Projects / Programmes
Quantification of the contribution of Rossby and inertia-gravity waves to the vertical velocity and momentum fluxes in the atmosphere
| Code |
Science |
Field |
Subfield |
| 1.02.00 |
Natural sciences and mathematics |
Physics |
|
| Code |
Science |
Field |
| P500 |
Natural sciences and mathematics |
Geophysics, physical oceanography, meteorology |
| Code |
Science |
Field |
| 1.03 |
Natural Sciences |
Physical sciences |
atmospheric vertical velocity, momentum fluxes, weather and climate modelling, Rossby and inertio-gravity waves, scale-dependent computation
Researchers (6)
Organisations (1)
Abstract
Motions in the atmosphere are three-dimensional. In average conditions, horizontal velocity components (u,v) are much greater than the vertical velocity (w), w(. Therefore, the majority of global weather and climate models applies the hydrostatic approximation which removes w as prognostic quantity. Global fields of vertical velocity w are instead diagnosed using the conservation of energy or mass. In practice, vertical motions are usually estimated at constant pressure levels in Pascals per second (so-called omega).
On one hand, omega is not an observable variable while on the other hand it is a crucial ingredient of weather and climate, especially the global water and energy cycle. The computation of vertical velocity using the thermodynamic equation or the mass continuity equation has become a part of the numerical weather prediction and climate hydrostatic models. However, there are significant differences in omega among the models and reanalysis datasets. There are also significant uncertainties in the estimates of vertical momentum fluxes associated with different wave oscillations in climate models, especially in the tropics.
Two kinds of wave motions used to understand basic atmospheric dynamics are the Rossby waves and inertia-gravity waves. The former describe large-scale, quasi-horizontal, quasi-geostrophic motions whereas the latter are characterized by much greater divergence and significant vertical propagation. In the extra-tropics, the two kinds of wave motions are well separated while in the tropics the inertia-gravity (IG) waves are important on all scales.
The project proposes a new approach for the computation of vertical velocity in global data that promises to separate vertical motions associated with the Rossby and IG waves across many scales. The approach is based on the normal-mode function decomposition for the separation of the Rossby and IG dynamics in the terrain-following coordinate that was established in the MODES project (http://modes.fmf.uni-lj.si). In the computation of vertical velocity, the continuity equation will be solved by replacing the horizontal wind divergence by analytical functions derived from the normal-mode function representation. The approach will provide 3D structure of vertical motions in the global atmosphere split into contributions from the Rossby and IG waves as a function of the zonal wavenumber, meridional mode and vertical structure function.
The new method will be applied for the quantification of the two omega components in reanalysis data and climate models. Their relative role in driving the middle atmosphere variability, such as the quasi-biennial oscillation, will be estimated. The final goal is to develop a new metric for the validation of the momentum fluxes and vertical transport in climate models.
Significance for science
Computation of the vertical velocities associated with Rossby and inertio-gravity waves by proposed method will quantify their respective roles in driving the circulation in the upper troposphere, stratosphere and mesosphere. The most relevant results and their impact are expected in the tropics where the role of various IG waves in atmospheric variability is less well understood. The IG component of vertical motion can further be split into the contribution from the Kelvin waves and large-scale and small-scale other IG waves. For example, the role of Kelvin waves and the mixed Rossby-gravity wave in driving the quasi-biennial oscillations (QBO) can be quantified as a function of the zonal wavenumber and vertical structure function more precisely than in previous studies.
Another promising aspect of the project is the role of the two components of vertical velocity on different scales in the global energy and water budgets (e.g. collocation of the precipitation and vertical motions, separation of convective and stratiform precipitation in the models). This is envisaged for the reanalysis data and then it can be applied to validate the climate models.
The project would provide a framework for a continued collaboration of the Ljubljana meteorology group with international community involved in the application of the modal methodology, research on IG and Rossby wave dynamics and numerical modelling. In particular, the project would enhance climate dynamics research in Slovenia
Significance for the country
Computation of the vertical velocities associated with Rossby and inertio-gravity waves by proposed method will quantify their respective roles in driving the circulation in the upper troposphere, stratosphere and mesosphere. The most relevant results and their impact are expected in the tropics where the role of various IG waves in atmospheric variability is less well understood. The IG component of vertical motion can further be split into the contribution from the Kelvin waves and large-scale and small-scale other IG waves. For example, the role of Kelvin waves and the mixed Rossby-gravity wave in driving the quasi-biennial oscillations (QBO) can be quantified as a function of the zonal wavenumber and vertical structure function more precisely than in previous studies.
Another promising aspect of the project is the role of the two components of vertical velocity on different scales in the global energy and water budgets (e.g. collocation of the precipitation and vertical motions, separation of convective and stratiform precipitation in the models). This is envisaged for the reanalysis data and then it can be applied to validate the climate models.
The project would provide a framework for a continued collaboration of the Ljubljana meteorology group with international community involved in the application of the modal methodology, research on IG and Rossby wave dynamics and numerical modelling. In particular, the project would enhance climate dynamics research in Slovenia
Most important scientific results
Interim report,
final report
Most important socioeconomically and culturally relevant results
Interim report,
final report
