 |
| Titel |
The Modulation of Tropopause-level Wave Breaking by the Madden Julian Oscillation |
| VerfasserIn |
R. W. Moore, O. Martius, T. Spengler, H. C. Davies |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250021348
|
|
|
|
|
|
| Zusammenfassung |
| The Madden Julian Oscillation (MJO), a large-scale coupled pattern between tropical deep
convection and atmospheric circulation, is known to be the dominant source of intraseasonal
variability in the tropics. Its impacts, however, are not limited to tropical regions: latent heat
release associated with MJO convection can force planetary scale Rossby wave trains that
propagate over the globe along the dynamical tropopause. On the synoptic scale, propagating
Rossby wave trains can culminate in Rossby wave breaking, a process that generates
so-called potential vorticity (PV) streamers. PV streamers have been linked to positive
upper-level PV anomalies that can influence surface weather, extreme precipitation events
and the enhanced exchange between the stratosphere and troposphere. The primary goal of
the present study is to investigate the possible relationship between the MJO and PV
streamers.
Ten MJO indices (representing MJO activity at ten specific tropical longitudes) have been
obtained from the Climate Prediction Center for the boreal winter between 1978 and 2001.
The data are subsequently separated into terciles (allowing for the designation of convectively
active and suppressed periods of the MJO) and compared with a unique PV streamer dataset
that has been previously computed from ECMWF Reanalysis data (ERA-40). The
streamer dataset allows for the dynamically useful separation of streamers into
cyclonically and anticyclonically breaking waves, referred to as LC2 and LC1 streamers,
respectively.
Statistically significant differences are found regarding the amount, location and type of
PV streamers during different phases of the MJO. When the MJO is convectively active over
the Indian Ocean and Indonesia, the north central pacific is dominated by a positive 500
hPa height anomaly, a co-located reduction in LC2 streamers and increased LC1
streamers to the south and southeast. As the convection enters the western Pacific warm
pool and approaches the international dateline, a distinct regime shift occurs: over
an approximately 10-15 day period, a negative 500 hPa height anomaly forms,
supplanting the previous positive anomaly. Subsequent to this time, the negative height
anomaly strengthens and there is a significant increase (decrease) in LC1 (LC2)
streamers.
To illustrate the connection between the MJO, Rossby wave breaking and surface weather
in the extratropics, a comparison between PV streamers and surface cyclone frequency is
made. A fairly good agreement between LC2 streamer and surface cyclone frequency
anomalies throughout the life cycle of the MJO is found in the north Pacific basin, further
highlighting the ability of organized tropical convection to modulate extratropical weather. |
|
|
|
|
|
|