Mohammad Ali Sharifi

Comparison of GPS precipitable water vapor and meteorological parameters during rainfalls in Tehran

In this study, the sensing of water vapor using the global positioning system (GPS) was investigated in Tehran. Water vapor mean temperature Tm is a key parameter in conversion of GPS zenith wet delay to precipitable water vapor (PWV). Then, by using 8xa0years of radiosonde and surface temperature data, we achieved a new site-specific Tm model in Tehran. After the comparison of Bevis et al. (J Geophys Res 97(D14):15787–15801, 1992) and the site-specific models, a mean bias error of −1.3xa0K was found for Bevis model, while this is less than 0.1xa0K for the new local model. Therefore, PWV time series were generated for the ground-based GPS site in Tehran from the beginning of 2005 to the end of 2013. Comparing the GPS with the radiosonde PWV, it was shown that the GPS can be used to measure the PWV with high precision. The root mean square error for differences between the GPS and radiosonde was derived as 1.5xa0mm. The PWV has significant relationship with precipitation in our case study. The thresholds of the relative humidity anomaly with different PWV anomaly related to rainfall occurrences are also considered in this research. The analyses show that use of PWV anomaly condition together with surface meteorological parameters reduces the number of false rainfall recognitions significantly.

GOCE gradiometry data processing using the Rosborough approach

The Rosborough approach was developed in the 1980s for the modeling of orbit perturbations of altimeter satellites. It is a formalism that is rooted in the so-called time-wise approach, in which gravitational functionals are described as an along-orbit time series. Nevertheless, through a transformation of the orbital variables, the along-orbit functional can be mapped back onto the sphere. As such, the Rosborough formulation is a so-called space-wise approach at the same time. Both the conventional time-wise and the space-wise approaches have been improved and optimized over the past decade. When we explore the utility of the Rosborough approach in this contribution, we do not expect improved solutions for this particular GOCE-based case study. However, we aim to show the special characteristics of the Rosborough approach for processing the GOCE gradiometry data. In particular, we show that this approach can successfully deal with the problems that come with real data like bandwidth limitation and mispointing. Based on the first 71 days of the GOCE gravity gradients, we obtain solutions up till spherical harmonic degree 200. Compared to a high-quality gradiometric-only time-wise model, our solution shows a similar performance with just 8xa0cm geoid RMS difference in the relevant bandwidth. Moreover, relative contributions from the individual components are provided for the geographically mean gravity gradient components

Least-squares harmonic estimation of the tropopause parameters using GPS radio occultation measurements

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Regional TEC dynamic modeling based on Slepian functions

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Dynamic orbit propagation in a gravitational field of an inhomogeneous attractive body using the Lagrange coefficients

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Harmonic analysis of the ionospheric electron densities retrieved from FORMOSAT-3/COSMIC radio occultation measurements

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