共查询到20条相似文献，搜索用时 318 毫秒
1.
A number of physical factors have been introduced to improve limited area model forecasts. The factors include land surface
fluxes, shallow convection and radiation. The model including these additional physical factors (modified physics) is run
for five cases of monsoon depression which made landfall over the Indian coast, and the results are compared with those of
the control run. The forecasts are verified by computing the root mean square and mean errors. The differences in these skill
scores between the two model runs are tested for their statistical significance. It is found that the modified physics has
a statistically significant effect on the model skill with the maximum impact on the mean sea level pressure and the temperature.
Detailed analyses of mean sea level pressure, wind, rainfall and temperature further confirm that the modified physics has
maximum impact on mean sea level pressure and temperature and marginal impact on wind and rainfall. Furthermore, analyses
of some model parameters related to physics at a grid point for one case of depression were done. The results show that the
inclusion of the land surface physics, shallow convection and radiative processes have produced a better precipitation forecast
over the grid point. 相似文献
2.
RegCM3模式在西北地区的应用研究Ⅱ:区域选择及参数化方案的敏感性 总被引：15，自引：3，他引：12
通过数值模拟方法,研究了降水对区域尺度、积云对流参数化等的敏感性.结果表明:由于较小区域尺度的模式内部场和大尺度分析场激发的外强迫之间有更强的束缚,这种束缚使得内外强迫更容易达到一致.小区域尺度模拟的降水型比大的区域尺度的模拟更好,但同时,大的区域尺度消弱了由于模式侧边界效应产生的虚假动力效应,模拟的降水在量值上更加接近于观测值.因此,进行区域气候模拟时,须根据需要对模式区域进行仔细的选择.结果同时表明,由于Grell方案倾向于模拟更多的对流降水,因此Kuo-Anthes方案对西北地区降水型和量值的模拟比Grell方案更接近于实际.由于地形对于降水的重要意义,在复杂地形下进行区域气候模拟时有必要在模式中仔细描述地形. 相似文献
3.
Prediction of the track and intensity of tropical cyclones is one of the most challenging problems in numerical weather prediction (NWP). The chief objective of this study is to investigate the performance of different cumulus convection and planetary boundary layer (PBL) parameterization schemes in the simulation of tropical cyclones over the Bay of Bengal. For this purpose, two severe cyclonic storms are simulated with two PBL and four convection schemes using non-hydrostatic version of MM5 modeling system. Several important model simulated fields including sea level pressure, horizontal wind and precipitation are compared with the corresponding verification analysis/observation. The track of the cyclones in the simulation and analysis are compared with the best-fit track provided by India Meteorological Department (IMD). The Hong-Pan PBL scheme (as implemented in NCAR Medium Range Forecast (MRF) model) in combination with Grell (or Betts-Miller) cumulus convection scheme is found to perform better than the other combinations of schemes used in this study. Though it is expected that radiative processes may not have pronounced effect in short-range forecasts, an attempt is made to calibrate the model with respect to the two radiation parameterization schemes used in the study. And the results indicate that radiation parameterization has noticeable impact on the simulation of tropical cyclones. 相似文献
4.
There have been very few mesoscale modelling studies of the Indian monsoon, with focus on the verification and intercomparison
of the operational real time forecasts. With the exception of Das et al (2008), most of the studies in the literature are either the case studies of tropical cyclones and thunderstorms or the sensitivity
studies involving physical parameterization or climate simulation studies. Almost all the studies are based on either National
Center for Environmental Prediction (NCEP), USA, final analysis fields (NCEP FNL) or the reanalysis data used as initial and
lateral boundary conditions for driving the mesoscale model. 相似文献
5.
Monica Laureano Bozeman Dev Niyogi S. Gopalakrishnan Frank D. Marks Jr. Xuejin Zhang Vijay Tallapragada 《Natural Hazards》2012,63(3):1543-1571
While tropical cyclones (TCs) usually decay after landfall, Tropical Storm Fay (2008) initially developed a storm central eye over South Florida by anomalous intensification overland. Unique to the Florida peninsula are Lake Okeechobee and the Everglades, which may have provided a surface feedback as the TC tracked near these features around the time of peak intensity. Analysis is done with the use of an ensemble model-based approach with the Developmental Testbed Center (DTC) version of the Hurricane WRF (HWRF) model using an outer domain and a storm-centered moving nest with 27- and 9-km grid spacing, respectively. Choice of land surface parameterization and small-scale surface features may influence TC structure, dictate the rate of TC decay, and even the anomalous intensification after landfall in model experiments. Results indicate that the HWRF model track and intensity forecasts are sensitive to three features in the model framework: land surface parameterization, initial boundary conditions, and the choice of planetary boundary layer (PBL) scheme. Land surface parameterizations such as the Geophysical Fluid Dynamics Laboratory (GFDL) Slab and Noah land surface models (LSMs) dominate the changes in storm track, while initial conditions and PBL schemes cause the largest changes in the TC intensity overland. Land surface heterogeneity in Florida from removing surface features in model simulations shows a small role in the forecast intensity change with no substantial alterations to TC track. 相似文献
6.
A number of sensitivity experiments have been conducted to investigate the influence of using synthetic data on cyclone forecasts
by a global spectral model. Some well known vortices have been used and the generated wind and pressure profiles are compared.
It is found that the Rankine vortex and Holland’s vortex show the best representation of cyclonic circulation. Hence these
two vortices are used in the sensitivity studies to simulate two cyclones, one of May 1979 and the other of August 1979. For
this purpose the FGGE level-III b data set, produced at ECM WF, UK is used. Synthetic temperature and humidity data are also
introduced to make the cyclones more realistic.
With the use of Holland’s vortex the system is found to move faster than with the Rankine vortex. Also, the tracks of the
cyclones simulated with Rankine vortex are found to be on the left side of the observed track while that of Holland’s vortex
is on the right side of the observed track. However, substantial filling up of the systems are noticed with introduction of
diabatic initialization of the mass and velocity fields and the forecasts of both the vortices behave differently. It is suggested
that proper selection of synthetic vortex, initialization scheme and resolution of the model are very important for better
forecast of cyclones. 相似文献
7.
用物理模拟研究地幔上隆与大陆裂陷伸展 总被引：4，自引：2，他引：2
通过脆延性双层模型,在满足相似要求的前提下,模拟了三种边界条件下的上隆与伸展。模拟结果表明:两侧边界固定时,上隆能产生拱张断裂,然而它引起的侧向分流比较小,基本不能形成伸展;存在半开放或开放边界时,可以产生大规模的伸展,但伸展主要沿上隆早期产生的张裂进行,显然,上隆产生的张裂为后续伸展奠定了基础,同时上隆加速了延性层向开放边界方向流动,促进了伸展;另外,在上隆-伸展过程中普遍存在延性层被动上隆。这些实验结果说明,地幔主动上隆引起伸展是有条件的,需要边界条件的配合;被动上隆是普遍存在的,它是重力均衡作用的必然结果。 相似文献
8.
A new finite element scheme is proposed, in this paper, for solving two-dimensional wave propagation problems in multilayered soils resting on a rigid base. The multilayered soils are treated as multiple horizontal layers of lateral infinite extension in geometry. Since these horizontal layers can be truncated by two artificially truncated vertical boundaries, two high-order artificial boundary conditions are applied for propagating the incoming waves from the interior domain into the far field of the system. Both the semi-analytical method and the truncated boundary migration procedure are used to derive the high-order artificial boundary conditions, which are comprised of a physically meaningful dashpot and a generalized energy absorber. The main advantage of using the proposed finite element scheme is that the derived artificial boundary condition can be straightforwardly implemented in the finite element analysis, without violating the band/sparse structure of the conventional finite element equation. The related numerical examples have demonstrated that the proposed finite element scheme is of high accuracy in dealing with wave propagation problems in multiple horizontal layers. 相似文献
9.
M MAHBUB ALAM 《Journal of Earth System Science》2014,123(2):259-279
In the present study, the Advanced Research WRF (ARW) version 3.2.1 has been used to simulate the heavy rainfall event that occurred between 7 and 9 October 2007 in the southern part of Bangladesh. Weather Research and Forecast (WRF–ARW version) modelling system with six different microphysics (MP) schemes and two different cumulus parameterization (CP) schemes in a nested configuration was chosen for simulating the event. The model domains consist of outer and inner domains having 9 and 3 km horizontal resolution, respectively with 28 vertical sigma levels. The impacts of cloud microphysical processes by means of precipitation, wind and reflectivity, kinematic and thermodynamic characteristics of the event have been studied. Sensitivity experiments have been conducted with the WRF model to test the impact of microphysical and cumulus parameterization schemes in capturing the extreme weather event. NCEP FNL data were used for the initial and boundary condition. The model ran for 72 h using initial data at 0000 UTC of 7 October 2007. The simulated rainfall shows that WSM6–KF combination gives better results for all combinations and after that Lin–KF combination. WSM3–KF has simulated, less area average rainfall out of all MP schemes that were coupled with KF scheme. The sharp peak of relative humidity up to 300 hPa has been simulated along the vertical line where maximum updraft has been found for all MPs coupled with KF and BMJ schemes. The simulated rain water and cloud water mixing ratio were maximum at the position where the vertical velocity and reflectivity has also been maximum. The production of rain water mixing ratio depends on MP schemes as well as CP schemes. Rainfall depends on rain water mixing ratio between 950 and 500 hPa. Rain water mixing ratio above 500 hPa level has no effect on surface rain. 相似文献
10.
《Atmósfera》2014,27(3):287-303
Given the growing interest of the general public in accessing commercial weather forecasts through various media outlets and the available impetuses for promoting tourism in Saudi Arabia (SA), a first attempt is made to present a forecast skill comparison for surface temperature in four cities (Wejh, Yenbo, Jeddah, and Gizan) along the west coast of SA, for the 61-day transitional period (from January 16 to March 16) between the December-January-February (DJF) and the March-April-May (MAM) seasons. A simple skill score comparison method is used to assess the next-day city forecasts for surface temperature from six commercial weather forecast providers based on the operational numerical weather prediction (NWP) model outputs. All the NWP model forecast providers performed better than the respective daily climatology (Clm) for each station. Depending upon the station and the provider, the absolute average maximum daily surface temperature difference between the forecasts and the observations was less than 2 °C. Daily surface temperature forecasts from two versions of an atmospheric-ocean general circulation model are also compared to assess their performance for these coastal locations. 相似文献
11.
In this study, the Florida State University Global Spectral Model (FSUGSM), in association with a high-resolution nested regional
spectral model (FSUNRSM), is used for short-range weather forecasts over the Indian domain. Three-day forecasts for each day
of August 1998 were performed using different versions of the FSUGSM and FSUNRSM and were compared with the observed fields
(analysis) obtained from the European Center for Medium Range Weather Forecasts (ECMWF). The impact of physical initialization
(a procedure that assimilates observed rain rates into the model atmosphere through a set of reverse algorithms) on rainfall
forecasts was examined in detail. A very high nowcasting skill for precipitation is obtained through the use of high-resolution
physical initialization applied at the regional model level. Higher skills in wind and precipitation forecasts over the Indian
summer monsoon region are achieved using this version of the regional model with physical initialization.
A relatively new concept, called the ‘multimodel/multianalysis superensemble’ is described in this paper and is applied for
the wind and precipitation forecasts over the Indian subcontinent. Large improvement in forecast skills of wind at 850 hPa
level over the Indian subcontinent is shown possible through the use of the multimodel superensemble. The multianalysis superensemble
approach that uses the latest satellite data from the Tropical Rainfall Measuring Mission (TRMM) and the Defense Meteorological
Satellite Program (DMSP) has shown significant improvement in the skills of precipitation forecasts over the Indian monsoon
region. 相似文献
12.
Impact of physical parameterization schemes on numerical simulation of super cyclone Gonu 总被引：2，自引：0，他引：2
The objective of this study is to investigate in detail the sensitivity of cumulus, planetary boundary layer and explicit
cloud microphysics parameterization schemes on intensity and track forecast of super cyclone Gonu (2007) using the Pennsylvania
State University-National Center for Atmospheric Research Fifth-Generation Mesoscale Model (MM5). Three sets of sensitivity
experiments (totally 11 experiments) are conducted to examine the impact of each of the aforementioned parameterization schemes
on the storm’s track and intensity forecast. Convective parameterization schemes (CPS) include Grell (Gr), Betts–Miller (BM)
and updated Kain–Fritsch (KF2); planetary boundary layer (PBL) schemes include Burk–Thompson (BT), Eta Mellor–Yamada (MY)
and the Medium-Range Forecast (MRF); and cloud microphysics parameterization schemes (MPS) comprise Warm Rain (WR), Simple
Ice (SI), Mixed Phase (MP), Goddard Graupel (GG), Reisner Graupel (RG) and Schultz (Sc). The model configuration for CPS and
PBL experiments includes two nested domains (90- and 30-km resolution), and for MPS experiments includes three nested domains
(90-, 30- and 10-km grid resolution). It is found that the forecast track and intensity of the cyclone are most sensitive
to CPS compared to other physical parameterization schemes (i.e., PBL and MPS). The simulated cyclone with Gr scheme has the
least forecast track error, and KF2 scheme has highest intensity. From the results, influence of cumulus convection on steering
flow of the cyclone is evident. It appears that combined effect of midlatitude trough interaction, strength of the anticyclone
and intensity of the storm in each of these model forecasts are responsible for the differences in respective track forecast
of the cyclone. The PBL group of experiments has less influence on the track forecast of the cyclone compared to CPS. However,
we do note a considerable variation in intensity forecast due to variations in PBL schemes. The MY scheme produced reasonably
better forecast within the group with a sustained warm core and better surface wind fields. Finally, results from MPS set
of experiments demonstrate that explicit moisture schemes have profound impact on cyclone intensity and moderate impact on
cyclone track forecast. The storm produced from WR scheme is the most intensive in the group and closer to the observed strength.
The possible reason attributed for this intensification is the combined effect of reduction in cooling tendencies within the
storm core due to the absence of melting process and reduction of water loading in the model due to absence of frozen hydrometeors
in the WR scheme. We also note a good correlation between evolution of frozen condensate and storm intensification rate among
these experiments. It appears that the Sc scheme has some systematic bias and because of that we note a substantial reduction
in the rain water formation in the simulated storm when compared to others within the group. In general, it is noted that
all the sensitivity experiments have a tendency to unrealistically intensify the storm at the later part of the integration
phase. 相似文献
13.
W. A. Mulder 《Computational Geosciences》1997,1(1):85-108
Simulation of wave propagation for seismic purposes is usually restricted to a small portion of the earth. Artificial boundary
conditions are required where the subsurface model is truncated. Absorbing boundaries should ensure that waves hitting the
artificial boundaries are not reflected. The vast amount of literature on the subject suggests that “good” conditions have
not been found, and only “reasonable” solutions exist. A cursory overview of existing and a few new ideas is presented that
may guide the construction of suitable boundary conditions. Because the intended application of the boundary conditions was
a high-order finite-difference code that runs on a parallel computer, we have restricted our attention to local boundary conditions.
A fundamental problem in the design of accurate local boundary conditions is pointed out: accuracy is required to keep the
amount of reflected energy small, but at the same time allows for growing low-frequency modes. We have settled for Higdon’s
boundary conditions. Higdon proposes to include some damping to suppress the growing low-frequency modes. We show that third-order
conditions provide acceptable results for the simple scalar wave equation and the acoustic equation. In the elastic case,
an additional low-frequency growing mode may occur. This mode can be suppressed by using a dissipative boundary scheme and
by increasing the amount of damping. The increase in damping results in an increase in the amount of reflected energy, which
is larger than in the scalar case. Numerical experiments exhibit a reasonable performance, although some improvement would
be useful, particularly in the anisotropic elastic case.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Application of a semi-implicit version of primitive equation barotropic model to predict monsoon depressions is proposed. Forecasts upto 48 hr have been quite satisfactory. The results are compared with those obtained from an explicit version of primitive equation barotropic model developed earlier. The flow patterns from these two versions are similar with few exceptions in isolated pockets, however, the forecast movement obtained from the semi-implicit version is comparable or slightly superior to those obtained from the explicit version. The computational time in semi-implicit and explicit schemes is approximately in the ratio of 1∶2. 相似文献
15.
通过数据同化方法合理地将实时水文观测数据融入到洪水预报模型中,可提高洪水预报模型的实时性和精确度。选取沿程断面流量、水位和糙率系数作为代表水流状态的基本粒子,以监测断面实测水位数据作为观测信息,建立了基于粒子滤波数据同化算法的河道洪水实时概率预报模型。模型应用于黄河中下游河道洪水预报计算的结果表明,采用粒子滤波方法同化观测水位后,不仅可以直接校正水位,同时也可以有效地校正流量和糙率,为未来时刻模型预报计算提供更准确的水流初始条件和糙率取值区间,进而有效地提高模型预报结果的精度,给出合理的概率预报区间。不同预报期的预报结果表明,随着预报期的增长,同化效果减弱,模型预报结果的精度会有所降低,水位概率预报结果受粒子间糙率不同的影响不确定性增加,而流量概率预报结果受给定模型边界条件的影响不确定性降低。所提出模型可以有效同化真实水位观测数据,适合应用于实际的洪水预报工作中。 相似文献
16.
C. V. Srinivas V. Yesubabu K. B. R. R. Hariprasad S. S. V. Ramakrishna B. Venkatraman 《Natural Hazards》2013,65(1):331-357
Real-time predictions for the JAL severe cyclone formed in November 2010 over Bay of Bengal using a high-resolution Weather Research and Forecasting (WRF ARW) mesoscale model are presented. The predictions are evaluated with different initial conditions and assimilation of observations. The model is configured with two-way interactive nested domains and with fine resolution of 9?km for the region covering the Bay of Bengal. Simulations are performed with NCEP GFS 0.5° analysis and forecasts for initial/boundary conditions. To examine the impact of initial conditions on the forecasts, eleven real-time numerical experiments are conducted with model integration starting at 00, 06, 12, 18 UTC 4 Nov, 5?Nov and 00, 06, 12 UTC 6 Nov and all ending at 00 UTC 8 Nov. Results indicated that experiments starting prior to 18 UTC 04 Nov produced faster moving cyclones with higher intensity relative to the IMD estimates. The experiments with initial time at 18 UTC 04 Nov, 00 UTC 05 Nov and with integration length of 78?h and 72?h produced best prediction comparable with IMD estimates of the cyclone track and intensity parameters. To study the impact of observational assimilation on the model predictions FDDA, grid nudging is performed separately using (1) land-based automated weather stations (FDDAAWS), (2) MODIS temperature and humidity profiles (FDDAMODIS), and (3) ASCAT and OCEANSAT wind vectors (FDDAASCAT). These experiments reduced the pre-deepening period of the storm by 12?h and produced an early intensification. While the assimilation of AWS data has shown meagre impact on intensity, the assimilation of scatterometer winds produced an intermittent drop in intensity in the peak stage. The experiments FDDAMODIS and FDDAQSCAT produced minimum error in track and intensity estimates for a 90-h prediction of the storm. 相似文献
17.
《Russian Geology and Geophysics》2015,56(7):1083-1090
This paper presents a numerical model for the effect of near-surface inhomogeneities over a one-dimensional horizontally layered geoelectric section and the distortions they cause during magnetotelluric sounding (MTS). The electromagnetic field within the layer of near-surface inhomogeneities is calculated using the Trefftz method. Expressions are derived for the boundary conditions on the day surface and on the roof of the underlying inhomogeneity of a horizontally layered medium. These boundary conditions allow for the excitation of TM-mode fields by subsurface inhomogeneities and their penetration into the atmosphere and the underlying medium. The spatial distribution and characteristics of galvanic and inductive distortions over different time periods during MTS have been studied. Experimental data show that accounting for galvanic distortions is possible with synchronous recording of the distribution of components of the electric and magnetic fields in a limited area of the Earth’s surface. 相似文献
18.
以福建金溪池潭水库流域为例,采用TIGGE数据中心的ECMWF、UKMO、NCEP等7种模式控制预报产品驱动新安江模型,开展径流集合预报。通过集合挑选、多模式集成前处理以及基于BMA模型的后处理等过程,探讨不同处理方案和初始集合质量对气象水文耦合径流预报精度及不确定性的影响。结果表明,不同的处理方案均能有效提高径流预报的精度和稳定性,同时进行前处理和后处理能从降低误差输入和控制误差输出两方面减小预报误差,相对于其他方案表现更好。初始集合质量对气象水文耦合径流集合预报有一定影响,但前处理或后处理对预报误差的有效控制使得该影响并不显著。总体而言,前处理和后处理过程是提高气象水文耦合径流预报准确性和可靠性必不可少的环节,应予以重视。 相似文献
19.
Vassiliki Kotroni Evangelos Floros Konstantinos Lagouvardos Goran Pejanovic Luka Ilic Momcilo Zivkovic 《Earth Science Informatics》2010,3(4):209-218
Weather forecasting is based on the use of numerical weather prediction (NWP) models that are able to perform the necessary
calculations that describe/predict the major atmospheric processes. One common problem in weather forecasting derives from
the uncertainty related to the chaotic behaviour of the atmosphere. A solution to that problem is to perform in addition to
“deterministic” forecasts, “stochastic” forecasts that provide an estimate of the prediction skill. A computationally feasible
approach towards this aim is to perform “ensemble forecasts”. Indeed, in the frame of SEE-GRID-SCI EU funded project a Regional
scale Multi-model, Multi-analysis ensemble forecasting system (REFS) was built and ported on the Grid infrastructure. REFS
is based on the use of four limited area models (namely BOLAM, MM5, ETA, and NMM) that are run using a multitude of initial
and boundary conditions over the Mediterranean. This paper presents the tools and procedures followed for developing this
application at a production level. 相似文献
20.
Frank Herrmann Christoph Jahnke Florian Jenn Ralf Kunkel Hans-Jürgen Voigt Jens Voigt Frank Wendland 《Hydrogeology Journal》2009,17(8):2049-2060
Groundwater recharge rates calculated with the GROWA model have been applied as the recharge boundary condition for the regional groundwater model Rurscholle. This model simulates groundwater dynamics in the Pleistocene aquifers of the Lower Rhine lignite mining area (Germany). GROWA uses an area-differentiated approach to calculate recharge rates depending on runoff-relevant site characteristics, which are represented by a set of baseflow indices. The regional accuracy of the coupled groundwater and GROWA models has been checked using groundwater hydrographs as validation criteria. The results suggest that the current (unadjusted) version of GROWA underestimates the regional groundwater recharge rate by 10–20 mm/yr. The comparative analysis identified areas where recharge calculations could be improved by adjusting the baseflow indices for areas where runoff is dominated by slope, low water-logging and a low degree of sealing. Using the adjusted set of baseflow indices, the mean groundwater recharge rate of the Rurscholle region was modelled as approx. 170 mm/yr. This study highlights the benefit of using a coupled approach and being able to independently calibrate and validate groundwater recharge boundary conditions in regional groundwater models. 相似文献