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TEC gradients are a new product of the TechTIDE services, which are provided in near real-time since May 2019. The analysis of the TEC gradients for the September 2017 event show that weak TEC gradients are present during the generation time of LSTIDs. An example is shown in the attached image. TEC gradients in the auroral region are suggested to be used as an indicator for the generation of LSTIDs.
TEC gradients in lower latitudes are generated by other mechanisms and are not associated with LSTID activity.
The Large scale TID detection algrorithms based on GNSS reveal hardly any LSTID activity during 23rd to 25th Apr. 2019. TEC perturbations are detected in high latitudes during the nigths from the 23rd to 24th and 24th to 25th April. These correspond well with the AATR amplitudes presented above by Chris_Tim and they also correspond well with the auroral activity presented by Anna. There are very weak TEC perturbation signatures that can be single LSTIDs at around 3 UT on the 24th and 25th April, that follow the auroral activity. On the 25th April in the evening hours there are rather weak perturbations in the auroral region, but no LSTIDs.
Large scale TID dectection methods based on GNSS measurements revealed lots of TID activity during 7th and 8th September 2017 over Europe. There were rather fast and large waves during daytime on the 7th September. During morning and afternoon hours on the 8th September slower waves are observed. They are associated to strong energy input from the solar wind.