Retrieval of Temperature and Humidity from GPS-Radio Occultation derived Refractivity using Physical Iterative Method: Operational Algorithm for MT-ROSA

摘要

This paper discusses the retrieval algorithm based on physical iterative method that demarcates the atmosphere into the dry and moisture-containing region at the threshold height, which is dynamically parameterized in terms of temperature that is verified through a sensitivity study. The algorithm retrieves the temperature and pressure for the entire atmosphere after neglecting the water vapour term in the refractivity forward model. The geophysical profiles are, to a very good approximation, true to the actual profile of temperature and pressure beyond the threshold height. Below this height, the true temperature varies quadratically with natural logarithm of pressure and is the basis of retrieval for the moisture-containing region. The algorithm is applied on refractivity forward modeled from NCEP analyses data and the retrieved geophysical parameters (GPs) are compared against NCEP. The temperature and water vapour partial pressure are largely within 1 K and less than 0.6 mb, respectively. The algorithm is subsequently applied on satellite-derived refractivity from COSMIC mission and the retrieved GPs are compared to collocated radiosonde with standard deviation within 2 K between 5 - 30 km for temperature and better than 2 mb between 5-16 km for the water vapour partial pressure. Differences between tropics and global statistics are seen below 5 km in both the parameters.