A Multivariable Study of a Traveling Ionosphere Disturbance Using the Arecibo Incoherent Scatter Radar

We present the first simultaneous observations of a traveling ionosphere wave (TID) event, measuring electron concentration (Ne), vertical plasma drift (Vz), and ion and electron temperatures (Ti, Te) using the Arecibo incoherent scatter radar. A TID with a period of 135 min was evident in all four state variables in the thermosphere. The amplitudes of Vz and relative Ti fluctuations show only small height variations from 200 to 500 km and their vertical wavelengths increase with altitude. The Te fluctuation shows different characteristics from EISCAT in both phase and amplitude. When the geomagnetic dip angle is 45 degrees, half of the driving gravity wave's (GW's) equatorward velocity is mapped to Vz. This meridional-to-vertical velocity coupling amplifies GW's effect in Ne through vertical transport. The amplifying and anisotropic effects of the geomagnetic field explain the ubiquitous presence of TIDs and their preferred equatorward propagation direction in the geomagnetic mid-latitudes, as well as the midnight collapse phenomenon observed at Arecibo.