TEC

About: TEC is a research topic. Over the lifetime, 5119 publications have been published within this topic receiving 84696 citations.

Variability of ionospheric TEC during solar and geomagnetic minima (2008 and 2009): external high speed stream drivers

Abstract: . We study solar wind–ionosphere coupling through the late declining phase/solar minimum and geomagnetic minimum phases during the last solar cycle (SC23) – 2008 and 2009. This interval was characterized by sequences of high-speed solar wind streams (HSSs). The concomitant geomagnetic response was moderate geomagnetic storms and high-intensity, long-duration continuous auroral activity (HILDCAA) events. The JPL Global Ionospheric Map (GIM) software and the GPS total electron content (TEC) database were used to calculate the vertical TEC (VTEC) and estimate daily averaged values in separate latitude and local time ranges. Our results show distinct low- and mid-latitude VTEC responses to HSSs during this interval, with the low-latitude daytime daily averaged values increasing by up to 33 TECU (annual average of ~20 TECU) near local noon (12:00 to 14:00 LT) in 2008. In 2009 during the minimum geomagnetic activity (MGA) interval, the response to HSSs was a maximum of ~30 TECU increases with a slightly lower average value than in 2008. There was a weak nighttime ionospheric response to the HSSs. A well-studied solar cycle declining phase interval, 10–22 October 2003, was analyzed for comparative purposes, with daytime low-latitude VTEC peak values of up to ~58 TECU (event average of ~55 TECU). The ionospheric VTEC changes during 2008–2009 were similar but ~60% less intense on average. There is an evidence of correlations of filtered daily averaged VTEC data with Ap index and solar wind speed. We use the infrared NO and CO2 emission data obtained with SABER on TIMED as a proxy for the radiation balance of the thermosphere. It is shown that infrared emissions increase during HSS events possibly due to increased energy input into the auroral region associated with HILDCAAs. The 2008–2009 HSS intervals were ~85% less intense than the 2003 early declining phase event, with annual averages of daily infrared NO emission power of ~ 3.3 × 1010 W and 2.7 × 1010 W in 2008 and 2009, respectively. The roles of disturbance dynamos caused by high-latitude winds (due to particle precipitation and Joule heating in the auroral zones) and of prompt penetrating electric fields (PPEFs) in the solar wind–ionosphere coupling during these intervals are discussed. A correlation between geoeffective interplanetary electric field components and HSS intervals is shown. Both PPEF and disturbance dynamo mechanisms could play important roles in solar wind–ionosphere coupling during prolonged (up to days) external driving within HILDCAA intervals.

Impact factor for the ionospheric total electron content response to solar flare irradiation

Abstract: On the basis of ionospheric total electron content (TEC) enhancement over the subsolar region during flares, and combined with data of the peak X-ray flux in the 0.1-0.8 nm region, EUV increase in the 0.1-50 and 26-34 nm regions observed by the SOHO Solar EUV Monitor EUV detector, also with the flare location on the solar disc, the relationship among these parameters is analyzed statistically. Results show that the correlation between ionospheric TEC enhancement and the soft X-ray peak flux in the 0.1-0.8 nm region is poor, and the flare location on the solar disc is one noticeable factor for the impact strength of the ionospheric TEC during solar flares. Statistics indicate clearly that, at the same X-ray class, the flares near the solar disc center have much larger effects on the ionospheric TEC than those near the solar limb region. For the EUV band, although TEC enhancements and EUV flux increases in both the 0.1-50 and 26-34 nm regions have a positive relation, the flux increase in the 26-34 nm region during flares is more correlative with TEC enhancements. Considering the possible connection between the flare location on the solar disc and the solar atmospheric absorption to the EUV irradiation, an Earth zenith angle is introduced, and an empirical formula describing the relationship of TEC enhancement and traditional flare parameters, including flare X-ray peak and flare location information, is given. In addition, the X-ray class of the flare occurring on 4 November 2003, which led the saturation of the X-ray detector on GOES 12, is estimated using this empirical formula, and the estimated class is X44.