A large volume of research has been devoted to the role
that troposphere-generated planetary scale waves play as
a dynamical mechanism driving the stratospheric
circulation. Equally well-known is the significant role
that planetary scale waves play in the passive transport
of middle atmosphere constituents such as ozone. Yet,
despite the seemingly intricate link between these two
phenomenon, little work has been done exploring the
dynamical link between ozone photochemistry and the
dynamics of the wave-driven stratospheric circulation.
Recent work has shown that the dynamic interaction
between ozone photochemistry and Kelvin and
Rossby-gravity waves plays an important role in
modulating the tropical quasi-biennial oscillation.
The Madden-Julian Oscillation (MJO) is the dominant component of
intraseasonal variability in the Tropics. Since the 1980s, the MJO has
received a great deal of attention in part because of its impact on weather
systems around the globe. A lot of work has been devoted in the accurate
simulating and forecasting of the MJO, which has become the holy grail of
tropical atmospheric dynamics and has not ceased to be a challenge for
the modeling community. Various studies have focused on comparing or
evaluating models, whether global climate, regional and multiscale
models, as well as analyzing the effectiveness of their parameterizations
and schemes. For example, the MM5 v.3 regional model was shown to
capture the dominant features of the MJO, such as the observed location
of convection, its eastward propagation and the strong first baroclinic
structure of the MJO (Gustafson and Weare 2004).
However, in this previous study, the statistical techniques used to analyze
the model results did not follow any systematic and standardized
diagnostics, developed in subsequent years, such as the procedure
described by Zhang (2005). Besides, the width of the domain allowed only
waves up to a size of global wavenumber 3 to develop without crossing
the boundaries, while the observed MJO is dominated by wavenumbers 1
3. At last, a single dataset, the NCEP/NCAR reanalysis, was used to force
the initial and boundary conditions of the model. Since uncertainties in
the accuracy of the input data could impact on the simulated MJO, the
use of another dataset could yield interesting results. For these reasons,
in this study, the MM5 model was ran with the ECMWF ERA-40 reanalysis
dataset for a time period of 26 months, over the tropics (22.5°S-22.5°N)
and half the globe in longitude (15°E-197.5°E). The aim of this study is to
use a standardized statistical procedure to assess the realism of the
simulated MJO, in particular the MJO convection-wind coupling.
Results show that upper- and lower-level zonal winds are very well
reproduced, as they display the correct MJO spatial and vertical structure,
phase speed and space-time power spectrum. On the other hand, the
model output exhibits a lack of organization and a weak propagation in
the OLR, specific humidity and precipitation. Overall, this study reveals
that the MM5 model is able to reproduce effectively the MJO circulation
without the associated convection.
Compressible signal recovery arises in many applications
from medical imaging to data mining. Given a signal
compressible with respect to some orthonormal basis, we
wish to reconstruct the signal accurately from few linear
measurements. In this talk I will discuss the major
approaches to this recovery as well as a new algorithm
CoSaMP which provides the advantages from both approaches
and is thus optimal in every important aspect.
In this study we extend this work by considering the
impact of wave-ozone feedbacks on the modulation of both
troposphere-generated planetary waves and the zonally
averaged wind in the extratropical stratosphere. Results
are generated using a quasi-geostropic beta-plane model
incorporating equations for ozone photochemistry, mean
zonal wind and potential vorticity. Results are viewed
in the context of the interactions between wave-mean flow
and wave-ozone feedbacks and the stratospheric circulation.
Some statistical diagnostics to evaluate the Madden-Julian Oscillation in the MM5 model
Erwan Monier, Bryan C. Weare
CoSaMP:Iterative Signal Recovery from Incomplete and Inaccurate Samples
Deanna Needell, Joel Tropp