Abstract
Abstract. The radio occultation retrieval product of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Radio Occultation sounding system was verified using the global radiosonde data from 2007 to 2010. Samples of 4 yr were used to collect quantities of data using much stricter matching criteria than previous studies to obtain more accurate results. The horizontal distance between the radiosonde station and the occultation event is within 100 km, and the time window is 1 h. The comparison was performed from 925 hPa to 10 hPa. The results indicated that the COSMIC's temperature data agreed well with the radiosonde data. The global mean temperature bias was −0.09 K, with a standard deviation (SD) of 1.72 K. According to the data filtration used in this paper, the mean specific humidity bias of 925–200 hPa is −0.012 g kg−1, with a SD of 0.666 g kg−1, and the mean relative error of water vapor pressure is about 33.3%, with a SD of 107.5%. The COSMIC quality control process failed to detect some of the abnormal extremely small humidity data which occurred frequently in subtropical zone. Despite the large relative error of water vapor pressure, the relative error of refractivity is small. This paper also provides a comparison of eight radiosonde types with COSMIC product. Because the retrieval product is affected by the background error which differed between different regions, the COSMIC retrieval product could be used as a benchmark if the precision requirement is not strict.
Highlights
M son was performed from 925 hPa to 10 hPa
The COSMIC Assessment of GPS/MET indicated that radio occultation quality control process failed to detect some of the abnormal sounding provides good temperature accuracy, with bias of extremely small humidity data which occurred frequently in subtropical zone
The wetPrf data are atmospheric occultation profiles with moisture information included, and it includes the parameters of atmospheric pressure, geometric height, temperature, water vapor pressure, retrieved refractivity, etc
Summary
The COSMIC 1DVAR retrieval product wetPrf profiles and global radiosonde profiles from 2007 to 2010 were used for this comparison. The wetPrf data are atmospheric occultation profiles with moisture information included, and it includes the parameters of atmospheric pressure, geometric height, temperature, water vapor pressure, retrieved refractivity, etc. To avoid errors due to interpolation of radiosonde profiles, the comparison was performed only on the standard pressure levels of the radiosonde profile. The comparison was performed at 15 pressure levels from 925 hPa to 10 hPa. The water vapor pressure of radiosonde data was given by Goff– Gratch equation (Goff, 1957). The comparison was performed in terms of temperature difference, T , specific humidity difference, q, relative error of water vapor pressure, RE Pw, and relative error of refractivity, RE N, which are given by Eqs. We used the absolute deviation of specific humidity and the relative error of water vapor in the comparison because the absolute deviation of specific humidity has been used much more frequently in other studies, it includes the error of atmospheric pressure, so the comparison of the relative error only used the water vapor pressure itself
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