 |
| Titel |
Climatological Ertel's potential-vorticity flux and mean meridional circulation in the extratropical troposphere - lower stratosphere |
| VerfasserIn |
J. Bartels, D. Peters, G. Schmitz |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 16, no. 2 ; Nr. 16, no. 2, S.250-265 |
| Datensatznummer |
250013161
|
| Publikation (Nr.) |
 copernicus.org/angeo-16-250-1998.pdf |
|
|
|
|
|
| Zusammenfassung |
We investigated to what extent the
isentropic, non-geostrophic formulation of zonally averaged circulation derived
for stratospheric conditions is applicable to climatological transport in the
extratropical troposphere and lower stratosphere. The study is based on 10 years
of daily data of ECMWF analysis and on the ECHAM3 climate model of the German
Climate Computing Centre. The main result is a scalar isentropic mixing
coefficient, Kyy, and a mean meridional transport circulation
consistently derived from the same data base. For both data sources, isentropic
mean meridional circulation is derived from horizontal mass flow rate for 4
representative months. Alternatively, a mean meridional circulation is
calculated from total diabatic heating rates of the ECHAM3 model. It is shown
that only the latter is in good agreement with the ECMWF mean meridional
circulation. Isentropic analysis also comprises the seasonal cycle of the
climatological meridional gradient and flux of Ertel's potential vorticity (PV).
Application of Tung's flux-gradient relation yields that for all seasons Kyy
is positive in height-latitude regions where statistical significance is
reached. Large Kyy values, marking regions of more efficient
mixing, have been found in the subtropical vertical band of weak westerly wind
and in mid-latitudes in regions of upward-propagating baroclinic wave activity
in the middle and upper troposphere. Based on the ECMWF data and results of
baroclinic-wave behaviour, strong indications are presented that positive
zonally averaged PV flux polewards of the jet core in the NH is strengthened by
stationary waves and nonlinear effects. Reduced eddy transport is apparent in
winter and spring slightly below the subtropical tropopause jet. The seasonal
cycle of Kyy from ECHAM3 data is to a great extent in
agreement with the result based on ECMWF analysis. In the model, reduced
interannual variability enlarges the height-latitude range where sign of Kyy
is significant.
Key words. Meteorology and atmospheric dynamics ·
Climatology · General circulation · Middle atmosphere is significant. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|