Reflective storm tops: a satellite method for inferring thunderstorm top microphysical structure

The utility of GOES channel 1 (visible) and channel 4 (longwave infrared) imagery has long been recognized in terms of thunderstorm nowcasting. However, few studies have addressed the application of the shortwave infrared channel 2 (3.9 μm) to storm top analysis. During the daytime, channel 2 has an emitted thermal component, but for cold thunderstorm tops, a reflected solar component makes a significant contribution to the total radiance. The amount of shortwave reflectance depends on the microphysical structure at cloud top; smaller ice crystals tend to reflect more incoming radiation. We therefore can make inferences about cloud-top microphysical structure based on channel 2 albedo values.

Though still under investigation, ice crystal size at cloud top may be related to updraft strength, moisture properties of the environment, and potentially other relevant parameters. A climatological study of “reflective” storm tops was performed, and a distinct maximum was found downwind of mountain ranges in the continental US, especially in the high plains of Colorado, Wyoming, and New Mexico. Additionally, if a storm top meets certain minimum reflectivity properties, the storm is five times more likely to produce severe weather (based on 3 months of data).

This presentation will introduce the concept of reflective storm tops, discuss the climatology of reflective ice clouds, and provide modeling results which link shortwave albedo to cloud-top microphysics. Potential applications to thunderstorm nowcasting will also be discussed.