Previous studies suggest that tidal friction gives rise to the secular deceleration of the Earth rotation by a quantity of about 2.25 ms/cy. Here we just consider additional contributions to the secular Earth rotation...Previous studies suggest that tidal friction gives rise to the secular deceleration of the Earth rotation by a quantity of about 2.25 ms/cy. Here we just consider additional contributions to the secular Earth rotation deceleration. Atmospheric solar semi-diurnal tide has a small amplitude and certain amount of phase lead. This periodic global air-mass excess distribution exerts a quasi-constant torque to accelerate the Earth＇s spin rotation. Using an updated atmospheric tide model, we re-estimate the amounts of this atmospheric acceleration torque and corresponding energy input, of which the associated change rate in LOD（length of day） is-0.1 ms/cy. In another aspect, evidences from space-geodesy and sea level rise observations suggest that Earth expands at a rate of 0.35 mm/yr in recent decades, which gives rise to the increase of LOD at rate of 1.0 ms/cy. Hence, if the previous estimate due to the tidal friction is correct, the secular Earth rotation deceleration due to tidal friction and Earth expansion should be 3.15 ms/cy.展开更多
Charcoal is abundant in most post-Silurian sedimentary sequences and even in some volcanic rocks. The study of charcoal can provide important information on not only what plants were being burned but also on how the c...Charcoal is abundant in most post-Silurian sedimentary sequences and even in some volcanic rocks. The study of charcoal can provide important information on not only what plants were being burned but also on how the charcoal residue was formed. Most charcoal encountered in the sedimentary record is a result of lightning-ignited wildfires but volcanic activity may also act as an ignition source. Charcoal preserves exquisite anatomical data that can be studied by a range of microscopical techniques including scanning electron microscopy that allows the identity of the plants to be determined. Fires have a major impact on a range of environments and ecosystems. The elevated oxygen content of the atmosphere indicates that the Cretaceous can be considered a "high-fire" world. Fire activity should be taken into account in Cretaceous vegetation and climate models. The occurrence of charcoal at the Cretaceous-Tertiary Boundary has been highlighted as evidence for a global fire following an asteroid impact, but this interpretation is questionable.Charcoal may be found within volcanic rocks, especially from deposits of pyroclastic flows and from basaltic lavas. This may provide data on the entombed vegetation but reflectance data may be used to provide interpretations of deposit temperatures. Charcoal is information-rich but yet is an under-utilized resource. Fire is an expression of life on Earth and an index of life's history and is relevant for geology, biology, human history, physics and global chemistry.展开更多
基金partly supported by National 973 Project China(2013CB733305)NSFC(41174011,41210006,41504019)supported by a fund from Korea Astronomy and Space Science Institute(2016 Space Geodesy Project about Atmospheric/Ocean Tidal Effects)
文摘Previous studies suggest that tidal friction gives rise to the secular deceleration of the Earth rotation by a quantity of about 2.25 ms/cy. Here we just consider additional contributions to the secular Earth rotation deceleration. Atmospheric solar semi-diurnal tide has a small amplitude and certain amount of phase lead. This periodic global air-mass excess distribution exerts a quasi-constant torque to accelerate the Earth＇s spin rotation. Using an updated atmospheric tide model, we re-estimate the amounts of this atmospheric acceleration torque and corresponding energy input, of which the associated change rate in LOD（length of day） is-0.1 ms/cy. In another aspect, evidences from space-geodesy and sea level rise observations suggest that Earth expands at a rate of 0.35 mm/yr in recent decades, which gives rise to the increase of LOD at rate of 1.0 ms/cy. Hence, if the previous estimate due to the tidal friction is correct, the secular Earth rotation deceleration due to tidal friction and Earth expansion should be 3.15 ms/cy.
文摘Charcoal is abundant in most post-Silurian sedimentary sequences and even in some volcanic rocks. The study of charcoal can provide important information on not only what plants were being burned but also on how the charcoal residue was formed. Most charcoal encountered in the sedimentary record is a result of lightning-ignited wildfires but volcanic activity may also act as an ignition source. Charcoal preserves exquisite anatomical data that can be studied by a range of microscopical techniques including scanning electron microscopy that allows the identity of the plants to be determined. Fires have a major impact on a range of environments and ecosystems. The elevated oxygen content of the atmosphere indicates that the Cretaceous can be considered a "high-fire" world. Fire activity should be taken into account in Cretaceous vegetation and climate models. The occurrence of charcoal at the Cretaceous-Tertiary Boundary has been highlighted as evidence for a global fire following an asteroid impact, but this interpretation is questionable.Charcoal may be found within volcanic rocks, especially from deposits of pyroclastic flows and from basaltic lavas. This may provide data on the entombed vegetation but reflectance data may be used to provide interpretations of deposit temperatures. Charcoal is information-rich but yet is an under-utilized resource. Fire is an expression of life on Earth and an index of life's history and is relevant for geology, biology, human history, physics and global chemistry.
