Investigation of Surface Duct Conditions over Istanbul, Turkey

Abstract

A comprehensive examination of 2 yr of radiosonde data to determine the surface duct conditions over Istanbul (4°N, 29°E), Turkey, was made. The refractivity of the atmosphere is a function of air temperature and water vapor pressure. Any negative gradient in the modified refractivity results in the presence of a duct in the atmosphere. Therefore, the occurrence of ducts strongly depends upon both the synoptic and the local meteorological conditions that prevail over the region. The characteristics of surface ducts occurring over Istanbul were examined statistically. It was found that most of the ducts occur in May and July. The highest occurrence rate of surface ducts was observed in the summer season, and the lowest rate was observed in the winter season. The median duct thickness and duct strength are found to be the highest and the strongest in summer, whereas they are the lowest and the weakest in winter. When the data are separated into stable and unstable atmospheric subgroups, it is seen that surface duct characteristics show clear seasonal differences. Surface ducts in a stable atmosphere are found to be stronger than those in an unstable atmosphere. Also, daytime (1200 UTC) surface ducts occur more frequently than nighttime (0000 UTC) surface ducts in Istanbul. These statistics are discussed in association with local meteorological conditions and weather systems affecting the Istanbul region, and comments are made on the importance of their possible consequences in the region.

Statistical estimations of atmospheric duct over the South China Sea and the tropical eastern Indian Ocean

“…An effective method for duct detection is to use radiosonde to measure height dependence of temperature, pressure and humidity [3][4][5]. Although there are roughly 850 radiosonde stations in the global range, their geographic distribution is inhomogeneous and the density over the oceans is very low [6].…”

“…Elevated duct occurrence is moderate of the three with probability of 43.7%. This occurrence distribution could be attributed to (1) in the tropical oceans, the seawater evaporation is very strong and the moisture decreases rapidly in very few meters, which provide good conditions for the formation of evaporation duct; (2) surface-based duct is always due to the presence of strong radiation cooling over land and/or prevalence of localized land-sea breeze [5]. However, these conditions are difficult to meet over the research region; and (3) temperature inversions are generally associated with a decrease in moisture and the result is often a trapping layer [11], which might be the reason for the formation of elevated duct.…”

Brief review on PE method application to propagation channel modeling in sea environment

“…4 (b 13 ration duct). In this case there is much better correlation between measured sus range for fixed height obtained using as input to the PE surface-duct M ear model, and data for z d and ∆M derived from a two year statistical study l. These statistical data are based on radiosonde measurements recorded at a Bosporus strait [26]. The parameters for Fig.…”

“…In addition, those parameters are easily extracted from the available duct statistics [26,107]. The bi-and tri-linear models set the slope above and below the M inversion to 0.118 M-units/m (which corresponds to the standard troposphere).…”

“…On a worldwide basis surface-based ducts are known to ear about 14 % of the time, in certain regions -up to 50 % of the time [22,23]. As for Europe, the climatology marized in von Engeln and Teixeira [22] and Lopez [24] shows high ducting probability mostly in the diterranean region (see also Bech et al [13]); some areas in the temperate zone are especially prone to anomalous pagation: the Black sea [25,26], the British Channel, and East Anglia [27][28][29]. Even the northern parts of Europe affected: data for duct occurrence and parameters has been reported for two coastal and one maritime iosondes station in Norway [30]; evaporation ducting over Baltic Sea has also been reported [31,32].…”