Solid particles in the tropical lowest stratosphere

Nielsen, Johannes K.; Larsen, N.; Cairo, F.; Donfrancesco, G. Di; Rosen, James M.; Durry, Georges; Held, Gerhard; Pommereau, Jean‐Pierre

doi:10.5194/acp-7-685-2007

Cited by 51 publications

(50 citation statements)

References 41 publications

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“…Also in situ measurements performed over Hector within SCOUT-O3 provide evidence that this storm is hydrating, not dehydrating the TTL and the stratosphere to 2 km above the tropopause (Corti et al, 2008). Similar evidence for the presence of ice particles injected into the lowermost stratosphere by deep convective overshoots had been presented previously for the Hector system by Kelly et al (1993) and for other tropical thunderstorms over Brasil by Nielsen et al (2007).…”

Section: Introductionsupporting

confidence: 58%

The SCOUT-O3 Darwin Aircraft Campaign: rationale and meteorology

et al. 2009

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Abstract. An aircraft measurement campaign involving the Russian high-altitude aircraft M55 Geophysica and the German DLR Falcon was conducted in Darwin, Australia in November and December 2005 as part of the European integrated project SCOUT-O3. The overall objectives of the campaign were to study the transport of trace gases through the tropical tropopause layer (TTL), mechanisms of dehydration close to the tropopause, and the role of deep convection in these processes. In this paper a detailed roadmap of the campaign is presented, including rationales for each flight, and an analysis of the local and large-scale meteorological context in which they were embedded. The campaign took place during the pre-monsoon season which is characterized by a pronounced diurnal evolution of deep convection including a mesoscale system over the Tiwi Islands north of Darwin known as "Hector". This allowed studying in detail the role of deep convection in structuring the tropical tropopause region, in situ sampling convective overshoots above storm anvils, and probing the structure of anvils and cirrus clouds by Lidar and a suite of in situ instruments onboard the two aircraft. The large-scale flow during the first half of the campaign was such that local flights, away from convection, samCorrespondence to: D. Brunner (dominik.brunner@empa.ch) pled air masses downstream of the "cold trap" region over Indonesia. Abundant cirrus clouds enabled the study of active dehydration, in particular during two TTL survey flights. The campaign period also encompassed a Rossby wave breaking event transporting stratospheric air to the tropical middle troposphere and an equatorial Kelvin wave modulating tropopause temperatures and hence the conditions for dehydration.

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Section: Introductionsupporting

confidence: 58%

The SCOUT-O3 Darwin Aircraft Campaign: rationale and meteorology

et al. 2009

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“…Besides polar stratospheric clouds, which are observed at cold temperatures over the Arctic and Antarctic, ice crystals have been observed in the tropical stratosphere as well. The presence of clouds in the tropical stratosphere has been attributed to overshooting convection (Chaboureau et al, 2007;Grosvenor et al, 2007;Nielsen et al, 2007;Corti et al, 2008). This paper shows direct evidence from in-situ measurements for the presence of ice crystals in the tropical stratosphere, immediately above a large convective system, indicating direct transport of cloud particles from the troposphere to the stratosphere.…”

Section: Introductionmentioning

confidence: 64%

Evidence for ice particles in the tropical stratosphere from in-situ measurements

et al. 2009

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Abstract. In-situ ice crystal size distribution measurements are presented within the tropical troposphere and lower stratosphere. The measurements were performed using a combination of a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP), which were installed on the Russian high altitude research aircraft M55 "Geophysica" during the SCOUT-O 3 campaign in Darwin, Australia. One of the objectives of the campaign was to characterise the Hector convective system, which appears on an almost daily basis during the pre-monsoon season over the Tiwi Islands, north of Darwin. In total 90 encounters with ice clouds, between 10 and 19 km altitude were selected from the dataset and were analysed. Six of these encounters were observed in the lower stratosphere, up to 1.4 km above the local tropopause. Concurrent lidar measurements on board "Geophysica" indicate that these ice clouds were a result of overshooting convection. Large ice crystals, with a maximum dimension up to 400 µm, were observed in the stratosphere. The stratospheric ice clouds included an ice water content ranging from 7.7×10 −5 to 8.5×10 −4 g m −3 and were observed at ambient relative humidities (with respect to ice) between 75 and 157%. Three modal lognormal size distributions were fitted to the average size distributions for different potential temperature intervals, showing that the Correspondence to: S. Borrmann (stephan.borrmann@mpic.de) shape of the size distribution of the stratospheric ice clouds are similar to those observed in the upper troposphere.In the tropical troposphere the effective radius of the ice cloud particles decreases from 100 µm at about 10 km altitude, to 3 µm at the tropopause, while the ice water content decreases from 0.04 to 10 −5 g m −3 . No clear trend in the number concentration was observed with altitude, due to the thin and inhomogeneous characteristics of the observed cirrus clouds.The ice water content calculated from the observed ice crystal size distribution is compared to the ice water content derived from two hygrometer instruments. This independent measurement of the ice water content agrees within the combined uncertainty of the instruments for ice water contents exceeding 3×10 −4 g m −3 .Stratospheric residence times, calculated based on gravitational settling, and evaporation rates show that the ice crystals observed in the stratosphere over the Hector storm system had a high potential of humidifying the stratosphere locally.

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“…µSDLA also shows a moist layer above 19 km, which again is close to the balloon float altitude and thus possibly contaminated by outgassing. The relative moistening between 16.5 and 18 km, correlated with a similar increase of CH 4 , was attributed by Durry et al (2006) and Nielsen et al (2007) to the signature of a convective uplift of ice crystals.…”

Section: Collocated Balloon In-situ and Satellites Remote Profilesmentioning

confidence: 86%

Evaluation of balloon and satellite water vapour measurements in the Southern tropical and subtropical UTLS during the HIBISCUS campaign

et al. 2009

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Abstract. Balloon water vapour in situ and remote measurements in the tropical upper troposphere and lower stratosphere (UTLS) obtained during the HIBISCUS campaign around 20 • S in Brazil in February-March 2004 using a tunable diode laser (µSDLA), a surface acoustic wave (SAW) and a Vis-NIR solar occultation spectrometer (SAOZ) on a long duration balloon, have been used for evaluating the performances of satellite borne remote water vapour instruments available at the same latitude and measurement period. In the stratosphere, HALOE displays the best precision (2.5%), followed by SAGE II (7%), MIPAS (10%), and SCIAMACHY (35%), all of which show approximately constant H 2 O mixing ratios between 20-25 km. Compared to HALOE of ±10% accuracy between 0.1-100 hPa, SAGE II and SAOZ show insignificant biases, MIPAS is wetter by 10% and SCIAMACHY dryer by 20%. The currently available GOMOS profiles of 25% precision show a positive vertical gradient in error for identified reasons. Compared to these, the water vapour of the Reprobus Chemistry Transport Model, forced at pressures higher than 95 hPa by the ECMWF analyses, is dryer by about 1 ppmv (20%).In the lower stratosphere between 16-20 km, most notable features are the steep degradation of MIPAS precision below 18 km, and the appearance of biases between instruments far larger than their quoted total uncertainty. HALOE and Correspondence to: N. Montoux (nadege.montoux@latmos.ipsl.fr) SAGE II (after spectral adjustment for reducing the bias with HALOE at northern mid-latitudes) both show decreases of water vapour with a minimum at the tropopause not seen by other instruments or the model, possibly attributable to an increasing error in the HALOE altitude registration. Between 16-18 km where the water vapour concentration shows little horizontal variability, and where the µSDLA balloon measurements are not perturbed by outgassing, the average mixing ratios reported by the remote sensing instruments are substantially lower than the 4-5 ppmv observed by the µSDLA. Differences between µSDLA and HALOE and SAGE II (of the order of −2 ppmv), SCIAMACHY, MIPAS and GOMOS (−1 ppmv) and SAOZ (−0.5 ppmv), exceed the 10% uncertainty of µSDLA, implying larger systematic errors than estimated for the various instruments.In the upper troposphere, where the water vapour concentration is highly variable, AIRS v5 appears to be the most consistent within its 25% uncertainty with balloon in-situ measurements as well as ECMWF. Most of the remote measurements show less reliability in the upper troposphere, losing sensitivity possibly because of absorption line saturation in their spectral ranges (HALOE, SAGE II and SCIA-MACHY), instrument noise exceeding 100% (MIPAS) or imperfect refraction correction (GOMOS). An exception is the SAOZ-balloon, employing smaller H 2 O absorption bands in the troposphere.

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Solid particles in the tropical lowest stratosphere

Cited by 51 publications

References 41 publications

The SCOUT-O3 Darwin Aircraft Campaign: rationale and meteorology

The SCOUT-O3 Darwin Aircraft Campaign: rationale and meteorology

Evidence for ice particles in the tropical stratosphere from in-situ measurements

Evaluation of balloon and satellite water vapour measurements in the Southern tropical and subtropical UTLS during the HIBISCUS campaign

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