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Summary A series of numerical experiments on an f plane are conducted using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale
Model, version 3 (MM5) to investigate how environmental vertical wind shear affects the motion, structure, and intensity of
a tropical cyclone. The results show that a tropical cyclone has a motion component perpendicular to the vertical shear vector,
first to the right of the shear and then to the left. An initially axisymmetric, upright tropical cyclone vortex develops
a downshear tilt and wavenumber-one asymmetry when embedded in environmental vertical wind shear.
In both small-moderate shears, a storm weakens slightly compared to that in a quiescent environment. The circulation centers
between 300 hPa and the surface varies from 20 km to over 80 km. The secondary circulation becomes quite asymmetric about
the surface cyclone center. As a result, convection on the upshear-right quadrant diminishes, limiting the upward heat transport
in the eyewall and thus lowering the warm core and leading to a weakening of the storm. In strong vertical shear (above 12 m s−1), the vertical tilt exceeds 160 km in 48 h of simulation and the secondary circulation on the upshear side is completely
destroyed with low-level outflow. The axisymmetric component of eyewall convection weakens remarkably and becomes much less
penetrative. As a result, the warm core becomes weak and appears at lower levels and the storm weakens rapidly accordingly.
This up-down weakening mechanism discussed in this study is different from those previously discussed. It emphasizes the penetrative
role of eyewall convection in transporting heat from the ocean to the mid-upper troposphere, maintaining the warm core structure
of the tropical cyclone. The vertical shear is found negative to eyewall penetrative convection. 相似文献
135.
Zaiyong Zhang Wenke Wang Chengcheng Gong Zhoufeng Wang Lei Duan Tian‐chyi Jim Yeh Peiyuan Yu 《水文研究》2019,33(9):1338-1348
In cold climates, the process of freezing–thawing significantly affects the ground surface heat balance and water balance. To better understand the mechanism of evaporation from seasonally frozen soils, we performed field experiments at different water table depths on vegetated and bare ground in a semiarid region in China. Soil moisture and temperature, air temperature, precipitation, and water table depths were measured over a 5‐month period (November 1, 2016, to March 14, 2017). The evaporation, which was calculated by a mass balance method, was high in the periods of thawing and low in the periods of freezing. Increased water table depth in the freezing period led to high soil moisture in the upper soil layer, whereas lower initial groundwater levels during freezing–thawing decreased the cumulative evaporation. The extent of evaporation from the bare ground was the same in summer as in winter. These results indicate that a noteworthy amount of evaporation from the bare ground is present during freezing–thawing. Finally, the roots of Salix psammophila could increase the soil temperature. This study presents an insight into the joint effects of soil moisture, temperature, ground vegetation, and water table depths on the evaporation from seasonally frozen soils. Furthermore, it also has important implications for water management in seasonally frozen areas. 相似文献
136.
Geochemical and environmental magnetic studies were carried out to identify the effect of iron oxyhydroxides on arsenic mobilization
in high arsenic aquifer system. Using high arsenic sediment samples from two boreholes, specifically drilled for this study,
chemical composition and magnetic properties including magnetic susceptibility, saturation remnant magnetization, and isothermal
remnant magnetization were measured. Results of correlation analysis of element contents show that arsenic and iron are closely
associated with each other (r
2 = 0.40, α = 0.05, n = 21). In contrast, the correlation of phosphorus with iron (r = 0.11, α = 0.05, n = 21) and arsenic (r
2 = 0.18, α = 0.05, n = 21) was poor, which might result from competitive adsorption of phosphorus and arsenic on the surface of Fe-oxyhydroxides.
The high correlation coefficients between arsenic contents and magnetic parameters suggest that the ferrimagnetic minerals
including maghemite and hematite are the dominant carrier of arsenic in aquifer sediments. The results of sequential extraction
experiments also revealed the association of arsenic with reducible iron oxides, such as maghemite and hematite in aquifer
sediments. Therefore, under reducing conditions, reductive dissolution and desorption of arsenic from Fe-oxyhydroxides into
the aqueous phase should be the dominant geochemical processes for its enrichment in groundwater at Datong.
An erratum to this article can be found at 相似文献
137.
YuLong Duan FaSi Wu DongPeng He RuiHong Xu HuYuan Feng Tuo Chen GuangXiu Liu WanFu Wang 《寒旱区科学》2021,13(6):522-532
In this study, a systematic survey of cultural airborne fungi was carried out in the occurrence environments of wall paintings that are preserved in the Tiantishan Grottoes and the Western Xia Museum, China. A bio-aerosol sampler was used for sampling in four seasons in 2016. Culture-dependent and -independent methods were taken to acquire airborne fungal concentration and purified strains; by the extraction of genomic DNA, amplification of fungal ITS rRNA gene region, sequencing, and phylogenetic analysis, thereafter the fungal community composition and distribution characteristics of different study sites were clarified. We disclosure the main environmental factors which may be responsible for dynamic changes of airborne fungi at the sampling sites. The concentration of cultural airborne fungi was in a range from 13 to 1,576 CFU/m3, no significant difference between the two sites at the Tiantishan Grottoes, with obvious characteristics of seasonal variation, in winter and spring were higher than in summer and autumn. Also, there was a significant difference in fungal concentration between the inside and outside of the Western Xia Museum, the outside of the museum was far more than the inside of the museum in the four seasons, particularly in the winter. Eight fungal genera were detected, including Cladosporium, Penicillium, Alternaria, and Filobasidium as the dominant groups. The airborne fungal community structures of the Tiantishan Grottoes show a distinct characteristic of seasonal variation and spatial distribution. Relative humidity, temperature and seasonal rainfall influence airborne fungal distribution. Some of the isolated strains have the potential to cause biodeterioration of ancient wall paintings. This study provides supporting information for the pre-warning conservation of cultural relics that are preserved at local sites and inside museums. 相似文献
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By use of 1948-2007 NCEP/NCAR reanalysis monthly geopotential data, a set of circulation indices are defined to characterize the polar vortex at 10 hPa in the Southern Hemisphere, including area-(S), intensity-(P) and centre position-(λc , φc) indices. Sea-sonal variation, interannual anomalies and their possible causes of 10 hPa polar vortex in the Southern Hemisphere are analyzed by using these indices, the relationship between 10 hPa polar vortex strength and the Antarctic Oscillation are analyzed as well. The results show that: (1) the polar region at 10 hPa in the Southern Hemisphere is controlled by anticyclone (cyclone) from Dec. to Jan. (from Mar. to Oct.), Feb. and Nov. are circulation transition seasons. (2) Intensity index (P) and area index (S) of anticy-clone (cyclone) in Jan. (Jul.) show a significant spike in the late 1970s, the anticyclone (cyclone) enhances (weakens) from ex-tremely weak (strong) oscillation to near the climatic mean before a spike, anticyclone tends to the mean state from very strong oscillation and cyclone oscillates in the weaker state after the spike. (3) There is significant interdecadal change for the anticyclone center in Jan., while markedly interannual variation for cyclone center in July. (4) The ozone anomalies can cause the interannual anomaly of the polar anticyclone at 10 hPa in the Southern Hemisphere in Jan. (positive correlation between them), but it is not related to the polar cyclone anomalies. (5) There is notable negative correlation between the polar vortex intensity index P and the Antarctic Oscillation index (AAOI), thus AAOI can be represented by P. 相似文献