Abstract
Abstract. Spaceborne precipitation radars, such as the Tropical Rainfall Measuring Mission (TRMM) and the Global Precipitation Measurement (GPM) Core Observatory, have been important platforms to provide a direct measurement of three-dimensional precipitation structure globally. Building upon the success of TRMM and GPM Core Observatory, the Japan Aerospace Exploration Agency (JAXA) is currently surveying the feasibility of a potential satellite mission equipped with a precipitation radar on a geostationary orbit. The quasi-continuous observation realized by the geostationary satellite radar would offer a new insight into meteorology and would advance numerical weather prediction (NWP) through their effective use by data assimilation. Although the radar would be beneficial, the radar on the geostationary orbit measures precipitation obliquely at off-nadir points. In addition, the observing resolution will be several times larger than those on board TRMM and GPM Core Observatory due to the limited antenna size that we could deliver. The tilted sampling volume and the coarse resolution would result in more contamination from surface clutter. To investigate the impact of these limitations and to explore the potential usefulness of the geostationary satellite radar, this study simulates the observation data for a typhoon case using an NWP model and a radar simulator. The results demonstrate that it would be possible to obtain three-dimensional precipitation data. However, the quality of the observation depends on the beam width, the beam sampling span, and the position of precipitation systems. With a wide beam width and a coarse beam span, the radar cannot observe weak precipitation at low altitudes due to surface clutter. The limitation can be mitigated by oversampling (i.e., a wide beam width and a fine sampling span). With a narrow beam width and a fine beam sampling span, the surface clutter interference is confined to the surface level. When the precipitation system is located far from the nadir, the precipitation signal is obtained only for strong precipitation.
Highlights
Knowing the distribution of precipitation in space and time is essential for scientific developments as precipitation plays a key role in global water and energy cycles in the Earth system
The first satellite equipped with precipitation radar was the Tropical Rainfall Measuring Mission (TRMM) launched in 1997 (Kummerow et al, 1998; Kozu et al, 2001), and the first satellite-borne dual-frequency precipitation radar on board the Global Precipitation Measurement (GPM) Core Observatory was launched in 2014 (Hou et al, 2014; SkofronickJackson et al, 2017)
The initial and lateral boundary conditions for D1 were taken from the National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) operational analyses at 0.5◦ resolution every 6 h
Summary
Knowing the distribution of precipitation in space and time is essential for scientific developments as precipitation plays a key role in global water and energy cycles in the Earth system. The observations produced by the precipitation radars on board the low-Earth-orbiting satellites have been contributing to enhancement of our knowledge on meteorology Their ability to see through clouds helps us to understand storm structures (Kelly et al, 2004) and the nature of convection (e.g., Takayabu, 2006; Hamada et al, 2015; Houze et al, 2015). GPR stays at the same location all the time and continuously measures precipitation in its range of observation These data are expected to help us understand important scientific issues. Lewis et al (2011) examined the feasibility of a 35 GHz Doppler radar to observe the wind field They showed that the direct measurement of winds from the geostationary orbit would be possible for a hurricane case.
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