings

Gupta

Upadhayaya

2017

Self Cite

The effect of sudden stratospheric warming (SSW) on the F2 region ionosphere has been extensively analyzed for the major event of year 2009, apart from a few reports on other major and minor events. Morphology of ionospheric responses during SSW can be better comprehended by analyzing such warming events under different solar, geomagnetic, and meteorological conditions. We investigate the features of F2 region variability following the SSW events of 2010, 2011, 2012, 2013, 2014, 2015, and 2016, using ionosonde data from the Asian region covering a broad latitudinal range from 26.6°N to 45.1°N. We find perceptible ionospheric variations in electron densities during these warming events which is accompanied by a large variation of ~117% within enhancements, as compared to a meagre variation of ~11% within depressions, during these events. We also examine 6 months data at these latitudes and longitudes and find that the maximum and minimum variations in F2 layer critical frequency are observed during each SSW period. The influence of quasi‐stationary 16 day planetary waves is seen during these SSW events. Further, a recently proposed parameter “SSW integrated strength” by Vieira et al. (2017) to characterize SSW event with respect to ionosphere is also examined. It is seen that it does not fit well for these seven SSW events at these latitudes and longitudes.