A step forward in predicting the evolution of volcanic plumes
Using the MIMOSA model developped within the LATMOS 1 together with modules able to transport aerosols, LATMOS scientists took advantage of the CALIPSO satellite observations and meteorological forecasts to study the evolution of a volcanic plume at a high spatial resolution (a few kilometers) and predict its position and optical properties several days in advance.
Dust particle loads in the vicinity of the tropopause after explosive volcanic eruptions have a potential impact on both climate and air traffic, enhanced by their long residence time in a stratified medium and isentropic horizontal motions around the earth. Forecasting their transport is complex as horizontal motions often induce filamentary small scale structures.
The present highlight features our recent investigations on the simulation and forecasts of the distribution of stratospheric dusts injected in the stratosphere after the recent eruption of Mount Merapi (Java Island - Indonesia), which started on November 3rd, 2010. This analysis corresponds to a one-month assimilation of the last expedited data from the spaceborne lidar
CALIOP
performed by a model coupling the
MIMOSA
high resolution advection model to a module resolving the microphysics and optics of stratospheric particles, considering volcanic aerosols in this case. The model, here running on the 380K isentrope (roughly 15-16km), adjusts at every time step (6 hours) and in each grid cell (2 points per degree) the aerosol load so that the associated optical backscatter ratio at 532nm matches the measurements performed by CALIOP on board
CALIPSO
(data can be obtained from
NASA
and, in France, from
ICARE/GTD
in Lille). Optical properties derived from the CALIOP lidar are used to distinguish the volcanic plume from ice clouds before assimilation. The lidar-measured backscatter ratio can be regarded as the relative contribution of aerosols to air molecules, unity meaning no aerosols. It is calculated from the aerosol distribution that depends on the size, shape and composition of the particles. Particle advection, diffusion and sedimentation will cause the plume to gradually fade as time goes by. The full particle field is actually calculated, the model ideally complementing an accurate yet windowed instrumental coverage.
This new first-order assimilation of spaceborne lidar measurements may be valuable in investigating the various properties of such volcanic plumes, in terms of microphysical, dynamical and radiative impacts. Volcanic eruptions have long been associated to potential temperature cooling due to the albedo effect. Besides, a heterogeneous chemistry on the surface of volcanic aerosols is also known to cause relative local ozone depletion. Global simulations encompassing microphysical processes and fueled by global measurements may thus provide material to further investigate these issues and interactions between ozone and climate.
This simulation uses the ECMWF
2
meteorological analyses and forecasts, and a prognostic volcanic plume may be simulated between 3 and 5 days in advance. This output could find a direct short-term application as a measurement planning tool for ground-based lidar instruments, thus easing the necessary validation step.
Notes
- Laboratoire Atmosphères, Milieux, Observations Spatiales (IPSL, CNRS/UPMC/UVSQ)
- European Centre for Medium-Range Weather Forecasts
Contacts
Julien Jumelet, LATMOS / IPSL, Tél. : (33)1 44 27 84 43, e-mail : julien.jumelet @ latmos.ipsl.fr
Jean-Paul Vernier, NASA / LaRC, e-mail : jeanpaul.vernier @ nasa.gov