共查询到20条相似文献,搜索用时 64 毫秒
1.
H. A. Flocas C. G. Helmis S. N. Blikas D. N. Asimakopoulos J. G. Bartzis D. G. Deligiorgi 《Theoretical and Applied Climatology》1998,59(3-4):237-249
Summary In this study an attempt is made to examine and analyse the mean characteristics of the katabatic flows at the western slope
foot of a 1024 m high knife edge mountain using a meteorological tower and three surface meteorological stations. In addition,
the frequency distribution of the occurrence of the katabatic flow over one year period is studied along the characteristics
of the flow arriving in the neighbouring urban area at a distance of 1.5 km. It was found that the katabatic flow occurs mainly
in autumn and spring with the highest frequency in April. The flow is generally characterised by small depth as it is affected
substantially by the background flow. The expected direction of the katabatic wind dominates mainly at the level of 7 m, where
the influence of the background flow is minimised. At the level of 18 m the wind direction shifts, due to the interaction
of the katabatic wind with the background flow. The katabatic flow can penetrate at a distance of 1.5 km being substantially
weakened.
Received September 18, 1996 Revised August 4, 1997 相似文献
2.
Summary ?Microclimatological data obtained during a field experiment in the nongrowing winter period were used to study the microclimatologically
stable night conditions of a 200 × 150 m miscanthus (Miscanthus cv. giganteus) stand and compared to open field conditions. The microclimatological pattern within the miscanthus canopy
was characterized by long-wave radiative cooling of the plant stand and by an established temperature inversion within the
canopy at calm nights. The results show that there are significant differences in air temperature and energy balance components
between the open field and the miscanthus field during calm and clear nights. In general, net radiation difference during
the cold and calm nights was relatively constant and about 20 W m−2 less negative in miscanthus (because of lower surface temperatures) than at the open field. Air temperature differences also
remained fairly constant and were up to 3 °C lower than at the open field (at the height of 1 m). Through thermal inversion
cold air accumulated in the lower parts of the canopy as shown by the vertical air temperature profiles. They showed a greater
amplitude within the diurnal cycle in the miscanthus stand than in the open field. Through the onset of wind, temperature
profiles changed rapidly and differences diminished. Vertical katabatic air drainage into the canopy layers was estimated
indirectly by using the energy balance approach. It was calculated from the significant energy balance closure gap and showed
a mean air exchange rate of up to 22 m3 m−2 h−1, related to a stand volume of 1 m2 area and 4 m height, during the mostly calm and clear nights, depending on the canopy net radiation and turbulent heat exchange
forced by slight wind spells. Quantitative uncertainties in calculated cold air drainage which are introduced by the measurement
method and certain assumptions in the calculations, were considered in a sensitivity analysis. In spite of these uncertainties
evidence of katabatic cold air flow is given.
Received July 29, 1999; revised June 11, 2001; accepted March 14, 2002 相似文献
3.
I. Bischoff-Gauß N. Kalthoff M. Fiebig-Wittmaack 《Theoretical and Applied Climatology》2006,85(3-4):227-241
Summary High-resolution model simulations were performed with the quadruple-nested version of the mesoscale model KAMM to investigate
the impact of the new storage lake ‘Embalse Puclaro’ on the arid environment. The storage lake covers an area of 1 to 2 km
in width and about 7 km in length. Model simulations were performed for a summer and a winter day.
Due to a change in the surface properties, the installation of the storage lake resulted in a modification of the energy balance.
Above the lake area, a stably stratified atmosphere establishes during the day and unstable stratification during the night.
During the day, the latent heat flux is similar to that of the replaced cultivated ground, but is higher at the night. The
influence of the storage lake on temperature and humidity can be seen to a height of about 300 m above ground level. During
the night, water vapour accumulation results in relative humidity values of 100%, as a result a greater number of days with
fog above the storage lake is likely when compared to the surrounding area. The storage lake does not produce its own lake
breeze during the day, because the larger-scale up-valley wind is too dominant. However, a significant modification of the
nocturnal down-valley wind above the lake area can be observed, especially in summer. As a consequence of the larger-scale
valley wind system, the influence of the storage lake on the temperature, humidity, and wind field can be identified up to
about 4 km on the downwind side. 相似文献
4.
T. Klein G. Heinemann D. H. Bromwich J. J. Cassano K. M. Hines 《Meteorology and Atmospheric Physics》2001,78(1-2):115-132
Summary
Simulations of the katabatic wind system over the Greenland ice sheet for the two months April and May 1997 were performed
using the Norwegian Limited Area Model (NORLAM) with a horizontal resolution of 25 km. The model results are intercompared
and validated against observational data from automatic weather stations (AWS), global atmospheric analyses and instrumented
aircraft observations of individual cases during that period. The NORLAM is able to simulate the synoptic developments and
daily cycle of the katabatic wind system realistically. For most of the cases covered by aircraft observations, the model
results agree very well with the measured developments and structures of the katabatic wind system in the lowest 400 m. Despite
NORLAM’s general ability of reproducing the four-dimensional structure of the katabatic wind, problems occur in cases, when
the synoptic background is not well captured by the analyses used as initial and boundary conditions for the model runs or
where NORLAM fails to correctly predict the synoptic development. The katabatic wind intensity in the stable boundary layer
is underestimated by the model in cases when the simulated synoptic forcing is too weak. An additional problem becomes obvious
in cases when the model simulates clouds in contrast to the observations or when the simulated clouds are too thick compared
to the observed cloud cover. In these cases, the excessive cloud amount prevents development of the katabatic wind in the
model.
Received September 22, 2000/Revised March 16, 2001 相似文献
5.
H. J. Beine S. Argentini A. Maurizi G. Mastrantonio A. Viola 《Meteorology and Atmospheric Physics》2001,78(1-2):107-113
Summary
Using a triaxial Doppler sodar the planetary boundary-layer structure and the wind flow dynamics at the Arctic site Ny-?lesund
have been studied. The relationship between winds measured at Ny-?lesund and at the nearby atmospheric research station on
Zeppelin mountain was investigated for the first time. While Ny-?lesund receives predominantly katabatic flow (from 120°)
from the Kongsvegen glacier, the field is rotated within the lowest 500 m and arrives at Zeppelin from southerly directions.
Received January 12, 2000/Revised November 21, 2000 相似文献
6.
1. IntroductionThe basic role of urban-rural boundary layer re-search is to study all kinds of physical process changesin the atmosphere boundary layer over urban and itssurrounding areas. Urban heat island (UHI) is a well-known feature of urban-rural climate. Attempts toincrease the understanding of the causes of the UHIand other urban-rural boundary layer phenomena haveused observational, theoretical and modelling methodssince long before. Seaman (1989) used a hydrostaticmodel, with real … 相似文献
7.
Hyun-Suk Koo Hae-Dong Kim Won-Tae Yun Soon-Hwan Lee 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(1):53-64
The urbanization of Daegu metropolitan region has progressed rapidly over the last 100 years, but changing land-use resulting from that urbanization has also caused the regional circulations to evolve. The effect of 100 years of urbanization on the regional circulations was simulated for the analysis using an A2C (Atmosphere to Computational Fluid Dynamics) model. Calm synoptic conditions and a stable lapse rate were assumed for the initial model atmosphere, with a horizontal grid resolution of 1 km. The simulation demonstrated that land-use changes have affected the Daegu metropolitan area’s regional circulations by deepening the convective boundary layer (CBL) over the urbanized area, resulting in deviations from mean surface temperature and surface wind fields. The last 100 years have seen the following changes in the region: 1) the urbanized area has increased by around 15 times, while the number of forests and paddy fields has rapidly decreased; 2) surface wind speeds have decreased by about 25% and 35% during the day and at night, respectively, and severe changes in wind direction have been noted over the urbanized areas; 3) regional warming has been around 1.5°C and 4°C in the daytime and early morning hours, respectively (in particular, warming in the early morning hours suggests the presence of overnight heat islands), and 4) sensible heat flux and CBL height have increased by about 40 W m?2 and 500 m for the period, respectively. 相似文献
8.
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
9.
A Study of the Internal Boundary Layer due to a Roughness Change in Neutral Conditions Observed During the LINEX Field Campaigns 总被引:1,自引:0,他引:1
Summary As an aspect of the LINEX field studies (1996–1997; Lindenberg near Beeskow, Germany), the characteristics of the internal
boundary layer (IBL) that is associated with a step change of the surface roughnesses in neutral constant stress layers was
investigated and is reported in this paper. Both smooth to rough (in 1996) and rough to smooth (in 1997) types of flow, have
been studied based upon the profiles of mean wind and temperature realised from a 10-m mast and eddy correlation measurements
taken at two levels (2 m and 5 m). Depending upon wind direction, the fetch at the site varied between 140 m and 315 m within
the wind sector (200° to 340°) used for the field investigations. The height of the IBL, δ, had been determined from the intersect
of the logarithmic wind-profiles below (< 2 m) and above (> 6 ) the interface. Values of δ obtained at the experimental site
compared fairly well to the existing theoretical/empirical fetch-height relationships of the form: δ=aċx
b
, where a, b, are empirical constants. The ratio for the friction velocities below and above the IBL as measured directly by the eddy
correlation techniques showed that for fetches less than 250 m there was an increase (decrease) of about 20% of the momentum
flux arising from the smooth to rough (rough to smooth) transitions. Influences of distant obstructions (e.g., bushes, pockets
of trees) on the surface flow were markedly important on the examined wind profiles and such can be indicative as multiple
IBLs.
Received September 1, 1997 Revised August 5, 1998 相似文献
10.
S. Khodayar N. Kalthoff M. Fiebig-Wittmaack M. Kohler 《Meteorology and Atmospheric Physics》2008,99(3-4):181-198
Summary The boundary-layer structure of the Elqui Valley is investigated, which is situated in the arid north of Chile and extends
from the Pacific Ocean in the west to the Andes in the east. The climate is dominated by the south-eastern Pacific subtropical
anticyclone and the cold Humboldt Current. This combination leads to considerable temperature and moisture gradients between
the coast and the valley and results in the evolution of sea and valley wind systems. The contribution of these mesoscale
wind systems to the heat and moisture budget of the valley atmosphere is estimated, based on radiosoundings performed near
the coast and in the valley.
Near the coast, a well-mixed cloud-topped boundary layer exists. Both, the temperature and the specific humidity do not change
considerably during the day. In the stratus layer the potential temperature increases, while the specific humidity decreases
slightly with height. The top of the thin stratus layer, about 300 m in depth, is marked by an inversion. Moderate sea breeze
winds of 3–4 m s−1 prevail in the sub-cloud and cloud layer during daytime, but no land breeze develops during the night.
The nocturnal valley atmosphere is characterized by a strong and 900 m deep stably stratified boundary layer. During the day,
no pronounced well-mixed layer with a capping inversion develops in the valley. Above a super-adiabatic surface layer of about
150 m depth, a stably stratified layer prevails throughout the day. However, heating can be observed within a layer above
the surface 800 m deep. Heat and moisture budget estimations show that sensible heat flux convergence exceeds cold air advection
in the morning, while both processes compensate each other around noon, such that the temperature evolution stagnates. In
the afternoon, cold air advection predominates and leads to net cooling of the boundary layer. Furthermore, the advection
of moist air results in the accumulation of moisture during the noon and afternoon period, while latent heat flux convergence
is of minor relevance to the moisture budget of the boundary layer.
Correspondence: Norbert Kalthoff, Institut für Meteorologie und Klimaforschung, Universit?t Karlsruhe/Forschungszentrum Karlsruhe,
Postfach 3640, 76021 Karlsruhe, Germany 相似文献
11.
The flow structure on a gentle slope at Vallon dOl in the northern suburbs of Marseille in southern France has been documented by means of surface wind and temperature measurements collected from 7 June to 14 July 2001 during the ESCOMPTE experiment. The analysis of the time series reveals temperature and wind speed oscillations during several nights (about 60--90 min oscillation period) and several days (about 120–180 min oscillation period) during the whole observing period. Oscillating katabatic winds have been reported in the literature from theoretical, experimental and numerical studies. In the present study, the dynamics of the observed oscillating katabatic winds are in good agreement with the theory.In contrast to katabatic winds, no daytime observations of oscillating anabatic upslope flows have ever been published to our knowledge, probably because of temperature inversion break-up that inhibits upslope winds. The present paper shows that cold air advection by a sea breeze generates a mesoscale horizontal temperature gradient, and hence baroclinicity in the atmosphere, which then allows low-frequency oscillations, similar to a katabatic flow. An expression for the oscillation period is derived that accounts for the contribution of the sea-breeze induced mesoscale horizontal temperature gradient. The theoretical prediction of the oscillation period is compared to the measurements, and good agreement is found. The statistical analysis of the wind flow at Vallon dOl shows a dominant north-easterly to easterly flow pattern for nighttime oscillations and a dominant south-westerly flow pattern for daytime oscillations. These results are consistent with published numerical simulation results that show that the air drains off the mountain along the maximum slope direction, which in the studied case is oriented south-west to north-east. 相似文献
12.
L. Cvitan 《Meteorology and Atmospheric Physics》2006,93(3-4):235-246
Summary The stability parameter μ is suggested as the one which is determinable with satisfying accuracy for routine application by
means of commonly accessible meteorological data at the Molve location (Croatia). The similarity functions applied for vertical
wind speed simulation in the planetary boundary layer (PBL) at Molve were useful for the determination of local stability
classes. Universal similarity functions were applied for unstable and neutral stability, whereas local similarity functions
were established for stable stratification. Wind speed simulations were performed using two types of wind models. The Monin-Obukhov
similarity theory was included in both types. However, it turned out that for the operative determination of the stability
of the 35 m deep lowest layer, the stability parameter μ was locally a better stability parameter than the Monin-Obukhov parameter
z/L. That was possibly because 35 m deep lowest layer sometimes (depending upon stability) includes a large proportion of
the Ekman layer and parameter μ is originally designed for the deeper part of PBL than z/L that is originally designed for
the surface layer. At Molve, the input data for local wind models as well as for the stability parameter μ were wind speed
at 35 m and temperature at 2 and 35 m above the ground. 相似文献
13.
Reconstruction of Northern Hemisphere 500 hPa geopotential heights back to the late 19th century 总被引:2,自引:0,他引:2
Summary In this study the authors have developed a statistical method and have reconstructed Northern Hemisphere 500 hPa heights back
to the late 19th century using one temperature and three sea level pressure (SLP) data sets. First, the relationship between
ERA40 500 hPa heights and surface temperature and SLP was screened using stepwise multiple regression based on the calibration
period of 1958–2002 (1998/2000 according to the availability of SLP data). All selected predictors (temperature and SLP) were
significant and their variance contribution was greater than 1%. On average, there were 8.1 variables retained in the final
regression equations. Second, the regression equations were applied to compute the 500 hPa height through to the late 19th
century for the whole Northern Hemisphere. As the SLP and temperature coverage improved over time, the number of predictors
decreased by about 1 in the most recent periods, and the root mean squared error decreased by about 0.8 m. A leave-one-out
cross-validation method was used to test the skill and stability of the regression models. The reduction of error during the
cross-validation period of 1958–1997 varied from 0.33 to 0.56, depending on the SLP data. Reconstructions were also checked
using NCEP/NCAR 500 hPa heights from January 1949 to December 1957, and compared with the historical reconstruction over Europe.
Reconstructions show high consistency with these independent data sets. Generally, the reconstruction provides a valuable
opportunity to analyze, as well as to validate climate simulations of the variability in free atmosphere circulations over
the past one hundred years. 相似文献
14.
Summary The local wind system in the upper Isar Valley (Bavarian Alps) near Mittenwald has the peculiarity that regularly strong foehn-like
nocturnal flows occur, mainly during clear nights in autumn and winter. We will refer to this phenomenon as “Minifoehn”, as
its properties are similar to the classical deep foehn in the sense that its breakthrough into the Isar Valley usually brings
a striking increase in temperature and a concomitant decrease in relative humidity. Numerical simulations with the MM5 model
reveal that this phenomenon is related to a nocturnal drainage flow originating from a plateau south of Mittenwald. This flow
is driven by the temperature difference between this plateau (1180 m) and the free atmosphere above Mittenwald (920 m, 15 km
north of the plateau) at the same level. The air masses flow through two different valleys that merge again further downstream.
The upper part of one of the two drainage currents goes over a small mountain ridge (1180 m) south-west of Mittenwald and
then descends into the Isar Valley, leading to an advection of potentially warm air towards Mittenwald. This branch of the
drainage current constitutes the Minifoehn. The remaining part of the drainage current flows through a narrow gap towards
the Isar Valley and then joins the drainage flow of this valley. As these air masses are significantly cooler than the Minifoehn
branch, large horizontal temperature gradients can be found around Mittenwald.
The dynamical behaviour of the cold air flow turns out to be qualitatively consistent with shallow-water theory only in the
absence of a forcing by large-scale winds. Otherwise, gravity-wave induced pressure perturbations interact with the drainage
flow and modify the low-level flow field. The simulations show that the gravity waves are excited by the mountain range that
separates the two valleys mentioned above. Moreover, the simulations indicate that the structure of this nocturnal wind system
is not very sensitive to the direction of synoptic-scale winds as long as they come from the southern sector. On the other
hand, ambient northerly winds are able to prevent the drainage flow and therefore the local foehn effects in the Isar Valley
provided that synoptic winds are strong enough. The results of the MM5 simulations are in good agreement with the measurements
and observations described in part 1 of this study. 相似文献
15.
The impact of the PBL scheme and the vertical distribution of model layers on simulations of Alpine foehn 总被引:1,自引:0,他引:1
Summary This paper investigates the influence of the planetary boundary-layer (PBL) parameterization and the vertical distribution
of model layers on simulations of an Alpine foehn case that was observed during the Mesoscale Alpine Programme (MAP) in autumn
1999. The study is based on the PSU/NCAR MM5 modelling system and combines five different PBL schemes with three model layer
settings, which mainly differ in the height above ground of the lowest model level (z
1). Specifically, z
1 takes values of about 7 m, 22 m and 36 m, and the experiments with z
1 = 7 m are set up such that the second model level is located at z = 36 m. To assess if the different model setups have a systematic impact on the model performance, the simulation results
are compared against wind lidar, radiosonde and surface measurements gathered along the Austrian Wipp Valley. Moreover, the
dependence of the simulated wind and temperature fields at a given height (36 m above ground) on z
1 is examined for several different regions.
Our validation results show that at least over the Wipp Valley, the dependence of the model skill on z
1 tends to be larger and more systematic than the impact of the PBL scheme. The agreement of the simulated wind field with
observations tends to benefit from moving the lowest model layer closer to the ground, which appears to be related to the
dependence of lee-side flow separation on z
1. However, the simulated 2 m-temperatures are closest to observations for the intermediate z
1 of 22 m. This is mainly related to the fact that the simulated low-level temperatures decrease systematically with decreasing
z
1 for all PBL schemes, turning a positive bias at z
1 = 36 m into a negative bias at z
1 = 7 m. The systematic z
1-dependence is also observed for the temperatures at a fixed height of 36 m, indicating a deficiency in the self-consistency
of the model results that is not related to a specific PBL formulation. Possible reasons for this deficiency are discussed
in the paper. On the other hand, a systematic z
1-dependence of the 36-m wind speed is encountered only for one out of the five PBL schemes. This turns out to be related to
an unrealistic profile of the vertical mixing coefficient.
Correspondence: Günther Z?ngl, Meteorologisches Institut der Universitat München, 80333 München, Germany 相似文献
16.
H. Kraus C. M. Ewenz M. Kremer J. M. Hacker 《Meteorology and Atmospheric Physics》2000,73(3-4):157-175
Summary In Southern Australia summertime deep cold fronts are frequently preceded by a shallow cold frontal line connected to a prefrontal
lower tropospheric trough. The advance of this line defines a “cool change” which in many cases causes severe weather events.
The goal of this paper is to analyze the multi-scale structure of these cool changes using aircraft observations and synoptic-scale
analyses. The aircraft measurements on cross-frontal tracks of horizontal lengths of up to 300 km are performed with an average
resolution of 3 to 4 m along the track. Thus a multi-scale analysis from micro-scale events up to the synoptic-scale phenomena
can be presented. All flights and thus all meso- and micro-scale analyses are performed over water only. The obviously very
different characteristics of the cool change structure elements over land are not investigated.
The synoptic analyses for one very typical case show a prefrontal trough as characterized by its position in relation to the
main deep cold front, its source region in Western Australia and its extent to the southeast. Fields of strong wind shear,
temperature gradients, vertical wind and Q-vectors are displayed.
The meso-β-scale x, z-cross-sections derived from two aircraft missions (data of the second one in brackets) show: a shallow cold front with a
160 (60) km wide transition zone in which the near surface potential temperature drops rather steadily by 9 °C (20 °C); a
shallow feeder flow topped by a strong inversion with a vertical gradient of potential temperature up to 5 °C/100 m between
the top of the feeder flow at 400 (200) m and 1500 (700) m; a cross-frontal circulation expressed by the ageostrophic wind
components u
ϕ,subscale and w with a center at 1200 m over the frontal edge of the feeder flow (for one mission only); a strong shear of the along-frontal
wind component v
ϕ with a large increase of the negative v
ϕ-values with height, which very well fits to the synoptic-scale view of the wave structure of the geostrophic wind (well-known
from the upper level synoptic charts) at different heights; a jet core of this along-frontal wind in the center of the cross-frontal
circulation, again for one mission only.
A very striking example of a micro-scale event is an approximately 1 km wide head of a frontal squall line. It shows dramatic
changes of all meteorological parameters. The event is displayed in a horizontal domain of 4 km with full resolution (∼ 4 m).
Derivatives of the measured parameters in the cross-frontal direction add information to the space series of the parameters
themselves. Deformation frontogenesis of potential temperature and specific humidity show very large values on the scale resolved
here. Fortunately the squall line could be sampled again at the same height, but in a somewhat degenerated state 1? h later.
Received September 3, 1999 Revised December 14, 1999 相似文献
17.
Summary ?Mountains profoundly impact precipitation systems in Taiwan, particularly in areas occupying roughly two-thirds of the island’s
landmass. This study examines the terrain structures possibly affecting the formation of rainfall systems in northern Taiwan
by analyzing radar data, surface rainfall data, and simulation results from MM5 (Fifth-Generation NCAR/Penn State Mesoscale
Model) under a weak synoptic influence condition. More specifically, this study analyzes precipitation systems formed in three
different days with different ambient wind directions (i.e., southwesterly, southerly and south-southeasterly flows) in a
low Froude number regime in Mei-Yu (or Baiu) season.
The southwesterly (southerly) predominant wind was blocked by CMR (central mountain range) over southwestern (southern) Taiwan.
Consequently, the southwesterly (southerly) winds were diverted around southern Taiwan, traveled northward following the terrain
contour of CMR and then converged in northeastern (northern) Taiwan to produce a NE-SW (N-S) orientated convergence area.
As anabatic flow and onshore flow intensified in northern Taiwan and thus enhanced the existing convergence in the late morning
and early afternoon, the precipitation system appeared over slope first and then moved down the slope following the predominant
wind direction. Upwards motion persisted in this convergence region, and initiated a new precipitation system. Consequently,
rainfall accumulation was orientated in a NE-SW (N-S) direction in northern Taiwan. On the windward side of CMR in central
Taiwan, precipitation was first produced in the slope by anabatic flow and was generated in lower land because of the interaction
between down slope and onshore flow in the late afternoon. When the flow was predominantly from the south-southeast, the convergence
due to the splitting of the predominant over western Taiwan became weaken after onshore flow over west coast developed since
the direction of onshore flow was against the splitting predominant flow. Precipitation only appeared in the sloping areas
of northwestern and central Taiwan in the relatively dry environment resulting from the anabatic flow.
Several sensitivity tests indicated that the lee-side convergence in a low Froude number regime superimposed by anabatic flow
and onshore flow is important for producing rainfall in northern Taiwan. The prevailing wind direction determined the orientation
of the rainfall accumulation in northern Taiwan. The high relative humidity is important for precipitation to form in lower
elevations.
Received February 9, 2001; Revised November 23, 2001 相似文献
18.
Summary Simulations of katabatic flow with a two-dimensional dynamic numerical model with a soil parameterization indicate that downslope flow developed over a moist slope is weaker than that over a dry slope. This agrees with earlier findings that daytime anabatic (upslope) flow is weaker over a moister slope. But, whereas the weaker anabatic flow is produced because surface evaporation prevents the moist slope from heating as much as a dry slope, the weaker katabatic flow is produced over moist slopes because (1) the soil thermal conductivity is greater in moist soil, and (2) downward longwave radiation flux from the atmosphere to the surface is greater because of higher humidity in the air near the surface from evaporation. The higher thermal conductivity allows warmer soil temperatures (heat) to diffuse upward to the soil surface and prevents the surface temperature from becoming as cold in the moist run as in the dry run.With 6 Figures 相似文献
19.
20.
G. Mastrantonio V. Malvestuto S. Argentini T. Georgiadis A. Viola 《Meteorology and Atmospheric Physics》1999,71(1-2):127-132
Summary The development of a convective boundary layer over the Antarctic Plateau is documented by a Doppler minisodar data-set recorded
during a 10 day campaign in January 1997. The vertical velocities associated with thermals do not exceed 1 m/s, while the
depth of the convective layer, usually less than 200 m, never surpasses 300 m. Measurements of momentum flux, sensible heat
flux, wind speed and radiation budget show characteristics that are typical of a convective boundary layer evolution. The
diurnal behaviour of absolute humidity, however, exhibits features that are not expected, e.g. anticorrelation with incoming
net radiation and air temperature.
Received October 30, 1998 Revised May 26, 1999 相似文献