@article {532, title = {Interplanetary magnetic field By control of prompt total electron content increases during superstorms}, journal = {Journal of Atmospheric and Solar-Terrestrial Physics}, volume = {115-116}, year = {2014}, month = {08/2014}, pages = {7 - 16}, abstract = {

Large magnitude increases in ionospheric total electron content (TEC) that occur over 1{\textendash}3\ h on the dayside are a significant manifestation of the main phases of superstorms. For the largest superstorms of solar cycle 23 (based on the Dst index), ground networks of GPS receivers measured peak total electron content increases greater than a factor of 2 relative to quiet time TEC averaged over the broad latitude band {\textpm}40{\textdegree} for local times 1200{\textendash}1600\ LT. Near 30{\textdegree} latitude, the Halloween storms of October 29{\textendash}30, 2003 appeared to produce storm-time TEC exceeding quiet time values by a factor of 5 within 2{\textendash}3\ h of storm onset, at 1300\ LT. The physical cause of these large positive phase ionospheric storms is usually attributed to prompt penetration electric fields (PPEFs) initiated by Region 1 current closure through the ionosphere ( Nopper and Carovillano, 1978 mechanism). An unresolved question is what determines variation of the TEC response for different superstorms. It has been suggested that the cross polar cap potential and Region 1 currents are significant factors in determining PPEF in the equatorial ionosphere, which are related to the solar wind reconnection electric field estimated by Kan{\textendash}Lee and others. In this paper, we show evidence that suggests By may be a significant factor controlling the TEC response during the main phase of superstorms. We analyzed the interplanetary conditions during the period that TEC was increasing for eight superstorms. We find that increasing daytime TEC during superstorms only occurs for large reconnection electric fields when By magnitude is less than Bz. The data suggest that Bz is a far more important factor in the TEC response than the reconnection electric field. We also find that TEC decreases following its peak storm-time value for two superstorms, even though Bz remains large and By magnitudes are less than Bz. Such decreases during the geomagnetic disturbance may indicate the role of magnetospheric shielding currents, or of changes in the thermosphere that have developed over the prolonged period of large solar wind electric field. Further analysis is warranted covering a wider range of storm intensities on the role of By in affecting the daytime TEC response for a range of storm intensities.

}, keywords = {Geomagnetic storms, Ionosphere}, issn = {13646826}, doi = {10.1016/j.jastp.2014.01.001}, url = {http://www.sciencedirect.com/science/article/pii/S136468261400008X}, author = {Mannucci, A.J. and Crowley, G. and Tsurutani, B.T. and Verkhoglyadova, O.P. and Komjathy, A. and Stephens, P.} } @article {412, title = {Ionospheric TEC, thermospheric cooling and Σ[O/N2] compositional changes during the 6{\textendash}17 March 2012 magnetic storm interval (CAWSES II)}, journal = {Journal of Atmospheric and Solar-Terrestrial Physics}, volume = {115-116}, year = {2014}, month = {08/2014}, pages = {41 - 51}, abstract = {

A series of four geomagnetic storms (the minimum SYM-H~-148\ nT) occurred during the March 6{\textendash}17, 2012 in the ascending phase of the solar cycle 24. This interval was selected by CAWSES II for its campaign. The GPS total electron content (TEC) database and JPL{\textquoteright}s Global Ionospheric Maps (GIM) were used to study vertical TEC (VTEC) for different local times and latitude ranges. The largest response to geomagnetic activity is shown in increases of the low-latitude dayside VTEC. Several GPS sites feature post-afternoon VTEC {\textquotedblleft}bite-outs{\textquotedblright}. During Sudden Impulse (SI+) event on March 8th a peak daytime VTEC restores to about quiet-time values. It is shown that the TIMED/SABER zonal flux of nitric oxide (NO) infrared cooling radiation correlates well with auroral heating. A factor of ~5 cooling increase is noted in some storms. The cooling radiation intensifies in the auroral zone and spreads towards the equator. Effects of the storm appear at lower latitudes ~18.6\ h later. The column density ratio Σ[O/N2] is analyzed based on TIMED/GUVI measurements. Both increases (at low latitudes) and decreases (from auroral to middle latitudes) in the ratio occurs during the geomagnetic storms. We suggest that the column density ratio could be enhanced at low to middle latitudes on the dayside partially due to the superfountain effect (atomic oxygen uplift due to ion-neutral drag). It is suggested that decreases in the Σ[O/N2] ratio at high to middle-latitudes may be caused by high thermospheric temperatures. During SI+s, there is an increase in Σ[O/N2] ratio at auroral latitudes.

}, keywords = {Geomagnetic storms, Ionosphere, Thermosphere}, issn = {13646826}, doi = {10.1016/j.jastp.2013.11.009}, url = {http://linkinghub.elsevier.com/retrieve/pii/S1364682613003088http://api.elsevier.com/content/article/PII:S1364682613003088?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S1364682613003088?httpAccept=text/plain}, author = {Verkhoglyadova, O.P. and Tsurutani, B.T. and Mannucci, A.J. and Mlynczak, M.G. and Hunt, L.A. and Paxton, L.J.} } @article {357, title = {The October 28, 2003 extreme EUV solar flare and resultant extreme ionospheric effects: Comparison to other Halloween events and the Bastille Day event}, journal = {Geophysical Research Letters}, volume = {32}, year = {2005}, month = {02/2005}, abstract = {

Some of the most intense solar flares measured in 0.1 to 0.8 nm x-rays in recent history occurred near the end of 2003. The Nov 4 event is the largest in the NOAA records (X28) and the Oct 28 flare was the fourth most intense (X17). The Oct 29 flare was class X7. These flares are compared and contrasted to the July 14, 2000 Bastille Day (X10) event using the SOHO SEM 26.0 to 34.0 nm EUV and TIMED SEE 0.1{\textendash}194 nm data. High time resolution, \~{}30s ground-base GPS data and the GUVI FUV dayglow data are used to examine the flare-ionosphere relationship. In the 26.0 to 34.0 nm wavelength range, the Oct 28 flare is found to have a peak intensity greater than twice that of the Nov 4 flare, indicating strong spectral variability from flare-to-flare. Solar absorption of the EUV portion of the Nov 4 limb event is a possible cause. The dayside ionosphere responds dramatically (\~{}2.5 min 1/e rise time) to the x-ray and EUV input by an abrupt increase in total electron content (TEC). The Oct 28 TEC ionospheric peak enhancement at the subsolar point is \~{}25 TECU (25 {\texttimes} 1012 electrons/cm2) or 30\% above background. In comparison, the Nov 4, Oct 29 and the Bastille Day events have \~{}5{\textendash}7 TECU peak enhancements above background. The Oct 28 TEC enhancement lasts \~{}3 hrs, far longer than the flare duration. This latter ionospheric feature is consistent with increased electron production in the middle altitude ionosphere, where recombination rates are low. It is the EUV portion of the flare spectrum that is responsible for photoionization of this region. Further modeling will be necessary to fully understand the detailed physics and chemistry of flare-ionosphere coupling.

}, issn = {0094-8276}, doi = {10.1029/2004GL021475}, url = {http://doi.wiley.com/10.1029/2004GL021475}, author = {Tsurutani, B. T. and Judge, D. L. and Guarnieri, F. L. and Gangopadhyay, P. and Jones, A. R. and Nuttall, J. and Zambon, G.A. and Didkovsky, L. and Mannucci, A.J. and Iijima, B. and Meier, R. R. and Immel, T.J. and Woods, T. N. and Prasad, S. and Floyd, L. and Huba, J. and Solomon, S. C. and Straus, P. and Viereck, R.} }