共查询到20条相似文献，搜索用时 312 毫秒
1.
K. P. Hoinka 《Boundary-Layer Meteorology》1987,40(1-2):199-203
The present note discusses physical mechanisms which may contribute to cold air channelling close to the Alps. This involves the modification of the prefrontal air by the warm foehn air and of the postfrontal air by blocking effects resulting in an increase in precipitation. Additionally the influence of a sloping surface in the vicinity of the orography is considered. The problems are discussed in term of a north-south-oriented cold front behaving as an atmospheric gravity current propagating along the east-west oriented Alps. 相似文献
2.
Summary This paper describes and documents the meteorological conditions which occur in association with a cold surface layer on the northern lee side of the Alps during foehn. A climatological study using four years' rawinsonde data shows that during many foehn events a weak advection from the east occurs in the cold surface layer beneath the southerly foehn flow. Three cases of foehn in the northern Alps were studied using data taken by instrumented aircraft. The analysis of various vertical soundings between the baseline of the Alps and Munich indicate that the cold surface layer is eroded up to 50 km north of the baseline but that further north, the foehn has not touched the ground. The analysis of data taken in the urban plume west of Munich shows that the pollution is trapped by the inversion in the cold air leading to high levels of air pollution west of Munich.With 13 Figures 相似文献
3.
Summary Regional and local scale windfield and air mass characteristics during two distinct synoptic foehn wind events over southern New Zealand are examined. The Southern Alps were observed to effectively block low level onshore gradient northwesterly airflow and to channel it through both Cook and Foveaux Straits. Blocking of the onshore synoptic northwesterly airstream also resulted in barrier jet formation along the western slopes of the Southern Alps. This feature of the regional windfield has not previously been documented and develops during favourable conditions to a height of between 1500 to 1800 m above sea level. In the immediate lee of the Southern Alps at Lake Tekapo, classic foehn conditions such as warm ambient air temperatures, low relative humidities and gusty winds were monitored throughout both foehn events examined. Differences in the local windfield were however observed, which reflect the importance of local topography on lee side windfield dynamics during foehn events. Spillover of precipitation to the lee of the mountains was monitored in the latter stages of each case study and appeared to be associated with the passage of the cold front over the Southern Alps. Observations made by this investigation have a number of applied and theoretical implications with respect to meso-scale modelling, orographic rainfall distribution and forecasting.With 12 Figures 相似文献
4.
Summary This study examines the exceptional Alpine south foehn event of 14–16 November 2002 using routine observations and high-resolution
numerical simulations. Besides its long duration and an extremely high temperature level related to warm-air advection from
the northern Sahara, this foehn event exhibited an unusual spatial structure of the low-level wind and temperature field.
Whereas the foehn was largely restricted to the first half of 14 November in the western part of the Alps (Switzerland), it
extended over the full period in the inner-Alpine valleys in the eastern Alps. The duration and intensity of the foehn also
tended to decrease from the Alpine crest towards the northern rim of the Alps. Most surprisingly, continuous foehn even occurred
on the windward side of the Alpine crest, namely in a basin located in the southeastern Alps. The distribution of the orographic
precipitation associated with the foehn case was unusual as well. In Switzerland, intense precipitation was not restricted
to the windward (southern) side of the Alps but extended to the northern side of the Alpine crest, particularly on 16 November.
The results indicate that the spatio-temporal distribution of the foehn in the northern Alps was related to the fact that
the western Alps were within a synoptic-scale transition zone between extremely warm air advected from the south and colder
air lying over western Europe. The colder air was advected around the western Alps whereas extremely warm air descended from
the Alpine crest farther east. Moreover, a small cyclone formed on 14 November north of the Alps and generated a shallow cold
front propagating eastward along the northern Alps. Thus, the tendency towards foehn decreased from west to east and from
the Alpine crest towards the north. The occurrence of foehn on the windward side of the Alpine crest was made possible by
the extreme strength of the large-scale southerly flow, combined with the fact that the upstream precipitation field did not
reach the southeastern edge of the Alps. Finally, the pronounced spillover of precipitation to the northern side in the Swiss
part of the Alps appears to be related to the colder air present north of the crest. This prevented the formation of orographic
gravity waves and downslope air motion, which usually leads to a rapid evaporation of the precipitation on the lee side of
the Alpine crest. 相似文献
5.
Dr. P. Seibert 《Meteorology and Atmospheric Physics》1990,43(1-4):91-103
Summary After the ALPEX Special Observing Period in 1982, further field measurement campaigns have been carried out to study the south foehn in the Eastern Alps. In addition, foehn situations were investigated statistically on the basis of a 4-years-record of upper-air and synoptic data combined with data from a special regional network. In this paper, distribution of air masses around the Alps, flow patterns and the typical evolution of a foehn situation are illustrated by the case 8 November 1982. Several possible definitions of shallow foehn are given, yielding a share of approximately 10% of shallow foehn observations. Mainly statistical data are used to falsify the wide-spread version of the thermodynamical foehn theory attributing the warmth of the foehn to release of latent heat and postulating foehn air rising from the ground of the Po Valley. Instead of this, the foehn air originates from 2000–2500 m asl over the Po Valley, while the air near ground remains blocked. The potential temperature difference between southern and northern valleys during foehn is to be explained by the stable stratification in the south, not by the effects of precipitation. These findings are in agreement with Hann's original theory.With 10 Figures 相似文献
6.
Summary Three different climates have been identified by our evaluation of AVHRR (Advanced Very High Resolution Radiometer) data
using APOLLO (AVHRR Processing scheme Over Land, Clouds and Ocean) for a five-years cloud climatology of the Alpine region.
The cloud cover data from four layers were spatially averaged in boxes of 15 km by 14 km. The study area only covers 540 km
by 560 km, but contains regions with moderate, Alpine and Mediterranean climate. Data from the period July 1989 until December
1996 have been considered. The temporal resolution is one scene per day, the early afternoon pass, yielding monthly means
of satellite derived cloud coverages 5% to 10% above the daily mean compared to conventional surface observation. At non-vegetated
sites the cloudiness is sometimes significantly overestimated. Averaging high resolution cloud data seems to be superior to
low resolution measurements of cloud properties and averaging is favourable in topographical homogeneous regions only. The
annual course of cloud cover reveals typical regional features as foehn or temporal singularities as the so-called Christmas
thaw. The cloud cover maps in spatially high resolution show local luff/lee features which outline the orography. Less cloud
cover is found over the Alps than over the forelands in winter, an accumulation of thick cirrus is found over the High Alps
and an accumulation of thin cirrus north of the Alps.
Received December 17, 1999 Revised July 18, 2000 相似文献
7.
Dr. D. Heimann 《Meteorology and Atmospheric Physics》1992,48(1-4):165-171
Summary The separation of potential temperature and equivalent-potential temperature patterns at cold fronts with pre-frontal foehn is explained by means of conceptual considerations and discussed with reference to observations and numerical simulations. It is shown that foehn increases the potential temperature north of the Alps but does not necessarily affect the equivalent-potential temperature. As a consequence potential temperature and equivalent-potential temperature may form different structures and generate zones of large gradients at different locations even if no diabatic heat conversions are present.With 5 Figures 相似文献
8.
G. Zängl 《Meteorology and Atmospheric Physics》2003,83(3-4):237-261
Summary ?Numerical simulations of the south foehn in the region of Innsbruck are presented. They are semi-idealized in the sense that
realistic orography but idealized initial and boundary conditions are used. The focus of this study is on typical features
of the fully developed foehn, the breakthrough phase of the foehn and the diurnal cycle of the foehn. In addition, the impact
of the large-scale wind direction is examined, including conditions leading to shallow foehn.
The simulated flow fields have been found to be in very good agreement with observations except for a few minor details. In
the lower part of the Sill Valley (the valley going from the Brenner pass down to Innsbruck), the wind speed is significantly
higher than in the upper part. The acceleration can be traced back to the three-dimensional propagation of gravity waves excited
over the adjacent mountain ridges. The amplitude of the gravity waves over the various mountain ridges depends sensitively
on the wind direction, large wave amplitudes occurring only when the angle between the wind direction and the ridge line is
not too small. For southwesterly or south–southwesterly large-scale flow, wave amplitudes are significantly larger to the
east of Innsbruck than to the west. Foehn breakthrough at Innsbruck is usually preceded by a moderate westerly (downvalley)
wind that is restricted to a rather small area around Innsbruck. The simulations reveal that this so-called pre-foehn is mainly
a consequence of the gravity wave asymmetry, producing an asymmetric pressure perturbation with lower pressure to the east
of Innsbruck. Shallow foehn, defined as a foehn occurring when the large-scale flow at crest height (700 hPa) is approximately
westerly, is associated with relatively weak wave activity along the Sill Valley. It is found that at least a weak southerly
wind component below crest height is necessary to maintain a significant shallow foehn over a longer time.
Received October 10, 2001; accepted June 20, 2002
Published online: February 20, 2003 相似文献
9.
H. Hoinkes 《Meteorology and Atmospheric Physics》1949,2(1):82-96
Zusammenfassung Der zwischen dem 2. und 4. Oktober 1941 in den n?rdlichen Alpent?lern beobachtete Südf?hn ist aus den in der Bodenwetterkarte
ersichtlichen Luftdruckgradienten nicht zu verstehen. Er verdankt seine Entstehung einem kleinen abgeschlossenen H?hentief,
das auf die mittleren Schichten der Troposph?re beschr?nkt ist, in dessen Str?mungsbereich sich der Alpenkamm in den genannten
Tagen befindet. Die w?hrend dieser Zeit zwischen Süd- und Nordseite der Alpen entstehenden Druckunterschiede sind durch Temperaturunterschiede
v?llig zu verstehen, die auf die H?henschicht zwischen 900 und 3700 m beschr?nkt sind und die durch das unter Kondensation
erfolgende Aufsteigen der Luftmassen auf der Südseite der Alpen und das Absinken auf deren Nordseite entstanden sind. Die
obere Südstr?mung kann in diesem Fall erst dann als F?hn bis zum Boden der n?rdlichen Alpent?ler durchbrechen, wenn durch
die Einstrahlung die Luft l?ngs der Talh?nge auf die potentielle Temperatur der oberen Südstr?mung erw?rmt worden ist. Die
Bedeutung dieses Vorganges auch bei normal verlaufenden F?hnf?llen ist aus dem t?glichen und j?hrlichen Gang der F?hnh?ufigkeit
in Innsbruck zu erkennen.
Mit 8 Textabbildungen. 相似文献
Summary A case of foehn from the south observed in the northern valleys of the Alps betweeen October 2 and 4, 1941 cannot be accounted for by the pressure gradient taken from the surface weather map. It has its origin in a small, limited high-level depression confined to the medium layers of the troposphere in the range of which the Alpine ridge lays on the above mentioned days. The differences of pressure between the southern and the northern side of the Alps occurring during this period can be perfectly explained by the differences of temperature which were confined to the atmospheric layer between 900 m and 3700 m and caused by the effect of air masses ascending with condensation on the south side and descending on the north side of the Alps. In this case the upper south wind can make its way as foehn to the bottom of the northern Alpine valleys until the air along the valley slopes is heated by insolation to the potential temperature of the upper southerly current. Also in cases of regular foehn the importance of this process is evident if the daily and yearly variation of foehn frequency at Innsbruck is considered.
Résumé Le foehn du Sud observé entre le 2 et le 4 octobre 1941 dans les vallées du Nord des Alpes ne peut trouver son explication dans le gradient de pression au sol des cartes isobariques correspondantes. Ce foehn doit son origine à une petite dépression limitée aux couches moyennes de la troposphère et au niveau de laquelle le fa?te alpin se trouvait ces jours là. Il est possible d'expliquer entièrement les différences de pression existant alors entre les versants sud et nord des Alpes par les différences de température localisées dans la couche de 900 à 3700 m., et qui ont pour origine l'ascension (avec condensation) des masses d'air au Sud des Alpes et l'affaissement de ces masses au Nord. Le courant supérieur du Sud ne peut dans ce cas atteindre comme foehn les vallées du Nord des Alpes que lorsque l'air des versants s'est réchauffé par irradiation et a atteint de cette manière la température potentielle du courant supérieur méridional. On peut reconna?tre l'importance de ce processus, même dans les cas normaux de foehn, dans la variation diurne et annuelle de la fréquence du foehn à Innsbruck.
Mit 8 Textabbildungen. 相似文献
10.
P. P. Alberoni S. Nanni M. Crespi M. Monai 《Meteorology and Atmospheric Physics》1996,58(1-4):123-138
Summary A case study of supercell thunderstorm development over Po Valley in northern Italy is discussed. The data were collected during MATREP, a field project operated in the month of June 1990. During the late morning hours of 8 June, before the passage of a cold front, a supercell and a single cell developed at the same time in eastern part of Po Valley, about 60 km apart from each other.Surface mesoscale analysis helps to explain these different storm evolutions due to interaction among local circulations, Adriatic Sea and orography. While dry wind (foehn) dumps the thermodynamic instability in single-cell environment, a moisture circulation affects the origin area of supercell. Computation of corresponding instability indices again supports the peculiar evolution of the two storms which is also analyzed by means of radar data.With 20 Figures 相似文献
11.
H. A. McGowan A. P. Sturman M. Kossmann P. Zawar-Reza 《Meteorology and Atmospheric Physics》2002,79(3-4):215-230
Summary Local scale windfield and air mass characteristics during the onset of two foehn wind events in an alpine hydro-catchment
are presented. Grounding of the topographically modified foehn was found to be dependent on daytime surface heating and topographic
channelling of flow. The foehn front was observed to advance down-valley until the valley widened significantly. The foehn
wind appeared to decouple from the surface downstream of the accelerated flow associated with the valley constriction, and
to be lifted above local thermally generated circulations including a lake breeze. Towards evening, the foehn front retreated
up valley in response to reduced surface heating and the intrusion into the study area of a deep and cool air mass associated
with a regional scale mountain-plain circulation. Differences in the local windfield observed during both case study events
reflect the importance of different thermal and dynamic forcings on airflow in complex terrain. These are the result of variation
in surface energy exchanges, channelling and blocking of airflow. Observations presented here have both theoretical and applied
implications with regard to forecasting foehn onset, wind hazard management, recreational activities and air quality management
in alpine settings.
Received January 23, 2001 Revised October 17, 2001 相似文献
12.
Significant changes have occurred in the Antarctic Peninsula (AP) including warmer temperatures, accelerated melting of glaciers, and breakup of ice shelves. This study uses the Weather Research and Forecasting model (WRF) forced by the Community Climate System Model 4 (CCSM) simulations to study foehn wind warming in AP. Weather systems responsible for generating the foehn events are two cyclonic systems that move toward and/or cross over AP. WRF simulates the movement of cyclonic systems and the resulting foehn wind warming that is absent in CCSM. It is found that the warming extent along a transect across the central AP toward Larsen C Ice Shelf (LCIS) varies during the simulation period and the maximum warming moves from near the base of leeward slopes to over 40 km away extending toward the attached LCIS. Our analysis suggests that the foehn wind warming is negatively correlated with the incoming air temperature and the mountain top temperature during periods without significant precipitation, in which isentropic drawdown is the dominant heating mechanism. On the other hand, when significant precipitation occurs along the windward side of AP, latent heating is the major heating mechanism evidenced by positive relations between the foehn wind warming and 1) incoming air temperature, 2) windward precipitation, and 3) latent heating. Foehn wind warming caused by isentropic drawdown also tends to be stronger than that caused by latent heating. Comparison of WRF simulations forced by original and corrected CCSM data indicates that foehn wind warming is stronger in the original CCSM forced simulation when no significant windward precipitation is present. The foehn wind warming becomes weaker in both simulations when there is significant windward precipitation. This suggests that model’s ability to resolve the foehn warming varies with the forcing data, but the precipitation impact on the leeward warming is consistent. 相似文献
13.
Dipl.-Met. M. Kurz 《Meteorology and Atmospheric Physics》1990,43(1-4):61-68
Summary In the paper results of investigations of the first two front events of the German Front Experiment 1987/88 are presented. In both cases a frontogenesis took place in the lower troposphere north of the Alps—in the first case directly at the cold front, in the second case ahead of it. The main reason for that was the incorporation of warm and dry air produced by foehn or advected along the Alps into the frontal zone of the approaching front. In the second case the cooling through evaporation of falling rain was an additional important factor for the increase of the temperature gradient. The computation of kinematic parameters yields as an interesting result the proof of areas with absolute vorticity near or below zero within the southwesterly current at the northwestern flank of the Alps.With 6 Figures 相似文献
14.
Summary In this paper, very-high-resolution numerical simulations are presented to analyze the small-scale dynamics of the foehn in
the lower Wipp Valley and the adjacent parts of the Inn Valley. This region was one of the target areas for foehn observations
during the Mesoscale Alpine Programme (MAP). Our simulations consider two MAP cases that markedly differed in the depth of
the foehn flow. To isolate the dynamical effect of the key orographic features in the Wipp Valley region, we performed sensitivity
experiments with different topography modifications. These involve lowering or even removing the Nordkette range, which constitutes
the northern side wall of the east–west-oriented Inn Valley, and closing the Stubai Valley, which is the northernmost and
largest tributary of the Wipp Valley. A comparison with surface and lidar observations indicates that our present model resolution
of 467 m significantly improves the realism of the simulations compared to a resolution of 800 m, as used in a previous study.
The Nordkette is found to have a twofold impact on the dynamics of foehn breakthrough into the Inn Valley. In reality, this
mountain chain deflects part of the southerly foehn current coming from the Wipp Valley into the perpendicularly oriented
Inn Valley. Our sensitivity tests indicate that this flow deflection tends to accelerate the foehn breakthrough into the Inn
Valley, while upstream blocking effects induced by the Nordkette act to slow down the process of foehn breakthrough. The flow
pattern in the Wipp Valley reveals that the upstream effects of the Nordkette are not quite far-reaching. The amplitude of
the gravity waves over the lower Wipp Valley gets somewhat reduced by these upstream effects, but the overall flow pattern
remains largely unaffected. Closing the Stubai Valley also has a minor effect of the wave structure and tends to reduce the
cross-valley variability of the foehn flow in the lower Wipp Valley. 相似文献
15.
A. P. Sturman 《Meteorology and Atmospheric Physics》1992,47(2-4):229-236
Summary The Southerly Change Experiment (SOUCHEX) was conducted to examine the influence of the New Zealand Southern Alps on the structure and evolution of cold fronts, locally called southerly changes, as they travel up the east coast. The extensive data obtained by the augmented surface weather station network is used to examine in detail the mesoscale wind field associated with the events observed during the experiment. A comparison of the wind fields observed during the different events illustrates the influence of local dynamic and thermal factors. In particular, lee trough-induced northeasterlies and thermally developed diurnal wind systems are seen to interact with the wind field created by the passage of the front over the Southern Alps.It is apparent that the wind field associated with southerly changes responds to a variety of factors as the cold fronts propagate northwards. For example, there is a tendency for the flow to turn onshore producing a southeast wind during daytime over the Canterbury Plains south of Banks Peninsula probably due to diabatic heating of the mountains and plains. This onshore flow is in direct opposition to pre-frontal foehn northwesterly flow which often continues in the mountain regions and aloft after the front has moved up the coast. The interaction of these air masses over Canterbury creates difficulties for local forecasting. Also, the nocturnal passage of a southerly change is often difficult to detect in surface anemograph traces because of the decoupling of the boundary layer air from that above, producing low level drainage flow over the Canterbury Plains. The overall effect is to create a complex mesoscale wind field resulting from interaction of cold fronts with regional orographic and thermal influences.With 8 Figures 相似文献
16.
Zusammenfassung Ein enges Netz von mit Thermohydgrographen ausgerüsteten Beobachtungsstationen im Nordabhang der Hohen Tauern im Rauriser Tal und Gasteiner Tal ergab die Möglichkeit, im Vergleich mit den Beobachtungen auf dem Sonnblick-Obervatorium (3106 m) und auf der nordwärts vorgelagerten Schmittenhöhe (1964 m) die Entwicklung des Föhns vom Alpenkamm bis in die unteren Talböden hin statistisch zu untersuchen. Diei Statistik bezieht sich auf die Häufigkeit der Föhntage und der Föhnstunden, die Föhndauer pro Föhntag, den Jahresgang und den Tagesgang der Föhnhäufigkeit, die Zahl der Tage mit zyklonalem und antizyklonalem (freiem) Föhn, die Häufigkeiten der Föhndauer nach Stunden, die Häufigkeiten von Beginn und Ende des Föhns zu den verschiedenen Zeiten des Tages, die Abhängigkeit der Föhnfälle vom Höhenwind und die Häufigkeiten der Windrichtungen und Windstärken bei Föhn im Tal. Die Unterschiede im Föhnvorkommen in den verschiedenen Höhenlagen werden eingehend diskutiert und erklärt. Besonders unterhalb von Talstufen finden sich tagsüber auch Föhnfällen mit talaufwärts gerichteter Bodenwindströmung, die als maskierter Föhn bezeichnet werden können und offenbar durch eine durch die Talstufen und durch die Talwindentwicklung begünstigte Ausbildung einer Zirkulation um eine quer zum Tal gelegene horizontale Achse erklärt werden können.
Mit 4 Textabbildungen.
Vorgetragen auf der dritten internationalen Tagung für alpine Meteorologie in Davos, 12. bis 14. April 1954. 相似文献
Summary A close network of observation stations outfitted with thermohygrographs on the northern side of the Hohe Tauern in the Rauris and the Gastein valley offered the possibility of investigationg statistically the development of foehn from the ridge of the Alps down to the bottom of the valleys by comparing observations with those of Sonnblick Observatory (3106 m) and the Schnittenhöhe station (1964 m) lying to the north of the Sonnblick. The statistical evaluation refers to frequency of foehn days and foehn hours, duration of foehn on a foehn day, annual and daily march of foehn frequency, number of days with cyclonic and anticyclonic (free) foehn, frequencies of foehn duration by hours, frequencies of beginning and ending of foehn at different times of the day, dependence of foehn on the uppe wind, frequencies of wind direction and wind velocity for foehn in the valleys. Differences in the occurrence of foehn at different levels are thoroughly discussed and explained. During day hours cases of foehn were also found, particularly at the lower end of valley steps with the surface wind blowing valleyupwards, which can be characterized as masked foehn and may be due to the formation of a circulation around a horizontal axis across the valley favoured by the valley steps and the development of the valley breeze.
Résumé Un réseau dense de stations équipées de thermohygrographes sur le versant Nord des Hohe Tauern, dans les vallées de Rauris et de Gastein, ainsi que les stations de l'Observatoire du Sonnblick (3106 m) et de Schmittenhöhe (1964 m), ont permis d'étudier par voie statistique le développment du foehn depuis de crête des Alpes jusqu'au fond des vallées. Cette étude porte sur la fréquence des jours et heures de foehn, la durée du vent par jour de foehn, les variations annuelle et diurne de la fréquence, le nombre de jours avec foehn cyclonique et anticyclonique, les fréquences de durée par heures, les fréquences du début et de la fin aux différents moments du jour, la dépendance du foehn à l'égard du vent en altitude et les fréquences d'azimuts et de force du vent par foehn dans les vallées. On examine les cas de foehn à différents niveaux et les différences de son comportement. Au-dessous de certains gradins de vallées apparaissent parfois par foehn des courants remontants que l'on peut désigner par foehn masqué et qui s'expliquent par une circulation autour d'un axe horizontal transverse due au gradin liu-même et à la brise d'aval.
Mit 4 Textabbildungen.
Vorgetragen auf der dritten internationalen Tagung für alpine Meteorologie in Davos, 12. bis 14. April 1954. 相似文献
17.
G. Zängl 《Meteorology and Atmospheric Physics》2006,91(1-4):85-105
Summary This study presents high-resolution numerical simulations of north foehn in the Austrian Inn Valley which have been performed
with the Penn State/NCAR mesoscale model MM5. As the Inn Valley is located north of the Alpine crest, north foehn occurs comparatively
rarely in this valley, and there are only sparse observations available for this phenomenon. Simulations of the 24 January
1993 case as well as idealized simulations are performed to get a deeper insight into the dynamics of the north foehn. Moreover,
the synoptic conditions leading to the occurrence of north foehn in the Inn Valley are investigated.
The simulations indicate that there are at least four different paths for the foehn to penetrate into the valley. Two of them
are running along side valleys entering the upper Inn Valley from the west. These flow paths appear to be most important when
the large-scale flow has a significant westerly component. The other possible flow paths enter the Inn Valley from the northwest
or north and require a strong northerly component of the large-scale flow. From a dynamical point of view, north foehn appears
to be similar to the well researched south foehn in that vertically propagating gravity waves force the descent of the ambient
flow into the valleys. However, there are also indications that trapped lee waves have a significant impact on the surface
wind field, which has not been reported for south foehn so far. Moreover, the model results show that a precondition for the
formation of north foehn in the Inn Valley is the absence of significant orographic precipitation. Evaporative cooling induced
by precipitation falling into subsaturated air not only reduces the surface temperatures but also inhibits the formation of
large-amplitude gravity waves, suppressing the development of stormy surface winds. 相似文献
18.
太行山东麓焚风天气的统计特征和机理分析Ⅰ:统计特征 总被引：2，自引：0，他引：2
利用2007-2008年京津冀区自动站资料,根据小时变温,对太行山东麓焚风天气进行了详细的统计和分析。结果表明,焚风具有明显的季节变化和日变化,其分布特征在夜间表现明显,强焚风一般出现在太行山东侧50km内,而弱焚风则可到达太行山以东100km范围内;太行山北段的东南侧和南段的东侧呈现出两个焚风中心,而中段附近焚风出现的相对较少;焚风出现的位置与风向的关系密切,西北风造成的焚风主要出现在太行山北段东侧,偏西风主要影响太行山南段,而西南风主要影响中段;焚风强度与风速大小有一定的对应关系,具有明显的阵性特征;在红外云图中焚风常表现为一条明显的暗带;太行山东麓焚风造成的加热区可向东或东南方向移动,影响河北平原。 相似文献
19.
Xia LI Keming ZHAO Shiyuan ZHONG Xiaojing YU Zhimin FENG Yuting ZHONG Ayitken MAULEN Shuting LI 《大气科学进展》2023,40(1):29-43
The air pollution in Urumqi which is located on the northern slope of the Tianshan Mountains in northwestern China,is very serious in winter. Of particular importance is the influence of terrain-induced shallow foehn, known locally as elevated southeasterly gale(ESEG). It usually modulates atmospheric boundary layer structure and wind field patterns and produces favorable meteorological conditions conducive to hazardous air pollution. During 2013–17, Urumqi had an average of 50 d yr–1... 相似文献
20.
不同地形和下垫面对冬季地中海气旋发展影响的数值模拟 总被引：1，自引：0，他引：1
通过数值模拟方法对一个冬季地中海气旋发生和发展的可能机制进行了研究。控制试验和对比试验结果指出，阿尔卑期山背风坡是气旋的有利生成地；但阿尔卑斯山和阿特拉斯山的存在与否，对冬季地中海气旋发展的影响不大。下垫面替代试验结果指出，冬季地中海作为一个非绝热加热源，对其气旋的发展有着十分重要的作用当以陆面或沙漠代替地中海面时，则气旋的发展显著减弱。地形替代试验结果指出，当青藏高原移到地中海西部，并且二者配合 相似文献