Tracing troposphere-to-stratosphere transport above a mid-latitude deep convective system

Max Planck Institute for Chemistry, Mayence, Rheinland-Pfalz, Germany
ATMOSPHERIC CHEMISTRY AND PHYSICS (Impact Factor: 5.05). 05/2004; 4(3). DOI: 10.5194/acp-4-741-2004
Source: DOAJ


Within the project SPURT (trace gas measurements in the tropopause region) a variety of trace gases have been measured in situ in order to investigate the role of dynamical and chemical processes in the extra-tropical tropopause region. In this paper we report on a flight on 10 November 2001 leading from Hohn, Germany (52ºN) to Faro, Portugal (37ºN) through a strongly developed deep stratospheric intrusion. This streamer was associated with a large convective system over the western Mediterranean with potentially significant troposphere-to-stratosphere transport. Along major parts of the flight we measured unexpectedly high NOy mixing ratios. Also H2O mixing ratios were significantly higher than stratospheric background levels confirming the extraordinary chemical signature of the probed air masses in the interior of the streamer. Backward trajectories encompassing the streamer enable to analyze the origin and physical characteristics of the air masses and to trace troposphere-to-stratosphere transport. Near the western flank of the intrusion features caused by long range transport, such as tropospheric filaments characterized by sudden drops in the O3 and NOy mixing ratios and enhanced CO and H2O can be reconstructed in great detail using the reverse domain filling technique. These filaments indicate a high potential for subsequent mixing with the stratospheric air. At the south-western edge of the streamer a strong gradient in the NOy and the O3 mixing ratios coincides very well with a sharp gradient in potential vorticity in the ECMWF fields. In contrast, in the interior of the streamer the observed highly elevated NOy and H2O mixing ratios up to a potential temperature level of 365 K and potential vorticity values of maximum 10 PVU cannot be explained in terms of resolved troposphere-to-stratosphere transport along the backward trajectories. Also mesoscale simulations with a High Resolution Model reveal no direct evidence for convective H2O injection up to this level. Elevated H2O mixing ratios in the ECMWF and HRM model are seen only up to about tropopause height at 340 hPa and 270hPa, respectively, well below flight altitude of about 200 hPa. However, forward tracing of the convective influence as identified by satellite brightness temperature measurements and counts of lightning strokes shows that during this part of the flight the aircraft was closely following the border of an air mass which was heavily impacted by convective activity over Spain and Algeria. This is evidence that deep convection at mid-latitudes may have a large impact on the tracer distribution of the lowermost stratosphere reaching well above the thunderstorms anvils as claimed by recent studies using cloud-resolving models.

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Available from: M. I. Hegglin
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    • "The authors use aircraft data and infrared satellite brightness temperature to associate the observed variability with coincident convection. [6] A considerable amount of attention has been given to the occurrence of convection that overshoots the lapse-rate tropopause [e.g., Poulida et al., 1996; Fischer et al., 2003; Wang, 2003; Hegglin et al., 2004; Ray et al., 2004; Setvák et al., 2008; Bedka et al., 2009; Pan and Munchak, 2011]. Although the chemical impacts of overshooting convection and convective injection into stratospheric intrusions may be comparable (both mix tropospheric boundary layer and stratospheric air), they occur under significantly different dynamical conditions. "
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    ABSTRACT: Stratospheric intrusions (tropopause folds) are known to be major contributors to stratosphere-troposphere exchange. The specific mixing processes that lead to irreversible exchange between stratospheric intrusions and the surrounding troposphere, however, are not entirely understood. This study presents direct observations of moist convection penetrating into stratospheric intrusions. The characteristics of convective injection are shown by using in situ aircraft measurements, radar reflectivities, and model analyses. Convective injection is observed at altitudes up to 5 km above the bottom of a stratospheric intrusion. Aircraft measurements from the Stratosphere-Troposphere Analyses of Regional Transport 2008 (START08) experiment show that convective injection in stratospheric intrusions can be uniquely identified by coincident observations of water vapor greater than about 100 ppmv and ozone greater than about 125 ppbv. Trajectory analyses show that convective injection can impact transport in both directions: from troposphere to stratosphere and from stratosphere to troposphere. We present a conceptual model of the synoptic meteorological conditions conducive to convective injection in stratospheric intrusions. In particular, convective injection is found to be associated with a "split front" where the upper-level frontal boundary outruns the surface cold front.
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    • "Many publications have examined the stratosphere‐ troposphere exchange and the resulting ozone flux, in terms of its magnitude, seasonality and geographic pattern [e.g., Gettelman et al., 1997; Roelofs and Lelieveld, 1997; Olsen et al., 2004; Hsu et al., 2005]. Others have examined the meteorological processes that drive STE, such as, tropopause folds near jet streams [Sprenger et al., 2003, Figure 3b], wave breaking [Scott et al., 2001], cutoff lows [Ebel et al., 1991], mid‐latitude deep convection [Poulida et al., 1996; Fischer et al., 2003; Gray, 2003; Hegglin et al., 2004]. [13] The link between deep convection and the STE O 3 flux has only been found for extreme events on a case‐study basis. "
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    • "[3] It is now clear that convection can also penetrate into the extratropical stratosphere. The impacts of convection are mainly seen in the so-called lowermost stratosphere [Poulida et al., 1996; Fischer et al., 2003; Hegglin et al., 2004; Hess, 2005], that part of the stratosphere with potential temperature q < 380 K [Hoskins, 1991]. But there is also evidence that convection can reach higher, into the overworld (q > 380 K), and have important impacts there [Fromm and Servranckx, 2003; Wang, 2003; Livesey et al., 2004; Jost et al., 2004], particularly in the amount of water vapor [e.g., Dessler and Sherwood, 2004; Hanisco et al., 2007]. "
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