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1.
Summary ?This paper describes a numerical study of the major spiral rainband in typhoon Flo (1990) using the Meteorological Research
Institute Mesoscale Nonhydrostatic Model (MRI-NHM). The effects of precipitation schemes and horizontal resolution on the
representation of the simulated rainband are discussed.
Dynamic and thermodynamic structures of the simulated major rainband to the north of the storm center are well represented
in the model with a 5 km horizontal resolution. The structures are consistent with observational results reported for other
tropical cyclones. Among the realistic features are: a cold pool and convergence on the inner side of the band; convergence
above low-level inflow layers; and the outward slope of the updraft with height. The band is caused by the motion of the storm
through its surroundings where horizontal wind has vertical shear.
The simulation of the structure and precipitation pattern associated with the major rainband depends on the precipitation
scheme rather than the horizontal resolution. The band appears more realistic when using explicit cloud microphysics as a
precipitation scheme, rather than moist convective adjustment. This result is attributable to the difference in scheme triggering.
In the simulation with moist convective adjustment, the elimination of vertical instability in low-level atmosphere is excessive,
suppressing band formation. The overall structure of the band is also more realistic in the simulation using explicit cloud
microphysics, because a cold pool exists in the lower layers and the vertical axis of upward flow tilts outward. This result
suggests that prediction will partly depend on variables associated with cloud microphysics, such as the mixing ratio of cloud
water.
The horizontal grid distance, which varied between 5 and 20 km, quantitatively influenced the rainfall amount, although the
large-scale band structure remained unchanged. The rainfall amount increased as the grid interval was reduced from 20 to 10-km
but decreased as the interval was further reduced from 10 to 5 km.
Received March 20, 2001; revised August 20, 2001 相似文献
2.
A. S. Broad 《Meteorology and Atmospheric Physics》2000,72(1):1-11
Summary. ?A hydrostatic numerical model is used to simulate the lee wave event IOP3 (0000 GMT to 1200 GMT 15th October 1990) from the PYREX mountain experiment. Results from integrations at different horizontal resolutions are used
to investigate the effect on surface pressure drag and the vertical flux of horizontal momentum due to orographically forced
gravity waves. In particular, results showing the dependence on resolution of the partitioning between resolved and parametrized
wave drag and fluxes are presented. With the model horizontal gridlength changing from 50 km to 10 km the majority of wave
momentum flux changes from being parametrized to becoming resolved. More significantly, there is a change in the profile of
flux with height. At 50 km resolution the largest inferred mean flow decelerations are at lower stratospheric level due to
the parametrization scheme. At 10 km resolution this is shifted, with less deceleration high up and more wave deceleration
lower down in the troposphere. Numerical weather prediction models are now beginning to take account of such low level drag
with beneficial results.
Received March 2, 1999/Revised July 15, 1999 相似文献
3.
Meso-gamma scale forecasts using the nonhydrostatic model LM 总被引：10，自引：0，他引：10
J. Steppeler G. Doms U. Schättler H. W. Bitzer A. Gassmann U. Damrath G. Gregoric 《Meteorology and Atmospheric Physics》2003,82(1-4):75-96
Summary ?The nonhydrostatic model LM was developed for small scale operational predictions. Advances in computer development will
give the possibility of operational models of a rather fine scale, which will cover the meso-gamma scale. The LM is currently
applied at a scale of 7 km and an increase of the operational resolution to 2.5 km is planned for the next few years. Predictions
of such high resolution require to abandon the hydrostatic assumption, which is used with most current operational weather
prediction models. The LM was designed to cover all resolutions from 50 m to 50 km with an efficiency making it suitable for
operational use. It is a fully elastic model, using second order centred finite differences. The time integration is done
using the Klemp–Wilhelmson method, treating the slow modes by a larger time step than the fast modes. The vertical propagation
of the fast waves is done implicitly.
After describing the design of the LM, this paper gives examples of model predictions at the meso-γ scale. Some results of
the current operational application at the resolution 7 km are presented. Deficiencies in the localisation of model generated
precipitation are investigated using an idealised bell shaped mountain and applying different resolutions. In this way the
convergence to the correct solution can be investigated. From these results it is concluded, that orographic filtering is
necessary and the effect of such filtering on precipitation forecasts is investigated. Finally, the prediction of a squall
line over northern Germany is shown in order to demonstrate the potential of the model in forecasting the meso-γ scale.
Received May 15, 2001; revised September 21, 2001 相似文献
4.
Summary The fourth generation of numerical weather prediction (NWP) models is currently under development at the Deutscher Wetterdienst
(DWD) consisting of a global grid point model (GME) and limited-area Lokal-Modell (LM). The nonhydrostatic fully compressible
LM has been designed to meet high-resol ution regional fore-cast requirements at meso-β and meso-γ scales. The initial LM
implementation is based on the NCAR/Penn State MM5 with the addition of a novel generalized terrain-following coordinate and
rotated lat-lon grid. A fully 3D semi-implicit time-stepping scheme has been implemented by retaining the full buoyancy term
instead of the approximate form found in MM5. In contrast with earlier schemes, mass-lumping is not applied to simplify the
elliptic operator on an Arakawa-C/Lorenz grid. The resulting variable-coefficient elliptic problem is solved using a minimal
residual Krylov iterative method with line relaxation preconditione rs. The new semi-implicit scheme is compared with a variant
of the Klemp–Wilhelmson split-explicit scheme (horizontal explicit, vertical implicit) on the basis of computational efficiency
and accuracy at resolutions ranging from 7 km to 400 m. Both idealized 3D mountain wave flows and naturally occuring flows
are analyzed. Below the tropopause, the 3D semi-implicit scheme can be more efficient for low Mach number M ≪ 1 flows when the number of small time steps Δt
s
of the split-explicit approach increases with the sound-speed Courant number.
Revised October 7, 1999 相似文献
5.
Summary Three cyclones developing between 28 August and 6 September 1995 were studied with respect to the temporal evolution of their
water budget components. The cyclones were simulated with the regional model REMO. Water budget values were determined from
hourly model output for circle areas with 500 km radius around the pressure minimum. The results show a maximum liquid water
path of about 0.12 kg m−2 and a maximum ice water path of 0.16 kg m−2. In the vertical cloud structure the medium cloud layer disappears at the end of the life cycle for all three cyclones. The
release of precipitation onto the Baltic Sea drainage basin is different for each cyclone. It lies between 13 and 22 · 1012 kg. This is about 50% of the total precipitation in the whole area for the strongest cyclone and 65% for the others. The
P — E (precipitation minus evaporation) is 15 · 1012 kg for two of the cyclones and 10 · 1012 kg for the third one.
Received August 7, 2000 Revised March 19, 2001 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.
T. Kato 《Meteorology and Atmospheric Physics》1997,63(1-2):39-51
Summary Quantitatively comparative experiments of moist convection using hydrostatic and non-hydrostatic models are reviewed and a further study is made of the suitability of the hydrostatic approximation for a high-resolution model when the grid size falls below 20 km. Idealized moist convection is treated, and then the torrential rain that occurred on 6 August 1993 in Kagoshima, southern Kyushu, Japan is simulated by each model. An explicit warm-rain process predicting cloud water and rainwater and the scheme of moist convective adjustment are individually or conjunctively employed in the model. The effect of hydrostatic water loading is also examined in detall.For the simulation of idealized convection, the hydrostatic simulation tends to overestimate and overexpand precipitation in comparison with the non-hydrostatic counterpart, and the drag effect of hydrostatic water loading is more significant for convective development than the non-hydrostatic effect. In the 20-km simulations, however, the hydrostatic simulation with hydrostatic water loading produces results that are comparable to the nonhydrostatic counterpart. For the simulation with real data, the comparative results well correspond to those of idealized convection. Furthermore, the 5 km hydrostatic simulation overestimates total precipitation more than that of dealized convection. On the basis of these results, when developing 1020 km numerical weather prediction (NWP) models, hydrostatic water loading should be evaluated in preference to adopting non-hydrostatic models, and a non-hydrostatic model with hydrostatic water loading is thought to be recommendable for a high-resolution NWP model.With 7 Figures 相似文献
8.
M. L. Kaplan A. W. Huffman K. M. Lux J. J. Charney A. J. Riordan Y.-L. Lin 《Meteorology and Atmospheric Physics》2005,88(3-4):129-152
Summary In this paper, we describe the results of 44 case study analyses of synoptic scale data sets that define the atmospheric structure prior to the development of accident-producing turbulence. First, the 44 case studies are categorized as a function of the location, altitude, time of year, time of day, and turbulence environment, i.e., in clear air, cloudiness, convection, near mountains, or in the proximity of deep convection. It is noteworthy that this later category was much more ubiquitous than was anticipated. Second, NCEP Reanalysis data sets as well as both visible and infrared satellite imagery are employed to diagnose predictor fields associated with the synoptic-scale environment preceding severe turbulence. These predictor fields are calculated based on jet stream configuration, kinematic, dynamical, and thermodynamic analyses of the synoptic-scale atmosphere.The results of these analyses indicate a prevalence of severe accident-producing turbulence within the entrance region of the polar or subtropical jet stream at the synoptic-scale. Typically, there is a region of flow curvature located just upstream within the jet entrance region, convection is present within 100km of the accident, the vertical motion is upward typically within the curved entrance region, absolute vorticity is low, the vertical wind shear is increasing with time, and horizontal cold air advection is substantial. Not all of the 44-case studies conform to this entrance region paradigm. However, most do and the most consistent predictor of severe turbulence is upstream curvature in the synoptic-scale flow. Nearby convection is the second most ubiquitous predictor field. Upward vertical motion, low absolute vorticity, and horizontal cold air advection are all typical predictors in case studies occurring both within the entrance and exit regions of the polar or subtropical jet stream.Current affiliation: USDA/Forest Service, North Central Research Station, East Lansing, MI 48823. 相似文献
9.
云顶温度和云顶高度作为基本的云参数,在云的热辐射强迫估计,航空气象保障,数值天气预报,天气气候研究等方面具有十分重要的意义。FY-3D/MERSI-II云顶温度产品基于云在红外波段的发射率假设,利用两个红外分裂窗通道(11.0 μm、12.0 μm)结合一维变分方法寻找最优云顶温度层,再利用数值天气预报廓线产品插值反演对应的云顶高度和压强。利用AQUA/MODIS所提供的云产品数据对FY-3D/MERSI-II云顶温度、云顶高度、云顶压强产品进行精度检验,结果表明:FY-3D/MERSI-II水云云顶温度精度为-1.2±4.6 K,云顶高度精度为1.4±1.8 km,云顶压强精度为-140.9±114.5 hPa;厚冰云云顶温度精度为7.0±6.0 K,云顶高度精度为-1.0±0.9 km,云顶压强精度为37.1±36.0 hPa;混合云云顶温度精度为1.5±8.5 K,云顶高度精度为0.8±2.2 km,云顶压强精度为-87.4±157.8 hPa,单层卷云和多层云的反演偏差较大。辐射传输模式在云顶性质反演中有十分关键的作用,但目前对冰云特别是卷云的性质认识不足,因此如何精确描述冰晶辐射特性,提高冰云特别是卷云辐射传输的模拟精度将是下一步的工作重点。 相似文献
10.
Summary An attempt has been made to simulate the unprecedented heavy precipitation of 94.4 cm in a day over Santacruz, Mumbai during
0300 UTC 26 July to 0300 UTC 27 July 2005. Three experiments have been conducted using Advanced Regional Prediction System
model developed by Center for Analysis and Prediction of Storms of Oklahoma University, USA. In first experiment the model
input at large domain size has been obtained using NCEP/NCAR reanalysis data at 2.5° × 2.5° lat.–lon. resolution. In other
two experiments model input at large as well as at small domain sizes, have been obtained from NCEP/NCAR FNL data of 1° ×
1° lat.–lon. resolution. In all three experiments model’s horizontal resolution is 40 km and integration period is 30 hours
from 0000 UTC 26 July 2005. Based on the temporal distribution of observed rainfall rates it is considered that the rainfall
of 38.1 cm during 0900–1200 UTC on 26 July could be due to cloud burst phenomenon and 56.3 cm from 1200 UTC of 26 July to
0300 UTC of 27 July has been due to continuous regeneration of thunderstorm activity under influence of mesoscale cloud complex.
It is found that model forecast of rainfall in first experiment was qualitatively as well as quantitatively very poor. Among
other two, experiment with large domain size has predicted better rainfall values and location compared to the experiment
with small domain size. The larger domain has produced rainfall of 41 cm as against observed rain rate of 56.3 cm. during
1200 UTC of 26 July to 0300 UTC of 27 July. Divergence, vorticity, vertical velocity and moisture parameters are examined
in relation with the various stages of the event. The maximum values of convergence, vorticity and moisture fluxes precede
the initial phase of mature stage, however vertical velocity follows the later phase of mature stage. Vorticity budget over
the location of maximum rainfall, revealed the significant role of tilting term in maintenance and dissipation of the cloud
complex responsible for the event. The model has simulated mixing ratios of ice, snow and hail up to height of 15 km which
matches with the observations that clouds reaching up to 15 km were present at the time of event of heavy precipitation. 相似文献
11.
Summary Cloud parameters and surface radiative fluxes predicted by regional atmospheric models are directly compared with observations
for a 10-day period in late summer 1995 characterized by predominantly large-scale synoptic conditions. Observations of total
cloud cover and vertical cloud structure are inferred from measurements with a ground-based network of Lidar ceilometers and
IR-radiometers and from satellite observations on a 100 kilometer scale. Ground-based observations show that at altitudes
below 3 km, implying liquid water clouds, there is a considerable portion of optically non-opaque clouds. Vertical distributions
of cloud temperatures simultaneously inferred from the ground-based infrared radiometer network and from satellite can only
be reconciled if the occurrence of optically thin cloud structures at mid- and high tropospheric levels is assumed to be frequent.
Results of three regional atmospheric models, i.e. the GKSS-REMO, SMHI-HIRLAM, and KNMI-RACMO, are quantitatively compared
with the observations. The main finding is that all models predict too much cloud amount at low altitude below 900 hPa, which
is then compensated by an underestimation of cloud amount around 800 hPa. This is likely to be related with the finding that
all models tend to underestimate the planetary boundary layer height. All models overpredict the high-level cloud amount albeit
it is difficult to quantify to what extent due to the frequent presence of optically thin clouds. Whereas reasonably alike
in cloud parameters, the models differ considerably in radiative fluxes. One model links a well matching incoming solar radiation
to a radiatively transparent atmosphere over a too cool surface, another model underpredicts incoming solar radiation at the
surface due to a too strong cloud feedback to radiation, the last model represents all surface radiative fluxes quite well
on average, but underestimates the sensitivity of atmospheric transmissivity to cloud amount.
Received August 31, 2000 Revised March 15, 2001 相似文献
12.
A three-level model system for the prediction of local flows in mountainous terrain is described. The system is based upon
an operational weather prediction model with a horizontal grid spacing of about 10 km. The large-scale flow is transformed
to a more detailed terrain, first by a mesoscale model with grid spacing of about 1 km, and then by a local-scale model with
a grid spacing of about 0.2 km. The weather prediction model is hydrostatic, while the two other models are non-hydrostatic.
As a case study the model system has been applied to estimate wind and turbulence over Várnes airport, Norway, where data
on turbulent flight conditions were provided near the runway. The actual case was chosen due to previous experiences, which
indicate that south-easterly winds may cause severe turbulence in a region close to the airport. Local terrain induced turbulence
seems to be the main reason for these effects. The predicted local flow in the actual region is characterized by narrow secondary
vortices along the flow, and large turbulent intensity associated with these vortices. A similar pattern is indicated by the
sparse observations, although there seems to be a difference in mean wind direction between data and predictions. Due to fairly
coarse data for sea surface temperature, errors could be induced in the turbulence damping via the Richardson number. An adjustment
for this data problem improved the predictions. 相似文献
13.
K. Prasad 《Meteorology and Atmospheric Physics》2006,91(1-4):183-199
Summary Results of an earlier study of cyclone track prediction using a quasi-Lagrangian model (QLM) to generate track forecasts of
up to 36 hours were reported by Prasad and Rama Rao (2003). Further experiments to produce track forecasts of up to 72 hours
with an updated version of the same model have been carried out in the present study. In this case, the ability of the model
to predict recent historical cyclones in the Bay of Bengal and Arabian Sea has been assessed. Analysis of some of the structural
features of analyzed and predicted fields has been carried out. Such fields include wind distribution and vertical motion
around the cyclone centre. In addition, the merging of an idealized vortex with the large scale initial fields provided by
a global model, has been carried out for a particular case study of a May 1997 storm, which hit the Bangladesh coast. This
current study has demonstrated that the model generates a realistic structure of a tropical cyclone with an idealized vortex.
Performance evaluation has been carried out by computing the direct position errors (DPE). The results of which show that
the mean error for a 24 h forecast is about 122 km, which increases to about 256 km for a 48 h forecast and 286 km for a 72 h
forecast. These figures are comparable to similar errors in respect of tropical cyclone forecasts produced by an advanced
NWP centre, viz., the UKMO global model during the corresponding period, 1997–2000 (obtained from UKMO web site). The average
forecast errors of the UKMO model are 160 km for 24 h, 265 km for 48 h, 415 km for 72 h forecast ranges. 相似文献
14.
I. Foyo-Moreno I. Alados F. J. Olmo J. Vida L. Alados-Arboledas 《Theoretical and Applied Climatology》2001,68(1-2):41-50
Summary Knowledge of ultraviolet radiation is necessary in different applications, in the absence of measurements, this radiometric
flux must be estimated from available parameters. To compute this flux under all sky conditions one must consider the influence
of clouds. Clouds are the largest modulators of the solar radiative flux reaching the Earth’s surface. The amount and type
of cloud cover prevailing at a given time and location largely determines the amount and type of solar radiation received
at the Earth’s surface. This cloud radiative effect is different for the different solar spectral bands. In this work, we
analyse the cloud radiative effect over ultraviolet radiation (290–385 nm). This could be done by defining a cloud modification
Factor. We have developed such cloud modification Factor considering two different types of clouds. The efficiency of the
cloud radiative effect scheme has been tested in combination with a cloudless sky empirical model using independent data sets.
The performance of the model has been tested in relation to its predictive capability of global ultraviolet radiation. For
this purpose, data recorded at two radiometric stations are used. The first one is located at the University of Almería, a
seashore location (36.83° N, 2.41° W, 20 m a.m.s.l.), while the second one is located at Granada (37.18° N, 3.58° W, 660 m
a.m.s.l.), an inland location. The database includes hourly values of the relevant variables that cover the years 1993–94
in Almería and 1994–95 in Granada. Cloud cover information provided by the Spanish Meteorological Service has been include
to compute the clouds radiative effect. After our study, it appears that the combination of an appropriate cloudless sky model
with the cloud modification Factor scheme provides estimates of ultraviolet radiation with mean bias deviation of about 5%
that is close to experimental errors. Comparisons with similar formulations of the cloud radiative effect over the whole solar
spectrum provides evidence for the spectral dependency of the cloud radiative effect.
Received November 15, 1999 Revised September 11, 2000 相似文献
15.
16.
为了研究垂直变量配置对静力适应过程的影响,本文从描写静力适应过程的方程组出发,分别在将所有变量置于整层上的非跳点N网格;将垂直速度和温度放置在整层,水平速度、气压和密度等变量放置在半层的Charney Phillips跳点网格(CP网格);将水平速度、气压和温度放置在整层,将垂直速度和密度放置在半层的Lorenz跳点网格(L网格);将密度变量放置在整层的Charney Phillips跳点网格(CP_N网格);将密度放置在整层的Lorenz跳点网格(L_N网格)上进行离散,垂直格距分1 km、0.5 km、0.2 km和0.01 km,研究了在这5种网格上产生的频率和垂直群速的相对误差。结果表明:(1)L_N网格和CP网格是完全等效的两种网格。(2)不论垂直格距为多少,CP网格和L网格的误差都是最小,N网格次之,CP_N网格的误差最大。(3)随着垂直格距的减少,在这几种网格上产生的误差都在减小。对于CP网格、L网格和N网格,在水平长波和垂直短波处产生的误差较大。而CP_N网格对水平波长变化不敏感,垂直波长越短,误差越大。(4)当垂直格距为0.01 km时,这几种网格都对水平波长的变化不敏感了,仅对垂直波长敏感。(5)CP网格、L_N网格和L网格在描写静力适应过程和斜压地转适应过程都是误差最小的垂直变量配置方案,因此在非静力完全可压缩深层大气数值预报模式中应优先选择这3种方案。 相似文献
17.
A nonhydrostatic model based on a new approach 总被引：4，自引：0，他引：4
Z. I. Janjic 《Meteorology and Atmospheric Physics》2003,82(1-4):271-285
Summary ?The nonhydrostatic Meso model developed at NCEP (Janjic et al, 2001) is based on a new approach. Namely, a hydrostatic NWP
model using mass based vertical coordinate has been extended to include the nonhydrostatic motions. In this way favorable
features of the hydrostatic formulation have been preserved. This procedure did not require any linearization or approximation.
The nonhydrostatic dynamics has been introduced through an add-on module. The nonhydrostatic module can be turned on and off,
so that easy comparison can be made of hydrostatic and nonhydrostatic solutions.
Here, the basic philosophy behind the discretization methods applied in the model, and not covered by Janjic et al (2001),
is discussed, and the latest developments are reviewed. The forecast examples shown indicate that significant differences
between hydrostatic and nonhydrostatic forecasts may develop even at relatively coarse resolution of 8 km. Possible future
developments are considered.
Received May 7, 2001; revised October 15, 2001 相似文献
18.
Summary ?For the LITFASS-98 experiment, from June 1 until June 30, 1998, the spatially resolved insolation at surface could be computed
from NOAA-14 AVHRR data applying the modular analysis scheme SESAT (Strahlungs- und Energiebilanzen aus Satellitendaten). The satellite inferred insolation for this period shows for clear-sky regions a good agreement with surface
based observations with a rms error of 76 Wm−2. For cloudy conditions the insolation is overestimated with respect to ground based observations, with a rms error between
83 and 118 Wm−2, depending on the cloud optical thickness. This overestimation can be explained by the surface heterogeneity, leading to
underestimated cloud optical thickness, and also by a fixed relative humidity below clouds (55%, dry atmosphere) and a fixed
horizontal visibility (50 km, clear atmosphere). A detailed study of comparable scales in space and time, considering the
different observation geometries and sampling intervals, shows that a 30 min ground based observation can be compared with
a 8 × 8 km2 mean by the satellite data.
Received July 12, 2001; revised April 29, 2002; accepted June 7, 2002 相似文献
19.
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
20.
为了深入理解非静力近似下的波-湍相互作用问题,本研究在σ坐标的海洋环境研究和预报模型(MERF)中引入常用的Mellor-Yamada两方程湍混合参数化方案(MY2.5),评估垂向湍混合对小尺度背风波传播过程的影响.瞬时状态场的模拟结果表明,无论是否为非静力近似条件,上述湍参数化方案的引入都会减弱背风波传播的模拟效果.从时间平均场的试验结果来看,垂向湍混合过程会显著减小非静力近似和静力近似之间的差异.此外,能量收支分析的诊断结果表明,MY2.5方案会显著抑制陆坡地形下的背风波传播过程,进而将更多的潮能转化到不可逆的湍混合过程中. 相似文献