Climatology of the nighttime ionospheric trough

Global vertical Total Electron Content (vTEC) maps produced by the International Global Navigation Satellite System (GNSS) Service are used to study the seasonal variation of the mid-latitud ionospheric trough (MIT). MIT shows a structure in longitude and latitude in the F2 region. The shape and behavior of the trough is different and its related with the spatial-temporal ocurrence. Some authors showed that the trough prevail during evening and night-times hours. Several physical mechanisms have been proposed to explain it formation which include plasma stagnation, periods of increasing geomagnetic activity, enhanced of the electric field between others. Also, the horizontal neutral wind was proposed as a possible cause in deepest MIT formation.By using the principal component analysis (PCA) numerical technique, this work studies the spatial and temporal variations of the MIT at nigth for the period 1999-2017 during differents hours: 22, 00 and 02 LT. The vTEC maps series are carefully choosen taken into account the Kp index to associate the MIT formation with the geomagnetic activity. Also, vTEC maps from the International Reference Ionosphere (IRI) 2012 and the Horizontal Wind Model 2007 (HWM07) are used to improve our climatology interpretation, by analyzing the relationship between vTEC and the horizontal neutral wind.