Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

NERC, NE/E011225/1 © Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 LicenseThe knowledge of properties of ice crystals such as size, shape, concavity and roughness is critical in the context of radiative properties of ice and mixed phase clouds. Limitations of current cloud probes to measure these properties can be circumvented by acquiring two-dimensional light scattering patterns instead of particle images. Such patterns were obtained in situ for the first time using the Small Ice Detector 3 (SID-3) probe during several flights in a variety of mid-latitude mixed phase and cirrus clouds. The patterns are analyzed using several measures of pattern texture, selected to reveal the magnitude of particle roughness or complexity. The retrieved roughness is compared to values obtained from a range of well-characterized test particles in the laboratory. It is found that typical in situ roughness corresponds to that found in the rougher subset of the test particles, and sometimes even extends beyond the most extreme values found in the laboratory. In this study we do not differentiate between small-scale, fine surface roughness and large-scale crystal complexity. Instead, we argue that both can have similar manifestations in terms of light scattering properties and also similar causes. Overall, the in situ data is consistent with ice particles with highly irregular or rough surfaces being dominant. Similar magnitudes of roughness were found in growth and sublimation zones of cirrus. The roughness was found to be negatively correlated with the halo ratio, but not with other thermodynamic or microphysical properties found in situ. Slightly higher roughness was observed in cirrus forming in clean oceanic airmasses than in a continental, polluted one. Overall, the roughness and complexity is expected to lead to increased shortwave cloud reflectivity, in comparison with cirrus composed of more regular, smooth ice crystal shapes. These findings put into question suggestions that climate could be modified through aerosol seeding to reduce cirrus cover and optical depth, as the seeding may result in decreased shortwave reflectivity.Peer reviewe

Light scattering by ice particles in the Earth's atmosphere and related laboratory measurements

The microphysical properties of ice crystals, such as size, shape, concavity and roughness, are important in the context of radiative properties of ice and mixed phase clouds. Limitations of current cloud probes to measure such properties can be circumvented by acquiring light scattering patterns instead of particle images. Recent in situ cloud data from the SID-3 probe is shown which is consistent with ice particles with rough surfaces being dominant

PHIPS-HALO: The airborne Particle Habit Imaging and Polar Scattering probe-Part 1: Design and operation

This is an Open Access article distributed under the terms ofthe Creative Commons Attribution 3.0 License https://creativecommons.org/licenses/by/3.0/The number and shape of ice crystals present in mixed-phase and ice clouds influence the radiation properties, precipitation occurrence and lifetime of these clouds. Since clouds play a major role in the climate system, influencing the energy budget by scattering sunlight and absorbing heat radiation from the earth, it is necessary to investigate the optical and microphysical properties of cloud particles particularly in situ. The relationship between the microphysics and the single scattering properties of cloud particles is usually obtained by modelling the optical scattering properties from in situ measurements of ice crystal size distributions. The measured size distribution and the assumed particle shape might be erroneous in case of non-spherical ice particles. There is a demand to obtain both information correspondently and simultaneously for individual cloud particles in their natural environment. For evaluating the average scattering phase function as a function of ice particle habit and crystal complexity, in situ measurements are required. To this end we have developed a novel airborne optical sensor (PHIPS-HALO) to measure the optical properties and the corresponding microphysical parameters of individual cloud particles simultaneously. PHIPS-HALO has been tested in the AIDA cloud simulation chamber and deployed in mountain stations as well as research aircraft (HALO and Polar 6). It is a successive version of the laboratory prototype instrument PHIPS-AIDA. In this paper we present the detailed design of PHIPS-HALO, including the detection mechanism, optical design, mechanical construction and aerodynamic characterization.Final Published versio

The Universal Cloud and Aerosol Sounding System (UCASS): a low-cost miniature optical particle counter for use in dropsonde or balloon-borne sounding systems

© Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. An earlier version of this work was published in Atmospheric Measurement Techniques Discussions: https://dx.doi.org/10.5194/amt-2019-70.A low-cost miniaturized particle counter has been developed by The University of Hertfordshire (UH) for the measurement of aerosol and droplet concentrations and size distributions. The Universal Cloud and Aerosol Sounding System (UCASS) is an optical particle counter (OPC), which uses wide-angle elastic light scattering for the high-precision sizing of fluid-borne particulates. The UCASS has up to 16 configurable size bins, capable of sizing particles in the range 0.4–40 µm in diameter. Unlike traditional particle counters, the UCASS is an open-geometry system that relies on an external air flow. Therefore, the instrument is suited for use as part of a dropsonde, balloon-borne sounding system, as part of an unmanned aerial vehicle (UAV), or on any measurement platform with a known air flow. Data can be logged autonomously using an on-board SD card, or the device can be interfaced with commercially available meteorological sondes to transmit data in real time. The device has been deployed on various research platforms to take measurements of both droplets and dry aerosol particles. Comparative results with co-located instrumentation in both laboratory and field settings show good agreement for the sizing and counting ability of the UCASS.Peer reviewe

AIITS: Preliminary light scattering data from Tropical Tropopause Layer cirrus

The new optical particle spectrometer AIITS (Aerosol Ice Interface Transition Spectrometer) is the next instrument in the Small Ice Detector (SID) family. Like SID3, it acquires two-dimensional forward scattering patterns from particles in the size range from about one to a few hundred micrometers (depending on variable settings). The patterns allow quantifying the phase, habit and fine surface features of large aerosol and ice crystals, which are frequently too small to be adequately characterised using traditional imaging techniques.Two 2D-forward scattering patterns are recorded per particle using two high-resolution cameras. The cameras fire simultaneously, recording the scattering pattern via a beamsplitter. AIITS can be configured such that the cameras measure either perpendicular polarisations (i.e. P-polarisation with one camera, S-polarisation with the other) or to have a different gain setting on each camera to encompass a larger dynamic range. The incident beam can be either circularly or linearly polarised. Backscatter depolarisation is also measured. The camera and beam configuration must be selected pre-flight.The probe was deployed on board the NASA Global Hawk aircraft during a recent ATTREX/CAST campaign over the tropical eastern Pacific. We present preliminary results from a case study from the 5th of March 2015 which showed the existence of a variety of particles, including rough surfaced ice crystals, some regular, hexagonal ones, as well as particles with smooth, curved surfaces (but not spherical). We compare AIITS data with co-located particle imaging from the SPEC Hawkeye probe.The Hawkeye probe combines a 2D-Stereo optical array probe, a Cloud Particle Imager (CPI), and a Fast Cloud Droplet Probe (FCDP) to provide high resolution images (2.3 micron pixel resolution) and particle size distributions of concentration, area, and mass for particles with diameter between one micron and a few centimeters.The TTL is known to be of importance due to the presence of subvisual cirrus, which contributes to net climate radiative feedback. Knowledge of the processes involved in the creation and persistence of such clouds is limited due to sparse observational data.Non peer reviewe

Quasi-spherical ice in convective clouds

Homogeneous freezing of supercooled droplets occurs in convective systems in low and midlatitudes. This droplet-freezing process leads to the formation of a large amount of small ice particles, so-called frozen droplets, that are transported to the upper parts of anvil outflows, where they can influence the cloud radiative properties. However, the detailed microphysics and, thus, the scattering properties of these small ice particles are highly uncertain. Here, the link between the microphysical and optical properties of frozen droplets is investigated in cloud chamber experiments, where the frozen droplets were formed, grown, and sublimated under controlled conditions. It was found that frozen droplets developed a high degree of small-scale complexity after their initial formation and subsequent growth. During sublimation, the small-scale complexity disappeared, releasing a smooth and near-spherical ice particle. Angular light scattering and depolarization measurements confirmed that these sublimating frozen droplets scattered light similar to spherical particles: that is, they had angular light-scattering properties similar to water droplets. The knowledge gained from this laboratory study was applied to two case studies of aircraft measurements in midlatitude and tropical convective systems. The in situ aircraft measurements confirmed that the microphysics of frozen droplets is dependent on the humidity conditions they are exposed to (growth or sublimation). The existence of optically spherical frozen droplets can be important for the radiative properties of detraining convective outflows.Peer reviewe

Why helping coworkers does not always make you poor:the contingent role of common and unique position within the sales team

In recent years, many companies have implemented sales teams as a way of streamlining accountability and promoting the development of sales expertise. The success of such work groups largely depends on experienced members' willingness to help coworkers. Previous studies indicate that group structure and individual position along individual attributes (e.g., experience) are important to understand interactions between coworkers. However, sales research on this topic is lacking. Drawing on a motivation-opportunity-ability framework, this study addresses this void by examining the impact of individual salesperson's job experience position within work groups on the motivation to help coworkers and his or her own sales performance. The findings of a multisource, multilevel empirical study reveal interesting effects. The results highlight the important role of job experience position: if a salesperson's level of job experience is common within the sales team, it activates identification as a driver of helping behaviors, which in turn negatively influences own performance. Conversely, if a salesperson's level of job experience is unique, it does not activate identification as a driver of helping, but does positively influence the effect of helping on own performance. The authors discuss implications for theory and practice

A Miniature Airborne Particle Classifier (APC)

This work was funded by an award from the Natural Environment Research Council (NE/H002316/1)The single greatest source of uncertainty in the estimates of climate sensitivity to either natural or man-made changes continues to be clouds (IPCC 2001, 2007). Much of this uncertainty arises from the lack of information relating to the properties of smaller cloud particles (droplets, ice crystals) and aerosol. The Particle Instruments & Diagnostics research group at the University of Hertfordshire has a successful history of developing laboratory and airborne particle counting and classification instruments to assess the size, shape and class (droplets, ice crystals, mineral aerosol, etc) of particles in the cloud. This NERC-funded project seeks to develop a miniature version of UH’s established SID-2 probe to allow it to be flown on a far wider range of aircraft, including UAVs.Peer reviewe

Retrieving the size of particles with rough surfaces from 2D scattering patterns

Scattered intensity measurement is a commonly used method for determining the size of small particles. However, it requires calibration and is subject to errors due to changes in incident irradiance or detector sensitivity. Analysis of two-dimensional scattering patterns offers an alternative approach. We test possible techniques, including morphological image processing operations, on a diverse range of particles. It is found that the average surface area of intensity peaks is inversely proportional to particle size.Peer reviewe