Improving Hurricane and Coastal QPFs through Direct Assimilation of GOES-R ABI Radiances in Regional Models

2017 ANNUAL REPORT

Background

Direct assimilation of radiance observations from GOES imagers on board Geostationary Operational Environmental Satellites (GOES) lagged behind the assimilation of radiances from POES. Since the GOES data are unique for capturing fast evolving weather systems such as tropical cyclones convections. In order to get ready for direct assimilation of GOES-R Advanced Baseline Imager (ABI) radiance measurements, which becomes available only recently. Some test runs could be conducted to assimilate the radiance data from a similar instrument —— the Advanced Himawari Imager (AHI). Specifically, the AHI infrared channels are assimilated into the Hurricane Weather Research and Forecasting (HWRF) system and Advance WRF (ARW) models. Both HWRF and ARW employ the National Centers for Environmental Prediction (NCEP) Gridpoint Statistical Interpolation (GSI) system for data assimilation. ABI and AHI have a total of three visible channels (AHI channels 1-3), three near infrared channels (AHI channels 4-6) and 10 infrared channels (AHI channels 7-16), while the previous and current GOES-11 to -15 have only one visible channel (GOES channel 1), one near infrared channel (GOES channel 2) and three infrared channels. Although a capability of GOES-11/-12 and GOES-13/-15 imager radiance assimilation were added to ARW/GSI [Zou et al., 2011; Qin et al., 2013] and HWRF/GSI [Zou et al., 2015] respectively, assimilation of ABI and AHI requires a new set of schemes related to bias estimate, cloud detection and quality control (QC) of AHI data.

Accomplishments

Assimilation of infrared channel radiances provided by geostationary imagers requires an infrared only cloud mask (CM) algorithm that could identify cloud-contaminated pixels without involving any visible or near-infrared channels. Such an infrared-only CM algorithm is developed using the Advanced Himawari Imager (AHI) radiance observations in this paper. It consists of a new CM test for optically thin clouds, two modified Advanced Baseline Imager (ABI) CM tests and seven other ABI CM tests. These ten CM tests are used to generate composite CMs for AHI data, which are validated by using the Moderate Resolution Imaging Spectroradiometer (MODIS) CMs. It is shown that the Probability of Correct Typing (PCT) of the new CM algorithm over ocean and land is 89.59% and 90.96%, respectively, and the corresponding Leakage Rate (LR) is 6.18% and 4.85%, respectively, The new infrared only CM algorithm achieves a higher PCT and a lower false alarm rate over ocean than the Clouds from the AVHRR Extended System (CLAVR-x) that makes not only the infrared channels, but also visible and near-infrared channels. However, a slightly higher LR of 7.54% occurred over land during daytime in the presence of low stratus clouds, which requires further investigation. Positive impacts are obtained on quantitative precipitation forecasts (QPFs) associated with a typical summer precipitation case over eastern China in both setups, i.e., one assimilating all ten AHI infrared channels (AHIA) and the other assimilating only four GOES-like AHI channels (AHIG).

Planned work   

• Complete updates of CRTM fast transmittance model using updated post-launch updated SRF
• Complete assessments of new CRTM cloud scattering LUTs for ABI cloudy-scene simulation
• Fine-tune AHI IR-only cloud mask algorithm in GSI for ABI applications
• Complete ABI bias estimate in clear-sky conditions 

·         Complete a comparison of data assimilation and forecast results with and without AHI and/or ABI radiance assimilations

• Publish the work on AHI/ABI data assimilation in refereed journals

Publications           

Zhuge, X. and X. Zou, 2016: Test of a modified infrared only ABI cloud mask algorithm for AHI radiance observations. J. App. Meteor. Climatol., 55, 2529-2546.doi: 10.1175/JAMC-D-16-0254.1.

Qin, Z., X. Zou and F. Weng, 2017: Impacts of assimilating all or GOES-like AHI infrared channels radiances on quantitative precipitation forecasts over Land. Quart. J. Roy. Meteor. Soc., (submitted)

Presentations       

The 97^th Annual Meeting of America Meteorology Society, 22-26 January 2017, Seattle, Washington. A poster presentation entitled“Assimilation of AHI Infrared Radiance Measurements for Improved Typhoon Track and Intensity Forecasts Using HWRF” by Zou, Qin, Zhuge, and Weng at the Fifth AMS Symposium on the Joint Center for Satellite Data Assimilation.