This working webpage is intended to support the collaboration on atmospheric modelling between the RSPP Group @ University of Leicester and the Danish Meteorological Institute (DMI), as part of the CAL research network.
Email: e.arnone[at]ion.le.ac.uk
Understanding of climate requires a knowledge of the atmospheric response to perturbations. Because of the highly non linear response of the middle atmosphere to chemical perturbations, feedback processes may cause indirectly important changes in the forcing to the troposphere. Whether this results in an impact on climate depends on the possibility of the forcing to propagate to the troposphere. For this reason, we have started a joint effort to study coupling mechanisms of the lower and upper atmosphere.
We study different scales of perturbations, from the solar cycle to local ones such as sprites. Sprites, believed to be NOx sources, are likely to cause local perturbations of no large entity. However, we can study the effect of repeated small impulsive perturbations, and how these can build up an observable response of the atmosphere.
We use the ARPEGE global circulation model (GCM) to study the lower atmosphere and the stratosphere-mesosphere model SMME for the upper region. Together they provide an extended view, from the troposphere (climate processes) to the lower thermosphere (directly affected by solar forcing and sprites).
The SMME model is a fully 3D, 72 levels longitude, 36 latitude, 32 height. It has a sophisticated radiation scheme and a Rayleigh approximation of gravity waves. It was originally derived from the UK-Met. Office Stratosphere-mesosphere model (e.g. Arnold and Robinson 2003). It was then improved by activating a transport code and a series of changes (e.g. vertical diffusion and relaxation of ozone to climatology) to stabilize it during perturbation studies. Ozone levels are prescribed and can be changed to simulate perturbations. We can thus use it to perform experiment altering the distribution of ozone and observing the response of the circulation to these changes. Furthermore, if these changes of ozone are fed back into the system (allowing feed-back processes), one can study how non-linear responses amplify the effect of perturbations.
References:
The ARPEGE model, from Meteo France (Dequé et al, 1994), is a full 3D spectral model, run in T21 resolution. It has 41 vertical layers from the ground to the upper mesosphere. The ozone is prescribed in a 2D scheme and includes transport. It can be perturbed in a similar way as the SMME scheme. The ocean is simply a climatology field, while the land has a three layer soil model with heat capacitance. The climatology ocean implies that impacts on the atmosphere happen quickly and there is no multi annual internal variability, i.e. atmospheric effects from a perturbation can be seen in quite short model runs.
Perturbations of the upper atmosphere can interact with the residual circulation. This may be seen in for example the downward propagation of zonal mean zonal winds. This phenomenon is quite strong at latitudes around 60N and can be seen as anomalies of the zonal wind that begin in the upper atmosphere and propagate down to the troposphere (Christiansen, 2001).
References:
This section outlines the experiments done in order to quantify the response of the middle atmosphere to solar forcing.
SMME
ARPEGE
This section outlines the experiments done in order to quantify the response of the middle atmosphere to perturbations that resemble the impact of solar proton events (SPEs).
SMME
ARPEGE
Here you find the results from other type of perturbations.
SMME
ARPEGE
Last update: 30 May 2005, E. Arnone