Vertical Structure of Ice Clouds and Vertical Air Motion from Vertically Pointing Cloud Radar Measurements
The vertical structure of ice clouds and vertical air motion (<i>V<sub>air</sub></i>) were investigated using vertically pointing Ka-band cloud radar. The distributions of reflectivity (<i>Z</i>), Doppler velocity (<i>V<sub>D</sub></i>), an...
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| Autores principales: | , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/72b16f9c4aec4962af382914c2d355b2 |
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| Sumario: | The vertical structure of ice clouds and vertical air motion (<i>V<sub>air</sub></i>) were investigated using vertically pointing Ka-band cloud radar. The distributions of reflectivity (<i>Z</i>), Doppler velocity (<i>V<sub>D</sub></i>), and spectrum width (SW) were analyzed for three ice cloud types, namely, cirrus, anvil, and stratiform clouds. The radar parameters of the cirrus clouds showed narrower distributions than those of the stratiform and anvil clouds. In the vertical structures, the rapid growth of <i>Z</i> and <i>V<sub>D</sub></i> occurred in the layer between 8 and 12 km (roughly a layer of −40 °C to −20 °C) for all ice clouds. The prominent feature in the stratiform clouds was an elongated “S” shape in the <i>V<sub>D</sub></i> near 7–7.5 km (at approximately −16 °C to −13 °C) due to a significant decrease in an absolute value of <i>V<sub>D</sub></i>. The mean terminal fall velocity (<i>V<sub>t</sub></i>) and <i>V<sub>air</sub></i> in the ice clouds were estimated using pre-determined <i>V<sub>t</sub></i>–<i>Z</i> relationships (<i>V<sub>t</sub></i> = <i>aZ<sup>b</sup></i>) and the observed <i>V<sub>D</sub></i>. Although the cirrus clouds demonstrated wide distributions in coefficients <i>a</i> and exponents <i>b</i> depending on cloud heights, they showed a smaller change in <i>Z</i> and <i>V<sub>t</sub></i> values compared to that of the other cloud types. The anvil clouds had a larger exponent than that of the stratiform clouds, indicating that the ice particle density of anvil clouds increases at a faster rate compared with the density of stratiform clouds for the same <i>Z</i> increment. The significant positive <i>V<sub>air</sub></i> appeared at the top of all ice clouds in range up to 0.5 m s<sup>−1</sup>, and the anvil clouds showed the deepest layer of upward motion. The stratiform and anvil clouds showed a dramatic increase in vertical air motion in the layer of 6–8 km as shown by the rapid decrease of <i>V<sub>D</sub></i>. This likely caused increase of supersaturation above. A periodic positive <i>V<sub>air</sub></i> linked with a significant reduction in <i>V<sub>D</sub></i> appeared at the height of 7–8 km (approximately −15 °C) dominantly in the stratiform clouds. This layer exhibited a bi-modal power spectrum produced by pre-existing larger ice particles and newly formed numerous smaller ice particles. This result raised a question on the origins of smaller ice particles such as new nucleation due to increased supersaturation by upward motion below or the seeder-feeder effect. In addition, the retrieved <i>V<sub>air</sub></i> with high-resolution data well represented a Kelvin-Helmholtz wave development. |
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