Physics – Optics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..843k&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Physics
Optics
Scientific paper
ABSTRACT Clouds can have an important effect on the climate (and thereby also on the habitability) of terrestrial planets. While clouds in the upper atmosphere increase atmospheric cooling by scattering of the incoming stellar radiation, clouds in the lower atmosphere are leading to an enhanced greenhouse effect, resulting in higher surface temperatures. Due to the shortage of observational detail regarding the atmospheres of terrestrial extrasolar planets, particular studies of clouds are limited to basic questions about the predominant processes at work, which have to be adressed. In this contribution we focus on the climatic effects of water droplet distributions in the lower tropospheres of Earth-like extrasolar planets. As a first approximation, parametrized distribution functions are used in our study for the description of the cloud particles. The distribution function used here is the log-normal distribution, which is known to be a good approximation to observed size spectra of cumulus clouds in the Earths atmosphere (cf. [3]). This size distribution function is given by the expression f(a) = N p 2 a ln g exp -(ln a - ln an)2 2(ln g)2 (1) and depends on the three parameters: particle number concentration N, geometric standard deviation g and the median radius an. The particle radius is denoted by a, respectively. Our simplified cloud description scheme is coupled with a one-dimensional radiative-convective climate-model (see e.g. [4] and [2] for a general overview of the model) in order to study the basic effects on the climate. Optical properties of the cloud particles are, thereby, calculated by Mie-theory (cf. e.g. [1]), assuming spherical particles composed of pure liquid water and have been included in the models radiative transfer scheme. Results for e.g. different types of central stars are presented and compared with the respective cloud-free situations. References [1] C.F. Bohren and D.R. Huffman, Absorption and scattering of light by small particles, 1983, Wiley [2] Grenfell et al. (2007) Planetary and Space Science, Vol. 55, Issue 5, 661-671 [3] A. A. Kokhanovsky, Cloud Optics, 2006, Springer [4] Segura et al. (2003) Astrobiology, Vol. 3, No. 4, 689- 708
Grenfell Lee
Kitzmann D.
Paris von Ph.
Patzer B. C. A.
Rauer Heike
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