The Extratropical Upper Troposphere and Lower Stratosphere

Gettelman, Andrew; Hoor, Peter; Pan, Laura L.; Randel, William J.; Hegglin, Michaela I.; Birner, Thomas

doi:10.1029/2011rg000355

Cited by 379 publications

(470 citation statements)

References 253 publications

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“…This temporary structure was tentatively assigned to the Redoubt eruption, HYSPLIT giving clear evidence on 26 May. A part of the Redoubt aerosol structure in the June examples was most likely advected also below the thermal tropopause, in agreement with the idea of a "mixing zone" around the thermal tropopause (e.g., Gettelman et al, 2011). This interpretation is supported by the fact that on 5 and 30 June the relative humidity (RH) for both the Munich and the Innsbruck (37 km to the southeast; launches at 03:00 UTC) radiosonde stayed below 50 % above 8.5 km, which suggests the absence of cirrus clouds in the uppermost troposphere.…”

Section: Increase Of Volcanic Activity Between 2006 and 2011supporting

confidence: 55%

35 yr of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

et al. 2013

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Lidar measurements at Garmisch-Partenkirchen (Germany) have almost continually delivered backscatter coefficients of stratospheric aerosol since 1976. The time series is dominated by signals from the particles injected into or formed in the stratosphere due to major volcanic eruptions, in particular those of El Chichon (Mexico, 1982) and Mt Pinatubo (Philippines, 1991). Here, we focus more on the long-lasting background period since the late 1990s and 2006, in view of processes maintaining a residual lower-stratospheric aerosol layer in absence of major eruptions, as well as the period of moderate volcanic impact afterwards. During the long background period the stratospheric backscatter coefficients reached a level even below that observed in the late 1970s. This suggests that the predicted potential influence of the strongly growing air traffic on the stratospheric aerosol loading is very low. Some correlation may be found with single strong forest-fire events, but the average influence of biomass burning seems to be quite limited. No positive trend in background aerosol can be resolved over a period as long as that observed by lidar at Mauna Loa. We conclude that the increase of our integrated backscatter coefficients starting in 2008 is mostly due to volcanic eruptions with explosivity index 4, penetrating strongly into the stratosphere. Most of them occurred in the mid-latitudes. A key observation for judging the role of eruptions just reaching the tropopause region was that of the plume from the Icelandic volcano Eyjafjallajökull above Garmisch-Partenkirchen (April 2010) due to the proximity of that source. The top altitude of the ash above the volcano was reported just as 9.3 km, but the lidar measurements revealed enhanced stratospheric aerosol up to 14.3 km. Our analysis suggests for two or three of the four measurement days the presence of a stratospheric contribution from Iceland related to quasi-horizontal transport, differing from the strong descent of the layers entering Central Europe at low altitudes. The backscatter coefficients within the first 2 km above the tropopause exceed the stratospheric background by a factor of four to five. In addition, Asian and Saharan dust layers were identified in the free troposphere, Asian dust most likely even in the stratosphere

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Section: Increase Of Volcanic Activity Between 2006 and 2011supporting

confidence: 55%

35 yr of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

et al. 2013

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“…Although there are a couple of ground-based lidar observations suggesting the presence of cirrus clouds in the lowermost stratosphere (LMS), a region strongly influenced by isentropic (quasi-horizontal) transport of air masses from the tropics (Gettelman et al, 2011), there are open questions: which microphysical process and specific meteorological conditions foster the formation of ice particles in this specific region, how frequently do these cirrus clouds occur on global scales, and are clouds tops or even complete clouds significantly above the tropopause?…”

Section: R Spang Et Al: Satellite Observations Of Cirrus Clouds In mentioning

confidence: 99%

Satellite observations of cirrus clouds in the Northern Hemisphere lowermost stratosphere

Spang¹,

Günther²,

Riese³

et al. 2015

Atmos. Chem. Phys.

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Abstract.Here we present observations of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) of cirrus cloud and water vapour in August 1997 in the upper troposphere and lower stratosphere (UTLS). The observations indicate a considerable flux of moisture from the upper tropical troposphere into the extratropical lowermost stratosphere (LMS), resulting in the occurrence of highaltitude optically thin cirrus clouds in the LMS.The locations of the LMS cloud events observed by CRISTA are consistent with the tropopause height determined from coinciding radiosonde data. For a hemispheric analysis in tropopause relative coordinates an improved tropopause determination has been applied to the European Centre for Medium-Range Weather Forecasts (ECMWF) temperature profiles. We found that a significant fraction of the cloud occurrences in the tropopause region are located in the LMS, even if a conservative overestimate of the cloud top height (CTH) determination by CRISTA of 500 m is assumed. The results show rather high occurrence frequencies ( ∼ 5 %) up to high northern latitudes (70 • N) and altitudes well above the tropopause (> 500 m at ∼ 350 K and above) in large areas at mid-and high latitudes.Comparisons with model runs of the Chemical Lagrangian Model of the Stratosphere (CLaMS) over the CRISTA period show a reasonable consistency in the retrieved cloud pattern. For this purpose a limb ray tracing approach was applied through the 3-D model fields to obtain integrated measurement information through the atmosphere along the limb path of the instrument. The simplified cirrus scheme implemented in CLaMS seems to cause a systematic underestimation in the CTH occurrence frequencies in the LMS with respect to the observations. The observations together with the model results demonstrate the importance of isentropic, quasi-horizontal transport of water vapour from the subtropics and the potential for the occurrence of cirrus clouds in the lowermost stratosphere and tropopause region.

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“…There is a considerable body of research about the TIL in the extratropics, establishing the TIL as an important feature of the extratropical upper-troposphere and lower-R. Pilch Kedzierski et al: Tropical TIL stratosphere (Gettelman et al, 2011). In the tropics, the transition between the troposphere and the stratosphere is considered to happen over several kilometers, dynamically and chemically (Fueglistaler et al, 2009;Gettelman and Birner, 2007), but less is known about the tropical TIL, as the following review will show.…”

Section: Introductionmentioning

confidence: 99%

The tropical tropopause inversion layer: variability and modulation by equatorial waves

2016

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Abstract. The tropical tropopause layer (TTL) acts as a transition layer between the troposphere and the stratosphere over several kilometers, where air has both tropospheric and stratospheric properties. Within this region, a fine-scale feature is located: the tropopause inversion layer (TIL), which consists of a sharp temperature inversion at the tropopause and the corresponding high static stability values right above, which theoretically affect the dispersion relations of atmospheric waves like Rossby or inertia-gravity waves and hamper stratosphere-troposphere exchange (STE). Therefore, the TIL receives increasing attention from the scientific community, mainly in the extratropics so far. Our goal is to give a detailed picture of the properties, variability and forcings of the tropical TIL, with special emphasis on small-scale equatorial waves and the quasi-biennial oscillation (QBO).We use high-resolution temperature profiles from the COSMIC satellite mission, i.e., ∼ 2000 measurements per day globally, between 2007 and 2013, to derive TIL properties and to study the fine-scale structures of static stability in the tropics. The situation at near tropopause level is described by the 100 hPa horizontal wind divergence fields, and the vertical structure of the QBO is provided by the equatorial winds at all levels, both from the ERA-Interim reanalysis.We describe a new feature of the equatorial static stability profile: a secondary stability maximum below the zero wind line within the easterly QBO wind regime at about 20-25 km altitude, which is forced by the descending westerly QBO phase and gives a double-TIL-like structure. In the lowermost stratosphere, the TIL is stronger with westerly winds. We provide the first evidence of a relationship between the tropical TIL strength and near-tropopause divergence, with stronger (weaker) TIL with near-tropopause divergent (convergent) flow, a relationship analogous to that of TIL strength with relative vorticity in the extratropics.To elucidate possible enhancing mechanisms of the tropical TIL, we quantify the signature of the different equatorial waves on the vertical structure of static stability in the tropics. All waves show, on average, maximum cold anomalies at the thermal tropopause, warm anomalies above and a net TIL enhancement close to the tropopause. The main drivers are Kelvin, inertia-gravity and Rossby waves. We suggest that a similar wave modulation will exist at mid-and polar latitudes from the extratropical wave modes.

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The Extratropical Upper Troposphere and Lower Stratosphere

Cited by 379 publications

References 253 publications

35 yr of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

35 yr of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

Satellite observations of cirrus clouds in the Northern Hemisphere lowermost stratosphere

The tropical tropopause inversion layer: variability and modulation by equatorial waves

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