排序方式： 共有5条查询结果，搜索用时 0 毫秒
1
1.
Abbas-Ali A Bidokhti Maryam Gharaylou Nafiseh Pegahfar Samaneh Sabetghadam Maryam Rezazadeh 《Journal of Earth System Science》2016,125(2):431-442
Determination of dust loading in the atmosphere is important not only from the public health point of view, but also for regional climate changes. The present study focuses on the characteristics of two major dust events for two urban areas in Iran, Kermanshah and Tehran, over the period of 4 years from 2006 to 2009. To detect extreme dust outbreaks, various datasets including synoptic data, dust concentration, reanalysis data and numerical results of WRF and HYSPLIT models were used. The weather maps demonstrate that for these events dusts are mainly generated when wind velocity is high and humidity is low in the lower troposphere and the region is under the influence of a thermal low. The event lasts until the atmospheric stability prevails and the surface wind speed weakens. The thermal low nature of the synoptic conditions of these major events is also responsible for deep boundary layer development with its thermals affecting the vertical dust flux over the region. Trajectory studies show that the dust events originated from deserts in Iraq and Syria and transported towards Iran. The main distinction between the two types of mobilizations seems to affect the dust concentrations in the Tehran urban area. 相似文献
2.
Natural Hazards - The first hourly observations of thunderclouds and associated lightning events for Tehran area are presented in this paper. Hourly data of Cloud to Ground (CG) lightning events in... 相似文献
3.
A one-dimensional Explicit Time-dependent cloud Model (ETM): Description and validation with a three-dimensional cloud resolving model 总被引：2，自引：0，他引：2
An algorithm for a one-dimensional Explicit Time-dependent cloud Model (ETM) that takes into account non-hydrostatic pressure, entrainment, cloud microphysics, lateral and vertical eddy mixing processes is developed and tested against a state-of-the-art cloud resolving three dimensional mesoscale model—the Advanced Regional Prediction System (ARPS). The numerical schemes and sub-grid scale processes are rather similar in both ETM and ARPS, although the dimensionality is different.Results show that the ETM is able to simulate the complete lifecycle for a cloud cell, featuring comparable zones of maximum vertical velocity, and overshooting layers on the cloud top. Heat and moisture fluxes within the cloud column of the ETM occur at the same level as ARPS, giving confidence towards adequate formulations in ETM. However, mass flux fields are not in good agreement; there is significant difference in intensity and the altitude where maxima occur. Sensitivity of the ARPS cloud to the amplitude and depth of the initial thermal bubble was examined; the resulting cloud showed sensitivity to both parameters. The maximum vertical velocity decreases with greater amplitude and occurs earlier. This was used as a tuning parameter to ensure similarity in the lifecycle of ETM and ARPS clouds. 相似文献
4.
Reza Khandan Seyed Kazem Alavipanah Arastoo Pour Biazar Maryam Gharaylou 《Asia-Pacific Journal of Atmospheric Sciences》2018,54(3):431-443
Geostationary satellites are able to nowcast Convective Initiation (CI) for the next 0–6 h. Compared to using satellite predictors only, the incorporation of satellite and Numerical Weather Prediction (NWP) predictors can provide the possibility to reduce false alarm rates in 0–1:30 Convective Initiation Nowcasting (COIN). However, the correlation among these predictors not only can cause error in COIN, but also increases the runtime. In this study for the first time, all effective predictors in Satellite Convection Analysis and Tracking version 2 (SATCASTv2) and NWP were applied over Iran from 22nd March 2015 to 9th January 2016. In applying SATCASTv2 over Iran, it was necessary to make some modifications to the algorithm, such as removing case specific thresholds of satellite predictors and rearranging COIN predictors. Then, SATCASTv2 was tested and evaluated with both the full and reduced set of predictors. The results suggested that using fixed thresholds for temporal difference predictors could miss COIN in some cases. To investigate the possibility of improving computational efficiency, a dimension reduction was conducted by Factor Analysis (FA) and the number of predictors was reduced from 22 to 11. The NWP-satellite, reduced NWP-satellite, and satellite predictors were used as input in Random Forest (RF), as a parametric machine learning method, for COIN evaluation. The Combination of NWP model and satellite predictors had lower false alarm rates in contrast with satellite predictors. This is in agreement with previous studies. The results from statistical metrics showed that the reduced NWP-satellite predictors had comparable performance to the NWP-satellite predictors over study area, but decreased the run time by almost 50%. The results indicated that Convective Inhibition (CIN) was the most significant predictor when the reduced set of predictors was used. 相似文献
5.
Maryam Gharaylou Peyman Zawar-Reza Abbas-Ali A. Bidokhti Majid-M. Farahani 《Meteorology and Atmospheric Physics》2013,122(3-4):145-158
A one-dimensional Explicit Time-dependent Tilting cloud Model (ETTM) that separates updraft and downdraft columns and takes into account the effect of cloud tilting on precipitation is introduced and incorporated into the Advanced Regional Prediction System (ARPS). Results of the stand-alone ETTM are compared with that of cloud resolving simulations using the ARPS mesoscale model. Inter-comparison is performed by qualitative examination of simulated parameters such as vertical distribution of fluxes of mass, heat, and moisture. Although there is a great degree of similarity between the vertical profiles, ETTM systematically underestimates magnitudes of all fluxes. Sensitivity tests carried with ETTM show that the effect of varying cloud radius and tilting angle is considerable on the simulated cloud behavior. Increasing the cloud radius, results in a corresponding increase in fluxes of mass, heat, and moisture, while increasing the cloud tilt angle has the opposite effect. Since ETTM showed promise as a suitable sub-grid cumulus parameterization scheme; it was incorporated into ARPS as an additional cumulus parameterization scheme (CPS) to be available for the wider community. Results of simulations using ETTM and other CPSs already available in ARPS were compared for 2, 4 and 10 km grid spacings to assess its utility. Simulation results of the 2 km grid showed that at this resolution, the simulated time series of updraft velocities using the new scheme (ETTM) compared well with the results of other schemes in the ARPS model. The simulations with horizontal resolution of 4 km that was compared with the convection resolving reference run (No-CPS-2KM) showed almost consistent results for all schemes except for one using KF scheme. The results of the simulation with the ETTM scheme and other schemes in the model with resolution of 10 km showed that at this resolution, there is not significant difference between the uses of these schemes. 相似文献
1