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21.
T. S. V. Vijaya Kumar J. Sanjay B. K. Basu A. K. Mitra D. V. Bhaskar Rao O. P. Sharma P. K. Pal T. N. Krishnamurti 《Natural Hazards》2007,41(3):471-485
This study entails the implementation of an experimental real time forecast capability for tropical cyclones over the Bay
of Bengal basin of North Indian Ocean. This work is being built on the experience gained from a number of recent studies using
the concept of superensemble developed at the Florida State University (FSU). Real time hurricane forecasts are one of the
major components of superensemble modeling at FSU. The superensemble approach of training followed by real time forecasts
produces the best forecasts for tracks and intensity (up to 5 days) of Atlantic hurricanes and Pacific typhoons. Improvements
in track forecasts of about 25–35% compared to current operational forecast models has been noted over the Atlantic Ocean
basin. The intensity forecasts for hurricanes are only marginally better than the best models. In this paper, we address tropical
cyclone forecasts over the Bay of Bengal for the years 1996–2000. The main result from this study is that the position and
intensity errors for tropical cyclone forecasts over the Bay of Bengal from the multimodel superensemble are generally less
than those of all of the participating models during 1- to 3-day forecasts. Some of the major tropical cyclones, such as the
November 1996 Andhra Pradesh cyclone and October 1999 Orissa super cyclone were well handled by this superensemble approach.
A conclusion from this study is that the proposed approach may be a viable way to construct improved forecasts of Bay of Bengal
tropical cyclone positions and intensity. 相似文献
22.
Sensitivity of Mesoscale Model Forecast During a Satellite Launch to Different Cumulus Parameterization Schemes in MM5 总被引:1,自引:0,他引:1
The identification of the model discrepancy and skill is crucial when a forecast is issued. The characterization of the model
errors for different cumulus parameterization schemes (CPSs) provides more confidence on the model outputs and qualifies which
CPSs are to be used for better forecasts. Cases of good/bad skill scores can be isolated and clustered into weather systems
to identify the atmospheric structures that cause difficulties to the forecasts. The objective of this work is to study the
sensitivity of weather forecast, produced using the PSU-NCAR Mesoscale Model version 5 (MM5) during the launch of an Indian
satellite on 5th May, 2005, to the way in which convective processes are parameterized in the model. The real-time MM5 simulations
were made for providing the weather conditions near the launch station Sriharikota (SHAR). A total of 10 simulations (each
of 48 h) for the period 25th April to 04th May, 2005 over the Indian region and surrounding oceans were made using different
CPSs. The 24 h and 48 h model predicted wind, temperature and moisture fields for different CPSs, namely the Kuo, Grell, Kain-Fritsch
and Betts-Miller, are statistically evaluated by calculating parameters such as mean bias, root-mean-squares error (RMSE),
and correlation coefficients by comparison with radiosonde observation. The performance of the different CPSs, in simulating
the area of rainfall is evaluated by calculating bias scores (BSs) and equitable threat scores (ETSs). In order to compute
BSs and ETSs the model predicted rainfall is compared with Tropical Rainfall Measuring Mission (TRMM) observed rainfall. It
was observed that model simulated wind and temperature fields by all the CPSs are in reasonable agreement with that of radiosonde
observation. The RMSE of wind speed, temperature and relative humidity do not show significant differences among the four
CPSs. Temperature and relative humidity were overestimated by all the CPSs, while wind speed is underestimated, except in
the upper levels. The model predicted moisture fields by all CPSs show substantial disagreement when compared with observation.
Grell scheme outperforms the other CPSs in simulating wind speed, temperature and relative humidity, particularly in the upper
levels, which implies that representing entrainment/detrainment in the cloud column may not necessarily be a beneficial assumption
in tropical atmospheres. It is observed that MM5 overestimates the area of light precipitation, while the area of heavy precipitation
is underestimated. The least predictive skill shown by Kuo for light and moderate precipitation asserts that this scheme is
more suitable for larger grid scale (>30 km). In the predictive skill for the area of light precipitation the Betts-Miller
scheme has a clear edge over the other CPSs. The evaluation of the MM5 model for different CPSs conducted during this study
is only for a particular synoptic situation. More detailed studies however, are required to assess the forecast skill of the
CPSs for different synoptic situations. 相似文献
23.
The Pecos River, situated in eastern New Mexico and western Texas, receives water from a drainage area of 91 000 km2. There are primarily two major water inputs, namely snowmelt from winter storms in the headwater region of the southern Rocky Mountains and runoff from warm-season monsoonal rainfall in the lower valley. The Pecos River suffers from high levels of total dissolved solids (TDS >5000 mg L−1) under normal flow conditions. This not only poses serious problems for agricultural irrigation and safe drinking water supply, but also results in a permanent loss of biodiversity. This study examines changes in stream flow and water chemistry of the Pecos River over the last 70 a to better understand the long-term variability in stream salinity and the role of agricultural practices in salt transfer. A TDS record from the lower Pecos River near Langtry (Texas) back to 1935 was extracted to show a distinct pattern of decadal variability similar to the Pacific Decadal Oscillation (PDO), in which stream salinity is overall above average when the PDO is in positive (warm) phase and below average when the PDO is in negative (cold) phase. This is due to: (1) the dissolved salts contributed to the river are largely from dissolution of NaCl and CaSO4-bearing minerals (e.g., halite and gypsum) in the upper basin, (2) the amount of the dissolved salts that reach the lower basin is mainly determined by the stream flow yield in the upper basin and (3) the stream flow yield from the upper basin is positively correlated with the PDO index. This further attests that large-scale climatic oscillation is the major source of long-term changes in stream flow and salinity of the Pecos River. On the other hand, there is also a strong indication that the rate of salt export has been affected by reservoir operations and water diversions for agricultural practices. 相似文献
24.
中国当代土地利用对区域气候影响的数值模拟 总被引:20,自引:0,他引:20
使用RegCM3区域气候模式,嵌套欧洲数值预报中心(ECMWF)ERA40再分析资料,分别进行了中国区域在实际植被和理想植被分布情况下各15年时间长度(1987-2001)的积分试验,以研究我国土地利用状况对气候的影响。通过两个试验结果的对比,研究了我国土地利用状况对气候的影响。分析主要集中于气温、降水等的变化上,并对结果进行了统计显著性检验。结果表明,当代土地利用/植被覆盖变化加强了中国地区冬、夏季的季风环流,同时改变了地表能量平衡状况,从而对各气候要素产生重要影响。冬季,植被改变引起长江以南降水减少、气温降低,长江以北降水增加。夏季,植被改变显著影响了南方地区的气候,使得这里降水增多,黄淮、江淮气温降低,华南气温上升;同时引起中国北方降水减少,气温在西北部分植被退化地区升高。植被变化对日最低、最高气温的影响更大。总体来说,土地利用引起了年平均降水在南方增加、北方减少,年平均气温在南方显著降低。 相似文献
25.
A simple theoretical method for the determination of bulk modulus and equation of state is investigated and applied for six
minerals of geophysical importance. The results obtained at different temperatures are found to present a good agreement with
the experimental data. The simplicity of the method is discussed in the light of other methods in high temperature research
on minerals.
Received: 7 January 1996 / Revised, accepted: 11 June 1997 相似文献
26.
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28.
The mapability of Landsat images has opened up a new potentiality for study of channel pattern changes which was earlier not so easy due to nonavailability of suitable evidences at different timespans. Middle Ganga plain covering largely the northern part of Bihar and parts of eastern Uttar Pradesh is in a slate of perpetual flux due to large scale channel migration and avulsion resulting in devastating floods. Mosaic of three Landsat images has helped to study the channel changes which have occurred since 1935. The course of the river Ganga has beeh digitised along a basal line and two dimensional coordinates are taken at as many as more than fifty sample points for studying the magnitude and direction of channel changes during 1935–1975 period. The analysis shows that the main multiple channel river Ganga is under the huge hydrostatic thrust to be shifted towards south of its basin annually at a very high rate of 100 Meter per year all along the course except at its upstream near Ghazipur and at Monghyr where the shifting is towards north. The northward bend at Monghyr may be due to the presence of the Precambrian outliers here. For the multi-and single channelld tributaries of Ganga in channel behaviour is mainly in three directions—the lower water channels in the floodplain of Ganga are shifting to the south in conformity with that of their parent stream, the tributaries in Gogra-Gandak doab are shifting towards east but the shifting of the Kosi-Mahananda group of tributaries in the eastern part of the basin is towards west These channel pattern changes thus known at the interregional scale from the Landsat images may further be integrated with the study in hydrogeomorphology and their pertinent environmental impact. 相似文献
29.
Surendra Pal 《Earth and Planetary Science Letters》1977,36(1):202-206
New paleomagnetic measurements have been made on Tertiary volcanic rocks from northeast Jalisco, Mexico (20.7°N, 102.3°W). The pole position obtained from this study (68°N, 181°E) is consistent with two other Oligocene poles from Mexico. Mexican poles form a coherent group which differs from poles of similar ages from North America. This suggests a possible tectonic rotation of the sampling sites of Mexico with respect to “stable” North America. 相似文献
30.