scholarly journals Vertical Structure of a Snowfall Event Based on Observations From the Aircraft and Mountain Station in Beijing

2021 ◽  
Vol 9 ◽  
Author(s):  
Yu Huang ◽  
Delong Zhao ◽  
Yuanmou Du ◽  
Yichen Chen ◽  
Lei Zhang ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Ice Crystals ◽  
Ice Formation ◽  
Growth Mechanisms ◽  
Small Particles ◽  
Cloud Radar ◽  
Mountain Station ◽  
Snowfall Event ◽  
Event Based ◽  
Automatic Station

An aircraft platform, ground-based disdrometer, cloud radar, radiometer, and automatic station were combined to study a snowfall case (16:30–21:00 observed by ground cloud radar) on the Yangqing Mountains in Beijing. Comparing the variation of ice habit and number concentration at aircraft altitude (2.9–3.2 km) and ground, we discussed the ice growth mechanisms in the Beijing Mountains. Results indicated that the snowfall was steady but not strong with reflectivity less than 20dBZ, and cloud top altitude less than 4.5 km. The number concentrations for both liquid and ice crystals at aircraft altitude and ground were very similar, both dominated by small particles at diameters of 0.1–1.2 mm, and the proportion of mean number concentrations at small diameters both in the aircraft and on the ground was large, peaking at 44 L−1 mm−1 and 8826 L−1 mm−1 respectively, and decreased rapidly as the diameter increased. There was no mixed phase in clouds with little liquid water. Particles were relatively regular, and were transparent with dendritic and disk-hexagonal shapes. The ice crystals and snowflakes were mainly grown by the deposition and aggregation, rarely by the riming process, and no secondary ice formation was observed.

scholarly journals Measurements of Ice Nucleating Particles and Ice Residuals

2017 ◽  
Vol 58 ◽  
pp. 8.1-8.13 ◽  
Author(s):  
Daniel J. Cziczo ◽  
Luis Ladino ◽  
Yvonne Boose ◽  
Zamin A. Kanji ◽  
Piotr Kupiszewski ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Condensed Phase ◽  
Atmospheric Aerosols ◽  
Aerosol Particles ◽  
Ice Crystals ◽  
Ice Formation ◽  
Similar Amount ◽  
Residual Material ◽  
History Of ◽  
Phase Water

Abstract It has been known that aerosol particles act as nuclei for ice formation for over a century and a half (see Dufour). Initial attempts to understand the nature of these ice nucleating particles were optical and electron microscope inspection of inclusions at the center of a crystal (see Isono; Kumai). Only within the last few decades has instrumentation to extract ice crystals from clouds and analyze the residual material after sublimation of condensed-phase water been available (see Cziczo and Froyd). Techniques to ascertain the ice nucleating potential of atmospheric aerosols have only been in place for a similar amount of time (see DeMott et al.). In this chapter the history of measurements of ice nucleating particles, both in the field and complementary studies in the laboratory, are reviewed. Remaining uncertainties and artifacts associated with measurements are described and suggestions for future areas of improvement are made.

Effects of lead width variation, re-freezing and mixing events on lead water structure in the central Arctic

2021 ◽  
Author(s):  
Daiki Nomura ◽  
Alison Web ◽  
Yuhong Li ◽  
Manuel Dall’osto ◽  
Katrin Schmidt ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Lower Boundary ◽  
Water Structure ◽  
Sampling Period ◽  
Ice Formation ◽  
Layer Surface ◽  
Mixing Process ◽  
Survey Period ◽  
Mixing Processes ◽  
Surface Ice

<p>We undertook a lead survey during the international drift campaign MOSAiC, Leg 5 (from 22 August to 17 September 2020) to understand the effects of lead width variation, re-freezing, and mixing events on lead water vertical structure. At the beginning of the survey period, the freshwater layer was occupied for the top 1 m depth and there were strong vertical gradients in temperature, salinity, and dissolved oxygen (DO) within 1 m depth: from 0.0°C to –1.6°C for temperature, from 0.0 to 31.4 psu for salinity, and 10.5 to 13.5 mg L<sup>–1</sup> for DO. A strong DO minimum layer corresponded with a salinity of 25 psu, and usually occurred at the freshwater–seawater interface at approx. 1 m depth, most likely as a result of an accumulation of organic matter and ongoing degradation/respiration processes at this interface. However, during the survey period, these strong gradients weakened and reduced the freshwater layer thickness (FLT). In the first half of the sampling period (until 4 September), FLT changed due to variations in lead width: as lead width increased, FLT decreased due to a stretching of the freshwater layer. In the second half of the sampling period, FLT was controlled by the surface ice formation (re-freezing) and mixing processes along the lower boundary of the freshwater layer. Surface ice formation removed freshwater and the formation of surface ice (about 0.2 m thick) explains 20% of the reduction of FLT. The remaining 80% of the reduction of FLT was due to the mixing process within the water column that was initiated by cooling and re-freezing. This mixing process diluted the salinity from 31.6 to 29.3 psu in the water below freshwater layer towards the end of the survey period. Our results indicate that lead water structure can change rapidly and dynamically and that this has significant effects on the biogeochemical exchange between lead systems and the atmosphere.</p>

scholarly journals Classification of Hydrometeors Using Measurements of the Ka-Band Cloud Radar Installed at the Milešovka Mountain (Central Europe)

2018 ◽  
Vol 10 (11) ◽  
pp. 1674 ◽  
Author(s):  
Zbyněk Sokol ◽  
Jana Minářová ◽  
Petr Novák
Keyword(s):  
Central Europe ◽  
Terminal Velocity ◽  
Small Particles ◽  
Cloud Droplets ◽  
Vertical Temperature Profile ◽  
Ka Band ◽  
Cloud Radar ◽  
Weather Radars ◽  
Cloud Particles ◽  
Linear Depolarization Ratio

In radar meteorology, greater interest is dedicated to weather radars and precipitation analyses. However, cloud radars provide us with detailed information on cloud particles from which the precipitation consists of. Motivated by research on the cloud particles, a vertical Ka-band cloud radar (35 GHz) was installed at the Milešovka observatory in Central Europe and was operationally measuring since June 2018. This study presents algorithms that we use to retrieve vertical air velocity (Vair) and hydrometeors. The algorithm calculating Vair is based on small-particle tracers, which considers the terminal velocity of small particles negligible and, thereby, Vair corresponds to the velocity of the small particles. The algorithm classifying hydrometeors consists of calculating the terminal velocity of hydrometeors and the vertical temperature profile. It identifies six hydrometeor types (cloud droplets, ice, and four precipitating particles: rain, graupel, snow, and hail) based on the calculated terminal velocity of hydrometeors, temperature, Vair, and Linear Depolarization Ratio. The results of both the Vair and the distribution of hydrometeors were found to be realistic for a thunderstorm associated with significant lightning activity on 1 June 2018.

scholarly journals Melting of Ice and Sea Ice into Seawater and Frazil Ice Formation

2014 ◽  
Vol 44 (7) ◽  
pp. 1751-1775 ◽  
Author(s):  
Trevor J. McDougall ◽  
Paul M. Barker ◽  
Rainer Feistel ◽  
Ben K. Galton-Fenzi
Keyword(s):  
Sea Ice ◽  
Vertical Velocity ◽  
Computer Software ◽  
Ice Crystals ◽  
Ice Formation ◽  
Thermodynamic Equation ◽  
Frazil Ice ◽  
Salinity Changes ◽  
Thermodynamic Relationships

Abstract The thermodynamic consequences of the melting of ice and sea ice into seawater are considered. The International Thermodynamic Equation Of Seawater—2010 (TEOS-10) is used to derive the changes in the Conservative Temperature and Absolute Salinity of seawater that occurs as a consequence of the melting of ice and sea ice into seawater. Also, a study of the thermodynamic relationships involved in the formation of frazil ice enables the calculation of the magnitudes of the Conservative Temperature and Absolute Salinity changes with pressure when frazil ice is present in a seawater parcel, assuming that the frazil ice crystals are sufficiently small that their relative vertical velocity can be ignored. The main results of this paper are the equations that describe the changes to these quantities when ice and seawater interact, and these equations can be evaluated using computer software that the authors have developed and is publicly available in the Gibbs SeaWater (GSW) Oceanographic Toolbox of TEOS-10.

scholarly journals Difficulties in Early Ice Detection with the Small Ice Detector-2 HIAPER (SID-2H) in Maritime Cumuli

2014 ◽  
Vol 31 (6) ◽  
pp. 1263-1275 ◽  
Author(s):  
Alexandria Johnson ◽  
Sonia Lasher-Trapp ◽  
Aaron Bansemer ◽  
Z. Ulanowski ◽  
Andrew J. Heymsfield
Keyword(s):  
High Performance ◽  
Water Environment ◽  
Ice Crystals ◽  
Environmental Research ◽  
Ice Formation ◽  
Cumulus Clouds ◽  
Irregular Particle ◽  
Water Drops ◽  
Ice Detection ◽  
Particle Shapes

Abstract The Small Ice Detector, version 2 (SID-2), High-performance Instrumented Airborne Platform for Environmental Research (HIAPER; SID-2H) was used to detect small ice particles in the early stages of ice formation in the high liquid water environment of tropical maritime cumulus clouds sampled during the Ice in Clouds Experiment—Tropical (ICE-T) field campaign. Its performance in comparison to other probes and the development of new corrections applied to the data are presented. The SID-2H detected small ice crystals among larger particles. It correctly identified water drops, and discriminated between round and irregular particle shapes in water-dominated clouds with errors less than 5%. Remaining uncertainties in the sensing volume and the volume over which coincidence of particles occurred, result in the data being used here in a qualitative manner to identify the presence of ice, and its habits and sizes.

scholarly journals A simple insect removal algorithm for 35-GHz cloud radar measurements

2017 ◽  
Author(s):  
Madhu Chandra R. Kalapureddy ◽  
Sukanya Patra ◽  
Subrata K. Das ◽  
Sachin M. Deshpande ◽  
Kaustav Chakravarty ◽  
...  
Keyword(s):  
High Resolution ◽  
Vertical Structure ◽  
Cloud Droplet ◽  
Radar Reflectivity ◽  
Noise Floor ◽  
Cloud Radar ◽  
Cloud Height ◽  
Radar Echoes ◽  
Sensitivity Curves ◽  
Radar Measurements

Abstract. One of the key parameters that must be included in the analysis of atmospheric constituents (gases and particles) and clouds is the vertical structure of the atmosphere. Therefore high-resolution vertical profile observations of the atmospheric targets are required for both theoretical and practical evaluation and as inputs to increase accuracy of atmospheric models. Cloud radar reflectivity profiles can be an important measurement for the investigation of cloud vertical structure in a resourceful way. However, extracting intended meteorological cloud content from the overall measurement often demands an effective technique or algorithm that can reduce error and observational uncertainties in the recorded data. In this work a technique is proposed to identify and separate cloud and non-hydrometeor returns from a cloud radar measurements. Firstly the observed cloud reflectivity profile must be evaluated against the theoretical radar sensitivity curves. This step helps to determine the range of receiver noise floor above which it can be identified as signal or an atmospheric echo. However it should be noted that the signal above the noise floor may be contaminated by the air-borne non-meteorological targets such as insects, birds, or airplanes. The second step in this analysis statistically reviews the continual radar echoes to determine the signal de-correlation period. Cloud echoes are observed to be temporally more coherent, homogenous and have a longer de-correlation period than insects and noise. This step critically helps in separating the clouds from insects and noise which show shorter de-correlation periods. The above two steps ensure the identification and removal of non-hydrometeor contributions from the cloud radar reflectivity profile which can then be used for inferring unbiased vertical cloud structure. However these two steps are insufficient for recovering the weakly echoing cloud boundaries associated with the sharp reduction in cloud droplet size and concentrations. In the final step in order to obtain intact cloud height information, identified cloud echo peak(s) needs to be backtracked along the either sides on the reflectivity profile till its value falls close to the mean noise floor. The proposed algorithm potentially identify cloud height solely through the characterization of high resolution cloud radar reflectivity measurements with the theoretical echo sensitivity curves and observed echo statistics for the cloud tracking (TEST). This technique is found to be more robust in identifying and filtering out the contributions due to insects and noise which may contaminate a cloud reflectivity profile. With this algorithm it is possible to improve monsoon tropical cloud characterization using cloud radar.

scholarly journals Technical Note: Formation of airborne ice crystals in a wall independent reactor (WIR) under atmospheric conditions

2008 ◽  
Vol 8 (4) ◽  
pp. 13017-13042
Author(s):  
E. Fries ◽  
W. Haunold ◽  
E. Starokozhev ◽  
K. Palitzsch ◽  
R. Sitals ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Flow Rate ◽  
Wall Temperature ◽  
Lead Time ◽  
Aerosol Particles ◽  
Ice Crystals ◽  
Ice Formation ◽  
Atmospheric Conditions ◽  
Ice Crystal ◽  
Temperature Variations

Abstract. Both, gas and particle scavenging contribute to the transport of organic compounds by ice crystals in the troposphere. To simulate these processes an experimental setup was developed to form airborne ice crystals under atmospheric conditions. Experiments were performed in a wall independent reactor (WIR) installed in a walk-in cold chamber maintained constantly at −20°C. Aerosol particles were added to the carrier gas of ambient air by an aerosol generator to allow heterogeneous ice formation. Temperature variations and hydrodynamic conditions of the WIR were investigated to determine the conditions for ice crystal formation and crystal growth by vapour deposition. In detail, the dependence of temperature variations from flow rate and temperature of the physical wall as well as temperature variations with an increasing reactor depth were studied. The conditions to provide a stable aerosol concentration in the carrier gas flow were also studied. The temperature distribution inside the reactor was strongly dependent on flow rate and physical wall temperature. At an inlet temperature of −20°C, a flow rate of 30 L•min−1 and a physical wall temperature of +5°C turned out to provide ideal conditions for ice formation. At these conditions a sharp and stable laminar down draft "jet stream" of cold air in the centre of the reactor was produced. Temperatures measured at the chamber outlet were kept well below the freezing point in the whole reactor depth of 1.0 m. Thus, melting did not affect ice formation and crystal growth. The maximum residence time for airborne ice crystals was calculated to at 40 s. Ice crystal growth rates increased also with increasing reactor depth. The maximum ice crystal growth rate was calculated at 2.82 mg• s−1. Further, the removal efficiency of the cleaning device for aerosol particles was 99.8% after 10 min. A reliable particle supply was attained after a preliminary lead time of 15 min. Thus, the minimum lead time was determined at 25 min. Several test runs revealed that the WIR is suitable to perform experiments with airborne ice crystals.

scholarly journals CHARACTERIZATION OF ICE FORMATION IN BLUEBERRY FLOWER BUDS

HortScience ◽  
1990 ◽  
Vol 25 (9) ◽  
pp. 1088a-1088
Author(s):  
Cindy L. Flinn ◽  
Edward N. Ashworth
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Low Temperature ◽  
Ice Crystals ◽  
Ice Formation ◽  
Flower Buds ◽  
Woody Tissue ◽  
Cooling Rates

Examination of both frozen specimens and -5C freeze-fixed buds showed that ice crystals were not uniformly distributed in blueberry flower buds. Localized freezing was also evidenced by detection of multiple freezing events using differential thermal analysis (DTA). Upon cooling, an initial exotherm occurred just below 0C and coincided with ice formation in adjacent woody tissue. Multiple low temperature exotherms (LTE), which have been reported to correspond with the freezing of individual blueberry florets (Bierman, et al. 1979. ASHS, 104(4):444-449), occurred between -7C and -28C. The presence and temperature of LTEs was influenced by cooling rates and whether buds were excised. LTE temperatures did not correlate with hardiness of buds frozen under field-like conditions. Results suggested that DTA of excised buds was not an appropriate method for determining hardiness.

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