A ship-borne imager: determining mesospheric gravity wave activity above the ocean

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Gravity waves are buoyancy waves in the atmosphere. They can be produced from a variety of sources, e.g. wind flowing over mountains or large weather systems. As they propagate upwards they become unstable and break (similar to waves on a beach) depositing their energy and momentum, driving the circulation and temperature patterns in the atmosphere. The region between 50km and 90km in altitude, known as the mesosphere, is dominated by gravity wave activity. In order to accurately reproduce their effects in atmospheric climate models, we need to observe gravity waves (and identify their sources) from all areas of the planet. As the oceans make up 70% of the Earth's surface it is vitally important to understand the gravity wave activity that occurs over them. Traditionally satellite observations are used to obtain global estimates of gravity wave activity in the atmosphere but, they have limitations in that they cannot view the whole range (full spectrum) of gravity waves. This proposal looks to finalise development of a ship-borne imager that will allow gravity wave measurements of the mesosphere to be made from the R.R.S. James Clarke Ross as it traverses the Atlantic Ocean to and from the Antarctic and the U.K. These measurements will provide a unique insight into a different section of the gravity wave range to that which satellites can observe.The ship-borne imager will use a novel system of 3 one-degree field of view imagers (radiometers) and the pitch and roll of the ship to scan the sky. The imagers will be observing gravity wave perturbations in a layer of airglow at around 90km altitude. Airglow is the term given to the weak emission of light by different gas layers in the atmosphere. As gravity waves pass through this airglow layer they alternately compress and rarefy it, resulting in a variation in the airglow emissions. Using these observations it is possible to determine the characteristics of the gravity waves.We propose to exploit the ships isolation from land-based gravity wave sources and the ships itineraries to do case studies and examine two influences on the mesospheric gravity wave field: large weather systems in the deep ocean and topography.