The Aberystwyth Egrett Experiment: Gravity Waves, Turbulence, Mixing and Filamentation in the Tropopause Region was a Upper Troposphere Lower Stratosphere (UTLS) Round 2 project led by Dr J. Whiteway and Dr G. Vaughan, Department of Physics, University of Wales, Aberystwyth.

Dataset contains: airborne measurements, by the Egrett aircraft, of turbulence, ozone, water vapour, CH4 and CFCs; Ground based measurements, by the NERC MST Radar, of atmospheric structure, mesoscale dynamics, and turbulence; Balloons measurements of ozone, water vapour, wind, temperature and pressure; Lidar of ozone, water vapour, temperature and cirrus clouds.

Objectives and Methodology

The main objectives are outlined as follows.

-Gravity waves, turbulence and mixing. The processes by which gravity waves break and cause turbulence has been investigated. It will be determined whether the mixing associated with this turbulence has a significant influence on the distribution of constituents in the tropopause region. Particular emphasis has been placed on mixing at and across the tropopause
-Gravity wave spectra. This involved measurements of the vertical, horizontal, and temporal spectra of temperature and wind fluctuations. The influence of specific meteorological conditions have been identified in each of the different types of spectra.
-Gravity wave variability. The spatial variability of gravity wave activity has been determined with respect to specific meteorological patterns (e.g. the jet stream).
-Distribution of filamentation. Determined whether and how filamentary structure becomes less prominent with altitude above the jet.
-Scale of filamentation. The across-flow scales of filaments will be determined at different altitudes above the jet stream, and this was compared to model predictions
-Filamentation and mixing. It was determined if there was a clear evidence of mixing (e.g. ozone-rich moist air) in filaments near the tropopause, in regions downstream of expected or observed gravity-wave breaking. Generally, the mixture of tracer concentrations were used to gauge the extent to which air near the tropopause region is genuinely mixed, with respect to the synoptic meteorological pattern.

Deliverables

Airborne measurements: A unique stratospheric research aircraft, the Egrett aircraft, performed 10 separate flights in the UTLS region above Aberystwyth. The Egrett was equipped with advanced instrumentation for measurements of turbulence, ozone and water vapour.

Ground based measurements: The ground based facilities at Aberystwyth were operated to their full capacity during the Egrett campaign. The NERC MST Radar provided measurements of atmospheric structure, mesoscale dynamics, and turbulence. Balloons carryed instruments for measuring ozone, water vapour, wind, temperature and pressure. Three separate lidar systems provided measurements of ozone, water vapour, temperature and cirrus clouds.

Analysis of gravity waves and turbulence: The above measurements were conducted when gravity waves were breaking and causing turbulence. The combination of the Egrett and ground based measurements have been used to determine if this process is significant for transport of chemical constituents in the UTLS region. These measurements also provided a new basis for testing theories and models of the wave breaking process.

Analysis of filamentation: The Egrett aircraft was directed to fly through regions of filamentation in the lower stratosphere. This provided new data to test theories and models of mixing through turbulence at the edges of filaments.