Abstract
High spectral resolution (or hyperspectral) infrared (IR) sounders onboard low earth orbiting satellites provide high vertical resolution atmospheric information for numerical weather prediction (NWP) models. In contrast, imagers on geostationary (GEO) satellites provide high temporal and spatial resolution which are important for monitoring the moisture associated with severe weather systems, such as rapidly developing local severe storms (LSS). A hyperspectral IR sounder onboard a geostationary satellite would provide four-dimensional atmospheric temperature, moisture, and wind profiles that have both high vertical resolution and high temporal/spatial resolutions. In this work, the added-value from a GEO-hyperspectral IR sounder is studied and discussed using a hybrid Observing System Simulation Experiment (OSSE) method. A hybrid OSSE is distinctively different from the traditional OSSE in that, (a) only future sensors are simulated from the nature run and (b) the forecasts can be evaluated using real observations. This avoids simulating the complicated observation characteristics of the current systems (but not the new proposed system) and allows the impact to be assessed against real observations. The Cross-track Infrared Sounder (CrIS) full spectral resolution (FSR) is assumed to be onboard a GEO for the impact studies, and the GEO CrIS radiances are simulated from the ECMWF Reanalysis v5 (ERA5) with the hyperspectral IR all-sky radiative transfer model (HIRTM). The simulated GEO CrIS radiances are validated and the hybrid OSSE system is verified before the impact assessment. Two LSS cases from 2018 and 2019 are selected to evaluate the value-added impacts from the GEO CrIS-FSR data. The impact studies show improved atmospheric temperature, moisture, and precipitation forecasts, along with some improvements in the wind forecasts. An added-value, consisting of an overall 5% Root Mean Square Error (RMSE) reduction, was found when a GEO CrIS-FSR is used in replacement of LEO ones indicating the potential for applications of data from a GEO hyperspectral IR sounder to improve local severe storm forecasts.
Highlights
Accurate initial conditions of the atmosphere are cri-GEO HYPERSPECTRAL IR ASSIMILATION FOR local severe storms (LSS)VOLUME 38 radar, lidar, etc. are widely used in numerical weather prediction (NWP) (Graham et al, 2000; Carbone et al, 2002, Adam et al, 2016; Bachmann et al, 2018; Reen and Dumais, 2018)
The Cross-track Infrared Sounder (CrIS) full spectral resolution (FSR) is assumed to be onboard a GEO for the impact studies, and the GEO CrIS radiances are simulated from the ECMWF Reanalysis v5 (ERA5) with the hyperspectral IR all-sky radiative transfer model (HIRTM)
Since the ERA5 analysis data serve as a replacement to the nature run (NR), the Gridpoint Statistical Interpolation (GSI) and WRFARW models are used for the experiments with GFS reanalysis as the initial and boundary conditions, to avoid the identical twin problem
Summary
VOLUME 38 radar, lidar, etc. are widely used in NWP (Graham et al, 2000; Carbone et al, 2002, Adam et al, 2016; Bachmann et al, 2018; Reen and Dumais, 2018). In a hybrid OSSE, all observations are real except those from a future observation system, which are instead simulated (with realistic noise added) from high temporal and spatial resolution reanalysis using radiative transfer models. This approach allows for the evaluation of the future sensors using what we already have from real observations and simulating what we plan to have, such as a hyperspectral GEO IR sounder with high temporal resolution.
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