 |
| Titel |
Sensitivity of the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) to different gravity-wave drag parameterisations |
| VerfasserIn |
P. Mieth, J. L. Grenfell, U. Langematz, M. Kunze |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 22, no. 8 ; Nr. 22, no. 8 (2004-09-07), S.2693-2713 |
| Datensatznummer |
250014957
|
| Publikation (Nr.) |
 copernicus.org/angeo-22-2693-2004.pdf |
|
|
|
|
|
| Zusammenfassung |
| We report the sensitivity of the Berlin Climate
Middle Atmosphere Model (CMAM) to different gravity-wave (GW) parameterisations.
We perform five perpetual January experiments: 1) Rayleigh friction (RF)
(control), 2) non-orographic GWs, 3) orographic GWs, 4) orographic and
non-orographic GWs with no background stress, and 5) as for 4) but with
background stress. We also repeat experiment 4) but for July conditions. Our
main aim is to improve the model climatology by introducing orographic and
non-orographic parameterisations and to investigate the individual effect of
these schemes in the Berlin CMAM. We compare with an RF control to determine
the improvement upon a previously-published model version employing RF.
Results are broadly similar to previously-published works. The runs having
both orographic and non-orographic GWs produce a statistically-significant
warming of 4-8K in the wintertime polar lower stratosphere. These runs also
feature a cooling of the warm summer pole in the mesosphere by 10-15K, more
in line with observations. This is associated with the non-orographic GW
scheme. This scheme is also associated with a heating feature in the winter
polar upper stratosphere directly below the peak GW-breaking region. The runs
with both orographic and non-orographic GWs feature a
statistically-significant deceleration in the polar night jet (PNJ) of
10-20ms-1 in the lower stratosphere. Both orographic and
non-orographic GWs individually produce some latitudinal tilting of the polar
jet with height, although the main effect comes from the non-orographic waves.
The resulting degree of tilt, although improved, is nevertheless still weaker
than that observed. Accordingly, wintertime variability in the zonal mean
wind, which peaks at the edge of the vortex, tends to maximise too far
polewards in the model compared with observations. Gravity-planetary wave
interaction leads to a decrease in the amplitudes of stationary planetary
waves 1 and 2 by up to 50% in the upper stratosphere and mesosphere, more
in line with observations. Comparing modelled and observed Eliassen-Palm
fluxes suggests that planetary wave (PW) breaking occurs too far polewards in
the model. The wind and temperature changes are consistent with changes in
the Brewer-Dobson (BD) circulation. Results suggest that the effect of
enforcing a minimum background wave stress in the McFarlane scheme could be
potentially important. In the Southern Hemisphere (SH) in July, the GW schemes had only a small
impact on the high-latitude lower stratosphere but there featured strong
warming near 0.1hPa. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|