Convective Stratospheric Hydration, AACPs, & Tropopause Height

Above-anvil cirrus plumes (AACPs) in midlatitude convection are important indicators of severe storms and stratospheric hydration events. Recent studies of AACPs have illustrated large variability in their characteristics, however many of the causes are still unclear. AACP infrared brightness temperatures are of particular interest due to their broadly bimodal distribution. Most frequently, AACPs appear warmer than the broader storm top in infrared satellite imagery (i.e. the enhanced-V signature). However, some AACPs appear equally as cold (or colder) than the associated storm anvil. To confidently identify the presence of an AACP, trained experts utilize infrared imagery to support the primary source of AACP identification, visible imagery. Nighttime AACPs are often left unidentified due to unavailable visible imagery, especially for cold AACPs. In this study, we identify 89 warm and 89 cold AACPs from 1-minute GOES-16 satellite imagery coupled with ground-based radar observations and reanalysis data 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? We hypothesize that these different temperature signatures are a result of 1) cold AACPs forming in double-tropopause regions, in contrast to warm AACPs forming in single-tropopause environments, 2) cold AACPs forming in higher tropopause, tropical, environments, as opposed to warm AACPs forming in lower tropopause, midlatitude, environments, and/or 3) cold AACPs that are too optically thin for their brightness temperature to be observed by infrared imagery compared to their warm AACP, optically thick counterparts.

We first match all manually identified AACPs to their corresponding radar-based storm tracks. Then, we examine storm characteristics and near-storm environments via tropopause-relative and absolute height temperature and moisture vertical profiles, echo-top heights, storm-relative winds, and levels of maximum detrainment (LMDs). Results indicate 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. Significant differences between warm and cold AACPs are only found when storm environments are incorporated, indicating that infrared temperature variability is driven by environmental differences. As such, these results suggest that cold AACPs are predominantly tropospheric phenomena, while warm AACPs reside in the lower stratosphere. Comparison of the variability of level of neutral buoyancy in these environments will also be discussed.