The work will use the 50 MHz radar at Jicamarca, Peru to observe high-frequency gravity waves in the equatorial mesosphere and lower thermosphere from about 60 to 170 km. The radar will be used in an extension of an existing MST-ISR mode. Besides transmitting long and coded pulses for interlaced detection of mesospheric echoes and ionospheric incoherent scatter radar returns (so-called MST and ISR signals), short and uncoded pulses will be transmitted to probe the turbulent equatorial electrojet height region (E-region proper) with high temporal and spatial resolution. Short-pulse data from the electrojet will be used to provide gravity wave signatures from the equatorial E region to complement the D-region and upper E-region (above 140 km) gravity wave data acquired in the MST-ISR mode. The overall objective will be to improve the current understanding of gravity wave propagation and guiding in the equatorial mesosphere and lower thermosphere and the role of gravity waves in the structuring of the region via neutral and plasma instability processes. Gravity waves are known to play a crucial role in the dynamic coupling of atmospheric regions. Waves that propagate upward through the mesosphere and lower thermosphere (or that may be generated as secondary waves) may grow to significant amplitudes in the E and F regions of the ionosphere. The fast continuous sampling by the Jicamarca radar provides important information on short period (5-15 minute) gravity wave oscillations and instabilities of the neutral atmosphere at low latitudes. Short period waves are always present in the equatorial mesosphere as evident in Jicamarca vertical wind data and also in the equatorial upper E-region as evident in enhanced backscatter from the 150-km altitude region observed at Jicamarca. The connection of these wave systems and their relation to gravity waves in the intervening E-region altitudes remain unknown and unexplored. Above Jicamarca, this region is occupied by a turbulent equatorial electrojet (EEJ) causing strong radar backscatter. The modulation of this backscatter signal is what will be exploited for a novel study of the gravity wave content of the region and its relationship to gravity waves observed in the mesosphere and the upper E-region.
