Tropical Cyclone Outflow and Warm Core Structure as Revealed by HS3 and TCI Dropsondes

Capitalizing on the unique ability of the WB-57 and Global Hawk aircraft to overfly the tropical cyclone (TC) core and release dropsondes from 60k feet, the structure of the outflow and warm core is investigated using data from 27 research flights spanning ten TCs from 2012-2015.  Results are evaluated with respect to current storm intensity as well as intensity trend.  Overall, strengthening TCs are found to be associated with greater upper-level divergence and radial outflow than weakening TCs, regardless of present intensity.  However, strong upper-level divergence does not always guarantee intensification, as non-intensifying 30-kt pre-Gabrielle (2013) demonstrates.  Hurricane Cristobal (2014) was sampled by HS3 during a period in which the system developed dual outflow channels, while Hurricane Joaquin (2015) was sampled during a period of trough interaction in which the primary outflow shifted from southward to northward.  For both cases, the maximum in the southward outflow occurs at higher altitude than the maximum in the northward outflow.  Additionally, both such periods were coincident with intensification, albeit modest intensification for Cristobal.  Similarities between the Joaquin trough interaction and an idealized COAMPS-TC simulation are noted. 

Other significant results include the fact that an upward bulge in the tropopause above the TC is observed for systems of hurricane strength, with the overall vertical displacement appearing to be correlated to storm intensity.  The downward slope of cyclone/anticyclone interface at outflow levels (i.e. the V_tan = 0 line) also appears to be correlated with storm intensity.  Lastly, some statistic about the height and strength of the warm core, the occurrence of a single maximum versus secondary warm cores, and implications of vertical wind shear on the outflow structure are presented.