پديد آورندگان :
حاتمي مهند، جلال الدين دانشگاه تهران - مؤسسه ژئوفيزيك , ثابت قدم، سمانه دانشگاه تهران - مؤسسه ژئوفيزيك - گروه فيزيك فضا , احمدي گيوي، فرهنگ دانشگاه تهران - مؤسسه ژئوفيزيك - گروه فيزيك فضا
چكيده فارسي :
ديد افقي به عنوان يكي از مهمترين ويژگيهاي نوري جو از جنبه هاي متفاوت حائز اهميت است. تعيين دقيق ديد از عوامل تاثيرگذار در سلامتي پرواز هنگام فرود و برخاست هواپيما به شمار مي رود. يك روش تعيين ديد در امتداد باند فرودگاهها، استفاده از دستگاههاي ترنسميسومتر و فوروارد اسكترومتر است كه پخش و عبوردهي نور را اندازه گيري مي كنند. در مقاله حاضر براي نخستين بار در كشور از داده هاي اين دستگاهها براي تعيين ميزان دقيق ديد در باند فرودگاه امام خميني استفاده شده است تا شرايط رخداد كمينه ديد در سالهاي 2013 و 2014 مطالعه شود. اطلاعات ايستگاه هم ديدي و متار به عنوان اطلاعات تكميلي در اين دو سال نيز به كار رفته است. داده هاي مورد استفاده شامل محدوده ديد، دما، دماي نقطه شبنم، رطوبت، تندي و جهت باد است. با در نظر گرفتن شرايط حدّي براي رخداد كمينه ديد مشاهده مي شود كه بيشترين رخداد كمينه ديد مربوط به فصل زمستان، اواخر پاييز و اوايل بهار است كه مي تواند بهدليل تاثير فعّاليت بيشتر سامانه هاي جوّي و شرايط آب و هوايي متغير در اين ماهها باشد. بررسي نوع پديدههاي جوي در ايستگاه هم ديدي فرودگاه امام در روزهاي بحراني نشان مي دهد كه عمدتاً گردوخاك، غبار، انواع مه و بارش پديدههاي غالب هستند. بر اساس نتايج دو مطالعه موردي، افزايش رطوبت نسبي و تغيير جهت باد از عواملي هستند كه در رخداد كمينه ديد نقش موثري دارند
چكيده لاتين :
Atmospheric visibility is defined as the greatest distance at which an observer can see a black object viewed against the horizon sky, which is usually known as visual range. It shows the degree to which the atmosphere is transparent to visible light, therefore its impairment results from light scattering and absorption that can originate from natural or anthropogenic sources. Visibility is an important atmospheric parameter in landing and takeoff of an aircraft. Reduced visibility due to snow, rain, fog, and haze is an important consideration in the landing and takeoff of aircraft. Visibility and the related quantity Runway Visible Range (RVR) are meteorological parameters that are crucial for the operations at an airport. The Runway Visible Range is defined as the range over which the pilot of an aircraft on the centre line of a runway can see the runway surface marking or lights delineating the runway or identifying its centre line. A large number of aviation accidents are happened cause many passengers to die. Today, safety is very important in aviation. In fact, it is a competitive factor among aviation companies. Measuring the exact visual range is one of the most important factors in flight security. According to the international standards, whenever the visual range is less than a certain threshold for runways, take-off and landing will not be authorized, and pilots will be ordered land on an alternative airport that costs airlines a lot of expenses.
One of the methods in determining the runway visual range is to use instruments such as transmisometer and forward scaterometer to measure the amount of scattering and absorption of light by the atmosphere. A transmissometer measures the extinction of light over an atmospheric path between an emitter and a receiver and it is directly related to the extinction. A forward scatter meter measures the amount of light scattered by a small measurement volume. RVR instruments usually locate at three places across each runway that is mandatory for operation in international airports.
For the first time in Iran, data obtained from the RVR system from Imam Khomeini International Airport are applied in this study to examine the circumstances under which the runway visual range reached its minimum during two years 2013 and 2014. The high accuracy of these devices is a valuable factor for researchers to get more precise results. The data used include visibility range, temperature, dew point temperature, humidity, wind speed and wind direction, which are measured using the RVR system. The main part of this study concentrates on fast decreases of RVR, meaning a decrease of visibility to below 1500 m which takes more than 10 minutes. Therefore some cases of RVR data have been investigated in more detail utilizing one-minute observations are presented. For these cases, some meteorological parameters are investigated before and after this fast decrease of RVR occurred. These parameters as well as RVR are plot to find out what happened before and during each specific event.
Results show that the critical low visibilities were mainly occurred in May and March and no cases of low visibility were seen between July to September. This can be due to the impact of more atmospheric systems and variable weather conditions in the relatively cold months. The highest visibilities were mostly occurred in July-September, due to the weakness of atmospheric systems and their less frequency of occurrences. Low visibility days were usually accompanied by dust, fog, mist and precipitation events.During 2013 and 2014, categorizing the weather events that may lead to the decrease of visibility to less than 1500 meter, shows that the 45 percent of the cases with the low visibilities caused by by dust, 35 percent by haze, 15 percent by fog and 5 percent caused by haze.
For the critical cases, case studies show that the high relative humidity and the change of wind direction were also favored in the occurrence of low visual range. Case studies of the events suggest that these factors differ from one another based on how they are formed. After the fast decreases of RVR, the relative percentage of RVR events show an increasing in relative humidity especially during fog and precipitation.
