التفاصيل البيبلوغرافية
| العنوان: |
Earth's Mesosphere During Possible Encounters With Massive Interstellar Clouds 2 and 7 Million Years Ago. |
| المؤلفون: |
Miller, Jesse A., Opher, Merav, Hatzaki, Maria, Papachristopoulou, Kyriakoula, Thomas, Brian C. |
| المصدر: |
Geophysical Research Letters; 9/16/2024, Vol. 51 Issue 17, p1-9, 9p |
| مصطلحات موضوعية: |
EARTH'S orbit, ATMOSPHERIC chemistry, NOCTILUCENT clouds, ATMOSPHERE, ATMOSPHERIC models, THERMOSPHERE |
| مستخلص: |
Our solar system's path has recently been shown to potentially intersect dense interstellar clouds 2 and 7 million years ago: the Local Lynx of Cold Cloud and the edge of the Local Bubble. These clouds compressed the heliosphere, directly exposing Earth to the interstellar medium. Previous studies that examined climate effects of these encounters argued for an induced ice age due to the formation of global noctilucent clouds (NLCs). Here, we revisit such studies with a modern 2D atmospheric chemistry model using parameters of global heliospheric magnetohydrodynamic models as input. We show that NLCs remain confined to polar latitudes and short seasonal lifetimes during these dense cloud crossings lasting ∼105 years. Polar mesospheric ozone becomes significantly depleted, but the total ozone column broadly increases. Furthermore, we show that the densest NLCs lessen the amount of sunlight reaching the surface instantaneously by up to 7% while halving outgoing longwave radiation. Plain Language Summary: As the Solar System moves through the interstellar medium, it encounters different astrophysical environments. By tracing back the path of the Sun, two possible crossings of dense interstellar clouds 2 and 7 million years ago have been identified. These clouds are dense enough to compress the solar wind to inside of Earth's orbit, exposing Earth's atmosphere to interstellar gas. Previous studies that explored terrestrial climate changes due to these event argued for a global cooling effect that could trigger an ice age. In this study, we revisit this topic with a modern computational atmospheric chemistry model. We find that high‐altitude water significantly enhances the density and coverage of noctilucent clouds (NLCs) near the mesopause. In contrast with previous studies, this effect is neither permanent nor global, though some denser NLCs may still block up to 7% of sunlight from reaching Earth's surface. Furthermore, HOx compounds greatly deplete mesospheric ozone. We find for the first time that this mesospheric ozone decrease allows for a stratospheric ozone increase, resulting in an increase in the total ozone column. In order to assess the complete global climate response to these events, a more complete 3D model is required. Key Points: As a result of colliding with interstellar clouds 2 and 7 million years ago, Earth's upper atmosphere received an abundance of hydrogenBy converting interstellar hydrogen to water in the lower thermosphere, thick noctilucent clouds would have formedHOx compounds could have depleted mesospheric ozone by up to 99%, though the total ozone column generally increases [ABSTRACT FROM AUTHOR] |
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