Wave dynamics of the mesosphere

Lead Research Organisation: University of Bath
Department Name: Electronic and Electrical Engineering

Abstract

Waves in the atmosphere are able to transport energy and momentum between different layers of the atmosphere. Understanding these waves is thus very important if we want to understand the atmosphere as a whole system in which the layers are coupled together. In this project we will use five radars to measure waves in the mesosphere, which is that part of the atmosphere at heights of between about 55 to 100 km. The radars are located at sites ranging from the Arctic to the Antarctic. We are particularly interested in detecting and measuring waves generated when strong winds blow over the Southern Andes and the Antarctic Peninsula - so-called 'mountain waves'. We are interested in understanding the conditions under which these waves can ascend to the mesosphere and plan to determine the effect they have on the large-scale winds of the mesosphere. We will also study how the intense, cold winter circulation system known as the stratospheric polar vortex filters and controls waves ascending into the mesosphere. We plan to take part in a major international experiment, SAANGRIA, to study these phenomena in collaboration with other instruments. Finally, we will study how the winds of the equatorial mesosphere control the cross-equator propagation of planetary-scale waves

Publications

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Beldon C (2010) Gravity wave-tidal interactions in the mesosphere and lower thermosphere over Rothera, Antarctica (68°S, 68°W) in Journal of Geophysical Research: Atmospheres

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Cho Y (2011) A study of temperature and meridional wind relationships at high northern latitudes in Journal of Atmospheric and Solar-Terrestrial Physics

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Davis R (2013) The diurnal and semidiurnal tides over Ascension Island (° S, 14° W) and their interaction with the stratospheric quasi-biennial oscillation: studies with meteor radar, eCMAM and WACCM in Atmospheric Chemistry and Physics

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Davis R (2012) The climatology, propagation and excitation of ultra-fast Kelvin waves as observed by meteor radar, Aura MLS, TRMM and in the Kyushu-GCM in Atmospheric Chemistry and Physics

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Day K (2011) Aura MLS observations of the westward-propagating <i>s</i>=1, 16-day planetary wave in the stratosphere, mesosphere and lower thermosphere in Atmospheric Chemistry and Physics

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Day K (2012) Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W) in Atmospheric Chemistry and Physics

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Day K (2013) Mean winds in the MLT, the SQBO and MSAO over Ascension Island (8° S, 14° W) in Atmospheric Chemistry and Physics

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De Wit R (2013) Interannual variability of mesopause zonal winds over Ascension Island: Coupling to the stratospheric QBO in Journal of Geophysical Research: Atmospheres

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Fritts D (2012) Assessment of gravity wave momentum flux measurement capabilities by meteor radars having different transmitter power and antenna configurations in Journal of Geophysical Research: Atmospheres

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Fritts D (2010) Southern Argentina Agile Meteor Radar: System design and initial measurements of large-scale winds and tides in Journal of Geophysical Research: Atmospheres

 
Description In this research project we investigated the atmospheric waves that dominate the dynamics of the stratosphere and mesosphere. We carried out studies of key physical processes in the field of waves at equatorial, middle and polar latitudes and investigated their variability, their latitudinal structure and their role in coupling together the different layers of the atmosphere (in this case the troposphere, stratosphere and mesosphere).

Studies of the equatorial atmosphere determined the climatology of Ultra-Fast Kelvin waves (UFKW) and used our results as diagnostics of the UFKW in the Kyushu GCM. We found no evidence to support the hypothesis that tropical rainfall modulates UFKW amplitudes in the mesosphere, indicating that either other sources or the propagation environment are more important in determining the amplitude of UFKW at these heights. However, intra-seasonal oscillations (ISOs) with periods 25-60 days were evident in the zonal background winds, zonal-mean temperature, UFKW amplitudes, UFKW accelerations and the rainfall rate. This suggests that UFKW play a role in carrying the signature of tropospheric ISOs to the mesosphere.

Our studies of the mesospheric quasi-biennial oscillation (MQBO) suggest that it does not, as has been hypothesized, play a role in modulating the ducting of planetary waves between the northern and southern hemispheres. We also investigated the role of gravity-wave filtering in the exceptional and anomalously large westward wind events sometimes observed in the equatorial mesosphere.

We used meteor radars to measure the winds and waves in the mesosphere over the Southern Andes. We did this using the advanced SAAMER meteor radar in Tierra del Fuego as part of an international collaboration. We also collaborated with international partners to use five meteor radars of different configurations and at different latitudes to benchmark and demonstrate their ability to make comparable results of gravity-wave momentum fluxes. These results demonstrated the existence of large gravity-wave fluxes at mesospheric heights.

One element if the project that we were not able to carry out as expected was to collaborate with US investigators in their proposed SAANGRIA gravity-wave campaign that was to be centred over the Southern Andes/Drake Passage/Antarctic Peninsula. This was eventually cancelled for logistical reasons and instead took place around New Zealand as DEEPWAVE. We were nevertheless able to carry out studies of waves at these latitudes using satellites and radars.

We investigated the variability and coupling of planetary waves at equatorial, middle and polar latitudes. We used the NASA MLS instrument to determine the component wavenumbers of the 2-day planetary wave and showed that they are different in the northern and southern hemisphere and that each component has a subtly different climatology. We used similar observations to determine the climatology, variability and latitudinal structure of the 5-day and 16-day planetary waves.
Exploitation Route The results of our studies are of interest to those involved in developing the computer Global Circulation Models (GCMs) used for numerical weather prediction and climate research. This is particularly so because these GCMs are now actively being extended upwards to include the mesospheric heights that were a focus of much of the research work carried out in this project.
Sectors Environment