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| Titel |
Climatology and trend of the extratropical dynamical and thermal tropopauses in ERA-40 |
| VerfasserIn |
Moises G. Chamorro, Guadalupe Saenz, David Barriopedro, Juan A. Añel |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250031915
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| Zusammenfassung |
| A climatological comparison of the extratropical tropopause pressure obtained from the
dynamical and thermal definitions is presented using the ERA-40 reanalysis for the period
1960-2001 and Northern Hemisphere. Temperature (T) at isobaric levels between 500
hPa and 70 hPa and isentropic potential vorticity (PVθ) between 270 and 440 K
were extracted from the 60 vertical levels of the model at 2.5ºx2.5º and 6 hours
resolution.
Following the WMO criterion, the thermal tropopause is defined as the first layer where
the temperature lapse rate is less than 2 K km-1 for a depth of at least 2 km. The dynamical
tropopause is determined from the lowest vertical level where PVθ exceeds a critical value. A
critical threshold of PVθ = 3.5 PVU was adopted, following Hoerling et al (1991). The
pressure at the thermal (dynamical) tropopause was computed by linear interpolation
assuming that p varies with T1-k (θ1-k).
Results reveal good agreement between both definitions. Maximum discrepancies tend to
occur at subtropical latitudes. Both definitions capture well global and regional signatures of
the atmospheric circulation, including strong gradients of the tropopause pressure around the
subtropical jet stream and maximum standard deviations over preferred regions of storm
tracks.
A linear regression applied to the extratropical seasonal mean values confirms the
decreasing trend in tropopause pressure for the second half of the twentieth century. |
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