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1.
湍流动能闭合方法在中尺度模式中的应用 总被引：3，自引：1，他引：2
湍流动能闭合方法是近年来发展起来的用以模拟大气边界层的一种方法,本文对其做了简化,仅在边界层内使用这一方法,进一步减少计算量,使之更适用于中尺度数值模拟。对一维旺加拉（Wangara）资料进行的试验表明,这种方法保留了边界层计算的精度,又能节省机时。然后将这种方法应用于三维中尺度钟形山地形的模拟,描述了湍流动能的分布,以及湍流活动对山后回流区面积和强度的影响。 相似文献
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本文建立一个三维非静力边界层模式对杭州湾附近复杂地形域区进行了数值模拟。要用常用的能量闭合和一 新的非局地反梯度闭合方案结合实测资料,以验证不同闭合方案模拟实际大气的能力,进一步分析三维边界层模式的效能结果表明,两种闭合方案都能较好的模拟澳陆环流及温度场,而反梯度闭合比能量闭合更能细致、敏感的模拟湍流场随地形的变化,且模拟结果与实测接近。 相似文献
4.
A nested grid regional model with a high vertical resolution in the atmospheric boundary layer is used to simulate various atmospheric processes during an active monsoon period. A turbulence kinetic energy closure scheme is used to predict the boundary-layer structure. Model predictions indicate different structures of the boundary layer over land and oceans, as observed. Significant diurnal variation in boundary-layer structure and associated processes is predicted over land and negligible variations over oceans. The Somali jet over the Arabian Sea is well predicted. Location of the predicted monsoon depression and the associated rainfall are in good agreement with the observations. Also, predicted rainfall and its spatial distribution along the west coast of India are in good agreement with the observations. 相似文献
5.
湍流能量（TKE）闭合方案是近年来大气边界层（PBL）模式中技推崇的方法,它具有11－2阶精度。大气环流模式的计算容量和垂直网络限制,不允许PBL方案过份精细。本文对TKE方案进行简化及网络稀疏化试验。并用Wangara资料验证。验证结果表明：此方案引入PBL内仅设置5层的大气环流模式是可行的。地面以上400米内模式结果与实测吻合。但中、上部位温计算值偏高。关于本方案在大尺度模式中的应用尚须进一步研究。 相似文献
6.
The three-dimensional variational data assimilation (3DVAR) technique in the advanced weather research and forecast model is used to study the impact of assimilating Moderate Resolution Spectroradiometer (MODIS) retrieved temperature and humidity profiles on the dynamic and thermodynamic features for three monsoon depressions over the Bay of Bengal, India. For better understanding of the role of various physical processes in the evolution of monsoon depression, a detailed diagnostic study is performed on all the three depression cases. Numerical experiments were conducted in a system of two-way nested domains with a horizontal resolution of 36 and 12 km, respectively. The assimilation of MODIS data did improve the mean sea level pressure patterns and spatial distribution of rainfall patterns in all the three monsoon depression cases studied. Higher values of equitable threat score and lower bias values are seen consistently for the entire rainfall threshold range and for all the three depression cases with 3DVAR assimilation of MODIS temperature and humidity profiles. The current operational regional models in India do not ingest the MODIS temperature and humidity profiles and hence the present study is particularly relevant to the operational forecasting community in India in their ongoing efforts to improve weather forecasting over India. 相似文献
7.
Summary The sensitivity of the simulation of the monsoon depressions to the cumulus parameterization schemes used in a numerical model
is studied using the Pennsylvania State University – National Center for Atmospheric Research (PSU-NCAR) model MM5 version
3.6.2. Three different cases of monsoon depressions were studied with a two way interacting domains of 45 km and 15 km resolutions.
Two different cumulus parameterization schemes namely Grell (GR) and Kain-Fritsch (KF) were used for the sensitivity study.
The model was integrated for 48 hours with the initial and boundary conditions of European Center for Medium Range Weather
Forecasting Reanalysis (ERA-40) data. The results show that both the schemes are able to simulate the large scale features
of the monsoon depressions realistically. However, both the schemes failed to simulate the exact location of the depression
after 24- and 48-hour simulation. The rainfall simulations of both the schemes were very different. The model with the GR
scheme tends to over predict the rainfall. The KF scheme could simulate the distribution of the rainfall comparable to the
observations. The KF scheme could simulate the maximum observed rainfall but due to locational errors of the simulated depression,
the location of the maximum rainfall was not exact. It is also seen that the resolution of the model has a positive impact
on the rainfall simulation. The GR and KF schemes were able to realistically simulate the apparent heat sources, but the apparent
moisture profile simulated with KF scheme was more comparable to the verifying analysis. The root mean square errors of mean
sea-level pressure, temperature, zonal wind and meridional wind were smaller for KF simulation compared to the GR simulation.
Permanent affiliation: Center for Development of Advanced Computing, Pune University Campus, Ganeshkhind, Pune-411 007, India. 相似文献
8.
A low pressure system that formed on 21 September 2006 over eastern India/Bay of Bengal intensified into a monsoon depression
resulting in copious rainfall over north-eastern and central parts of India. Four numerical experiments are performed to examine
the performance of assimilation schemes in simulating this monsoon depression using the Fifth Generation Mesoscale Model (MM5).
Forecasts from a base simulation (with no data assimilation), a four-dimensional data assimilation (FDDA) system, a simple
surface data assimilation (SDA) system coupled with FDDA, and a flux-adjusting SDA system (FASDAS) coupled with FDDA are compared
with each other and with observations. The model is initialized with Global Forecast System (GFS) forecast fields starting
from 19 September 2006, with assimilation being done for the first 24 hours using conventional observations, sounding and
surface data of temperature and moisture from Advanced TIROS Operational Vertical Sounder satellite and surface wind data
over the ocean from QuikSCAT. Forecasts are then made from these assimilated states. In general, results indicate that the
FASDAS forecast provides more realistic prognostic fields as compared to the other three forecasts. When compared with other
forecasts, results indicate that the FASDAS forecast yielded lower root-mean-square (r.m.s.) errors for the pressure field
and improved simulations of surface/near-surface temperature, moisture, sensible and latent heat fluxes, and potential vorticity.
Heat and moisture budget analyses to assess the simulation of convection revealed that the two forecasts with the surface
data assimilation (SDA and FASDAS) are superior to the base and FDDA forecasts. An important conclusion is that, even though
monsoon depressions are large synoptic systems, mesoscale features including rainfall are affected by surface processes. Enhanced
representation of land-surface processes provides a significant improvement in the model performance even under active monsoon
conditions where the synoptic forcings are expected to be dominant. 相似文献
9.
复杂下垫面地域边界层结构的三维细网格数值模拟 总被引：8，自引：0，他引：8
建立了一个可供复杂下垫面地域使用的非静力的三维细网格边界层模式，就复杂下垫面条件下的边界层结构和湍流特征作了以实例为对照的数值模拟试验，模式采用能量闭合方案，舍弃了静力近似。以实测资料为初台输入，同时还做了一些数值试验，分别获得了采用静力与非静力模式和不同闭合方案对ＰＢＬ模型的结果。 相似文献
10.
Summary In this study, the authors analyse the observational features of the onset of the South China Sea (SCS) monsoon in 1998 shown in reanalysis data and use a numerical model to understand the mechanisms responsible for these features.The onset of SCS summer monsoon in 1998 occurred around 21 May. Prior to this period, monsoon depression activity was strong over the Bay of Bengal (BOB) and warm temperature anomalies appeared at the mid-upper troposphere over the northern BOB. In the meantime, warm horizontal thermal advection occurred over the northern Indo-China peninsula and South China. This warm advection seemed to play an important role in the winter-to-summer transition of the patterns of mean meridional temperature gradient in the 500–200-mb layer over South Asia.The PSU/NCAR Mesoscale Model Version 5 (MM5) is used to understand the physical link between the latent heating associated with the monsoon depression over BOB and the establishment of SCS monsoon. Full-physics simulations, for a 6-day period coinciding with the onset of the observed monsoon, reproduce realistically the evolution of the monsoon depression and monsoon onset process. It is found that the condensational heating over BOB is important for the formation of large-scale circulation pattern that favors the establishment of SCS monsoon. In an experiment without latent heating, the winter-to-summer reversal of meridional temperature gradient over South Asia was delayed and the onset of SCS summer monsoon did not occur during the simulation period. 相似文献
11.
In this study, the impact of different land initial conditions on the simulation of thunderstorms and monsoon depressions is investigated using the Weather Research and Forecasting (WRF) model. A control run (CNTL) and a simulation with an improved land state (soil moisture and temperature) using the High Resolution Land Data Assimilation System (HRLDAS, experiment name: EHRLDAS) are compared for three different rainfall cases in order to examine the robustness of the assimilation system. The study comprises two thunderstorm cases (one in the pre-monsoon and one during the monsoon) and one monsoon depression case that occurred during the Interaction of Convective Organisation, Atmosphere, Surface and Sea (INCOMPASS) field campaign of the 2016 Indian monsoon. EHRLDAS is shown to yield improvements in the representation of location-specific rainfall, particularly over land. Further, it is found that surface fluxes as well as convective indices are better captured for the pre-monsoon thunderstorm case in EHRLDAS. By analysing components of the vorticity tendency equation, it is found that the vertical advection term is the major contributor towards the positive vorticity tendency in EHRLDAS compared to CNTL, hence improving localised convection and consequently facilitating rainfall. Significant improvements in the simulation of the pre-monsoon thunderstorm are noted, as seen using Automatic Weather Station (AWS) validation, whereas improvements in the monsoon depression are minimal. Further, it is found that vertical advection (moisture flux convergence) is the major driver modulating the convective circulation in localised thunderstorm (monsoon depression) cases and these dynamics are better represented by EHRLDAS compared to CNTL. These findings underline the importance of accurate and high resolution land-state conditions in model initial conditions for forecasting severe weather systems, particularly the simulation of localised thunderstorms over India. 相似文献
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In this study, a smaller domain over India alone and a larger South Asia (SA) domain have been used in the Regional Climate Model version 4.2 (RegCM4.2) to examine the effect of the domain size on the Indian summer monsoon simulations. These simulations were carried out over a period of 36 years at 50 km horizontal resolution with the lateral boundary forcings of the UK Met Office Hadley Centre Global Circulation Model Version 2.0. Results show that the Indian summer monsoon rainfall is significantly reduced when the domain size for the model integration is reduced from SA to the Indian domain. In case of SA domain simulation, the Equitable Threat Scores have higher values in case of very light, light and moderate rainfall events than those in case of the Indian domain simulation. It is also found that the domain size of model integration has dominant impact on the simulated convective precipitation. The cross-equatorial flow and the Somali Jet are better represented in the SA simulation than those in the Indian domain simulation. The vertically integrated moisture flux over the Arabian Sea in the SA domain simulation is close to that in the NCEP/NCAR reanalysis while it is underestimated in the Indian domain simulation. It is important to note that when RegCM4.2 is integrated over the smaller Indian domain, the effects of the Himalayas and the moisture advection from the Indian seas are not properly represented in the model simulation and hence the monsoon circulation and associated rainfall are underestimated over India. 相似文献
14.
Large eddy simulation and study of the urban boundary layer 总被引：7，自引：1，他引：6
15.
The Advanced Research Weather Research and Forecasting (AR-WRF) model is used to study the influence of Western Ghats situated along the west cost of peninsular India in the mean characteristics of the Asian summer monsoon (ASM) through numerical simulations. A control simulation (CTRL) is carried out using 11-year (2000–2010) mean initial and lateral boundary conditions from the ERA-Interim reanalysis to simulate the mean atmospheric features of the ASM. The Modern-Era retrospective analysis for research and applications (MERRA) data along with the Tropical Rainfall Measuring Mission (TRMM, 3B42 daily rainfall) data are used to validate the CTRL simulation. The simulated dynamical features and precipitation characteristics during the ASM period agree well with the MERRA reanalysis and TRMM observations. In order to examine the role of Western Ghats on the mean characteristics of the ASM, a sensitivity simulation (NoWG) is carried out with orography reduced to surface over a domain bound between 5°–28°N and 72°–90°E, keeping all other conditions unchanged. This sensitivity analysis showed an enhancement in the low level monsoon flow over the Indian Ocean and peninsular India in the absence of Western Ghats. The prominent up-draft over the west coast of peninsular India observed in the CTRL simulation also decrease in the absence of Western Ghats. The simulated rainfall show a considerable decrease over the west coast and an enhancement over the east coast of peninsular India in the absence of Western Ghats. These simulations clearly depict the importance of Western Ghats in the circulation dynamics and rainfall features during the ASM period. 相似文献
16.
An attempt is made to study the planetary boundary layer (PBL) characteristics during the winter period at Anand (22.4°N, 72.6°E), a semi-arid region, which is located in the western part of India. A one-dimensional turbulent kinetic energy (TKE) closure model is used for the study. The structure of the PBL,which consists of profiles of zonal and meridional components of wind,potential temperature and specific humidity, is simulated. A one-dimensional soil heat and moisture transport parameterization scheme is incorporated for the accurate representation of the energy exchange processes at the soil-atmosphere interface. The diurnal variation of fluxes of sensible heat, latent heat, shortwave radiation, net radiation and soil flux, soil temperature at different depths, Richardson number and TKE at the height of the constant flux layer is studied. The model predictions are compared with the available observations obtained from a special Land Surface Processes (LSP) experiment. 相似文献
17.
Circumglobal wave train and the summer monsoon over northwestern India and Pakistan: the explicit role of the surface heat low 总被引：2，自引：1，他引：1
Sajjad Saeed Wolfgang A. M��ller Stefan Hagemann Daniela Jacob 《Climate Dynamics》2011,37(5-6):1045-1060
This study examines the influence of the mid-latitude circulation on the surface heat low (HL) and associated monsoon rainfall over northwestern India and Pakistan using the ERA40 data and high resolution (T106L31) climate model ECHAM5 simulation. Special emphasis is given to the surface HL which forms over Pakistan and adjoining areas of India, Iran and Afghanistan during the summer season. A heat low index (HLI) is defined to depict the surface HL. The HLI displays significant correlations with the upper level mid-latitude circulation over western central Asia and low level monsoon circulation over Arabian Sea and acts as a bridge connecting the mid-latitude wave train to the Indian summer monsoon. A time-lagged singular value decomposition analysis reveals that the eastward propagation of the mid-latitude circumglobal wave train (CGT) influences the surface pressure anomalies over the Indian domain. The largest low (negative) pressure anomalies over the western parts of the HL region (i.e., Iran and Afghanistan) occur in conjunction with the upper level anomalous high that develops over western-central Asia during the positive phase of the CGT. The composite analysis also reveals a significant increase in the low pressure anomalies over Iran and Afghanistan during the positive phase of CGT. The westward increasing low pressure anomalies with its north?Csouth orientation provokes enormous north?Csouth pressure gradient (lower pressure over land than over sea). This in turn enables the moist southerly flow from the Arabian Sea to penetrate farther northward over northwestern India and Pakistan. A monsoon trough like conditions develops over northwestern India and Pakistan where the moist southwesterly flow from the Arabian Sea and the Persian Gulf converge. The convergence in association with the orographic uplifting expedites convection and associated precipitation over northwestern India and Pakistan. The high resolution climate model ECHAM5 simulation also underlines the proposed findings and mechanism. 相似文献
18.
Fluctuations of Tropical Easterly Jet during contrasting monsoons over India: A GCM study 总被引：1，自引：0，他引：1
Summary The fluctuations of intensity of the Tropical Easterly Jet (TEJ) and its association with the Indian summer monsoon rainfall
have been examined using the diagnostics from NCEP/NCAR (National Centre for Environmental Prediction/National Centre for
Atmospheric Research) reanalyses project for the period 1986 to 1994. The intensity of TEJ is found to be well correlated
with India summer monsoon rainfall. The TEJ is weaker/stronger during the El Ni?o/La Ni?a year of 1987/1988 and is associated
with deficient (excess) summer monsoon rainfall over India.
A numerical study was carried out for the same period using the Centre for Ocean-Land-Atmosphere studies General Circulation
Model (COLA GCM, T30L18) with observed Sea-Surface Temperature (SST). The GCM simulates the TEJ with reasonable accuracy.
The strong interannual variability of TEJ during the El Ni?o/La Ni?a years of 1987/1988 are well simulated in the GCM. Like
observations, the intensity of the TEJ is positively correlated with the summer monsoon rainfall over India in the model simulation.
The intensity of Tibetan anticyclone and diabatic heating over the Tibetan Plateau diminished during the El Ni?o-year of 1987.
The divergence centre in the upper troposphere associated with Asian monsoon becomes weaker and shifts eastward during the
weak monsoon season of 1987. However, the opposite happens for the strong monsoon season of 1988. Also the middle and upper
tropospheric meridional temperature gradient between the Tibetan High and Indian Ocean region decreased (increased) during
the weak(strong) monsoon season of 1987 (1988).
Received May 27, 1999/Revised March 20, 2000 相似文献
19.
本文对5个西行路径的南海季风低压进行了合成结构分析,结果发现它在热力结构与动力结构方面均与台风(包括其前期的热带低压)和印度季风低压有很大不同。降水区主要集中在低压东北部100—200公里处。 相似文献
20.
Nachiketa Acharya Sarat C. Kar U. C. Mohanty Makarand A. Kulkarni S. K. Dash 《Theoretical and Applied Climatology》2011,105(3-4):505-520
The 2009 drought in India was one of the major droughts that the country faced in the last 100?years. This study describes the anomalous features of 2009 summer monsoon and examines real-time seasonal predictions made using six general circulation models (GCMs). El Ni?o conditions evolved in the Pacific Ocean, and sea surface temperatures (SSTs) over the Indian Ocean were warmer than normal during monsoon 2009. The observed circulation patterns indicate a weaker monsoon in that year over India with weaker than normal convection over the Bay of Bengal and Indian landmass. Skill of the GCMs during hindcast period shows that neither these models simulate the observed interannual variability nor their multi-model ensemble (MME) significantly improves the skill of monsoon rainfall predictions. Except for one model used in this study, the real-time predictions with longer lead (2- and 1-month lead) made for the 2009 monsoon season did not provide any indication of a highly anomalous monsoon. However, with less lead time (zero lead), most of the models as well as the MME had provided predictions of below normal rainfall for that monsoon season. This study indicates that the models could not predict the 2009 drought over India due to the use of less warm SST anomalies over the Pacific in the longer lead runs. Hence, it is proposed that the uncertainties in SST predictions (the lower boundary condition) have to be represented in the model predictions of summer monsoon rainfall over India. 相似文献