The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored. 相似文献
Summary A pilot tropical cyclone reanalysis project was conducted to construct a reliable, high temporal and spatial resolution tropical
cyclone dataset for selected western Pacific typhoons in summer 2004, with the application of the latest satellite observations
and a 4-dimensional variational data assimilation method. Primary data used for the reanalysis include SSM/I rain rate, GOES-retrieved
upper-level wind, QuikSCAT surface wind, Aqua AIRS/AMSU retrieved temperature and moisture profiles, and JTWC best track data.
A regular reanalysis procedure was established and up to 12 western Pacific typhoons have been reanalyzed. The reanalysis
period covers the entire life cycle of a tropical cyclone, from a few days prior to its genesis to its final decay stage.
A preliminary analysis shows that the reanalysis product significantly improves typhoon intensity, structure, and track, compared
to the NCEP operational final analysis. The validation of the TC structure against independent observations shows that the
reanalysis reproduces well the asymmetric characteristics of TC rain bands and cloud bands. A further modeling experiment
with an initial condition from the reanalysis product reveals a significant improvement in typhoon intensity forecast compared
to a parallel experiment with an initial condition from the NCEP final analysis, which provides a further indication of quality
of the tropical cyclone reanalysis. The reanalysis product and the raw observational data will soon be posted on the data
server of the IPRC Asia-Pacific Data-Research Center () for public use. 相似文献
In the context of August 1982- July 1983 radiation balance data of the Qinghai-Xizang Plateau, detailed study is made of the relation between the active-surface temperature and surface temperature, proposing two parameterization schemes on surface long-wave radiation(SLWR)of the form U=kδσ(T0+273)4 and U=δσ[(T0+273)4+△T)]4, where k and △T are indicated by parameterization equations, separately, others being in conventional notation. Retrieved verification shows the two formulae to be of the same fitting accuracy with the mean relative error of 3.6% and suitable for computing instantaneous and mean flux density, alongside analyzed daily and annual variations of k and △T. Eventually. SLWR in the target area is investigated and its climatic characteristics examined. 相似文献
Radio-frequency interference (RFI) affects greatly the quality of the data and retrieval products from space-borne microwave radiometry. Analysis of the Advanced Microwave Scanning Radiometer on the Earth Observing System (AMSR-E) Aqua satellite observations reveals very strong and widespread RFI contam- inations on the C- and X-band data. Fortunately, the strong and moderate RFI signals can be easily identified using an index on observed brightness temperature spectrum. It is the weak RFI that is diffi- cult to be separated from the nature surface emission. In this study, a new algorithm is proposed for RFI detection and correction. The simulated brightness temperature is used as a background signal (B) and a departure of the observation from the background (O-B) is utilized for detection of RFI. It is found that the O-B departure can result from either a natural event (e.g., precipitation or flooding) or an RFI signal. A separation between the nature event and RFI is further realized based on the scattering index (SI). A positive SI index and low brightness temperatures at high frequencies indicate precipitation. In the RFI correction, a relationship between AMSR-E measurements at 10.65 GHz and those at 18.7 or 6.925 GHz is first developed using the AMSR-E training data sets under RFI-free conditions. Contamination of AMSR-E measurements at 10.65 GHz is then predicted from the RFI-free measurements at 18.7 or 6.925 GHz using this relationship. It is shown that AMSR-E measurements with the RFI-correction algorithm have better agreement with simulations in a variety of surface conditions. 相似文献
Based on lab-culture experiments analyzing limitation and combination of iron and phosphorus on the growth of Cryptomonas sp. (Cryptophyceae), and the study of accumulation and release of Fe-bound P in sediment cores collected from the marine region of the Pearl River Estuary, China, reasons for the high frequency of phytoplankton bloom therein are discussed. Results show that the combined effect of Fe and P can obviously accelerate algal development, and the optimum culture conditions maintaining maximum growth rate are 0.05 μM Fe and 50 μM P. Cellular contents of Fe and P is consistent and the P:Fe molar ratio is 159:1. The optimum range of the P:Fe molar ratio in culture experiments for cell incubation is 500–1400. The vertical trends of total Fe and total P variations in sediments are parallel. Fe-bound P is the main species of inorganic sedimentary P. Through continuous leaching with agitation, 34–80% of exchangeable P and 4–23% of exchangeable Fe are concurrently released from the surficial sediments. This is a possible way by which nutrients are made available to phytoplankton. These factors might be responsible for a high frequency of harmful algal blooms in the Pearl River Estuary. 相似文献
Extreme weather has recently caused many disasters worldwide. In August 8, 2009, Southern Taiwan suffered from serious floods during Typhoon Morakot. In this extreme rainfall event, the Chiuliao first levee in the Laonong River basin experienced catastrophic failure. Therefore, this study focuses on the levee failure mechanisms based on variations in levee water levels. Specifically, this study investigates four mechanisms based on limit state equilibrium. The first mechanism involves the slope stability under hydrostatic conditions at various water levels. The results of this analysis show that the levee cannot fail under this mechanism. The second mechanism involves the levee slope stability with steady-state seepage. Because the water levels are different on the protected and flood sides, the water recedes much faster on the flood side than the protected side. Based on this analysis, the levee slope might fail when the water level at the protected side is close to the top of levee and the water level at the flood side starts to recede. The third and fourth mechanisms involve the levee foundation failure in terms of sliding and overturning failure. The results of this study indicate that the levee foundation is more prone to sliding failure than overturning failure. Based on these results, this study shows that the levee failed when the water level at the protected side neared the top of levee while the water level at flood side started to recede. At this moment, the levee may fail because of both the slope failure with seepage and sliding failure of the levee foundation. 相似文献
Mega-earthquakes and extreme climate events accompanied by intrinsic fragile geology lead to numerous landslides along mountain highways in Taiwan, causing enormous life and economic losses. In this study, a system for rapid slope disaster information integration and assessment is proposed with the aim of providing information on landslide occurrence, failure mechanisms, and subsequent landslide-affected areas to the highway authority rapidly. The functionality of the proposed system is deployed into three units: (1) geohazard rapid report (GeoPORT I), (2) multidisciplinary geological survey report (GeoPORT II), and (3) site-specific landslide simulation report (GeoPORT III). After landslide occurrence, the seismology-based monitoring network rapidly provides the initial slope disaster information, including preliminary location, event magnitude, earthquake activity, and source dynamics, within an hour. Within 3 days of the landslide, a multidisciplinary geological survey is conducted to collect high-precision topographical, geological, and remote-sensing data to determine the possible failure mechanism. After integrating the aforementioned information, a full-scale three-dimensional landslide simulation based on the discrete element method is performed within 10 days to reveal the failure process and to identify the areas potentially affected by subsequent disasters through scenario modeling. Overall, the proposed system can promptly provide comprehensive and objective information to relevant authorities after the event occurrence for hazard assessment. The proposed system was validated using a landslide event in the Central Cross-Island Highway of Taiwan.