利用重力资料精化大陆岩石圈热结构的理论模型

由于地表观测大地热流值的精度较低 ,并且测点分布不均匀 ,加之我们对地球内部介质热学参数随深度分布的了解也很模糊 ,因此 ,由通常解热传导方程获得的岩石层温度模型比较粗糙。本文提出一种利用重力异常资料精化传统的单纯依赖地热资料确定岩石层温度模型的方法 ,并对方法的有效性与局限性进行了讨论。     

Seismic imaging of the Formosa Ridge cold seep site offshore of southwestern Taiwan

Multi-scale reflection seismic data, from deep-penetration to high-resolution, have been analyzed and integrated with near-surface geophysical and geochemical data to investigate the structures and gas hydrate system of the Formosa Ridge offshore of southwestern Taiwan. In 2007, dense and large chemosynthetic communities were discovered on top of the Formosa Ridge at water depth of 1125 m by the ROV Hyper-Dolphin. A continuous and strong BSR has been observed on seismic profiles from 300 to 500 ms two-way-travel-time below the seafloor of this ridge. Sedimentary strata of the Formosa Ridge are generally flat lying which suggests that this ridge was formed by submarine erosion processes of down-slope canyon development. In addition, some sediment waves and mass wasting features are present on the ridge. Beneath the cold seep site, a vertical blanking zone, or seismic chimney, is clearly observed on seismic profiles, and it is interpreted to be a fluid conduit. A thick low velocity zone beneath BSR suggests the presence of a gas reservoir there. This “gas reservoir” is shallower than the surrounding canyon floors along the ridge; therefore as warm methane-rich fluids inside the ridge migrate upward, sulfate carried by cold sea water can flow into the fluid system from both flanks of the ridge. This process may drive a fluid circulation system and the active cold seep site which emits both hydrogen sulfide and methane to feed the chemosynthetic communities.     

Multiple impact events on the L-chondritic parent body: Insights from SIMS U-Pb dating of Ca-phosphates in the NWA 7251 L-melt breccia

Here we report in situ secondary ionization mass spectrometry Ca-phosphate U-Pb ages for an L-impact melt breccia (NWA 7251), which are integrated with petrological and mineral chemical studies of this meteorite. NWA 7251 is a heavily shocked rock that is composed mainly of the chondrite host, impact melt portion, and melt veins (crosscutting and pervasive type). The host is an L4 chondrite that has been shocked to S4. The impact melt portion has a fine-grained igneous texture, and is composed mainly of olivine, low-Ca pyroxene, high-Ca pyroxene, and albitic glass. The impact melt was generated at pressure of >30–35 GPa and temperature of >1300–1500 °C during an impact event. The Ca-phosphate grains in the host were affected by a shock heating event. Most of the Ca-phosphate grains in the melt were neocrystallized, but relatively large grains enclosed by or adjacent to metal veins or melt globules are likely inherited. The U-Pb isotopic systematics of Ca-phosphates in NWA 7251 yield an upper intercept age of 4457 ± 56 Ma and a lower intercept age of 574 ± 82 Ma on the normal U-Pb concordia diagram. The age of 4457 ± 56 Ma is interpreted to be related to an early shocking event rather than the thermal metamorphism of the parent body. The impact melt and veins in NWA 7251 were generated at 574 ± 82 Ma, resulting from disruption of the L chondrite parent body.     

Laboratory flume studies on monochromatic wave-fine sandy bed interactions Part 2. Sediment suspensions

As reported in preceding paper (Part 1. Soil Fluidization), the observed phenomena of sediment suspensions above a fluidized sandy bed of Sand II (d₅₀ = 0.092 mm) under monochromatic wave actions are quantitatively investigated. The suspended sediment concentration (SSC) at a single point within 5 cm above the bed was synchronously measured with water waves and bed soil's pore pressures with an intrusive optical sediment-concentration probe. The measurements show that SSC initiates several wave cycles after initiation of bed soil's fluidized response and grows to a peak value mainly in the post-fluidization phase. Under similar wave loadings in the same test series, SSC is usually higher over a resonantly fluidized (RF) bed than over a non-resonantly fluidized (NRF) bed. On the contrary, only relatively low SCC can be identified above an unfluidized bed. The analyses illustrate that to certain extent, peak values of SSC are directly proportional to the thickness of fluidized soil layer d_f. Values of d_f usually decrease with repeated fluidized response, longer consolidation periods, and in deeper water depths. Once the fluidized responses initiate, pore pressures are generally much significantly amplified in both shallow fluidized soil layers and near below the fluidized layer, especially during the resonance event. The resulting depth gradients of dynamic pore pressure amplitudes in shallow layers are likely to have caused higher initial rises of SSC in a RF bed than in the subsequent NRF bed. Those in deeper layer should have contributed to sustain the fluidization state for further SSC increments. Immediately after termination of wave loading, re-deposited suspended sediments always result in a typical flat bed form. For a pre-fluidized bed, wave-induced drastic sediment suspensions are still obtainable very near above the bed with even a rather thin fluidized surface soil layer.     

Ephemeral sand waves in the hurricane surf zone

Airborne bathymetric LIDAR observations along the Florida panhandle after Hurricane Dennis (2005) show the first unequivocal observations of surf-zone sand wave trains.

These are found in depths of 5m along the trough of the hurricane bar, where hindcasts show strong longshore currents only during severe storms. The waves extend over tens of kilometers of coast after Dennis but are absent from the same area in four other datasets. Observed wavelength to water depth ratios are comparable to river dunes and tidal sand waves but height to depth ratios are smaller, with the largest wave heights around 0.1 times the water depth. The sand wave generation mechanism is hypothesized to be from wind-and-wave-induced longshore currents, which were hindcast to be large during Dennis, with destruction from water wave orbital velocities.     

A GIS-based Decision Support System for Typhoon Emergency Response in Taiwan

The effective response actions can significantly reduce the damage caused by disasters, but the emergency managers require plenty of information before setting up appropriate strategies. The data gathering and analyzing processes are complex and the time is constrained during emergency. A GIS-based decision support system was developed to enhance the emergency operations during typhoon attacks in Taiwan. The system integrates the real time rainfall monitor and forecast information, the hazard potential, and the basic spatial database to help the emergency managers making decisions efficiently.     

Multi-model MJO forecasting during DYNAMO/CINDY period

The present study assesses the forecast skill of the Madden–Julian Oscillation (MJO) observed during the period of DYNAMO (Dynamics of the MJO)/CINDY (Cooperative Indian Ocean Experiment on Intraseasonal Variability in Year 2011) field campaign in the GFS (NCEP Global Forecast System), CFSv2 (NCEP Climate Forecast System version 2) and UH (University of Hawaii) models, and revealed their strength and weakness in forecasting initiation and propagation of the MJO. Overall, the models forecast better the successive MJO which follows the preceding event than that with no preceding event (primary MJO). The common modeling problems include too slow eastward propagation, the Maritime Continent barrier and weak intensity. The forecasting skills of MJO major modes reach 13, 25 and 28 days, respectively, in the GFS atmosphere-only model, the CFSv2 and UH coupled models. An equal-weighted multi-model ensemble with the CFSv2 and UH models reaches 36 days. Air–sea coupling plays an important role for initiation and propagation of the MJO and largely accounts for the skill difference between the GFS and CFSv2. A series of forecasting experiments by forcing UH model with persistent, forecasted and observed daily SST further demonstrate that: (1) air–sea coupling extends MJO skill by about 1 week; (2) atmosphere-only forecasts driven by forecasted daily SST have a similar skill as the coupled forecasts, which suggests that if the high-resolution GFS is forced with CFSv2 forecasted daily SST, its forecast skill can be much higher than its current level as forced with persistent SST; (3) atmosphere-only forecasts driven by observed daily SST reaches beyond 40 days. It is also found that the MJO–TC (Tropical Cyclone) interactions have been much better represented in the UH and CFSv2 models than that in the GFS model. Both the CFSv2 and UH coupled models reasonably well capture the development of westerly wind bursts associated with November 2011 MJO and the cyclogenesis of TC05A in the Indian Ocean with a lead time of 2 weeks. However, the high-resolution GFS atmosphere-only model fails to reproduce the November MJO and the genesis of TC05A at 2 weeks’ lead. This result highlights the necessity to get MJO right in order to ensure skillful extended-range TC forecasting.     

East Asian,Indochina and Western North Pacific Summer Monsoon - An update

This review provides a summary of the major research progress in the variability of East Asian, Indochina and Western North Pacific Summer Monsoon. Time scales of the reviewed phenomena range from diurnal to interannual and interdecadal. Research results published in the past decades are the major sources for this review.     

The early 1950s regime shift in temperature in Taiwan and East Asia

A summer climate regime shift in temperature in Taiwan and East Asia during the early 1950s was identified in this study. The event was characterized by a cooling land-warming ocean dipole in East Asia and the western North Pacific, marking the decreasing land–sea thermal contrast from the 1940s to the 1950s. The corresponding sea surface temperature (SST) anomaly was characterized by the sign flipping of a north–south dipole in the western North Pacific from north/cool-south/warm to north/warm-south/cool, indicating a weakening north–south SST gradient in the area. The corresponding change in mean sea level pressure was characterized by the rising pressure in continental East Asia and the Philippine Sea, and the falling pressure over the extratropical western North Pacific to the east of Japan. This change was the reflection of a weakening thermal low in the continental East Asia, a weakening monsoon trough in the tropical western North Pacific, a strengthening and southwestward-expanding ridge in the subtropical western North Pacific, and a deepening mid-latitude trough over eastern China and Japan. The phase reversal of the SST anomaly in the western North Pacific exhibited the characteristics of the Pacific Decadal Oscillation (PDO), but lagged behind the phase reversal of the PDO in the extratropical North Pacific by several years. The connection with the PDO is speculated, although the mechanism is not understood. This paper is a contribution to the AMIP-CMIP Diagnostic Sub-project on General Circulation Model Simulation of the East Asian Climate, coordinated by W.-C. Wang.