河西走廊夏季强沙尘暴数值模拟试验

影响我国的沙尘暴灾害性天气多发生在春季,很少在夏季发生。文章利用我国科学家自主研发的GRAPES-DAM沙尘气溶胶模式对2005年7月一次罕见的影响河西走廊地区的群发性强沙尘暴进行了数值模拟,对夏季小概率强沙尘暴灾害天气的可预报性进行了个例研究。试验结果表明:模式对此次过程的地面大风、沙尘暴的范围、移动等均能做出较好的模拟;对于夏季群发性强沙尘暴过程,基于数值预报方法的沙尘气溶胶模式在天气模式预报准确的条件下,可以对这种小概率事件做出有应用意义的预报结果。     

Hurricanes and tropical storms: A necessary evil to ensure water supply?

Several parts of the globe including Southeast North America, the Caribbean, Southeast Asia, Australia, and China are often hit by hurricanes and tropical storms (HTSs), which can deliver a large amount of rainfall within a period of a few days. Although HTSs are mostly studied as disaster agents, considering that they occur during the period when water supply systems are generally depleted, it is important to ascertain their potential contributions toward sustaining water supply. Using the Lake Michie–Little River reservoir system that supplies water to the city of Durham (North Carolina) as a representative test case, we implemented an integrated watershed and reservoir management model, supported by publicly available observations, to evaluate the extent to which HTSs impact water storages. Results indicate that HTSs can have a significant impact on reservoir water storage, with their effects being felt for more than a year for some storms. The impact on reservoir water storage is identified to be primarily controlled by 3 factors, namely, streamflow response size from HTSs, storage in the reservoir right before the event, and streamflow succeeding the event response to HTS (henceforth referred as postevent streamflow). Although the impact of streamflow response size on water storage is generally proportional to its magnitude, initial water storage in the reservoir and postevent streamflow have a nonmonotonic influence on water storage. As all the 3 identified controls are a function of antecedent hydrologic conditions and meteorological forcings, these 2 factors indirectly influence the impact of HTS on water storage in a reservoir. The identification of controlling factors and assessment of their influence on reservoir response will further facilitate implementation of more accurate estimation and prediction frameworks for within‐year reservoir operations.     

The effects of tropical storm Dennis on coastal phytoplankton

The effects of tropical storm Dennis were documented in the coastal waters of South Carolina during August 1981. Phytoplankton photosynthesis vs. irradiance curves showed initial depression of the parameter a followed by three- to five-fold increase of both a and the asymptotic maximum rate of photosynthesis P_m^B. Productivity rates were depressed in most samples immediately after the storm. Surface samples at the inshore stations were around 50 mg C m^?3 h^?1 at saturating light intensities, while the offshore station rates were around 10 mg C m^?3 h^?1. After a 10-day lag these rates had increased to about 200 mg C m^?3 h^?1 inshore and 75 mg C m^?3 h^?1 offshore. These changes are thought to be primarily caused by changes in species composition. Some of the dominant diatom species changed and dinoflagellate species were introduced. No significant changes in nutrient concentrations were observed. Transient depressions of water temperature, salinity and light intensity may have contributed to the observed changes.     

Low frequency 1/f-like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere

Low frequency stochastic variations of the geomagnetic AE-index characterized by 1/f^b-like power spectrum (where f is a frequency) are studied. Based on the analysis of experimental data we show that the B_z-component of IMF, velocity of solar wind plasma, and the coupling function of Akasofu are insufficient factors to explain these behaviors of the AE-index together with the 1/f^b fluctuations of geomagnetic intensity. The effect of self-organized criticality (SOC) is proposed as an internal mechanism to generate 1/f^b fluctuations in the magnetosphere. It is suggested that localized spatially current instabilities, developing in the magnetospheric tail at the initial substorm phase can be considered as SOC avalanches or dynamic clusters, superposition of which leads to the 1/f^b fluctuations of macroscopic characteristics in the system. Using the sandpile model of SOC, we undertake numerical modeling of space-localized and global disturbances of magnetospheric current layer. Qualitative conformity between the disturbed dynamics of self-organized critical state of the model and the main phases of real magnetospheric substorm development is demonstrated. It is also shown that power spectrum of sandpile model fluctuations controlled by real solar wind parameters reproduces all distinctive spectral features of the AE fluctuations.     

Inconsistent palaeomagnetic recording of the Blake event in Chinese loess related to sedimentary environment

Three loess sequences located east of the Liupan mountain region, China, were studied to obtain records of the Blake polarity event. Palaeomagnetic records from the appropriate stratigraphic interval of these three sequences, however, record the Blake event poorly in one case and not at all in the other two cases. It is important to understand why these loess sequences miss the Blake event, whereas others record it quite well. We conclude that regional variations in the sedimentary environment over the Chinese loess plateau are responsible for the inconsistent recording of the Blake event. The palaeomagnetic records suggest a threefold subdivision of the Chinese loess plateau into (1) the central and southern portions of the part of the plateau that lies east of the Liupan Mountains, where the primary record of the Blake event has been severely smoothed or wiped out by pedogenic processes during palaeosol (S1) formation; (2) the northern margin of the loess plateau to the east of the Liupan Mountains, where frequent, severe dust storms have resulted in discontinuous records with a high probability of missing the Blake event; and (3) the region west of the Liupan Mountains, where loess sequences are deposited rapidly and nearly continuously with only minor pedogenesis, and are thus capable of recording short events like the Blake.     

Stratigraphical evidence of Late Holocene barrier breaching and extreme storms in lagoonal sediments of Ria Formosa, Algarve, Portugal

Stratigraphical, sedimentological and paleoecological studies undertaken in lagoonal sediments of the Ria Formosa barrier lagoon indicate that a number of present-day aligned beaches outcropping within the marsh and detached from mainland (marsh detached beaches, MDB) represent the remnants of former ephemeral flood deltas, which established following barrier breaching induced by extreme storms from circa 1270 BC onwards. Dating of these beaches suggests that they resulted from multiple events of flooding separated both in time and space. Repeated emplacement of tidal deltas following overwash of the same location of the barrier is represented in the stratigraphical record by buried and partly overlapping marsh beaches. It is suggested that further refinement of the data presented in this paper and the extension of the stratigraphic survey to the entire lagoonal space will substantiate the usefulness of the stratigraphic record as a proxy to hindcast a time series of extreme storminess extending far beyond the instrumental and historical records.     

Are solar activity and sperm whale Physeter macrocephalus strandings around the North Sea related?

In the final decades of the last century, an increasing number of strandings of male sperm whales (Physeter macrocephalus) around the North Sea led to an increase in public interest. Anthropogenic influences (such as contaminants or intensive sound disturbances) are supposed to be the main causes, but natural environmental effects may also explain the disorientation of the animals. We compared the documented sperm whale strandings in the period from 1712 to 2003 with solar activity, especially with sun spot number periodicity and found that 90% of 97 sperm whale stranding events around the North Sea took place when the smoothed sun spot period length was below the mean value of 11 years, while only 10% happened during periods of longer sun spot cycles. The relation becomes even more pronounced (94% to 6%, n = 70) if a smaller time window from November to March is used (which seems to be the main southward migration period of male sperm whales). Adequate chi-square tests of the data give a significance of 1% error probability that sperm whale strandings can depend on solar activity. As an alternative explanation, we suggest that variations of the earth's magnetic field, due to variable energy fluxes from the sun to the earth, may cause a temporary disorientation of migrating animals.     

The brightness temperature adjusted dust index: An improved approach to detect dust storms using MODIS imagery

Moderate Resolution Imaging Spectroradiometer (MODIS) imagery provides a good data source for timely and accurate monitoring of dust storms. However, effective MODIS-based dust indices are inadequate. In this study, we proposed an improved brightness temperature adjusted dust index (BADI) by integrating the brightness temperatures of three thermal infrared MODIS bands: band₂₀ (3.66–3.84 μm), band₃₁ (10.78–11.28 μm) and band₃₂ (11.77–12.27 μm). We used the BADI to monitor several representative dust storms over the Northeast Asia between 2000 and 2011. When compared to commonly used MODIS-based dust indices, such as the brightness temperature difference index in band₃₂ and band₃₁ (BTD_32-31) and the normalized difference dust index (NDDI), the BADI captured the spatial extent and density of dust storms more accurately. The BADI detected dust storm extent with an overall accuracy >90%, which was 7% and 29% higher than the results derived from BTD_32-31 and NDDI, respectively. The BADI also demonstrated good agreement with the density indicator of MODIS Deep Blue Aerosol Optical Depth (R² = 0.59, P < 0.01). We suggest that the BADI is an effective tool to monitor large-scale dust storms.     

灰色拓扑预测模型在初台预测中的应用

本文应用灰色系统理论，建立了南海初台的拓扑预测模型，并利用这些模型对南海初台未来十年出现日期作了预测分析，为南海台风的长期预测提供信息。     

Difference infiltrometer: a method to measure temporally variable infiltration rates during rainstorms

We developed a difference infiltrometer to measure time series of non‐steady infiltration rates during rainstorms at the point scale. The infiltrometer uses two, tipping bucket rain gages. One gage measures rainfall onto, and the other measures runoff from, a small circular plot about 0.5‐m in diameter. The small size allows the infiltration rate to be computed as the difference of the cumulative rainfall and cumulative runoff without having to route water through a large plot. Difference infiltrometers were deployed in an area burned by the 2010 Fourmile Canyon Fire near Boulder, Colorado, USA, and data were collected during the summer of 2011. The difference infiltrometer demonstrated the capability to capture different magnitudes of infiltration rates and temporal variability associated with convective (high intensity, short duration) and cyclonic (low intensity, long duration) rainstorms. Data from the difference infiltrometer were used to estimate saturated hydraulic conductivity of soil affected by the heat from a wildfire. The difference infiltrometer is portable and can be deployed in rugged, steep terrain and does not require the transport of water, as many rainfall simulators require, because it uses natural rainfall. It can be used to assess infiltration models, determine runoff coefficients, identify rainfall depth or rainfall intensity thresholds to initiate runoff, estimate parameters for infiltration models, and compare remediation treatments on disturbed landscapes. The difference infiltrometer can be linked with other types of soil monitoring equipment in long‐term studies for detecting temporal and spatial variability at multiple time scales and in nested designs where it can be linked to hillslope and basin‐scale runoff responses. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.