Large-scale gravity wave influences on the propagation of short-period gravity waves to higher altitudes

Abstract:

We investigate the impacts of large-scale gravity waves (periods of multiple hours) on propagation environments for smaller-scale gravity waves (periods less than an hour). Large-scale gravity waves account for wind and temperature perturbations that can modulate the large-scale flow and either enhance or suppress the propagation of short-period waves to higher altitudes, thus also modulating their vertical transport of momentum. Specific cases are discussed using data from the DEEPWAVE mission, which took place from Christchurch, New Zealand in June and July 2014.

The measurements used in this investigation utilize sodium and Rayleigh lidars that were aboard the NSF Gulfstream V research aircraft, as well as temperatures from Advanced Mesospheric Temperature Mappers (AMTMs) aboard the aircraft and stationed at the Lauder research station in New Zealand. The AMTM allows for temperatures to be derived from hydroxyl layer emissions. The Rayleigh lidar allows for temperatures to be measured vertically from ~25-50km. The sodium lidar allows for sodium density perturbations to be measured from ~80-100km. The combination of these instruments allows for more complete assessments of large-scale wave activity (hundreds of km) as well as smaller scale wave events (<100 km). The temperature measurements from both the lidars and AMTMs allow for the phase of the gravity waves at given locations and times to be determined.

An example of an event is given in the attached keogram figure for June 21-22, 2014 from the Lauder AMTM. This night shows a gravity wave that appears to be propagating from ~10:00-12:30 UT in a distinct phase of a larger scale wave with a period in the range of 4-6 hours. Using case studies such as this, we aim to further understand the influences of such dynamics in the mesosphere and lower thermosphere.