Mesoscale Weather Systems
Mesoscale weather systems research in the Department of Meteorology at the University of Reading covers a wide spectrum of phenomena and applications ranging from investigation of chemical transport in convection and midlatitude weather systems to investigation of gravity waves generated by deep convection. Work performed in the group makes extensive use of the UK Met Office Unified Model (UM) --- a state of the art operational weather forecasting model --- for both case study and idealised numerical experiments. The group benefits from interactions with Met Office scientists via the Joint Centre for Mesoscale Meteorology (JCMM) based at Reading.
Recent Results on convectively-generated gravity waves
Convectively-generated gravity waves can induce various effects in the ambient flow through which they propagate including a) the generation of clear air turbulence and mixing above cloud top, b) the transport of energy to the middle atmosphere and the acceleration of the larger scale flow, and c) triggering and/or modification of convection in the troposphere. Dr. Chagnon's research seeks to understand the basic properties of the waves that precede these effects using a variety of investigative tools. Analytical and idealised numerical modelling studies are being performed in order to determine how energy that originates in the troposphere is transported through the tropopause. Other work involves the analysis of real case studies using high resolution numerical model simulation with the Met Office Unified Model (UM) validated against observations from the NERC supported Mesosphere-Stratosphere-Troposphere (MST) radar wind profiler located at Aberystwyth in Wales. Using wavelet transforms, the wave spectra obtained from case study analysis reveal a series of distinct, previously unidentified, preferred scales that cannot be unambiguously attributed to the scale of the convective forcing. An example of these spectra is provided in the accompanying figure in which the power associated with a vertical velocity field (shown in the right panel for a level in the lower stratosphere in a simulation with 1 km horizontal grid lengths) in and around deep convection is plotted as a function of horizontal scale. Multiple peaks at scales less than 50 km are clearly evident in the high resolution simulation. The cause and consequence of these multiple peaks --- which could have implications for the design of gravity wave drag parameterisations --- is presently under investigation. Additional ongoing work aims to determine the role of gravity waves in mixing along the tropopause by using passive tracers in UM simulation of real events.
For more information on Mesoscale Weather Processes, see:
Staff involved in this activity are:
Dr Sue Gray and Dr Jeffrey Chagnon (University of Reading)