Ship tracks
Ship tracks are
Ship tracks study
In 1965, the first "anomalous cloud lines" were observed in images from the
Scientists who study how human-produced aerosols affect cloud formation observe ship tracks because in most urban areas, they are unable to discern exactly how pollutants contribute to forming clouds because the atmosphere over the land is too tumultuous. In contrast, ships release their exhaust into the relatively clean and still marine air, where the scientists have an easier time of measuring the effects of fossil fuel emissions on cloud formation.[citation needed]
In general, the air above the oceans suffers from less
Findings
It is theorised that
Although ship tracks can sometimes be visible, researchers usually scan the near-infrared light coming off the clouds. At this wavelength many ship tracks appear as bright lines that can be distinguished from the surrounding, uncontaminated clouds. On average, polluted clouds reflect more sunlight than their unaffected counterparts.[citation needed]
When compared to normal clouds, the number of water droplets per volume of air in ship tracks is more than doubled, the radius of the drops is decreased by roughly six percent and the total volume of liquid water per volume of air is increased twofold.[contradictory][citation needed] In other words, this excessive cloud seeding from the ship causes the clouds to retain more water. Normally, rain forms when cloud drops coagulate and reach a size at which gravity can pull them to the ground. Yet, in ship tracks, the cloud seeding makes the drops so small that they can no longer easily merge to reach the size needed to escape. Since no drizzle comes out of the seeded clouds, the liquid water just keeps building in the cloud. This makes the cloud brighter and more reflective to incoming sunlight, especially in the near-infrared part of the spectrum.[citation needed]
Discoveries from satellite observations of several hundred ship tracks from 2006 to 2009 revealed that approximately 25% had a lower cloud albedo (reflectivity) than the surrounding unpolluted clouds.[7] These dimmer ship tracks tended to have significantly less water despite the strong suppression of precipitation by the aerosol plume.[8] Dimmer ship tracks are hypothesized to occur when the air above the cloud tops is sufficiently dry. Smaller droplets in polluted clouds enhance cloud-top evaporation and entrainment. The polluted clouds thus engulf more of the overlying dry air causing them to rigorously evaporate and thin under dry meteorological conditions. Under a moist/unstable atmosphere the entrainment effect is smaller and the pollutants from the ship cause the clouds to thicken and the albedo to increase.[9]
As part of a strategy to reduce ship emissions, the International Maritime Organization implemented a global standard in 2020 requiring a fuel sulfur content reduction of 86%.[10] A study by NASA found that the frequency of ship tracks was reduced to its lowest level in decades due largely to the 2020 global standards, and to a lesser degree by trade disruptions related to the COVID-19 pandemic.[10][11]
See also
References
- ^ "Ship Tracks over the Atlantic". earthobservatory.nasa.gov. 2005-05-12. Retrieved 2018-09-11.
- ^ "Ship Tracks over the Atlantic". NASA Earth Observatory. Archived from the original on 2005-05-26. Retrieved 2006-05-11. Not available as NASA no longer supports Earth Observatory press releases (accession attempt 2017-09-21
- ^ a b Sutherland, Scott (March 23, 2017). "Cloud Atlas leaps into 21st century with 12 new cloud types". The Weather Network. Pelmorex Media. Retrieved 24 March 2017.
- ISSN 1520-0469.
- ISSN 1520-0469.
- S2CID 46152332.
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- ^ a b Younger, Sally (18 October 2022). "NASA Study Finds Evidence That New Rule Reduced Shipping Air Pollution". NASA.
- PMID 35867791.