Detection and Modeling of Medium-Scale Travelling Ionospheric Disturbances in Iran Region

Ionosphere layer variations are divided into regular and irregular. Regular changes can be considered as daily changes, changes depending on latitude and changes due to solar activity. Travelling Ionospheric Disturbances (TID) is one of the irregular changes of ionosphere which categorized in small, medium and large scales. Medium-scale Travelling Ionospheric Disturbance (MSTID) which are propagated because of Atmospheric Gravity Waves (AGW) is the main obstacle for accurate interpolation of ionospheric correction in a Global Positioning System (GPS) network, so detection and simulation of these perturbations is necessary. The purpose of this paper is discovering MSTID using carrier phase, which in addition to the values of the total electron content recovered from the observations of GPS also confirm the values detected using the carrier phase observations. MSTIDs are waveforms that have parameters such as amplitude, velocity, direction and wavelength that extracting these parameters are goal of simulation of MSTID. Generally, MSTIDs are planar and longitudinal waves, so to calculate their parameters, first a profile of or dSTEC by constant latitude is considered, then by examining displacement of maximum values of these parameters in a period of time, velocity will be determined. To calculate wavelength, wavelet analysis was used. Results of  and TEC observations were almost identical. MSTIDs have movement in southwest-northeast direction by velocity of 100 meters per second and wavelength of 232 kilometers and amplitude of 0.02 TECU. It means that these perturbations cause an error of 4 millimeters in L1 measurement. Since, phase observation’s precision is 1 millimeter, this error value is significant.  However, the carrier phase observations can be measured with an accuracy of one hundredth of a cycle, which by multiplying this value by the wavelengths of the GPS signal will be about 2 mm. Therefore, error that occurs due to MSTID, it is significant and should be considered.