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. <br><br> We use the infrared NO and CO<sub>2</sub> 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 × 10<sup>10</sup> W and 2.7 × 10<sup>10</sup> 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

Weak ionization of the global ionosphere in solar cycle 24

“…These studies point to certain aspects of research that deserve close attention, such as a minimum in geomagnetic activity related to low solar and interplanetary magnetic fields and the disappearance of low-latitude coronal holes (Tsurutani et al, 2011), response of the ionosphere to extremely low solar EUV irradiance (Liu et al, 2011a, b), as well as the considerable energy input of high-speed solar wind streams (HSSs) and its impact on the thermosphereionosphere system (Lei et al, 2008a, b;Verkhoglyadova et al, 2013).…”

Characteristics of low‐latitude TEC during solar cycles 23 and 24 using global ionospheric maps (GIMs) over Indian sector

“…Thus, CODE‐GIM provides an effective tool to study the ionospheric variation over varied scales. For example, in recent past, GIMs have been efficiently applied to understand variety of ionospheric phenomena ranging from effects of extreme events due to space weather [ Maltseva et al , ; Verkhoglyadova et al , ] and earthquake [ Zhao et al , ], forcing to quiet time mean variations of diurnal [ Shim et al ., 2008], seasonal and solar cycle scales [ Liu et al ., ] and effect of solar terminator [ Afraimovich et al , ], retrieval of electron density profiles [ Yue et al , ; Gulyaeva et al , ], and last but not the least for climatic variations in ionosphere [ Liu et al ., ].…”

Ionospheric response to CIR‐induced recurrent geomagnetic activity during the declining phase of solar cycle 23

“…Most of the studies, however, were focused on strong to severe storm events [e.g., Prölss , , ; Fuller‐Rowell et al ., ; Mendillo , , Mendillo and Narvaez , ; Wang et al ., ; Zhao et al ., , ; Lu et al ., ]. Recently, researchers began to pay more attention to ionosphere variations associated with weak to moderate geomagnetic activity driven by coronal hole high‐speed streams (HSS/CIR) [ Wang et al ., ; Burns et al ., ; Solomon et al ., ; Liu et al ., ; Verkhoglyadova et al ., ] when more ionospheric data became available and HSS/CIR‐associated geomagnetic activity occurred periodically and frequently during the declining phase of the last solar cycle. Burns et al .…”

“…Verkhoglyadova et al . [] studied the variability of ionospheric TEC during 2008–2009 and showed that the daily averaged vertical TEC in middle to low latitudes increased by 60% on average during HSS/CIR events.…”