Preliminary Development and Assessment of the NOAA Microwave Integrated Retrieval System for Tropical Cyclones (MiRS-TC) : A Passive Satellite Microwave Retrieval Algorithm Optimized for the Tropical Cyclone Environment

Tropical Cyclones (TCs) represent a significant threat to human life and property relating to multiple hazards including high winds, heavy rainfall, and storm surge flooding. TCs occur in multiple ocean basins including the western Atlantic, eastern and western Pacific, and Indian Oceans. TC formation and intensification occurs over oceans, and can often take place in remote regions making frequent direct in situ observations by instrumented aircraft more challenging. Satellite observations, particularly from cloud-penetrating microwave measurements, can provide a critical component of the global observing system and can supplement traditional observations. In fact, NOAA operational algorithms in place (e.g. HISA, Hurricane Intensity and Structure Algorithm) utilize microwave retrievals of the temperature and moisture structure from the operational MiRS algorithm to estimate current cyclone intensity. We present recent work with the operational NOAA Microwave Integrated Retrieval System (MiRS) the goal of which is to develop a version that is optimized for performance in TC environmental conditions. The work is motivated by the fact that in the current operational version of MiRS several key components of the retrieval system are designed to optimize retrieval accuracy and precision in a globally-averaged sense, not for the unique conditions present in the vicinity of TCs. For example, a priori constraints on the temperature and water vapor profiles in terms of means and covariances, EOF basis functions for temperature and water vapor, and channel selection are all based on global data and validation results. Here we will present results based on a set of TC case studies across multiple ocean basins (e.g. Hurricanes Florence in 2018, and Edouard in 2014) showing that, by adjusting the various critical components of the retrieval system, a TC-specific version of MiRS can produce retrievals that are consistently more accurate than the baseline operational global version. In particular, we examine the ability to retrieve the temperature warm core anomaly structure and its horizontal and vertical dependence, which is known to be a strong indicator of TC intensity. Sensitivity tests will show which of the retrieval components is most relevant to obtaining an accurate result.