Using GPS data to study the global tropopause

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Using GPS data to studythe global tropopause
Bill Randel ACD/NCAR
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Vertical temperature profile
tropopause (tropics)
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Vertical temperature profile
tropical tropopause
midlatitude tropopause
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Latitudinal structure of the tropopause
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Latitudinal structure of the tropopause
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Ozone
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The tropopause is interesting because

• boundary between stratosphere and troposphere
• (air masses with different chemical and
• dynamical characteristics)
• tropical tropopause sets boundary condition for
  air
• entering the stratosphere (key for water
  vapor
• also for short-lived chemical species)
• details of extratropical mass and chemical fluxes
  poorly known
• relevant for understanding climate variability
  and
• change (a sensitive indicator of climate
  change?)

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• GPS data are particularly useful for tropopause
  studies because of their high vertical resolution
  
• Much of the temperature variability is on scales
• lt 5 km, poorly resolved by nadir sounding
  satellites
• Two science problems
• Tropical tropopause variability
• Long-term changes in global tropopause

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Tropical tropopause temperatures
NH winter climatology
deep convection
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Variability of tropopause temperature
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Sample of GPS tropical temperature profiles
note enhanced variability above 15 km
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Kelvin waves near the tropopause
eastward traveling Kelvin waves
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Kelvin wave vertical structure
tropopause
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Correlation of waves with transient deep
convection
wave variance at 17 km
OLR near Indonesia
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Residual temperature variance (small scales)
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Residual (small-scale) wave variance
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Model simulation of gravity waves forced by deep
convection
Alexander and Holton, 2000
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Gravity waves interacting with a critical level
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Gravity waves interacting with a critical level
critical level
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Residual (small-scale) wave variance
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Long-term changes in global tropopause

• Science issues
• Is the tropopause a sensitive indicator of
  climate change?
• What changes have occurred, and what has caused
  them?
• Can we accurately model tropopause variability
  (and change)?

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Contributions of Anthropogenic and Natural
Forcing to Recent Tropopause Height
ChangesSanter et al.Science, July 2003
observations (NCEP data)
climate model with changing CO2, ozone, aerosols,
...
decrease in tropopause pressure (increase
in altitude)
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Extratropical temperature profiles often have
multiple tropopauses
radiosonde at Charleston SC (lat 32 N)
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statistical distribution of tropopause heights
from radiosondes at Charleston 1950-2003
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Tropopause structure associated with
developing baroclinic wave
Shapiro, 1978
double tropopause
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aircraft ozone measurements
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two examples from GPS data
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statistics at Charleston from radiosonde and GPS
data
radiosondes
GPS
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statistics at Annette Island, AK (latitude 55 N)
GPS
radiosondes
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seasonal variation of profiles with multiple
tropopauses
radiosondes
GPS
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tropopause climatology from GPS data
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Where do multiple tropopauses occur? A GPS
climatology
January
July
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Key points

• Multiple tropopauses often occur in extratropics
• (mean tropopause is a misnomer)
• GPS statistics agree well with (isolated)
  radiosondes
• (can use GPS data to study global
  variability)
• Use caution in studying long-term variability

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long-term variability in occurrence of
multiple tropopauses
are increases in mean height attributable to
more frequent upper-level tropopauses?
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How do models simulate tropopause variability
(and change)?
tropopause statistics from WACCM
note absence of second peak
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Some uses for COSMIC data

• study ubiquitous waves in UTLS
• coupling with cloud parameters and chemical data
• (e.g. NASA A-train satellite data)
• UTLS initiative at NCAR
• (HIAPER, satellites and models)

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12 km snapshot of ozone from MOZART3
Courtesy Doug Kinnison