What Determines Above-Anvil Cirrus Plume Infrared Temperature?

Above-anvil cirrus plumes (AACPs) in midlatitude convection are important indicators of severe storms and stratospheric hydration events. Recent studies of AACPs have shown large variability in their characteristics, although many of the causes remain unknown. Notably, some AACPs appear equally as cold (or colder) than the broader storm top when compared to the more frequently observed warm AACP feature in infrared satellite imagery. To confidently identify the presence of an AACP, trained experts utilize infrared imagery to support the primary source of AACP identification, visible imagery. Thus, nighttime AACPs are often left unidentified due to unavailable visible imagery, especially for cold AACPs. In this study, 89 warm and 89 cold AACPs from 1-min GOES-16 satellite imagery coupled with ground-based radar observations and reanalysis data are comparatively evaluated to answer the following research questions: 1) Why do some AACPs exhibit a warm feature in infrared imagery while others do not, and 2) what observable storm and environment differences exist between warm and cold AACPs? It is found that cold AACPs tend to occur in tropical environments, which feature higher, cold-point tropopauses. Conversely, warm AACPs tend to occur in midlatitude environments, with lower tropopauses accompanied by an isothermal region (or tropopause inversion layer) in the lower stratosphere. Similar storm characteristics are found for warm and cold AACP events, implying that infrared temperature variability is driven by environmental differences. Together, these results suggest that cold AACPs are predominantly tropospheric phenomena, while warm AACPs reside in the lower stratosphere.