Value-Added Impact from Geostationary Hyperspectral Infrared Sounder on Nowcasting and Forecasting High-Impact Weather Events

Atmospheric water vapor information with high temporal and spatial resolution is one of the key parameters needed in the regional numerical weather prediction (NWP) models for reliable prediction of high impact weather events such as tropical cyclones (TCs) and local severe storms (LSS). The high spectral resolution or hyperspectral infrared (IR) sensors from geostationary orbit (GEO) provide nearly time continuous three-dimensional temperature and moisture profiles that allow substantial improvements in monitoring the mesoscale environment for HIW forecasts. These measurements would be an unprecedented source of information on the dynamic and thermodynamic atmospheric fields, an important benefit for nowcasting and NWP based forecasting.

The concept of GEO hyperspectral IR sounder has been developed in early 1990s starting with NOAA GHIS (GOES High-Resolution Interferometer Sounder), later demonstrated with a NASA prototype instrument called GIFTS (Geostationary Imaging Fourier Transform Spectrometer). A GEO hyperspectral sounder called HES (Hyperspectral Environment Suite) was planned for U.S. GOES-R series, but was removed due to budget constraints. The InfraRed Sounder (IRS) has been developed by Europe and is designed to fly onboard EUMETSAT’s next generation of three-axis stabilized GEO satellites, Meteosat Third Generation (MTG) in 2020 timeframe and beyond. The GIIRS (Geosynchronous Interferometric Infrared Sounder), onboard the Chinese FengYun-4A (FY-4A) launched on 11 December 2016, is the first hyperspectral IR sounder onboard a GEO satellite,

A convective initiation event from the International H2O Project (IHOP) field experiment is used to demonstrate the utility of a GEO hyperspectral IR sounder for LSS nowcasting applications. A GEO hyperspectral IR sounder provides detailed stability information (e.g., lifted index and other parameters) with high temporal resolution useful for determining favorable locations for convective initiation. It demonstrates in this IHOP case that the current GOES Sounder provides limited stability information before the storm development as a result of the limited spectral IR information for temperature and moisture profiling, the high spatial and temporal GEO hyperspectral IR sounder, however, can provide critical information about the destabilization much earlier than the current GOES Sounder.

In order to demonstrate the impact of GEO high spectral resolution IR sounder radiances on HIW forecasts, a regional quick Observing System Simulation Experiment (R-OSSE) frame has been developed, the first step is to simulate both the GEO and current polar orbit (LEO) satellite based high spectral resolution IR sounder radiances from a suitable high spatial resolution natural runs (NRs). A fast radiative transfer model (RTM) has been developed for radiance simulation, and simulated GEO based hyperspectral IR radiances from NRs are compared with the collocated GOES Imager radiance measurements to examine the quality of the simulation, including channels consistency, diurnal variations, cloud coverage etc. Quick R-OSSEs are performed using the high resolution NRs to investigate the potential value-added impact of a GEO high spectral resolution IR sounder on TC and LSS forecasts. It is found that compared with a LEO based advanced IR sounder, a GEO advanced IR sounder has potential to provide value-added impact on both TC and LSS forecasts due to large spatial coverage and high temporal resolution. The technical approaches developed in this study have the potential for operational transition once the GEO hyperspectral IR sounder measurements are available.