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1.
The pre-monsoon convective atmosphere over Kolkata (22.52°N, 88.37°E) during STORM field phase 2006–2008 is investigated using 12 UTC radiosonde data and thermodynamic indices. In the present study, an attempt has been made to assess the skill of various indices and parameters and to propose suitable threshold values in forecasting the occurrence of thunderstorm activity at Kolkata. The thermodynamic indices and parameters used in the present study are lifted index (LI), K index (KI), severe weather threat index (SWEAT), total totals index (TTI), convective available potential energy (CAPE), deep convection index (DCI), humidity index (HI), Boyden index (BI), dew point temperature at 850 hpa (DEW), relative humidity at 700 hpa (RH), and bulk Richardson number (BRN). Validation of the suggested threshold values of indices was conducted on the days of thunderstorm activity. It was found that one index alone cannot predict the occurrence of thunderstorm over Kolkata region. The present study suggests that the indices with highest skill for thunderstorm prediction are KI, DCI, SWEAT, DEW, HI, RH, LI, TTI, while the prediction efficiency is poor for CAPE, BRN, and BI. Observed values of these indices also reveal that scattered, multi-cellular thunderstorms are possible over Kolkata during pre-monsoon months.  相似文献   

2.
S. Chaudhuri  A. Middey 《Atmósfera》2013,26(1):125-144
Studying the boundary layer is imperative because severe weather in this portion of the atmosphere impacts on environment and various facets of national activities and affects the socioeconomic scenario of a region. Near surface boundary layer characteristics are investigated through the vertical variation of fluxes of heat, moisture, momentum, kinetic energy and Richardson number during the pre-monsoon season (April-May) at Kharagpur (22° 30’ N, 87° 20’ E) and Ranchi (23° 32’ N, 85° 32’ E) with 50 and 32 m tower data, respectively, on thunderstorm and non-thunderstorm days. The temporal variation of fluxes within the boundary layer and the kinetic energy at different logarithmic heights are observed to vary significantly between thunderstorm and non-thunderstorm days. The heat and momentum fluxes show a maximum peak while the moisture flux shows a sudden attenuation just before the occurrence of thunderstorms. The wind field depicts to play a crucial role at the inland station Kharagpur, which is in the proximity of the Bay of Bengal, compared to the station Ranchi, situated over hilly terrain on Chotanagpur. The micrometeorological study of the boundary layer reveals a significant finding pertaining to observe the passage of thunderstorms. It is observed that the ratio of the potential temperature (θ) and equivalent potential temperature (θe) remains confined within a critical range between 0.85 and 0.90 during the passage of thunderstorms.  相似文献   

3.
The upper air RS/RW (Radio Sonde/Radio Wind) observations at Kolkata (22.65N, 88.45E) during pre-monsoon season March–May, 2005–2012 is used to compute some important dynamic/thermodynamic parameters and are analysed in relation to the precipitation associated with the thunderstorms over Kolkata, India. For this purpose, the pre-monsoon thunderstorms are classified as light precipitation (LP), moderate precipitation (MP) and heavy precipitation (HP) thunderstorms based on the magnitude of associated precipitation. Richardson number in non-uniformly saturated (R i *) and saturated atmosphere (R i ); vertical shear of horizontal wind in 0–3, 0–6 and 3–7 km atmospheric layers; energy-helicity index (EHI) and vorticity generation parameter (VGP) are considered for the analysis. The instability measured in terms of Richardson number in non-uniformly saturated atmosphere ( \(R_{i}^{\mathrm {\ast } })\) well indicate the occurrence of thunderstorms about 2 hours in advance. Moderate vertical wind shear in lower troposphere (0–3 km) and weak shear in middle troposphere (3–7 km) leads to heavy precipitation thunderstorms. The wind shear in 3–7 km atmospheric layers, EHI and VGP are good predictors of precipitation associated with thunderstorm. Lower tropospheric wind shear and Richardson number is a poor discriminator of the three classified thunderstorms.  相似文献   

4.
Thunderstorms are of much importance in tropics, as this region is considered to have central role in the convective overturn of the atmosphere and play an important role in rainfall activity. It is well known that El Niño and La Niña are well associated with significant climate anomalies at many places around the globe. Therefore, an attempt is made in this study to analyze variability in thunderstorm days and rainfall activity over Indian region and its association with El Niño and La Niña using data of thunderstorm day’s for 64 stations well distributed all over India for the period 1981–2005 (25 years). It is seen that thunderstorm activity is higher and much variable during pre-monsoon (MAM) and southwest monsoon (JJAS) than the rest of the year. Positive correlation coefficients (CCs) are seen between thunderstorms and rainfall except for the month of June during which the onset of the southwest monsoon sets over the country. CCs during winter months are highly correlated. Composite anomalies in thunderstorms during El Niño and La Niña years suggest that ENSO conditions altered the patterns of thunderstorm activity over the country. Positive anomalies are seen during pre-monsoon (MAM) and southwest monsoon months (JAS) during La Niña years. Opposite features are seen in southwest monsoon during El Niño periods, but El Niño favors thunderstorm activity during pre-monsoon months. There is a clear contrast between the role of ENSO during southwest monsoon and post-monsoon on thunderstorm activity over the country. Time series of thunderstorms and precipitation show strong association with similarities in their year-to-year variation over the country.  相似文献   

5.
This study assesses the impact of Doppler weather radar (DWR) data (reflectivity and radial wind) assimilation on the simulation of severe thunderstorms (STS) events over the Indian monsoon region. Two different events that occurred during the Severe Thunderstorms Observations and Regional Modeling (STORM) pilot phase in 2009 were simulated. Numerical experiments—3DV (assimilation of DWR observations) and CNTL (without data assimilation)—were conducted using the three-dimensional variational data assimilation technique with the Advanced Research Weather Research and Forecasting model (WRF-ARW). The results show that consistent with prior studies the 3DV experiment, initialized by assimilation of DWR observations, performed better than the CNTL experiment over the Indian region. The enhanced performance was a result of improved representation and simulation of wind and moisture fields in the boundary layer at the initial time in the model. Assimilating DWR data caused higher moisture incursion and increased instability, which led to stronger convective activity in the simulations. Overall, the dynamic and thermodynamic features of the two thunderstorms were consistently better simulated after ingesting DWR data, as compared to the CNTL simulation. In the 3DV experiment, higher instability was observed in the analyses of thermodynamic indices and equivalent potential temperature (θ e) fields. Maximum convergence during the mature stage was also noted, consistent with maximum vertical velocities in the assimilation experiment (3DV). In addition, simulated hydrometeor (water vapor mixing ratio, cloud water mixing ratio, and rain water mixing ratio) structures improved with the 3DV experiment, compared to that of CNTL. From the higher equitable threat scores, it is evident that the assimilation of DWR data enhanced the skill in rainfall prediction associated with the STS over the Indian monsoon region. These results add to the body of evidence now which provide consistent and notable improvements in the mesoscale model results over the Indian monsoon region after assimilating DWR fields.  相似文献   

6.
Thunderstorms are the recurrent features of India and are responsible for the redistribution of excess heat and moisture in the atmosphere. However, the thunderstorms that occur over the urban station Kolkata (22°34′N, 88°22′E), India, during the pre-monsoon months of April and May are extremely devastating while accompanied with high wind speed, lightning flashes, torrential rain and occasional hail and tornadoes. The development and verification of a model output are described in this study. The system consists of multiple linear regression (MLR) equations, and the purpose is to nowcast the categories of thunderstorms over Kolkata, both ordinary (wind speed <65 km h?1) and severe (wind speed ≥65 km h?1) as per the warning provided by the India Meteorological Department for the prevalence of thunderstorms. The MODIS terra/aqua satellite data of cloud parameters, ground-based Radiosonde/Rawinsonde upper air observations and records of wind speed accompanied with thunderstorms over Kolkata are considered for the study. The MLR models are formulated with the cloud parameters as input and the target output being the peak wind speed associated with the pre-monsoon thunderstorms. The MLR model is trained with the data and records from 2002 to 2009, and the results are validated with the observations of 2010 and 2011. The results reveal that the accuracy in nowcasting the ordinary and severe categories of thunderstorms during the pre-monsoon season over Kolkata with MLR models are 94.26 and 91.29 %, respectively, with lead time <12 h.  相似文献   

7.
In this study, an attempt has been made to bring out the observational aspects of vertical wind shear in thunderstorms over Minicoy. Case studies of thunderstorm events have been examined to find out the effect of vertical wind shear and instability on strength and longevity of thunderstorms. Role of vertical wind shear in thunderstorms and its mechanism has been explored in this study. Results reveal that for prolonged thunderstorms high and low instability along with moderate to high vertical wind shear (moderate: 0.003 S−1 ≤ vertical wind shear ≤ 0.005 S−1 and high: > 0.005 S−1) play a significant role in longevity and strength of thunderstorms. The mechanism of vertical wind shear in thunderstorms was investigated in a few cases of thunderstorm events where the duration of thunderstorm was covered by the radiosonde/rawin ascent observation taken at Minicoy. Empirical model has been developed to classify thunderstorm type and to determine the strength and longevity of thunderstorms. Model validation has been carried out for selected cases. Model could classify thunderstorm type for most of the cases of thunderstorm events over island and coastal stations.  相似文献   

8.
Relationship of outgoing long-wave radiation (OLR) with convective available potential energy (CAPE) and temperature at the 100-hPa pressure level is examined using daily radiosonde data for a period 1980–2006 over Delhi (28.3°N, 77.1°E) and Kolkata (22.3°N, 88.2°E), and during 1989–2005 over Cochin (10°N, 77°E) and Trivandrum (8.5°N, 77.0°E), India. Correlation coefficient (R xy) between monthly OLR and CAPE shows a significant (~???0.45) anti-correlation at Delhi and Kolkata suggesting low OLR associated with high convective activity during summer (seasonal variation). Though, no significant correlation was found between OLR and CAPE at Cochin and Trivandrum (low latitude region); analysis of OLR and temperature (at 100-hPa) association suggests that low OLR peaks appear corresponding to low temperature at Delhi (R xy~ 0.30) and Kolkata (R xy ~ 0.25) during summer. However, R xy between OLR and temperature becomes opposite as we move towards low latitudes (~8°–10°N) due to strong solar cycle influence. Large scale components mainly ENSO and quasi-biennial oscillaton (QBO) that contributed to the 100-hPa temperature variability were also analyzed, which showed that ENSO variance is larger by a factor of two in comparison to QBO over Indian region. ENSO warm conditions cause warming at 100-hPa over Delhi and Darwin. However, due to strong QBO and solar signals in the equatorial region, ENSO signal seems less effective. QBO, ENSO, and solar cycle contribution in temperature are found location-dependent (latitudinal variability) responding in consonance with shifting in convective activity regime during El Niño, seasonal variability in the tropical easterly jet, and the solar irradiance.  相似文献   

9.
Monthly variations of lightning activity over typical land and oceanic regions of India were examined using satellite data (OTD) for a 5-year period (1995–1999). It is noted that the nature of variation between surface air maximum temperature (T max), thunderstorm days (Thn), and lightning flash count over ER and WR showed remarkable correspondence and sensitivity with each other on monthly time scale. As we move out of winter season and enter the monsoon season, via pre-monsoon season, the WR undergoes cooling relative to the ER in the range 0.1–1.2°C. As a result, WR experiences reduction of thunder days and lowering in flash count. This decrease in T max, Thn, and flash count over WR may also be associated with relatively small values of T θw and CAPE in comparison with similar values over ER during the monsoon season. Our observation of associated reduction in Thn and lightning count per 1°C cooling in surface air maximum temperature suggests reduction of ∼3.5 thunderstorms per station and 73 flashes. Comparison of lightning flashes between pairs of coastal, oceanic, arid-zone, hilly, and island stations reveals distinct relationship between climate regime and intensity of lightning activity. We may conclude the results of this study by saying that the overhead lightning activity is a clear reflection of the status of the underlying ground-earth properties. A close and continuous monitoring of lightning activity may be considered as a need of present day scientific studies.  相似文献   

10.
Extreme weather events such as cloudburst and thunderstorms are great threat to life and property. It is a great challenge for the forecasters to nowcast such hazardous extreme weather events. Mesoscale model (ARPS) with real-time assimilation of DWR data has been operationally implemented in India Meteorological Department (IMD) for real-time nowcast of weather over Indian region. Three-dimensional variational (ARPS3DVAR) technique and cloud analysis procedure are utilized for real-time data assimilation in the model. The assimilation is performed as a sequence of intermittent cycles and complete process (starting from reception, processing and assimilation of DWR data, running of ARPS model and Web site updation) takes less than 20 minutes. Thus, real-time nowcast for next 3 h from ARPS model is available within 20 minutes of corresponding hour. Cloudburst event of September 15, 2011, and thunderstorm event of October 22, 2010, are considered to demonstrate the capability of ARPS model to nowcast the extreme weather events in real time over Indian region. Results show that in both the cases, ARPS3DVAR and cloud analysis technique are able to extract hydrometeors from radar data which are transported to upper levels by the strong upward motion resulting in the distribution of hydrometeors at various isobaric levels. Dynamic and thermodynamic structures of cloudburst and thunderstorm are also well simulated. Thus, significant improvement in the initial condition is noticed. In the case of cloudburst event, the model is able to capture the sudden collisions of two or more clouds during 09–10 UTC. Rainfall predicted by the model during cloudburst event is over 100 mm which is very close to the observed rainfall (117 mm). The model is able to predict the cloudburst with slight errors in time and space. Real-time nowcast of thunderstorm shows that movement, horizontal extension, and north–south orientation of thunderstorm are well captured during first hour and deteriorate thereafter. The amount of rainfall predicted by the model during thunderstorm closely matches with observation with slight errors in the location of rainfall area. The temporal and spatial information predicted by ARPS model about the sudden collision/merger and broken up of convective cells, intensification, weakening, and maintaining intensity of convective cells has added value to a human forecast.  相似文献   

11.
We estimate, from the moisture budget the bulk aerodynamic coefficient for latent heat flux (C e) during the monsoon season over the central Arabian Sea. The average value ofC eunder active monsoon conditions was found to be 2.25 × 10−3 which is nearly 60% higher than those previously used.  相似文献   

12.
Deterministic seismic microzonation of Kolkata city   总被引：1，自引：0，他引：1  
This paper presents the deterministic seismic microzonation of densely populated Kolkata city situated on the world’s largest delta island with very soft and thick soil deposit in the surficial layers. A fourth-order accurate staggered-grid finite-difference algorithm for SH-wave propagation simulation in visco-elastic medium is used for the linear computation of ground motion amplifications in sedimentary deposit. Different maps such as for fundamental frequency (F 0), peak ground acceleration (PGA), peak ground velocity, and peak ground displacement are developed for variety of end-users communities, including structural and geotechnical engineers for performance-based designs, building officials, emergency managers, land-use planners, private businesses, and the general public. The scenario of simulated amplification factors in the different frequency bands revealed that the Kolkata city is very much prone to severe damage even during a moderate earthquake and very selective damage may occur at some of the localities during local and distant earthquakes. The deterministically predicted PGA at bedrock level is 0.0844 g and the maximum PGA predicted at the free surface is 0.6 g in Kolkata city due to maximum credible earthquake (M w = 5.4) associated with Eocene Hinge Zone at a depth of 36 km. The seismic microzonation of Kolkata city reveals that the Nager Bazar and Nimtala areas are the safest regions with earthquake point of view.  相似文献   

13.

The frequency and severity of occurrence of meteorological droughts in different climatic regions depend on regional climatic factors. This study has made an effort to explore the relationship of range of annual temperature variation at a given place with the frequency of occurrence of drought and the maximum magnitude of seasonal rainfall deficit (i.e., severity). The seasonal rainfall refers to sum of monsoon season (rainy season) rainfall in India. The monthly precipitation data of 113 years (1901–2013) for 256 stations in different parts of India have been used to estimate the return period of meteorological drought at different stations. The daily normal values of observed maximum and minimum temperatures from 40 years of records have been utilized to estimate range of temperature variation (θR) during the year at each stations. In various parts of India, the θR ranges from 10 °C in humid regions to 40 °C in arid regions. The various climatic regions have been experiencing maximum deficiency of annual rainfall ranging from 30% (humid) to 90% (arid). The results reveal that places exhibiting θR values between 40 to 30 °C face more frequent droughts with average frequency of once in 3 to once in 6 years. The occurrence of extreme and severe drought events is more frequent in the regions with higher values of θR compare to that in lesser values of θR. The regions with θR values between 30 to 25 °C mostly face severe and moderate events having the average drought return period of 6–9 years, and the occurrence of extreme droughts in these regions is rare. Furthermore, regions with θR?<?20 °C face moderate droughts only with an average return period of 14 years. This study divulges that the average return period and magnitude of deficiency of drought events have notable relationship with the range of temperature variation during the year at a given place.

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14.
The paper deals with the study of the physical and dynamical characteristics of a severe thunderstorm, which had occurred on April 5, 2015, at about 2100 UTC in the southwestern Bangladesh with location around 23.3–23.7N and 89.0–89.4E within the upazilas (sub-districts) of Kumarkhali and Shailkupa under the districts of Kushtia and Jhenaidah, respectively. The thunderstorm was associated with numerous hails of large size. More than 5000 birds which used to live in the bird sanctuary at Shailkupa and 22,011 birds in Chhaglapara Bird Sanctuary of Kumarkhali died as they were hit by the hails. Large hails also damaged crops, houses and forests over the thunderstorm hit areas. The evolution of the thunderstorm is studied by the WRF model, which is initialized using the National Centers for Environmental Prediction Final reanalysis data of 0000 UTC of April 5, 2015. The simulated results provide a basis to study the physical and dynamical characteristics of the thunderstorm, which are generally not identified by the meteorological observations which are too sparse. The model has captured a micro-low over Kumarkhali and its neighborhood, which favored the occurrence of the severe thunderstorm. The model simulated rainfall is about 26 mm near the place of occurrence, which matches well with the area where the reflectivity of hydrometeor is maximum. The convective available potential energy is found to be 1600 J kg?1 at 1730 UTC near the place of occurrence of the thunderstorm; this indicates high atmospheric instability over the thunderstorm location for the formation of the thunderstorm. The vertical velocity, convergence, cloud water mixing ratio and the ice water mixing ratio and their vertical extensions are found to be satisfactory and responsible for the occurrence of large hails associated with the thunderstorm.  相似文献   

15.
Shen  Chaomin  Liu  Sihong  Xu  Siyuan  Wang  Liujiang 《Acta Geotechnica》2019,14(4):991-1001

Maximum and minimum void ratios (emax and emin) of granular soils are commonly used as indicators of many engineering properties. However, few methods, apart from laboratory tests, are available to provide a rapid estimation of both emax and emin. In this study, we present a theoretical model to map the densest and the loosest packing configurations of granular soils onto the void space. A corresponding numerical procedure that can predict both emax and emin of granular soils with arbitrary grain size distributions is proposed. The capacity of the proposed method is evaluated by predicting the maximum and minimum void ratios of medium to fine mixed graded sands with different contents of fines. The influence of the grain size distribution, characterized quantitatively by uniformity parameter and the fractal dimension, on emax and emin is discussed using the proposed method. Moreover, application of this method in understanding the controlling mechanism for the void ratio change during grain crushing is presented.

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16.
Priya  Kumari  Nadimpalli  Raghu  Osuri  Krishna K. 《Natural Hazards》2021,109(2):1655-1674

The timely prediction of thunderstorms (TS) is always a challenging task for operational and research community. The present study is aimed to address the credibility of the high grid-spacing and downscaling approach for improved simulation of TS. Fourteen TS are simulated with different domain configurations using weather research and forecasting (WRF) model. Two nested domains with 9–3 km (known as DD3), and 6–2 km (DD2), and 3 km single domain (SD3) are considered for simulations. Results indicate that the high-resolution DD2 has improved 2-m temperature (T2), 2-m relative humidity (RH2), and 10-m wind speed (WS10) at different stages of TS. The average mean error of T2 and RH2 in the DD2 experiment is 0.7 °C, ??6% during the mature stage, and 0.2 °C, ??4% at dissipating stage. The error in SD3 and DD3 is relatively higher (9–17% for T2 and 20–60% for RH2). Better horizontal and vertical representation of thermodynamic variables in DD2 run reinforces the atmosphere to initiate and intensify the convection in the right place. The DD2 could show slightly higher instability (convective available potential energy, CAPE, 3188 J kg?1) as compared with DD3 (3164 J kg?1) and SD3 (3020 J kg?1). The model is biased to simulate early TS activity. DD2 run could simulate the formation, mature and dissipation stages with fewer timing errors (??1.35 h, ??1.5 h, and ??2.6 h, respectively) than other experiments. The critical success index of the DD2 run is higher for all the rainfall thresholds; however, it is more than 0.2 up to 2.5 mm h?1. The results highlight that high resolution nested configuration yields better simulation skills than the single domain configuration.

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17.
PENG GAO 《Sedimentology》2012,59(6):1926-1935
A recently developed bedload equation (Abrahams & Gao, 2006) has the form ib = ωG3˙4, where ib is the immersed bedload transport rate, ω is the stream power per unit area, G = 1?θc/θ, θ is the dimensionless shear stress and θc is the associated threshold value for the incipient motion of bed grains. This equation has a parsimonious form and provides good predictions of transport rate in both the saltation and sheetflow regimes (i.e. flows with low and high θ values, respectively). In this study, the equation was validated using data independent of those used for developing it. The data represent bedload of identical sizes transported in various steady, uniform, fully rough and turbulent flows over plane, mobile beds. The equation predicted ib quite well over five orders of magnitude. This equation was further compared with six classic bedload equations and showed the best performance. Its theoretical significance was subsequently examined in two ways. First, based on collision theory, the parameter G was related to the ratio of grain‐to‐grain collisions to the total collisions including both grain‐to‐grain and grain‐to‐bed collisions, Pg by Pg = G2, suggesting that G characterizes the dynamic processes of bedload transport from the perspective of granular flow, which partly accounts for the good performance of the equation. Moreover, examining the ability of two common equations to predict bedload in gravel‐bed rivers revealed that G can also be used to simplify equations for predicting transport capacities in such rivers. Second, a simple dimensionless form of the equation was created by introducing B = ib/ω. The theoretical nature of the term B was subsequently revealed by comparing this equation with both the Bagnold model and two commonly used parameters representing dimensionless bedload transport rates.  相似文献   

18.
Raddatz  R. L. 《Natural Hazards》2003,29(2):113-122
On the Canadian Prairies, a significantportion of the transpiration is derived from a ratherhomogenous agro-ecosystem comprised of springwheat and other annual C3 field crops with similar water use patterns. The seasonal pattern oftranspiration is determined, to alarge extent, by crop phenology. By increasing thespecific humidity of the atmospheric boundarylayer, regional transpiration has a large positive effect on themagnitude of the potential energy available fordeep convection and thus, on the likelihood of occurrence andintensity of severe thunderstorms. Acomparison of the average wheat phenologycurve, for a representative aridgrassland and for a representativetransitional grassland site, with theaverage number of tornado days per week inthe entire eco-climatic zone demonstrated that the twoare linked. With increasing atmospheric concentrations ofCO2, the physiological response of C3 cropsmight lower transpiration rates and climate warming may advance cropseeding dates. The former would reduce the specifichumidity of the convective boundary layer, and thereby, reducethe potential energy available for deep convection.Thus, future summer severe weather seasons might, on average,be more benign and occur earlier in the seasonthan at present. This conclusion is far from certain as there are amultitude of complex feedback mechanisms. What ismore certain is that global circulation models (GCMs) mustadequately handle the inter-action between theatmosphere and the agro-ecosystem of the Canadian Prairies beforethey can correctly simulate the thermodynamic propertiesof the convective boundary layer and determine the impactof increasing atmospheric concentrations of CO2 onfuture summer severe weather.  相似文献   

19.
In this study, monthly, quarterly, and annual frequency data of thunderstorm days of 25 long-term synoptic weather stations during the period from 1960 to 2010 were analyzed applying Ward’s Hierarchical Cluster Analysis (WHCA) Method and Kriging Geostatistical Method (KGM). The results of temporal analysis of Thunderstorm Days (TD) in Iran showed that in terms of frequency, seasonal occurrence of this phenomenon is mostly in transitional seasons of spring and autumn. The results of WHCA to find homogeneous places in terms of synchronization and timing of TD reflects the fact that there are five clusters with similar memberships, including the North West, West, the southern part, northern, central, and northeastern parts, eastern regions, and center of Iran, and in this classification, the frequency of occurrence of TD reduces in the same order the regions are mentioned. In contrast, the lowest frequency of TD is in summer and winter seasons. In this study, it was found that among various deterministic and geostatistical methods, KGM is the most suitable one for thunderstorms hazard zonation and for classifying the different regions based on thunderstorm occurrence; WHCA is more suitable than other methods. The results of spatial analysis of thunderstorms point to the fact that the core of the mentioned thunderstorms is mostly in mountainous areas, particularly, highlands of North West and West of Iran. With regard to place, in the West part of the country, especially North West (Tabriz, Oroomieh, and Zanjan stations) and West, thunderstorms have higher frequencies, while the South East, South, Central, and eastern regions are less affected by the thunderstorm hazard.  相似文献   

20.
Calcite and aragonite have been modeled using rigid-ion, two-body Born-type potentials, supplemented by O-C-O angular terms inside the CO3 groups. A shell model has also been developed for calcite. Atomic charges, repulsive parameters and force constants have been optimized to reproduce the equilibrium crystal structures, the elastic constants and the Raman and infrared vibrational frequencies. The rigid-ion potential RIM (atomic charges:z O= -0.995e,z C = 0.985e,z Ca = 2.0e) fitted to calcite properties is able to account for those of aragonite as well. Experimental unit-cell edges, elastic constants, internal and lattice frequencies are reproduced with average relative errors of 2.1, 5.5, 2.4, 15.1% for calcite and of 0.2, 19.4, 2.5, 11.8% for aragonite, respectively. The RIM potential is suitable for thermodynamic and phase diagram simulations in the CaCO3 system, and is discussed and compared to other potentials.  相似文献   

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