Tropical Convective Transport and TTL Structure in the UM global model

1
Tropical Convective Transport and TTL Structure
in the UM global model

• Scott Hosking1, Maria Russo2, Peter Braesicke2,
  John Pyle2
• NERC funded PhD, University of Cambridge
• NCAS Climate, University of Cambridge

Manchester, 21 May 2009
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Transport of VSLS to the Stratosphere

• Possible Transport Pathways
• Direct stratospheric Injection
• Loading the Upper TTL followed by slow ascent
• Quasi-Horizontally from the TTL

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Scientific Questions

• How well is the TTL represented in current
  atmospheric models and how much tropical
  convection reaches the TTL?
• Are there preferential regions and seasons for
  Troposphere-to-Stratosphere exchange?
• Is convection fast and deep enough to loft
  biogenic very short lived species (VSLS) to the
  lower stratosphere?

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Experiments

• We use the UKMO-UM at 60km global resolution and
  run for 30 days to evaluate statistical
  properties of convection.
• We investigate 4 months in 2005 Feb, May, Aug,
  Nov
• Model is evaluated against observations (OLR and
  Precipitation rate)
• We analyse regional and seasonal preferences for
  deep convection overshooting the Q0 level

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Model evaluation Nov
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TTL representation in 60km global UM
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Vertical extent of convection and regional
preference for deep convection
NOAA Satellite
Model mass flux integrated between 12-14 km
Percentage of days with convection overshooting
Q0 level
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Convective Mass flux into the TTL
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Convective Mass flux into the TTL
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Seasonal variations of convective transport
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Conclusions

• The location of tropical deep convection in the
  model is evaluated against monthly mean OLR and
  precipitation from satellite. The model is able
  to capture the pattern of convection and
  correlates well with observations.
• We show that the model representation of the
  surfaces delimiting the TTL is realistic.
• The model shows a regional preference for deep
  convection to occur over the Indian Ocean and the
  Maritime continent in Nov.
• The model shows highest convective transport
  above Q0 level in February compared to other
  months.
• Passive tracers with various lifetimes and
  emission regions have been included in these
  model runs and we plan to investigate preferred
  entry regions into the UTLS and how they vary
  with tracer lifetime and season.