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1.
Summary The performance of evaporation schemes with and approach and their combination within resistance representation of evaporation from bare soil surface is discussed. For this purpose nine schemes, based on different functions of or , on the ratio of the volumetric soil moisture content and its saturated value are used.The quality of the chosen schemes has been evaluated using the results of time integration by the coupled soil moisture and surface temperature prediction model, BARESOIL, using in situ data. A sensitivity analysis was made using two sets of data derived from the volumetric soil moisture content of the top soil layer. One with values below the wilting point (0.17 m3m–3) and the second with values above 0.20m3m–3. Data sets were obtained at the experimental site Rimski anevi, Yugoslavia, from the bare surface of a chernozem soil.With 4 Figures  相似文献   

2.
Flux densities of carbon dioxide were measured over an arid, vegetation-free surface by eddy covariance techniques and by a heat budget-profile method, in which CO2 concentration gradients were specified in terms of mixing ratios. This method showed negligible fluxes of CO2, consistent with the bareness of the experimental site, whereas the eddy covariance measurements indicated large downward fluxes of CO2. These apparently conflicting observations are in quantitative agreement with the results of a recent theory which predicts that whenever there are vertical fluxes of sensible or latent heat, a mean vertical velocity is developed. This velocity causes a mean vertical convective mass flux (= cw for CO2, in standard notation). The eddy covariance technique neglects this mean convective flux and measures only the turbulent flux c w. Thus, when the net flux of CO2 is zero, the eddy covariance method indicates an apparent flux which is equal and opposite to the mean convective flux, i.e., c w = – c w. Corrections for the mean convective flux are particularly significant for CO2 because cw and c w are often of similar magnitude. The correct measurement of the net CO2 flux by eddy covariance techniques requires that the fluxes of sensible and latent heat be measured as well.  相似文献   

3.
Six locations across mainland Portugal were selected for exposing Parmelia sulcata, for a one-year period (8 months for one site), with simultaneous measurement of total (dry + wet) deposition (one-month periods). The exposed lichens and the total (dry + wet) deposition were analysed for cobalt contents by INAA (instrumental neutron activation analysis) and ICP-MS (inductively coupled plasma mass spectroscopy), respectively. The designated wet deposition was evaluated through the collected water volume; the designated dry deposition was assessed after the (dried) residual mass of the wet deposition. An excellent agreement between Co contents in exposed lichens and the cumulative (1) Co contents in the dry deposition, (2) dry deposition, and (3) wet deposition has been found for the locations with alternate drought and precipitation months, high dry deposition, and high Co contents in the latter. Continuous rainfall was found to hinder the Co accumulation in the lichen due to its release from the lichen and/or lower Co contents in the dry deposition. At three locations, P. sulcata Co contents, after subtraction of the background (before exposure), equalled or exceeded the Co contents in the cumulative dry deposition at the end of the exposure time. The optimal exposure period for this species likely depends on the exposure conditions.  相似文献   

4.
Surface-Layer Fluxes in Stable Conditions   总被引：2，自引：2，他引：0  
Micrometeorological tower data from the Microfronts experiment are analyzed. Scale-dependencies of the flux and flux sampling error are combined to automatically determine Reynolds turbulence cut-off time scales for computing fluxes from time series. The computed downward heat flux at the 3 m height averaged over nine nights with 7.3 hours each night is 20% greater than the downward heat flux computed at the 10 m height. In contrast, there is only a 1.2% difference between 3 m and 10 m heat fluxes averaged over daytime periods, and there is less than a 2% difference between 3 m and 10 m momentum fluxes whether averaged over nighttime or daytime periods.Stability functions, M(z/L) and H(z/L) are extended to z/L up to 10, where z is the observational height and L is the Obukhov length. For 0.01 < z/L < 1 the estimated functions generally agree with Businger-Dyer formulations, though the H estimates include more scatter compared to the M estimates. For 1 < z/L < 10, the flux intermittency increases, the flux Richardson number exceeds 0.2, and the number of flux samples decreases. Nonetheless the estimates of the stability function M based on 3-m fluxes are closer to the formula proposed by Beljaars and Holtslag in 1991 while the M functions based on 10-m fluxes appears to be closer to the formula proposed by Businger et al. in 1971. The stability function H levels off at z/L = 0.5.  相似文献   

5.
Thermal comfort of man in different urban environments   总被引：2，自引：4，他引：2  
Summary On July 29, 1985, a hot summer day, biometeorological measurements were performed simultaneously in three different urban structures within the city of Munich and in the trunk space of a nearby tall spruce forest. Based on the results of these experiments the following thermophysiologically relevant biometeorological indices were calculated: Predicted mean vote, skin wettedness and physiologically equivalent temperature. These three indices are derived from different models for the human energy balance. They allow the assessment of the thermal components of the microclimates at the selected sites with regard to application in urban planning. The results quantitatively show the great heat stress in the urban structure street canyon, exposed to south, whereas in the trunk space of the tall spruce forest there is nearly an optimal climate even on hot summer days. Between these extremes the results for street canyon, exposed to north show a little higher heat load than for backyard with trees.
Zusammenfassung An einem heißen Sommertag, dem 29. Juli 1985, wurden in drei Stadtstrukturen in München und im Stammraum eines nahegelegenen Fichtenhochwaldes zeitgleich biometeorologische Messungen durchgeführt. Mit den Meßergebnissen wurden folgende thermophysiologisch relevante biometeorologische Indizes berechnet: Predicted mean vote, Hautbenetzungsgrad und physiologisch äquivalente Temperatur. Diese drei Indizes beruhen auf verschiedenen Modellen zur menschlichen Energiebilanz. Mit den drei Indizes wurden die thermischen Komponenten der Mikroklimate an den ausgewählten Meßplätzen im Hinblick auf Stadtplanungsaufgaben bewertet. Die Ergebnisse zeigen quantitativ die relativ große Hitzebelastung bei der Stadtstruktur Straßenschlucht, nach Süd exponiert, während im Stammraum des Fichtenhochwaldes selbst an heißen Sommertagen nahezu optimale Bedingungen herrschen. Zwischen diesen Extremen liegen die Ergebnisse für die anderen Meßplätze, wobei für Straßenschlucht, nach Nord exponiert die Wärmebelastung etwas höher als für Innenhof mit Bäumen ist.

With 6 Figures  相似文献   

6.
A numerical study of stably stratified flow over a three-dimensional hill is presented. Large-eddy simulation is used here to examine in detail the laboratory experimental flows described in the landmark work of Hunt and Snyder about stratified flow over a hill. The flow is linearly stratified and U/Nh is varied from 0.2 to 1.0. Here N and U are the buoyancy frequency and freestream velocity respectively, and h is the height of the hill. The Reynolds number based on the hill height is varied from 365 to 2968. The characteristic flow patterns at various values of U/Nh have been obtained and they are in good agreement with earlier theoretical and experimental results. It is shown that the flow field cannot be predicted by Drazin's theory when recirculation exists at the leeside of the hill even at UNh 1. The wake structure agrees well with a two-dimensional wake assumption when U/Nh 1 but lee waves start to influence the wake structure as U/Nh increases. The dividing-streamline heights obtained in the simulation are in accordance with experimental results and Sheppard's formula. The energy loss along the dividing streamline due to friction/turbulence approximately offsets the energy gained from pressure field. When lee waves are present, linear theory always underestimates the amplitude and overestimates the wavelength of three-dimensional lee waves. The simulated variations of drag coefficients with the parameterK (=ND/ U) are qualitatively consistent with experimental data and linear theory. Here D is the depth of the tank.  相似文献   

7.
Recently Wilson and Flesch (Boundary-Layer Meteorology, 84, 411-426, 1997) suggested that the average increment d z to the orientation = arctan(w/u) of the Lagrangian velocity-fluctuation vector can be used to distinguish the better Lagrangian stochastic models within the well-mixed class. Here it is demonstrated that the specification of d z constitutes neither a sufficient or universally applicable criterion to distinguish the better Lagrangian stochastic models within the well-mixed class. The hypothesis made by Wilson and Flesch that Lagrangian stochastic models with /PE irrotational are zero-spin models, having d z=0, is proven  相似文献   

8.
Zusammenfassung An einem Material von 100 Fällen eindeutig gesicherten Herztodes, die im Institut für Gerichtliche und Soziale Medizin in Frankfurt am Main aus einem bestimmten Bereich — Raum Frankfurt am Main — und einer bestimmten zeit—Kalenderjahre 1948 bis 1950—zur Autopsie gelangten, einerseits und den bioklimatischen Daten für den gleichen Raum und die gleiche Zeit anderseits, wurde der Zusammenhang von Herztodesfällen und Wettervorgängen mit der Wahrscheinlichkeitsüberlegung, dem Wahrscheinlichkeitsintegral und formalstatistischen Methoden überprüft. Die Auswertung ergab, daß eine starke Abhängigkeit des Herztodes vom Wettergeschehen besteht. Die Häufung der Herztodesfälle konnte für die Sammelgruppe Wetterstörungen, für labiles Aufgleiten, Warmfront mit Aufgleiten und Kaltfront mit Turbulenz ebenso eindeutig gesichert werden, wie die Verminderung der Herztodesfälle in störungsfreien Zeiten. Die hohe Wahrscheinlichkeit einer Beziehung besteht ferner für Kaltfront mit Aufgleiten und in geringerem Maße auch für Föhndurchbruch. Während bei Okklusion das Material zu einem abschließenden Urteil zu gering war, konnte bei allen übrigen Wetterlagen eine Beziehung zum plötzlichen Herztod nicht nachgewiesen werden. Auch für die Gruppen, bei denen eine enge Beziehung statistisch gesichert werden konnte, sei betont, daß die Wettervorgänge nicht die alleinige Ursache des plötzlichen Herztodes, sondern nur ein auslösendes Moment bei schon vorher schwer geschädigten Herzen darstellen.
Summary On the basis of 100 ascertained cases of cardiac death from a certain region—province Frankfort on-the-Main—and a certain period—calendar years 1948 to 1950—, submitted to autopsy in the Institute for Legal and Social Medicine at Frankfort on-the-Main, and of bioclimatic data from the same region and period, the relation between cardiac death and meteorological phenomena was examined by means of probability considerations, the probability integral, and methods of formal statistics. Evaluation of this material showed cardiac death to be strongly dependent on weather conditions. Increase of frequency of cardiac death could be established without any doubt for the collective groups weather disturbances, unstable ascending motion, warm front with ascending motion, cold front with turbulence, whereas decrease of frequency was found in undisturbed periods. Furthermore, high probability of an existing relation was found for cold front with ascending motion and, to a lesser degree, also for foehn invasion. As to occlusion no definite conclusions could be drawn for scarcity of observations. For all the other weather types no relation to sudden cardiac death could be proved. Meteorological phenomena are by no means the only cause of sudden cardiac death, not even for the groups in which a close relation could be established statistically. They have but an initiatory effect in case of prior severe heart diseases.
Résumé Disposant d'un matériel médical de 100 cas de mort cardiaque qui ont fait l'objet d'autopsies à l'Institut de médecine légale et sociale de Francfort sur le Mein (région de Francfort et période de 1948 à 1950), et disposant d'autre part pour la même région et pour la même période d'observations bioclimatologiques, l'auteur a étudié la relation de ces décès avec les phénomènes météorologiques à l'aide des méthodes modernes de statistique, de l'intégrale de probabilité etc. Le résultat montre une étroite dépendance centre les cas de mort cardiaque et les conditions météorologiques. On a pu vérifier sans doute possible l'augmentation des décès lors de «perturbations», d'«ascendances labiles», de «fronts chauds avec glissement ascendant», de «fronts froids avec turbulence», de même que leur diminution lors de périodes non troublées. La forte corrélation subsiste avec les «fronts froids avec ascendance» et à un moindre degré avec «l'invasion du foehn». Tandis que pour les «occlusions» le matériel disponible était trop restreint pour aboutir à une conclusion, l'examen des situations autres que les précédentes n'a pas conduit à une relation intime. Il convient de remarquer que pour tous les groupes de météores ayant donné une corrélation statistique très nette, les phénomènes météorologiques n'ont joué qu'un rôle déclancheur chez des malades déjà gravement atteints.

Mit 2 Textabbildungen.  相似文献   

9.
Summary The interannual variations in sea surface temperature (SST) in the equatorial east Pacific, which are dominated by the El Niño phenomenon, are shown for the period 1870–1983. Since 1870 25 significant warm events have occurred. These events are classified as weak, moderate, strong and very strong, according to the normalized SST anomalies in the region 130° W–80° W, 0°–5° S.The spatial and temporal development of a composite El Niño/Southern Oscillation (ENSO) episode, based on 10 very strong or strong events, is presented in terms of SST, surface wind and divergence anomalies for the tropical Pacific (10° N–30° S). During its evolution the following phases are distinguished: Antecedent Conditions, Onset Phase, Peak Phase, Mature Phase and Dissipation Stage.Some aspects of ocean-atmosphere interaction associated with this evolution and, more specifically, the initiation of the composite event, are described. Seasonally varying feedback processes between SST, surface wind and convergence anomaly patterns in the western Pacific/Indonesian region suggest a possible mechanism for the initiation of typical ENSO events.
Zusammenfassung Die interannuären Variationen der Meeresoberflächentemperatur (SST) im äquatorialen Ostpazifik, die von dem El Niño-Phänomen dominiert werden, werden für die Periode 1870–1983 aufgezeigt. Seit 1870 traten 25 signifikante Ereignisse auf. Diese Ereignisse werden entsprechend den normierten SST-Anomalien in der Region 130° W–80° W, 0°–5° S als schwach, mittel, stark und sehr stark klassifiziert.Die räumliche und zeitliche Entwicklung einer Komposit-El Niño/Southern Oscillation (ENSO)-Episode, die auf 10 sehr starken bzw. starken Ereignissen basiert, wird anhand von SST-, Bodenwind- und Divergenzanomalien für den tropischen Pazifik (10° N–30° S) dargestellt. Während ihrer Entwicklung werden die folgenden Phasen unterschieden: Vorausgehende Bedingungen, Einsetzphase, Spitzenphase, Reifestadium und Auflösungsstadium.Einige Aspekte der Wechselbeziehungen Ozean—Atmosphäre werden im Zusammenhang mit der Entwicklung und insbesondere der Auslösung des Komposit-Ereignisses beschrieben. Jahreszeitlich variierende Rückkopplungsprozesse zwischen SST-, Bodenwind- und Konvergenzanomalien in der westpazifischen/indonesischen Region stellen einen möglichen Mechanismus für die Auslösung typischer ENSO-Ereignisse dar.

With 9 Figures  相似文献   

10.
In the summer of 1988/89 flights were carried out in the Coorong coastal area of South Australia to investigate sea-breeze fronts. The flights yielded data sets of the structure of the fronts in the cross-frontal direction with a spatial resolution of approximately 3 m. The study is focused on the budgets of sensible and latent heat in the vicinity of the front and on frontogenesis/frontolysis processes which are closely related to budget considerations.The frontogenesis relationships and the budgets were established on a 2 km length scale by low-pass filtering of the space series. As the wind components were measured with high accuracy, all processes which determine frontogenesis could be evaluated and are displayed in x,z-cross-sections: these are the confluence, shear and diabatic effects, all of which play a role in q/x-, q/z-, /x- as well as /z-frontogenesis. A detailed analysis is given for two different states of frontal development. The presented results shed much light on the governing physical processes in the frontal region with strong emphasis on the effects of confluence-generated updrafts, on shear instabilities causing bulges and clefts in the frontal surface as well as producing the elevated frontal head, and on processes related to differential heating and moistening.  相似文献   

11.
Summary Interannual modes are described in terms of three-month running mean anomaly winds (u,v), outgoing longwave radiation (OLR), and sea surface temperature (T * ). Normal atmospheric monsoon circulations are defined by long-term average winds (u n,v n) computed every month from January to December. Daily winds are grouped into three frequency bands, i.e., 30–60 day filtered winds (u L,v L); 7–20 day filtered winds (u M,v M); and 2–6 day filtered winds (u S,v S). Three-month running mean anomaly kinetic energy (signified asK L , K M , andK S , respectively) is then introduced as a measure of interannual variation of equatorial disturbance activity. Interestingly, all of theseK L , K M , andK S perturbations propagate slowly eastward with same phase speed (0.3 ms–1) as ENSO modes. Associated with this eastward propagation is a positive (negative) correlation between interannual disturbance activity (K L , K M , K S ) and interannualu (OLR) modes. Namely, (K L , K M , K S ) becomes more pronounced than usual nearly simultaneously with the arrival of westerlyu and negativeOLR (above normal convection) perturbutions. In these disturbed areas with (K L , K M , K S >0), upper ocean mixing tends to increase, resulting in decreased sea surface temperature, i.e.T * 0. Thus, groups (not individual) of equatorial disturbances appear to play an important role in determiningT * variations on interannual time scales. HighestT * occurs about 3 months prior to the lowestOLR (convection) due primarily to radiational effects. This favors the eastward propagation of ENSO modes. The interannualT * variations are also controlled by the prevailing monsoonal zonal windsu n, as well as the zonal advection of sea surface temperature on interannual time scales. Over the central Pacific, all of the above mentioned physical processes contribute to the intensification of eastward propagating ENSO modes. Over the Indian Ocean, on the other hand, some of the physical processes become insignificant, or even compensated for by other processes. This results in less pronounced ENSO modes over the Indian Ocean.With 10 FiguresContribution No. 89-6, Department of Meteorology, University of Hawaii, Honolulu, Hawaii.  相似文献   

12.
Summary An analysis of the report of the (U.S.) National Academy of Sciences (NAS) on atmospheric effects of a nuclear exchange leads to conclusions that differ from those of the NAS and of the earlier TTAPS and AMBIO studies. Any cooling of the earth's surface is likely to beshort-lived because of rapid removal of the smoke clouds originating from nuclear burst-initiated fires, andminor because of appreciable green-house effects due to several distinct physical causes. (One of these, neglected in prior analyses, is the infrared absorption from cirrus clouds produced directly by the nuclear bursts.) Taken together, these effects may even induce slight surface warming (nuclear summer) instead of cooling (nuclear winter). The consequences to atmospheric ozone are similarly ambiguous; depending on the detailed nuclear scenario, the net ozone content may increase-rather than decrease as argued by TTAPS. Experiments could settle some uncertainties.With 2 Figures  相似文献   

13.
Analyses indicate that the Atlantic Ocean seasurface temperature (SST) was considerably colder at the beginning than in the middle of the century. In parallel, a systematic change in the North Atlantic sea-level pressure (SLP) pattern was observed. To find out whether the SST and SLP changes analyzed are consistent, which would indicate that the SST change was real and not an instrumental artifact, a response experiment with a low-resolution (T21) atmospheric GCM was performed. Two perpetual January simulations were conducted, which differ solely in the Atlantic Ocean (40° S-60° N) SST: the cold simulation utilizes the SSTs for the period 1904–1913; the warm simulation uses the SSTs for the period 1951–1960. Also, a control run with the model's standard SST somewhat between the cold and warm SST was made. For the response analysis, a rigorous statistical approach was taken. First, the null hypothesis of identical horizontal distributions was subjected to a multivariate significance test. Second, the level of recurrence was estimated. The multivariate statistical approaches are based on hierarchies of test models. We examined three different hierarchies: a scale-dependent hierarchy based on spherical harmonics (S), and two physically motivated ones, one based on the barotropic normal modes of the mean 300 hPa flow (B) and one based on the eigenmodes of the advection diffusion operator at 1000 hPa (A). The intercomparison of the cold and warm experiments indicates a signal in the geostrophic stream function that in the S-hierarchy is significantly nonzero and highly recurrent. In the A-hierarchy, the low level temperature field is identified as being significantly and recurrently affected by the altered SST distribution. The SLP signal is reasonably similar to the SLP change observed. Unexpectedly, the upper level stream-function signal does not appear to be significantly nonzero in the B-hierarchy. If, however, the pairs of experiments warm versus control and cold versus control are examined in the B-hierarchy, a highly significant and recurrent signal emerges. We conclude that the cold versus warm response is not a small disturbance that would allow the signal to be described by eigenmodes of the linear system. An analysis of the three-dimensional structure of the signal leads to the hypothesis that two different mechanisms are acting to modify the model's mean state. At low levels, local heating and advection are dominant, but at upper levels the extratropical signal is a remote responce to modifications of the tropical convection.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dilmenil.AWI Publication no. 254  相似文献   

14.
Stable Isotope Ratios: Hurricane Olivia   总被引：1，自引：0，他引：1  
The oxygen and hydrogen isotopic compositions of rains from HurricaneOlivia (1994) in the eastern Pacific were measured. The rains werecollected on 24 and 25 September during airplane flights conducted at anelevation of 3 km. Hurricane Olivia peaked in intensity to a category-4storm between the two dates. Isotope ratios of rains from HurricaneOlivia were markedly lower ( 18O = –13.9to –28.8) than that of rain collected from a thunderstormat an elevation of 2.3 km outside the influence of Olivia (18O = –3.8). A distinct decrease in isotoperatios from the first day to the next ( 18O =–18.4 to –21.9) in Hurricane Olivia wasattributed to decreased updraft velocities and outflow aloft. Thisshifted the isotopic water mass balance so that fewer hydrometeors werelifted and more ice descended to flight level. A decrease in the averagedeuterium excess from the first day to the next (d = 15.5 to 7.1)was attributed to an increase in the relative humidity of the watervapor `source' area. We hypothesize that the `source' region for therain was in the boundary layer near the storm center and that becausethe hurricane was at peak intensity prior to the second day the relative humidity was higher.  相似文献   

15.
Parameterizing turbulent diffusion through the joint probability density   总被引：3，自引：3，他引：0  
The convective mass flux parameterization often used in meteorological modeling expresses the vertical flux of a transported scalar as proportional to the product of the difference in mean values of the scalar in updrafts and downdrafts and their characteristic velocity. The proportionality factor is a constant to be specified. We show that this proportionality factor also appears in the relaxed eddy accumulation technique of Businger and Oncley. That associates the surface-layer flux of a scalar with the product of the standard deviation of vertical velocity and the mean concentration difference between updrafts and downdrafts.We show that this constant (b) is determined uniquely by the joint probability density (jpd) of vertical velocity and the scalar. Using large-eddy simulation, we generate this jpd for a conservative scalar diffusing through a convective boundary layer. It has quite different forms in top-down and bottom-up diffusion geometries. The bottom-up jpd is fairly well represented by a jointly Gaussian form and implies b ~ 0.6, in good agreement with the surface-layer value reported by Businger and Oncley. The top-down jpd is strikingly non-Gaussian and gives b ~ 0.47. Updrafts carry the bulk of the scalar flux - 70% in the bottom-up case, 60% in the top-down case.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

16.
This study examines the statistical properties of the concentration derivative, , for a dispersing plume in a near-neutrally stratified atmospheric surface layer. Towards this goal, the probability density function (pdf) of , and the conditional pdf of given a fixed concentration level, , have been measured. These pdfs are found to be modeled well by a generalizedq-Gaussian (gqG) distribution with intermittency exponent,q, equal to 0.3 and 3/4, respectively. These results highlight the strong intermittency effect (patchiness) of the small-scale concentration eddy structures in the plume. The distribution of time intervals between successive high peaks in the squared derivative process, x2, is found to be well approximated by a power-law distribution, implying that occurrences of these high peaks are much more clustered than would be predicted by a Poisson or shot-noise process. The results are used to improve models for the joint pdf of and , and for the expected number of upcrossings per unit time interval of a fixed concentration level that have been proposed by Kristensenet al. (1989). The predictions of the improved models are in accord with observations, and suggest that the intercorrelation between and must be explicitly incorporated if good estimates of the upcrossing intensity are to be obtained.  相似文献   

17.
Analytical solutions for the Ekman layer   总被引：1，自引：0，他引：1  
The PBL equation that governs the transition from the constant-stress surface layer to the geostrophic wind in a neutrally stratified atmosphere for which the eddy viscosityK(z) is assumed to vary smoothly from the surface-layer value U *z (0.4,U *=friction velocity,z=elevation) to the geostrophic asymptoteK GU *d forzd is solved through an expansion in fd/U *1 (f=Coriolis parameter). The resulting solution is separated into Ekman's constant-K solution an inner component that reduces to the classical logarithmic form forzd and isO() relative to the Ekman component forzd. The approximationKU *d is supported by the solution of Nee and Kovasznay's phenomenological transport equation forK(z), which yieldsK–U *d exp(–z/d), where is an empirical constant for which observation implies, 1. The parametersA andB in Kazanskii and Monin's similarity relation forG/U * (G=geostrophic velocity) are determined as functions of . The predicted values ofG/U * and the turning angle are in agreement with the observed values for the Leipzig wind profile. The predicted value ofB based on the assumption of asymptotically constantK is 4.5, while that based on the Nee-Kovasznay model is 5.1; these compare with the observed value of 4.7 for the Leipzig profile. A thermal wind correction, an asymptotic solution for arbitraryK(z) and 1, and an exact (unrestricted ) solution forK(z)=U *d[1–exp(–z/d)] are developed in appendices.  相似文献   

18.
ALPEX-Simulation     
Summary In a project ALPEX-Simulation, sponsored by the Österreichischer Fond zur Förderung der wissenschaftlichen Forschung (FWF), all eight cases of ALPEX-SOP cyclones were numerically simulated with a fine mesh isentropic model of the atmosphere. These numerical simulations in six-hourly intervals allow a deeper insight into the synoptics and dynamics of the cyclogeneses in the Western Mediterranean, especially into the genesis of the two basic types of cyclones: the so-called Überströmungs-type and Vorderseiten-type. In the first phase of cyclogenesis of the Überströmungs-type, the blocking and flow splitting of the cold air due to the Alps and the canalization between the Alps and the Massif Central are important. Cold air flows cyclonically around the western part of the Alps, creating a vorticity maximum at the south western edge of the Alpine, bow and leads also to an enhanced PV. In connection with warm air in the Mediterranean, a strong baroclinic zone is generated. The interaction between the arriving PV maximum in the upper troposphere and the enhanced PV at the bottom leads to cyclogenesis in the Western Mediterranean. In the case of the Vorderseiten-type warm air advection dominates with the exception of a shallow layer of cold air in the inner Po-Valley, which is shielded by the Alpine ridge. A well-pronounced PV maximum builds up and couples with the PV maximum arriving at upper levels, even before the cold air, coming from the north-west, has surrounded the Alps. The cold air only intensifies the development by raising the baroclinity. Therefore, the Vorderseiten-cyclogenesis is an orographically modified cyclogenesis, in the course of which the cyclonic development is triggered by the Alps, whereas the Überströmungs-cyclogenesis is an orographically induced cyclogenesis i.e. a true lee cyclogenesis.With 14 FiguresDied in a tragic traffic accident on June 6, 1993.  相似文献   

19.
E- turbulence model predictions of the neutralatmospheric boundary layer (NABL) are reinvestigated to determine thecause for turbulence overpredictions found in previous applications. Analytical solutions to the coupled E and equations for the case of steady balance between transport and dissipation terms, the dominant balance just below the NABL top, are derived. It is found that analytical turbulence profiles laminarizeat a finite height only for values of closure parameter ratio c 2 /e equal toor slightly greater than one, with laminarization as z for greater . The point = 2 is additionally foundthat where analytical turbulent length scale (l) profilesmade a transition from ones ofdecreasing ( < 2) to increasing ( > 2)values with height. Numerically predicted profiles near the NABL topare consistent with analytical findings. The height-increasingvalues of l predicted throughout the NABL with standard values ofclosure parameters thus appear a consequence of 2.5(> 2), implied by these values (c 2 = 1.92, = 1.3, e = 1). Comparison of numericalpredictions with DNS data shows that turbulence overpredictions obtained with standard-valued parameters are rectifiedby resetting and e to 1.1 and 1.6, respectively, giving, with c 2 = 1.92, 1.3, and laminarization of the NABL's cappingtransport-dissipation region at a finite height.  相似文献   

20.
Wind and temperature profiles in the stable boundary layer were analyzed in the context of MoninObukhov similarity. The measurements were made on a 60-m tower in Kansas during October 1999 (CASES-99). Fluxprofile relationships, obtained from these measurements in their integral forms, were established for wind speed and temperature. Use of the integral forms eliminates the uncertainty and accuracy issues resulting from gradient computations. The corresponding stability functions, which were nearly the same for momentum and virtual sensible heat, were found to exhibit different features under weakly stable conditions compared to those under strongly stable conditions. The gradient stability functions were found to be linear, namely m = 1+ 5.8 and h = 1 + 5.4 up to a limit of the MoninObukhov stability parameter = 0.8; this is consistent with earlier findings. However, for stronger stabilities beyond a transition range, both functions were observed gradually to approach a constant, with a value of approximately 7. To link these two distinct regimes, a general but pliable functional form with only two parameters is proposed for the stability functions, covering the entire stability range from neutral to very stable conditions.  相似文献   

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