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SPARC Gravity wave initiative / ISSI

The Stratospheric Processes And their Role in Climate (SPARC) program is a subdivision of the World Climate Research Programme (WCRP), which coordinates world wide activities in climate research and formulates recommendations based on the common understanding of the scientific community. As we gain a higher level of understanding, more detailed knowledge on climate change and prediction on the synoptic and regional scale is requested. Recent results of climate chemistry models have demonstrated that the dynamical downward coupling from the stratosphere is essential for understanding the synoptic and regional behaviour of the Earth's troposphere and surface climate.

gravity wave momentum flux @ 26km altitude - January 2005-2007

gravity wave momentum flux at 26km altitude - July 2005-2007Gravity wave momentum flux at 26km altitude: Global distribution of absolute values of GW momentum flux @ 26km altitude for January and July averaged over years 2005-2007. High activity is found collocated with the strong wind speeds associated with the winter polar vortex. On the summer hemisphere convective forcing generates three distinct maxima in the subtropics.

Any model which aims at a realistic representation of the stratosphere must include the effects of gravity waves. Gravity waves are an important upward coupling process conveying momentum and energy from tropospheric sources to higher altitudes where they dissipate. However, gravity waves and in particular their sources are too small in scale to be resolved in climate models. They are also very challenging to measure. Only in recent years a number of measurement techniques provided climatological information on the most important quantity, i.e. gravity wave momentum flux.

The aim of the SPARC gravity wave initiative is to bring together experts from the fields of measurement techniques and global modeling in order to provide a consistent set of observational constraints suited to guide climate modelers. Focus is on such measurement techniques which can provide informations on at least large parts of the globe. The role of gravity waves for the stratosphere and the current knowledge on gravity waves and available measurement techniques was reviewed by Alexander et al, QJRMS, 2010. Most recently work was coordinated in an ISSI team ( which prepares further review papers on global constraints and model-measurement comparisons.