Analysis of Cumulus Cloud-Top Properties for 0-1 hour Convective Initiation Nowcasting using Himawari-8 Infrared and Visible Fields

The main focus of this study is the current status of 0-1 hour convective initiation (CI) nowcasting, and how infrared and visible reflectance data from the newly launched Himawari-8 and forthcoming GOES-R satellites could be used in this nowcasting algorithm. Because the channels on the Advanced Himawari Imager (AHI) are nearly identical to those on the GOES-R Advanced Baseline Imager (ABI), use of Himawari-8 represents a risk-reduction focused project with respect to GOES-R. Since the advent of CI nowcasting algorithm (GOES-R CI; Mecikalski and Bedka 2006; Mecikalski et al. 2015), there have been a number of studies done toward improving CI detection through using Meteosat Second Generation (Mecikalski et al. 2010a, b) and involving the integration of NOAA Rapid Refresh (RAP) model fields into the algorithm (Mecikalski et al. 2015). Prior to the launching of GOES-R, this study seeks to understand how the improved spatial, spectral, and temporal resolutions of Himawari-8 could provide insights in CI nowcasting. The universal definition of CI is the radar reflectivity of ≥ 35-dBZ at -10ºC altitude.

There are many advantages Himawari-8 (and hence GOES-R) will offer in CI nowcasting. The improved spatial resolution (0.5 km and 2 km for visible and infrared channels, respectively) provides an opportunity to detect developing cumulus clouds in greater detail. Having extra spectral channels (specifically, 1.6, 2.3, 6.2, 6.9, 7.3, 8.5, and 10.4 µm) will help gain better understanding of cloud-top properties within growing cumulus clouds. While the temporal resolution does not seem to make much difference – 15 min for GOES and MSG vs. 10 min for Himawari-8, it provides critical background information on the future use of CI algorithm in GOES-R, especially in cases where cloud development in advance of CI is rapid. As noted, given the similarities between Himawari-8 and GOES-R, this study will provide solid information for CI detection within the GOES-R era.

The areas of interest in this study are within the Himawari-8 coverage: Guam and Japan. Initially, 154 potential satellite-based CI “interest fields” (139 infrared and 15 visible reflectance) are developed, with correlation and principal component analysis then used to distinguish the most unique and relevant “CI fields” when using Himawari-8 data for CI nowcasting. Similar to Mecikalski et al. (2010a, b), three processes during CI are examined: cloud depth and its changes, updraft strength, and cloud-top glaciation. The addition of 2.3 µm channel in Himawari-8 also enables us to evaluate the cloud particle size distribution and its influence in CI nowcasting; the potential application of this process will be discussed in this study. Other aspects of this study include:

1)      The utility of improved spatial resolution of Himawari-8 compared to the current GOES series (2 km vs. 4-8 km)

2)      The role of added channels – e.g., 2.3, 6.2, 6.9, 7.3, 8.5, and 10.4 µm – in CI nowcasting

3)      Comparison of cloud-top properties in tropical (Guam) and mid-latitude (Japan) regions

Thanks to the NOAA Satellite and Information Service (NESDIS) and Japan Meteorological Agency (JMA), we are able to examine the results from this study in the aforementioned regions for improvement in current GOES-R CI algorithm. The importance of this study in future GOES-R applications will also be discussed.