Analysis of the Influence of the Superrefraction Effect on the Earth's Neutral Atmospheric Parameters Retrieval

摘要

The superrefraction, which can be frequently found in the moist lower troposphere, degrades the accuracy of the retrieved atmospheric parameters from GPS/LEO occultation data. The GPS/LEO occupation data containing superrefraction effect can be simulated by using multiple phase screens technique, with the refractivity model or high resolution ecmPrf profile (echPrf data). Simulation results show that superrefraction effect can lead to refractivity error in the moist lower troposphere, which in some case can be as large as about -9.6%. About 24530 echPrf profiles from DOY(day of year) 151 to DOY 161 in 2007, are divided into A, B, C, D 4 categories. According to the minimum of refractivity gradient of the echPrf data, the minimum of the refractivity gradient of the echPrf data is decreasing from category A to category D. The category C and category D contain the occultation profiles with the superrefraction effect. The refractivity profiles in 4 categories are compared with those of the corresponding COSMIC(Constellation Observing System for Meteorology, Ionosphere and Climate) data. Statistical comparison results show: about 5.6% of the echPrf profiles with superrefraction effect can be found. The mean and standard deviation of the fractional difference of refractivity between COSMIC observation and echPrf data near the ground are about -0.51% and 2.71% for set A, -1.64% and 4.27% for set B, -3.59% and 5.49% for set C, -8.50% and 7.21% for set D. The locations of the superrefraction phenomenon in the tropics are mainly near the following regions: North America (Mexico), South America (the western coast of Peru), North Africa (the Sahara desert), and South Africa on the Atlantic side.