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  • Alta data for "Measurement and Analysis for the Parameterization of Arctic Snow with Frequent Occurrence of Riming"

    Description:
    Detailed ground-based observations of snow are scarce in remote regions such as the Arctic. Here, Multi-Angle Snowflake Camera (MASC) measurements of over 55,000 solid hydrometeors — obtained during a two-year period from August 2016 to August 2018 at Oliktok Point, Alaska — are analyzed and compared to similar measurements from an earlier experiment at Alta, Utah. In general, distributions of hydrometeor fall speed, fall orientation, aspect ratio, flatness, and complexity (i.e., riming degree) were observed to be very similar between the two locations, except that Arctic hydrometeors tended to be smaller. In total, the slope parameter defining a negative exponential of the size distribution was approximately 50% steeper in the Arctic as at Alta. 66% of particles were observed to be rimed or moderately rimed, with some suggestion that riming is favored by weak boundary layer stability. On average, the fall speed of rimed particles was not notably different from aggregates. However, graupel density and fall speed increase as cloud temperatures approach the melting point.
    Keyword:
    Oliktok Point, Alaska, hydrometeor fall orientation, Alta, fhydrometeor latness, snow, hydrometeor aspect ratio, hydrometeors, hydrometeor complexity, and hydrometeor fall speed
    Subject:
    Atmospheric Science
    Creator:
    Kyle E. Fitch and Timothy J. Garrett
    Owner:
    Based Near Label Tesim:
    Oliktok Point, Alaska, United States and Alta, Utah, United States
    Date Uploaded:
    02/06/2022
    Date Modified:
    12/06/2023
    Date Created:
    2013-01-07 to 2013-04-22
    License:
    CC BY – Allows others to use and share your data, even commercially, with attribution.
    Resource Type:
    Dataset
    Identifier:
    https://doi.org/10.7278/S50d-0nmg-6bs4

  • MATLAB code for "Arctic observations and numerical simulations of surface wind effects on Multi-Angle Snowflake Camera measurements"

    Description:
    Ground-based measurements of frozen precipitation are heavily influenced by interactions of surface winds with gauge-shield geometry. The Multi-Angle Snowflake Camera (MASC), which photographs hydrometeors in free-fall from three different angles while simultaneously measuring their fall speed, has been used in the field at multiple mid-latitude and polar locations both with and without wind shielding. Here we present an analysis of Arctic field observations — with and without a Belfort double Alter shield — and compare the results to computational fluid dynamics (CFD) simulations of the airflow and corresponding particle trajectories around the unshielded MASC. MASC-measured fall speeds compare well with Ka-band Atmospheric Radiation Measurement (ARM) Zenith Radar (KAZR) mean Doppler velocities only when winds are light (< 5 m/s) and the MASC is shielded. MASC-measured fall speeds that do not match KAZR measured velocities tend to fall below a threshold value that increases approximately linearly with wind speed but is generally < 0.5 m/s. For those events with wind speeds < 1.5 m/s, hydrometeors fall with an orientation angle mode of 12 degrees from the horizontal plane, and large, low-density aggregates are as much as five times more likely to be observed. Simulations in the absence of a wind shield show a separation of flow at the upstream side of the instrument, with an upward velocity component just above the aperture, which decreases the mean particle fall speed by 55% (74%) for a wind speed of 5 m/s (10 m/s). We conclude that accurate MASC observations of the microphysical, orientation, and fall speed characteristics of snow particles require shielding by a double wind fence and restriction of analysis to events where winds are light (< 5 m/s). Hydrometeors do not generally fall in still air, so adjustments to these properties' distributions within natural turbulence remain to be determined.
    Subject:
    Meteorology and Atmospheric Science
    Creator:
    Talaei, Ahmad, Hang, Chaoxun, Fitch, Kyle E., and Garrett, Timothy J.
    Owner:
    Language:
    English
    Date Uploaded:
    07/20/2020
    Date Modified:
    12/14/2020
    Date Created:
    20120521 to 20200719
    Resource Type:
    Software or Program Code
    Identifier:
    https://doi.org/10.7278/S50DQTX9K7QY

  • mascpy

    Creator:
    Konstantin Shkurko
    Owner:
    Date Uploaded:
    06/02/2020
    Date Modified:
    07/05/2022