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1.
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
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.
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
4.
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
5.
太行山东麓焚风天气的统计特征和机理分析Ⅱ:背风波对焚风产生和传播影响的个例分析 总被引：1，自引：0，他引：1
利用中尺度模式WRF3.3对太行山东麓焚风典型个例进行了数值模拟。结果表明,太行山东麓焚风的发生和移动与山脉背风波密切相关。由此建立了太行山东麓焚风的概念模型:西北或偏西气流途经山西盆地、山西境内的山脉或高原,再越过太行山,在其东麓形成背风波。背风波的下沉气流气温按干绝热方式上升,同时下沉气流也会对低层大气产生压缩增温效应,使得太行山东麓产生焚风。背风波即为重力波,可以伴随着下沉气流向下游移动,正变温区同时也向东移动。变温区移动的速度和重力波的传播速度相同。背风波的产生,需要Scorer数向上足够的减小,而且不连续,即要求大气是稳定的且存在明显的风速切变。 相似文献
6.
Prof Dr. W. Georgii 《Meteorology and Atmospheric Physics》1967,16(2-3):137-152
Zusammenfassung Unter Zugrundelegung der Theorie des südalpinen Föhns vonH. Ficker werden der Kaltluftföhn der argentinischen Kordillere, der Polarluftföhn des Tessins und die Bora der mittleren Apenninen behandelt. Drei Phasen kennzeichnen den Kordillerenföhn. Eingeleitet durch Tropikluftföhn folgen Polar- und Antarktikluftföhn; erst der letztere dringt bis zur Niederung durch. Der Kaltluftföhn des Tessins wird entsprechend der Theorie vonH. Ficker durch die instabile Phase der abgehobenen Warmluft eingeleitet, auf die der Absturz der Kaltluft in die Niederung erfolgt. Die Tramontana der Apenninen zeigt in ihrer Hauptphase einen ausgeprägten Tropopausentrichter mit sehr niedriger Tropopause. Kinematisch ist wichtig, daß die stationäre Leewellenströmung des Polarluftföhns und noch ausgeprägter die Tramontana häufiger hochreichende Stratosphärenwellen entwickeln können.
Mit 15 Textabbildungen 相似文献
Summary TakingFicker's theory of the South-Alpine foehn as a base the author investigates the cold air foehn of the Argentine Cordillera, the polar air foehn of Ticino (Switzerland) and the bora of the Central Apennines. Three phases characterize the foehn of the Cordillera. After the initiation by tropical air foehn the phases of polar air and antarctic air foehn follow and only the last named can penetrate to the bottom of the valleys. The cold air foehn of Ticino is initiated in accordance to the theory ofFicker by the instable phase of the lifted warm air which is followed by the downfall of the cold air to the valley. The tramontana of the Apennines in its main phase shows a pronounced tropopause funnel with extremely low tropopause. From the point of kinematics it is important that the stationary lee-wave flow of the polar air foehn and, still more pronounced, of the tramontana frequently can develop high reaching stratospheric waves.
Résumé En partant de la théorie établie parH. Ficker pour le foehn au sud des Alpes, on examine le foehn d'air froid de la Cordillère argentine, le foehn d'air polaire au Tessin et la Bora des Apennins moyens. Trois phases caractérisent le foehn de la Cordillère. Il débute par un afflux d'air tropical suivi par de l'air polaire, puis par de l'air arctique. Ce n'est que ce dernier courant de foehn qui pénètre jusque dans les vallées. Le foehn d'air froid du Tessin débute, selon la théorie deFicker, par la phase instable de l'air chaud soulevé. Ce n'est qu'ensuite que cet air froid se précipite dans les vallées. La Tramontane des Apennins est accompagnée dans sa phase principale d'une sorte d'entonnoir dans la tropopause qui s'abaisse alors fortement. Il est important de retenir, du point de vue cinématique, ques les ondulations stationnaires sous le vent du foehn d'air polaire, et encore plus de la tramontane, peuvent souvent développer des ondes atteignant de grandes altitudes dans la stratosphère.
Mit 15 Textabbildungen 相似文献
7.
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
8.
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
9.
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
10.
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