StratosphereTroposphere Exchange:

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StratosphereTroposphere Exchange
Isabel Ramos
Álvaro
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Simulations for an Ozone-like Tracer
Valdebenito
Laura Gallardo
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• We simulate the intrusion and dispersion of
  ozone-like tracer subject to dry deposition and
  photolysis deposition according to the method
  described in Follows and Austin (1992).
• For that purpose we apply the Multiscale
  Atmospheric Transport and Chemistry model (MATCH,
  Robertson et al, 1999). We focus on the
  treatement of the stratospheric influx and the
  subsequent dispersion of the intruded tracer.
• The photolysis rates are derived on-line
  using the procedures included in the
  photochemical scheme of MATCH, designed to
  provide a good description under high and low
  reactive nitrogen regimes. The dry deposition
  flux is proportional to the tracer's
  concentration and the inverse of the sum of the
  aerodynamic and surface resistance (See Robertson
  et al, 1999 for details).

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We use two set of meteorological data to drive
the dispersion model 1) Reanalysis fields from
the European Center for Middle Range Weather
Forecast (ECMWF). These fields have a horizontal
resolution of about 1 or 125 km in the
horizontal and 31 levels in the vertical from the
surface up to about 10 hPa. 2) Dynamically
interpolated ECMWF reanalysis fields using the
dynamical model HIRLAM (High Resolution Limited
Area Model (Undén et al, 2000). These fields
have a horizontal resolution of 0.1 ( 11 km),
every 3 hours. The stratospheric influx is
represented in the model as a boundary condition
(BC), either as a fixed mixing ratio at the top
and lateral boundaries (Dirichlet) or as a mass
flux at the upper and lateral boundaries
(Neumann). At the bottom the only boundary
condition is dry deposition.
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• Performed simulations of intrusions of an O3
  like tracer at the tropopause are very sensitive
  to the treatment of lateral BC. These problems
  are further enhanced by the steep Andean
  topography. We have performed several runs
  testing different model set ups
• 1) Large-scale fields (ECMWF), using Dirichlet BC
  at the top and the lateral boundaries, and zero
  initial conditions (IC)
• 2) High-resolution fields (HIRLAM), using
  Dirichlet BC at the top and the lateral
  boundaries, and zero initial conditions (IC)
• 3) High-resolution fields (HIRLAM), using
  Dirichlet BC at the top and the lateral
  boundaries, and NON-zero initial conditions (IC)
• 4) High-resolution fields (HIRLAM), using
  Dirichlet BC at the top and Neumann BC at the
  lateral boundaries, and zero initial conditions
  (IC)
• The output fields obtained using large-scale
  fields are smooth and selfconsistent and show no
  numerical instabilities or noise. When we
  increase the resolution instabilities and noise
  appear. At first we thought that this was due to
  the use of Dirichlet BC at lateral boundaries or
  the use of zero-initial conditions. This does not
  seem to be the case. Reasons that may explain
  this are connected to the narrow (E-W) domain,
  and the effects of the Andean slope perturbing
  the upper westerly flow.
• To be continued...Any suggestions?

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• References
• Follows, M.J., and Austin, J.F., 1992. A
  zonal average model of the stratospheric
  contributions to the tropospheric ozone budget.
  J.
• Geophys. Res. , 97, 18047-18060.
• Robertson, L., Langner, J., and Engardt, M.
  1999. An Eulerian limited-area atmospheric
  transport model. J. Appl. Met. 38, 190-210.
• Simmons A.J. and J.K. Gibson, 2000. The
  ERA-40 Project Plan, ERA-40 Project Report Series
  No. 1, ECMWF, Reading RG29AX, UK., 63 pp.,
• available from www.ecmwf.int/publications/
• Undén et al, 2002. HIRLAM-5 Scientific
  documentation.
• (Available at http//www.knmi.nl/hirlam/)

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Ozone Like Tracer ... Non Trivial Lateral
Boundaries
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ECMWF (1x1) Nov 1989(Dirichlet BC)
CTOP300 ppb
CEAST1 ppb
CWEST1 ppb
Rapanui
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Hirlam (0.1x0.1) Oct 1999(Higher Resolution,
Dirichlet BC)
CTOP300 ppb
CWEST1 ppb
CEAST1 ppb
Tololo
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Hirlam (0.1x0.1) Oct 1999Non Zero Initial
Conditions
Tololo
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Hirlam (0.1x0.1) Oct 1999(Lateral Boundaries
Conditions as Fluxes, Neumann)
Flux
Flux
Tololo