Hurricane Outflow Jet Structure and Evolution Derived from Dropsondes and Satellite High-Level Atmospheric Motion Vectors (AMVs)

Dropsonde profiles through hurricane outflow layers were obtained during the Hurricane and Severe Storms Sentinel (HS3) experiment (2012-2014) and the Tropical Cyclone Intensity (TCI) experiment (2014). Using mini-dropsondes deployed with the Airborne Vertical Atmospheric Profiling System (AVAPS) from a NASA Global Hawk and eXpendable Digital Dropsondes (XDDs) deployed with the High Definition Sounding System (HDSS) from a NASA WB-57F, new insights into the vertical structure of the TC outflow layer have been obtained within the context of rapid time changes documented by CIMSS AMVs. Detailed fine structure within the complete outflow layer has been obtained that distinguishes this region from lower layers in Tropical Cyclones (TCs).

Atmospheric Motion Vectors (AMVs) show that ‘far-field' outflow jet dropsondes in Hurricane Leslie (2012) were obtained during a period of jet development and deformation in response the ‘pincer effect' of an upper trough to the east and an upper cold low to west of Leslie. We speculate that the resulting deformation of the outflow layer and associated jet feature may have been responsible for limiting further development of Leslie. AMVs in Hurricane Nadine (2012) and pre-TC Gabrielle (2013) showed that outflow jets sampled by dropsondes developed rapidly over time scales of several hours. Wind profile observations in outflow jet ‘roots' near ‘convective bursts' showed that they were weaker and thicker near the convection and became thinner and stronger downstream as the ‘far-field' region was sampled.

All dropsonde profiles showed that the outflow layer contained numerous thin isothermal layers and layers of enhanced vertical wind shear. These numerous thin unstable layers were characterized by a super-critical Richardson number in excess of ¼. The outflow layer therefore appears to contain multiple transient thin unstable layers generating turbulence that may play a role in the dynamics of the outflow layer and its impact on TC predictability. In addition, the intense shear at the tropopause near the top of the outflow layer was capped by a stable layer that secondary wind maximum. Implications of these observations and possible linkages with TC intensity changes will be discussed.