Search results for "Ice cloud"

Analysis of a jet stream induced gravity wave associated with an observed ice cloud over Greenland

2004

International audience; A polar stratospheric ice cloud (PSC type II) was observed by airborne lidar above Greenland on 14 January 2000. It was the unique observation of an ice cloud over Greenland during the SOLVE/THESEO 2000 campaign. Mesoscale simulations with the hydrostatic HRM model are presented which, in contrast to global analyses, are capable to produce a vertically propagating gravity wave that induces the low temperatures at the level of the PSC afforded for the ice formation. The simulated minimum temperature is ~8 K below the driving analyses and ~4.5 K below the frost point, exactly coinciding with the location of the observed ice cloud. Despite the high elevations of the Gre…

Microphysical and radiative characterization of a subvisible midlevel Arctic ice cluod by airborne observations - a case study

2009

During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign, which was conducted in March and April 2007, an optically thin ice cloud was observed south of Svalbard at around 3 km altitude. The microphysical and radiative properties of this particular subvisible midlevel cloud were investigated with complementary remote sensing and in situ instruments. Collocated airborne lidar remote sensing and spectral solar radiation measurements were performed at a flight altitude of 2300 m below the cloud base. Under almost stationary atmospheric conditions, the same subvisible midlevel cloud was probed with various in situ sensors roughly 30 min later. <br><br> …

In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

2011

New particle formation (NPF), which generates nucleation mode aerosol, was observed in the tropical Upper Troposphere (UT) and Tropical Tropopause Layer (TTL) by in situ airborne measurements over South America (January–March 2005), Australia (November–December 2005), West Africa (August 2006) and Central America (2004–2007). Particularly intense NPF was found at the bottom of the TTL. Measurements with a set of condensation particle counters (CPCs) with different <i>d</i><sub>p50</sub> (50% lower size detection efficiency diameter or "cut-off diameter") were conducted on board the M-55 <i>Geophysica</i> in the altitude range of 12.0–20.5 km and on board …

2018

Abstract. Air traffic affects cloudiness, and thus climate, by emitting exhaust gases and particles. The study of the evolution of contrail properties is very challenging due to the complex interplay of vortex dynamics and the atmospheric environment (e.g. temperature, supersaturation). Despite substantial progress in recent years, the optical, microphysical, and macrophysical properties of contrails and ambient cirrus during contrail formation and subsequent ageing are still subject to large uncertainties due to instrumental and observational limitations and the large number of variables influencing the contrail life cycle. In this study, various contrail cases corresponding to different a…

2020

Abstract. An ice cloud chamber was developed at the Johannes Gutenberg University of Mainz for generating several thousand data points for mass and sedimentation velocity measurements of ice crystals with sizes less than 150 µm. Ice nucleation was initiated from a cloud of supercooled droplets by local cooling using a liquid nitrogen cold finger. Three-dimensional tracks of ice crystals falling through the slightly supersaturated environment were obtained from the reconstruction of sequential holographic images, automated detection of the crystals in the hologram reconstructions, and particle tracking. Through collection of the crystals and investigation under a microscope before and after …

Ice supersaturations and cirrus cloud crystal numbers

2009

Upper tropospheric observations outside and inside of cirrus clouds indicate water vapour mixing ratios sometimes exceeding water saturation. Relative humidities over ice (RHice) of up to and more than 200% have been reported from aircraft and balloon measurements in recent years. From these observations a lively discussion continues on whether there is a lack of understanding of ice cloud microphysics or whether the water measurements are tainted with large uncertainties or flaws. Here, RHice in clear air and in ice clouds is investigated. Strict quality-checked aircraft in situ observations of RHice were performed during 28 flights in tropical, mid-latitude and Arctic field experiments in…

Environmental scanning electron microscopy (ESEM) as a new technique to determine the ice nucleation capability of individual atmospheric aerosol par…

2007

Abstract Heterogeneous ice nucleation on synthetic silver iodide, natural kaolinite and montmorillonite particles via condensation, freezing and deposition modes was studied by environmental scanning electron microscopy (ESEM) in the temperature range of 250–270 K. By increasing the H2O pressure in the sample chamber at constant temperature, ice formation can be studied in situ and can be related to the chemical composition of the particles that can be determined simultaneously. For silver iodide and kaolinite, supersaturation values of first ice formation are in good agreement (1–2% absolute) with diffusion chamber experiments. For both substances, threshold temperatures for the condensati…

In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone - Part 2: NPF inside ice c…

2021

From 27 July to 10 August 2017, the airborne StratoClim mission took place in Kathmandu, Nepal, where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New particle formation (NPF) was identified by the abundant presence of nucleation-mode aerosols, with particle diameters dp smaller than 15 nm, which were in-situ-detected by means of condensation nuclei (CN) counter techniques. NPF fields in clear skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere–lowermost stratosphere (UTLS) levels and within the Asian monsoon anticyclone (AMA). NPF-generated nucleation-mode particles in elevated concentration…

Comparing irradiance fields derived from Moderate Resolution Imaging Spectroradiometer airborne simulator cirrus cloud retrievals with solar spectral…

2007

[1] During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment, the Moderate Resolution Imaging Spectroradiometer (MODIS) airborne simulator (MAS) and the solar spectral flux radiometer (SSFR) operated on the same aircraft, the NASA ER-2. While MAS provided two-dimensional horizontal fields of cloud optical thickness and effective ice particle radius, the SSFR measured spectral irradiance in the visible to near-infrared wavelength range (0.3–1.7 μm). The MAS retrievals, along with vertical profiles from a combined radar/lidar system on board the same aircraft were used to construct three-dimensional cloud fields, which were input into Monte Carlo ra…

Effects of ice crystal habit on thermal infrared radiative properties and forcing of cirrus

2007

[1] The impact of assumed ice crystal morphology on thermal infrared (IR) radiative properties of subtropical cirrus is quantified. In particular, the crystal-shape-dependent profiles of downwelling and upwelling thermal IR (broadband and spectral) irradiances and the radiative forcing of cirrus (at the top and bottom of the atmosphere) are investigated. For this purpose, airborne measurements of ice crystal size distribution (in terms of ice crystal maximum dimension) from the CRYSTAL-FACE campaign and a recently published library of thermal IR optical properties of nonspherical ice crystal habits are implemented into radiative transfer simulations. Two cirrus cases are studied in detail: …