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1.
索马里跨赤道气流对南海夏季风爆发的重要作用 总被引：33，自引：8，他引：25
通过分析NCEP/NCAR多年再分析资料,清楚地揭露了南海夏季风爆发与索马里跨赤道南风气流建立之间的重要关系.对应南海夏季风爆发,总是已先期在赤道印度洋地区有西风加强和索马里跨赤道南风气流的建立;而且,若南海夏季风爆发偏早(晚),赤道印度洋地区西风的加强和索马里跨赤道南风气流的建立也偏早(晚).可以认为,索马里跨赤道南风气流的稳定建立是南海夏季风爆发的重要物理机制之一,它的建立导致赤道印度洋地区西风的持续加强和向东扩展,并最终在南海地区形成西南气流. 相似文献
2.
The characteristics of the boundary layer over complex terrain (Lannemezan - lat.: 43.7° N and, long.: 0.7 ° E) are analyzed for various scales, using measurements obtained during the COCAGNE Experiment. In this first part, the dynamic characteristics of the flow are studied with respect to atmospheric stability and the relief at small (~20 km) and medium scales (~100 km). These relief scales depend on the topographical profile of the Lannemezan Plateau along the dominant axis of the wind (E-W) and the Pyrénées Mountains located at the south of the experimental site. The terrain heterogeneities have a standard deviation of ~48 m and a wavelength of ~2 km.The averaged vertical profiles of wind speed and direction over the heterogeneous terrain are analyzed. The decrease of wind speed within the boundary layer is greater than over flat terrain (WANGARA Experiment). However, a comparison between ETTEX (complex terrain) and COCAGNE vertical wind speed profiles shows good agreement during unstable conditions. In contrast, during neutral conditions a more rapid increase with normalized height is found with COCAGNE than with ETTEX and WANGARA data. The vertical profiles of wind direction reveal an influence of the Pyrénées Mountains on the wind flow. The wind rotation in the BL is determined by the geostrophic wind direction-Pyrénées axis angle (negative deviation) as the geostrophic wind is connected with the Mountain axis.When the geostrophic wind does not interact with the Pyrénées axis, the mean and turbulent wind flow characteristics (drag coefficient C
D, friction velocity u
*) depend on the topography of the plateau. When the wind speed is strong (>6 m s -1), an internal boundary layer is generated from the leading edge of the Plateau. 相似文献
3.
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
4.
This study examines the role of the marginal sea surface temperature (SST) on heat waves over Korea. It is found that sea surface warming in the south sea of Korea/Japan (122-138°E, 24- 33°N) causes heat waves after about a week. Due to the frictional force, the positive geopotential height anomalies associated with the south sea warming induce divergent flows over the boundary layer. This divergent flow induces the southerly in Korea, which leads to a positive temperature advection. On the other hand, over the freeatmosphere, the geostrophic wind around high-pressure anomalies flows in a westerly direction over Korea during the south sea warming, which is not effective in temperature advection. Therefore, the positive temperature advection in Korea due to the south sea warming decreases with height. This reduces the vertical potential temperature gradient, which indicates a negative potential vorticity (PV) tendency over Korea. Therefore, the high-pressure anomaly over the south sea of Korea is propagated northward, which results in heat waves due to more incoming solar radiation. 相似文献
5.
Based on the remote sensing data, the radiosonde data and precipitation data observed by weather stations, distributions of atmospheric water-vapor and cloud motion wind over the Qilian Mountains are analyzed. Moreover, on the basis of water-vapor and cloud motion wind analyses, relations of atmospheric water-vapor distribution with precipitation~ atmospheric circulation, and terrain are investigated. The results show that distributions of atmospheric water-vapor and precipitation in the Qilian Mountains are affected by the westerly belt, the southerly monsoon （the South Asian monsoon and plateau monsoon）, and the East Asian monsoon. In the northwest Qilian Mountains, water-vapor and precipitation are entirely affected by the westerly belt, and there is no other direction water-vapor transport except westerly watervapor flux, hence, the northwest region is regarded as the westerly belt region. In the south and middle of the mountaili, water-vapor is mainly controlled by the southerly monsoon, 37.7% of the total watervapor is from the south, especially in summer, the southerly water-vapor flux accounts for 55.9% of the total, and furthermore the water-vapor content in the southerly flow is more than that in the westerly flow. The southerly monsoon water-vapor is influenced by the South Asian monsoon from the Indian Ocean and the plateau monsoon in the Qinghai-Tibetan Plateau, thus, the south and middle region is called southerly monsoon region. But in the northeast Qilian Mountains, the East Asian monsoon is the main climate system affecting the water-vapor. Besides west and northwest water-vapor fluxes, there are a lot of easterly water-vapor fluxes in summer. The frequency of easterly cloud motion winds in summer half year accounts for 27.1% of the total, though the frequency is not high, it is the main water-vapor source of summer precipitation in this region, therefore, the northwest region is a marginal region of the East Asian monsoon. On the other hand, atmospheric water-vapor, precipitation, and conver 相似文献
6.
利用Lamb-Jenkinson大气环流分型方法,对西江流域1971—2015年逐日平均850 hPa和500 hPa高度场进行环流客观分型,分析流域降水天气环流型出现概率及主导环流型变化特征,探讨主导环流型对西江流域总面雨量和子流域面雨量的贡献率及环流型配置与降水的关系。结果表明:当850 hPa为西南风型、500 hPa为西风型时,流域出现降水天气的概率最大;850 hPa气旋型和500 hPa西风型对年总面雨量和各子流域面雨量的贡献率均为最大,且对东部子流域面雨量的贡献率大于西部子流域,850 hPa南风型与500 hPa反气旋型的环流配置是西部子流域秋季降水偏多的主导环流型配置;春季850 hPa气旋型与500 hPa西风型、夏季850 hPa气旋型与500 hPa西风型、秋季850 hPa南风型与500 hPa反气旋型、冬季850 hPa西南风型与500 hPa西风型的环流配置时,出现强降水天气的概率分别为18.7%,21.1%,4.0%和2.0%,即夏季最大,其次为春季,冬季最小。近45年,850 hPa气旋型、500 hPa西风型对流域年总面雨量的贡献率呈增加趋势,是西江流域面雨量呈偏多趋势的主导环流型。 相似文献
7.
The surface wind field is an important factor controlling the surface mass balance of Antarctica. This paper focuses on the observed atmospheric circulation during summer of an Antarctic blue ice area in Queen Maud Land. Blue ice areas are characterised by a negative surface mass balance and henceforth provide an interesting location to study the influence of meteorological processes on large local mass balance gradients. During lapse conditions, synoptic forcing determines the surface-layer flow. No significant horizontal temperature gradient with coastal stations could be detected along isobaric surfaces, indicating weak or absent thermal wind. Observations performed at the coastal stations Halley and Georg von Neumayer show the pronounced effects of synoptic forcing. The surface winds in the valley of the blue ice area could be divided into two distinct flow patterns, occurring with about equal frequency during the experiment. Flow type I is associated with cyclonic activity at the coast, resulting in strong easterly winds, precipitation and drifting snow. Flow characteristics inside and outside of the valley are similar during these conditions. Flow type II occurs when a high pressure system develops in the Weddell Sea, weakening the free atmosphere geostrophic winds. A local circulation is able to develop inside the valley of the blue ice area during these tranquil conditions. The transition from flow type II to flow type I is associated with front-like phenomena inside the valley. Some simple theoretical considerations show that surface-layer stability and the upper air geostrophic wind determine the surface flow direction in the valley. Finally, the influence of the observed circulation on the energy and mass balance of the blue ice area is discussed. 相似文献
8.
The impact of weak synoptic forcing on the valley-wind circulation in the Alpine Inn Valley 总被引：1，自引：0，他引：1
Günther Zängl 《Meteorology and Atmospheric Physics》2009,105(1-2):37-53
This paper investigates the impact of weak synoptic-scale forcing on the thermally induced valley-wind circulation in the Alpine Inn Valley and one of its largest tributaries, the Wipp Valley. To this end, high-resolution numerical simulations with realistic topography but idealized large-scale atmospheric conditions are performed. The large-scale flow has a speed increasing linearly from 5 m s?1 at sea level to 12.5 m s?1 at tropopause level, but its direction is varied between each experiment. For reference, an experiment without large-scale winds is conducted as well. The results indicate that the sensitivity to ambient flow forcing differs substantially between the Inn Valley and the Wipp Valley. The valley-wind circulation of the Inn Valley is found to be fairly robust against weak ambient forcing, changing by a much smaller amount than the along-valley component of the imposed large-scale flow. The valley wind tends to be intensified (weakened) when the ambient flow is aligned with (opposite to) the local valley orientation. However, the flow response is complicated by larger-scale interactions of the ambient flow with the Alpine massif. Most notably, northerly and northwesterly flow is deflected around the Alps, leading to the formation of a low-level jet along the northern edge of the Alps which in turn affects the valley-wind circulation in the lower Inn Valley. For the Wipp Valley, which is oriented approximately normal to the Alpine crest line and constitutes a deep gap in the Alpine crest, two distinctly different flow regimes are found depending on whether the large-scale flow has a significant southerly component or not. In the absence of a southerly flow component, the valley-wind circulation is similarly robust against ambient forcing as in the Inn Valley, with a fairly weak response of the local wind speeds. However, southerly ambient flow tends to force continuous downvalley (southerly) wind in the Wipp Valley. The flow dynamics can then be described as a pressure-driven gap flow during the day and as a mixture between katabatic flow and gap flow during the night. The responsible pressure forcing arises from the larger-scale interaction of the ambient flow with the Alpine massif, with southerly flow causing lifting on the southern side of the Alps and subsidence in the north. 相似文献
9.
Summary The present paper is the continuation of two recent studies investigating the foehn-like valley wind system around Mittenwald
(Bavarian Isar Valley). We deal with the synoptic/mesoscale conditions causing the local foehn (“Minifoehn”), considering
field campaigns from both the mesoscale and the climatological point of view. Furthermore, we describe the structure and further
features of the local foehn at smaller scales, using both the results of the VERTIKATOR field campaign and numerical simulations.
We obtain as a new result that the foehn-caused local warm air pool around Mittenwald induces slight nocturnal upvalley winds
between an adjacent valley basin located some 8 km north of Mittenwald and the basin of Mittenwald. Furthermore, a weak northerly
flow may also occur at Mittenwald prior to the onset of the Minifoehn. Numerical simulations indicate that the local pressure
gradient responsible for this phenomenon is related to a gravity wave forming over the hill range southwest of Mittenwald.
Observations within a five-year period indicate that Minifoehn frequently occurs when ambient winds coming from the southern
sector are predominant, but, contrary to deep foehn, weather conditions with northerly synoptic-scale flows do not necessarily
exclude the development of the local foehn which comes from the southwest. We also present further evidence that in the presence
of southerly synoptic-scale winds, orographic gravity waves interact with the drainage flow. Another new result is that strong
synoptic-scale westerly winds are able to suppress the occurrence of Minifoehn. In addition, the possible influence of the
Inn Valley wind system as well as dynamical differences between the thermally driven up- and downvalley winds are briefly
discussed. 相似文献
10.
本文以850 hPa、200 hPa月平均风场和西太平洋副热带高压脊线北抬至25°N日期资料及福建省25个代表站(县)5—7月的降水资料为基本分析素材。首先标定福建入夏异常的标准与年例,其次揭示850 hPa2、00 hPa 6月风场与异常年例的基本特征,进而探讨了对福建入夏早晚的影响关系。结果表明:在低层索马里-阿拉伯海区的越赤道气流强劲,南海至东亚低纬区域西南风偏大,西太平洋区域低纬度地区南风减弱、东风强劲,且东西风交汇区偏西;而在高层辐合区东风范围偏大,索马里-阿拉伯海区的区域东风风速强劲,青藏高原南侧和副高主体季节性位移的关键区以吹东风为主,东亚区域经向度小,位于青藏高原至我国东部区域范围内,形成一逆时针“距平”风环流;在此高低层风场特征的匹配下,有利于福建提早进入夏季;反之亦然。 相似文献
11.
祁连山山区空中水汽分布特征研究 总被引：34，自引：0，他引：34
将卫星遥感资料与探空资料和地面观测降水资料相结合,分析了祁连山山区空中水汽含量和云迹风的空间分布特征。并且,以此为基础,研究了祁连山大气水汽和地面降水的空间分布及其与大气环流和地形的关系。结果表明:祁连山大气水汽和地面降水受西风带、偏南季风(南亚季风和高原季风)和东亚季风的共同影响,在祁连山西北部大气水汽主要受西风带气流控制,在祁连山中南部偏南季风占主导地位;在祁连山的东北部则是东亚季风的影响比较明显。同时,祁连山大气水汽、降水和降水转化率与海拔高度和坡向以及环流影响区的关系均十分密切。一般,迎风坡上大气水汽含量在3500—4500 m海拔高度会出现一个峰值;而在背风坡上除东亚季风影响区外大气水汽含量只出现随海拔高度单调递减趋势,基本上不出现任何峰值。背风坡大气水汽含量总体上要比迎风坡少得多,最多大约能少4.49 kg/m2。无论是大气水汽含量、地面降水还是降水转化率均在东亚季风影响区最大;东亚季风影响区大气水汽含量在迎风坡上的峰值要更强,出现的海拔高度更低。 相似文献
12.
We analyzed wind profiler data collected over Ulsan airport during the period from 2008 to 2009 to examine the characteristics of low level jets (LLJs). The Ulsan airport is located within the narrow valley with north-south axis. The frequency analysis results indicates that the nearly 19% of the total nocturnal periods have the presence of jets and LLJ occurrence rate is high in winter (32%) and low in summer (10%). The mode in the wind speed histogram is 4?C6 m s?1. A majority of jet occurs below 100 m (about 77.8 m) above ground. The predominant wind direction of jet is northerly. In order to examine the favorable conditions for LLJ formation of Ulsan airport, we investigated temperature difference between valley and plain at the surface and synoptic wind direction and speed at 850 hPa. Our results show that air temperature in the valley is lower than over the plain during the nighttime, indicating the existence of thermal forcing for along-valley wind. Under a significant temperature difference along the valley, westerly wind speed at 850 hPa is slightly weaker on LLJs event night than no event night, indicating weaker north-south large-scale pressure gradient on LLJ event night. The magnitude of northerly wind at 850 hPa is much stronger on event night than no event night, implying higher downward transfer of northerly wind on event night. Our findings suggest that jet formation over Ulsan airport is related to the strong northerly wind at 850 hPa in the presence of thermal forcing due to temperature contrast between valley and plain. 相似文献
13.
Observations and numerical modelling of Lake Ontario breezes 总被引：1，自引：0，他引：1
Abstract Analysis of two years of land‐based data shows that the Lake Ontario breeze develops on 30% of the days during summer. It typically develops in mid‐morning and persists until the late evening when it is replaced by a well developed land‐breeze regime. Simulations of 4 cases with the Colorado State University mesoscale model show good agreement with observations and suggest that local lake breezes are strongly influenced by adjacent water bodies (e.g. Lake Erie), the elongated shape of the lake, and the large‐scale wind direction. With gradient flows across the long axis of the lake, a broad band of along‐lake flow develops during the afternoon (easterly winds during southerly gradient flows and westerly winds during northerly gradient flows). Furthermore, during west‐to‐northwesterly gradient flow a nocturnal cyclonic eddy is predicted at the western end of the lake. These results imply that wind‐field models applied in the vicinity of Lake Ontario should incorporate the entire lake in their modelling domain. 相似文献
14.
Kenneth E. Kunkel 《Boundary-Layer Meteorology》1982,23(4):473-487
Acoustic sounder measurements of the temperature structure parameter were obtained at the edge of an escarpment which is part of a ridge of mountains. These measurements indicate that in mountainous terrain, the daytime two-dimensional field of thermal turbulence is strongly affected by relative sun-slope orientation and wind direction out to ranges of at least 200–300 m. For the geometry of this site, westerly flow results in a field which tends to decrease rapidly to the west in the morning with a much less rapid decrease in the afternoon. At night, easterly flow results in significantly higher thermal turbulence compared to that obtained during westerly flow.These measurements show an increase in thermal turbulence at horizontal ranges of 100–200 m to the west of the escarpment during early afternoon on days with deep mixed layers. It is conjectured that this is due to the mountain upslope wind. 相似文献
15.
利用1970—2009年南澳县气象局地面气象观测站风向、风速记录资料进行统计分析。结果表明：近40 a南澳县年平均风速为3.7m/s,秋季最大,冬季次之,夏季最小;年平均最大风速为13.8m/s,春季最大,冬季次之,夏季最小;年平均大风日数为68 d,冬季最多,春季次之,夏季最少;近40 a来的年平均风速、平均最大风速和年大风日数均呈减少趋势;大风日数年内变化呈一峰一谷型;最多风向为ENE风向,NNE和NE风向位居第二,偏西风最少。 相似文献
16.
J. C. Doran 《Boundary-Layer Meteorology》1991,55(1-2):177-189
The interaction of katabatic winds with ambient winds has been investigated for an idealized valley using Clark's nonhydrostatic model. Ambient ridgetop wind speeds ranged from 0.5 to 6 m/s, and made angles with the valley axis ranging from 0 ° to 90 °: cooling of the valley was based on measured values of sensible heat fluxes taken from observations in Colorado's Brush Creek Valley. The depth and strength of the down-valley winds decreased with increasing ambient wind speeds but showed relatively little sensitivity to wind directions in the range of 10 ° to 60 ° from the valley axis. An observed inverse linear decrease of drainage depth with wind speed in a 100 m thick layer above the ridgetops was also found in the simulations for parts of the valley but not near the valley mouth. Vertical motions over the valley showed marked patchiness, and implications of this structure on valley flow dynamics are discussed.This work was supported by the U.S. Department of Energy (DOE) under Contract DE-AC06-76RLO 1830. 相似文献
17.
Detailed spatiotemporal structures for the submonthly-scale (7–25 days) intraseasonal oscillation (ISO) in summer monsoon rainfall and atmospheric circulation were investigated in South Asia using high-quality rainfall and reanalysis datasets. The Meghalaya–Bangladesh–coast of the western Myanmar (MBWM) region is the predominant area of submonthly-scale ISO in the Asian monsoon regions. The distinct rainfall ISO is caused by a remarkable alternation of low-level zonal wind between westerly and easterly flows around the Gangetic Plain on the same timescales. In the active ISO phase of the MBWM, a strong low-level westerly/southwesterly flows around the plain and a center of cyclonic vorticity appears over Bangladesh. Hence, a local southerly flows toward the Meghalaya Plateau and there is strong southwesterly flow towards the coast along southeastern Bangladesh and western Myanmar, resulting in an increase in orographic rainfall. Rainfall also increases over the lowland area of the MBWM due to the low-level convergence in the boundary layer under the strong cyclonic circulation. The submonthly-scale low-level wind fluctuation around the MBWM is caused by a westward moving n = 1 equatorial Rossby (ER) wave. When the anticyclonic (cyclonic) anomaly related to the ER wave approaches the Bay of Bengal from the western Pacific, humid westerly/southwesterly (easterly/southeasterly) flows enhance around the Gangetic Plain on the northern fringe of the anticyclone (cyclone) and in turn promote (reduce) rainfall in the MBWM. Simultaneously, robust circulation signals are observed over the mid-latitudes. In the active phase, cyclonic anomalies appear over and around the TP, having barotropic vertical structure and also contributing to the enhancement of low-level westerly flow around the Gangetic Plain. In the upper troposphere, an anticyclonic anomaly is also observed upstream of the cyclonic anomaly over the TP, having wavetrain structure. The mid-latitude circulation around the TP likely helps to induce the distinct ISO there in conjunction with the equatorial waves. Thus, the distinct ISO in the MBWM is strongly enhanced locally (~500 km) by the terrain features, although the atmospheric circulation causing the ISO has a horizontal scale of ~6,000 km or more, extending across the whole Asian monsoon system from the tropics to mid-latitudes. 相似文献
18.
E. L. Deacon 《Boundary-Layer Meteorology》1973,5(3):321-340
Data on the relationship of the surface wind to the geostrophic wind at Porton Down, Salisbury Plain, are presented for various
stability conditions and analysed in the light of the Rossbynumber similarity theory. For near-neutral conditions, the geostrophic
drag coefficients for geostrophic wind speeds 5 to 15 m s-1 are close to those found by other workers but at higher speeds the values are low. Comparisons of geostrophic and radar wind
speeds for ⋍900-m height, suggest that undetectably small mean cyclonic curvatures of the trajectories of the air are responsible
for this departure.
A value of the geostrophic drag coefficient for the open sea at wind speeds around 8 m s-1 (neutral conditions) is deduced from recent observations of the drag in relation to the surface wind, combined with the ratios
of 900-mb radar wind to surface wind obtained from the North Atlantic weather ship data tabulations of Findlater et al. (1966). 相似文献
19.
Onset of southwesterly wind over eastern China and associated atmospheric circulation and rainfall 总被引：9，自引：0，他引：9
Using the 5-day averaged data from the National Center for Environmental Prediction/National Center for Atmospheric Research
(NCEP/NCAR) reanalysis, and precipitation from rain gauge stations in China for the period 1981–2000, we investigated seasonal
variations and associated atmospheric circulation and precipitation of the southwesterly wind over eastern China. The southwesterly
wind over eastern China begins earliest over southeastern China and strengthens gradually from spring to the early summer,
as it extends northward. The strengthening of the spring southwesterly wind, the tropospheric upward motion, and the convergence
of low-level water vapor over southeastern China results in the beginning of the local rainy season. The beginning of the
Mei-yu (Plum rainfall) is connected with the northward march of the southwesterly wind. The southwesterly wind reaches the
valley of the Yangtze River in the early summer and northern China in the middle summer. This signifies an onset of the large-scale
southwesterly wind over eastern China. Accordingly, the rain belt over southeastern China moves to the valley of the Yangtze
River in the early summer and to northern China in the middle summer. Moreover, the southerly wind extends southward to the
South China Sea from the spring to summer, though it does not stretch from the South China Sea to southeastern China at those
times. The strengthening of the southerly wind over southeastern China is associated with a weakening/strengthening of the
eastward/westward subtropical tropospheric temperature gradient between southwestern China and the western North Pacific.
The developments of a low-pressure system over southwestern China and the subtropical high-pressure system over the western
North Pacific may contribute to the strengthening of the southwesterly wind. A northward advance of the high-pressure system
favors the southwesterly wind stretching from southeastern China to northern China. The onset of the Indian summer monsoon
also strengthens the summer southwesterly wind over eastern China. 相似文献
20.
Summary Surface weather observations are analyzed to investigate the temporal and spatial distributions of dust loading associated with the southwest Indian summer monsoon region. The 1979 annual distribution of dust days for the region 10°N-37°N and 35°E-90°E are presented. Five year composites of dust loading for the months May, June and July are derived. Results are analyzed with respect to preferred wind direction and wind speed associated with dust loading, potential source regions and regions of deposition. A case study of the meteorological conditions of a dust outbreak that occurred over the Arabian Peninsula in June of 1979 is given. Rawinsonde temperature observations are analyzed to locate the top of the dust layer over the Rub al Khali desert. The top of the dust layer was found to vary from 400 mb during the summer to 600 mb in the late spring and early fall.With 9 Figures 相似文献