Xiaocong Wang

40Ar/39Ar dating of ignimbrite from Inner Mongolia, northeastern China, indicates a post‐Middle Jurassic age for the overlying Daohugou Bed

The Ar-40/Ar-39 step heating analyses of K-feldspar derived from the ignimbrite in Inner Mongolia, China indicates that they were formed at 159.8 +/- 0.8 Ma, which provides a maximum age for the overlying fossil-bearing lacustrine deposits (Daohugou Bed). This result favors a post-Middle Jurassic ( Late Jurassic or younger), rather than the Middle Jurassic age for the Daohugou Bed. Such a result is generally consistent with vertebrate biostratigraphic evidence, providing a maximum known age for the first appearance of several major animal groups such as Cryptobranchidae of Urodela ( salamanders) and Maniraptora ( birds and their closest dinosaurian relatives).

The 40Ar/39Ar dating of the early Jehol Biota from Fengning, Hebei Province, northern China

The bird fossil-bearing deposits at the Jiecaigou section, correlative to the Dabeigou Formation, in Fengning, Hebei Province, northern China, is well known for yielding a fossil assemblage representing the earliest evolutionary stage of the Jehol Biota. The precise age of the fossil-bearing deposits, however, is unknown. The Ar-40/Ar-39 age spectrum obtained on bulk K-feldspars from the tuff layer about 2 m below the bird fossil-bearing layer gave a plateau age of 129.0 +/- 1.3 Ma (2 sigma, full external error) and an isochron age of 132.3 +/- 4.5 Ma (2 sigma, full external error). Seventeen total-fusion Ar-40/Ar-39 ages on K-feldspars from the interbedded tuff about 6 m below the fossil-bearing layer resulted in a weighted mean of 130.7 +/- 1.4 Ma (2 sigma, full external error). These dates suggest an age of similar to 131 Ma for the early Jehol Biota and combined with previous dating indicate that this biota lasted at least from 131 Ma to 120 Ma (Late Hauterivian to Aptian). These dates also represent the earliest absolute age for known enantiornithine birds in the world.

40Ar/39Ar dating of Lujiatun Bed (Jehol Group) in Liaoning, northeastern China

The Lujiatun bed of the Yixian Formation is famous for its extraordinary preservation of three-dimensional fossils and its implication for the most dramatic catastrophic mass mortality event in the Jehol Biota. The precise age of the fossil bearing deposits, however, remains to be established. Ar-40/Ar-39 step heating analyses on bulk K-feldspars from the fossil bearing tuff gave a weighted mean age of 123.2 +/- 1.0 Ma (2 sigma). This date suggests the Lujiatun bed was most likely deposited at about the same time as the Jianshangou bed of the lower Yixian Formation, representing a stage when the dinosaurs displayed the most significant radiation in the Early Cretaceous.

Vertical velocity in shallow convection for different plume types

This study investigates the bulk budgets of the vertical velocity and its parameterization in convective cores, convective updrafts, and clouds by using large-eddy simulation (LES) of four shallow convection cases in the Global Energy and Water Cycle Experiment (GEWEX) Cloud System Study (GCSS) programs. The relative magnitudes of the dominant momentum budget terms for the three types of plumes are presented. For all shallow cumulus except stratocumulus, the buoyancy force and the subplume transport in the core plume are the momentum source that offset the pressure gradient force. In the cloud updraft and cloud plumes, the buoyancy source is dominant in the lower and middle parts of the clouds, while the subgrid transport is a dominant source in the upper part, and the entrainment term is also a momentum source. For the stratocumulus, the subplume transport is a sink almost in the whole convective layer. For all types of plumes, the Simpson and Wiggert (1969) equation is found to be good paramaterization of the mean plume vertical velocity when appropriate scaling coefficients to buoyancy and entrainment terms are used. Optimal forms of the Simpson and Wiggert equation are given for convective cores, convective updrafts, and convective clouds. Results are compared with other studies published in the literature.

The coupling of mixed Rossby-Gravity Waves with diabatic heating during the TRMM-KWAJEX field campaign

Composite dynamic and thermodynamic structures of mixed Rossby-gravity (MRG) waves are presented with their coupling with diabatic heating and moisture sources/sinks, using Tropical Rainfall Measuring Mission-Kwajalein Experiment (TRMM-KWAJEX) field campaign data. A significant departure of convectively coupled waves from dry waves exists in the phases of wave component: maximum low-level wind convergence is accompanied by midtropospheric divergence and upper tropospheric convergence that is preceded by increase of moisture in the boundary layer. These phases correspond to surface turbulent transport, shallow and midlevel convections that cause moistening and heating of the lower and middle troposphere. They are followed by deep convection with maximum heating centered in the upper troposphere. The deep convective heating evolves to stratiform-like upper tropospheric heating and lower tropospheric cooling that precedes the quick demise of convection. Such a structure on convectively coupled MRG waves is summarized by four phases, which sheds lights on how tropical waves are coupled with convective processes in all their phases.