Contrail study with ground-based cameras

Schumann, U.; Hempel, Rolf; Flentje, H.; Garhammer, Markus; Graf, Kaspar; Kox, Stephan; Lößlein, Horst; Mayer, Bernhard

doi:10.5194/amt-6-3597-2013

Cited by 24 publications

(26 citation statements)

References 38 publications

(59 reference statements)

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“…The contrail model bridges the gap between the different scales of the aircraft wake and the global atmosphere. Various of the model results compare reasonably well with observations (Voigt et al, 2010;Jeßberger et al, 2013;Schumann and Graf, 2013;Schumann et al, 2013a, b). In the past, the model has been run in an offline mode for given meteorological fields, without exchange of humidity between contrails and background air.…”

Section: U Schumann Et Al: Dehydration Effects From Contrails In a supporting

confidence: 59%

Dehydration effects from contrails in a coupled contrail–climate model

et al. 2015

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Abstract. The uptake of water by contrails in icesupersaturated air and the release of water after ice particle advection and sedimentation dehydrates the atmosphere at flight levels and redistributes humidity mainly to lower levels. The dehydration is investigated by coupling a plumescale contrail model with a global aerosol-climate model. The contrail model simulates all the individual contrails forming from global air traffic for meteorological conditions as defined by the climate model. The computed contrail cirrus properties compare reasonably with theoretical concepts and observations. The mass of water in aged contrails may exceed 10 6 times the mass of water emitted from aircraft. Many of the ice particles sediment and release water in the troposphere, on average 700 m below the mean flight levels. Simulations with and without coupling are compared. The drying at contrail levels causes thinner and longer-lived contrails with about 15 % reduced contrail radiative forcing (RF). The reduced RF from contrails is on the order of 0.06 W m −2 , slightly larger than estimated earlier because of higher soot emissions. For normal traffic, the RF from dehydration is small compared to interannual variability. A case with emissions increased by 100 times is used to overcome statistical uncertainty. The contrails impact the entire hydrological cycle in the atmosphere by reducing the total water column and the cover by high-and low-level clouds. For normal traffic, the dehydration changes contrail RF by positive shortwave and negative longwave contributions on the order of 0.04 W m −2 , with a small negative net RF. The total net RF from contrails and dehydration remains within the range of previous estimates.

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Section: U Schumann Et Al: Dehydration Effects From Contrails In a supporting

confidence: 59%

Dehydration effects from contrails in a coupled contrail–climate model

et al. 2015

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“…This plot includes the SCOUT-O3 results as if they were contrail cirrus. The data extend the available information for long-lived contrails and low tem- (Schumann et al, 2015) with minimum and maximum values and white lines representing 10, 50, and 90 % percentiles versus age, and the black symbols with error bars are the results from previous in situ and remote sensing measurements . The colored symbols are the data from Table 3 for events E1 to E10, 30 November 2005.…”

Section: Arguments For Stratospheric Hector Cirrus Being Caused By Comentioning

confidence: 56%

“…Contrails are generally expected to survive several minutes, essentially the wake vortex phase, only as long as ambient humidity exceeds ice saturation (Paoli and Shariff, 2016;Unterstrasser, 2016), though contrails have also often been observed below ice saturation (Kübbeler et al, 2011;Jeßberger et al, 2013). If contrails persist long for icesubsaturated conditions, the contrail coverage could be larger than expected (Schumann et al, 2015;Bock and Burkhardt, 2016;Chen and Gettelman, 2016).…”

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confidence: 99%

Long-lived contrails and convective cirrus above the tropical tropopause

et al. 2017

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This study has two objectives: (1) it characterizes contrails at very low temperatures and (2) it discusses convective cirrus in which the contrails occurred. (1) Long-lived contrails and cirrus from overshooting convection are investigated above the tropical tropopause at low temperatures down to −88 °C from measurements with the Russian high-altitude research aircraft M-55 "Geophysica", as well as related observations during the SCOUT-O3 field experiment near Darwin, Australia, in 2005. A contrail was observed to persist below ice saturation at low temperatures and low turbulence in the stratosphere for nearly 1 h. The contrail occurred downwind of the decaying convective system "Hector" of 16 November 2005. The upper part of the contrail formed at 19 km altitude in the tropical lower stratosphere at ∼ 60 % relative humidity over ice at −82 °C. The ∼ 1 h lifetime is explained by engine water emissions, slightly enhanced humidity from Hector, low temperature, low turbulence, and possibly nitric acid hydrate formation. The long persistence suggests large contrail coverage in case of a potential future increase of air traffic in the lower stratosphere. (2) Cirrus observed above the strongly convective Hector cloud on 30 November 2005 was previously interpreted as cirrus from overshooting convection. Here we show that parts of the cirrus were caused by contrails or are mixtures of convective and contrail cirrus. The in situ data together with data from an upward-looking lidar on the German research aircraft "Falcon", the CPOL radar near Darwin, and NOAA-AVHRR satellites provide a sufficiently complete picture to distinguish between contrail and convective cirrus parts. Plume positions are estimated based on measured or analyzed wind and parameterized wake vortex descent. Most of the non-volatile aerosol measured over Hector is traceable to aircraft emissions. Exhaust emission indices are derived from a self-match experiment of the Geophysica in the polar stratosphere in 2010. The number of ice particles in the contrails is less than 1 % of the number of non-volatile aerosol particles, possibly because of sublimation losses and undetected very small ice particles. The radar data show that the ice water content in convective overshoots is far higher than measured along the flight path. These findings add insight into overshooting convection and are of relevance with respect to hydration of the lower stratosphere

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“…Most of the systems developed in the last decade are similarly based on a digital camera coupled with an upwardlooking fish-eye lens (e.g., Souza-Echer et al, 2006;Seiz et al, 2007;Calbó and Sabburg, 2008;Jayadevan et al, 2015). Cazorla et al (2008) used a CCD camera for the purpose of cloud cover estimation and characterization.…”

Section: Rapace Systemmentioning

confidence: 99%

ELIFAN, an algorithm for the estimation of cloud cover from sky imagers

et al. 2019

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Abstract. In the context of a network of sky cameras installed on atmospheric multi-instrumented sites, we present an algorithm named ELIFAN, which aims to estimate the cloud cover amount from full-sky visible daytime images with a common principle and procedure. ELIFAN was initially developed for a self-made full-sky image system presented in this article and adapted to a set of other systems in the network. It is based on red-to-blue ratio thresholding for the distinction of cloudy and cloud-free pixels of the image and on the use of a cloud-free sky library, without taking account of aerosol loading. Both an absolute (without the use of a cloud-free reference image) and a differential (based on a cloud-free reference image) red-to-blue ratio thresholding are used. An evaluation of the algorithm based on a 1-year-long series of images shows that the proposed algorithm is very convincing for most of the images, with about 97 % of relevance in the process, outside the sunrise and sunset transitions. During those latter periods, however, ELIFAN has large difficulties in appropriately processing the image due to a large difference in color composition and potential confusion between cloud-free and cloudy sky at that time. This issue also impacts the library of cloud-free images. Beside this, the library also reveals some limitations during daytime, with the possible presence of very small and/or thin clouds. However, the latter have only a small impact on the cloud cover estimate. The two thresholding methodologies, the absolute and the differential red-to-blue ratio thresholding processes, agree very well, with departure usually below 8 % except in sunrise–sunset periods and in some specific conditions. The use of the cloud-free image library gives generally better results than the absolute process. It particularly better detects thin cirrus clouds. But the absolute thresholding process turns out to be better sometimes, for example in some cases in which the sun is hidden by a cloud.

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Contrail study with ground-based cameras

Cited by 24 publications

References 38 publications

Dehydration effects from contrails in a coupled contrail–climate model

Dehydration effects from contrails in a coupled contrail–climate model

Long-lived contrails and convective cirrus above the tropical tropopause

ELIFAN, an algorithm for the estimation of cloud cover from sky imagers

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