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《气象研究与应用》2016,(1)
利用广西典型石漠化区28个气象站逐日降水资料,分析该地区1971-2013年的年际、季节变化特征,并利用线性倾向估计法,计算其变化趋势,结合Mann-Kendall检验法检验其变化的突变时间及显著性。结果表明:近43a广西典型石漠化地区的年降水量总体呈不显著的减少趋势,但降水年际变化较大。70年代和90年代为多雨期,80年代和00年代以后为少雨期。同时,各季降水量都具有明显的阶段性,春、夏、秋季呈减少趋势,其中秋季减少较明显,为-15.7mm/10a,春季和夏季次之,分别为-13.4mm/10a和-1.8mm/10a;冬季呈略增加趋势,为3.9mm/10a。在突变特征方面,典型石漠化区年降水量与各季降水量突变时间不同,其中年降水量比春、夏、秋季的减少突变时间偏早,比冬季增加的突变时间偏晚,且年降水量与春、夏、秋季减少的突变均发生在80年代中后期。 相似文献
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黄秋霞 《沙漠与绿洲气象(新疆气象)》2014,8(4):61-68
基于哈萨克斯坦5个代表站的降水资料,利用一元线性回归法、Mann-Kendall突变检验和Morlet小波的方法,分析历年降水变化特征,结果表明：东部和中部降水呈减少趋势,其余为增加趋势,东部于1962年发生突变,西部和中部分别于1970年和1984年发生突变。东部春季和夏季的降水呈减少趋势,秋季和冬季为增加趋势。西部的春季、秋季和冬季降水呈增加趋势,夏季降水呈减少趋势。北部春季和秋季降水为增加趋势,夏季和冬季降水呈减少趋势。南部的春季、夏季和秋季降水呈增加趋势,冬季降水呈减少趋势。中部春季、夏季和秋季的降水呈减少趋势,冬季降水呈增加趋势。哈萨克斯坦不同区域的降水量均存在多个尺度的周期变化,但其共同点是均存在2～3a和6a的短周期变化。 相似文献
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近50年黄河流域降水量及雨日的气候变化特征 总被引：1，自引：0，他引：1
利用1961-2010年黄河流域143个测站降水量和雨日资料,分析了黄河流域年、季降水和雨日的时空变化特征。结果表明:(1)多年平均年降水量和年雨日空间分布特征均呈北少南多。(2)年降水量和年雨日变化趋势相一致,二者均呈减少趋势,年降水量负趋势的测站数达81.8%,年雨日负趋势达88.8%,即年雨日较年降水的减少趋势更显著。(3)在季节变化方面,除冬季外,春、夏和秋季的降水量和雨日都是负趋势,特别是秋季减少最显著。四季降水量通过显著性水平检验的负趋势站数从多到少依次为秋季春季夏季冬季,雨日则为秋季夏季春季冬季。(4)流域年降水和年雨日一致突变点为1985-1986年,其降水量及雨日减少主要原因是大气环流发生了变化,1986年以前黄河流域降水和雨日偏多是由于季风较强,使水汽得到有效输送和河套西北部的风向辐合造成的,而突变后降水和雨日减少与季风偏弱、缺乏有效的水汽输送和蒙古至河套的反气旋环流有关。 相似文献
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利用小兴安岭五营林区1958—2007年历年旬平均气温、降水量、日照时数和相对湿度等气象资料．通过对气象要素月、季节、年际变化等一系列讨论,分析了五营林区的气候特征,得出：五营50a平均气温为0．1℃,各月平均温度7月达到最高点,1月为最低值。50a平均年降雨量为617．1mm,降水量主要集中在7、8月,冬季降水较少。五营林区1960—2007年年日照时数平均值为2227．6h,本地区可照时数、阴天日数均在7月份达到峰值。五营林区夏、冬两季相对湿度较大,而春、秋两季相对湿度较低。 相似文献
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根据阜新地区2个观测站1951-2010年逐月和逐年降水资料,通过趋势分析、Mexicohat小波变换和Mann-Kendall突变检验等方法,分析了阜新地区降水的气候变化特征。结果表明：阜新地区近60 a来年降水量呈下降趋势,下降速率为10.7 mm/10a;降水量年际变化明显,极易出现旱涝灾害。除春季降水略有增加外,其他三季均呈减少趋势。年降水量和季节降水量均有准12 a和18 a的周期振荡。除春季降水外,夏、秋、冬三季均存在突变点,其中夏季降水量存在3个突变年份,分别为1967年、1978年和1986年,秋季降水量在1996年存在突变,冬季降水量在2004年存在突变。 相似文献
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根据阜新地区2个观测站1951-2010年逐月和逐年降水资料,通过趋势分析、Mexicohat小波变换和Mann-Kendall突变检验等方法,分析了阜新地区降水的气候变化特征。结果表明：阜新地区近60 a来年降水量呈下降趋势,下降速率为10.7 mm/10a;降水量年际变化明显,极易出现旱涝灾害。除春季降水略有增加外,其他三季均呈减少趋势。年降水量和季节降水量均有准12 a和18 a的周期振荡。除春季降水量没有明显突变点外,夏、秋、冬三季均存在突变点,其中夏季降水量存在3个突变年份,分别为1967年、1978年和1986年,秋季降水量在1996年存在突变,冬季降水量在2004年存在突变。 相似文献
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The following Henry's law constants (K
H/mol2kg-2atm-1) for HNO3 and the hydrohalic acids have been evaluated from available partial pressure and other thermodynamic data from 0°–40°C, 1 atm total pressure: HNO
3
, 40°C–5.85×105; 30°C–1.50×106; 25°C–2.45×106; 20°C–4.04×106; 10°C–1.15×107; 0°C–3.41×107. HF, 40°C–3.2; 30°C–6.6; 25°C–9.61; 20°C–14.0; 10°C–32.0; 0°C–76. HCl, 40°C–4.66×105; 30°C–1.23×106; 25°C–2.04×106; 20°C–3.37×106; 10°C–9.71×106; 0°C–2.95×107. HBr, 40°C–2.5×108; 30°C–7.5×108; 25°C–1.32×109; 20°C–2.37×109; 10°C–8.10×109; 0°C–3.0×1010. HI, 40°C–5.2×108; 30°C–1.5×109; 25°C–2.5×109; 20°C–4.5×109; 10°C–1.5×1010; 0°C–5.0×1010. Simple equilibrium models suggest that HNO3, CH3SO3H and other acids up to 10x less soluble than HCl displace it from marine seasalt aerosols. HF is displaced preferentially to HCl by dissolved acidity at all relative humidities greater than about 80%, and should be entirely depleted in aged marine aerosols. 相似文献
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The relationship between the geometrical structure of a canopy layer and the bulk transfer coefficient was investigated using a numerical canopy model. The following results were obtained:
- The bulk transfer coefficients for momentum and heat, C M and C H , change with non-dimensional canopy density C * each has a maximum.
- The value of C M is always larger than the value of C H for a canopy with c m > c h , c m and c h being the drag coefficient and the heat transfer coefficient of an individual canopy element, respectively.
- The value of C * at which C H has its maximum value is larger than the value of C * at which C M has its maximum. Therefore, the reciprocal of the sublayer Stanton number b h ?1 ranges between 50 and 65 for C * around 0.1 while it ranges between 0 and 30 for C * < 10?2 and C * > 2 (when c m = 0.5).
- The value of B H ?1 in the present study is consistent with most available observations, except for canopies of medium density (when C * is around 0.1) for which no observational value has been obtained.
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Ronald B. Smith 《Boundary-Layer Meteorology》2008,129(3):371-393
Dispersion estimates with a Gaussian plume model are often incorrect because of particle settling (β), deposition (γ) or the vertical gradient in diffusivity (K
v
(z) = K
0 + μz). These “non-Gaussian” effects, and the interaction between them, can be evaluated with a new Hankel/Fourier method. Due
to the deepening of the plume downwind and reduced vertical concentration gradients, these effects become more important at
greater distance from the source. They dominate when distance from the source exceeds L
β
= K
0
U/β
2, L
γ
= K
0
U/γ
2 and L
μ
= K
0
U/μ
2 respectively. In this case, the ratio β/μ plays a central role and when β/μ = 1/2 the effects of settling and K gradient exactly cancel. A general computational method and several specific closed form
solutions are given, including a new dispersion relation for the case when all three non-Gaussian effects are strong. A more
general result is that surface concentration scales as C(x) ~ γ
−2 whenever deposition is strong. Categorization of dispersion problems using β/μ, L
γ
and L
μ
is proposed. 相似文献
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S. A. Hsu 《Boundary-Layer Meteorology》1994,71(1-2):205-209
Under growing wind-wave conditions the shear velocity,u
*, over the water surface equalsg
2
H
s
2
B
a
2
C
p
3
, whereg is the gravitational acceleration,H
s
is the significant wave height,B
a
is a constant, andC
p
is the wave celerity. From an independent field experiment in a lake environment which provided all three parameters (u
*,H
s
, andC
p
), the value ofB
a
is found to be 0.89, which is slightly lower than but consistent (within 20%) with the literature value between 0.90 and 1.06 obtained from an oceanic environment. Since thisu
* equation does not include the wind speed,U
10, anotheru
* formulation withU
10 in addition to the wave information is also evaluated. It is shown that the latter equation which includesU
10 is superior to the former withoutU
10. 相似文献
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Derek D. Stretch James W. Rottman S.Karan Venayagamoorthy Keiko K. Nomura Chris R. Rehmann 《Dynamics of Atmospheres and Oceans》2010
Mixing efficiency in stratified flows is a measure of the proportion of turbulent kinetic energy that goes into increasing the potential energy of the fluid by irreversible mixing. In this research direct numerical simulations (DNS) and rapid distortion theory (RDT) calculations of transient turbulent mixing events are carried out in order to study this aspect of mixing. In particular, DNS and RDT of decaying, homogeneous, stably-stratified turbulence are used to determine the mixing efficiency as a function of the initial turbulence Richardson number Rit0=(NL0/u0)2, where N is the buoyancy frequency and L0 and u0 are initial length and velocity scales of the turbulence. The results show that the mixing efficiency increases with increasing Rit0 for small Rit0, but for larger Rit0 the mixing efficiency becomes approximately constant. These results are compared with data from towed grid experiments. There is qualitative agreement between the DNS results and the available experimental data, but significant quantitative discrepancies. The grid turbulence experiments suggest a maximum mixing efficiency (at large Rit0) of about 6%, while the DNS and RDT results give about 30%. We consider two possible reasons for this discrepancy: Prandtl number effects and non-matching initial conditions. We conclude that the main source of the disagreement probably is due to inaccuracy in determining the initial turbulence energy input in the case of the grid turbulence experiments. 相似文献
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A time series of microwave radiometric profiles over Arctic Canada’s Cape Bathurst (70°N, 124.5°W) flaw lead polynya region
from 1 January to 30 June, 2008 was examined to determine the general characteristics of the atmospheric boundary layer in
winter and spring. A surface based or elevated inversion was present on 97% of winter (January–March) days, and on 77% of
spring (April–June) days. The inversion was the deepest in the first week of March (≈1100 m), and the shallowest in June (≈250 m).
The mean temperature and absolute humidity from the surface to the top of the inversion averaged 250.1 K (−23.1°C), and 0.56 × 10−3 kg m−3 in winter, and in spring averaged 267.5 K (−5.6°C), and 2.77 × 10−3 kg m−3. The median winter atmospheric boundary-layer (ABL) potential temperature profile provided evidence of a shallow, weakly
stable internal boundary layer (surface to 350 m) topped by an inversion (350–1,000 m). The median spring profile showed a
shallow, near-neutral internal boundary layer (surface to 350 m) under an elevated inversion (600–800 m). The median ABL absolute
humidity profiles were weakly positive in winter and negative in spring. Estimates of the convergence of sensible heat and
water vapour from the surface that could have produced the turbulent internal boundary layers of the median profiles were
0.67 MJ m−2 and 13.1 × 10−3 kg m−2 for the winter season, and 0.66 MJ m−2 and 33.4 × 10−3 kg m−2 for the spring season. With fetches of 10–100 km, these accumulations may have resulted from a surface sensible heat flux
of 15–185 W m−2, plus a surface moisture flux of 0.001–0.013 mm h−1 (or a latent heat flux of 0.7–8.8 W m−2) in winter, and 0.003–0.033 mm h−1 (or a latent heat flux of 2–22 W m−2) in spring. 相似文献
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A spectral approach is applied to shear-induced turbulence in stratified layers. A system of spectral equations for stationary balance of turbulent energy and temperature variances was deduced in the vicinity of the local shear scale LU = (ε/UZ3)1/2. At wavenumbers between the inertial-convective (k−5/3) and wak turbulence (k−3) subranges, additional narrow spectral intervals—‘production’ subranges—may appear (E k−1, ET k−2). The upper boundary of these subranges is determined as LU, and the lower boundaries as LR (ε/UZN2)1/2(χ/TZ2). It is shown that the scale LU is a unique spectral scale that is uniform up to a constant value for every hydrophysical field. It appears that the spectral scale LU is equivalent to the Thorpe scale LTh for the active turbulence model. Therefore, if turbulent patches are generated in a background of permanent mean shear, a linear relation between temperature and mass diffusivities exists. In spectral terms, the fossil turbulence model corresponds to the regime of the Boldgiano-Obukhov buoyancy subrange (E k−11/5, ET k−7/5). During decay the buoyancy subrange is expanded to lower and higher wavenumbers. At lower wavenumbers the buoyancy subrange is bounded by L** = 3(χ1/2/N1/2TZ), which is equivalent to the Thorpe scale LTh. In such a transition regime only, when the viscous dissipation rate is removed from the set of main turbulence parameters, the Thorpe scale does not correlate with the buoyancy scale LN ε1/2/N3/2 and fossil turbulence is realized. Oceanic turbulence measurements in the equatorial Pacific near Baker Island confirm the main ideas of the active and fossil turbulence models. 相似文献