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91.
2004年冬季华北平原持续大雾天气的诊断分析 总被引:26,自引:8,他引:26
利用GTS1型数字式探空仪探测的资料、NCEP 1°×1°的6小时资料和常规观测资料,对2004年冬季华北平原历史上少见的持续大雾天气进行了天气动力学诊断分析。结果表明:华北平原近地面气层900hPa以下的负涡度平流、冷温度平流和弱辐合上升运动引起该层气温下降,900-500hPa的正涡度平流、暖温度平流和辐散下沉运动造成该层气温升高,在上升和下沉运动区的界面层中形成逆温层,逆温层的高度和强度影响雾的形成和状况。夜间辐射热力强迫作用和950hPa以下的微风是大雾形成的动力因子。大雾边界层中存在的水汽饱和层是在特定的环流形势下华北平原低空盛行东和东南向岸气流,将北部海面的水汽向西向北平流到冷近地面气层中的结果。 相似文献
92.
We have performed a one-dimensional and transient radiative heat transfer analysis in order to investigate interaction between atmospheric radiation and convective instability within a nocturnal fog. The radiation element method using the Ray Emission Model (REM2), which is a generalized numerical method, in conjunction with a line-by-line (LBL) method, is employed to attain high spectral resolution calculations for anisotropically scattering fog. The results show that the convective instability has a strong dependence on radiative properties of the fog. For the condition of a 20-m droplet diameter and liquid water content of 0.1 × 10–3 kg m–3;, the temperature profile within the fog becomes S shaped, and a convective instability layer forms in the middle or lower level of the fog. However, for the same water content and a 40-m diameter droplet, no strong convective instability layer forms, whereas for a 10-m diameter droplet a strong convective instability is observed. 相似文献
93.
Four months of eddy correlation data collected over a grass field and a nearby sage brush community are analyzed to examine
the adjustment of the boundary-layer structure as it flows from the heated brush to the snow-covered grass. The grass site
includes a 34-m tower with seven levels of eddy correlation data. The midday heat flux over the snow-covered grass and bare
ground surfaces is often downward particularly with melting conditions, while the corresponding heat flux over the brush is
almost always upward. For most of these cases, a stable internal boundary layer over the snow is well defined in terms of
vertical profiles of the buoyancy flux over the snow-covered grass. The stable internal boundary layer is generally embedded
within a deeper layer of flux divergence corresponding to increasing upward heat flux with height above the internal boundary
layer. With thin snow cover, the surface heat flux over the grass is weak upward due to heating of grass protruding above
the snow so that the flow adjusts to a decrease of the upward surface heat flux in the downwind direction. This common case
of an adjusting boundary layer contrasts with the formation of an internal boundary layer due to a change of sign of the surface
heat in flux the downwind direction. The adjustment of the boundary layer to the decrease of the surface heat flux leads to
vertical divergence of the upward heat flux in contrast to the usual heated boundary layer over homogeneous surfaces. The
consequences of the cooling due to the vertical divergence of the heat flux are discussed in terms of the heat budget of the
adjusting and internal boundary layers. 相似文献
94.
A Spectrum-Independent Procedure for Correcting Eddy Fluxes Measured with Separated Sensors 总被引:1,自引:0,他引:1
We investigate flux underestimates in eddy correlation measurements that are caused by horizontal separation of the sensors. A common eddy correlation setup consists of a sonic anemometer and a humidity sensor which, because of its bulk, must be placed some distance away from the sonic path, leading to a flux loss (of latent heat). Utilizing an additional fast temperature sensor placed near the humidity sensor, we develop a procedure for correcting for this loss. The procedure simultaneously corrects the sensible heat flux for the difference between true temperature and sonic temperature. Our correction procedure, which does not depend on the shape of the cospectrum, is then compared to the widely-used procedure following Moore (1986), which assumes a cospectral model ('Kansas Model). Both correction methods are applied to data collected within the internal boundary layer over a rice paddy, downwind of arid land. Under conditions of good fetch, they were found to agree well. Under poor fetch conditions, the model-based correction tended to be too small, while the spectrum-independent combined correction was robust. The latter is thus recommended for situations where the cospectral shape can be expected to deviate from the 'Kansas shape. 相似文献
95.
Unsteadiness as a cause of non-equality of eddy diffusivities for heat and vapour at the base of an advective inversion 总被引:8,自引:8,他引:0
This paper examines the effect of non-stationarity of the wind on similarity of the eddy diffusivities for heat and vapour within a stable layer at the bottom of an internal boundary layer formed downwind of a dry-to-wet transition. First, we present some experimental data taken above a rice crop downwind of very extensive dry range lands at Warrawidgee, NSW, Australia. These data establish that periods of higher wind speed were associated with periods of higher saturation deficit in the canopy of the rice crop, and lower Bowen ratio. It is shown that Bowen ratios calculated for 30-second sub-intervals varied three-fold within a single 20-minute averaging period. Thus periods of higher wind speed corresponded to periods of higher moisture flux and smaller sensible heat flux.An idealized situation is then analysed theoretically. It is assumed that the time scale of the slow variations of the wind is long compared with the surface-layer time scale and that fetch is sufficient that the air near the ground is in continuous equilibrium with the surface. Using a two-scale Reynolds decomposition of the fluctuating wind and scalar variables into active and inactive components, it is shown that unsteadiness can lead to an eddy diffusivity for saturation deficit, calculated as the ratio of average flux to average gradient, that is larger than that for total energy calculated in a similar way. Using this ratio to calculate the ratio of diffusivities for temperature and humidity, KT/Kq, it is found that the latter can be much larger than one if the Bowen ratio is small and negative. Despite this, assuming KT = Kq and using the Bowen ratio method to calculate surface energy fluxes will usually incur only minor errors. 相似文献
96.
Norimichi Takenaka Tohru Daimon Akihiro Ueda Keiichi Sato Masaru Kitano Hiroshi Bandow Yasuaki Maeda 《Journal of Atmospheric Chemistry》1998,29(2):135-150
Nitrite oxidation in the tropospheric aqueous phase by freezing was evaluated by freezing a field sample. Nitrite oxidation by dissolved oxygen in the freezing process is much faster than by other oxidation processes, such as reactions with ozone, hydrogen peroxide or dissolved oxygen in an aqueous solution at pHs 3 to –6. At pH 4.5 and 25°C, the lifetime of nitrite in the aqueous phase is ca. 1 hr in oxidation by ozone (6×10-10 mol dm-3), ca. 10 hr in oxidation by H2O2 (2×10-4 mol dm-3), and 7.5 hr (Fischer and Warneck, 1996) in photodissociation at midday in summer. Under the same conditions at a temperature below 0°C, the lifetime of nitrite in the freezing process is estimated as ca. 2 sec when the droplets are frozen within a second. The reaction by freezing is affected by the presence of salts, such as NaCl or KCl, or orgnaic compounds, such as methanol or acetone. The results of freezing a field rain or fog sample showed that nitrite oxidation proceeds below pH 6, and the conversion ratio of nitrate from nitrite increases with decreasing pH. The oxidation of nitrite by freezing was also observed in freezing fog particles generated by an ultrasonic humidifier. The ratios of the concentrations of ions in the winter sample to those in the summer sample (or those in the fog sample) were almost the same values. However, the concentration of nitrite in the winter sample was lower than that estimated by the ratios of other ions. From the present study, it seems that the freezing process plays an important role in the nitrite sink process in the tropospheric aqueous phase. 相似文献
97.
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99.
再论水平和垂直分辨率之间的协调 总被引:5,自引:1,他引:5
在计算域面积为常数的约束下,给出了几种不同精度的平流方程和ω方程的“最优垂直网格距”,以及在极限情况下的“协调垂直网格距”的表达式。还讨论了在水平和垂直分辨率不协调时数值解对能量传播和计算稳定性的影响。 相似文献
100.
Pre-weighed blocks of a Jurassic Limestone were exposed on the ground surface in the coastal Namib Desert for a period of 2 years. The environment is both salty and foggy. Some of the blocks suffered extensive disintegration, and laboratory analyses (including geochemistry, XRD and SEM) indicate that the weathered samples have a high halite (sodium chloride) content. Cycles of wetting and drying associated with the frequent fog events of the area cause cycles of halite crystallization. Rocks exposed at the surface absorb salts from the surrounding desert surface and then disintegrate, contributing to planation of the landscape. 相似文献