Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower
The effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and...
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| Format: | Article |
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MDPI AG
2020-11-01
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| Series: | Atmosphere |
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| Online Access: | https://www.mdpi.com/2073-4433/11/11/1210 |
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| author | Hiroki Okachi Tomohito J. Yamada Yasuyuki Baba Teruhiro Kubo |
| author_facet | Hiroki Okachi Tomohito J. Yamada Yasuyuki Baba Teruhiro Kubo |
| author_sort | Hiroki Okachi |
| collection | DOAJ |
| description | The effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and seasonality. Over the ocean, small rain and large sea spray droplets co-exist in the same diameter size class (0.072 to 1000 mm); hence, sea spray creates uncertainty when seeking to characterize the drop size distribution (DSD) of rain droplets over the ocean. We measured droplet sizes at a marine tower using a state-of-the-art optical disdrometer, a tipping-bucket rain gauge, a wind anemometer, and a time-lapse camera, over a period that included typhoon Krosa of 2019. The number of rain droplets of diameter less than 1 mm increased monotonically as the horizontal wind speed became stronger. Thus, the shape parameter <i>μ</i> of the Ulbrich distribution decreased. This decreasing trend can be recognized as an increase in sea spray. During no-rainfall hours (indicated by rain gauges on the ocean tower and nearby land), sea spray DSDs were obtained at various horizontal wind speeds. Furthermore, the proportions of sea spray to rainfall at different rainfall intensities and horizontal wind speeds were determined; at a horizontal wind speed of 16 to 20 m s<sup>−1</sup>, the average sea spray proportions were 82.7%, 19.1%, and 5.3% during total rainfall periods of 2.1 mm h<sup>−1</sup>, 8.9 mm h<sup>−1</sup>, and 32.1 mm h<sup>−1</sup>, respectively. Representation of sea spray DSDs, as well as rainfall DSDs, is a key element of calculating real rainfall intensities over the open ocean. |
| first_indexed | 2024-03-10T14:58:56Z |
| format | Article |
| id | doaj.art-7fee30e7880d4ccbaf3436463bee6f3c |
| institution | Directory Open Access Journal |
| issn | 2073-4433 |
| language | English |
| last_indexed | 2024-03-10T14:58:56Z |
| publishDate | 2020-11-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Atmosphere |
| spelling | doaj.art-7fee30e7880d4ccbaf3436463bee6f3c2023-11-20T20:20:45ZengMDPI AGAtmosphere2073-44332020-11-011111121010.3390/atmos11111210Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine TowerHiroki Okachi0Tomohito J. Yamada1Yasuyuki Baba2Teruhiro Kubo3Graduate School of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-9628, JapanFaculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-9628, JapanDisaster Prevention Research Institute, Kyoto University, 2500-106, Katata, Shirahama, Nishimuro, Wakayama 649-2201, JapanDisaster Prevention Research Institute, Kyoto University, 2500-106, Katata, Shirahama, Nishimuro, Wakayama 649-2201, JapanThe effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and seasonality. Over the ocean, small rain and large sea spray droplets co-exist in the same diameter size class (0.072 to 1000 mm); hence, sea spray creates uncertainty when seeking to characterize the drop size distribution (DSD) of rain droplets over the ocean. We measured droplet sizes at a marine tower using a state-of-the-art optical disdrometer, a tipping-bucket rain gauge, a wind anemometer, and a time-lapse camera, over a period that included typhoon Krosa of 2019. The number of rain droplets of diameter less than 1 mm increased monotonically as the horizontal wind speed became stronger. Thus, the shape parameter <i>μ</i> of the Ulbrich distribution decreased. This decreasing trend can be recognized as an increase in sea spray. During no-rainfall hours (indicated by rain gauges on the ocean tower and nearby land), sea spray DSDs were obtained at various horizontal wind speeds. Furthermore, the proportions of sea spray to rainfall at different rainfall intensities and horizontal wind speeds were determined; at a horizontal wind speed of 16 to 20 m s<sup>−1</sup>, the average sea spray proportions were 82.7%, 19.1%, and 5.3% during total rainfall periods of 2.1 mm h<sup>−1</sup>, 8.9 mm h<sup>−1</sup>, and 32.1 mm h<sup>−1</sup>, respectively. Representation of sea spray DSDs, as well as rainfall DSDs, is a key element of calculating real rainfall intensities over the open ocean.https://www.mdpi.com/2073-4433/11/11/1210rain dropsea spraysize distributionmarine observationextreme weather event |
| spellingShingle | Hiroki Okachi Tomohito J. Yamada Yasuyuki Baba Teruhiro Kubo Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower Atmosphere rain drop sea spray size distribution marine observation extreme weather event |
| title | Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower |
| title_full | Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower |
| title_fullStr | Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower |
| title_full_unstemmed | Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower |
| title_short | Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower |
| title_sort | characteristics of rain and sea spray droplet size distribution at a marine tower |
| topic | rain drop sea spray size distribution marine observation extreme weather event |
| url | https://www.mdpi.com/2073-4433/11/11/1210 |
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