Free-fall experiments of volcanic ash particles using a 2-D video disdrometer
<p>Information of aerodynamic parameters of volcanic ash particles, such as terminal velocity, axis ratio, and canting angle, are necessary for quantitative ash-fall estimations with weather radar. In this study, free-fall experiments of volcanic ash particles were accomplished using a two-dim...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2019-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/5363/2019/amt-12-5363-2019.pdf |
| _version_ | 1818309454260600832 |
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| author | S.-H. Suh M. Maki M. Iguchi D.-I. Lee A. Yamaji T. Momotani |
| author_facet | S.-H. Suh M. Maki M. Iguchi D.-I. Lee A. Yamaji T. Momotani |
| author_sort | S.-H. Suh |
| collection | DOAJ |
| description | <p>Information of aerodynamic parameters of volcanic ash particles, such as
terminal velocity, axis ratio, and canting angle, are necessary for
quantitative ash-fall estimations with weather radar. In this study,
free-fall experiments of volcanic ash particles were accomplished using a
two-dimensional video disdrometer under controlled conditions.</p>
<p>Samples containing a rotating symmetric axis were selected and divided into
five types according to shape and orientation: oblate spheroid with
horizontal rotating axis (OH), oblate spheroid with vertical axis (OV),
prolate spheroid with horizontal rotating axis (PH), prolate spheroid with
vertical rotating axis (PV), and sphere (Sp). The horizontally (OH and PH)
and vertically (OV and PV) oriented particles were present in proportions of
76 % and 22 %, and oblate and prolate spheroids were in proportions of
76 % and 24 %, respectively. The most common shape type was OH (57 %).</p>
<p>The terminal velocities of OH, OV, PH, PV, and Sp were obtained analyzing
2-D video disdrometer data. The terminal velocities of PV were highest compared to those of
other particle types. The lowest terminal velocities were found in OH
particles. It is interesting that the terminal velocities for OH decreased
rapidly in the range <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.5</mn><mo><</mo><mi>D</mi><mo><</mo><mn mathvariant="normal">1</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="57pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="3be87230942768d167ea0bb447be7b94"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-12-5363-2019-ie00001.svg" width="57pt" height="10pt" src="amt-12-5363-2019-ie00001.png"/></svg:svg></span></span> mm, corresponding to the
decrease in axis ratio (i.e., smaller the particle, the flatter the shape).
The axis ratios of all particle types except Sp were found to be converged
to 0.94 at <span class="inline-formula"><i>D</i>>2</span> mm.</p>
<p>The histogram of canting angles followed unimodal and bimodal distributions
with respect to horizontally and vertically oriented particles,
respectively. The mean values and the standard deviation of entire particle
shape types were close to 0 and 10<span class="inline-formula"><sup>∘</sup></span>, respectively,
under calm atmospheric conditions.</p> |
| first_indexed | 2024-12-13T07:30:25Z |
| format | Article |
| id | doaj.art-6c3b3212dc2f4fb991bc20df1ab01cce |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-13T07:30:25Z |
| publishDate | 2019-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-6c3b3212dc2f4fb991bc20df1ab01cce2022-12-21T23:55:13ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482019-10-01125363537910.5194/amt-12-5363-2019Free-fall experiments of volcanic ash particles using a 2-D video disdrometerS.-H. Suh0M. Maki1M. Iguchi2D.-I. Lee3A. Yamaji4T. Momotani5Department of Environmental Atmospheric Sciences, Pukyong National University, Nam-gu, Busan, Republic of KoreaResearch and Education Center for Natural Hazards, Kagoshima University, Korimoto, Kagoshima, JapanSakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, Sakurajima, Kagoshima, JapanDepartment of Environmental Atmospheric Sciences, Pukyong National University, Nam-gu, Busan, Republic of KoreaJapan Weather Association, Higashi-Ikebukuro, Toshima, Tokyo, JapanJapan Weather Association, Higashi-Ikebukuro, Toshima, Tokyo, Japan<p>Information of aerodynamic parameters of volcanic ash particles, such as terminal velocity, axis ratio, and canting angle, are necessary for quantitative ash-fall estimations with weather radar. In this study, free-fall experiments of volcanic ash particles were accomplished using a two-dimensional video disdrometer under controlled conditions.</p> <p>Samples containing a rotating symmetric axis were selected and divided into five types according to shape and orientation: oblate spheroid with horizontal rotating axis (OH), oblate spheroid with vertical axis (OV), prolate spheroid with horizontal rotating axis (PH), prolate spheroid with vertical rotating axis (PV), and sphere (Sp). The horizontally (OH and PH) and vertically (OV and PV) oriented particles were present in proportions of 76 % and 22 %, and oblate and prolate spheroids were in proportions of 76 % and 24 %, respectively. The most common shape type was OH (57 %).</p> <p>The terminal velocities of OH, OV, PH, PV, and Sp were obtained analyzing 2-D video disdrometer data. The terminal velocities of PV were highest compared to those of other particle types. The lowest terminal velocities were found in OH particles. It is interesting that the terminal velocities for OH decreased rapidly in the range <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.5</mn><mo><</mo><mi>D</mi><mo><</mo><mn mathvariant="normal">1</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="57pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="3be87230942768d167ea0bb447be7b94"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-12-5363-2019-ie00001.svg" width="57pt" height="10pt" src="amt-12-5363-2019-ie00001.png"/></svg:svg></span></span> mm, corresponding to the decrease in axis ratio (i.e., smaller the particle, the flatter the shape). The axis ratios of all particle types except Sp were found to be converged to 0.94 at <span class="inline-formula"><i>D</i>>2</span> mm.</p> <p>The histogram of canting angles followed unimodal and bimodal distributions with respect to horizontally and vertically oriented particles, respectively. The mean values and the standard deviation of entire particle shape types were close to 0 and 10<span class="inline-formula"><sup>∘</sup></span>, respectively, under calm atmospheric conditions.</p>https://www.atmos-meas-tech.net/12/5363/2019/amt-12-5363-2019.pdf |
| spellingShingle | S.-H. Suh M. Maki M. Iguchi D.-I. Lee A. Yamaji T. Momotani Free-fall experiments of volcanic ash particles using a 2-D video disdrometer Atmospheric Measurement Techniques |
| title | Free-fall experiments of volcanic ash particles using a 2-D video disdrometer |
| title_full | Free-fall experiments of volcanic ash particles using a 2-D video disdrometer |
| title_fullStr | Free-fall experiments of volcanic ash particles using a 2-D video disdrometer |
| title_full_unstemmed | Free-fall experiments of volcanic ash particles using a 2-D video disdrometer |
| title_short | Free-fall experiments of volcanic ash particles using a 2-D video disdrometer |
| title_sort | free fall experiments of volcanic ash particles using a 2 d video disdrometer |
| url | https://www.atmos-meas-tech.net/12/5363/2019/amt-12-5363-2019.pdf |
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