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| Titel |
Stratospheric gravity waves at southern hemisphere orographic hotspots: 2003-2014 AIRS/Aqua observations |
| VerfasserIn |
Lars Hoffmann, Alison W. Grimsdell, M. Joan Alexander |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140251
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| Publikation (Nr.) |
 EGU/EGU2017-3614.pdf |
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| Zusammenfassung |
| Stratospheric gravity waves from small-scale orographic sources are currently not
well-represented in general circulation models. This may be a reason why many simulations
have difficulty reproducing the dynamical behaviour of the southern hemisphere polar
vortex in a realistic manner. Here we discuss a 12-year record (2003 – 2014) of
stratospheric gravity wave activity at southern hemisphere orographic hotspots as observed
by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics
and Space Administration’s (NASA’s) Aqua satellite. We introduce a simple and
effective approach, referred to as the ‘two-box method’, to detect gravity wave
activity from infrared nadir sounder measurements and to discriminate between
gravity waves from orographic and other sources. From austral mid fall to mid
spring (April – October) the contributions of orographic sources to the observed
gravity wave occurrence frequencies were found to be largest for the Andes (90%),
followed by the Antarctic Peninsula (76%), Kerguelen Islands (73%), Tasmania
(70%), New Zealand (67%), Heard Island (60%), and other hotspots (24 – 54%).
Mountain wave activity was found to be closely correlated with peak terrain altitudes,
and with zonal winds in the lower troposphere and mid stratosphere. We propose
a simple model to predict the occurrence of mountain wave events in the AIRS
observations using zonal wind thresholds at 3 hPa and 750 hPa. The model has
significant predictive skill for hotspots where gravity wave activity is primarily due to
orographic sources. It typically reproduces seasonal variations of the mountain
wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from
near zero to over 60% with mean absolute errors of 4 – 5 percentage points. The
prediction model can be used to disentangle upper level wind effects on observed
occurrence frequencies from low level source and other influences. The data and
methods presented here can help to identify interesting case studies in the vast
amount of AIRS data, which could then be further explored to study the specific
characteristics of stratospheric gravity waves from orographic sources and to support model
validation.
Reference: Hoffmann, L., Grimsdell, A. W., and Alexander, M. J.: Stratospheric
gravity waves at Southern Hemisphere orographic hotspots: 2003–2014 AIRS/Aqua
observations, Atmos. Chem. Phys., 16, 9381-9397, doi:10.5194/acp-16-9381-2016, 2016. |
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