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951.
Weakly nonlinear triad interactions between spherical Rossby harmonics are studied. Each of the harmonics has the form APnm(sin θ)exp[i(mλ − σt)], where A is an amplitude and Pnm is the associated Legendre function. Equations for the amplitudes are derived and resonance conditions are analysed. The resonance conditions differ substantially from the usual resonance conditions on a β-plane and include a Diophantine equation and a few inequalities for the integer wavenumbers n and m of the interacting modes. Particular analytical series of solutions to the resonance conditions are constructed, which show that modes with arbitrary large wavenumbers can participate in the interactions. A numerical study of the resonance conditions reveals that no more than 21% of the Rossby harmonics can participate in the triad interactions and that chains of the interacting triads soon break. Thus precise interactions (for which the resonance conditions hold exactly) do not result in any significant redistribution of energy over the spectrum. On the other hand, approximate interactions (for which the resonance conditions hold approximately) generate an intensive energy redistribution among short Rossby modes with typical scales much smaller than the Earth's radius. Thus the energy cascade is concentrated mainly in the short-wave part of the spectrum and is very weak in the large-scale domain. The efficiency of the triad interaction of Rossby modes with scales much smaller than the Earth's radius depends strongly on the existence of the so-called interaction latitude at which the local wave-vectors and frequencies of the interacting modes satisfy resonance conditions for plane Rossby waves on the β-plane approximating the neighbourhood of the latitude. If the interaction latitude exists, the interaction is intensive; in the opposite case, it is weak. 相似文献
952.
Synoptic and mesoscale study of a severe convective outbreak with the nonhydrostatic Global Environmental Multiscale (GEM) model 总被引:1,自引:0,他引:1
A. Erfani A. Méthot R. Goodson S. Bélair K.-S. Yeh J. Côté R. Moffet 《Meteorology and Atmospheric Physics》2003,82(1-4):31-53
Summary ?A nonhydrostatic 4-km version of the Global Environmental Multiscale (GEM) model, with detailed microphysics included, was
used to forecast the initiation, development, and structure of a tornado-producing supercell storm that occurred near Pine
Lake (Alberta, Canada) on 15 July 2000. Examination of observations and comparison with conceptual models indicate that this
storm is a good example of supercell storms that regularly produce summertime severe weather over Alberta.
It was found that the high-resolution model was able to reproduce the early initiation of convective activity along the Rocky
Mountains foothills, as well as the rapid northeastward propagation towards the Pine Lake area and the subsequent intensification
into a supercell storm. The general structures of the forecasted convective system correspond well with conceptual representations
of such events. Overall, this high-resolution forecast of the Pine Lake supercell storm was a significant improvement over
the current operational version of the GEM model (24 km), which was not able to intensify the foothills’ convection into a
supercell storm. Finally, it was found that the nonhydrostatic version of the model produces better trajectory and propagation
speed of the convective system, as compared with the hydrostatic one.
Received March 20, 2001; revised August 24, 2001 相似文献
953.
Partitioning of volatile chemicals among the gas, liquid, and solid phases during freezing of liquid water in clouds can impact
trace chemical distributions in the troposphere and in precipitation. We describe here a numerical model of this partitioning
during the freezing of a supercooled liquid drop. Our model includes the time-dependent calculation of the coupled processes
of crystallization kinetics, heat transport, and solute mass transport, for a freezing hydrometeor particle. We demonstrate
the model for tracer partitioning during the freezing of a 1000 μm radius drop on a 100 μm ice substrate, under a few ambient
condition scenarios. The model effectively simulates particle freezing and solute transport, yielding results that are qualitatively
and quantitatively consistent with previous experimental and theoretical work. Results suggest that the ice shell formation
time is governed by heat loss to air and not by dendrite propagation, and that the location of ice nucleation is not important
to freezing times or the effective partitioning of chemical solutes. Even for the case of nucleation at the center of the
drop, we found that dendrites propagated rapidly to form surface ice. Freezing then proceeded from the outside in. Results
also indicate that the solid-liquid interfacial surface area is not important to freezing times or the effective partitioning
of chemical solutes, and that the rate aspects of trapping are more important than equilibrium solid-liquid partitioning to
the effective partitioning resulting from freezing. 相似文献
954.
Actual surface fields of meteorological variables 1–3 hours before the heavy showers are analyzed in detail for the purpose
of their specification with WRF-ARW model. The complex of hygrothermodynamic characteristics needed for this purpose is discovered.
The detailed satellite, radar, and synoptic data are also considered. 相似文献
955.
UV attenuation in the cloudy atmosphere 总被引:1,自引:0,他引:1
Jianhui Bai 《Journal of Atmospheric Chemistry》2009,62(3):211-228
Ultraviolet (UV) energy absorption plays a very important role in the Earth–atmosphere system. Based on observational data
for Beijing, we suggest that some atmospheric constituents utilize or transfer UV energy in chemical and photochemical (C&P) reactions, in addition to those which absorb UV energy directly. These constituents are primarily volatile organic compounds
(VOCs) emitted from both vegetative and anthropogenic sources. The total UV energy loss in the cloudy atmosphere for Beijing
in 1990 was 78.9 Wm−2. This attenuation was caused by ozone (48.3 Wm−2), other compounds in the atmosphere (26.6 Wm−2) and a scattering factor (4.0 Wm−2). Our results for a cloudy atmosphere in the Beijing area show that the absorption due to these other compounds occurs largely
through the mediation of water vapor. This fraction of energy loss has not been fully accounted for in previous models. Observations
and previous models results suggest that 1) a cloudy atmosphere absorbs 25∼30 Wm−2 more solar shortwave radiation than models predict; and 2) aerosols can significantly decrease the downward mean UV-visible
radiation and the absorbed solar radiation at the surface by up to 28 and 23 Wm−2, respectively. Thus, quantitative study of UV and visible absorption by atmospheric constituents involved in homogeneous
and heterogeneous C&P reactions is important for atmospheric models. 相似文献
956.
José Luís Argaín Miguel A. C. Teixeira Pedro M. A. Miranda 《Boundary-Layer Meteorology》2017,165(1):145-160
A method is proposed for estimating the surface-layer depth \((z_s)\) and the friction velocity \((u_*)\) as a function of stability (here quantified by the Obukhov length, L) over the complete range of unstable flow regimes. This method extends that developed previously for stable conditions by Argaín et al. (Boundary-Layer Meteorol 130:15–28, 2009), but uses a qualitatively different approach. The method is specifically used to calculate the fractional speed-up \((\varDelta S)\) in flow over a ridge, although it is suitable for more general boundary-layer applications. The behaviour of \(z_s \left( L\right) \) and \(u_*\left( L\right) \) as a function of L is indirectly assessed via calculation of \(\varDelta S\left( L\right) \) using the linear model of Hunt et al. (Q J R Meteorol Soc 29:16–26, 1988) and its comparison with the field measurements reported in Coppin et al. (Boundary-Layer Meteorol 69:173–199, 1994) and with numerical simulations carried out using a non-linear numerical model, FLEX. The behaviour of \(\varDelta S\) estimated from the linear model is clearly improved when \(u_*\) is calculated using the method proposed here, confirming the importance of accounting for the dependences of \(z_s\left( L \right) \) and \(u_*\left( L \right) \) on L to better represent processes in the unstable boundary layer. 相似文献
957.
Juan Huang Yanli Feng Jian Li Bin Xiong Jialiang Feng Sheng Wen Guoying Sheng Jiamo Fu Minghong Wu 《Journal of Atmospheric Chemistry》2008,61(1):1-20
The levels of carbonyl compounds in Shanghai ambient air were measured in five periods from January 2007 to October 2007 (covering
winter, high-air-pollution days, spring, summer and autumn). A total of 114 samples were collected and eighteen carbonyls
were identified. Formaldehyde, acetaldehyde and acetone were the most abundant carbonyls and their mean concentrations of
19.40 ± 12.00, 15.92 ± 12.07 and 11.86 ± 7.04 μg m−3 respectively, in the daytime for five sampling periods. Formaldehyde and acetaldehyde showed similar diurnal profiles with
peak mixing ratios in the morning and early afternoon during the daytime. Their mean concentrations were highest in summer
and lowest in winter. Acetone showed reversed seasonal variation. The high molecular weight (HMW, ≥C5) carbonyls also showed
obvious diurnal variations with higher concentrations in the daytime in summer and autumn, while they were all not detected
in winter. Formaldehyde and acetaldehyde played an important role in removing OH radicals in the atmosphere, but the contribution
of acetone was below 1%. The carbonyls levels in high-air-pollution days were reported. More carbonyl species with higher
concentrations were found in high-air-pollution days than in spring. These carbonyls were transported with other pollutants
from north and northwest in March 27 to April 2, 2007 and then mixed with local sources. Comparing with Beijing and Guangzhou,
the concentrations of formaldehyde and acetaldehyde in Shanghai were the highest, which indicated that the air pollution in
Shanghai was even worse than expected. 相似文献
958.
General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations
without a large extent of ver- tical flow. Vertical flow, however, plays an important role in the formation of local breezes,
such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of
atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a
general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their
high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account
by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model
equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model
nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical
solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach
can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface
energy balance are important further steps towards the practical application of the method. 相似文献
959.
Bento Sanches Dorta was an astronomer and geographer in the Portuguese colony of Rio de Janeiro in Brazil from 1781 to 1788. He recorded daily readings of meteorological and geomagnetic variables during that period. This dataset provides, to the best of our knowledge, the earliest known continuous 8-year-long instrumental meteorological observations for any South American site. His data show that the winters in this period were relatively cool, and that 1785 was the rainiest and hottest year, and 1787 the driest and coolest. The records display a distinct seasonal cycle and a variability that are comparable with the modern data. 相似文献
960.
Summary The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces
an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with
the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared
utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These
sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal
components (PCs).
A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E
Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to
PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts
associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the
lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC
IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features,
such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric
anticyclones to the south.
The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition,
synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner
by such PCA.
Received July 18, 1997 Revised April 30, 1999 相似文献