Atlantic Tropical Cyclone Interactions with Upper Tropospheric Flow

Interactions of Atlantic tropical cyclones (TCs) with upper tropospheric flow are identified in 37 years of ERA-Interim reanalysis data and analyzed from multiple perspectives. Upper tropospheric troughs are identified in a more comprehensive way than past methodologies, targeting features on the dynamic tropopause to reduce exclusivity of feature selection and sensitivity to the background environment. To overcome some limitations of the trough perspective, a new approach to analyzing TC-environment interactions is developed through the identification of upper tropospheric jets near TCs. Jet axes are identified in 200-hPa wind fields within 3000 km of TCs using a robust, objective algorithm, forming a novel dataset that provides a unique way of characterizing and subsetting environmental flow. The climatology of these jets is explored through various means, including an objective clustering technique, which yielded seven statistically distinct groups of jets associated with recognizable flow patterns near TCs. The dynamical coupling between TCs and nearby jets is also quantified, with acceleration of jets downstream of the TC found to be a nearly ubiquitous feature, and entrance regions of jet streaks are observed to significantly enhance the strength of the TC secondary circulation. The influence of nearby upper tropospheric troughs and jets on TC intensity is also assessed through a variety of approaches. In order to minimize systematic sampling biases when quantifying this impact, a spatially varying climatology of TC intensification rate is developed using a second-order, generalized least squares regression model, allowing TC intensity responses to external forcing to be evaluated as departures from their expected value. Both troughs and jets are found to be net negative influences on TC intensity, on average, primarily due to increasing vertical shear with proximity to the vortex. Differences between rapidly intensifying (RI) and rapidly weakening (RW) cases during TC-trough-jet interactions depend not only on shear, but on dynamic forcing imposed by baroclinic processes and eddy momentum fluxes that can counter the influence of shear. Intensifying cases are primarily associated with jets that approach the poleward side of the TC and possess jet streaks that amplify over time, increasing dynamic forcing for ascent near the TC core while maintaining enough distance to prevent shear from overwhelming those effects. This study expands the set of tools for analyzing TC interactions with upper tropospheric flow by improving trough identification and introducing a new perspective through the use of jets. Jets afford greater specificity in describing environmental flow, and allow unique methods of quantifying its impact on TCs. Close links are found between jet proximity and vertical shear, as well as jet acceleration and dynamically-forced ascent, both relationships that have been physically understood, but until now unidentified in bulk observational datasets. Some measures of jet entrance region orientation are found to correlate with the relative magnitude of shear and baroclinic forcing, exposing the subtlety in how flow geometries differ between intensifying and weakening TC cases. Prior research has tended to evaluate upper tropospheric influences on TCs individually or relied on case studies to elucidate their collective impact on a single storm. This body of work seeks to illuminate relationships between TCs and upper tropospheric flow that are robust across large samples of TCs and storm environments, utilizing novel approaches such as the jet perspective to extract previously unquantified information.