Wave modulation of the extratropical tropopause inversion layer
This study aims to quantify how much of the observed strength and variability in the zonal-mean extratropical tropopause inversion layer (TIL) comes from the modulation of the temperature field and its gradients around the tropopause by planetary- and synoptic-scale waves. By analyzing high-resoluti...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/4093/2017/acp-17-4093-2017.pdf |
| Summary: | This study aims to quantify how much of the observed strength and variability
in the zonal-mean extratropical tropopause inversion layer (TIL) comes from
the modulation of the temperature field and its gradients around the
tropopause by planetary- and synoptic-scale waves. By analyzing
high-resolution observations, it also puts other TIL enhancing mechanisms
into context.<br><br>Using gridded Global Positioning System radio occultation (GPS-RO)
temperature profiles from the COSMIC mission (2007–2013), we are able to
extract the extratropical wave signal by a simplified wavenumber–frequency
domain filtering method and quantify the resulting TIL enhancement. By
subtracting the extratropical wave signal, we show how much of the TIL is
associated with other processes, at mid- and high latitudes, for both
hemispheres and all seasons.<br><br>The transient and reversible modulation by planetary- and synoptic-scale
waves is almost entirely responsible for the TIL in midlatitudes. This means
that wave-mean flow interactions, inertia–gravity waves and the residual
circulation are of minor importance for
the strength and variability in the midlatitude TIL.<br><br>At polar regions, the extratropical wave modulation is dominant for the TIL
strength as well, but there is also a clear fingerprint from sudden
stratospheric warmings (SSWs) and final warmings in both hemispheres.
Therefore, polar vortex breakups are partially responsible for the observed
polar TIL strength in winter (if SSWs occur) and spring. Also, part of the
polar summer TIL strength cannot be explained by extratropical wave
modulation.<br></br>We suggest that our wave modulation mechanism integrates several TIL
enhancing mechanisms proposed in previous literature while robustly
disclosing the overall outcome of the different processes involved. By analyzing observations only, our study
identifies which mechanisms dominate the extratropical TIL strength and their
relative contribution. It remains to be
determined, however, which roles the different planetary- and synoptic-scale
wave types play within the total extratropical wave modulation of the TIL,
as well as what causes the observed amplification of extratropical waves near the
tropopause. |
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| ISSN: | 1680-7316 1680-7324 |