第28回 ESCセミナー
Cosmic rays, Clouds and Climate
- 日時
- 2007年10月26日 (金) 13:30-14:30
- 場所
- 横浜研究所 シミュレータ研究棟1階 会議室
- 講演者
- Torsten Bondo (Center for Sun-Climate Research, Danish National Space Center, Danish Technical University)
- 使用言語
- 英語
要旨
This work aims to improve our understanding of the role cosmic ray induced ionization has on cloud properties and to quantify the resulting climate response.
Galactic Cosmic Rays has been studied since the creation of the first electrometers early in the 20th century and primarily consists of a flux of very high energy charged particles that originate from galactic processes. In the upper atmosphere of the Earth cosmic rays collide with atmospheric nuclei and create a cascade of charged particles that are the main source of ionization in the lower part of the atmosphere (below 35 km). The number of cosmic rays entering the Earth’s atmosphere is modulated by both the solar wind and the Earth’s magnetic field. The solar wind shields the Earth from galactic cosmic rays such that a weaker field allows for higher GCR fluxes.
It was already suggested back in 1959 by Ney that ionization from GCR is the variable of the lower atmosphere subject to the largest solar cycle modulation. However, it wasn’t until 1996 that a significant correlation was identified in the atmosphere between GCR and the total cloud cover over the solar cycle period (11 years). This correlation was subsequently shown to be restricted to low clouds, which has important implications for understanding the radiative impact on Earth’s climate. Clouds play an important role in the Earth’s radiation budget by both reflecting incoming short wave radiation from the Sun and trapping outgoing long wave radiation from the surface and lower atmosphere. Low clouds cool the atmosphere, thus the observations suggests that an increase in GCR leads to an increase in the amount of low clouds resulting in a cooling of the atmosphere. This radiative response is consistent with a number of studies demonstrating a correlation between GCR and climate over many time scales from the 11 year solar activity cycle to geological processes over millions of years. However, it remains to be confirmed what the underlying physical mechanism is for this connection.
Recent experimental results from the CSCR experimental facility SKY support the existence of a connection between cosmic rays and the properties of low clouds. The results indicate that ions play a role in nucleating new particles in the atmosphere and that the rate of production is sensitive to the number of ions and take place on short time scales.
If this sensitivity is relevant for Cloud Condensation Nuclei (CCN) it could provide a possible link between ions created by cosmic rays and cloud production.
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