Abstract
This paper presents a conceptual approach for near real time Global Positioning System (GPS) meteorology in Malaysia using combined space- and ground-based GPS observations. Data from a single GPS station is utilised to derive wet refractivities for comparison with radio occultation (RO). This study shows that the wet refractivities from the ground-based GPS present similar patterns and better correlation with the radiosonde data than that from the space-based GPS RO data at altitudes between 0 - 5 km. Similarly, the wet refractivities derived from RO are more highly correlated with the radiosonde data than the ground-based GPS at altitudes above 5 km. The residual Nwvary from -9.25 - 21.136 N-unit at 00 h UTC for the ground-based GPS while for the GPS RO, it is -19 - 9.259 N-unit at 00 h UTC.
Highlights
Atmospheric water vapour plays a crucial role in the Earth’s energy and hydrological cycles due to its high variability
The vertical profiles of bending angle and refractivity, temperature, pressure and water vapour in the neutral atmosphere can be derived from the raw radio occultation (RO) measures of the excess Doppler shift to the radio signal transmitted by the Global Positioning System (GPS) satellite (Kursinski et al 1997; Lin 2010)
Several studies (e.g., Bevis et al 1992; Liou et al 2001; de Haan et al 2009; Rizos et al 2009) demonstrated the efficiency of ground-based GPS meteorology, especially in neutral atmospheric sensing, but the atmospheric profiling concept from ground-based GPS observations became popular following the development of GPS tomography for 3-D and 4-D variational tropospheric analysis, as well as retrieval of the horizontal and vertical refractivity field (e.g., Hirahara 2000; Flores et al 2000; Davies et al 2001; Macdonald et al 2002)
Summary
Atmospheric water vapour plays a crucial role in the Earth’s energy and hydrological cycles due to its high variability. Ground-based GPS meteorology has been predominantly used to estimate Integrated Water Vapour (IWV) over a GPS site utilising the ZPD, but this approach has limitations in resolving atmospheric refractivity in the upper troposphere and lacks the capability to profile the atmosphere. The space-based GPS radio occultation (RO) technique has been developed, providing global coverage with a capability to generate atmospheric refractivity profiles. It has limitations in resolving the lower tropospheric refractivity. Since water vapour is responsible for atmospheric stabilisation, the warmer the air, the more water vapour it can hold to form droplets that eventually produce rain This circumstance is responsible for the peculiar atmospheric dynamics and climatic uncertainty in the tropics. The concept of G-MeM relies on a combination of GPS RO measurements with ground-based GPS observations
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