جستجوی مقالات مرتبط با کلیدواژه « داده های ماهواره » در نشریات گروه « زمین شناسی »

Convective storms are the most atmospheric hazards that can cause significant dangers to sectors such as agriculture, industry, aviation industry and urban and rural facilities in different parts of the world. These storms are often accompanied by thunderstorms, hails, floods or severe winds. Severe dust from some convective phenomena has also been identified as air and environmental pollutant. Therefore, studing their various aspects has provided the basis for many atmospheric studies in different parts of the world.Accurate and timely forecasting of convective storms is still challenging in operational weather forecasting centers. Given that conventionally configured numerical models did not accurately predict this phenomenon in most cases, their nowcasting using satellite data is of great importance. Meanwhile, geostationary satellites have been recognized as a useful tool for identifying areas with potential convection. In this paper, an attempt is made to provide an algorithm using the Meteosat8 data to identify areas prone to the convection initiation and to improve the issuance of timely warnings in a very short time. This work has been done by studying the convective events during the day and night hours of spring and summer of 1397 in Tehran province. The present algorithm is based on  selecting 22 fields using the brightness temperature of infrared channels, the reflectance of visible and near-infrared channels and the differences and their 15 and 30 minute trends. The preprocessing performed on the satellite data are radiometric and geometric corrections. To do this, after calculating the radiance of individual channels from the digital counts, the brightness temperature of the infrared and reflectance of the visible and near infrared channels are calculated. Also to calculate the trend of the fields between two time steps, a spatial low-pass filter using the box-averaging method has been used. Large-Scale atmospheric pattern analysis of the ten strongest dust convective storm events in Tehran in the last decade shows that in most of them, at least five days before the storm, a ridge of geopotential height at the 500 hPa level developed on the area. On the day of the storm, the passage of the geopotential trough and the cold front of the surface destroyed the atmospheric stability and released the energy necessary for the development of the cumulonimbus cloud and the occurrence of the storm. Finally results show that using this algorithm to nowcasting the convective initiation, the probability of detection and correct alarm rate are 62 and 79 percent, respectively.

Dust storms are significant phenomenon in south west Asian countries like Iraq, Syria and Iran. Mineral dust is generated by wind erosion over arid and semiarid land surfaces and is transported locally and over vast distances, causing adverse environmental and weather problems. Recent draughts over dust sources in Iraq and Syria have remarkably increased dust events in the area particularly over west of Iran. Real time prediction of dust storms especially quantitative forecasting of dust concentration has become highly desirable to alleviate its damaging consequences. In this study the impact of the assimilation of satellite radiance, prepbufr and GPSro data in the wind speed and dust load forecasts of WRF-Chem model using WRFDA system are investigated. Prepbufr data are a collection of surface and upper air observations and GPSro data are GPS radio occultation data. These data are operationally collected by the National Centers for Environmental Prediction (NCEP). Data assimilation is applied to two dust events starting from Iraq and Syria borders on August 31st 2015 and June 15th 2016. For each case, two experiments are conducted. An experiment assimilating above mentioned data with three dimensional variational (3D-Var) intermittent assimilation method and a control simulation with no assimilation. The assimilation cycles in the intermittent method consist of three subsequent analyses at 00, 06 and 12 UTC. After the last assimilation cycle, the model is integrated for 48 hours in the future. In variational data assimilation a key element to get a qualified analysis is the accurate specification of error statistics for the background forecast. For the calculation of background error, the model with the same specification for the experiments is run for the whole January 2014 at 0000 and 1200 UTC and the 12- and 24-h forecasts are used to calculate the background error using the National Meteorological Center (NMC) method with CV5 option. The horizontal resolution of the domain is 21 km with 142×130 grid points covering Iran and western neighboring countries. The model has 41 vertical levels with the model top at 25 hPa. Initial and boundary conditions are taken from NCEP Global Forecast System (GFS) model with the horizontal resolution of 0.5º×0.5º.Results show that the agreement between spatial distribution of dust load prediction of the model and Meteosat-10 satellite RGB images is improvedusing data assimilation especially in first forecast hours. Quantitative comparison of 10 m, 850 hPa and 700 hPa model wind speed with surface observation data and ERA-Interim ECMWF reanalysis data show up to 11% improvement in RMSE especially in first forecast hour times. The positive impact of data assimilation is decreased as the forecast length increases

Dust aerosols make a considerable contribution to the climate system through their radiative effects due to their abundance in the atmosphere. Recent observations suggest that over the past decade, dust events have become more frequent in many parts of Iran, especially in the west and southwest. Through their radiative forcing, dust aerosols have significant effects on the regional radiation budget of the atmosphere, while their adverse effects on human health have also raised serious concerns. The primary aim of the present study is to examine the radiation effects associated with a severe dust storm that occurred in west and southwest Iran on 16 to 21 June 2012. To this end, the Weather Research and Forecasting with Chemistry (WRF-Chem) model was used. Two simulations were conducted: a model setup that did not include dust aerosols, and the one that included dust aerosols and their feedback to the atmosphere. A two-way interactive nested domain (nesting ratio:1:3) simulations were performed using 98 Í 90 and 151 Í 139 horizontal grid points, respectively. In the vertical, 27 σ-levels were used. The grid spacing for the two domains were 45 and 15 km, respectively. Simulations ran from 16 to 22 June 2012, and the first 24 hours was considered as the spin-up time. Meteorological initial conditions were obtained from the Global Forecast System (GFS) data at 0.5˚Í 0.5˚ resolution. The performance of the model was evaluated using the available observed data, including PM10 observations in Ahwaz located in southwest Iran, available AErosol RObotic NETwork (AERONET) data in nearby areas, and aerosol products of the Moderate Resolution Imaging Spectroradiometer (MODIS), the Ozone Monitoring Instrument (OMI) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) carried on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) spacecraft. Results indicate that PM10 concentration in Ahwaz is overestimated by the model, while simulated aerosol optical depth (AOD) is underestimated compared to the observed AERONET data. Relatively, good agreement is found between the model results and satellite products, and temporal evolution of the dust events is also well-simulated. Thus, generally, the performance of the model is acceptable for accurate simulation of the dust event. Our analysis indicated that radiative effects of dust particles cause cooling at the surface and top of the atmosphere, but warming in the middle of the troposphere. On average, perturbation of shortwave radiation by dust aerosols in the west, and southwest Iran is estimated to be -7.27, 1.79 and -5.47 W m-2 at the surface, in the middle and at the top of the atmosphere, respectively. Average perturbation of the longwave radiation by dust aerosols over the same region was estimated to be 2.2, -1.61 and 0.59 W m-2 at the surface, in the middle and at the top of the atmosphere, respectively. Thus, the net (shortwave longwave) radiative effect of dust aerosols averaged in west and southwest Iran is found to be -5.07, 0.19 and -4.88 W m-2 at the surface, in the middle and at the top of the atmosphere, respectively.