Search results for "Cirrus"
showing 10 items of 82 documents
Contrail formation in the tropopause region caused by emissions from an Ariane 5 rocket
2016
Rockets directly inject water vapor and aerosol into the atmosphere, which promotes the formation of ice clouds in ice supersaturated layers of the atmosphere. Enhanced mesospheric cloud occurrence has frequently been detected near 80 km altitude a few days after rocket launches. Here, we present unique evidence for cirrus formation in the tropopause region caused by ice nucleation in the exhaust plume from an Ariane 5-ECA rocket. Meteorological reanalysis data from the European Centre for Medium-Range Weather Forecasts show significant ice supersaturation at the 100 hPa level in the American tropical tropopause region on 26 November 2011. Near 17 km altitudes temperatures are below the Sch…
Biofuel blending reduces particle emissions from aircraft engines at cruise conditions.
2017
Aviation-related aerosol emissions contribute to the formation of contrail cirrus clouds that can alter upper tropospheric radiation and water budgets, and therefore climate1. The magnitude of air-traffic-related aerosol–cloud interactions and the ways in which these interactions might change in the future remain uncertain. Modelling studies of the present and future effects of aviation on climate require detailed information about the number of aerosol particles emitted per kilogram of fuel burned and the microphysical properties of those aerosols that are relevant for cloud formation. However, previous observational data at cruise altitudes are sparse for engines burning conventional fuel…
Dehydration potential of ultrathin clouds at the tropical tropopause
2003
[1] We report on the first simultaneous in situ and remote measurements of subvisible cirrus in the uppermost tropical troposphere. The observed cirrus, called UTTCs ( ultrathin tropical tropopause clouds), are the geometrically (200-300 m) and optically (t approximate to 10(-4)) thinnest large-scale clouds ever sampled (approximate to10(5) km(2)). UTTCs consist of only a few ice particles per liter with mean radius approximate to5 mum, containing only 1-5 % of the total water. Yet, brief adiabatic cooling events only 1-2 K below mean ambient temperature destabilize UTTCs, leading to large sedimenting particles (r approximate to 25 mm). Due to their extreme altitude above 17 km and low part…
HNO3 partitioning in cirrus clouds
1999
During the 1997 POLSTAR-1 winter campaign in northern Sweden a flight was performed across a cold trough of air (similar or equal to 196 K) in the tropopause region. Measurements of total water vapour, nitric acid, particles and reactive nitrogen (NOy) were taken. The particle measurements indicate that about 3% of the particles in the moist tropospheric air were ice particles. Forward and backward facing NOy inlets were used simultaneously to determine condensed phase HNO3. The combined NOy and particle measurements reveal that less than 1% of a monolayer of NOy could have resided on the ice particles. This casts doubt on the hypothesis that sedimenting cirrus particles generally lead to a…
Upper tropospheric water vapour and its interaction with cirrus clouds as seen from IAGOS long-term routine in-situ observations
2017
IAGOS (In-service Aircraft for a Global Observing System) performs long-term routinein situobservations of atmospheric chemical composition (O3, CO, NOx, NOy, CO2, CH4), water vapour, aerosols, clouds, and temperature on a global scale by operating compact instruments on board of passenger aircraft. The unique characteristics of the IAGOS data set originate from the global scale sampling on air traffic routes with similar instrumentation such that the observations are truly comparable and well suited for atmospheric research on a statistical basis. Here, we present the analysis of 15 months of simultaneous observations of relative humidity with respect to ice (RHice) and ice crystal number …
In Situ Observations of Ice Particle Losses in a Young Persistent Contrail
2018
We describe results of in situ observations of a 1 to 2-min old contrail in the vortex Phase generated from soot-rich exhaust (> 10^15 emitted soot particles per kg-fuel burned). Simultaneous measurements of soot (EIsoot) and apparent ice (AEIice) particle number emission indices show a pronounced anti-correlation in the vertical contrail profile. AEIice decrease by about 75% with increasing distance below the contrail-producing aircraft,while EIsoot increase by an equivalent relative fraction, therefore strongly suggesting sublimation causing the ice particle losses. Quantifying these losses in measurements helps to validate and improve contrail parameterizations used to estimate the clima…
Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
2012
Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measure…
In situ and lidar observations of tropopause subvisible cirrus clouds during TC4
2010
[1] During the Tropical Composition, Clouds, and Climate Coupling (TC4) experiment in July–August 2007, the NASA WB-57F and ER-2 aircraft made coordinated flights through a tropopause subvisible cirrus (SVC) layer off the Pacific Coast of Central America. The ER-2 aircraft was equipped with a remote sensing payload that included the cloud physics lidar (CPL). The WB-57F payload included cloud microphysical and trace gas measurements, and the aircraft made four vertical profiles through the SVC layer shortly after the ER-2 flew over. The in situ and remotely sensed data are used to quantify the meteorological and microphysical properties of the SVC layer, and these data are compared to the l…
In situ measurements of ice saturation in young contrails
2014
Relative humidity with respect to ice (RHi) is a major factor controlling the evolution of aircraft contrails. High-resolution airborne H2O measurements in and near contrails were made at a rate of 4.2 Hz using the novel water vapor mass spectrometer AIMS-H2O with in-flight calibration during the CONtrail, volcano, and Cirrus ExpeRimenT (CONCERT) 2011. Three 2 min old contrails were sampled near 11 km altitude. Independent of the ambient supersaturation or subsaturation over ice, the mean of the RHi frequency distribution within each contrail is shifted toward ice saturation. This shift can be explained by the high ice surface area densities with corresponding RHi relaxation times on the or…
Effect of multizone refractive multifocal contact lenses on the Cirrus HD OCT retinal measurements
2011
Background Simultaneous vision multifocal contact lenses are widely used to alleviate the symptoms of presbyopia. These contact lenses create simultaneous retinal images due to the incoming light distribution being divided into two or more focuses. Our aim was to evaluate whether the multizone refractive multifocal contact lenses affect the measurements of the retinal nerve fibre layer (RNFL) and macular thickness using optical coherence tomography (OCT). Methods In this cross-over study, 30 eyes of 30 subjects with a mean age of 50.42 ± 7.82 years were fitted with multizone refractive multifocal contact lenses. Using the RNFL Thickness Analysis mode of the Cirrus HD (Carl Zeiss, Meditec, D…