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Climate variations on Earth-like circumbinary planets

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ABSTRACT

The discovery of planets orbiting double stars at close distances has sparked increasing scientific interest in determining whether Earth-analogues can remain habitable in such environments and how their atmospheric dynamics is influenced by the rapidly changing insolation. In this work we present results of the first three-dimensional numerical experiments of a water-rich planet orbiting a double star. We find that the periodic forcing of the atmosphere has a noticeable impact on the planet's climate. Signatures of the forcing frequencies related to the planet's as well as to the binary's orbital periods are present in a variety of climate indicators such as temperature and precipitation, making the interpretation of potential observables challenging. However, for Earth-like greenhouse gas concentrations, the variable forcing does not change the range of insolation values allowing for habitable climates substantially.

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Amplitudes of the oscillations with the periods OB and OP.Amplitudes of the TSI (a), of the surface temperature (b), of the OLR (c) and of the total precipitation (d) for the binary period OB and for the planetary period OP. Circles denote the amplitudes of the global-mean quantities (s.g.m.) for the two periods and the triangles denote the global-mean of the amplitudes of the zonal-mean quantities (g.m.z.s.). The experiments are from left to right the one with a planetary semi-major axis of 1.140 a.u. (yellow), of 1.165 a.u. (red), 1.195 a.u. (magenta) and 1.225 (blue). The grey and the black marks denote the experiment in which the semimajor axis of the binary orbit is increased to 0.25 a.u. in a 10,800-Earth-day period of high planetary eccentricity (grey) and low planetary eccentricity (black). The marks are arranged in two groups: The left group shows the amplitudes with respect to OB and the right group shows the amplitude with respect to OP. Note that the horizontal separation within the two groups only serves the purpose of clarity and does not correspond to the small differences in OB and OP across simulations.
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f5: Amplitudes of the oscillations with the periods OB and OP.Amplitudes of the TSI (a), of the surface temperature (b), of the OLR (c) and of the total precipitation (d) for the binary period OB and for the planetary period OP. Circles denote the amplitudes of the global-mean quantities (s.g.m.) for the two periods and the triangles denote the global-mean of the amplitudes of the zonal-mean quantities (g.m.z.s.). The experiments are from left to right the one with a planetary semi-major axis of 1.140 a.u. (yellow), of 1.165 a.u. (red), 1.195 a.u. (magenta) and 1.225 (blue). The grey and the black marks denote the experiment in which the semimajor axis of the binary orbit is increased to 0.25 a.u. in a 10,800-Earth-day period of high planetary eccentricity (grey) and low planetary eccentricity (black). The marks are arranged in two groups: The left group shows the amplitudes with respect to OB and the right group shows the amplitude with respect to OP. Note that the horizontal separation within the two groups only serves the purpose of clarity and does not correspond to the small differences in OB and OP across simulations.

Mentions: The amplitudes of the response of these quantities change with the mean climate (Fig. 5). Temperature variations are larger for both OB and OP in a colder climate (Fig. 5b), because of the smaller thermal inertia of ice compared to open water and because of the smaller thermal inertia of the atmosphere in colder and thus drier atmospheres. The variations in precipitation on the other hand increase with the global-mean surface temperature (Fig. 5d). This may be partly due to the general increase of precipitation and atmospheric water-vapour with increasing gST. The OLR shows a non-monotonic behaviour with the largest amplitudes in Moist Greenhouse and Snowball states (Fig. 5c). Understanding the variations in total precipitation and OLR is challenging. This becomes apparent, when comparing the amplitude of the global-mean precipitation with the global-mean of the amplitude of the zonal-mean precipitation (Fig. 5d). These two quantities would be identical if the lag of the maximum in precipitation with respect to maximum in TSI did not change with latitude. However, they differ, implying that the maximum in precipitation has a different lag with respect to the maximum in TSI at different latitudes. This suggests that the mechanisms by which precipitation changes due to the variations in TSI changes with latitude. A similar behaviour is also seen in the OLR (Fig. 5c), implying that the amplitude of global-mean quantities does not necessarily give a good approximation of the mean variations in single regions of a planet. Therefore, understanding the impact of periodic variations in TSI on the climate is crucial to correctly interpret observations of periodically varying quantities.


Climate variations on Earth-like circumbinary planets
Amplitudes of the oscillations with the periods OB and OP.Amplitudes of the TSI (a), of the surface temperature (b), of the OLR (c) and of the total precipitation (d) for the binary period OB and for the planetary period OP. Circles denote the amplitudes of the global-mean quantities (s.g.m.) for the two periods and the triangles denote the global-mean of the amplitudes of the zonal-mean quantities (g.m.z.s.). The experiments are from left to right the one with a planetary semi-major axis of 1.140 a.u. (yellow), of 1.165 a.u. (red), 1.195 a.u. (magenta) and 1.225 (blue). The grey and the black marks denote the experiment in which the semimajor axis of the binary orbit is increased to 0.25 a.u. in a 10,800-Earth-day period of high planetary eccentricity (grey) and low planetary eccentricity (black). The marks are arranged in two groups: The left group shows the amplitudes with respect to OB and the right group shows the amplitude with respect to OP. Note that the horizontal separation within the two groups only serves the purpose of clarity and does not correspond to the small differences in OB and OP across simulations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384241&req=5

f5: Amplitudes of the oscillations with the periods OB and OP.Amplitudes of the TSI (a), of the surface temperature (b), of the OLR (c) and of the total precipitation (d) for the binary period OB and for the planetary period OP. Circles denote the amplitudes of the global-mean quantities (s.g.m.) for the two periods and the triangles denote the global-mean of the amplitudes of the zonal-mean quantities (g.m.z.s.). The experiments are from left to right the one with a planetary semi-major axis of 1.140 a.u. (yellow), of 1.165 a.u. (red), 1.195 a.u. (magenta) and 1.225 (blue). The grey and the black marks denote the experiment in which the semimajor axis of the binary orbit is increased to 0.25 a.u. in a 10,800-Earth-day period of high planetary eccentricity (grey) and low planetary eccentricity (black). The marks are arranged in two groups: The left group shows the amplitudes with respect to OB and the right group shows the amplitude with respect to OP. Note that the horizontal separation within the two groups only serves the purpose of clarity and does not correspond to the small differences in OB and OP across simulations.
Mentions: The amplitudes of the response of these quantities change with the mean climate (Fig. 5). Temperature variations are larger for both OB and OP in a colder climate (Fig. 5b), because of the smaller thermal inertia of ice compared to open water and because of the smaller thermal inertia of the atmosphere in colder and thus drier atmospheres. The variations in precipitation on the other hand increase with the global-mean surface temperature (Fig. 5d). This may be partly due to the general increase of precipitation and atmospheric water-vapour with increasing gST. The OLR shows a non-monotonic behaviour with the largest amplitudes in Moist Greenhouse and Snowball states (Fig. 5c). Understanding the variations in total precipitation and OLR is challenging. This becomes apparent, when comparing the amplitude of the global-mean precipitation with the global-mean of the amplitude of the zonal-mean precipitation (Fig. 5d). These two quantities would be identical if the lag of the maximum in precipitation with respect to maximum in TSI did not change with latitude. However, they differ, implying that the maximum in precipitation has a different lag with respect to the maximum in TSI at different latitudes. This suggests that the mechanisms by which precipitation changes due to the variations in TSI changes with latitude. A similar behaviour is also seen in the OLR (Fig. 5c), implying that the amplitude of global-mean quantities does not necessarily give a good approximation of the mean variations in single regions of a planet. Therefore, understanding the impact of periodic variations in TSI on the climate is crucial to correctly interpret observations of periodically varying quantities.

View Article: PubMed Central - PubMed

ABSTRACT

The discovery of planets orbiting double stars at close distances has sparked increasing scientific interest in determining whether Earth-analogues can remain habitable in such environments and how their atmospheric dynamics is influenced by the rapidly changing insolation. In this work we present results of the first three-dimensional numerical experiments of a water-rich planet orbiting a double star. We find that the periodic forcing of the atmosphere has a noticeable impact on the planet's climate. Signatures of the forcing frequencies related to the planet's as well as to the binary's orbital periods are present in a variety of climate indicators such as temperature and precipitation, making the interpretation of potential observables challenging. However, for Earth-like greenhouse gas concentrations, the variable forcing does not change the range of insolation values allowing for habitable climates substantially.

No MeSH data available.


Related in: MedlinePlus