I study interesting phenomenon in Physics of the upper atmosphere. I employ the use of GNSS data to study MIT (magnetosphere-ionosphere-thermosphere) coupling and the phase delay irregularities in trans-ionospheric propagation, traveling Ionospheric disturbances (TID) in GNSS and total electron content (TEC) during Ionospheric substorms and storms, TID coupling with stratospheric warming during propagation of AGW (atmospheric gravity waves). I also use the rate of change of the TEC (ROTI) index