The extratropical tropopause inversion layer observed with GPS data

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The extratropical tropopause inversion
layerobserved with GPS data
Bill Randel, NCAR
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Using GPS temperatures to study the extratropical
tropopause
1) Observational characteristics of
double tropopauses Occurs frequently, related
to interaction between tropics and
extratropics Preprint on my web site
acd.ucar.edu/randel (see also Schmidt
et al., GRL, 2006) 2) The tropopause inversion
layer
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What is the tropopause inversion layer?
Birner, JGR, 2006
average vertical structure from high-resolution
radiosondes near 45o N, calculated using
ground-based and tropopause-based coordinates
temp
stability
tropopause- based coordinate
sharp maximum in N2
ground-based coordinate
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ground-based coordinates
tropopause-based coordinates
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• Key points
• persistent inversion layer observed above
  extratropical tropopause
• observed using high resolution radiosondes
  (limited US network)
• only evident in tropopause-based coordinates
• important (?) for understanding dynamics of
  tropopause,
• and transport in tropopause region
• 5) no theoretical explanation yet

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examples using GPS data
temp
stability
height relative to tropopause
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Hypothesis TIL mainly associated with
anticyclones
Wirth, JAS, 2003
cyclonic circulation
average
anticyclonic
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sampling GPS data according to upper tropospheric
vorticity
contours 200 hPa relative vorticity
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distribution of vorticity at GPS locations DJF,
30-60 N
height of tropopause binned by vorticity
anticyclonic cyclonic
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profiles binned according to vorticity
temp
stability
inversion evident for all circulation types
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global structure of stability in tropopause
coordinates
shaded N2 gt 4.5
maximum in both hemispheres both seasons
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global structure of stability in tropopause
coordinates
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longitudinal structure of inversion layer
temperature difference Ztrop2 km - Ztrop
NH, DJF SH, JAS
weak maximum
result relatively little zonal structure during
winter (and none in summer)
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Summary Tropopause inversion layer is evident
in GPS temperatures Evident for all types of
circulation (cyclonic -gt anticyclonic)
stronger for anticyclonic flow, as expected
(but presence for cyclonic flow
unexplained) Ubiquitous occurrence both
hemispheres, all seasons Question what
causes the inversion layer?
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Balanced Structure in Extratropical Cyclone
(Hoskins et al. 1985)
warm
isentropes
cold
winds
low tropopause